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Saturated atomic fluorescence as a diagnostic tool for flames and plasmas

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Title:
Saturated atomic fluorescence as a diagnostic tool for flames and plasmas
Creator:
Bower, James Neill, 1950-
Publication Date:
Copyright Date:
1979
Language:
English
Physical Description:
vi, 170 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Atoms ( jstor )
Box cars ( jstor )
Density ( jstor )
Dyes ( jstor )
Flames ( jstor )
Fluorescence ( jstor )
Laser power ( jstor )
Lasers ( jstor )
Noise spectra ( jstor )
Quantum efficiency ( jstor )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Flame spectroscopy ( lcsh )
Fluorimetry ( lcsh )
Plasma spectroscopy ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis--University of Florida.
Bibliography:
Bibliography: leaves 166-169.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by James N. Bower.

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University of Florida
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Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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SATURATED ATOMIC FLUORESCENCE AS A DIAGNOSTIC TOOL
FOR FLAMES AND PLASMAS




By

JAMES N. BOWER














A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY CF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY












UNIVERSITY OF :-LORIDA

1979


























This thesis is dedicated

to my wife, Esther,

whose support and love have made the

difference between night and day.













ACKNOWLEDGEMENTS


Help and real human understanding have been available at all

times from my chairman, Dr. Winefordner, for these four years. He

has been a guiding light and a friend.

I would like to thank John Bradshaw for much of my basic under-

standing of analytical atomic spectroscopy. He has been a tireless

teacher.

Dr. Nicolo Omenetto has been a great help in understanding the

physical processes of laser excitation.

Dr. Winefordner's research group is certainly one of the most

stimulating in the world. Thanks to all members for many discussions

and helpful suggestions.

Thanks are in order for two unnamed souls whose joyless scien-

tific interactions with me persuaded me to return to school and

remain there.













TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS. . . . . . . . . . . . iii

ABSTRACT . . . . . . . . ... . . . .. vi

CHAPTER

1 INTRODUCTION . . . . . . . . ... . . 1

Quantum Efficiency . . . . . . . . . 1
Total Number Density . . . . . . . . 3
Noise Power Density. . . . . . . . . . 4
Reaction Rates . . . . . . . .... . 5
Tunable Dye Lasers . . . . . . . . 6

2 THEORETICAL CONSIDERATIONS . . . . . . . 8

Quantum Efficiency for a Two-Level Atom. . . . . 8
Quantum Efficiency for a Three-Level Atom. . . .. 17
Saturation . . . . . . . . ... 21
Quantum Efficiency Via the Slope Method. . ...... 22
Total Number Density . . . . . . . . 27
Possibility of Absolute Calibration. . . . . ... 27
Noise Power Density. .. . . . . . . 29

3 EXPERIMENTAL . . . . . . . .... .. .. 32

General Comments . . . . . . . .... . 32
Radio Frequency Shielding. . . . . . . .. 36
Photomultiplier. . . . . . . . . 37
Fluorescence Flux Collection. . . . . . 37
Detection Electronics. . . . . . . . . 38
Nitrogen Laser . . . . . . . . . 38
Dye Laser Operation. . . . . . . . . . 40
Flame System . . . . . . . . . . . 42
Solutions . . . . . . . . . . . 43
Measurement Procedure for Y and nT . . . . .. 43
Noise Power Density . . . . . . . . . 50

4 DATA . . . . . . . . . . . . . 54

Notation . . . . . . . .... ..... . 54
Strontium. . . . . . . . ... . .. 55
Sodium . . . . . . . . .. . . . 74
Calcium. . . . . . . . .. . . . 77







Page

Indium . . . . . . . . . . .. 80
Noise Power Density. . . . . . . . . .. 87

5 RESULTS AND DISCUSSION . . . . . . ... 100

Quantum Efficiency and Total Number Density. . . ... 100
Noise Power Density. . . . . . . . . .. 103

6 CONCLUSIONS AND FUTURE WORK. . . . . . . ... 105

System Temporal Response . . . . . . .... 105
Complete Saturation. . . . . . . . . .. 105
Measurement of E . . . . . . . . .. 106
Photometer Calibration . . . . . . . . 106
General Considerations . . . . . . .. 106
Noise Power Density. . . . . . . . . .. 107
General Comments . . . . . . . .... 108

APPENDIX

1 SUBSIDIARY MEASUREMENTS. . . . . . . . ... 10

2 COMPUTER PROGRAMMING AND PLOTTING. . . . . . 140

REFERENCES. . . . . . . . . ... ....... 166

BIOGRAPHICAL SKETCH . . . . . . .. .. ... 170










Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy


SATURATED ATOMIC FLUORESCENCE AS A DIAGNOSTIC TOOL
FOR FLAMES AND PLASMAS

By

James N. Bower

December 1979

Chairman: Dr. J.D. Winefordner
Major Department: Chemistry

A new experimental approach to the determination of three flame

diagnostic parameters is developed. The experimental application of

saturated atomic fluorescence to the measurement of quantum efficiency,

total number density, and noise power is discussed. Data for quantum

efficiency and total number density are compared to the scant litera-

ture values. Four elements and three different flame compositions

are investigated. Preliminary noise power spectra are discussed as

background for the use of saturated atomic fluorescence to measure

noise in the atomization and nebulization processes.












CHAPTER 1

INTRODUCTION


Characterization of physical and chemical parameters of flames

and plasmas has been a goal of chemists (1, 2, 3), physicists (4, 5, 6),

and combustion engineers (7, 8, 9) for many years. The goal of

physicists, physical chemists, and combustion engineers has been to

understand on a quite fundamental basis the processes which go on in

flames and plasmas, i.e., oxidations, reductions, free-radical reac-

tions, ionizations, etc. In recent years, an even larger impetus has

been seen for this research as sources of economical energy have

dwindled and better combustion understanding and design have become

paramount in importance. Analytical chemists, on the other hand, have

become interested in flames and plasmas because of the extremely

important role of these devices in quantitation of elemental species

in various samples. The coincidental research interests have brought

all together to try and provide a better understanding of basic

processes common to both.



Quantum Efficiency

A quantity of great interest to the analytical chemist and other

scientists is the quantum efficiency, the measure of the relative

yield of fluorescence processes to absorption processes. The quantum

efficiency has a strong influence on the performance of normally (low







intensity) excited atomic fluorescence spectrometry, which has become

an important flame diagnostic (3, 10, 11) and analytical tool (12, 13,

14) in recent years. In addition, quantum efficiency is an indication

of (rates of) deexcitation processes in flames and plasmas which can

be invaluable for unraveling many basic spectroscopic and fundamental

properties.

The traditional method of measurement for this quantity (Y) has

been to measure atomic absorption from a continuum source, then to

measure atomic fluorescence with the same source positioned at 90

degrees to the absorption axis. Great pains had to be taken to ensure

that solid angle effects, flame edge effects, etc. were eliminated

(15, 16). At best, this yielded a spatially unresolved picture of

deexcitation processes (i.e., absorption is a line of sight tech-

nique). In addition, no hope could be held cut for temporal resolu-

tion. Also, the measurement involved two highly different electronic

gains (those typical of absorption and fluorescence measurements),

which must be calibrated against each other.

The measurement of quantum efficiency via saturated atomic fluor-

escence, however, allows both spatial and temporal resolution under

the proper conditions. It is inherently easier to measure, as it

involves only one optical train for which the sclid angle must be

found. However, the photomultiplier tube and optical system must

be calibrated via a standard source. Along with the system used for

this investigation (a nitrogen-pumped dye laser) comes the need for

quite sophisticated electronics. Signal processing and cross-checks

for problems become much more involved.







Total Number Density


Total number density has been another sought after quantity in

flame and plasma spectroscopy. An important figure of merit in atomic

spectroscopy has been the efficiency by which a particular atomizer is

able to convert solution or solids introduced into it into the form of

neutral atoms. In most cases, this efficiency has been separated into

two parts:

1. efficiency of nebulization-yield of fog droplets from a

volume of solution introduced,

2. efficiency of atomization-yield of neutral atoms from sub-

microscopic species, i.e., atoms, molecules, ions, etc.

The former quantity is a very tedious one to measure, involving long

periods of aspiration of a relatively high concentration solution of

a suitable element, collection of waste solution and washdown from

the nebulization chamber, and dilution to volume. Then, the concen-

tration of the analyte in the diluent must be determined. Typically

(for most nebulizers in atomic spectroscopy), this is a low efficiency

process. Therefore, the accuracy is subject to determinate errors in

procedures.

The problem of determination of efficiency of atomization follows

directly on these results, unless a separate procedure is developed.

This is virtually impossible unless a vapor generation technique is

available. The efficiency measurement must be made via determination

of the total number density in the flame. The classical method for

this measurement has been to use absorption from a continuum source

(17, 18), which provides the desired quantity only after a tedious







calibration procedure, including correction for reflectivity of

multiple surfaces in the optical collection train. An expensive,

high-resolution monochromator is also required, as the atomic absorp-

tion line is quite narrow. In addition, this method does not allow

spatial or temporal resolution.

Saturation of the pertinent atomic transition provides a fluor-

escence signal (therefore a spatially resolvable signal in the usual

configuration), that is not a function of flame conditions (except as

a function of atom production capability), and is a function only of

basic atomic properties.



Noise Power Density

Noise power density measurements have been used typically by

information transfer and electrical engineers as a means of discovering

the sources of systematic and random noises in hopes of eliminating

them and being able to transmit data with fewer errors at ever in-

creasing rates. The techniques of noise measurement and theoretical

treatment have been growing in importance for analytical chemists

(19-28), as the science grows in depth and sophistication. The

attempts at measurement to date, however, have been troubled by lack

of definite calibration and lack of willingness to track down and

eliminate sources of instrumental noise in analytical techniques.

The difficulty of this task, while formidable, is not insurmountable

(29). If calibration can become complete, and the sophistication of

analytical chemists can be improved in areas which are now subsidiary

(flow engineering, electrical engineering, etc.),substantial improve-

ments should be forthcoming.







Saturated atomic fluorescence stands to provide a substantial

contribution to noise analysis in atomic spectroscopy. Saturation

provides several features:

1. elimination of dependence on quantum efficiency (flame

conditions),

2. spatial resolution,

3. possible loss of dependence upon the atomization step

(if correct analyte is chosen),

4. possible relative freedom from emission background noise

(if conditions are chosen carefully), and

5. freedom from source variation.

Therefore, saturation can further the understanding of noise

sources in atomic analytical spectroscopy. It can provide separation

of noise of nebulization from noise of atomization (if such a noise

exists), allowing better understanding, and design, of nebulization

systems.


Reaction Rates


Since analytical flames and plasmas are used at atmospheric

pressure and are quite hot (2000 K to 6000 K), reactions are myriad

and fast. In most flames and plasmas, some sort of local thermodynamic

equilibrium (LTE) is assumed. In several cases, however, the mechanism

of excitation of atomic species is unclear (e.g., the induction coupled

plasma, which is not in LTE). Engineers and physicists share with

chemists the need to understand these and other phenomena kinetically.

Saturated fluorescence (atomic or molecular) can be a very useful







tool in this pursuit, as a means of simplifying kinetic schemes by

swamping. Reactions such as photoionization, quenching, and inter-

system crossing can all be studied by means of saturated fluorescence.



Tunable Dye Lasers


The advent of the tunable dye laser (30, 31) and the power it

gives to observe atomic and molecular populations have given flame and

plasma spectroscopists an invaluable tool for diagnostic procedures.

The general properties of these and other lasers include:

1. directionality (low divergence),

2. monochromaticity,

3. coherence (spatial and temporal), and

4. high irradiance.

All of these laser properties have been useful for analytical

atomic fluorescence spectroscopy since Fraser and Winefordner (32) first

used a dye laser to excite atomic fluorescence. Their work covered

nine elements in hydrogen-air and acetylene-air flames. Limits of

detection obtained were within 10 to 100-fold of those obtained with

conventional sources, and linear dynamic ranges were about four decades.

Progress in both theory and experimental achievements has been rapid

in the ensuing years (12, 33-38). With more and more powerful lasers

available (37, 39-45), the possibility and theory of non-linear

phenomena has been investigated (40-44). Several authors have ex-

perimentally achieved near or complete saturation of atomic (46-50)

and molecular systems (51, 52).




-7-



Laser saturation of atomic transitions in this work has made

possible diagnostic procedures with spatial, temporal, and flame com-

position independence. This will allow analytical chemists to measure

the quantum efficiency, total number density, and noise power density

spectrum in an atomizer without the above mentioned problems of linear

spectroscopy. However, the benefits of this freedom must be weighed

against the need for sophisticated measurement systems (fast time

scale) and laser temporal and spatial inhomogeneity effects.












CHAPTER 2

THEORETICAL CONSIDERATIONS


Quantum Efficiency for a Two-Level Atom


A two-level atom is one which, although it may have many quantum

states, has only one excited state available for thermal population in

addition to the ground state. After it has been delivered to the

excited state by absorption of a photon, it can be returned to the

ground state by either of two paths, emission of a photon or colli-

sional deactivation (quenching). Quantum efficiency (Y) is a measure

of the efficiency of the radiative process with respect to the absorp-

tion process. A schematic diagram of a three-level atom and its

processes is depicted in Figure 1. A two-level atom can be pictured

by ignoring all processes connecting the third level and the other

two levels. A real example of a two-level atom is shown in Figure 2.

Only the 4s level is available for thermal population in analytical

flames (temperature range from about 2000 K to 40CO K, kT is therefore

0.2 to 0.37 eV).

The basic fluorescence radiance expression (53) is given by:


BF 47 Y21E 12 jk dv (1)

where

1 = path length in direction of detection system, mr

4r = number of steradians in a sphere (fluorescence is
isotropic), sr



























Figure 1. Three level atom model photon and collisional
processes are illustrated. Symbols are explained
below. The lower state is symbolized by "1" and
the upper by "u."

B Einstein coefficient of induced absorption
lu (m3 j-1 s- Hz)

Bu Einstein coefficient of induced emission
ul (m3 j-1 s-1 Hz)

A Einstein coefficient of spontaneous emission
ul (s-1)

E,1 Spectral irradiance of exciting radiation
u(W m-2 Hz-1)

k Rate constant for collisional process con-
niecting state m wi h state n








4p2


5s


4p0
2-


4p0


4s2
1~


Figure 2. Calcium term diagram levels 1 and 2 are indicated.


1,2,3


4d







Y21 = fluorescence power (quantum) efficiency, W fluor-
esced/W absorbed

Ev12 = spectral irradiance 9f exciting radiation at absorption
line, v12, W m"- Hz-1 (1 W = 1 Js-1)

f k dv = integrated absorption coefficient over absorption
0 line, m-1 Hz

The product Ev,2 f k dv is the power absorbed from the source by the

analyte atoms per meter cubed of atomic species. The integrated

absorption coefficient is given by:


hv, gn, -1
fk dv = n1 ) 812[ ], 1 Hz (2)
V 1 12'


where

Nh12 = energy of the exciting photon, j
c = speed of light, m s-1

B12 = Einstein coefficient of induced absorption, m3 J-
B s-1 Hz

g1' 92 = statistical weights of states 1 and 2, respectively,
dimensionless

nI, n2 = concentration of states 1 and 2, respectively, m-3
(note that n1 + n2 nT, the total concentration of
atoms in all states)

The bracketed quantity corrects for the effective decrease in absorp-

tion caused by stimulated emission from the upper state.

Using the rate equation approach, and invoking steady state, we
arrive at

B 2Ev12 B 2112
(k12 + c = (k21 + 21 c A n2 (3)


where







k12' k21 = excitation and deexcitation non-radiational
(collision) rate constants, s"

A21 = Einstein coefficient of spontaneous emission, s-1
21 = Einstein coefficient of induced emission, m3 J-1
1 s-1 Hz

B12 = Einstein coefficient of induced absorption, m3 J'1
s-1 Hz

nI, n2 = concentrations of electronic states 1 and 2, m-3
c = speed of light, m s-1

The quantum efficiency is defined as

A
Y1 A 21 k (4)
Y21 A21 + k21


and A21 is related to B21 and 812 by

3 3
8rhv312 8hv 12 1
A21= (c3 ) B21= ) (2 12 (5)

Combining these expressions, one arrives at


6h (L-) Y E*1 (6)
BF= () 21E12n1 12) 12 (E*vl2 + E'12


where E*j12 is a modified saturation spectral irradiance (W m-2 Hz-1)
evaluated at frequency v12 and is defined as

cA21
E*12 (7)
21Y21


The term E*v12 can be expressed in terms of the saturation spectral
irradiance Es 12, which is the spectral irradiance required to bring







about 50% of the maximum fluorescence radiance possible. If Es 12 is

expressed as a function of E .12, then


Es 12 = E* 12 9+ 12) (8)


Substituting for nI in terms of nT (nT = n1 + n, and using Eqs. 3,

6, and 8)

hK 12 F 12
BF )Y21E 12nT( c E 12
ES1 +
E 12


The maximum fluorescence is then

g2
BFm (a )hA21 nT (g ) (10)


When E 12 = Es12 then BF = BFmax/2.
max


cA21 8Thv3 ()
12 1Y21 c2Y21
2-


g1 7.6 x 1023 (12)
Es12 glg2) ( 2Y) (12)


A theoretical plot of BF vs. Ev12 appears in Figure 3. If a plateau in
fluorescence radiance can be observed as laser power is varied, and the

laser power at 50% of this maximum fluorescence radiance can be found,

then the quantum efficiency can be found from the quantity Es 12. For

calculations in this work the quantity Esx12 will be used (see Eq.

12).




















Figure 3. Theoretical saturation curve.















100


log EA (relative)


-I---------- _,.-- ----_







The necessary conditions for the measurement of quantum efficiency

in this way are

1. Saturation must be completely achieved, so that BFmax can
Fmax
be evaluated.

2. One must measure E12 by measuring the following quanti-

ties:

a. laser peak power (W),

b. laser cross-sectional area (m2,

c. laser optical bandwidth (Hz).

3. Self-absorption must be negligible.

4. The source must be a spectral continuum with respect to

the absorption line width.

5. A steady-state condition must be achieved.

6. No coherence effects can be manifested. The rate equation

approach must be valid.

The achievement or measurement of these conditions is described in

Appendix 1.



Quantum Efficiency for a Three-Level Atom

The same approach (as used for the two-level atom) yields for a

three-level atom like Na (see Figure 4)


Es 13 g 31 k32 E*13 )
V13 93 91 k32 r!1


where









21/2, 1 1/2




4p0


21D 1 /2, 2 1/2





3d


4s


3 ... 3o
I
2


3s
1


Figure 4. Sodium term diagram levels 1, 2, and 3 are indicated.


251/2




-19-


cA31 87hv3
E*13 B131 c-h (14)
31


kmn = collisional rate constant connecting atoms in the
m m state with those in the n state

The E5,13 is again related to Y31, but no simple relationship

exists. The collisional constants, which are unknown in the litera-

ture, interfere with the interpretation.

For some limiting cases, where level 2 is close to level 3 (e.g.,

sodium, see Figure 4) or is close to level 1 (e.g., indium, see

Figure 5), certain assumptions can be made.

With sodium, for instance, if the assumption is made that


k23 >> k21 + A21

then

k32 k32 2
A21 + k21 + k23 = k23 93


Then


E13 (1)( 2) E*13 (15)
93 1 gl g2)
1 + -- + --
93 g3



E 13 g + g2 g3) E*13 (16)


This is equivalent to a two-level system, as the top 2 levels have

merged into one, effectively.












2P/2,1 1/2


21 1/2, 2 1/2


6d


7s


5p2


5d


6s
3-


2
4p0
1

Figure 5. Indium term diagram levels 1, 2, and 3 are indicated.


41/2, 2 1/2







For a three-level atom like In


s 13A= 32 + k32 + k21 E13
= t-~ 13 L k3 2 + k2 1 v13

93 k21+ k12 -

The same type of assumption should hold for levels 1 and 2 as

previously for level 2 and 3. Therefore, if


k21 >> k32 + A32

then

k21 1 1_ 91
21 + 12 1 2 + 2 1 + 2
1 + 1 + -
k21 91
and

s g1 + 92 (17)
E13 =g1 + 92 + 93) E1317)


This is again equivalent to a two-level system.


Saturation

Complete saturation means that the population of the excited
state and the ground state are equalized (with due regard to the re-

spective degeneracies). Therefore, the kinetic drains on the excited
state are negligible with respect to the optical pumping rate. A

further increase in irradiance cannot effect an increase in fluorescence
radiance.

A measurement of this (saturated) state usually means that when
the irradiance is reduced, via some suitable filter, the fluorescence







signal does not decrease. By placing calibrated filters in the beam,

one can determine the point at which only half of the signal is left;

this point is the saturation spectral irradiance.


Quantum Efficiency Via the Slope Method

Two-Level System

From the two-level theory, it can be shown that


1 1 1 (g4)
BF 12 g2 3 5 5
F '12 92 6.6 x 103 Y211hv211A21nT


+ ((1 2) 4h ) (18)
g2 hv12!A21n T

A plot of the theoretical shape of 1/BF vs. 1/Es is shown in Figure 6.

The pertinent features are the slope and the intercept. The slope
of this plot contains the quantum efficiency (and n-), and the inter-

cept contains nT.

For this procedure, all of the above mentioned criteria must be
met with the exception of completeness of saturation. The closer
saturation can be achieved, however, the less extrapolation is

necessary. In addition, the fluorescence collection depth, 1, must
be measured, and the collection photometer calibrated.

If both sides of Eq. 18 are multiplied by the quantity


nThvl21A21
4th

then the 1/BF axis can be scaled absolutely, as the intercept is















Figure 6. Theoretical 1/BF vs. 1/E curves. Curves shown are
for two different quantum efficiencies (Y) and two
different total number densities (nT).



























/-- -slope proportional
to 1/Y



(Q





intercept proportional to nT






1/E (relative)







equal to the quantity


91+ g
g2


which is well known.


Three-Level Case


A rearrangement of the three-level fluorescence expres-


1
BF 3
1+3


4w 1, 1
41Tyl31L nT
(A31 hv131nTL


+ ( k32 +__
A21 + k21 + k23 g3


+ gl( )I
g3 Y31 3EXj


When this is rearranged, we have


A31h131nT
4


1 g18rhc2 1 1 + 93 k32
1 1 1 i __e_ /_
B .5 E g A k + k (20)
Fl+3 g3Y31X13 13 3 21 21 23
1+3


A plot of these quantities cannot be scaled absolutely because the
intercept includes unknown collisional rate constants. The same
speculation as before can still be made, however, regarding the rate
constants, allowing calibration to be made in certain limiting cases.
That is, k23 can be expected to be much larger than either A21 or k21.
The term

k32
A21 + k21 + k23


Sodium.

sion yields







then reduces to

k32
k23

By the law of mass action at equilibrium

k32 n3 2
T n- -g
23 2 93

The fluorescence slope method equation reduces to


1 4r 1 g2+g1 1
1 (_43 )T 92 91 +
BF13 A31hvl3)1 nT 93 93


8 rhc2
Y( X l
Y31 3EX


Rearranged this equation resembles that for two levels


A31hv131
4 B F 1+3
1+3
1+3


g18 fhc2
gy 5 +
93 31 13E


g2 + 91
1 +
93


Indium. For an atom of the indium type, where the second ex-
cited state is very close to the ground state,the slope method equa-
tion is


nT1A31h313
S 4ir


1
BF 3
1+3


1 g2 )(8hc2
)(+ -1 exp[-E2/kT])( 31E
93 gl V


+ g9 + g3
g93
93


+ 2 exp[-E21/kT] + A32k 32


In this case k21 can be assumed to be much larger than A32 + k32'
and this term then is negligible.







Total Number Density
Two-Level Absolute Plateau Method

A measurement of BFx


B -(1 )[h 92
BF = (4, )[hvl2A21nT (g
gmax nT-


produces nT easily if the measurement of BF is absolute (see Appendix
max
1) and if 1, A21, and the g's are known.


Two-Level-Slope Method

The calibration of the 1/BF axis is direct for total number density

if gl1 9g, h, v12, BF, and A21 are known, as the intercept of the

1/BF axis is

1 4 g 1 + 32
BF Ihv12A21n g2


Three-Level Case--Absolute Plateau Method

Unless assumptions or experiments are made for the relative size

of the collisional constants, calibration is impossible. Relative

measurements are still valid, and saturation still assures immunity

to quantum efficiency effects as in the two-level case.


Three-Level Case--Slope Method

Once again assumptions must be made for collisional constants in

order to permit calibration of BF in terms of n .



Possibility of Absolute Calibration


If the ratio of resonance to anti-stokes fluorescence is taken,

in saturation, we have








BF 92 g A31 + k31
13 1 + + -- exp[E21/kT] + k
1+3max 93 93 112 k
BF g92 A32 k32 (22)
f3max 1 + + exp[-E21/kT] + k21
2--3ax 93 93

Both ratios
A31 + k31
kl
k21

and

A32 + k32 A +k g
Ak32 k k32 312 3 exp[E2 /kT]
k1 2 k 21 gg2 12

are probably not much greater than one, as k21 is expected to be at
least comparable to either numerator. Then, if E21 >> kT, two con-
ditions are satisfied

1 g1 A31 + k31
i. -->>
93 92 k21

g2 A32 +k32
2. !3 exp[-E21/kT- << 32 k32
93 k21

Equation 22 then reduces to

BF +2 1
1+3max 1 +--+--exp[E 21/kT]
1+3max g3 93 21
F 1 + A32 + k32(23)
1+3 i + g- +
23max g k21

If a flame of known temperature can be produced, then the ratio
(A32+k32)/k21 can be evaluated. This allows Y (and nT) to be obtained
in absolute units. For a flame with a temperature of 2300 K and







thallium as a probe (E12 = 0.966 eV),the exponential term is as
follows:

exp[+0.966/2300 x 0.861 x 10-4] = 131


For thallium


91= 1
92=3
g3= 1


Then


BF 2 + A32 k32
2-3"m k21
BF3max 135
!+3


The difference between the ratio and 2/135 = 0.0148 is the contribu-
tion of A32 + k32/k21. This value, when inserted into Eq. 21 (for
measurement of thallium, in this case), would allow the intercept of

the

nT1A31hv13
4fBF13
1+3
1+3

axis to be completely calibrated, as the intercept then contains only
known quantities. If BF is known absolutely (calibrated),then nT can
also be arrived at unambiguously.


Noise Power Density

The theory and practical measurement of power spectra (power vs.
frequency data) have been adequately covered by Blackman and Tukey (54).







Two approaches are possible to measure noise power spectra. The first

is to compute the autocovariance function for the data collected. The

Fourier transform of this is the power spectrum. The second procedure

is to compute the Fourier transform of the data, then to square and

add the frequency and phase components to find the power spectrum.

Although both methods were available, the second one was chosen for

its conceptual familiarity. The use of a discrete data collection

system (analog to digital converter) required a discrete Fourier

transform, with attendant aliasing and bandwidth problems.

The application of saturated atomic fluorescence will result in

an ability to separate the noises resulting from the nebulization pro-

cess from those stemming from the atomization of the analyte. Since

these two sources of noise are independent, their noise power spectra

add linearly. Since the measure being computed in our case is the

noise current spectrum, these would add quadratically. If an analyte

such as copper, which is completely atomized in a standard flame, is

measured, the noise power under known conditions can be found.

This noise power should be reproducible in nature with the ex-

ception of certain non-stationary noise sources. If this proves to be

the case then the total noise and the 1/f noise pertinent to most

spectroscopic measurements can be investigated with respect to design

elements and operating characteristics common to atomic spectroscopy.

These include burner, chamber, torch, and nebulizer design, as well as

gas flows and flame stoichiometry. Noises involved in the flame or

plasma processes up to the point of atomization could then be sub-

tracted from the noises seen for an incompletely atomized analyte,

producing the noise inherent in the atomization process.







The unfortunate truth, however, is that many of the underlying

noise sources in analytical spectroscopy are non-stationary.

Examples of non-stationary noises are nebulizer clogging, RF noise,

60 Hz mains noise, some source drift noises, stray light noise (room

and daylight), and some electronic drift noise. These are not really

approachable via the technique or theory of noise power spectra, though

often a reasonable idea of the noises can be found (55).












CHAPTER 3

EXPERIMENTAL


General Comments

A variety of experimental systems were used for collection of data

pertinent to these measurements. The basic system shown in Figure 7

is the laser excited atomic fluorescence system described by Weeks

et al. (13). The system has been modified slightly, as reported by

Bower et al. (56) and Bradshaw et al. (10). Several of the features

changed since the measurements of Weeks et al. are of high importance.

The spatial effects of saturation in the wings of focused Gaussian

laser beams, as observed by Blackburn et al. (50), and previously

predicted by Rodrigo (57) and theoretically approached by Daily (58)

have been eliminated by moving the observation point approximately 10

feet further from the laser. At this point, the spatially homogeneous

section of the laser beam was enveloping the whole seeded flame (see

Appendix 1).

In order to facilitate alignment, it was necessary to add folding

mirrors (M) with adjustments in the horizontal and vertical planes.

A problem involving dye changes leading to a different angle of

emergence has been circumvented by the use of the folding mirrors

and the combined aperture-scatter shields (ASS). The two apertures

initially were set to define the beam line of interaction of the dye

laser and the flame. When subsequent dye changes produced non-colinear


-32-














Figure 7. Laser excited atomic fluorescence system. System
components are as follows: LPS = laser power supply,
NPL = nitrogen pump laser, DL = dye laser, M = folding
mirrors, TG = trigger generator, B = boxcar, SCR =
strip chart recorder, ASS = aperture-scatter shield,
LT = light trap, BU = burner, L = lenses, MO = mono-
chromator, PMT = photomultiplier tube, PS = high
volLage power supply. For source of major equipment
see Table 1.












a ~~9









Table 1

Laser Excited Atomic Fluorescence Equipment List


Manufacturer


Model UV-14 Nitrogen Laser

Model DL-300 Tunable Dye Laser

Model FL-2000 Tunable Dye Laser

Nebulizer chamber

Capillary burner

Flame-shielded burner

Model H-10 monochromator

Model 412B High Voltage
Power Supply

Model R106 Photomultiplier
Tube

Model 160 boxcar


Model 162 boxcar mainframe


Model 163 boxcar plug-in
module

Model 164 boxcar plug-in
module

Type S-2 sampling heat

Servoriter strip chart recorder

Apertures (iris diaphragms)


Molectron Corp., Sunnyvale, Cal.

Molectron Corp., Sunnyvale, Cal.

Lambda Physik, Gottingen, W. Ger.

Perkin-Elmer Corp., Norwalk, Conn.

laboratory built

laboratory built

Jobin-Yvon, % ISA, Metuchen, N.J.


John Fluke, Seattle, Wash.


Hamamatsu Corp., Middlesex, N.J.

Princeton Applied Research,
Princeton, N.J.

Princeton Applied Research,
Princeton, N.J.

Princeton Applied Research,
Princeton, N.J.

Princeton Applied Research,
Princeton, N.J.

Tektronix, Portland, Oregon

Texas Instruments, Dallas, Texas

Edmund Scientific, Barrington, N.J.


Item







beams, these could be adjusted with the mirrors to pass through the

apertures.

The collection system was aligned at a 90 degree angle to the in-

coming beam by the use of helium-neon alignment laser crossed with the

dye laser beam.



Radio Frequency Shielding


Radio Frequency (RF) shielding of the entire Molectron nitrogen

pump laser enabled the output to be freed of the large drift-type noise

associated with people and objects moving in proximity to the experi-

mental system. This involved enclosing the whole pump laser and power

supply in a brass screen Faraday case. All electronics were connected

via grounding straps to a salt-bed earth ground. All cables leading

from the photomultiplier to the detection electronics were double-

shielded by a coaxial woven shield augmenting the internal shield.

These modifications enabled RF noise-free measurements into the milli-

volt level, which corresponded (with a 50 n 2-fold attenuator) to

40 uA of peak current. This was possible even with a background

current of 100 pA. For most measurements, the limiting noise was the

electronic noise of the boxcar average.









Photomultiplier

The photomultiplier was wired for fast pulse, high current

output, as reported by Fraser and Winefordner (32) and operated at

-1000 V. Cable of 50 n impedance (RG-58U) was used for all

connections.




Fluorescence Flux Collection


A Jobin-Yvon H-10 low dispersion monochromator was used

for collection of fluorescence. Dispersion is low and collection

efficiency high, as suggested by Weeks et al. (13). A two lense

collection system with an intervening aperture was used to help

cut down on scatter for resonance collection cases. Scatter in

these cases was reduced by liberal use of light traps (LT), aper-

ture scatter-shields (ASS), and black felt cloth. In many cases,

this scatter signal was Rayleigh scatter (indicated by an increase

when the flame was turned off), and could not be completely elimi-

nated. In such cases, the noise limit for measurements was due to

laser carried (peak to peak variation) scatter noise. The image

formed by the two lenses at the slit of the monochromator was of

unit magnification.







Detection Electronics

A PAR 162 boxcar average was used for detection and measurement

of fast fluorescence pulses. Two different inserts (plug-ins) were

used in measurement and alignment. The 164 plug-in offered fixed

sensitivity (100 mV full scale) and several integration times. It was

quite hardy, and was used for preliminary alignment, when a very large

scatter signal was used to set the gate delay. The 50 a input im-

pedance was always used to match the cable and minimize ringing.

Some ringing was still apparent, however. The 163 plug-in with an .S-2

sampling head was used for the main measurement scheme. The gate was

75 ps (S-2 sampling head); jitter in the boxcar gating circuits led to

some distortion of this aperture. This head was used to find plateau

(saturation) values on top of the fluorescence temporal pulses, which

corresponded to saturation of the atomic fluorescence.

The synchronous trigger of the laser could not be used, as RF

feedback occurred at the time of each trigger and interfered with data

collection. A separate trigger generator was used, which had a delayed

pulse feature. This enabled correct timing between laser firing and

boxcar gating.



Nitrogen Laser

The nitrogen pump laser was run according to manufacturer'sin-

structions. The high-voltage power supply was kept at 22 kV to give

better longevity of the critical components (thyratron and capacitor),

as these had been problematical in the past. The nitrogen flow rate

was 15 liters per minute for all experiments. Operating pressure was







maintained at 55 torr. The pressure transducer had to be replaced

and calibrated twice, however. This involved approximately half a

day to a day's work, since the entire pump head had to be removed from

the Faraday cage. All connections had to be made again outside the

cage in order to test fire and calibrate the unit.

The repetition rate was kept at about 15-20 Hz for all experi-

ments. Greater repetition rates led to lower peak powers. High peak

power was necessary for saturation. However, a rate below ca. 20 Hz

would lead to signal leakage problems on the boxcar mainframe.

An interesting phenomenon was observed at the 20 Hz repetition

rate. A beat frequency appeared on the dye laser output. This was

first attributed to the power supply of the laser, as its voltage

dipped when the laser was fired. This idea was discarded when it was

noticed that the beat frequency was about 2 Hz. The observation was

made that as the dye fluoresced in the cuvette on each nitrogen laser

pulse, the magnetic stirrer appeared to be processing at about 2 Hz.

The motor provided was an AC motor running at a multiple of 60 Hz.

The stirring of the dye cell seemed to be incomplete enough that when

the nitrogen pulse came at a sub-multiple of the stirring rate, a

beat frequency due to excitation of spent dye appeared. A need for

improvement in stirring was quite apparent. This beat frequency

effect had never appeared in the literature.

Voltage drifts during the day were so bad (1 V on regulated

supplies, 10 V on unregulated lines) that severe trigger drift became

apparent. The nitrogen pump laser was very susceptible to trigger

drifts through its high voltage threshold performance. A voltage

change of 1 V on the 120 VAC line can induce a 20 ns drift in the




-40-


trigger to firing delay. Using a 164 plug-in on the boxcar, this was

annoying. When a 163 plug-in is used the signal can entirely dis-

appear inside of 5 min time. Therefore, all of the experiments had

to be done at night when stability was much better, but still trouble-

some, however. Generally during each series of measurements the

trigger had to be reset at least once.

An optical trigger was used for subsequent experiments. The

163 plug-in, however, was not used. Indications were that this

arrangement was much more stable with respect to jitter, especially

if triggered from the pump laser. Use of the optical trigger necessi-

tated placing a delay line (V155Z050, Allen Avionics, Mineola, NY)

into the signal line from the photomultiplier to produce a 75 ns delay

necessary to compensate for the internal gate delay of the boxcar.

A 50 0 attenuator was placed before the delay line to produce a

voltage pulse from the current pulse. Indications were that distor-

tion and noise introduction by the delay line were minimal.



Dye Laser Operation


The dye laser was also operated according to manufacturers in-

structions. Dyes were prepared according to Table 2. Adjustments of

the dye cell carriage were made after each new dye cell was introduced

into the beam line. This should not have been necessary if the laser

was functioning correctly. There was some indication that this was

an artifact due to the state of our dye cells. Possibly the anti-

reflective coating had worn off in several years of use (see Appen-

dix 1).









Table 2

Laser Dye Preparation


Wavelength
Dye Concentration Solvent Range (nm)
M) (10% points)*

DPS Saturated p-dioxane 396-416
1.2 x 10-3

Bis-MSB 1.2 x 10-3 p-dioxane 411-430

7D4MC 10-2 ethanol 440-478

R6G 5 x 10-3 ethanol 568-605


*The 10% points are the wavelengths at which laser output is 10%
of the peak output.







Dye was changed frequently to avoid power loss due to dye deteri-

oration. This was done in one of two ways. The method of exchange

recommended by the manufacturer was to remove the dye via a pipet,

rinse the cell with fresh dye, and refill with fresh dye. This was

moderately successful. Some dyes (7D4MC in particular) seemed to

function better when the dye cell was removed entirely from the dye

head, rinsed thoroughly with alcohol, then fresh dye, and then re-

filled with fresh dye. Peak power with 7D4MC exchanged in this manner

was enhanced at least 2-fold over the more cursory method of exchange.

Bubbling of pure nitrogen for two minutes through the dyes (as sug-

gested by Exciton) did not seem to make a substantial change in dye

longevity. Perhaps nitrogen saturation during preparation and storage

would have helped more.



Flame System


A gas-flow stabilization system consisting of individual pressure

gauges and rotameters was used for each gas flow. The entire system

was calibrated by means of a linear mass flow meter (ALK-50K, Hastings,

Hampton, Virginia). Each time a flow was measured, the pressure was

readjusted, and the flow and rotameter readings recorded. The com-

bination of a fixed pressure and the rotameter readings led to a very

reproducible and precise system. Premixing of flame gases was done

to avoid background noise due to poor mixing in the chamber of the

burner. The flows passed into the appropriate ports of a nebulizer-

flow chamber (Perkin-Elmer Corporation, Norwalk, Conn.). The same

composition (premixed) passed into a separated shielding flame for







hydrogen-based flames. The fog and premixed combustion gases left

the flow chamber and passed into a capillary, flame-shielded burner

for hydrogen based flames (previously described by Snelleman (59)).

There they were combusted. The flame-shielded flame was surrounded

by an inert gas sheath to avoid background DC emission and noise as

much as possible.

Acetylene based flames were combusted above a capillary burner (Haragu-

chi and Winefordner (60)) supported on the same nebulizer chamber.

Flows for the different flames used are shown in Table 3.



Solutions


Stock solutions of 1000 Ig/ml for all elements were made from

reagent grade chemicals in deionized water per Parsons et al. (61)

(see Table 4).



Measurement Procedure for Y and n


The necessary criteria for evaluation of quantum efficiency and

total number density via the two different schemes are

1. Saturation must be complete (for plateau method) or nearly

complete (for the slope method); that is, an increase in laser

power must not result in an increase in fluorescence

radiance.

2. One must measure laser spectral irradiance via measurement

of the following quantities:

a. laser optical bandwidth--via some type of wavelength

scan,




-44-




Table 3

Flame Gas Flow Rates


Air-Acetylene Flame

Air 9.88 1/min

Acetylene 1.65 1/min


Hydrogen-Oxygen-Inert Gas Flame

Hydrogen 1.62 1/min

Oxygen 0.81 1/min

Nitrogen or Argon 4.51 1/min




-45-




Table 4

Source of Reagents


Sodium NaC1


Calcium CaCO3


Strontium SrCO3


Indium In203


Mallinckrodt Chemical Works,
St. Louis, Mo.

Mallinckrodt Chemical Works,
St. Louis, Mo.

Fisher Scientific,
Fair Lawn, N.J.

Apache Chemicals, Seward, Ill.







b. laser peak power--via calibrated photosensitive device,

c. laser cross-sectional area--via geometrical considera-

tions; b and c measurements may be combined.

3. Self-absorption must be negligible. (This is automatically

achieved if saturation is complete, as the absorption coef-

ficient then goes to zero.)

4. The source must be a (pseudo-)continuum across the line-

width of absorption; i.e., the wavelength spread of the laser

must be measured and determined not to vary substantially

across the absorption linewidth.

5. Steady state fluorescence must be achieved. The temporal

behavior of the atomic fluorescence pulse must be observed.

Measurement of the saturated value must be during a suitable

steady state.

6. The rate equation approach must be valid. No coherence

effects may be seen.

7. The fluorescence depth 1 must be found (Figure 8).

In addition, if the possibility of absolute values of Y and nT

is. to be evaluated for a three-level atom, the ratio of resonance to

stokes fluorescence must be found in a flame with a known temperature.

Since the proof of validity of these criteria is somewhat

tedious, it will be assigned to Appendix 1, with the exception of the

first point, completeness of saturation, because this is the basis

of the whole measurement scheme.

For each dye change, alignment of the laser beam with the burner

head was undertaken. Side to side position of the laser was checked

with the flame off, by the use of the aperture-scatter shields and a














Laser beam illumination
axis

---------------> ----77


Inner (seeded) flan


Collection axis
with monochromator
slit projected
onto flame


Fluorescence
collection
depth (1)



Fe
Flame volume investigated


Figure 8. Fluorescence illumination and collection schematic.


r







card over the burner. Vertical positioning was accomplished by using

the card to project an image of the laser beam through the first col-

lection lens onto the slit-shaped aperture. After spatial alignment

was completed, the gate delay was peaked up on a scatter signal.

Next, the flame was lit, and analyte was introduced. The dye laser

was wavelength scanned, using the scan control until a substantial

signal was found. Since saturated atoms show a broadened response

to wavelength (see Appendix 1), a calibrated neutral density filter

was set in an accessory optics holder in the laser beam. In this way,

a linear response to laser illumination was ensured. Neutral density

filters of about 2.0 to 3.0 were generally required. When illumina-

tion was in the linear region, the dye laser output could be easily

centered on the wavelength of the atomic transition. When the

neutral density filter was removed, the atoms were saturated.

Generally analyte concentration was chosen to yield a high enough

signal so that a linear portion of the laser fluorescence vs. power

plot could be reached as the laser power was decreased. In some

cases, this involved using a higher concentration at low laser power

to ensure sufficient signal to noise ratio. Linearity of fluorescence

with respect to concentration was always checked when this was done.

The upper limit of concentration was set to avoid problems of vapor-

ization (especially prevalent in the low temperature hydrogen-based

flames used here) and self-absorption. No absorption was noticed,

however, with solutions up to 1000 Pg/ml in concentration, although

the measurement of absorption was complicated by severe shot to shot

peak power variations on the dye laser. In most cases, concentra-

tions were in the 1 to 20 vg/ml range.







The procedure for measurements started with a check for PMT

linearity. Even with the use of a low resistance (high current)

dynode chain and capacitor charge storage for each dynode, the PMT

output current could become non-linear with respect to illumination

when the light levels became high enough. Each time data were taken,

a 0.3 neutral density filter was inserted in front of the mono-

chromator. If the signal did not decrease by 50%, a lower concen-

tration was aspirated, and checked for linearity. Approximately half

of the full scale (1 V) was usable for the 163-S-2 plug-in combina-

tion. This corresponded (with a 50 0 2-fold attenuator) to a 10 mA

peak current. This compared with a limit of 0.3 mA peak current limit

of Olivares (46), for a 220 kn resistor chain with no added capaci-

tance, for a 1P28 PMT. A linear dynamic range of 30-fold higher

(based on current) was obtained in our case.

After the linearity check, the actual saturation curve measure-

ment was performed. This consisted of measuring full scale fluorescence,

blank scatter, and several reduced fluorescence and scatter values

when calibrated neutral density filters were placed in the laser beam

singly or in combination. Scatter corrections for resonance measure-

ments were generally significant until the laser intensity was re-

duced 1 to 2 orders of magnitude by neutral density filters.

These fluorescence measurements were converted to absolute

radiance values following calibration of the optical collection

system, the boxcar, and the recorder used to collect data (see

Appendix 1).

From the absolute radiance measurements, values were computed

for quantum efficiency and total number density. In some cases rela-

tive data only were computed for different flames.




-bU-


Noise Power Density


The measurement of noise power density spectra in academic analy-

tical chemistry is generally accomplished via the discrete fast

Fourier transform (DFFT). This approach is necessitated by the lack

of continuous measurement power spectrum analysis instrumentation in

most laboratories. The dedicated instrumentation required by this

method is generally too inflexible to be affordable under tight

budgeting restrictions of this time. On the other hand, the general

availability of digital computers and analog to digital data collec-

tion systems makes discrete (or sampled) data collection fit reason-

ably within the price and flexibility range of most laboratories.

This leaves one with only the DFFT approach to noise power spectra

evaluation possible. This enforced choice leads to a loss of flexi-

bility in one way, and to a gain in another direction. The disadvan-

tages of discretely sampled records for approximating a power spectrum

are very well covered in Blackman and Tukey (54) and include aliasing

(necessitating very well designed filters for spectra with wide dynamic

ranges and wide frequency ranges), intermodulation distortion, and

finite bandwidth.

The flexibility advantages are those which stem from the com-

puter itself:

1. ease of collection,

2. ease of calibration,

3. fast data reduction,

4. ease of presentation,

5. flexibility of handling of data and power spectra.




-51-


The primary purpose of noise power spectra collection in this work

was to establish a background for later possible saturated noise power

spectra, which should show the advantages enumerated in the Introduc-

tion section.

The primary sources of noise for atomic spectroscopy consist of

the following:

1. Source related noise

a. white,

b. whistle or proportional,

c. flicker or 1/f.

2. Background noise-non-source related


a. white,

b. whistle or proportional,

c. flicker or 1/f.

3. Sample related noise

a. white,

b. whistle or proportional,

c. flicker or 1/f.

The preliminary experiments presented

types of noises. The first type will

ments.


here measured the latter two

be the subject of later experi-


Background noise can be somewhat artificially separated into two

types. The first type is related to the bulk properties of the flame

gases; this type could be exemplified by the emission from the C2

molecule, a product of partially completed combustion. This molecule

has a major emission at 516.5 nm called the Swan band. While it does

not interfere with most atomic transitions, other bands can interfere




-52-


with DC and fluorescence measurements with pulsed sources. The

Swan band is sensitive and can be used as an indicator of formation of C2,

and therefore as an indicator of combustion completeness. This

molecule has been used as a measure of success for premixing com-

bustion gases (29). Noise power spectra collected under fixed con-

ditions also provide a useful figure of merit for the evaluation of

success of mixing.

A second type of background emission noise source is one which is

more indicative of external conditions. An example is the OH molecule,

which is strongly indicative of the success of sheathing a flame.

The pertinent (and sensitive) band is centered on 306 nm, and extends

to the red far enough to interfere severely with copper and silver

measurements while a companion band at 285 nm interferes with

lead and magnesium measurements. Noise power spectra at this band

can hopefully lead to better design and construction for flame

sheathing systems.

Sample related noise can be evaluated as a preliminary to satura-

tion measurements by using atomic emission. In order to collect data

on both nebulization and atomization noises without source noises

interfering, it is necessary to measure the noise involved in atomic

emission, unless saturated measurements lead to an improvement in

signal to noise ratio. An atom must be chosen which has strong emis-

sion, and is not near a background spectral region which would

interfere. Strontium is a likely candidate. Its emission is in a

relatively background-free region, and should therefore yield infor-

mation on nebulization and atomization efficiency noise. Strontium

is quite sensitive to flame temperature, and therefore composition.




-53-


It should be a good candidate for the proposed separation of information

from the two sources of noise. In addition, it is among the most

strongly saturated atoms found in this work. The general scheme of

investigation is as follows. The nebulization chambers and nebulizers

of three companies are to be investigated within the guidelines

established above. Conditions to be varied are use of an inert gas

sheath, premix chamber, and removal of the nebulizer. In addition,

data collection will be made in three frequency ranges (0-50 Hz,

0-500 Hz, 0-10,000 Hz).












CHAPTER 4

DATA


Notation

A general notation system is developed here for the reporting of

the experimental results in this chapter. Ratios will be listed as "R,"

with addition of one or more of the following subscripts for clarifica-

tion of the meaning:

HON Hydrogen-oxygen-nitrogen

HOA Hydrogen-oxygen-argon

S Slope method of calculating a quantum efficiency or ratio
of quantum efficiencies

E Es method of calculating a quantum efficiency or ratio of
quantum efficiencies

B BF method of calculating a total number density or ratio
ofmotal number densities

I Intercept method of calculating a total number density or
ratio of total number densities

A Measurements made in the argon diluted hydrogen based flame

N Measurements made in the nitrogen diluted hydrogen based
flame

Y Quantum efficiency

nT Total number density

References to the use of these methods can be found in Chapter 2

(Theoretical Considerations). Ratios "R" will always refer to argon

diluted flame values over nitrogen diluted flame values.




-bb-


Strontium

Boxcar Survey


The need to use the most versatile and least complicated equipment

possible was recognized at the commencement of this work. One of the

goals of the work was to find the optimal instrumentation for flame

diagnostic measurement via saturated atomic fluorescence, choosing from

the available choices in this laboratory. A series of measurements were

made under set conditions for the comparison of three boxcar average

measurement systems. The first pair of measurements (Figure 9) shows

saturation curves under identical illumination conditions for the

Princeton Applied Research (PAR) 160 boxcar and the PAR 162 mainframe

with the 164 plug-in. The two curves are very nearly identical, though

the scatter on this data was fairly great. (A substandard burner system

was used for these two preliminary curves. It was replaced after these

two experiments with the system described in the text.) The gates on

both boxcars were the same (15 ns). The 10 us stretch feature of the

160 boxcar did not seem to affect the extent of saturation. The second

pair of measurements (Figure 10) shows a comparison of the 160 boxcar

with the 162 mainframe using a 163 plug-in and a S-2 sampling head (75 ps

aperture). In addition to the boxcar change, a change of dye was per-

formed. As expected, the extent of saturation improved. The shorter

gate "viewed" mainly the temporal plateau section of the fluorescence

pulse (see Appendix 1), while the longer gate averaged substantially

unsaturated portions of the pulse with the saturated portion. The higher

power output of the new dye probably accounted for some portion of the

behavior.

















Figure 9. Strontium saturation curves using the PAR 162-164 boxcar
(x) and the PAR 160 boxcar (0). Actual BF values were
different. Plotted values were ratioed to highest signal
observed for each boxcar. A = e = 460.7 nm.
ex em















Figure 10. Strontium saturation curves using the PAR 162-163 boxcar
(x) and the PAR 160 boxcar (0). Actual BF values were
different for each boxcar. Each plotted value was ratioed
to the largest value observed for that boxcar.
m = ex = 460.7 nm.
em ex




-60-


Based on the results of these measurements the rest of the measure-

ments were made with the 162 mainframe 163 plug-in combination to achieve

an accurate representation of the saturation condition.


Flame vs. Inductively Coupled Plasma (ICP)


An acetylene-air flame and an ICP were compared to determine whether

saturation resulted in information about quantum efficiency. Two

parameters were evaluated under equal illumination in the flame and ICP,

namely the saturation curve and the saturation broadening (Appendix 1)

for strontium. The half-power points Ds for the saturation curve (re-

lated to E, see Chapter 2) is inversely proportional to the quantum

efficiency of a flame or plasma. For a given element and excitation

line, here strontium at 460.7 nm, the ICP was expected to have a higher

quantum efficiency than the flame. This was due to the prevailing argon

atmosphere of the ICP, as opposed to the predominantly molecular atmo-

sphere of the flame. The saturation curves (Figure 11) indicated that

the quantum efficiency of strontium in the ICP was slightlyhigher than in the

flame. A second measure of the quantum efficiency of strontium in the

flame or plasma was the saturation broadened excitation profile (Appen-

dix 1 and Reference (62)). A broader profile indicates a higher quantum

efficiency, as shown by:


p(X ) 1/2
6, = b6L (1 + )-- )
exc L S

where

6e = full width at half maximum (FWHM) of the excitation profile
exc of the atom (nm)

SAL = FWHM of the Lorentzian (undisturbed) profile of the atom
(nm)
















Figure 11. Strontium saturation curves in the air-acetylene flame (D)
and the induction coupled plasma (ICP) (x). The ICP had a
slightly lower E than the flame, and therefore, a slightly
higher quantum efficiency. The log-log scale of this
figure reduces the visualization of this small change.
Se= X e = 460.7 nm.
ex em



















1







l2
o- O

o



-1 0



-I i I I I
-3 -2 -1 0 1 2

log E (relative)







P(A;) = power density of the laser (W/m2

ps (X) = saturation power density (W/m2)
The term p (AX) is inversely proportional to the quantum efficiency (see

Chapter 2). Therefore, the exc depends upon quantum efficiency.

Saturation broadened exc are given below for strontium in the flame

and in the ICP under identical power density conditions.

Atom Cell 6xexc (full power)

flame 0.66

ICP 1.13
The increase in 6Xexc in the ICP also bears out the expected increase in

quantum efficiency in the argon atmosphere.


Hydrogen Based Flames

Hydrogen based, rather than hydrocarbon based, flames were chosen

for the major investigation of saturation because of the expected im-

provement in saturation due to a much less complex and reactive small

molecule (quenching) mixture in the flame gas. Two inert gas diluents

were investigated to find the role they play in quantum efficiency in

flames. Nitrogen was chosen for its obvious place in any air oxidant

flame. Nitrogen is a good diatomic quencher. It is often replaced for

atomic fluorescence purposes by a monatomic species, argon, which is a

very poor excited state quencher. Therefore, it allows a higher quantum

efficiency. This yields a higher sensitivity in application of atomic

fluorescence to analysis.

Saturation curves for the two diluent gases are shown in Figure 12.

The two curves are very close in plateau values and in shape. This was

an indication that the change in flame gas had very little effect in
















Figure 12. Strontium saturation curves in two hydrogen based flames.
The flames were diluted with argon (x) and nitrogen (0).
While the plotted values were ratioed to the individual maxi-
mum values, the relative magnitude between the curves was
retained. The value of Ex for the data plotted here was
measured using a round (1 cm diameter) aperture.
x = X = 460.7 nnm.
ex em







either the atomization of strontium or the quenching of excited state

strontium atoms. Relative information was derived for Y and nT from

this plot. Relative saturation powers (proportional to Es) were found

from the points at which the fluorescence was 50% of the maximum. The

saturation powers are proportional to 1/Y (see Chapter 2). In addition,

the slopes of the 1/BF vs. 1/E, curves were taken as measures of 1/Y also.

The values for RYS and RYE were computed, and are shown below.

RyS 1.2

RyE 1.1
The plateaus of fluorescence were used as relative measures of nT

(see Chapter 2). The intercept values of the 1/BF vs. 1/E, curves were

used also as relative measures of nT. The values for RNI and RNB are

shown below.

RNI 0.91

RNB 0.87
The agreement of the two methods for finding relative Y's and nT's

for the two flames was quite good. The percent relative error for the

Y measurement was 9%. The percent relative error for nT was less than

5%.

The errors in the ratios are probably random in nature. The percent

relative standard deviation for these measurements was about 5-10%.

Absolute Y's were measured by means of the E5 method using equation

12 from Chapter 2 under the conditions of Figure 12, and additionally

under the conditions of Figure 13 using the flame-shielded flame and

the small slit mentioned in Appendix 1 placed in front of the photodiode.

The results are shown below. Both flame stoichiometries were the

same.
















Figure 13. Strontium saturation curve for the argon diluted flame.
The values plotted were ratioed to the highest value
observed. The Ex values were measured using the slit
shaped aperture mentioned in Appendix 1.
e = Xem = 460.7 nm.
ex em











X X XXX
X
xx
X
X




4-,



X
X



0-
I I I
-2 -1 0 1 2


log Ex (relative)
























time -


DT4

SDT3


DTI




+






DT2


Figure 14. Composite boxcar scan of fluorescence pulse of
strontium. The gate was halted at several delay
times (DT) to record the saturation curves seen
in Figure 15. x = X = 460.7 nm.
ex em







Strontium Y21,in capillary burner 0.50

Strontium Y21,in flame-shielded flame 0.24

As the results indicate, careful attention must be placed on select-

ing a correct and representative aperture. The capillary burner, with

no flame shield, certainly had an edge effect, producing a substantially

poorer quantum efficiency. This was entirely masked, however, by the

inadequacy of the measurement of the E5 caused by using an aperture

larger than the laser beam. As can be seen in equation 12, the quantum

efficiency is inversely proportional to EX, and therefore directly pro-

portional to the measured laser beam cross-sectional area. The approxi-

mately 2-fold increase of quantum efficiency corresponded in this case

to the same decrease in the estimate of Es

Total number density was figured from the slope of the 1/BF vs.

1/Ex curve after calibration of the intercept, and then the slope, under

the conditions of Figure 13. This procedure resulted in nT = 1.3 x 1012

cm-3, a very reasonable nT for 100 ppm Sr in a hydrogen based flame. A

second value, derived from equation 10, yielded a value of nT = 3.1 x 1011

cm-3. This value agreed very well with the prior value. The small

discrepancy could have been due to calibration of the boxcar plug-in

module or the photometer. The boxcar module had been under repair prior

to these experiments, but had not been calibrated. Unfortunately the

equipment required for a check of this value was not available.

A temporal scan of the fluorescence pulse from the photomultiplier

produced an interesting observation for strontium. Several overlapping

scans were taken to define the composite temporal shape shown in

Figure 14. The delay time for the boxcar was set at 4 different points

on the peak, and 4 sets of saturation measurements were taken. These







data are shown in Figure 15. As expected, the leading edge of the pulse

was not saturated. Surprisingly, however, the trailing edge of the pulse

was saturated. Normally, assuming two levels available for laser and

thermal processes, a decrease in signal could not be observed while the

system was saturated. This meant that a third, presumably photon-

induced, process was necessary to explain the phenomenon. Two possi-

bilities existed for the explanation of these data, compound formation

and laser-induced ionization. Compound formation was rejected as a cause

of this effect, as a two body collision would be necessary. Presumably

the only suitable species available in this flame for compound formation

would be oxygen atoms or hydroxyl molecules. Even with favorable orien-

tation of the collisions, they probably could not happen fast enough to

account for the subnanosecond phenomena which were seen here. A more

probable explanation was the absorption of a second photon of wavelength

460.7 nm, which could bring the atom within 0.3 eV of its ionization

potential. A thermal event, not so selective as a compound forming

collision, could then easily ionize the atom. Unfortunately, an experi-

ment to measure electron current generated via laser-induced ionization

with the aid of the nitrogen pumped dye laser was unsuccessful (63).

In private communication with the investigator it was found that poor

results were attributed to laser pulse width considerations. (While

the instantaneous power produced ions, the time spread on the electron

bunch produced only a small signal. The best type of laser for this

experiment has been found to be one with a longer pulse width and

highpower, i.e., high pulse energy.)

















Figure 15. Strontium saturation curves collected at several
delay times (DT). The plotted values do not contain
relative magnitude data, which can be inferred from
Figure 14. The plotted values are for DT1 (x),
DT2 (0), DT3 (A), and DT4 (+). Note the substan-
tially less saturated data from the leading edge
data (x). x = x = 460.7 nm.
ex em












2B m $A



A x
X

A x


I 1-

u-
cn





0
00
-1 0 1 2

log E (relative)
A







Sodium


Measurement of sodium parameters was hampered by an experimental

inconsistency. In all other measurements, the monochromator bandwidth

was narrow enough to exclude any other radiating wavelengths from the

saturated atoms. For sodium, however, both resonance lines fell within

the monochromator bandpass. Estimation of the nT values from BFmax and
max
continuum absorption required inclusion of both sodium resonance lines

in the theoretical treatment. The nT value for sodium was arrived at

via two different routes. A value was calculated from the saturation

plateau for the argon diluted flame by the use of equation 10 from

Chapter 2. In addition, a continuum absorption experiment was used to

give an independent measure of nT, as described by DeGalan and Winefordner

(17). The lack of a suitable bandwidth monochromator ( mono 5 x atom)
mono atom
in a suitable position necessitated substitution of an argon ion pumped

dye laser as a continuum source for this technique. The dye laser out-

put bandwidth was measured by the use of a high-dispersion monochromator

(used in the second order). The optical bandwidth was 0.174 nm. As

the sodium atomic absorption linewidth was only ca. 0.005 nm (61), this

laser was considered a continuum source. The monochromator bandwidth

described in (17) was taken as the laser bandwidth. Measurements of a

(fraction absorbed) were made in both the argon and nitrogen diluted

flames. In addition, saturation curves were taken in both flames

(Figure 16). The nT's calculated from both methods are shown below.

Method Value (1 ppm)

continuum absorption 3.6 x 1010 cm-3

BF 2.9 x 1011 cm-3
max















Figure 16. Sodium saturation curves for hydrogen based flames.
Relative magnitude for the argon diluted (x) and the
nitrogen diluted (0) flames has been preserved. The
value of Ex used for calculations has been measured
using the slit shaped aperture mentioned in Appendix 1.
Aex = 589.0, Aem = includes both 589.0 nm and 589.6 nm.











SXX XXX
iOO

X
x x D
0




Sx D 0
x
XX


AX


X o

0

-2 -1 0 1 2


log E (relative)
A







The agreement between these values was considered quite good in

light of the fact that the methods are independent, and several calibra-

tions of different types are involved. Calibrations of absolute optical

radiances are considered to be quite difficult and error prone. An

agreement of 2-fold is considered state of the art for inexperienced

laboratories.

The value for RNI was determined, and augmented by an RN derived

from the continuum measurements. However, in the case of sodium in the

nitrogen diluted flame, the saturation was incomplete. Therefore, the

RNB value could not be calculated. Ratio values (RN) are given below.

The valueswere corrected for differing aspiration rates for the two

flames.

Method Value

RN, continuum absorption 0.89

RN, intercepts 0.84

The agreement is quite good.

Since the ratios calculated by these two methods did agree so well,

the intercept ratio was used to calculate the saturation plateau value

for the nitrogen diluted flame. This enabled evaluation of the E.

parameter, which was otherwise unavailable. This allowed a second

means of determining Ry. The values are shown below.

RyS 5.3

RyE 14.0


Calcium

In Figure 17, saturation curves for calcium in HOA and HON flames

are given. The Ry values for the two flames via two methods are given

below.















Figure 17. Calcium saturation curves in hydrogen based flames.
Relative magnitude for the argon diluted (x) and the
nitrogen diluted (0) values has been preserved. The
value of Ex used for calculations was measured using
the round (1 cm diameter) aperture. x = x = 422.7 nm.
ex em













X

X
1- X
X
X


m0
2 X
X O

-1


-2 -1 0 1 2
log E (relative)







RyS 1.81

RyE 1.83
A Y value was calculated from equation 12 for the HOA flame, and is

shown below.

YHOAE 0.52
An nT value calculated from equation 10 is shown below.

nTHOAB 2.6 x 1011 cm-3

Values of RN derived from the two methods are shown below.

RNI 0.81

RNB 0.83


Indium

Indium was marginally saturated in the stoichiometric air-acetylene

flame (Figure 18), which is a highly quenching flame with respect to the

HOA flame.

In contrast with this flame Figure 19 shows the saturation curve in

the HOA flame. The much lower power and much more complete saturation

shown in the resonance (A = A = 410 nm) measurement in this figure
ex em
indicated a much higher quantum efficiency. In addition, the observation

of A32 (451 nm) fluorescence followed the expected behavior in showing

the same saturation shape as A31 observation. The 2 3 transition

(451 nm) could also be marginally saturated, as seen in the same figure.

The measurement of power for these curves, however, was not reliable

enough to provide anything but the relative data given above.

A more reliable power measurement was made for the data shown in

Figure 20. The values for Y and nT in the HOA flame given below were

arrived at by the calibration of the 1/BF vs. 1/E. curve.





















Figure 18. Indium saturation curve for an air-acetylene
flame. X = e = 410 nm.
ex em



















1-I








0
SAA

A
A














0)
0 1 2
log EX (relative)















Figure 19. Indium saturation curves in the argon diluted hydrogen
flame. ex = em = 410 nm (+), Xex = em = 451 nm (0),
Xex = 410 ni em = 451 nm (x). The plotted data do not
retain relative magnitudes of the three curves.















EE


2.



2-






L

rs
l -


+
xL


log E (relative)


t


I














Figure 20. Indium saturation curve in two hydrogen based flames.
Relative magnitude of values for the argon diluted (x)
and nitrogen diluted (0) flames has been retained.







YHOA 0.28

nTHOA 2.0 x 1010 cm-3 (1 jg/ml)
An Ry value was available only from the slope method. The plateaus of

the two flames were not developed enough to find Es values.

RyS 1.03
An RN value was only available from the intercept method, and is shown

below.

RNI 1.05


Noise Power Density

Noise power density (W/Hz1/2) measurements preliminary to satura-

tion noise power density were made under the conditions shown in Figures

21-26. Since the measurement of saturation noise power density will

only be possible in the lower frequency ranges (up to about 50 Hz, due

to repetition rate limitations on pulsed lasers), the low frequency

range (0-50 Hz) data collectedwere chosen for these figures. The

higher collection rate (higher frequency spread) data had no interesting

features except for harmonics of 60 Hz, and a band of discrete fre-

quencies (centered on 6 kHz) introduced through the electronics power

supply.















Figure 21. Noise power spectrum of the OH region. Slit
width = 500 pm; A = 306 nm, no premixing of com-
bustion gases, viewing height = 2 cm above capil-
laries, Perkin-Elmer nebulizer and chamber, acqui-
sition rate 100 Hz, low pass filter 3 dB point-30
Hz, DC current = 0.57 pA, no sheath, stoichiometric
air-acetylene flame.

























































Frequency (Hz)


0.2-


4-~ N


C 0

o 0

01 0


If)


2:


0.1.


U I --

















Figure 22. Noise power spectrum of the OH region with sheath,
DC current = 0.8 x 10-9 A, all other conditions
same as Figure 21.
















0.8





0.6



o




CO
- r












0.0 0
a) 0
L 0









0.0-

0 25 50

Frequency (Hz)
















Figure 23. Noise power spectrum of the C2 region. = 516.5 nm,
slit width = 250 pm, DC current = 0.38 x 10- A, no
sheath, other conditions as Figure 21, the zeroeth
harmonic has been dropped (to expand the scale).
















































I I
0 25 50


Frequency (Hz)


0.4,


N
c~

r C
C

L o

L C
U -


0.3-






0.2-







0.1.-


0.0-
















Figure 24. Noise power spectrum of the C2 region. With sheath,
DC current = 0.31 x 10-7 A, slit width = 500 um,
other conditions as Figure 23.




Full Text

PAGE 1

SATURATED ATOMIC FLUORESCENCE AS A DIAGNOSTIC TOOL FOR FLAMES AMD PLASMAS By JAMES N. BOWER A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY CF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1979

PAGE 2

This thesis is dedicated to my wife, Esther, whose support and love have made the difference between night and day.

PAGE 3

ACKNOWLEDGEMENTS Help and real human understanding have been available at all times from my chairman, Dr. Winefordner, for these four years. He has been a guiding light and a friend. I would like to thank John Bradshaw for much of my basic understanding of analytical atomic spectroscopy. He has been a tireless teacher. Dr. Nicolo Omenetto has been a great help in understanding the physical processes of laser excitation. Dr. Winefordner 's research group is certainly one of the most stimulating in the world. Thanks to all members for many discussions and helpful suggestions. Thanks are in order for two unnamed souls whose joyless scientific interactions with me persuaded me to return to school and remain there. iv

PAGE 4

TABLE OF CONTENTS ACKNOWLEDGEMENTS iii ABSTRACT vi CHAPTER 1 INTRODUCTION 1 Quantum Efficiency 1 Total Number Density 3 Noise Power Density 4 Reaction Rates . . 5 Tunable Dye Lasers 6 2 THEORETICAL CONSIDERATIONS 8 Quantum Efficiency for a Two-Level Atom 8 Quantum Efficiency for a Three-Level Atom 17 Saturation 21 Quantum Efficiency Via the Slope Method 22 Total Number Density 27 Possibility of Absolute Calibration 27 Noise Power Density 29 3 EXPERIMENTAL 32 General Comments 32 Radio Frequency Shielding 36 Photomultiplier 37 Fluorescence Flux Collection 37 Detection Electronics 38 Nitrogen Laser 38 Dye Laser Operation 4G Flame System 42 Solutions 43 Measurement Procedure for Y and nj 43 Noise Power Density 50 4 DATA 54 Notation 54 Strontium 55 Sodium 74 Calcium 77 TV

PAGE 5

Page Indium 80 Noise Power Density 87 5 RESULTS AND DISCUSSION 100 Quantum Efficiency and Total Number Density 100 Noise Power Density 103 6 CONCLUSIONS AND FUTURE WORK 105 System Temporal Response 105 Complete Saturation 105 Measurement of Ex 106 Photometer Calibration 105 General Considerations 106 Noise Power Density 107 General Comments 108 APPENDIX 1 SUBSIDIARY MEASUREMENTS 109 2 COMPUTER PROGRAMMING AND PLOTTING 140 REFERENCES 166 BIOGRAPHICAL SKETCH 170

PAGE 6

Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SATURATED ATOMIC FLUORESCENCE AS A DIAGNOSTIC TOOL FOR FLAMES AND PLASMAS By James N. Bower December 1979 Chairman: Dr. J.D. Winefordner Major Department: Chemistry A new experimental approach to the determination of three flame diagnostic parameters is developed. The experimental application of saturated atomic fluorescence to the measurement of quantum efficiency, total number density, and noise power is discussed. Data for quantum efficiency and total number density are compared to the scant literature values. Four elements and three different flame compositions are investigated. Preliminary noise power spectra are discussed as background for the use of saturated atomic fluorescence to measure noise in the atomization and nebulization processes. vi

PAGE 7

CHAPTER 1 INTRODUCTION Characterization of physical and chemical parameters of flames and plasmas has been a goal of chemists (1, 2, 3), physicists (4, 5, 6), and combustion engineers (7, 8, 9) for many years. The goal of physicists, physical chemists, and combustion engineers has been to understand on a quite fundamental basis the processes which go on in flames and plasmas, i.e., oxidations, reductions, free-radical reactions, ionizations, etc. In recent years, an even larger impetus has been seen for this research as sources of economical energy have dwindled and better combustion understanding and design have become paramount in importance. Analytical chemists, on the other hand, have become interested in flames and plasmas because of the extremely important role of these devices in quantitation of elemental species in various samples. The coincidental research interests have brought all together to try and provide a better understanding of basic processes common to both. Quantum Efficiency A quantity of great interest to the analytical chemist and other scientists is the quantum efficiency, the measure of the relative yield of fluorescence processes to absorption processes. The quantum efficiency has a strong influence on the performance of normally (low -1-

PAGE 8

intensity) excited atomic fluorescence spectrometry, which has become an important flame diagnostic (3, 10, 11) and analytical tool (12, 13, 14) in recent years. In addition, quantum efficiency is an indication of (rates of) deexcitation processes in flames and plasmas which can be invaluable for unraveling many basic spectroscopic and fundamental properties. The traditional method of measurement for this quantity (Y) has been to measure atomic absorption from a continuum source, then to measure atomic fluorescence with the same source positioned at 90 degrees to the absorption axis. Great pains had to be taken to ensure that solid angle effects, flame edge effects, etc. were eliminated (15, 16). At best, this yielded a spatially unresolved picture of deexcitation processes (i.e., absorption is a line of sight technique). In addition, no hope could be held cut for temporal resolution. Also, the measurement involved two highly different electronic gains (those typical of absorption and fluorescence measurements), which must be calibrated against each other. The measurement of quantum efficiency via saturated atomic fluorescence, however, allows both spatial and temporal resolution under the proper conditions. It is inherently easier to measure, as it involves only ore optical train for which the solid angle must: be found. However, the photomultipl ier tube and optical system must be calibrated via a standard source. Along with the system used for this investigation, (a nitrogen-pumped dye laser) comes the need for quite sophisticated electronics. Signal processing and cross-checks for problems become much mors involved.

PAGE 9

-3T otal Number Density Total number density has been another sought after quantity in flame and plasma spectroscopy. An important figure of merit in atomic spectroscopy has been the efficiency by which a particular atomizer is able to convert solution or solids introduced into it into the form of neutral atoms. In most cases, this efficiency has been separated into two parts: 1. efficiency of nebul ization-yield of fog droplets from a volume of solution introduced, 2. efficiency of atomization-yield of neutral atoms from submicroscopic species, i.e., atoms, molecules, ions, etc. The former quantity is a very tedious one to measure, involving long periods of aspiration of a relatively high concentration solution of a suitable element, collection of waste solution and washdown from the nebul ization chamber, and dilution to volume. Then, the concentration of the analyte in the diluent must be determined. Typically (for most nebulizers in atomic spectroscopy), this is a low efficiency process. Therefore, the accuracy is subject to determinate errors in procedures. The problem of determination of efficiency of atomization follows directly on these results, unless a separate procedure is developed. This is virtually impossible unless a vapor generation technique is available. The efficiency measurement must be made via detenrri nation of the total number density in the flame. The classical method for this measurement has been to use absorption from a continuum source (17, 18), which provides the desired quantity only after a tedious

PAGE 10

calibration procedure, including correction for reflectivity of multiple surfaces in the optical collection train. An expensive, high-resolution monochromator is also required, as the atomic absorption line is quite narrow. In addition, this method does not allow spatial or temporal resolution. Saturation of the pertinent atomic transition provides a fluorescence signal (therefore a spatially resolvable signal in the usual configuration), that is not a function of flame conditions (except as a function of atom production capability), and is a function only of basic atomic properties. Noise Power Density Noise power density measurements have been used typically by information transfer and electrical engineers as a means of discovering the sources of systematic and random noises in hopes of eliminating them and being able to transmit data with fewer errors at ever increasing rates. The techniques of noise measurement and theoretical treatment have been growing in importance for analytical chemists (19-28), as the science grows in depth and sophistication. The attempts at measurement to date, however, have been troubled by lack of definite calibration and lack of willingness to track down and eliminate sources of instrumental noise in analytical techniques. The difficulty of this task, while formidable, is not insurmountable (29). If calibration can become complete, and the sophistication of analytical chemists can be improved in areas which are now subsidiary (flow engineering, electrical engineering, etc.),substantial improvements should be forthcoming.

PAGE 11

Saturated atomic fluorescence stands to provide a substantial contribution to noise analysis in atomic spectroscopy. Saturation provides several features: 1. elimination of dependence on quantum efficiency (flame conditions) , 2. spatial resolution, 3. possible loss of dependence upon the atomization step (if correct analyte is chosen), 4. possible relative freedom from emission background noise (if conditions are chosen carefully), and 5. freedom from source variation. Therefore, saturation can further the understanding of noise sources in atomic analytical spectroscopy. It can provide separation of noise of nebulization from noise of atomization (if such a noise exists), allowing better understanding, and design, of nebulization systems. Reaction Rates Since analytical flames and plasmas are used at atmospheric pressure and are quite hot (2000 K to 6000 K), reactions are myriad and fast. In most flames and plasmas, some sort of local thermodynamic equilibrium (LTE) is assumed. In several cases, however, the mechanism of excitation of atomic species is unclear (e.g., the induction coupled plasma, which is not in LTE). Engineers and physicists share with chemists the need to understand these and other phenomena kinetically. Saturated fluorescence (atomic or molecular) can be a very useful

PAGE 12

-6tool in this pursuit, as a means of simplifying kinetic schemes by swamping. Reactions such as photoionization, quenching, and intersystem crossing can all be studied by means of saturated fluorescence. Tunable Dye Lasers The advent of the tunable dye laser (30, 31) and the power it gives to observe atomic and molecular populations have given flame and plasma spectroscopists an invaluable tool for diagnostic procedures. The general properties of these and other lasers include: 1. directionality (low divergence), 2. monochromaticity, 3. coherence (spatial and temporal), and 4. high irradiance. All of these laser properties have been useful for analytical atomic fluorescence soectroscopy since Fraser and Winefordner (32) first used a dye laser to excite atomic fluorescence. Their work covered nine elements in hydrogen-air and acetylene-air flames. Limits of detection obtained were within 10 to 100-fold of those obtained with conventional sources, and linear dynamic ranges were about four decades. Progress in both theory and experimental achievements has been rapid in the ensuing years (12, 33-38). With more and more powerful lasers available (37, 39-45), the possibility and theory of non-linear phenomena has been investigated (40-44). Several authors have experimentally achieved near or complete saturation of atomic (46-50) and molecular systems (51, 52).

PAGE 13

Laser saturation of atomic transitions in this work has made possible diagnostic procedures with spatial, temporal, and flame composition independence. This will allow analytical chemists to measure the quantum efficiency, total number density, and noise power density spectrum in an atomizer without the above mentioned problems of linear spectroscopy. However, the benefits of this freedom must be weighed against the need for sophisticated measurement systems (fast time scale) and laser temporal and spatial inhomogeneity effects.

PAGE 14

CHAPTER 2 THEORETICAL CONSIDERATIONS Quantum Efficiency for a Two-Level Ato m A two-level atom is one which, although it may have many quantum states, has only one excited state available for thermal population in addition to the ground state. After it has been delivered to the excited state by absorption of a photon, it can be returned to the ground state by either of two paths, emission of a photon or collisional deactivation (quenching). Quantum efficiency (Y) is a measure of the efficiency of the radiative process with respect to the absorption process. A schematic diagram of a three-level atom and its processes is depicted in Figure 1. A two-level atom can be pictured by ignoring all processes connecting the third level and the other two levels. A real example of a two-level atom is snown in Figure 2. Only the 4s level is available for thermal population in analytical flames (temperature range from about 2000 K to 40C0 K, k7 is therefore 0.2 to 0.37 eV). The basic fluorescence radiance expression (53) is given by: B p = (JL) Y 2l E Vl2 7\dv (1) where 1 = path length in direction of detection system, m 4ir = number of steradians in a sphere (fluorescence is isotropic), sr

PAGE 15

Figure 1. Three level atom model photon and collisional processes are illustrated. Symbols are explained below. The lower state is symbolized by "1" and the upper by "u. " B, Einstein coefficient of induced absorption lu (n.3 j-1 s-I Hz) B i Einstein coefficient of induced emission ul (m3 j-1 s-1 Hz) A , Einstein coefficient of spontaneous emission Ul (s-1) E v , Spectral irradiance of exciting radiation lu (W m2 Hz'l) k Rate constant for collisional process connecting state m with state n

PAGE 16

103 -x i £b^« c 32 *'. it "*—*" k 23 k 32 IJ _ n 01 n ')l -7— 31 c c Zl k l2 k 21 Ji__ik_ afc >k ^ _*

PAGE 17

-11l s Ip 0,1,2 4P 2 1,2,3 4d 4p l ^3' 5s Figure 2. Calcium term diagram levels 1 and 2 are indicated

PAGE 18

12Y«j = fluorescence power (quantum) efficiency, W fluoresced/W absorbed L,j, 9 = spectral irradiance of exciting radiation at absorption iC line, Vl2 , W m" 2 Hz" 1 (1 W = 1 Js" 1 ) J k dv = integrated absorption coefficient over absorption line, m-1 Hz ; c°° The product Ey 1? J k dv is the power absorbed from the source by the analyte atoms per meter cubed of atomic species. The integrated absorption coefficient is given by: hv 1? g.n, where hv, 9 = energy of the exciting photon, J 1 c = speed of light, m s B.o = Einstein coefficient of induced absorption, m° J u s" 1 Hz 3 ,-1 g.., g ? = statistical weights of states 1 and 2, respect"! ve]y : dimension! ess n.., n 2 = concentration of states 1 and 2, respectively, {note that nj + n? = n-p the total concentrate m ion o atoms in all 'states' The bracketed quantity corrects for the effective decrease in absorption caused by stimulated emission from the upper state. Using the rate equation approach, and invoking steady state, we arrive at (k 12 B -^) n, (k n A 21 + bitty , z (3! where

PAGE 19

13k, ? , k ? , = excitation and deexcitation non-radiational (collision) rate constants, s~* Ap-, = Einstein coefficient of spontaneous emission, s~ B , = Einstein coefficient of induced emission, m J" 21 s-1 Hz 3 B, 9 = Einstein coefficient of induced absorption, m J ' u s" 1 Hz _3 n, , n ? = concentrations of electronic states 1 and 2, m c = speed of light, m s~ The quantum efficiency is defined as A. 21 21 A n + k 21 (4) and A 2 i is related to ELand B.p by 3 3 8irhv 19 8irhv 10 gA 21 ' t-^ 2 ' B 21 ' (-T^) *& B 12 W c c 3 2 Combining these expressions, one arrives at ip . (|j) v 21 E vl2 [ ni (^) b 12 h'*Te v12 >] (6} -2 -1 where E*vio "" s a modified saturation spectral irradiance (W m Hz ) evaluated at frequency v.p anc! 1S defined as CM 21 U B 21 T 21 The term E* v . can be expressed in terms of the saturation spectral irradiance E v .p, which is the spectral irradiance required to bring

PAGE 20

14about 50% of the maximum fluorescence radiance oossible. If E s ,,, n is 12 expressed as a function of E v 2 , then s 9i F = F* ( L v 12 vi2 ^g 1+ g 2 (8) Substituting for r^ in terms of n T (n T = n. + n ? and using Eqs. 3, 6, and 8) = (1_) Y E n (-'^ I " 12 F v 4ir"21"n2T x c 1 + -vi 2 vi2 (9) The maximum fluorescence is then 1 9-, 'F v 4ir y 21 t v q, + q„' max b l y 2 (10) When E V12 = E 2 then B p = B p /2, max cA 21 8uhv 3 v]2 BY 2 u d 21 Y 21 c^Y 91 (n: ;v i2 = v g x + g 2 -2? -5 7.6 x 10 " A ) ( a °—) Y 21 (12) A theoretical plot of B p vs. E v 2 appears in Figure 3. If a plateau in fluorescence radiance can be observed as laser power is varied, and trie laser power at 50% of this maximum fluorescence radiance can be found, then the quantum efficiency can be found from the quantity E S V , ? . For calculations in this work the quantity E S x 2 will be used (see Eq. 12).

PAGE 22

T o 4(BAL^eLa^i) g 5oi.

PAGE 23

-17The necessary conditions for the measurement of quantum efficiency in this way are 1. Saturation must be completely achieved, so that B F can max be evaluated. 2. One must measure E Vl2 by measuring the following quantities: a. laser peak power (W) , 2 b. laser cross-sectional area (m ), c. laser optical bandwidth (Hz). 3. Self-absorption must be negligible. 4. The source must be a spectral continuum with respect to the absorption line width. 5. A steady-state condition must be achieved. 6. No coherence effects can be manifested. The rate equation approach must be valid. The achievement or measurement of these conditions is described in Appendix 1. Quantum Efficiency for a Three-Level Atom The same approach (as used for the two-level atom) yields for a three-level atom like Na (see Figure 4) V 13 go 1 1 + '32 v 13 (13) 9 3 A 23 + k 2l + k 23 where

PAGE 24

18'1/2 1/2, 1 1/2 11/2,2 1/2 4s 3s 4p^ \ 3d' i 3d Figure 4. Sodium term diagram levels 1, 2, and 3 are indicated

PAGE 25

•19E* = C 31 = §jhv_ (1 a\ iJ b 31 Y 31 c Y 31 k = collisional rate constant connecting atoms in the mn m state with those in the n state The E S v -.3 is again related to Y-.., but no simple relationship exists. The collisional constants, which are unknown in the literature, interfere with the interpretation. For some limiting cases, where level 2 is close to level 3 (e.g., sodium, see Figure 4) or is close to level 1 (e.g., indium, see Figure 5), certain assumptions can be made. With sodium, for instance, if the assumption is made that then k 23 >:> k 21 + A 21 k k K 32 -v, K 32 A„, + k„, + k „ = k Then 21 21 k 23 K 23 g 3 E$ n3 " 'I" gj g > E ^13 I"! E 'vl3 ' < g * I] * ^ > E *n3 < 16 ' This is equivalent to a two-level system, as the top 2 levels have merged into one, effectively.

PAGE 26

75 6 s 202 S 2 ° 2 D 4 P 1/2 1/2, 1 1/2 u l 1/2, 2 1/2 P l/2, 2 1/2 6d 5p £ 5 a 4p v Figure 5. Indium term diagram levels 1, 2, and 3 are indicated,

PAGE 27

-21For a three-level atom like In i — 9E S = ft 13 9 3 ( !l) + A 32 + g 3 k 21 + k l2 E* L v 13 The same type of assumption should hold for levels 1 and 2 as previously for level 2 and 3. Therefore, if then k 21 >> k 32 + A 32 k 21 1 1 and k 21 + k 12 " i + ^2 " g 2 " q 1 + 9 2 K 21 g l s _ , 9 1 + g 2 E "vi3 = ( 9l + g 2 + g 3 ) E *v 13 (17] This is again equivalent to a two-level system. Saturation Complete saturation means that the population of the excited state and the ground state are equalized (with due regard to the respective degeneracies). Therefore, the kinetic drains on the excited state are negligible with respect to the optical pumping rate. A further increase in irradiance cannot effect an increase in fluorescence radiance. A measurement of this (saturated) state usually means that when the irradiance is reduced, via some suitable filter, the fluorescence

PAGE 28

signal does not decrease. By placing calibrated filters in the beam, one can determine the point at which only half of the signal is left; this point is the saturation spectral irradiance. Quantum Efficiency Via the Slope Method Two-Level System From the two-level theory, it can be shown that 1 = J_ (<% 4* R R. . Un ' F Ev l2 9 2 6.6 x 10 3 Y 2 l4l hv 21 1A 21 n T (t-V^ ndSbd < 18 > A plot of the theoretical shape of 1/B F vs. l/E, is shown in Figure 6. The pertinent features are the slope and the intercept. The slope of this plot contains the quantum efficiency (and ru), and the intercept contains n T> For this procedure, all of the above mentioned criteria must be met with the exception of completeness of saturation. The closer saturation can be achieved, however, the less extrapolation is necessary. In addition, the fluorescence collection depth, 1, must be measured, and the collection photometer calibrated. If both sides of Eq. 18 are multiplied by the quantity 4rr then the 1/B F axis can be scaled absolutely, as the intercept is

PAGE 29

S3 c -o 3 £= > 4+J SM.r3 0) to 0) i. 4jc o -r|— 4-o

PAGE 30

24(aA.ueLau) -g/i

PAGE 31

equal to the quantity which is well known. Three-Level Case -25'1 T y 2 Sodium . A rearrangement of the three-level fluorescence expression yields 1 . , 4-rr ) i_ *F W . A 31 hv 13 ] n T 1+3 1 + ( ^32 A 21 + k 21 + k 23 9 3 + !i ( STrhc 2 9 3 Y A" 1 E (19) When this is rearranged, we have 2 A 31 hv 13 ln T, 1 4tt = (g^irhc 1 g l + 9 3 ^32 ' F K3 9 3 Y 31 X 13 E ^3 ' 9 3 ' A 21 + k 21 + k 23 1+3 (20) A plot of these quantities cannot be scaled absolutely because the intercept includes unknown collisional rate constants. The same speculation as before can still be made, however, regarding the rate constants, allowing calibration to be made in certain limiting cases, That is, k 23 can be expected to be much larger than either A 01 or k 01 . 21 "' "21 The term ^32 A 21 + k 21 + k 23

PAGE 32

then reduces to •26^2 C 23 By the law of mass action at equilibrium k 32 _ n 3 _ 9 2 ^23 The fluorescence slope method equation reduces to 1 / 4tt T w ' A 31 hv 13 ] n T l-*3 1 + 9 2 + h »!, S^rhc 2 9 3 Y X b E Rearranged this equation resembles that for two levels .2 A 31 hv3 1 g.&rhc 4ttB f y 5 f r l+39 3 T 31 A 13 t x + 1 + 9 2 + 9 l g 3 Indium . For an atom of the indium type, where the second excited state is very close to the ground state, the slope method equation is n T 1A 31 hv ^ 1 / •T"'31"13 x 1 _ , a l u , , 3 2 ovnr /]f Tl\t^ML_\ . s l ( — ^ ) q(r-)(l + rexp[-E 21 /kT])( 5 ) + 9i + g< 'F g h l-«-3 AY 31 E X + f exp[-E 21 /kT] -^ A + k M 32 K 32 21 (21) In this case k 21 can be assumed to be much larger than A2 + k~ ?: and this term then is negligible.

PAGE 33

•27Total Number Density Two-Level Absolute Plateau Method A measurement of B f max h \ ax te^,^^ produces n-j. easily if the measurement of B p is absolute (see Appendix 1) and if 1, A and the g's are known. max Two-Level-Slope Method The calibration of the l/EL axis is direct for total number density if g^ , g. p , h, \>.„ t Bp, and A 21 are known, as the intercept of the 1/Baxis is 4ir 9 1 + 3 2 Blhv 12 A 2l n T g 2 Three-Level Case— Absolute Plateau Method Unless assumptions or experiments are made for the relative size of the collisional constants, calibration is impossible. Relative measurements are still valid, and saturation still assures immunity to quantum efficiency effects as in the two-level case. Three-Level Case— Slope Metho d Once again assumptions must be made for collisional constants in order to permit calibration of B p in terms of ru. Possibility of Absolute Calibration If the ratio of resonance to anti-stokes fluorescence is taken, in saturation, we have

PAGE 34

Hax l + if + i exp[E 21 /kT] 1+3" A 31 + k 31 k 12 A„„ + k K3 max l + a + / exp[ " E 2 l /kT] + "V 2+3 max g 3 g 3 ^ K 21 32 (22) Both ratios A 31 + k 31 k 21 and A 32 + k 32 k 12 A 31 + k 31 '21 |i exp[E 12 /kT] are probably not much greater than one, as k ? . is expected to be at least comparable to either numerator. Then, if E«i » kT, two conditions are satisfied 1 9 1 :: 9 l A 31 +k 31 ' 9o g 9 k '21 A + V 32 K 32 2. ^ exp[-E 2l /kT-} « -^Equation 22 then reduces to 1*3 1+3 max 1 + i + it exp[E 2i/ kT ^ 1*3 2+3 max y l 1 + 7T + g 3 "A" +T rt 32 K 32 k 21 (23) If a flame of known temperature can be produced, then the ratio ^ A 32 +k 32^ k 21 can ^ e evaluated. This allows Y (and n-J to be obtaine in absolute units. For a flame with a temperature of 2300 K and

PAGE 35

-29thallium as a probe (E. 2 = 0.966 eV),the exponential term is as follows: exp[+0. 966/2300 x 0.861 x 10" 4 ] = 131 For thallium Then l1 g 2 = 3 g, = i ! F^3 2 + A 32 + k 32 2+3 max . k 2l B F 135 l-e-3 : ,max l-»3 The difference between the ratio and 2/135 = 0.0148 is the contribution of A-2 + kop/koi* This value, when inserted into Eq. 21 (for measurement of thallium, in this case), would allow the intercept of the n T 1A 31 hv l3 4ttB p r l«-31+3 axis to be completely calibrated, as the intercept then contains only known quantities. If B F is known absolutely (calibrated), then n T can also be arrived at unambiguously. Noise Power Density The theory and practical measurement of power spectra (power vs. frequency data) have been adequately covered by Blackman and Tukey (54).

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30Two approaches are possible to measure noise power spectra. The first is to compute the autocovariance function for the data collected. The Fourier transform of this is the power spectrum. The second procedure is to compute the Fourier transform of the data, then to square and add the frequency and phase components to find the power spectrum. Although both methods were available, the second one was chosen for its conceptual familiarity. The use of a discrete data collection system (analog to digital converter) required a discrete Fourier transform, with attendant aliasing and bandwidth problems. The application of saturated atomic fluorescence will result in an ability to separate the noises resulting from the nebulization process from those stemming from the atomization of the analyte. Since these two sources of noise are independent, their noise power spectra add linearly. Since the measure being computed in our case is the noise current spectrum, these would add quadratically. If an analyte such as copper, which is completely atomized in a standard flame, is measured, the noise power under known conditions can be found. This noise power should be reproducible in nature with the exception of certain non-stationary noise sources. If this proves to be the case then the total noise and the 1/f noise pertinent to most spectroscopic measurements can be investigated with respect to design elements and operating characteristics common to atomic spectroscopy. These include burner, chamber, torch, and nebulizer design, as well as gas flows and flame stoichiometry. Noises involved in the flame or plasma processes up to the point of atomization could then be subtracted from the noises seen for an incompletely atomized analyte, producing the noise inherent in the atomization process.

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-31The unfortunate truth, however, is that many of the underlying noise sources in analytical spectroscopy are non-stationary. Examples of non-stationary noises are nebulizer clogging, RF noise, 60 Hz mains noise, some source drift noises, stray light noise (room and daylight), and some electronic drift noise. These are not really approachable via the technique or theory of noise power spectra, though often a reasonable idea of the noises can be found (55).

PAGE 38

CHAPTER 3 EXPERIMENTAL General Comments A variety of experimental systems were used for collection of data pertinent to these measurements. The basic system shown in Figure 7 is the laser excited atomic fluorescence system described by Weeks et al . (13). The system has been modified slightly, as reported by Bower et al . (56) and Bradshaw et al . (10). Several of the features changed since the measurements of Weeks et al. are of high importance. The spatial effects of saturation in the wings of focussed Gaussian laser beams, as observed by Blackburn et al. (50), and previously predicted by Rodrigo (57) and theoretically approached by Daily (58) have been eliminated by moving the observation point approximately 10 feet further from the laser. At this point, the spatially homogeneous section of the laser beam was enveloping the whole seeded flame (see Appendix 1). In order to facilitate alignment, it was necessary to add folding mirrors (M) with adjustments in the horizontal and vertical planes. A problem involving dye changes leading to a different angle of emergence has been circumvented by the use of the folding mirrors and the combined aperture-scatter shields (ASS). The two apertures initially were set to define the beam line of interaction of the dye laser and the flame. When subsequent dye changes produced non-col1near -32-

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r— -o -a Q-i— II i— E CL O CD CD 3

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Table 1 Laser Excited Atomic Fluorescence Equipment List Item Manufacturer Model UV-14 Nitrogen Laser Model DL-300 Tunable Dye Laser Model FL-2000 Tunable Dye Laser Nebul izer chamber Capillary burner Flame-shielded burner Model H-10 monochromator Model 412B High Voltage Power Supply Model R106 Photomultiplier Tube Model 160 boxcar Model 162 boxcar mainframe Model 163 boxcar plug-in module Model 164 boxcar plug-in modul e Type S-2 sampling heat Servoriter strip chart recorder Apertures (iris diaphragms) Molectron Corp., Sunnyvale, Cal. Molectron Corp., Sunnyvale, Cal. Lambda Physik, Gottingen, W. Ger. Perkin-Elmer Corp., Norwalk, Conn. laboratory built laboratory built Jobin-Yvon, % ISA, Metuchen, N.J. John Fluke, Seattle, Wash. Hamamatsu Corp., Middlesex, N.J. Princeton Applied Research, Princeton, N.J. Princeton Applied Research, Princeton, N.J. Princeton Applied Research, Princeton, N.J. Princeton Applied Research, Princeton, N.J. Tektronix, Portland, Oregon Texas Instruments, Dallas, Texas Edmund Scientific, Barrington, N.J.

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-36beams, these could be adjusted with the mirrors to pass through the apertures. The collection system was aligned at a 90 degree angle to the incoming beam by the use of helium-neon alignment laser crossed with the dye laser beam. Radio Frequency Shielding Radio Frequency (RF) shielding of the entire Molectron nitrogen pump laser enabled the output to be freed of the large drift-type noise associated with people and objects moving in proximity to the experimental system. This involved enclosing the whole pump laser and power supply in a brass screen Faraday case. All electronics were connected via grounding straps to a salt-bed earth ground. All cables leading from the photomultipl ier to the detection electronics were doubleshielded by a coaxial woven shield augmenting the internal shield. These modifications enabled RF noise-free measurements into the millivolt level, which corresponded (with a 50 SI 2-fold attenuator) to 40 yA of peak current. This was possible even with a background current of 100 yA. For most measurements, the limiting noise was the electronic noise of the boxcar averaaer.

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•37Photomu 1 ti pi i er The photomultiplier was wired for fast pulse, high current output, as reported by Fraser and Winefordner (32) and operated at -1000 V. Cable of 50 n impedance (RG-58U) was used for all connections. Fluorescence Flux Collection A Jobin-Yvon H-10 low dispersion monochromator was used for collection of fluorescence. Dispersion is low and collection efficiency high, as suggested by Weeks et al. (13). A two Tense collection system with an intervening aperture was used to help cut down on scatter for resonance collection cases. Scatter in these cases was reduced by liberal use of light traps (LT), aperture scatter-shields (ASS), and black felt cloth. In many cases, this scatter signal was Rayleigh scatter (indicated by an increase when the flame was turned off), and could not be completely eliminated. In such cases, the noise limit for measurements was due to laser carried (peak to peak variation) scatter noise. The image formed by the two lenses at the slit of the monochromator was of unit magnification.

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38Detection Electronics A PAR 162 boxcar averager was used for detection and measurement of fast fluorescence pulses. Two different inserts (plug-ins) were used in measurement and alignment. The 164 plug-in offered fixed sensitivity (100 mV full scale) and several integration times. It was quite hardy, and was used for preliminary alignment, when a very large scatter signal was used to set the gate delay. The 50 a input impedance was always used to match the cable and minimize ringing. Some ringing was still apparent, however. The 163 plug-in with an S-2 sampling head was used for the main measurement scheme. The gate was 75 ps (S-2 sampling head); jitter in the boxcar gating circuits led to some distortion of this aperture. This head was used to find plateau (saturation) values on top of the fluorescence temporal pulses, which corresponded to saturation of the atomic fluorescence. The synchronous trigger of the laser could not be used, as RF feedback occurred at the time of each trigger and interfered with data collection. A separate trigger generator was used, which had a delayed pulse feature. This enabled correct timing between laser firing and boxcar gating. Nitrogen Laser The nitrogen pump laser was run according to manufacturer's instructions. The high-voltage power supply was kept at 22 kV to give better longevity of the critical components (thyratron and capacitor), as these had been problematical in the past. The nitrogen flow rate was 15 liters per minute for all experiments. Operating pressure was

PAGE 45

•39maintained at 55 torr. The pressure transducer had to be replaced and calibrated twice, however. This involved approximately half a day to a day's work, since the entire pump head had to be removed from the Faraday cage. All connections had to be made again outside the cage in order to test fire and calibrate the unit. The repetition rate was kept at about 15-20 Hz for all experiments. Greater repetition rates led to lower peak powers. High peak power was necessary for saturation. However, a rate below ca. 20 Hz would lead to signal leakage problems on the boxcar mainframe. An interesting phenomenon was observed at the 20 Hz repetition rate. A beat frequency appeared on the dye laser output. This was first attributed to the power supply of the laser, as its voltage dipped when the laser was fired. This idea was discarded when it was noticed that the beat frequency was about 2 Hz. The observation was made that as the dye fluoresced in the cuvette on each nitrogen laser pulse, the magnetic stirrer appeared to be precessing at about 2 Hz. The motor provided was an AC motor running at a multiple of 60 Hz. The stirring of the dye cell seemed to be incomplete enough that when the nitrogen pulse came at a sub-multiple of the stirring rate, a beat frequency due to excitation of spent dye appeared. A need for improvement in stirring was quite apparent. This beat frequency effect had never appeared in the literature. Voltage drifts during the day were so bad (1 V on regulated supplies, 10 V on unregulated lines) that severe trigger drift became apparent. The nitrogen pump laser was yery susceptible to trigger drifts through its high voltage threshold performance. A voltage change of 1 V on the 120 VAC line can induce a 20 ns drift in the

PAGE 46

-40trigger to firing delay. Using a 164 plug-in on the boxcar, this was annoying. When a 163 plug-in is used the signal can entirely disappear inside of 5 min time. Therefore, all of the experiments had to be done at night when stability was much better, but still troublesome, however. Generally during each series of measurements the trigger had to be reset at least once. An optical trigger was used for subsequent experiments. The 163 plug-in, however, was not used. Indications were that this arrangement was much more stable with respect to jitter, especially if triggered from the pump laser. Use of the optical trigger necessitated placing a delay line (V155Z050, Allen Avionics, Mineola, NY) into the signal line from the photomultiplier to produce a 75 ns delay necessary to compensate for the internal gate delay of the boxcar. A 50 q attenuator was placed before the delay line to produce a voltage pulse from the current pulse. Indications were that distortion and noise introduction by the delay line were minimal. Dye Laser Operation The dye laser was also operated according to manufacturers instructions. Dyes were prepared according to Table 2. Adjustments of the dye cell carriage were made after each new dye cell was introduced into the beam line. This should not have been necessary if the laser was functioning correctly. There was some indication that this was an artifact due to the state of our dye cells. Possibly the antireflective coating had worn off in several years of use (see Appendix 1).

PAGE 47

-41-

PAGE 48

-42Dye was changed frequently to avoid power loss due to dye deterioration. This was done in one of two ways. The method of exchange recommended by the manufacturer was to remove the dye via a pi pet, rinse the cell with fresh dye, and refill with fresh dye. This was moderately successful. Some dyes (7D4MC in particular) seemed to function better when the dye cell was removed entirely from the dye head, rinsed thoroughly with alcohol, then fresh dye, and then refilled with fresh dye. Peak power with 7D4MC exchanged in this manner was enhanced at least 2-fold over the more cursory method of exchange. Bubbling of pure nitrogen for two minutes through the dyes (as suggested by Exciton) did not seem to make a substantial change in dye longevity. Perhaps nitrogen saturation during preparation and storage would have helped more. Flame System A gas-flow stabilization system consisting of individual pressure gauges and rotameters was used for each gas flow. The entire system was calibrated by means of a linear mass flow meter (ALK-50K, Hastings, Hampton, Virginia). Each time a flow was measured, the pressure was readjusted, and the flow and rotameter readings recorded. The combination of a fixed pressure and the rotameter readings led to a very reproducible and precise system. Premixing of flame gases was done to avoid background noise due to poor mixing in the chamber of the burner. The flows passed into the appropriate ports of a nebulizerflow chamber (Perkin-Elmer Corporation, Norwalk, Conn.). The same composition (premixed) passed into a separated shielding flame for

PAGE 49

hydrogen-based flames. The fog and premixed combustion gases left the flow chamber and passed into a capillary, flame-shielded burner for hydrogen based flames (previously described by Snelleman (59)). There they were combusted. The flame-shielded flame was surrounded by an inert gas sheath to avoid background DC emission and noise as much as possible. Acetylene based flames were combusted above a capillary burner (Haraguchi and Winefordner (60)) supported on the same nebulizer chamber. Flows for the different flames used are shown in Table 3. Solutions Stock solutions of 1000 ug/ml for all elements were made from reagent grade chemicals in deionized water per Parsons et al . (61) (see Table 4). Measurement Procedure for Y and n T The necessary criteria for evaluation of quantum efficiency and total number density via the two different schemes are 1. Saturation must be complete (for plateau method) or nearly complete (for the slope method); that is, an increase in laser power must not result in an increase in fluorescence radiance. 2. One must measure laser spectral irradiance via measurement of the following quantities: a. laser optical bandwidth--via some type of wavelength scan,

PAGE 50

-44Table 3 Flame Gas Flow Rates Air-Acetylene Flame Air 9.88 1/min Acetylene 1.65 1/min Hydrogen-OxygenInert Gas Flame Hydrogen 1.62 1/min Oxygen 0.81 1/min Nitrogen or Argon 4.51 1/min

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-45Table 4 Source of Reagents Sodium NaCl Mallinckrodt Chemical Works, St. Louis, Mo. Calcium CaCCL Mallinckrodt Chemical Works, St. Louis, Mo. Strontium SrC0 3 Fisher Scientific, Fair Lawn, N.J. Indium Ir^CL Apache Chemicals, Seward, 111

PAGE 52

•46b. laser peak power— via calibrated photosensitive device, c. laser cross-sectional area—via geometrical considerations; b and c measurements may be combined. 3. Self-absorption must be negligible. (This is automatically achieved if saturation is complete, as the absorption coefficient then goes to zero.) 4. The source must be a (pseudo-)continuum across the linewidth of absorption; i.e., the wavelength spread of the laser must be measured and determined not to vary substantially across the absorption linewidth. 5. Steady state fluorescence must be achieved. The temporal behavior of the atomic fluorescence pulse must be observed. Measurement of the saturated value must be during a suitable steady state. 6. The rate equation approach must be valid. No coherence effects may be seen. 7. The fluorescence depth 1 must be found (Figure 8). In addition, if the possibility of absolute values of Y and n T is_ to be evaluated for a three-level atom, the ratio of resonance to stokes fluorescence must be found in a flame with a known temperature. Since the proof of validity of these criteria is somewhat tedious, it will be assigned to Appendix 1, with the exception of the first point, completeness of saturation, because this is the basis of the whole measurement scheme. For each dye change, alignment of the laser beam with the burner head was undertaken. Side to side position of the laser was checked with the flame off, by the use of the aperture-scatter shields and a

PAGE 53

-47-

PAGE 54

-48card over the burner. Vertical positioning was accomplished by using the card to project an image of the laser beam through the first collection lens onto the slit-shaped aperture. After spatial alignment was completed, the gate delay was peaked up on a scatter signal. Next, the flame was lit, and analyte was introduced. The dye laser was wavelength scanned, using the scan control until a substantial signal was found. Since saturated atoms show a broadened response to wavelength (see Appendix 1), a calibrated neutral density filter was set in an accessory optics holder in the laser beam. In this way, a linear response to laser illumination was ensured. Neutral density filters of about 2.0 to 3.0 were generally required. When illumination was in the linear region, the dye laser output could be easily centered on the wavelength of the atomic transition. When the neutral density filter was removed, the atoms were saturated. Generally analyte concentration was chosen to yield a high enough signal so that a linear portion of the laser fluorescence vs. power plot could be reached as the laser power was decreased. In some cases, this involved using a higher concentration at low laser power to ensure sufficient signal to noise ratio. Linearity of fluorescence with respect to concentration was always checked when this was done. The upper limit of concentration was set to avoid problems of vaporization (especially prevalent in the low temperature hydrogen -based flames used here) and self-absorption. No absorption was noticed, however, with solutions up to 1000 yg/ml in concentration, although the measurement of absorption was complicated by severe shot to shot peak power variations on the dye laser. In most cases, concentrations were in the 1 to 20 yg/ml range.

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-49The procedure for measurements started with a check for PMT linearity. Even with the use of a low resistance (high current) dynode chain and capacitor charge storage for each dynode, the PMT output current could become non-linear with respect to illumination when the light levels became high enough. Each time data were taken, a 0.3 neutral density filter was inserted in front of the monochromator. If the signal did not decrease by 50%, a lower concentration was aspirated, and checked for linearity. Approximately half of the full scale (1 V) was usable for the 163-S-2 plug-in combination. This corresponded (with a 50 a 2-fold attenuator) to a 10 mA peak current. This compared with a limit of 0.3 mA peak current limit of Olivares (46), for a 220 kft resistor chain with no added capacitance, for a 1P28 PMT. A linear dynamic range of 30-fold higher (based on current) was obtained in our case. After the linearity check, the actual saturation curve measurement was performed. This consisted of measuring full scale fluorescence, blank scatter, and several reduced fluorescence and scatter values when calibrated neutral density filters were placed in the laser beam singly or in combination. Scatter corrections for resonance measurements were generally significant until the laser intensity was reduced 1 to 2 orders of magnitude by neutral density filters. These fluorescence measurements were converted to absolute radiance values following calibration of the optical collection system, the boxcar, and the recorder used to collect data (see Appendix 1). From the absolute radiance measurements, values were computed for quantum efficiency and total number density. In some cases relative data only were computed for different flames.

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-50Noise Power Density The measurement of noise power density spectra in academic analytical chemistry is generally accomplished via the discrete fast Fourier transform (DFFT). This approach is necessitated by the lack of continuous measurement power spectrum analysis instrumentation in most laboratories. The dedicated instrumentation required by this method is generally too inflexible to be affordable under tight budgeting restrictions of this time. On the other hand, the general availability of digital computers and analog to digital data collection systems makes discrete (or sampled) data collection fit reasonably within the price and flexibility range of most laboratories. This leaves one with only the DFFT approach to noise power spectra evaluation possible. This enforced choice leads to a loss of flexibility in one way, and to a gain in another direction. The disadvantages of discretely sampled records for approximating a power spectrum are very well covered in Blackman and Tukey (54) and include aliasing (necessitating very well designed filters for spectra with wide dynamic ranges and wide frequency ranges), intermodulation distortion, and finite bandwidth. The flexibility advantages are those which stem from the computer itself: 1. ease of collection, 2. ease of calibration, 3. fast data reduction, 4. ease of presentation, 5. flexibility of handling of data and power spectra.

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51The primary purpose of noise power spectra collection in this work was to establish a background for later possible saturated noise power spectra, which should show the advantages enumerated in the Introduction section. The primary sources of noise for atomic spectroscopy consist of the following: 1. Source related noise a . wh i te , b. whistle or proportional, c. flicker or 1/f. 2. Background noise-non-source related a . wh i te , b. whistle or proportional, c. fl icker or 1/f. 3. Sample related noise a . wh i te , b. whistle or proportional, c. flicker or 1/f. The preliminary experiments presented here measured the latter two types of noises. The first type will be the subject of later experiments. Background noise can be somewhat artificially separated into two types. The first type is related to the bulk properties of the flame gases; this type could be exemplified by the emission from the C ? molecule, a product of partially completed combustion. This molecule has a major emission at 516.5 nm called the Swan band. While it does not interfere with most atomic transitions, other bands can interfere

PAGE 58

-52with DC and fluorescence measurements with pulsed sources . The Swan band is sensitive and can be used as an indicator of formation of C«, and therefore as an indicator of combustion completeness. This molecule has been used as a measure of success for premixing combustion gases (29). Noise power spectra collected under fixed conditions also provide a useful figure of merit for the evaluation of success of mixing. A second type of background emission noise source is one which is more indicative of external conditions. An example is the OH molecule, which is strongly indicative of the success of sheathing a flame. The pertinent (and sensitive) band is centered on 306 nm, and extends to the red far enough to interfere severely with copper and silver measurements while a companion band at 285 nm interferes with lead and magnesium measurements. Noise power spectra at this band can hopefully lead to better design and construction for flame sheathing systems. Sample related noise can be evaluated as a preliminary to saturation measurements by using atomic emission. In order to collect data on both nebulization and atomization noises without source noises interfering, it is necessary to measure the noise involved in atomic emission, unless saturated measurements lead to an improvement in signal to noise ratio. An atom must be chosen which has strong emission, and is not near a background spectral region which would interfere. Strontium is a likely candidate. Its emission is in a relatively background-free region, and should therefore yield information on nebulization and atomization efficiency noise. Strontium is quite sensitive to flame temperature, and therefore composition.

PAGE 59

53It should be a good candidate for the proposed separation of information from the two sources of noise. In addition, it is among the most strongly saturated atoms found in this work. The general scheme of investigation is as follows. The nebulization chambers and nebulizers of three companies are to be investigated within the guidelines established above. Conditions to be varied are use of an inert gas sheath, premix chamber, and removal of the nebulizer. In addition, data collection will be made in three frequency ranges (0-50 Hz, 0-500 Hz, 0-10,000 Hz).

PAGE 60

CHAPTER 4 DATA Notation A general notation system is developed here for the reporting of the experimental results in this chapter. Ratios will be listed as "R," with addition of one or more of the following subscripts for clarification of the meaning: HON Hydrogen-oxygen-nitrogen HOA Hydrogen-oxygen-argon S Slope method of calculating a quantum efficiency or ratio of quantum efficiencies E E.. method of calculating a quantum efficiency or ratio of quantum efficiencies B B F m ax me ' tnoci °^ calculating a total number density or ratio of total number densities I Intercept method of calculating a total number density or ratio of total number densities A Measurements made in the argon diluted hydrogen based flame N Measurements made in the nitrogen diluted hydrogen based f 1 ame Y Quantum efficiency n-j. Total number density References to the use of these methods can be found in Chapter 2 (Theoretical Considerations). Ratios "R" will always refer to argon diluted flame values over nitrogen diluted flame values. -54-

PAGE 61

-55Strontium Boxcar Survey The need to use the most versatile and least complicated equipment possible was recognized at the commencement of this work. One of the goals of the work was to find the optimal instrumentation for flame diagnostic measurement via saturated atomic fluorescence, choosing from the available choices in this laboratory. A series of measurements were made under set conditions for the comparison of three boxcar averager measurement systems. The first pair of measurements (Figure 9 ) shows saturation curves under identical illumination conditions for the Princeton Applied Research (PAR) 160 boxcar and the PAR 162 mainframe with the 164 plug-in. The two curves are very nearly identical, though the scatter on this data was fairly great. (A substandard burner system was used for these two preliminary curves. It was replaced after these two experiments with the system described in the text.) The gates on both boxcars were the same (15 ns). The 10 ps stretch feature of the 160 boxcar did not seem to affect the extent of saturation. The second pair of measurements (Figure 10) shows a comparison of the 160 boxcar with the 162 mainframe using a 163 plug-in and a S-2 sampling head (75 ps aperture). In addition to the boxcar change, a change of dye was performed. As expected, the extent of saturation improved. The shorter gate "viewed" mainly the temporal plateau section of the fluorescence pulse (see Appendix 1), while the longer gate averaged substantially unsaturated portions of the pulse with the saturated portion. The higher power output of the new dye probably accounted for some portion of the behavior.

PAGE 62

CO +-> CD CO 3 CD CL n3 T3 «» •P<+J •r-— . O) II CJ O
PAGE 63

-57SI XD XI X a x a (9AL^B[9J) ^g 60 [

PAGE 64

u

PAGE 65

59ca 81 XI XD XD X X D X a (9AL^8[3vl) ^g 60L

PAGE 66

-60Based on the results of these measurements the rest of the measurements were made with the 162 mainframe 163 plug-in combination to achieve an accurate representation of the saturation condition. Flame vs. Inductively Coupled Plasma (ICP) An acetylene-air flame and an ICP were compared to determine whether saturation resulted in information about quantum efficiency. Two parameters were evaluated under equal illumination in the flame and ICP, namely the saturation curve and the saturation broadening (Appendix 1) for strontium. The half-power points §* for the saturation curve (related to E , see Chapter 2) is inversely proportional to the quantum X r qpp Than for 7\ k inuofcol efficiency of a flame or plasma. For a given element and excitation line, here strontium at 460.7 nm, the ICP was expected to have a higher quantum efficiency than the flame. This was due to the prevailing argon atmosphere of the ICP, as opposed to the predominantly molecular atmosphere of the flame. The saturation curves (Figure 11) indicated that the quantum efficiency of strontium in the ICP was slightly higher than in the flame. A second measure of the quantum efficiency of strontium in the flame or plasma was the saturation broadened excitation profile (Appendix 1 and Reference (62)). A broader profile indicates a higher quantum efficiency, as shown by: p(U 1/2 SA = 6\. (1 + — ) exc L v s,. J p UJ where 5A = full width at half maximum (FWHM) of the excitation profile exc of the atom (nm) 6X. = FWHM of the Lorentzian (undisturbed) profile of the atom (nm)

PAGE 67

— "O jC (O en QJ JZ -iE i— ui (T3 CD 0) CD c m o — Sr— o oj i— ti — (13 • CD (O E — * SO ol X CD CO — >.e oi •rq. -a <— 4-> (O O S= I i— i ro cn4CD O O +-> (T3 CD C E E CD O C 01 Q£l•I03 . — i — +-> i — <+(C 01 Q. N CD d) . t> -O JC >,rs<_> ra 3 i— C 3 CJ Q. E CD Ol Sfflfi. C 0£ U > E O U +-> tc •iMCD +J coi^rx: r~^ io ouj oi-p • 5TO 3 -U SE Ol (X) +-> O CD 3 CD «* (O 3 3+J D IfltlOC 3 II E •<3d) e 3 >, aS_ CD •iCD i— r< +J J= 4-> iCD C -P £ CJ SII o oi-c 3 ST3 tOl Ol X M C i— ttCD 00 fO Ol JZ <+,•<

PAGE 68

-62S3 XJ SI X] D T o D . o . CM (8Aiq.ei.9a) ^g 6o[

PAGE 69

-63o p(?0 = power density of the laser (W/m ) s ? p (X ) = saturation power density (W/m ) The term p (x ) is inversely proportional to the quantum efficiency (see Chapter 2). Therefore, the 6X depends upon quantum efficiency. Saturation broadened SX are given below for strontium in the flame and in the ICP under identical power density conditions. Atom Cell ^exc (full power) flame 0.66 ICP 1.13 The increase in
PAGE 70

a « •^C -r> S_ ai > sa> -a OT-r3 _c I) OT3 u l/l SC "O cu ro J-> t0) (UScu

PAGE 71

CK €K LX ex CX DX K -65XD XD S3 (3AL^e[9u) J g 60 [

PAGE 72

-66either the atomization of strontium or the quenching of excited state strontium atoms. Relative information was derived for Y and n y from this plot. Relative saturation powers (proportional to E^) were found A from the points at which the fluorescence was 50% of the maximum. The saturation powers are proportional to 1/Y (see Chapter 2). In addition, the slopes of the 1/Bp vs. 1/E^ curves were taken as measures of 1/Y also. The values for R„ s and R y£ were computed, and are shown below. R YS 1.2 R YE 1.1 The plateaus of fluorescence were used as relative measures of n T (see Chapter 2). The intercept values of the 1/Bp vs. 1/E curves were used also as relative measures of n-p The values for R... and R NB are shown below. R NI °' 91 R NB 0.87 The agreement of the two methods for finding relative Y's and n's for the two flames was quite good. The percent relative error for the Y measurement was 9%. The percent relative error for n_ was less than J/o • The errors in the ratios are probably random in nature. The percent relative standard deviation for these measurements was about 5-10%. Absolute Y's were measured by means of the E? method using equation 12 from Chapter 2 under the conditions of Figure 12, and additionally under the conditions of Figure 13 using the flame-shielded flame and the small slit mentioned in Appendix 1 placed in front of the photodiode. The results are shown below. Both flame stoichiometrics were the same.

PAGE 73

re O l-H s-j: a) x ra -M S-r3 -O a; o to c ^r +j ra aj +-> CD Cl -a £ a. C C •rT3 0) (T3 +-> LU 4+-> 0)0 3 O HI S-ifl +)r-r 3<(13 CL(— in 0/1 SII a> g •rr— (O > T3 c > sai ii O O) CL SCU to ra > »-> .c .a sz o oo i — o to ,-<

PAGE 74

-68X X X X X X O i— 31 c (9Ai4e1.au) d g 6ol

PAGE 75

69time Figure 14. Composite boxcar scan of fluorescence pulse of strontium. The gate was halted at several delay times (DT) to record the saturation curves seen in Figure 15. X = X = 460.7 nm. ex em

PAGE 76

-70Strontium Y~, ,in capillary burner 0.50 Strontium Y ? , ,in flame-shielded flame 0.24 As the results indicate, careful attention must be placed on selecting a correct and representative aperture. The capillary burner, with no flame shield, certainly had an edge effect, producing a substantially poorer quantum efficiency. This was entirely masked, however, by the inadequacy of the measurement of the E^ caused by using an aperture larger than the laser beam. As can be seen in equation 12, the quantum efficiency is inversely proportional to E, , and therefore directly proportional to the measured laser beam cross-sectional area. The approximately 2-fold increase of quantum efficiency corresponded in this case to the same decrease in the estimate of E:. A Total number density was figured from the slope of the 1/Bp vs. 1/E curve after calibration of the intercept, and then the slope, under 12 the conditions of Figure 13. This procedure resulted in n_ = 1.3 x 10 _3 cm , a very reasonable n T for 100 ppm Sr in a hydrogen based flame. A second value, derived from equation 10, yielded a value of n, = 3.1 x 10 _3 cm . This value agreed very well with the prior value. The small discrepancy could have been due to calibration of the boxcar plug-in module or the photometer. The boxcar module had been under repair prior to these experiments, but had not been calibrated. Unfortunately the equipment required for a check of this value was not available. A temporal scan of the fluorescence pulse from the photomultipl ier produced an interesting observation for strontium. Several overlapping scans were taken to define the composite temporal shape shown in Figure 14. The delay time for the boxcar was set at 4 different points on the peak, and 4 sets of saturation measurements were taken. These

PAGE 77

-71data are shown in Figure 15. As expected, the leading edge of the pulse was not saturated. Surprisingly, however, the trailing edge of the pulse was saturated. Normally, assuming two levels available for laser and thermal processes, a decrease in signal could not be observed while the system was saturated. This meant that a third, presumably photoninduced, process was necessary to explain the phenomenon. Two possibilities existed for the explanation of these data, compound formation and laser-induced ionization. Compound formation was rejected as a cause of this effect, as a two body collision would be necessary. Presumably the only suitable species available in this flame for compound formation would be oxygen atoms or hydroxyl molecules. Even with favorable orientation of the collisions, they probably could not happen fast enough to account for the subnanosecond phenomena which were seen here. A more probable explanation was the absorption of a second photon of wavelength 460.7 nm, which could bring the atom within 0.3 eV of its ionization potential. A thermal event, not so selective as a compound forming collision, could then easily ionize the atom. Unfortunately, an experiment to measure electron current generated via laser-induced ionization with the aid of the nitrogen pumped dye laser was unsuccessful (63). In private communication with the investigator it was found that poor results were attributed to laser pulse width considerations. (While the instantaneous power produced ions, the time spread on the electron bunch produced only a small signal. The best type of laser for this experiment has been found to be one with a longer pulse width and highpower, i.e., high pulse energy.)

PAGE 78

CD X -Q CD > 4->

PAGE 79

73«x «x 9 X <©X
PAGE 80

-74S odium Measurement of sodium parameters was hampered by an experimental inconsistency. In all other measurements, the monochromator bandwidth was narrow enough to exclude any other radiating wavelengths from the saturated atoms. For sodium, however, both resonance lines fell within the monochromator bandpass. Estimation of the n, values from B F and max continuum absorption required inclusion of both sodium resonance lines in the theoretical treatment. The n T value for sodium was arrived at via two different routes. A value was calculated from the saturation plateau for the argon diluted flame by the use of equation 10 from Chapter 2. In addition, a continuum absorption experiment was used to give an independent measure of ru, as described by DeGalan and Winefordner (17). The lack of a suitable bandwidth monochromator (ax fc 5 x 6\ . ) v mono atom' in a suitable position necessitated substitution of an argon ion pumped dye laser as a continuum source for this technique. The dye laser output bandwidth was measured by the use of a high-dispersion monochromator (used in the second order). The optical bandwidth was 0.174 nm. As the sodium atomic absorption linewidth was only ca. 0.005 nm (61), this laser was considered a continuum source. The monochromator bandwidth described in (17) was taken as the laser bandwidth. Measurements of a (fraction absorbed) were made in both the argon and nitrogen diluted flames. In addition, saturation curves were taken in both flames (Figure 16). The n 's calculated from both methods are shown below. Method Value (1 ppm) 10 ? continuum absorption 3.6 x 10 cm B p 2.9 x 10 11 cm" 3 max

PAGE 81

to +-> a» E -o a;
tu SE a> CO C a) a) s0) Q.-Q c en 0) CO Q.LO < -a C 3 <1J r— CTVrO T3 i-a c >> o c o o • ^i : E CO +J > s_ i0) i 0) << (T3 C 3 3 •!i. OTf— I— «> 3 (T3 -rKi/IO +-> E "O LU fa a> en CO d) C 4-E CO > 0) O +-> LO = — a> o |—TX 'rBJ 1/1 3 r< "J '_ 3 CD

PAGE 82

•76X X X X D X D X E X X D (3AL^B[9J) J g SO].

PAGE 83

77The agreement between these values was considered quite good in light of the fact that the methods are independent, and several calibrations of different types are involved. Calibrations of absolute optical radiances are considered to be quite difficult and error prone. An agreement of 2-fold is considered state of the art for inexperienced laboratories. The value for R... was determined, and augmented by an R N derived from the continuum measurements. However, in the case of sodium in the nitrogen diluted flame, the saturation was incomplete. Therefore, the R^ B value could not be calculated. Ratio values (R«) are given below. The values were corrected for differing aspiration rates for the two f 1 ames . Method Value R N , continuum absorption 0.89 R„, intercepts 0.84 The agreement is quite good. Since the ratios calculated by these two methods did agree so well, the intercept ratio was used to calculate the saturation plateau value for the nitrogen diluted flame. This enabled evaluation of the E? parameter, which was otherwise unavailable. This allowed a second means of determining R Y . The values are shown below. Rye 5.3 R YE 14.0 Calcium In Figure 17, saturation curves for calcium in HOA and HON flames are given. The Ry values for the two flames via two methods are given below.

PAGE 84

CD J=

PAGE 85

-79LX CK s XD XD X D X D

PAGE 86

-80R ys 1.31 R YE 1.83 A Y value was calculated from equation 12 for the HOA flame, and is shown below. Y H0AE °52 An n,. value calculated from equation 10 is shown below. n TH0AB 2 ' 6 x 1qU cm " 3 Values of R.. derived from the two methods are shown below. R NI 0.81 R NB °83 Indium Indium was marginally saturated in the stoichiometric air-acetylene flame (Figure 18), which is a highly quenching flame with respect to the HOA flame. In contrast with this flame Figure 19 shows the saturation curve in the HOA flame. The much lower power and much more complete saturation shown in the resonance ( A ex = x em = 410 nm) measurement in this figure indicated a much higher quantum efficiency. In addition, the observation of x 32 (451 nm) fluorescence followed the expected behavior in showing the same saturation shape as A... observation. The 2 * 3 transition (451 nm) could also be marginally saturated, as seen in the same figure. The measurement of power for these curves, however, was not reliable enough to provide anything but the relative data given above. A more reliable power measurement was made for the data shown in Figure 20. The values for Y and n-j. in the HOA flame given below were arrived at by the calibration of the 1/B F vs. 1/E curve.

PAGE 87

1) c £ £ 0) o > .-1 O II

PAGE 88

-82< < (aALq.BL3u) ^g 60 l

PAGE 89

OV T3 O 5g (0 >> fO -C i— l T3 • O «* T3 CJ d) > +J II +J i. 3 4-> 3 i— EO O •ta>i— X» .-< Q. 0) a; c II oj so .c .= en x}— +j s
PAGE 90

-34D -BO D -X -iX +X D +X D + X (9AL^e[3j) d g 6ol

PAGE 91

E "O -O m Src c .a o c CD -C >> -C S_ (/> O — i43 O T3 0) O -rT3 rO C 5. Die 3 ra OJ +-> E CD (C O to a> i_ > +-> E 'I-i3 +-> C •>re -a r-o c a; c i— < cc ra

PAGE 92

-86X

PAGE 93

-87Y HOA °' 28 n TH0A 2.0 x 10 10 cm" 3 (1 yg/ml ) An R v value was available only from the slope method. The plateaus of the two flames were not developed enough to find E s values. A R ys 1.03 An R^ value was only available from the intercept method, and is shown below. R NI 1.05 Noise Power Density 1/2 Noise power density (W/Hz ' ) measurements preliminary to saturation noise power density were made under the conditions shown in Figures 21-26. Since the measurement of saturation noise power density will only be possible in the lower frequency ranges (up to about 50 Hz, due to repetition rate limitations on pulsed lasers), the low frequency range (0-50 Hz) data collected were chosen for these figures. The higher collection rate (higher frequency spread) data had no interesting features except for harmonics of 60 Hz, and a band of discrete frequencies (centered on 6 kHz) introduced through the electronics power supply.

PAGE 95

89o o Z / T ( Z H 6KT0)/,0I * V . i|lpL«puegAu9jano SWH

PAGE 96

!T3

PAGE 97

-91r 00 o o a Z/T (ZH 6fr0'0)/ 0I 0T * V 2/1 q^pLMpuegAuajuno SWU

PAGE 98

r-l S_ 0) irxo ci> i — no o H J) « o
PAGE 99

-93u V rs cr
PAGE 100

CD 2 0) S4J <*-

PAGE 101

95p»o „ ld >, o o 2 / T ( z H 6i70*0)/ 6 0T x V Zl\ q^piMpueaAuaa-ino SWU

PAGE 102

o a> +-> c 01 So u r-

PAGE 103

•97= o rs — 2 o 2/1 2 / T ( z H 6W0)/ 6 0I x V i|apLMpueg/}ua-uno sua

PAGE 104

r— +J

PAGE 105

•99cr cu i. r o I o o o 2/ T ( z H 6frO*0)/ g OI x V 2/1 il^pLMpuBg/^usjJino swy

PAGE 106

CHAPTER 5 RESULTS AND DISCUSSION Quantum Efficiency and Total Number Density Quantum efficiency, Y, and total number density, n T , values are notably lacking from the literature, though they are of great interest to analytical chemists, physicists, and engineers. The reason for this lack of literature support is the tedium of this type of measurement, as mentioned in Chapter 1. Nevertheless, several items are available for comparisons in flames of the type investigated here. The quantum efficiency (or yield factor) has been previously estimated in flames yery similar to the HOA and HON flames used here (64). A value for Y. for Sr in an HOA flame yery close in proportions to the one in this work was 0.16, as compared to 0.24 in this work. In addition, the ratio of this Y to a Y evaluated in a HON flame (gas proportions somewhat different from this work) was 2.3, as compared with 1.2 from this work. The agreement here is very good, considering that the initial use of laser excited saturated atomic fluorescence for these measurements was in this work. The HOA flame Y values are remarkably similar. The difference in the ratio values can be explained by the increased proportion of the strong quencher nitrogen in the flame used in Reference (64). Another source of literature data of this type is the work by Hooymayers and Alkemade (65). Data on sodium quantum efficiency in HO -100-

PAGE 107

-101type flames were measured by these authors. When values for Y were taken for the two flames with gas ratios closest to those in this work, the R Y value was 8.2. The R y values found via two different methods in this work were R ys = 5.3 and R yE = 14. The numerical average of these is 9.5, which is quite close to the published value. The ratio derived from E^ for the two flames, 14, is based on an indirect calculation of n TH0N from n TH0A' as the P lateau condition was not reached in the HON flame. Therefore, the R yE is somewhat suspect. The R ys , 5.3, is somewhat more substantial, and does not differ significantly from the value in Reference (65). As the quantum efficiency is a strong function of gas composition (even with the same diluent gas), the difference between the slope data ratio and the published data was quite reasonable. The absolute value of the published Y HQA (65) for Na is 0.32. The value arrived at from E^ in the present work is 0.03. If the estimation of power were in error for any reason, this would be reflected in the Y value found by this method. The quantum efficiency for calcium in the HOA flame from the present work, 0.52, seemed quite reasonable, in light of the quantum efficiency seen for strontium, which should behave similarly in the flame. No literature data were available for direct comparison, however. The quantum efficiency for indium was of the same order of magnitude as strontium and calcium, and therefore seemed reasonable. Again, no direct literature comparison could be made. The R y values seemed to be rather lower, in general, than expected. Nitrogen was expected to be a much better quencher than argon. In addition, the concentrations of the two diluent gases were predominant in the

PAGE 108

-102flarnes, leading to the presumption that they would dominate the quenching rate. In the sodium case, however, the R v value was several times higher, more in line with expectations. The literature available pertains to sodium (64) and strontium (65). Quenching cross-sections (a, A ) in HO type flames are given below for both atoms in Table 5. Table 5 Quenching Cross-Sections for Sodium and Strontium in Hydrogen Flames Na (64) Sr (65) Quencher a (A) 2 a (A) 2 N 2 40 21 2 62 400 H 2 1 67 Ar 2.3 < 1 The sodium case (high R ) seemed to fit the expectation that a large quenching change could be expected from a change of the major diluent (
PAGE 109

-103mixture used here can grossly affect oxygen concentration, this could greatly affect the trend caused by nitrogen. The R N values for this work were all quite close to 1, indicating a very small role for nitrogen in the atomization process. It would be expected that a large change in the flame gas composition from a monatomic constituent (argon) to a diatomic diluent (nitrogen) should make a gross difference in the atomization process, through thermal equilibration. Apparently this does not happen in these flames, however. Here again, no comparative data were available in the literature for the two diluent gases. Noise Power Density A very preliminary evaluation of the results of the noise power experiments is given below in Table 6. Experimental conditions for the data are found in Figures 21-26. Changes in different types of noise are indicated by arrows pointing in the direction of change. Table 6 Noise Changes Induced by Adding an Inert Gas Sheath Wavelength Region Noise Types 1/f White Proportional OH (306 nm) J | \ C 2 (516.5 nm) — t t Sr (460.7 nm) — f f

PAGE 110

-104The OH region, as was expected, exhibited a lower white noise component when an inert gas sheath was added. The inert sheath minimized entrapment of 2 at the edge of the flame, producing less OH. This, in turn, caused the white noise (shot noise) component to decrease. Increased turbulence caused the 1/f noise and also the proportional noise to increase. Proportional (or whistle) noise was nonexistent in any case until the sheath was added. It appeared in all cases when the sheath was added. The C 2 region was enhanced by addition of the sheath, since a richer atmosphere favored C,, production. The white noise therefore increased. The low frequency (1/f) noise remained the same, since turbulence at the flame edge did not grossly affect C ? production. Strontium 1/f noise remained the same with addition of the sheath. The lack of a change in 1/f noise could have been due to a cancellation of two effects. The overall strontium signal was 3-fold lower when the sheath was on. This could have resulted in lower 1/f noise, which would have been cancelled by an increase due to increased turbulence.

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CHAPTER 6 CONCLUSIONS AND FURTHER WORK The use of a nitrogen -pumped dye laser was investigated for the measurement of flame diagnostic parameters. The assurance that all the conditions necessary for these measurements were fulfilled was a very time-consuming and tedious project. The following points were especially critical in development of the method. System Temporal Response The establishment of atomic fluorescence pulse widths via reliable means (streak camera) enabled us to choose the correct measurement system (75 ps aperture) from the choices available. The existence of a steady state temporal plateau, while certain to occur somewhere within the pulse, had to be long enough to measure without averaging unsaturated portions of the pulse. The photomultiplier rise time had to be fast enough to follow the pulse without distorting its shape unduly. Complete Saturation Complete saturation was desirable for several reasons. It eliminated concern over the necessity for spatial homogeneity in illumination of the flame volume under investigation. Complete saturation also provided B F and a way to find E? for easy calculation of n T and Y. These values r max A •105-

PAGE 112

106(Bp and E,) also provided confirmatory data for ratios of n_ and Y max ' ' in the different flames. Measurement of Ex Laser power, bandwidth, and area also had to be evaluated very carefully in order to provide realistic absolute data for Y. The latter two quantities do not affect ratios of Y, of course. As seen in the strontium section of Chapter 5, an improper evaluation of E, can easily A cause a 3-fold change in absolute Y estimation. Laser spectral bandidth had to be evaluated in order to satisfy the requirement for a spectral continuum for illumination, also. Photometer Calibration w The photometer had to be calibrated in order to find B p in an max absolute way, to get n T . General Considerations Careful corrections had to be made for laser scatter into the monochromator at high irradiances. Typically, scatter from the laser contributed significantly to the observed signal until laser irradiance was reduced by about 2 orders of magnitude. The data evaluated, after these parameters were controlled, were reasonable and generally in agreement with literature values of n T and Y available. A complication arose when the discovery of a further photoinduced process came about. Photoionization and thermally assisted photoinduced

PAGE 113

-107ionization were discussed as possible explanations for these data. Two photons of the same wavelength (460.7 ran) were enough to bring strontium close to ionization (0.3 eV from the ionization potential). For indium two photons (410 nm) were enough to exceed the ionization potential. Further work by another student found recombination ion lines upon scanning the emission monochromator while illuminating indium with the laser. The current theory does not include the processes of ionization or recombination. At laser powers of the order necessary for saturation of some elements these effects may have to be considered in the future. The possibility exists, with the advent of the excimer laser, that peak powers can be had at visible and ultraviolet wavelengths to completely ionize atoms in a reasonable volume in a flame. If this power, and the longer pulse widths of this type of laser, can completely and selectively ionize a given atomic population, good sensitivity and a certain immunity to kinetic (recombination) factors should result. This type of saturation should readily avail itself of theoretical calibration via geometric collection efficiency factors. A second possibility for measurement of n T in three-level atoms is to use two dye lasers to saturate both transitions and to thereby equalize populations (according to their degeneracies). This would allow measurement with no assumptions about kinetic quenching constants. Noise Power Density Since only preliminary noise power spectra have been measured so far, much work remains. The expected reduction in noise during saturation has yet to be observed. Further characterization remains to be

PAGE 114

-108done on the temporal behavior of the different atoms under laser excitation. It is hoped that the application of saturation to noise power spectra measurement will allow real progress to come about in the critical areas of nebulization and burner design. General Comments Saturated atomic fluorescence has been developed and critically evaluated as a tool for flame diagnostic measurements. It promises to be more straightforward and less tedious than other methods of arriving at values for Y and rip Hopefully saturated atomic fluorescence will enable the evaluation of noises basic to design features in atomic analytical instrumentation. Spatial and temporal information obtainable through the means of saturated atomic fluorescence are available by no other means.

PAGE 115

APPENDIX 1 SUBSIDIARY MEASUREMENTS Since the measurement system used in these studies was to be used for the measurement of fast signals, it was necessary to characterize its response on a very short (ns) time scale. The temporal response of the system was investigated in several ways, using several auxiliary systems to the one mentioned previously. The points which needed to be investigated were 1. PMT pulse response, 2. laser pulse width, 3. atomic fluorescence pulse width. Photomultiplier Pulse Response The response of the photomultiplier tube and base combination was measured by the use of a small laboratory-built nitrogen-pumped dye laser. The laser pulse duration had previously been measured at about 600 ps. This pulse was directed through the same collection system used for the saturation measurements. For all practical purposes, this represented an impulse of light to the photomultiplier tube. The pulse time response of the PMT was then measured by scanning a 75 ps gate across the output pulse. The result, shown in Figure 27, was a pulse response width of 2.9 ns. -109-

PAGE 116

-1103 ns H Figure 27. Boxcar temporal scan of photomultiplier pulse response. Laser input pulse width was ca. 600 ps, Photomultiplier response width was 2.9 ns.

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•IllLaser Pulse Width The temporal features of the laser output were checked in two independent ways. The output of a calibrated vacuum photodiode (risetime I 500 ps) was scanned using the 75 ps gate (Figure 28). The data collected in this manner were checked against the manufacturers calibration via the use of a borrowed joulemeter. The joulemeter response indicating pulse energy could be reconciled with peak power measurements, made via connection of the output of the photodiode through a 50 Q load to a fast oscilloscope (Type 454, Tektronix, Portland, OR). The pulse energy and peak power could be related if a pulse shape and pulse width were found. Pulse width from the photodiode-boxcar measurements did not agree with the manufacturer's calibration data, using the peak energy found with the joulemeter. However, using a variety of other sources, pulsed and continuous wave, the diode calibration was upheld. Therefore, a need to further investigate the laser temporal distribution was expressed, as the laser pulse width and time response of the PMT to the fluorescence caused by the pulse needed to be understood thoroughly. Manufacturer's literature (66) and several publications featuring the use of this laser list the duration of the dye laser pulse width as 4-5 ns. The joulemeter data indicated times ranging from 300 ps to approximately 2 ns as pulse widths for different dyes. As these were considered somewhat nonsensical for this laser system, it was decided to use a very fast response system for time dependence of the dye laser pulses. A Hamamatsu streak camera (Temporal Dispersor, Hamamatsu, Middlesex, NJ) was used in conjunction with a microprocessor

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•1122 ns Figure 28. Boxcar temporal scan of photodiode pulse response. Laser input pulse width was ca. 600 ps. Photodiode response width was 2.2 ns .

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.13based data collection and display system (Temporal Analyzer, Hamamatsu, Middlesex ,NJ) . This system could trigger the laser and the streak camera with the use of suitable delay lines and trigger generators to ensure overlap of the camera firing and the laser pulse. The laser was directed through suitable neutral density filters (to avoid damage to the very sensitive streak tube) and into a monochromator via two front surface mirrors. The exit slit of the monochromator was focused by streak camera optics on the streak camera entrance slit. Several streaks were observed to find the general temporal shape for the given dye. As these experiments were done during the daytime, severe triggering jitter existed. Only 10% or so of the streaks collected were usable. Several representative streaks were collected. Each of these was recorded via a digital to analog converter and a strip chart recorder (Model SRG, Sargent-Welch, Cleveland, OH). The results for several dyes are shown in Figures 29-32. The results indicated that the dye laser system used here was either producing much shorter and more temporally complicated pulses than expected, or a serious systematic error was being committed. Therefore, the temporal output of a second dye laser (DL2000, Lambda-Physik, Interactive Radiation, Northvale, NJ), an oscillator-amplifier configuration, was also investigated. This laser was expected to give a temporal pulse width in the same 4-5 ns range. The streak results are shown in Figure 33. This result was as expected, and the other results were therefore trusted. The calibration of the photodiode via the joulemeter could then be reconciled with the manufacturer's calibration.* *Note: Further data collected since experimental work for this dissertation was finished indicate that variations in pulse width and jitter of the laser depend strongly on repetition rate and gas flow velocity.

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-114Figure 29. Streak of Molectron dye laser scatter (7D4MC) , 1.5 ns per inch.

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•115Figure 30. Streak of Molectrondye laser scatter (DPS), 1.5 ns per inch.

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•116Figure 31. Streak of Molectron dye laser scatter (R6G) , 1.5 ns per inch.

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117Figure 32. Streak of Molectron dye laser scatter (bis-MSB) 1.5 ns per inch.

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•118Completeness of Saturation The completeness of saturation was shown for the several atomic species chosen by the plateau region in the plot of fluorescence radiance vs. laser irradiance (Figures 9-20). In addition, this provided proof that the precautions against spatial laser beam inhomogeneity were working. Laser Power Measurement Laser power (peak power) was measured by the use of the abovementioned vacuum photodiode. This was placed in front of the laser with a large enough calibrated neutral density filter to provide a signal still linear with respect to the power (typically 4.0 neutral density). The output was connected through a 50 n attenuator, and the peak voltage was read on the oscilloscope. The laser power could be arrived at after consultation of the manufacturer's calibration table. Laser Bandwidth The laser bandwidth calibration was approached in two separate ways. When the first bandwidth data were taken, a suitable monochrcmator (high resolution) was not accessible for direct measurement of the bandwidth of the laser output. Inasmuch as saturation of an atomic transition can give a larger fluorescence excitation bandwidth than the naturally occurring bandwidth, an experiment was undertaken to find the excitation bandwidth of the laser. After a transition was found, a wavelength scan of the laser output was made. The

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-119Figure 33. Streak of LambdaPhys i k dye laser scatter (7D4MC), 8.7 ns per inch.

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120fluorescence, collected by the same low-resolution monochromator was that of the integrated emission bandwidth. A suitable theory was developed in Omenetto et al . (62) to understand this manifestation of saturation broadening in terms of the laser wavelength spread and laser power density. The low power limit of the excitation bandwidth vs. laser power phenomena turns out to be the laser bandwidth, as might be surmised. Plots of excitation bandwidth low and high power limits are shown for the dyes used in this study (Figures 34-37). In order to confirm the low power limits as a source of laser bandwidths, a suitable monochromator (HR1000, Jobin-Yvon, Instruments SA, Inc., Metuchen, NJ) was used. Resolution (bandwidth) of the monochromator was found by wavelength scanning a mercury line from a low pressure pen lamp source in the second order. This resulted in a o 0.12 A bandwidth for the monochromator. The dye laser outputs for the pertinent atomic transitions were scanned directly (with suitable neutral density filters). These scans were done with the use of the scanning attachment for the Molectron dye laser, as this was easier than monochromator scanning. The bandwidth results for both measurements are shown in Table 7.* In several years of use the antireflective coating of the dye laser cells had apparently been destroyed. This allowed the development of a second laser cavity, coupled to the front surface of the dye cell, which resonated at a different wavelength, and with a different temporal position. This *Note: An anomalous side-lobe structure is seen in the results of both monochromator scan and saturation broadening bandwidth for the dye 7D4MC. This structure is probably related to the anomalous second pulse seen in some temporal scans of this dye.

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-1210.39 A M Figure 34. Excitation broadening of strontium. Relative atomic fluorescence (vertical axis) vs. wavelength (horizontal axis), obtained by scanning the dye laser wavelength past the atomic wavelength (460.7 nm) , while continuously recording the atomic fluorescence signal (7D4MC dye). a. low power limit—represents laser bandwidth. b. high power limit—represents broadened sensitivity under saturation conditions.

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122I 0.34 K l-H kJ*W Figure 35. Excitation broadening of indium. Relative atomic fluorescence (vertical axis) vs. wavelength (horizontal axis) (DPS dye, center wavelength, 410 nm). a. low power limit—laser bandwidth. b. high power limit.

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•123Figure 36. Excitation broadening of sodium. Relative atomic fluorescence (vertical axis) vs. wavelength (horizontal axis) (R6G dye, center wavelength, 589.0 run). a. high power limit. b. low power limit—laser bandwidth.

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-124Figure 37. Excitation broadening of calcium. Relative atomic fluorescence (vertical axis) vs. wavelength (horizontal axis) (bis-MSB dye, center wavelength, 422.7 nm) . a. low power limit— laser bandwidth b. high power limit

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-125Table 7 Excitation Profile vs. Scanned Laser Bandwidth sx (A) Element Direct Fluorescence Excitation Profile Measurement — Ar/0 2 /H 2 N 2 /0 2 /H, Ca 0.23 0.20 0.20 Sr 0.23 0.42 0.23 Na 0.36 0.23 0.40 In 0.24 0.19 0.28

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-126observation was further born out by the abbreviated pulse width of the other dyes, and the limiting spectral bandwidths exhibited. These were approximately three times those specified by the manufacturer. The further evidence of some temporal mode structures on most of the dyes' output seemed to concur with the above. The times between maxima of the temporal modes corresponded to a distance of about 1 cm, the width of the dye cell. This indicated a strong coupling within the cell with an additional coupling to the entire cavity. Further experiments will be done with a new dye cell to confirm this line of reasoning. In the meantime, the sensitivity of the temporal width to tuning of the cavity invites the goal of very short laser pulses from a commercial system not designed for this type of work. In atomic spectroscopy, this invites the study of rate constants of quenching, etc. Laser Cross-Section The evaluation of the cross -sect ion involved in the excitation of atoms in the viewing area was purely based on the geometry of collection. The vertical distance was the slit width, as the monochromator was fixed on its side. The horizontal distance was assumed to be the width of the inner (seeded) flame, which was somewhat smaller than the laser beam. Therefore a mask was placed over the face of the photodiode before peak power was measured. The aperture measured 0.5 mm by 4 mm, and was centered in the laser beam, which had been centered at the correct vertical and horizontal displacement during alignment. The homogeneity of the laser beam is discussed in the following section.

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•127Laser Seam Homogeneity The necessity of a spatially homogeneous laser beam for meaningful diagnostic measurements has been discussed at length previously (67). In order to use the data from these experiments, it was necessary to prove the homogeneity via direct sampling, as well as by the results of the diagnostic experiments. The laser beam, suitably filtered as previously described was measured at the edge of the flame cell farthest from the laser. The same vacuum photodiode as used previously was masked with a 100 ym pinhole and suitable neutral density filters. It was then translated through the beam in two dimensions via a laboratory-built screw translator mechanism. The output of the photodiode was measured with the boxcar system using the 164 plug-in. The resulting voltage was recorded on a strip chart recorder. These data were then entered manually into a digital computer. The data were plotted using a three-dimensional plotting routine developed by the author (see Appendix 2). These results are shown in Figure 38. The homogeneity in the central portion was quite good. This central portion (0.5 mm by 4 mm) was the portion directly exciting the field of view. Self-Absorption Self-absorption was proved to be negligible for all measurements by introducing a 10-fold higher concentration of analyte into the flame with a 1.0 neutral density filter inserted between the flame and the PMT. In all cases, this produced the same size signal as the 10-fold lower concentration. The lower concentration was used,

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128O CD 1T3 M -a O -ryi

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-129however, for the measurements because of the tendency for higher concentrations to reduce the degree of saturation (68). Spectral Continuum The laser bandwidth of approximately 0.25 & was assumed to be a continuum despite the possibility of a saturation broadened absorption profile. Power broadening should not be present at these laser power levels. Achievement of Steady State The achievement of a steady state in the population of the excited state is necessary to measure a meaningful quantum efficiency or total number density. While steady state could be achieved in at least two ways, only one of these was suitable for these measurements. The first steady state has been predicted (67) as a condition in which (in a three-level system) the populations of the ground state and the highest excited state are equalized by the fast rising edge of a laser pulse. This steady state relaxes to a second steady state plateau involving the second level. It is this feature which accurately reflects the quantities that we are interested in. As a means of determining that such a steady state exists, a temporal scan (streak) was made of the fluorescence of the highest excited state of indium as a function of laser excitation tuning. The tuning, as mentioned before, strongly affected the pulse width of the dye used. Fluorescence corresponding to X.excitation and a 23 excitation are shown in Figures 39 and 40. In order to

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•130Figure 39. Streak of indium atomic fluorescence. Excitation wavelength 410 nm (see streak in Figure 41). Emission wavelength 451 nm. Concentration 1000 ug/ml. 19 ns per inch.

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L31Figure 40. Streak of indium atomic fluorescence. Excitation wavelength 451 nm (see streak in Figure 33). Emission wavelength 410 nm. Concentration 1000 yg/ml. 19 ns per inch.

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-132Figure 41. Streak of Molectron dye laser scatter (DPS), 8.7 ns per inch.

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-133collect these streaks a very high (ca. 1000 ug/ml) concentration solution was necessary. In addition, the non-resonance transition had to be used, as scatter was too high for resonance measurements. This transition also had to be in steady state for the measurements to be meaningful. No evidence of peaking in the highest excited state was found. It was evident that the temporal width of the fluorescence was far longer than that of the laser, and that a significant plateau existed at the top of the pulse. The steady state was quite evident. It was also evident that either the threshhold of saturation had to be quite low on the laser excitation pulse or that the combined decay rate connecting the third excited state with the other states had to be very low. If the latter were true, the plateau would be much shorter than it is, as the laser drops off with quite a fast fall time compared to the length of the plateau (see Figure 41). Therefore, it can be considered that saturation occurred quite early in the pulse. Although there is no data representing the relative timing of the leading edges of the laser and the fluorescence pulses, it could be assumed that if the laser shape were not changed grossly that the falling edge of the atomic fluorescence pulse represented a relaxation of the excited state population. A later section on rate constants discusses this possibility. Coherence Effects Coherence effects (population changes synchronous with the electric field of the laser output) would destroy the approach used in the theoretical section to find quantum efficiency and total number density. These effects are not expected to be seen in high pressure

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•134environments at the power levels used here, as collisions of the dephasing type are quite frequent (47). Measurement of Fluorescence Depth Since the laser beam exceeded the width of the inner (seeded) flame, the fluorescence collection depth was taken as the width of the flame in the collection axis, 4 mm. . Calibration of Photometer A DC calibration procedure was used for calibration of the photometer used for collection of pulsed data. Pulsed calibration procedures and calibrated sources are not available. A tungsten strip lamp (GE pyrometer 6818, S6, GE, Nela Park Cleveland, OH) calibrated against a National Bureau of Standards calibrated strip lamp (EPUV 1068, National Bureau of Standards, Washington, D.C.) was placed at the focus of the optical system for fluorescence collection. The lamp was operated at the standard 35 A current (AC) specified, and allowed to stabilize for 1/2 hour, shielded on all sides by drop cloths. Measurement of output current was made under the experimental conditions at the wavelengths specified in the lamp calibration table. The resulting data are shown in Figure 42. Quenching Rate Constants The atomic fluorescence streak data exhibit the plateau mentioned in the Steady State section of this appendix. This feature means that if the saturating pulse is short enough, yet intense enough to populate

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-135X r . o o o 01 (M/ lu uiu js v) /CiLAL^LSuas -ta^aiuo^oqd

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-136substantially the highest state, that a combined quenching and radiative lifetime for that level could be found from streak data. The signal to noise ratio of the present data is quite poor, but if a smoothed decay profile were used, it could establish an upper limit for a decay lifetime. The problem with this approach is that the laser temporal response cannot be seen with enough amplitude resolution (with the present equipment) to determine if some response to the tail of the pulse is determining the observed decay. In addition, with the jitter problems as they stand, no temporal relationship could be established between onset of lasing and onset of fluorescence, although they should coincide closely. A computer acquisition of several temporal streaks of the laser, and then the fluorescence, followed by alignment of the leading edges has been tried by one author (69) to eliminate problems of this sort. In the present case, this was out of the question, as the jitter was far too large. Noise Power Density Measurement The system used to collect these data has been used before (69), but will be described here briefly. Figure 43 depicts the system. The source of the noise for the spectra collected was an ordinary laboratory flame (nebulizer and spray chamber: Perkin-Elmer Corporation, Norwalk, Conn.) with a laboratory-built capillary burner (Haraguchi et al . (70)) and an inert gas sheath (laboratory-built). A stabilized gas flow system similar to the one mentioned previously was used. Emission signals were collected by a simple point to point lens system at the slit of a medium resolution monochromator

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Figure 43. Noise power density collection system. Component symbols are as follows: F = flame, L = lens, MO = monochromator , PMT = photomultiplier tube, PS = power supply, R = load resistor, ACA = AC amplifier, C = blocking capacitor, A/D = analog to digital converter, D/A = digital to analog converter, MC = minicomputer, = oscilloscope, X-Y = X-Y recorder, T = terminal.

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•138— «YA — | MC ACA 1 ( A/D

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-139(EU-700, McPherson Instrument Co., Acton, Ma.). A 1P28 PMT (RCA, ElectroOptics and Devices Div., Lancaster, Pa.) was used at -700 V (Model 240, High Voltage Supply, Keithley, Cleveland, OH). The output current was converted to a voltage with one of two load resistors (1 kft or 16.2 kn). An AC amplifier was used to block the DC voltage and amplify the AC or noise signal, in order to best use the dynamic range of the data acquisition system. The output of this amplifier was taken, after suitable adjustment of an upper cut-off RC filter, through another blocking capacitor (1 pF, mylar, used to block DC offset from the amplifier) to an analog to digital converter (LPS-11, Digital Equipment Corporation, Maynard, Mass.). This ADC was interrogated by the computer at programmable intervals to collect 2048 samples of noise voltage. These were Fourier transformed. The average of 100 Fourier transforms at a given acquisition rate were converted to a power spectrum, which could be displayed in several ways (see Figure 43). The digital data were transferred in a parallel fashion to another digital computer (PDP-11/20, Digital Equipment Corporation). These data were stored in binary fashion for fast acquisition by a sequential data plotting program (see Appendix 2).

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APPENDIX 2 COMPUTER PROGRAMMING AND PLOTTING A useful and necessary function of a computer system is the ability to express the results of its computations in a way which is intelligible to the programmer and the user. It has been said that man, since he lives in a three-dimensional world, has a limited ability to visualize in higher dimensions. Mechanical considerations limit his ability to display data in more than two. At best, he can produce a pseudo-three-dimensional display. The PDP 11/20 system used for some of this research has lacked for many years even the most rudimentary display system. A need was established for plotted data from several sources, of two types, sequential (or channel) type data, and paired X-Y data. Both types lend themselves to two and (pseudo-)three-dimensional plotting. Therefore, a project was undertaken to produce a stepping motor plotter to fulfill the need for this type of display and for creation of simple diagrams. An old X-Y analog plotter chassis was scavenged for the bed and pen movement. Stepping motors were attached via gears and belts. Driving cards were installed, as well as end of travel microswitches. As our computer had no general digital input-output function, a request was made to local software support specalists to install and/or -140-

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-141modify existing routines as part of the group's BASIC language package. This included a stepper drive command capable of addressing eight separate motors. This enabled the plotter to be programmed in a somewhat wasteful way from BASIC. A modular program of providing plotting packages was commenced at that time. The basis of the total package was a 45 line subroutine which plotted a best line between two points on the plotter. No provision was made for runoff, so scaling and manipulation of data had to provide for the plotter size internal to a driving program utilizing the best line routine. The routine could have been made shorter, but included the following points necessitated by the present form of BASIC: 1. software integerization to provide symmetry in the function, 2. skip-out to delta X-delta Y change when the pen is up, 3. skip-out to single axis call when only one axis is changed, 4. mini -vector approximation with correction after each mini-vector in only one dimension. The basic best-line routine has been used as the core of several data-plotting routines: 1. sequential— e.g., optical multichannel analyzer, noise power spectra, or streak camera data, 2. X-Y format--e.g., scans of intensity vs. a single dimension, as in profiling cuts of a flame or a plasma, 3. X-Y-Z format— e.g., scans of intensity vs. two dimensions, as in multidimensional profiling, wavelength-intensity-time profiles, etc. These programs were used on various types of computer files, as suited each program, and type and volume of data.

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-142In addition, the best-line routine served the etch-a-sketch or box diagram routine via a very simple language containing a number of symbols for commonly used figures in spectroscopic diagrams. This was useful for slide and figure preparation for talks and journal articles. A third utilization of this routine was for the character generation module. This type of programming has generally been done in assembly language to facilitate speed. In this case, the generation has all been done in BASIC with approximately a ten times reduction in speed from a commercial system. All of the letters and numbers and several of the ASCII symbols have been provided for labelling of charts, etc., created by the other programs. In some cases, the character generation module has been integrated with other graphics modules. Specifics follow for the best-line routine and programs utilizing it. Best-Line Routine Lines 5000-5020 This is a set-up section. It saves current position (C is the X axis position, D is the Y axis position) in CI and Dl. Flags J and K are set to indicate the sign of change for each axis, for the purpose of the software integerization. Line 5025 This line transfers to a short form when the pen is raised (i.e., when B(0) = 1). The short form (lines 5900-5915) steps off the X axis change first, then the Y axis change, to save time.

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143Lines 5028, 5029 These lines transfer control to short form sections when only one axis is changed, again to save time. Lines 5520-5530 The Y axis only is changed. Lines 5500-5520 The X axis only is changed. Lines 5030-5050 These lines decide whether the greater change is in the X axis or the Y axis and steers the program to the correct subroutine. In addition, a true slope is computed and the best integer approximation (absolute value) is found. Lines 5600-5665 This is the best line generator for a change in X axis larger than a change in Y axis. Lines 5800-5870 This subroutine generates the best line for the opposite case, change in the Y axis larger than the change in the X axis. The inverse of the original slope is computed, and the integer of the absolute value is found. The integerized slope is a minivector, when used in conjunction with the direction flags J and K. This minivector is the closest approximation to the real line that can be made by

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-144discrete steps. At every repetition, it is correct in the dimension on the bottom of the slope (in this case the X axis change) since steps of unit size are always taken on this axis. On the other axis, if the correct position is kept track of, a correction can be made whenever the correction amounts to at least one step (as computed in lines 5830-5850). If the minivector is repeated as many times as there are steps between the points on the lower axis (X in this case), the best line has been plotted. This is the basis of all the graphics functions. New position is provided to the subroutine in XI and Yl. The change in terms of steps is computed from the present position, C and D. A variable list can be found in Table 8. Sequential Data Plots 0P1.BAS Lines 1-4 and 1000-2000 A virtual data file must be provided with values ranging from to 35,565. Scaling is done at the keyboard to provide for expansion. The file is searched for the maximum integer value. Line 1100 The actual working value is assigned to this integer. Line 1105 The expansion is decided here by the actual largest value to be displayed. All values topping this value are limited to it (cropped) in a subroutine (lines 1600-1610). The X axis is treated similarly, except no cropping is provided. Therefore, care must be taken when expanding via lines 1070-1090.

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-145Table 8 Variable List for Best-Line Routine CI Saves present X position Dl Saves present Y position C Present X position D Present Y position J Delta X sign flag K Delta Y sign flag XI New X position Yl New Y position B Digital output matrix for word 1 51 Actual slope 52 Integerized absolute slope P9 Loop variable for best-line 56 Actual pen position 57 Difference between actual and correct pen positions M Sign flag for S7 for X/Y L Sign flag for S7 for Y/X

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146Lines 1110-1390 These lines provide for axis drawing and tic marks on either axis or both. The position of the tic marks is remembered for later labelling. Lines 1400-1500 These lines provide for actual plotting, using the best-line routine and either placing dots or drawing lines between each data point. Axis Labelling and Numbering 0P1.BAS Lines 200-760 Lines 200-351 These lines allow numbering at remembered tic mark positions and multiple line labellingfor the X axis. Lines 355-465 The same function is performed for the Y axis. Lines 500-760 This is the caption section subroutine, which services the labeling and numbering sections. It cuts up the caption into individual ASCII characters, finds out the size of the caption, and steps back half of this length to center it. The captions can be plotted horizontally or vertically, and character size is at the

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-147operator's choice. This routine makes use of the best-line routine via the character generation routine. Character Generation Subroutine Lines 4400-4456 This is the look-up table which provides the look-up in variable J8 for the character mini vectors. This variable accesses a binary virtual data file containing the mini vectors and pen up-down commands comprising the 57 ASCII characters and special symbols. These symbols were coded and converted into the binary virtual file via the program LEDAT.BAS. The file name is LEI. DAT. The data file may be output in an intelligible manner by running VFP1.BAS, and referring to the character sort section of this subroutine. The manner in which the virtual data file is used is straightforward. The file is arranged as follows: Item 1— the number of symbols contained in the file. Item 2— the number of symbols plus one--the beginning number of the minivector data for the corresponding symbol. Items through the end of the file-symbol minivector tables as follows: the first item in each table is the number of vectors in the symbol, starting at the lower left corner of a 7 by 7 dot matrix, and ending at the lower right corner. The following items are minivector components by threes, 1. Pen up (0) or down (1) bit

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-1482. X change in steps 3. Y change in steps. The character routine uses the BASIC table to find the virtual file element pointing to the minivector set. A loop is run through the correct number of times (specified by the first element), each time using the pen set routine and scaling the minivector as desired before calling the best-line section to draft the pen stroke. At the finish of the letter, the pen is moved a space corresponding to half a letter. Then, the loop is used for the next letter. Data Passage Between Computers Passage of sequential data files from the PDP 11/34 in a parallel fashion to the PDP 11/20 was accomplished via the PSTRN program (11/34) and the REC program (11/20). The only formality necessary for communication in this fashion is the handshake routine. This was performed on the 11/34 end with "peek" and "poke" commands. The 11/20 used the augmented BASIC commands "INPB" and "PLSB." A 1000 by 16 bit word transfer takes about 1/2 minute, which is not ^/ery spectacular, but quite easy to program. The major holdup was in BASIC, which was quite slow. An assembly language program transferring to the 11/34 from a hardware device ran about an order of magnitude faster. The ease of use of this method balanced the time consumed. The transfer of ten or more files at a stretch would be accomplished with no intervention. Passage the other way has not been developed in great detail yet. Test programs have run with only hardware-caused errors.

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149Plans are under way for bit-parallel character-serial passage of ASCII files as a completely general method of exchange for programs and data files. BASIC (on the 11/20) has ASCII coding and decoding statements for alphanumeric sending and receiving. Fortran (on the 11/34) does not have these features. However, a look-up table should suffice.

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-150Best-line routine-This subroutine serves all plotting functions . > 5 y ) STEP" (K 0) 5000 C1=C\D1=IJ 5005 J=l 5010 IF r (X.l-C)>-~OGO 10 5015 \J~-J 5015 K=l 5020 IF (Y1-D)>=0G0 TO 5025 \K~-1 5025 IF B<0)=1G0 TO 5020 5026 GOSUB 5900 \RETURN 5028 IF X1=CG0 TO 5520 5029 IF Y1=DG0 10 5500 5030 S J . = ( X 1-C ) / ( Y 1. -D ) \S2=INT < ADO ( J. ) • 5040 I!ABS(Sl)>=iGO TO 5600 5050 GOSUB 5000 \G0 TO 5400 5400 RETURN 5500 CALL "SIEP" (INT (ABS>( XI -C) !' ;': l»50»l) 5505 C=C+IKT(ADS(X1-C) >*J 5510 GO TO 54 00 5520 CALL ' STEP "< INT CABS ( Yl-B) ) 5525 D=D+INT(ABS(Yl-rO >*K 5530 GO TO 54 00 5600 FOK P9-1 TO ADS(Yl-D) 5610 CALL , STKP , (S2*J»S0»1)\CALI 5625 C = C + S 2 * J \ D D + K 5630 S6=P9#ABS--"0G0 TO 5650 \tf~-l 5650 CALL " SI LF ' ( INT ( APS ( 07 ) > *M , 00 . 1 ) 56^5 C=C+INT(ABS~000 TO 0050 \l...= ~.l 5050 CALL STir(j'N'K AI.:G< 07) )*L?50,0'> 5355 D~IH it'j (r,l'C(0/) ) :; L 5860 NEXT P9 5070 RETURN 5900 CALL , SrEP'(IMT(rtCS(Xl-C))^Jr50»l)\C-CiINT*J ')LL "OTL!"' ( J? 00 « 1 )

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1510P1.BAS--A section of the program dealing with sequential plotting DEF DEF DEF GO 1 DIM FNA(A'B»C)~A*BX:200/C FNB(W»X> Y>Z)-=WX.X*Y/2 FNC(D>ErF,GylO~D*E*F/(G Uc BETWEEN •iLUE IN M.UE ON SCALE (IMC!-! Y VALUE IN X •! IT EC) TO J. OOO 1000 PRINT TILE NAMED FOR INPU1 1001 PRINT * (UP TO 1024 INTEGERS 1005 A-0 1010 PRINT 'FIEF NAME' J \ INPUT 7?'!1020 OPEN 79% FOR INPUT AS I LI.. L 1025 PRINT ' t OF POT Ml C TO PLOT" 1030 FOR J6-0 TO X3-1 1040 ] F F 1 ( J 6 ) < = A G 1 1 6 1050 A=VF.1(J6) 1060 NEXT J 6 1070 PRINT '# OF STEP 1080 PRINT 'MAXIMUM X 1090 PRINT 'MAXIMUM X 1095 PRINT U Y AX I 1100 PRINT "MAXIM 1105 PRINT 1110 PRINT 1120 IF Y4$='N"G0 1130 30 SUB 4 900 1140 X1=FNB(X2» 1145 Y1=0\G0SUB 1150 Xl=-50 1160 GO SUB 5000 1170 Y1=FNA(Y2> Y6 7 Y6) CALL r STEP"(Ylf3C CALL "STEP" (~Y1 -70? GOSUB 4950 PRINT "TIC MARKS (Y IF T*-B N"GO TO 14 00 P=l PRINT "X VALUE" »\IN B ( 1 5 ) f R ( 1 ) r C ( 1 ) I) it.' ST BE JES

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-1521375 13 80 1385

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•1530P1.BAS--A subsection of this program dealing with axis labelling and generation is shown here. X AX IB AND NUMBER iXIS CND NUMBER 200 P R INT " X " 5 \ I N P U T X 1 210 PRINT , Y" ?\ INPUT Yl 220 GO SUB 5000 230 RETURN 250 PRINT "CP ACE BE THE CM 255 Y1--U4 260 FOR Pl-1 TO P-l 270 X1=R(P1 ) 230 GOSUB 5000 290 GOSUB 500 300 NEXT P.1 301 GO TO 3:1.0 305 PRINT 'ANOTHER LINE OF X AXIS L, 306 IF V$O"Y"G0 TO 355 310 PRINT "SPACE BETWEEN X AXIS AND 320 Yl=-W4 330 Xl-FND(X??X3.X6?X5)/2 340 GOSUB 5000 350 GOSUB 500 351 GO TO 305 355 PRINT 'SPACE BETWEEN Y 360 Xl=-W4-50 370 FOR Pl-1 TO Q-l 380 Y1=S(P1) 390 GOSUB 5000 4 00 GOSUB 500 410 NEXT PI 411 GO TO 4 20 415 PRINT "ANSI HER LINE OF 416 IF 0$<>"Y"GO TO 490 420 PRINT ' SPACE BETWEEN 430 Xl=-U4-50 440 Yl=PNA(Y2?Y6vY6)/2 450 GOSUB 5000 460 GOSUB 500 4 65 GO TO
PAGE 160

-154551 B4--0 555 conuo 700 560 IF L.1*="V"UG TO 5V0 569 Y1=D 570 Xl-C( 54/2 ) ( C9/2 > * ( LEN < CI * ) -1 > /2 575 GOSUB 5000 580 GO TO 600 590 X1«C 591 Y1~D~< S4/2) •(CB/2) * (LENCCl* ) -1 '> /2 595 GOSUB 5000 600 FOR 09=1 TO I... E N < C ]. 620 GOSUB -4400 650 NEXT 09 640 X1«U1\Y1«W2\GGSUB 5000 650 RETURN 700 P6--1 710 FOR G9==l TO LEN09) 725 P6=l 730 GOSUB 4400 735 P6 = C 740 NEXT 09 760 RETURN

PAGE 161

•1550P1.BAS--A subsection of the program dealing with character generation is shown here. 4400

PAGE 162

-1564432

PAGE 163

157LEDAT.BAS--A program to create a binary vector file for the generation of characters and symbols. 1005

PAGE 164

1582170

PAGE 165

•1592655 DATA 1 , -2y 0» t A t 2 2660 DA I A 6t0rZ'.rA>lrljQrlr2>~At0r 2670 DATA ? t , 1 , 2* 1 r 1 r 1 f 1 t 2 ? y 1 , 1 2675 DATA t -2 t rltO r 3 t r A t -3 2680 DATA 5»0»4r0»lv-2»0»lr0»2yl» 2690 DATA 6 y Or 2 y r 1 y y 3 y y 0* -1 y .1 y 2710 DATA 6f0t2t r Jrl?0t -S > y » 2 » !. » 2720 DATA ? y y 2 y 2 y 1 y 2 y 2 y y y I <1 y 2725 DATA 1 » 2 , -2 r r --1 1 y 1 y » 2 » y 3 Ly2 1 rO l»-2»0*3»0 1 » 1 y » 3 y » y 2 y y y .1. y y y v 1 » r 2 j :> y 7 1 2 t . 2 y

PAGE 166

•160PSTRN.FOR --A program to send sequential data files to r the 11 /2p computer, ........ | LOGICAL* 1 FLi ! A f 1 (20? 10) . '."7.7. •'. 20 ) O JLl U „l U >' 1 1 > .1 :.) TYPE 10 10 rO!vi"ii'»T( ' ENTER FILEi !AiIE • 10 A,' F.'ir-;n r EF; ENTL "* ( ' 'l

PAGE 167

-1611000 COMflilUL L-THP 'i:Vt.:' 20 ZYOP 'EG I LAUADv F< I" C i ; L r T run SI.II'.'ROWT LiJi: t.'L'l AC <[ IAU! -i>? I'll .ir i'.'VI ,',j' I ;:(l| ( ; i.v;: 1 ) c, '•!.!. ilall ( " i. 6 /'WO/ " o> DG iOOrJAA. r A iiXT;-.:o ir-ri:.;;', " iw.\ ; i! (iiXT^o j;:q, i ..:;:;) c.-g i g :: call, ii-okl* " !.>:, 7 ;"'.: :•:? isur GALL ]. F-'GI J:. ( " x ..'7 '70 ? " 1 ) Ir i. A. -Li 2C * L -C. 1 ' i ,.• 70 call i pes 2: ( " 1 6 :-"7 ;•:•? "o; 1G< 1 1 I AAL IPOKIK " 16; EMB

PAGE 168

162REC.BAS--A program to receieve sequential data from the 11/34 computer and store it in a binary data file. 9000 PRINT "TRANSFERRING DEC 11/34 DATA FILES TO DEC 11/20 VIRTUAL DATA 9010 PRINT "FILES (MAXIMUM VALUE 32767MINIMUM VALUE 0>." 9015 PRINT "1023 VALUES MAXIMUM TO BE TRANSFERRED," 9020 PRINT XPK'INT 9030 PRINT "HOW MANY FILES TO RE TRANSFERRED f \INPUT NJ 9050 POR 1=1 TO Nl 9060 PRINT "FILE I ' JIJ* IS'JMNPUT Lt < I ) 9070 PRINT L*(I)»" " ? "ON (Y OR N)N\INPUT Ot 9080 IF 0$='N'GO TO 9060 \NEXT I 9100 FOR 1 = 3, TO Nl 9105 A*«"RL1 : "SL*
PAGE 169

•163OUTPLT.BAS-A proaram to plot X-Y data 1 DI 2 Z2 5 DC-I 20CO 2010 2020 2030 2040 20^;. 2060 2110 212:; 21^:: 2140 2150 2155 2156 2160 2170 2210 2220 2225 2230 n 2 3 p 2240 224 2 2244 2246 2 "^ 4 7 O 9 er g 2260 2270 2275 2295 2300 2305 2310 2315 2320 2325 2330 2340 2350 M B < 1 5 ) = 256 F FNA-B9*1000/4.75 DIM X(256) , Y<256) P R .1 NT ' F I 1 F N A M ! :: : ' > \ I N P U T Z 9 * OPEN Z9$ FUR INPUT AS FILE 5 1 INPUT tl : ZO* > Z9 i X7 » X6 » Y7 , Y6 PRINT Z8* r 7.9 :X7 , X6 » Y 7 » Y6 FOR 1=1 TO Z? INPUT tl :xc I ) , Y< I ) NEXT I CLOSE 41 A$="I"\GOSUB 4000 PRINT *X SPAN IS " JX7--X6 PRINT ' Y SPAN IS " 5 Y7-Y6 PRINT "LOWEST X VALUE " J X6 PRINT LOSES:' Y MAUL:: " ?Y6 PRINT "NORMALIZE X SPAN TO HOW PRINT "NORMALIZE Y SPAN TO HON PRINT "DRAW AXL'S'fMNPUT A9$ IF A??:.:"Y"GO TO 2240 GOSUB 4900 \X1«FNA<1*25*C4)\G0 X1=0\G03UB 4950 \GOSUB 5000 GOSUB 4900 \Y1-"FNA(1.25#D4)\G0 Y1=0\G0SUB 4950 \GOSUB 5000 PRINT 'OFFSET X HOW MANY IN CUE PRINT "OFFSET Y HOW MANY INCHE X1-FNA " "CIRCLE (C)" ° )Rj ANGLE UP (Tl ) " "TRIANGLE DOWN (T2) " "TRIANGLE RIGHT < T3 > " "TRIANGLE LEFT'' ( T"4 ) " •CROSS
PAGE 170

-1642360 GOSUB 5000 2370 GOSUB 4000 2380 NEXT T 2385 CALL ' SI EP " ( -C •> 30 , 1 ) \CALL " STEP u (-D / 30 » ) 2386 C=O\D=0 2390 PRINT "WOULD YOU I.. I K E T I C h A R K S • J \ I N P U T 9 $ 2400 IF V9*<>"Y"GG TO 24 30 2410 PRINT "X VALUE (-999 FOR Y VALUES ) " ? \ INPUT MS 2411 IF M8--999GQ TO 2430 2415 Y1=0\X1= ( MS-X6 ) *FNA < C4 ) / ( X7-X6 ) -! C6 2416 GOSUB 5000 \GOSUB 4900 \Xi=C\Yl--20\G0SUB 5000 2417 GOSUB 4950 \Y1»0\G0SUB 50C0 24 IS GO TO 2410 2430 PRINT «Y VALUE (-999 FOR CONTINUE) ' J \INPUT NO 2431 IF N8=-99960 TO 24 70 2435 X1=0\Y1 = ( NS-Y6 ) *FNA ( B4 ) / ( Y7-Y6 ) +D6 2436 GOSUB 5000 \GOSUB 4900 \Y1=D\X1=-20\60SUB 5000 2437 GOSUB 4950 \XJ.-0\GOSUB 5000 243S GO 10 2430 2470 X1=0\Y1=0\G0SUB 5000 2480 PRIN1 "ANOTHER PLOT (Y OR N)"J\INPL»T A9* 2490 IF A9*--'Y"G0 TO 2010 2500 END This section is followed by the best-line routine

PAGE 171

-165LASPLT.BAS--A program to plot laser intensity in a pseudo-three dimensional manner. 900 DIM B(15) 1000 PRINT 'X SIZE" rMNPUT X5 1005 PRINT "Y SIZE" J \ INPUT Y5 1010 PRINT "Z SIZE" J\ INPUT 2! 5 1015 PRINT "ANGLE" ?\ INPUT A 5 1030 GOSUB 4900 1035 X1=2£X5\G0SUB 5000 1040 X1=0\G0SUB 5000 1045 Y1-2*ZS\60GUE 5000 1050 Y1=0\G0SUD 5000 1055 X1~2*X5 1056 A6~A5*2*3 .141 59/360 1057 Yl=Xi*SIN
PAGE 172

REFERENCES 1. Bleekrode, R., and Niewpoort, J. Chem Phys. 43, 3680 (1965). 2. Bennett, R.G., and Dalby, F.W., J. Chem. Phys. 32, 1716 (1960). 3. Baronavski, A. P., and McDonald, J.R., J. Chem. Phys. 66, 3300 (1977). 4. Mitchell, A.C.G., and Zemansky, M.S., Resonance Radiation and Excited Atoms, Cambridge University Press (1934). 5. Foster, E.W., "Measurement of Oscillator Strengths," Rep. Prog. Phys. 27, 469 (1964). 6. Wiese, W.L., "Transition Probabilities," Methods of Experimental Physics 7A, 117 (1968). 7. Eckbreth, A.C., Bonczyk, P. A., and Verdieck, J.F., Appl . Spect. Rev. 13, 15 (1978). 8. Jessen, P.F., and Gaydon, A.G., Comb, and Flame 11, 11 (1967). 9. Bulewicz, E.M., Padley, P.J., and Smith, R.E., Fourteenth Symposium on Combustion, 329, The Combustion Institute (1973). 10. Bradshaw, J.D., Omenetto, N. , Bower, J.N., and Winefordner, J.D., "Temperature Evaluation in Flames by Means of Laser Excited Atomic Fluorescence Spectroscopy," in preparation. 11. Haraguchi, H. , Weeks, S.J., and Winefordner, J.D., Can. J. Spectros. 22, 61 (1977). 12. Omenetto, N., Hatch, N.N., Fraser, L.M., and Winefordner, J.D., Spectrochim. Acta 28B, 65 (1973). 13. Weeks, S.J., Haraguchi, H. , and Winefordner, J.D., Anal. Chem. 50, 360 (1978). 14. Bolshov, M.A., Zybin, A.V., Zybina, L.A., Koloshnikov, V.G., and Majarov, I. A., Spectrochim. Acta _3Jj3, 493 (1973). 15. Hooymayers, H.P., and Alkemade, C. Th. J., J. Quant. Spectrosc. Radiat. Transfer 6, 847 (1966). •166-

PAGE 173

16716. Hooymayers, H.P., and Nienhuis, G. , J. Quant. Spectrosc. Radait. Transfer 8, 955 (1968). 17. DeGalan, L. , and Winefordner, J.D., J. Quant. Spectrosc. Radiat. Transfer 7, 251 (1967). 18. Zeegers, P.J.Th., Townsend, W.P., and Winefordner, J.D., Spectrochim. Acta 248, 243 (1969). 19. Alkemade, C.Th.J., Snelleman, W. , Boutilier, G.D., Pollard, B.D. Winefordner, J.D., Chester, T.L., and Omenetto, N., Spectrochim. Acta 33B, 383 (1978). 20. Boutilier, G.D., Pollard, B.D., Windfordner, J.D., Chester, T.L., and Omenetto, N., Spectrochim. Acta 33B, 401 (1978). 21. Boutilier, G.D., Bradshaw, J.D., Weeks, S.J., and Winefordner, J.D., Appl. Spectros. 31, 307 (1977). 22. Belyaev, Yu.I., Ivantson, L.M., Karyakin, A.V., Phi, P.H., and Shemet, V.V., J. Anal. Chem. USSR 2_3, 855 (1968). 23. Marinkovic, M. , and Vickers, T.J., Anal. Chem. 42, 1613 (1970). 24. Alkemade, C.Th.J., Hooymayers, H.P., Lijnse, P.L., and Vierbergen, T.J.M.J., Spectrochim. Acta 27B, 149 (1972). 25. Cooley, J.W., and Tukey, J.W., Math. Com. 19, 297 (1965). 26. Cooper, J.W. , The Minicomputer in the Laboratory, WileyInterscience, Inc., New York (1977). 27. Talmi, Y., Crosmun, R., and Larson, N.M., Anal. Chem. 48, 326 (1976). — 28. Hieftje, G.M., and Bystroff, R.I., Spectrochim. Acta 30B, 187 (1975). 29. Bradshaw, J.D., and Winefordner, J.D., "Noise Sources in Flame Spectroscopy," in preparation. 30. Sorokin, P.P., and Lankard, J.R., IBM J. Res. Develop. 10, 162 (1966). — 31. Schafer, F.P., Schmidt, W., and Volze, J. App. Phys. Lett. 9, 306 (1966). 32. Fraser, L.M., and Winefordner, J.D., Anal. Chem. 43, 1693 (1971). — 33. Webb, J. P., Anal. Chem. 44, 30A (1972).

PAGE 174

-16834. Allkins, J.R., Anal. Chem. 47, 752A (1975). 35. Steinfeld, J.I., MIT report, 1975; CRC Crit. Rev. Anal. Chem. 5, 225 (1975). 36. Alkemade, C.Th.J., and Zeegers, P.J.Th., Spectrochemical Methods of Analysis (J.D. Winefordner, Ed.), John Wiley, New York (1972). 37. Winefordner, J.D., Schulman, S.G., and 0' Haver, T.C., "Luminescence Spectrometry in Analytical Chemistry," in Chemical Analysis, Vol. 38 (P.J. Elving, J.D. Winefordner, Eds.), John Wiley, New York (1972). 38. Lijnse, P.L., and Elsenaar, R.J., J. Quant. Spectrosc. Radiat. Transfer _12, 1115 (1972). 39. Browner, R.F., Analyst 99, 617 (1974). 40. West, T.S., Analyst 99, 886 (1974). 41. Winefordner, J.D., Chem. Tech. _5, 123 (1975). 42. Winefordner, J.D., Fitzgerald, J.J., and Omenetto, N., Appl . Spectrosc. 29, 369 (1975). 43. Kirkbright, G.F., and Sargent, M. , Atomic Absorption and Fluorescence Spectroscopy, Academic Press, New York (1974). 44. Sychra, V., Svoboda, V., and Rubeska, I., Atomic Fluorescence Spectroscopy, Van Nostrand Reinhold Co., London (1975). 45. Winefordner, J.D., Ed., "Trace Analysis," Atomic Fluorescence Spectroscopic Methods for Elements (J.D. Winefordner, Ed.), John Wiley, New York (1976). 46. Olivares, D.R., Ph.D. Thesis, Indiana University (1976). 47. Omenetto, N., and Winefordner, J.D., "Atomic Flurescence Spectroscopy with Laser Excitation," Analytical Laser Spectroscopy (N. Omenetto, Ed.), John Wiley, New York (1979). 48. Smith, B.W., Ph.D. Dissertation, University of Florida (1977). 49. Blackburn, M.B., Ph.D. Dissertation, University of Florida (1977). 50. Blackburn, M.B., Mermet, J.M., Boutilier, 6.D., and Winefordner, J.D., App. Op. JL8, 1804 (1979). 51. Mailander, M. , J. App. Phys. 49, 1256 (1978). 52. Bonczyk, P. A., and Shirley, J. A., "Measurement of CH and CN Concentration in Flames by Laser-Induced Saturated Fluorescence," presented at Central States Section of Combustion Institute Meeting, West Lafayette, Indiana, 3-5 April, 1978.

PAGE 175

-16953. Winefordner, J.D., J. Chem. Ed. 55, 72 (1978). 54. Blackman, R.B., and Tukey, J.W., The Measurement of Power Spectra, Dover, New York (1958). 55. Walden, G.L., Bower, J.N., Bolton, D. , and Nikdel , S. , "Noise Power Spectra of the Inductively Coupled Plasma," submitted to Spectrochim. Acta B. 56. Bower, J.N., Bradshaw, J.D., Horvath, J.J., and Winefordner, J.D., "Further Improvements in Detection Limits in Laser Excited Atomic Fluorescence Spectrometry," in preparation. 57. Rodrigo, A.B., and Measures, R.M. , IEEE J. Quantum Electron. QE-9, 972 (1973). 58. Daily, J.W., Appl . Op. V, 225 (1978). 59. Snelleman, W., Ph.D. Thesis, University of Utrecht, 1965. 60. Haraguchi, H., and Winefordner, J., App. Spectrosc. 31, 195 (1977). — 61. Parsons, M.L., Smith, B.W. , and Bentley, G.E., Handbook of Flame Spectroscopy, Plenum Press, New York (1975). 62. Omenetto, N., Bower, J.N., Bradshaw, J.D., Van Dijk, C.A. , and Winefordner, J.D., "A Theoretical and Experimental Approach to Laser Saturation Broadening in Flames," in preparation. 63. Turk, G., National Bureau of Standards, private communication, 9/79. 64. Hollander, Tj., Lijnse, P., Franken, L. , Jansen, B., and Zeegers, P., J. Quant. Spectrosc. Radiat. Transfer _12, 1067 (1972). 65. Hooymayers, H., and Alkemade, C, J. Quant. Spectrosc. Ratiat. Transfer 6, 847 (1966). 66. Molectron Corp., DL Series Dye Laser Operation Manual, Sunnyvale, Cal . (n.d.). 67. Rodrigo, A.B., UTIAS Report No. 180, Institute for Aerospace Studies, University of Toronto (1972). 68. Kuhl, J., Neumann, S., and Kriese, M. , Z. Naturforsch. 28a, 273 (1973). 69. Walden, G.L., Ph.D. Dissertation, University of Florida (1979). 70. Haraguchi, H., Smith, B., Weeks, S., Johnson, D., and Winefordner, J.D., Appl. Spectrosc. 31, 156 (1977).

PAGE 176

BIOGRAPHICAL SKETCH James Neil! Bower was born March 30, 1950, in Ithaca, New York. After graduating from the local excuse for a high school, he attended Cornell University, there learning several important lessons in abnormal psychology. After holding several jobs, including one at Cornell University, he returned to school at U.F., where he learned a good deal about bureaucracy (as well as a good deal about analytical chemistry). •170-

PAGE 177

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. §D QjuJjoAs**^. Dr./J.D. Winefopdner, Chairman Graduate Research Professor of Chemistry I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Y.UL^Jt Dr\i G.M. Schmid Associate Professor of Chemistry I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Hanrahan ssor of Chemistry

PAGE 178

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. & B J. Dorsey Assistant Professor of Chemistry^ I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. / 9+r Dr. P. Urone Professor of Environmental Engineering Sciences This dissertation was submitted to the Graduate Faculty of the Department of Chemistry in the College of Liberal Arts and Sciences and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. December 1979 Dean, Graduate School

PAGE 179

UNIVERSITY OF FLORIDA 3 1262 08553 3809


SATURATED ATOMIC FLUORESCENCE AS A DIAGNOSTIC TOOL
FOR FLAMES AMD PLASMAS
By
JAMES N. BOWER
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR Or PHILOSOPHY
UNIVERSITY OF FLORIDA
1979

This thesis is dedicated
to my wife, Esther,
whose support and love have made the
difference between night and day.

ACKNOWLEDGEMENTS
Help and real human understanding have been available at all
times from my chairman, Dr. Winefordner, for these four years. He
has been a guiding light and a friend.
I would like to thank John Bradshaw for much of my basic under¬
standing of analytical atomic spectroscopy. He has been a tireless
teacher.
Dr. Nicolo Omenetto has been a great help in understanding the
physical processes of laser excitation.
Dr. Winefordner's research group is certainly one of the most
stimulating in the world. Thanks to all members for many discussions
and helpful suggestions.
Thanks are in order for two unnamed souls whose joyless scien¬
tific interactions with me persuaded me to return to school and
remain there.

TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS iii
ABSTRACT vi
CHAPTER
1 INTRODUCTION 1
Quantum Efficiency 1
Total Number Density 3
Noise Power Density 4
Reaction Rates 5
Tunable Dye Lasers 6
2 THEORETICAL CONSIDERATIONS 3
Quantum Efficiency for a Two-Level Atom 8
Quantum Efficiency for a Three-Level Atom 17
Saturation 21
Quantum Efficiency Via the Slope Method 22
Total Number Density 27
Possibility of Absolute Calibration 27
Noise Power Density 29
3 EXPERIMENTAL 32
General Comments 32
Radio Frequency Shielding 36
Photomultiplier 37
Fluorescence Flux Collection 37
Detection Electronics 38
Nitrogen Laser 38
Dye Laser Operation 40
Flame System 42
Solutions 43
Measurement Procedure for Y and ny 43
Noise Power Density 50
4 DATA 54
Notation 54
Strontium 55
Sodium 74
Calcium 77
iv

Mi
Indium 80
Noise Power Density 87
5 RESULTS AND DISCUSSION 100
Quantum Efficiency and Total Number Density 100
Noise Power Density 103
6 CONCLUSIONS AND FUTURE WORK 105
System Temporal Response 105
Complete Saturation 105
Measurement of E^ 106
Photometer Calibration 106
General Considerations 106
Noise Power Density 107
General Comments 108
APPENDIX
1 SUBSIDIARY MEASUREMENTS 10S
2 COMPUTER PROGRAMMING AND PLOTTING 140
REFERENCES 166
BIOGRAPHICAL SKETCH 170
V

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
SATURATED ATOMIC FLUORESCENCE AS A DIAGNOSTIC TOOL
FOR FLAMES AND PLASMAS
By
James N. Sower
December 1979
Chairman: Dr. J.D. Winefordner
Major Department: Chemistry
A new experimental approach to the determination of three flame
diagnostic parameters is developed. The experimental application of
saturated atomic fluorescence to the measurement of quantum efficiency,
total number density, and noise power is discussed. Data for quantum
efficiency and total number density are compared to the scant litera¬
ture values. Four elements and three different flame compositions
are investigated. Preliminary noise power spectra are discussed as
background for the use of saturated atomic fluorescence to measure
noise in the atomization and nebulization processes.
vi

CHAPTER 1
INTRODUCTION
Characterization of physical and chemical parameters of flames
and plasmas has been a goal of chemists (I, 2, 3), physicists (4, 5, 6),
and combustion engineers (7, 8, 9) for many years. The goal of
physicists, physical chemists, and combustion engineers has been to
understand on a quite fundamental basis the processes which go on in
flames and plasmas, i.e., oxidations, reductions, free-radical reac¬
tions, ionizations, etc. In recent years, an even larger impetus has
been seen for this research as sources of economical energy have
dwindled and better combustion understanding and design have become
paramount in importance. Analytical chemists, on the other hand, have
become interested in flames and plasmas because of the extremely
important role of these devices in quantitation of elemental species
in various samples. The coincidental research interests have brought
all together to try and provide a better understanding of basic
processes common to both.
Quantum Efficiency
A quantity of great interest to the analytical chemist and other
scientists is the quantum efficiency, the measure of the relative
yield of fluorescence processes to absorption processes. The quantum
efficiency has a strong influence on tfie performance of normally (low
-1-

-2-
intensity) excited atomic fluorescence spectrometry, which has become
an important flame diagnostic (3, 10, 11) and analytical tool (12, 13,
14) in recent years. In addition, quantum efficiency is an indication
of (rates of) deexcitation processes in flames and plasmas which can
be invaluable for unraveling many basic spectroscopic and fundamental
properties.
The traditional method of measurement for this quantity (Y) has
peen to measure atomic absorption from a continuum source, then to
measure atomic fluorescence with the same source positioned at 90
degrees to the absorption axis. Great pains had tG be taken to ensure
that solid angle effects, flame edge effects, etc. were eliminated
(15, 15). At best, this yielded a spatially urresolved picture of
deexcitation processes (i.e., absorption is a line of sight tech¬
nique). In addition, no hope cculo be held cut for temporal resolu¬
tion. Also, the measurement involved two highly different electronic
gains (those typical of absorption and fluorescence measurements),
which must be calibrated against each other.
The measurement of quantum efficiency via saturated atomic fluor¬
escence, however, allows both spatial and temporal resolution under
the proper conditions. It is inherently easier to measure, as it
involves only one optical train for which the sc7 id angle must oe
found. However, the photomultiplier tube and optical system must
be calibrated via a standard source. Along with the system used for
this investigation (a nitrogen-pumped dye laser) comes the need for
quite sophisticated electronics. Signal processing and cross-checks
for problems become much more involved.

-3-
Total Numper Density
Total number density has been another sought after quantity in
flame and plasma spectroscopy. An important figure of merit in atomic
spectroscopy has been the efficiency by which a particular atomizer is
able to convert solution or solids introduced into it into the form of
neutral atoms. In most cases, this efficiency has been separated into
two oarts:
1. efficiency of nebulization-yield of fog droplets from a
volume of solution introduced,
2. efficiency of atomization-yield of neutral atoms from sub-
microscopic species, i.e., atoms, molecules, ions, etc.
The former quantity is a very tedious one to measure, involving long
periods of aspiration of a relatively high concentration solution of
a suitable element, collection of waste solution and washdown from
the nebulization chamber, and dilution to volume. Then, the concen¬
tration of the analyte in the diluent must be determined. Typically
(for most nebulizers in atomic spectroscopy), this is a low efficiency
process. Therefore, the accuracy is subject to determinate errors in
procedures.
The problem of determination of efficiency of atomization follows
directly on these results, unless a separate procedure is developed.
This is virtually impossible unless a vapor generation technique is
available. The efficiency measurement must be made via determination
of the total number density in the flame. The classical method for
this measurement has been to use absorption from a continuum source
(17, 18), which provides the desired quantity only after a tedious

-4-
calibration procedure, including correction for reflectivity of
multiple surfaces in the optical collection train. An expensive,
high-resolution monochromator is also required, as the atomic absorp¬
tion line is quite narrow. In addition, this method does not allow
spatial or temporal resolution.
Saturation of the pertinent atomic transition provides a fluor¬
escence signal (therefore a spatially resolvable signal in the usual
configuration), that is not a function of flame conditions (except as
a function of atom production capaoility), and is a function only of
basic atomic properties.
Noise Power Density
Noise power density measurements have been used typically by
information transfer and electrical engineers as a means of discovering
the sources of systematic and random noises in hopes of eliminating
then and being able to transmit data with fewer errors at ever in¬
creasing rates. The techniques of noise measurement and theoretical
treatment have been growing in importance for analytical chemists
(19-28), as the science grows in depth and sophistication. The
attempts at measurement to date, however, have been troubled by lack
of definite calibration and lack of willingness to track down and
eliminate sources of instrumental noise in analytical techniques.
The difficulty of this task, while formidable, is not insurmountable
(29). If calibration can become complete, and the sophistication of
analytical chemists can be improved in areas which are now subsidiary
(flow engineering, electrical engineering, etc.^substantial improve¬
ments should be forthcoming.

-5-
Saturated atomic fluorescence stands to provide a substantial
contribution to noise analysis in atomic spectroscopy. Saturation
provides several features:
1. elimination of dependence on quantum efficiency (flame
conditions),
2. spatial resolution,
3. possible loss of dependence upon the atomization step
(if correct analyte is chosen),
4. possible relative freedom from emission background noise
(if conditions are chosen carefully), and
5. freedom from source variation.
Therefore, saturation can further the understanding of noise
sources in atomic analytical spectroscopy. It can provide separation
of noise of nebulization from noise of atomization (if such a noise
exists), allowing better understanding, and design, of nebulization
systems.
Reaction Rates
Since analytical flames and plasmas are used at atmospheric
pressure and are quite hot (2000 K to 6000 K), reactions are myriad
and fast. In most flames and plasmas, some sort of local thermodynamic
equilibrium (LTE) is assumed. In several cases, however, the mechanism
of excitation of atomic species is unclear (e.g., the induction coupled
plasma, which is not in LTE). Engineers and physicists share with
chemists the need to understand these and other phenomena kinetically.
Saturated fluorescence (atomic or molecular) can be a very useful

-6-
tool in this pursuit, as a means of simplifying kinetic schemes by
swamping. Reactions such as photoionization, quenching, and inter¬
system crossing can all be studied by means of saturated fluorescence.
Tunable Dye Lasers
The advent of the tunable dye laser (30, 31) and the power it
gives to observe atomic and molecular populations have given flame and
plasma spectroscopists an invaluable tool for diagnostic procedures.
The general properties of these and other lasers include:
1. directionality (low divergence),
2. monochromaticity,
3. coherence (spatial and temporal), and
4. high irradiance.
All of these laser properties have been useful for analytical
atomic fluorescence soectroscopy since Fraser and Winefordner (32) first
used a dye laser to excite atomic fluorescence. Their work covered
nine elements in hydrogen-air and acetylene-air flames. Limits of
detection obtained were within 10 to 100-fold of those obtained with
conventional sources, and linear dynamic ranges were about four decades.
Progress in both theory and experimental achievements has been rapid
in the ensuing years (12, 33-38). With more and more powerful lasers
available (37, 39-45), the possibility and theory of non-linear
phenomena has been investigated (40-44). Several authors have ex¬
perimentally achieved near or complete saturation of atomic (46-50)
and molecular systems (51, 52).

-7-
Laser saturation of atomic transitions in this work has made
possible diagnostic procedures with spatial, temporal, and flame com¬
position independence. This will allow analytical chemists to measure
the quantum efficiency, total number density, and noise power density
spectrum in an atomizer without the above mentioned problems of linear
spectroscopy. However, the benefits of this freedom must be weighed
against the need for sophisticated measurement systems (fast time
scale) and laser temporal and spatial inhomogeneity effects.

CHAPTER 2
THEORETICAL CONSIDERATIONS
Quantum Efficiency for a Two-Level Atom
A two-level atom is one which, although it may have many quantum
states, has only one excited state available for thermal population in
addition to the ground state. After it has been delivered to the
excited state by absorption of a photon, it can be returned to the
ground state by either of two paths, emission of a photon or colli-
sional deactivation (quenching). Quantum efficiency (Y) is a measure
of the efficiency of the radiative process with respect to the absorp¬
tion process. A schematic diagram of a three-level atom and its
processes is depicted in Figure 1. A two-level atom can be pictured
by ignoring all processes connecting the third level and the other
two levels. A real example of a two-level atom is shown in Figure 2.
Only the 4s level is available for thermal population in analytical
flames (temperature range from about 2000 K to 40C0 K, kT is therefore
0.2 to 0.37 eV).
The basic fluorescence radiance expression (53) is given by:
BF = Y21En2 /\d- (l>
where
1 = path length in direction of detection system, m
4tt = number of steradians in a sphere (fluorescence is
isotropic), sr
-S-

Figure 1. Three level atom model photon and collisional
processes are illustrated. Symbols are explained
below. The lower state is symbolized by "1" and
the upper by "u."
EL Einstein coefficient of induced absorption
lu (m3 j-1 s-1 Hz)
B , Einstein coefficient of induced emission
ul (m3 j-1 s-1 Hz)
A . Einstein coefficient of spontaneous emission
Ul (s-1)
Ev, Spectral irradiance of exciting radiation
(W m"3 Hz'l)
k Rate constant for collisional process con¬
necting state m wiLh state n

-10-

Energy
-11-
1 K0,1,2 Ul,2,3
4p
4d
5s
4p
4p
O
Figure 2. Calcium term diagram levels 1 and 2 are indicated.

-12-
Y,, = fluorescence power (quantum) efficiency, W fluor-
esced/W absorbed
E^,? = spectral irradiance of exciting radiation at absorption
1 line, v12. W m'2 Hz'1 (1 W = 1 Js’1)
I*00
/ k dv = integrated absorption coefficient over absorption
0 line, m-1 Hz
co /
k^dv is the power absorbed from the source by the
analyte atoms per meter cubed of atomic species. The integrated
absorption coefficient is given by:
The product Ef
hv
/ k dv = n, (—r^-)
A v 1 c
12L
3in? -i
ik1"
(2)
where
h\>i2 = energy of the exciting photon, 0
c = speed of light, m s^
B,, = Einstein coefficient of induced absorption, J-^
u s'1 Hz
g,, g2 = statistical weights of states 1 and 2, respectively,
dimension! ess
. _'V
n^, n2 = concentration of states 1 and 2, respectively, in
(note that n^ + = nj, the total concentration of
atoms in all states)
The bracketed quantity corrects for the effective decrease in absorp¬
tion caused by stimulated emission from the upper state.
Using the rate equation approach, and invoking steady state, we
arrive at
(k12 + n}
(k2l + AZ1 + -2-fe) n2
(3)
where

-13-
k.p, k?1 = excitation and deexcitation non-radiational
1 (collision) rate constants, s'*
A22 = Einstein coefficient of spontaneous emission, s'*
Bt, = Einstein coefficient of induced emission, m2 j'1
21 s-1 Hz
B19 = Einstein coefficient of induced absorption, m J'1
u s'1 Hz
.3
n^, np = concentrations of electronic states 1 and 2, m
c = speed of light, ms’*
The quantum efficiency is defined as
21
+ k
21
(4)
and 1S related to B91 and Bl9 by
8irhv
A21 ( 3
c
21
3
12
12
8irhv g„
) B2! ’ l-V1! (57) =12
C J2
(5)
Combining these expressions, one arrives at
BF = ^ Y21Ev12^nl
(411) {?
E*,
12
v12
J12
-)]
(6)
-2 -1
where E*j12 is a modifTed saturation spectral irradiance (W m Hz )
evaluated at frequency and is defined as
cA
E*.
21
vi? BY
.z b21t21
(7)
The term E*v12 can be expressed in terms of the saturation spectral
irradiance ESv12> which is the spectral irradiance required to bring

-14-
about 50% of the maximum fluorescence radiance possible. If E ls
expressed as a function of EV12> then
Es - E* / 91 )
v12 v12 {gx+ g2 1
(8)
Substituting for in terms of (n^ = + n7 and using Eqs. 3,
6, and 8)
BF ~ ^ 4tt^ ^21Ev 12nT c
12» 12
|l +-^-j
L E5 J
t V12
(9)
The maximum fluorescence is then
“'.ax ■ rT (Sl i ,2>
(10)
ílhen Ev 2 = E V12 then B_ = BF /2.
1 r hmax
CA21 _ 8irhv3
Vl2 B21Y21 c2Y21
(11)
. g, 7.6 x 10'23 x '5
E1\12 = (^4"T) ( 7 2-)
u gl g2 r2l
(12)
A theoretical plot of Bp vs. E 2 appears in Figure 3. If a plateau in
fluorescence radiance can be observed as laser power is varied, and the
laser power at 50% of this maximum fluorescence radiance can be found,
then the quantum efficiency can be found from the quantity E5^. Eor
calculations in this v/ork the quantity EsXl2 te usei:i (see Eq.
12).

Figure 3. Theoretical saturation curve.

100
cu
>
10
—
i
log E (relative)
A
1
1
~r
o
10
100

-17-
The necessary conditions for the measurement of quantum efficiency
i n thi s way are
1. Saturation must be completely achieved, so that B_ can
hmax
be evaluated.
2. One must measure Ev^ measuring the following quanti¬
ties :
a. laser peak power (W) ,
2
b. laser cross-sectional area (m ),
c. laser optical bandwidth (Hz).
3. Self-absorption must be negligible.
4. The source must be a spectral continuum with respect to
the absorption line width.
5. A steady-state condition must be achieved.
6. Ho coherence effects can be manifested. The rate equation
approach must be valid.
The achievement or measurement of these conditions is described in
Appendix 1.
Quantum Efficiency for a Three-Level Atom
The same approach (as used for the two-level atom) yields for a
three-level atom like Na (see Figure 4)
_J
k32
ñ + k + V
«23 r21 r k23
^13
(13)
where

Energy
-18-
Pl/2, 1 1/2
D1 1/2, 2 1/2
4p
O
3d
4s
3s
Figure 4. Sodium term diagram levels 1, 2, and 3 are indicated.

-19-
(14)
k = collisional rate constant connecting atoms in the
mn m state with those in the n state
The is again related to Y^, but no simple relationship
exists. The collisional constants, which are unknown in the litera¬
ture, interfere with the interpretation.
For some limiting cases, where level 2 is close to level 3 (e.g.,
sodium, see Figure 4) or is close to level 1 (e.g., indium, see
Figure 5), certain assumptions can be made.
With sodium, for instance, if the assumption is made that
then
k32 3, k32 . g2
A21 + k21 + k23 ” k23 g3
Then
(15)
(16)
v13
This is equivalent to a two-level system, as the top 2 levels have
merged into one, effectively.

Energy
-20-
1/2, 1 1/2
-D
1 1/2, 2 1/2
1/2,
7s
6d
5p
5d
6s
3
2
1
4p
0
2 1/2
Figure 5, Indium term diagram levels 1, 2, and 3 are indicated.

-21-
For a three-level atom like In
E*
v13
The same type of assumption should hold for levels 1 and 2 as
previously for level 2 and 3. Therefore, if
E v13 =
(—) +
.V
A32 * k32 + k21
<91 + ^19 J
then
k21 >:> k32 + A32
and
21
k21 + k12 . , k12 . , g2 gl + g2
k21 9Í
c 9i + 9p
Fs = ( 1 *- ^ r*
v13 + g2 + g3; 11 v13
(17)
This is again equivalent to a two-level system.
Saturation
Complete saturation means that the population of the excited
state and the ground state are equalized (with due regard to the re¬
spective degeneracies). Therefore, the kinetic drains on the excited
state are negligible with respect to the optical pumping rate. A
further increase in irradiance cannot effect an increase in fluorescence
radiance.
A measurement of this (saturated) state usually means that when
the irradiance is reduced, via some suitable filter, the fluorescence

-22-
signal does not decrease. By placing calibrated filters in the beam,
one can determine the point at which only half of the signal is left;
this point is the saturation spectral irradiance.
Quantum Efficiency Via the Slope Method
Two-Level System
From the two-level theory, it can be shown that
J_ = 4rr
BF E'j12 g2 6.6 x 103 Y01A3
21A21hv211A21nT
g, + g7
4tt i
hvl21A21nT
(18)
A plot of the theoretical shape of 1/Bp vs. 1/E^ is shown in Figure 6.
The pertinent features are the slope and the intercept. The slope
of this plot contains the quantum efficiency (and ru), and the inter¬
cept contains ny.
For this procedure, all of the above mentioned criteria must be
met with the exception of completeness of saturation. The closer
saturation can be achieved, however, the less extrapolation is
necessary. In addition, the fluorescence collection depth, 1, must
be measured, and the collection photometer calibrated.
If both sides of Eq. 18 are multiplied by the quantity
n.j.hv12lA21
4u
then the 1/Bp axis can be scaled absolutely, as the intercept is

Figure 6. Theoretical 1/lip vs. 1/t curves. Curves shown are
for two different quantum efficiencies (Y) and two
different total number dens i ties (nj).

1/8,. (relative)
1/E (relative)
-24-

-25-
equal to the quantity
91 + g2
92
which is well known.
Three-Level Case
Sodium. A rearrangement of the three-level fluorescence expres¬
sion yields
1
1+3
1+3
7T 1 + ('
( } L
Asíais1 nT
£l_ ^8Trhc^
93 y \3 F
_ k32 , + ^1
A21 + k21 + k23 g3
(19)
When this is rearranged, we have
.2
A31hv131rY 1
4tt
B
= (•
g^uhc
E
1 91 + g3
+■ —i +
32
Fl+3 93Y31X13 ^X13 3
1+3
A + k + k
*21 k21 k23
(20)
A plot of these quantities cannot be scaled absolutely because the
intercept includes unknown collisional rate constants. The same
speculation as before can still be made, however, regarding the rate
constants, allowing calibration to be made in certain limiting cases.
That is, k£3 can be expected to be much larger than either or ^1 ■
The term
32
A + k + V
*2i r k21 k23

-26-
then reduces to
By the law of mass action at equilibrium
k32 = ül = H
^23 n2 93
The fluorescence slope method equation reduces to
J = (_$2E ) i_
BFK3 A31hv131 nT
1+3
92 + 91
93
8-whc2 j
Y31X13EX -
Rearranged this equation resembles that for two levels
2
A31^1 v13^ 9i®lr^lc
4-irBp y i5 F
rl+3- 93,31A13tx
1+3
92 + 91
93
Indium. For an atom of the indium type, where the second ex¬
cited state is very close to the ground state,the slope method equa¬
tion is
,nT1A31hv13v 1
k 4-n- 1 Bf
*1+3
1+3
(^)(1 +^exp[-E2 /kT])(-j
93 91
8irhc
31EX
+
91 + 93
93
+ ^ exp[-E21/kT] +
A 4- V
M32 *32
k21
(21)
In this case k21 can be assumed to be much larger than A32 + k32,
and this term then is negligible.

-27-
Total Number Density
Two-Level Absolute Plateau Method
A measurement of Br
max
max
(L^hv12A2lnT^g1 + ^
produces nT easily if the measurement of Bp
hmax
l) and if 1, A0^, and the g's are known.
is absolute (see Appendix
Two-Level-Slope Method
The calibration of the 1/Bp axis is direct for total number density
if g^, g.?, h, Bp, and A^ are known, as the intercept of the
1/Bp axis is
i_ = 4tt 91 + g2
B- lhv17A, nT g.
Three-Level Case--Absclute Plateau Method
Unless assumptions or experiments are made for the relative size
of the collisions! constants, calibration is impossible. Relative
measurements are still valid, and saturation still assures immunity
to quantum efficiency affects as in the two-level case.
Three-Level Case—Slope Method
Once again assumptions must be made for ccllisional constants in
order to permit calibration of Bp in terms of n-j..
Possibility or Absolute Calibration
If the ratio of resonance to anti-stokes fluorescence is taken,
in saturation, we have

-28-
1-3.
max
1 + ^ exp[E21/kT] +
93
A31 + k31
k12
rl+3;
2+3'
max
1 + y + y exp[-E21/kT] +
A32 * k32
k21
(22)
Both ratios
and
A31 + k31
k21
A32 + k32
fA31 + k3ll
pll
k12
k21
g2_
exp[E12/kT]
are probably not much greater than one, as is expected to be at
least comparable to either numerator. Then, if » kT, two con¬
ditions are satisfied
1.
£l £l A31 + k31
93 92 k21
9o ^00
2. cxpt-E^/kT-} « á¿
32
21
Equation 22 then reduces to
'^max 1 + + «PCEgi/fcT:
1+3
1+3,
2+3
max
1 +
*1 j A32 + k32~
93
'21
(23)
If a flame of known temperature can be produced, then the ratio
(A22+k22)/k2i can be evaluated. This allows Y (and n-j.) to be obtained
in absolute units. For a flame with a temperature of 2300 K and

-29-
thallium as a probe (E^ = 0.966 eV),the exponential term is as
follows:
exp[+0.966/2300 x 0.861 x 10'4] = 131
For thallium
Si
= 1
s2
= 3
S3 = 1
Then
l+3,
2-^-3
max
2 +
A32 + k32
k21
135
1+3
1+3
max
The difference between the ratio and 2/135 = 0.0148 is the contribu¬
tion of A32 + ^32^^21" Thls value’ when inserted into Eq. 21 (for
measurement of thallium, in this case), would allow the intercept of
the
4nB p
1+3
axis to be completely calibrated, as the intercept then contains only
known quantities. If Bp is known absolutely (calibrated), then n^ can
also be arrived at unambiguously.
Noise Power Density
The theory and practical measurement of power spectra (power vs.
frequency data) have been adequately covered by Blackman and Tukey (54).

-30-
Two approaches are possible to measure noise power spectra. The first
is to compute the autocovariance function for the data collected. The
Fourier transform of this is the power spectrum. The second procedure
is to compute the Fourier transform of the data, then to square and
add the frequency and phase components to find the power spectrum.
Although both methods were available, the second one was chosen for
its conceptual familiarity. The use of a discrete data collection
system (analog to digital converter) required a discrete Fourier
transform, with attendant aliasing and bandwidth problems.
The application of saturated atomic fluorescence will result in
an ability to separate the noises resulting from the nebulization pro¬
cess from those stemming from the atomization of the analyte. Since
these two sources of noise are independent, their noise power spectra
add linearly. Since the measure being computed in our case is the
noise current spectrum, these would add quadratically. If an analyte
such as copper, which is completely atomized in a standard flame, is
measured, the noise power under known conditions can be found.
This noise power should be reproducible in nature with the ex¬
ception of certain non-stationary noise sources. If this proves to be
the case then the total noise and the 1/f noise pertinent to most
spectroscopic measurements can be investigated with respect to design
elements and operating characteristics common to atomic spectroscopy.
These include burner, chamber, torch, and nebulizer design, as well as
gas flows and flame stoichiometry. Noises involved in the flame or
plasma processes up to the point of atomization could then be sub¬
tracted from the noises seen for an incompletely atomized analyte,
producing the noise inherent in the atomization process.

-31-
The unfortunate truth, however, is that many of the underlying
noise sources in analytical spectroscopy are non-stationary.
Examples of non-stationary noises are nebulizer clogging, RF noise,
60 Hz mains noise, some source drift noises, stray light noise (room
and daylight), and some electronic drift noise. These are not really
approachable via the technique or theory of noise power spectra, though
often a reasonable idea of the noises can be found (55),

CHAPTER 3
EXPERIMENTAL
General Comments
A variety of experimental systems were used for collection of data
pertinent to these measurements. The basic system shown in Figure 7
is the laser excited atomic fluorescence system described by Weeks
et al. (13). The system has been modified slightly, as reported by
Bower et al. (56) and Bradshaw et al. (10). Several of the features
changed since the measurements of Weeks et al. are of high importance.
The spatial effects of saturation in the wings of focussed Gaussian
laser beams, as observed by Blackburn et al. (50), and previously
predicted by Rodrigo (57) and theoretically approached by Daily (58)
have been eliminated by moving the observation point approximately 10
feet further from the laser. At this point, the spatially homogeneous
section of the laser beam was enveloping the whole seeded flame (see
Appendix 1).
In order to facilitate alignment, it was necessary to add folding
mirrors (M) with adjustments in the horizontal and vertical planes.
A problem involving dye changes leading to a different angle of
emergence has been circumvented by the use of the folding mirrors
and the combined aperture-scatter shields (ASS). The two apertures
initially were set to define the beam line of interaction of the dye
laser and the flame. When subsequent dye changes produced non-col inear
-32-

Figure 7. Laser excited atomic fluorescence system. System
components are as follows: LPS = laser power supply,
NPL = nitrogen pump laser, DL = dye laser, M = folding
mirrors, TG = trigger generator, B = boxcar, SCR =
strip chart recorder, ASS = aperture-scatter shield,
LT = light trap, BU = burner, L = lenses, HO = mono¬
chromator, PMT = photomultiplier tube, PS = high
voltage power supply. For source of major equipment
see Table 1.

DL
NPL
LPS
PS
SCR
-34-

-35-
Table 1
Laser Excited Atomic Fluorescence Equipment List
Item
Model UV-14 Nitrogen Laser
Model DL-300 Tunable Dye Laser
Model FL-2000 Tunable Dye Laser
Nebulizer chamber
Capillary burner
Flame-shielded burner
Model H-10 monochromator
Model 4128 High Voltage
Power Supply
Model R106 Photomultiplier
Tube
Model 160 boxcar
Model 162 boxcar mainframe
Model 163 boxcar plug-in
module
Model 164 boxcar plug-in
module
Type S-2 sampling heat
Servoriter strip chart recorder
Apertures (iris diaphragms)
Manufacturer
Molectron Corp., Sunnyvale, Cal.
Molectron Corp., Sunnyvale, Cal.
Lambda Physik, Gottingen, W. Ger.
Perkin-Elmer Corp., Norwalk, Conn,
laboratory built
laboratory built
Jobin-Vvon, % ISA, Metuchen, N.J.
John Fluke, Seattle, Wash.
Hamamatsu Corp., Middlesex, N.J.
Princeton Applied Research,
Princeton, N.J.
Princeton Applied Research,
Princeton, N.J.
Princeton Applied Research,
Princetcn, N.J.
Princeton Applied Research,
Princeton, N.J.
Tektronix, Portland, Oregon
Texas Instruments, Dallas, Texas
Edmund Scientific, Barrington, N.J.

-36-
beams, these could be adjusted with the mirrors to pass through the
apertures.
The collection system was aligned at a 90 degree angle to the in¬
coming beam by the use of helium-neon alignment laser crossed with the
dye laser beam.
Radio Frequency Shielding
Radio Frequency (RF) shielding of the entire Molectron nitrogen
pump laser enabled the output to be freed of the large drift-type noise
associated with people and objects moving in proximity to the experi¬
mental system. This involved enclosing the whole pump laser and power
supply in a brass screen Faraday case. All electronics were connected
via grounding straps to a salt-bed earth ground. All cables leading
from the photomultiplier to the detection electronics were double-
shielded by a coaxial woven shield augmenting the internal shield.
These modifications enabled RF noise-free measurements into the milli¬
volt level, which corresponded (with a 50 n 2-fold attenuator) to
40 uA of peak current. This was possible even with a background
current of 100 yA. For most measurements, the limiting noise was the
electronic noise of the boxcar averager.

-37-
Photomultiplier
The photomultiplier was wired for fast pulse, high current
output, as reported by Fraser and Winefordner (32) and operated at
-1000 V. Cable of 50 n impedance (RG-58U) was used for all
connections.
Fluorescence Flux Collection
A Jobin-Yvon H-10 low dispersion monochromator was used
for collection of fluorescence. Dispersion is low and collection
efficiency high, as suggested by Weeks et al. (13). A two lense
collection system with an intervening aperture was used to help
cut down on scatter for resonance collection cases. Scatter in
these cases was reduced by liberal use of light traps (LT), aper¬
ture scatter-shields (ASS), and black felt cloth. In many cases,
this scatter signal was Rayleigh scatter (indicated by an increase
when the flame was turned off), and could not be completely elimi¬
nated. In such cases, the noise limit for measurements was due to
laser carried (peak to peak variation) scatter noise. The image
formed by the two lenses at the slit of the monochromator was of
unit magnification.

-38-
Detection Electronics
A PAR 162 boxcar averager was used for detection and measurement
of fast fluorescence pulses. Two different inserts (plug-ins) were
used in measurement and alignment. The 164 plug-in offered fixed
sensitivity (100 mV full scale) and several integration times. It was
quite hardy, and was used for preliminary alignment, when a very large
scatter signal was used to set the gate delay. The 50 a input im¬
pedance was always used to match the cable and minimize ringing.
Some ringing was still apparent, however. The 163 plug-in with an S-2
sampling head was used for the main measurement scheme. The gate was
75 ps (S.-2 sampling head); jitter in the boxcar gating circuits led to
some distortion of this aperture. This head was used to find plateau
(saturation) values on top of the fluorescence temporal pulses, which
corresponded to saturation of the atomic fluorescence.
The synchronous trigger of the laser could not be used, as RF
feedback occurred at the time of each trigger and interfered with data
collection. A separate trigger generator was used, which had a delayed
pulse feature. This enabled correct timing between laser firing and
boxcar gating.
Nitrogen Laser
The nitrogen pump laser was run according to manufacturer’sin¬
structions. The high-voltage power supply was kept at 22 kV to give
better longevity of the critical components (thyratron and capacitor),
as these had been problematical in the past. The nitrogen flow rate
was 15 liters per minute for all experiments. Operating pressure was

-39-
main tai ned at 55 torr. The pressure transducer had to be replaced
and calibrated twice, however. This involved approximately half a
day to a day's work, since the entire pump head had to be removed from
the Faraday cage. All connections had to be made again outside the
cage in order to test fire and calibrate the unit.
The repetition rate was kept at about 15-20 Hz for all experi¬
ments. Greater repetition rates led to lower peak powers. High peak
oower was necessary for saturation. However, a rate below ca. 20 Hz
would ’ead to signal leakage problems on the boxcar mainframe.
An interesting phenomenon was observed at the 20 Hz repetition
rate. A beat frequency appeared cn the dye laser output. This was
first attributed to the power supply of the laser, as its voltage
dipped when the laser was fired. This idea was discarded when it was
noticed that the beat frequency was about 2 Hz. The observation was
made that as the dye fluoresced in the cuvette on each nitrogen laser
pulse, the magnetic stirrer appeared to be precessing at about 2 Hz.
The motor provided was an AC motor running at a multiple of 60 Hz.
The stirring of the dye cell seemed to be incomplete enough that when
che nitrogen pulse came at a sub-multiple of the stirring rate, a
beat frequency due to excitation of spent dye appeared. A need for
improvement in stirring was quite apparent. This beat frequency
effect had never appeared in the literature.
Voltage drifts during the day were so bad (1 V on regulated
supplies, 10 V on unregulated lines) that severe trigger drift became
apparent. The nitrogen pump laser was very susceptible to trigger
drifts through its high voltage threshold performance. A voltage
change of 1 V cn the 120 VAC line can induce a 20 ns drift in the

-40-
trigger to firing delay. Using a 164 plug-in on the boxcar, this was
annoying. When a 163 plug-in is used the signal can entirely dis¬
appear inside of 5 min time. Therefore, all of the experiments had
to be done at night when stability was much better, but still trouble¬
some, however. Generally during each series of measurements the
trigger had to be reset at least once.
An optical trigger was used for subsequent experiments. The
163 plug-in, however, was not used. Indications were that this
arrangement was much more stable with respect to jitter, especially
if triggered from the pump laser. Use of the optical trigger necessi¬
tated placing a delay line (V155Z050, Allen Avionics, Mineóla, NY)
into the signal line from the photomultiplier to produce a 75 ns delay
necessary to compensate for the internal gate delay of the boxcar.
A 50 Q attenuator was placed before the delay line to produce a
voltage pulse from the current pulse. Indications were that distor¬
tion and noise introduction by the delay line were minimal.
Dye Laser Operation
The dye laser was also operated according to manufacturers in¬
structions. Dyes were prepared according to Table 2. Adjustments of
the dye cell carriage were made after each new dye cell was introduced
into the beam line. This should not have been necessary if the laser
was functioning correctly. There was some indication that this was
an artifact due to the state of our dye cells. Possibly the anti-
reflective coating had worn off in several years of use (see Appen¬
dix 1).

-41-
Table 2
Laser Dye Preparation
Dye
Concentration
(M)
Solvent
Wavelength
Range (nm)
(10% points)*
DPS
Saturated
1.2 x 10-3
p-dioxane
396-416
Bis-MSB
1.2 x 10"3
p-dioxane
411-430
7D4MC
10-2
ethanol
440-478
R6G
5 x 10'3
ethanol
568-605
*The 10% points are the wavelengths at which laser output is 10%
of the peak output.

-42-
Dye was changed frequently to avoid power loss due to dye deteri¬
oration. This was done in one of two ways. The method of exchange
recommended by the manufacturer was to remove the dye via a pi pet,
rinse the cell with fresh dye, and refill with fresh dye. This was
moderately successful. Some dyes (7D4MC in particular) seemed to
function better when the dye cell was removed entirely from the dye
head, rinsed thoroughly with alcohol, then fresh dye, and then re¬
filled with fresh dye. Peak power with 7D4MC exchanged in this manner
was enhanced at least 2-fold over the more cursory method of exchange.
Bubbling of pure nitrogen for two minutes through the dyes (as sug¬
gested by Exciton) did not seem to make a substantial change in dye
longevity. Perhaps nitrogen saturation during preparation and storage
would have helped more.
Flame System
A gas-flow stabilization system consisting of individual pressure
gauges and rotameters was used for each gas flow. The entire system
was calibrated by means of a linear mass flow meter (ALK-50K, Hastings,
Hampton, Virginia). Each time a flow was measured, the pressure was
readjusted, and the flow and rotameter readings recorded. The com¬
bination of a fixed pressure and the rotameter readings led to a very
reproducible and precise system. Premixing of flame gases was done
to avoid background noise due to poor mixing in the chamber of the
burner. The flows passed into the appropriate ports of a nebulizer-
flow chamber (Perkin-Elmer Corporation, Norwalk, Conn.). The same
composition (premixed) passed into a separated shielding flame for

-43-
hydrogen-based flames. The fog and premixed combustion gases left
the flow chamber and passed into a capillary, flame-shielded burner
for hydrogen based flames (previously described by Snelleman (59)).
There they were combusted. The flame-shielded flame was surrounded
by an inert gas sheath to avoid background DC emission and noise as
much as possible.
Acetylene based flames were combusted above a capillary burner (Haragu-
chi and Winefordner (60)) supported on the same nebulizer chamber.
Flows for the different flames used are shown in Table 3.
Solutions
Stock solutions of 1000 yg/ml for all elements were made from
reagent grade chemicals in deionized water per Parsons et al. (61)
(see Table 4).
Measurement Procedure for Y and n^.
The necessary criteria for evaluation of quantum efficiency and
total number density via the two different schemes are
1. Saturation must be complete (for plateau method) or nearly
complete (for the slope method); that is, an increase in laser
power must not result in an increase in fluorescence
radiance.
2. One must measure laser spectral irradiance via measurement
of the following quantities:
a. laser optical bandwidth--via some type of wavelength
scan,

-44-
Table 3
Flame Gas Flow Rates
Air-Acetylene Flame
Air 9.88 1 /min
Acetylene 1.65 1/min
Hydroqen-Oxygen-Inert Gas Flame
Hydrogen 1.62 1/min
Oxygen 0.81 1/min
Nitrogen or Argon 4.51 1/min

-45-
Table 4
Source of Reagents
Sodium NaCl
Mallinckrodt Chemical Works,
St. Louis, Mo.
Calcium CaCOj
Mallinckrodt Chemical Works,
St. Louis, Mo.
Strontium SrCO^
Fisher Scientific,
Fair Lawn, N.J.
Indium IngOj
Apache Chemicals, Seward, 111.

-46-
fa. laser peak power--via calibrated photosensitive device,
c. laser cross-sectional area—via geometrical considera¬
tions; fa and c measurements may be combined.
3. Self-absorption must be negligible. (This is automatically
achieved if saturation is complete, as the absorption coef¬
ficient then goes to zero.)
4. The source must be a (pseudo-)continuum across the line-
width of absorption; i.e., the wavelength spread of the laser
must be measured and determined not to vary substantially
across the absorption linewidth.
5. Steady state fluorescence must be achieved. The temporal
behavior of the atomic fluorescence pulse must be observed.
Measurement of the saturated value must be during a suitable
steady state.
6. The rate equation approach must be valid. No coherence
effects may be seen.
7. The fluorescence depth 1 must be found (Figure 8).
In addition, if the possibility of absolute values of Y and n-¡-
is to be evaluated for a three-level atom, the ratio of resonance to
stokes fluorescence must be found in a flame with a known temperature.
Since the proof of validity of these .criteria is somewhat
tedious, it will be assigned to Appendix 1, with the exception of the
first point, completeness of saturation, because this is the basis
of the whole measurement scheme.
For each dye change, alignment of the laser beam with the burner
head was undertaken. Side to side position of the laser was checked
with the flame off, by the use of the aperture-scatter shields and a

Figure 8
Fluorescence illumination and collection schematic.

card over the burner. Vertical positioning was accomplished by using
the card to project an image of the laser beam through the first col¬
lection lens onto the slit-shaped aperture. After spatial alignment
was completed, the gate delay was peaked up on a scatter signal.
Next, the flame was lit, and analyte was introduced. The dye laser
was wavelength scanned, using the scan control until a substantial
signal was found. Since saturated atoms show a broadened response
to wavelength (see Appendix 1), a calibrated neutral density filter
was set in an accessory optics holder in the laser beam. In this way,
a linear response to laser illumination was ensured. Neutral density
filters of about 2.0 to 3.0 were generally required. When illumina¬
tion was in the linear region, the dye laser output could be easily
centered on the wavelength of the atomic transition. When the
neutral density filter was removed, the atoms were saturated.
Generally analyte concentration was chosen to yield a high enough
signal so that a linear portion of the laser fluorescence vs. power
plot could be reached as the laser power was decreased. In some
cases, this involved using a higher concentration at low laser power
to ensure sufficient signal to noise ratio. Linearity of fluorescence
with respect to concentration was always checked when this was done.
The upper limit of concentration was set to avoid problems of vapor¬
ization (especially prevalent in the low temperature hydrogen-based
flames used here) and self-absorption. No absorption was noticed,
however, with solutions up to 1000 yg/ml in concentration, although
the measurement of absorption was complicated by severe shot to shot
peak power variations on the dye laser. In most cases, concentra¬
tions were in the 1 to 20 ug/ml range.

-4S-
The procedure for measurements started with a check for PMT
linearity. Even with the use of a low resistance (high current)
dynode chain and capacitor charge storage for each dynode, the PMT
output current could become non-linear with respect to illumination
when the light levels became high enough. Each time data were taken,
a 0.3 neutral aensity filter was inserted in front of the mono¬
chromator. If the signal did not decrease by 50%, a lower concen¬
tration was aspirated, and checked for linearity. Approximately half
of the full scale (1 V) was usable for the 163-S-2 plug-in combina¬
tion. This corresponded (with a 50 Q 2-fold attenuator) to a 10 mA
peak current. This compared with a limit of 0.3 mA peak current limit
of Olivares (46), for a 220 kn resistor chain with no added capaci¬
tance, for a 1P28 PMT. A linear dynamic range of 30-fold higher
(based on current) was obtained in our case.
After the linearity check, the actual saturation curve measure¬
ment was performed. This consisted of measuring full scale fluorescence,
blank scatter, and several reduced fluorescence and scatter values
when calibrated neutral density filters were placed in the laser beam
singly or in combination. Scatter corrections for resonance measure¬
ments were generally significant until the laser intensity was re¬
duced 1 to 2 orders of magnitude by neutral density filters.
These fluorescence measurements were converted to absolute
radiance values following calibration of the optical collection
system, the boxcar, and the recorder used to collect data (see
Appendix 1).
From the absolute radiance measurements, values were computed
for quantum efficiency and total number density. In some cases rela¬
tive data only were computed for different flames.

-bü-
Noise Power Density
The measurement of noise power density spectra in academic analy¬
tical chemistry is generally accomplished via the discrete fast
Fourier transform (DFFT). This approach is necessitated by the lack
of continuous measurement power spectrum analysis instrumentation in
most laboratories. The dedicated instrumentation required by this
method is generally too inflexible to be affordable under tight
budgeting restrictions of this time. On the other hand, the general
availability of digital computers and analog to digital data collec¬
tion systems makes discrete (or sampled) data collection fit reason¬
ably within the price and flexibility range of most laboratories.
This leaves one with only the DFFT approach to noise power spectra
evaluation possible. This enforced choice leads to a loss of flexi¬
bility in one way, and to a gain in another direction. The disadvan¬
tages of discretely sampled records for approximating a power spectrum
are very well covered in Blackman and Tukey (54) and include aliasing
(necessitating very well designed filters for spectra with wide dynamic
ranges and wide frequency ranges), intennodulation distortion, and
finite bandwidth.
The flexibility advantages are those which stem from the com¬
puter itself:
1. ease of collection,
2. ease of calibration,
3. fast data reduction,
4. ease of presentation,
5. flexibility of handling of data and power spectra.

-51-
The primary purpose of noise power spectra collection in this work
was to establish a background for later possible saturated noise power
spectra, which should show the advantages enumerated in the Introduc¬
tion section.
The primary sources of noise for atomic spectroscopy consist of
the following:
1. Source related noise
a. white,
b. whistle or proportional,
c. flicker or 1/f.
2. Background noise-non-source related
a. white,
b. whistle or proportional,
c. fl icker or 1/f.
3. Sample related noise
a. white,
b. whistle or proportional,
c. flicker or 1/f.
The preliminary experiments presented here measured the latter two
types of noises. The first type will be the subject of later experi¬
ments.
Background noise can be somewhat artificially separated into two
types. The first type is related to the bulk properties of the flame
gases; this type could be exemplified by the emission from the Cg
molecule, a product of partially completed combustion. This molecule
has a major emission at 516.5 nm called the Swan band. While it does
not interfere with most atomic transitions, other bands can interfere

-52-
with DC and fluorescence measurements with pulsed sources . The
Swan band is sensitive and can be used as an indicator of formation of C,,,
and therefore as an indicator of combustion completeness. This
molecule has been used as a measure of success for premixing com¬
bustion gases (29). Noise power spectra collected under fixed con¬
ditions also provide a useful figure of merit for the evaluation of
success of mixing.
A second type of background emission noise source is one which is
more indicative of external conditions. An example is the OH molecule,
which is strongly indicative of the success of sheathing a flame.
The pertinent (and sensitive) band is centered on 306 nm, and extends
to the red far enough to interfere severely with copper and silver
measurements while a companion band at 285 nm interferes with
lead and magnesium measurements. Noise power spectra at this band
can hopefully lead to better design and construction for flame
sheathing systems.
Sample related noise can be evaluated as a preliminary to satura¬
tion measurements by using atomic emission. In order to collect data
on both nebulization and atomization noises without source noises
interfering, it is necessary to measure the noise involved in atomic
emission, unless saturated measurements lead to an improvement in
signal to noise ratio. An atom must be chosen which has strong emis¬
sion, and is not near a background spectral region which would
interfere. Strontium is a likely candidate. Its emission is in a
relatively background-free region, and should therefore yield infor¬
mation on nebulization and atomization efficiency noise. Strontium
is quite sensitive to flame temperature, and therefore composition.

-53-
It should be a good candidate for the proposed separation of information
from the two sources of noise. In addition, it is among the most
strongly saturated atoms found in this work. The general scheme of
investigation is as follows. The nebulization chambers and nebulizers
of three companies are to be investigated within the guidelines
established above. Conditions to be varied are use of an inert gas
sheath, premix chamber, and removal of the nebulizer. In addition,
data collection will be made in three frequency ranges (0-50 Hz,
0-500 Hz, 0-10,000 Hz).

CHAPTER 4
DATA
Notation
A general notation system is developed here for the reporting of
the experimental results in this chapter. Ratios will be listed as "R,"
with addition of one or more of the following subscripts for clarifica¬
tion of the meaning:
HON Hydrogen-oxygen-nitrogen
HOA Hydrogen-oxygen-argon
S Slope method of calculating a quantum efficiency or ratio
of quantum efficiencies
E EÍ? method of calculating a quantum efficiency or ratio of
quantum efficiencies
B Be method of calculating a total number density or ratio
o-rtotal number densities
I Intercept method of calculating a total number density or
ratio of total number densities
A Measurements made in the argon diluted hydrogen based flame
N Measurements made in the nitrogen diluted hydrogen based
fl ame
Y Quantum efficiency
n-j. Total number density
References to the use of these methods can be found in Chapter 2
(Theoretical Considerations). Ratios "R" will always refer to argon
diluted flame values over nitrogen diluted flame values.
-54-

Strontium
Boxcar Survey
The need to use the most versatile and least complicated equipment
possible was recognized at the commencement of this work. One of the
goals of the work was to find the optimal instrumentation for flame
diagnostic measurement via saturated atomic fluorescence, choosing from
the available choices in this laboratory. A series of measurements were
made under set conditions for the comparison of three boxcar averager
measurement systems. The first pair of measurements (Figure 9 ) shows
saturation curves under identical illumination conditions for the
Princeton Applied Research (PAR) 160 boxcar and the PAR 162 mainframe
with the 164 plug-in. The two curves are very nearly identical, though
the scatter on this data was fairly great. (A substandard burner system
was used for these two preliminary curves. It was replaced after these
two experiments with the system described in the text.) The gates on
both boxcars were the same (15 ns). The 10 ps stretch feature of the
160 boxcar did not seem to affect the extent of saturation. The second
pair of measurements (Figure 10) shows a comparison of the 160 boxcar
with the 162 mainframe using a 163 plug-in and a S-2 sampling head (75 ps
aperture). In addition to the boxcar change, a change of dye was per¬
formed. As expected, the extent of saturation improved. The shorter
gate "viewed" mainly the temporal plateau section of the fluorescence
pulse (see Appendix 1), while the longer gate averaged substantially
unsaturated portions of the pulse with the saturated portion. The higher
power output of the new dye probably accounted for some portion of the
behavior.

Figure 9. Strontium saturation curves using the PAR 162-164 boxcar
(x) and the PAR 160 boxcar (D). Actual Bp values were
different. Plotted values were ratioed to highest signal
observed for each boxcar. X = X = 460.7 nm.
ex em

log E (relative)
log Bp (relative)
Â¥-1 ro
-¿s-

Figure 10.
Strontium saturation curves using the PAR 162-163 boxcar
(x) and the PAR 160 boxcar (â–¡). Actual Bp values were
different for each boxcar. Each plotted value was ratioed
to the largest value observed for that boxcar.
X = X = 460.7 nm.
em ex

2
cu
>
4->
X
X
â–¡
X
-2
r
-i
X
X o
X â–¡
â–¡
â–¡
I
en
to
log (relative)
r
i
-i
2

-60-
Based on the results of these measurements the rest of the measure¬
ments were made with the 162 mainframe 163 plug-in combination to achieve
an accurate representation of the saturation condition.
Flame vs. Inductively Coupled Plasma (ICP)
An acetylene-air flame and an ICP were compared to determine whether
saturation resulted in information about quantum efficiency. Two
parameters were evaluated under equal illumination in the flame and ICP,
namely the saturation curve and the saturation broadening (Appendix 1)
for strontium. The half-power points of for the saturation curve (re-
A
lated to E^, see Chapter 2) is inversely proportional to the quantum
efficiency of a flame or plasma. For a given element and excitation
line, here strontium at 460.7 nm, the ICP was expected to have a higher
quantum efficiency than the flame. This was due to the prevailing argon
atmosphere of the ICP, as opposed to the predominantly molecular atmo¬
sphere of the flame. The saturation curves (Figure 11) indicated that
the quantum efficiency of strontium in the ICP was slightlyhigher than in the
flame. A second measure of the quantum efficiency of strontium in the
flame or plasma was the saturation broadened excitation profile (Appen¬
dix 1 and Reference (62))- A broader profile indicates a higher quantum
efficiency, as shown by:
p(*,) 1/2
5Aexc = 6XL U + T7fT)
p (v
where
6A = full width at half maximum (FWHM) of the excitation profile
of the atom (nm)
5A. = FWHM of the Lorentziari (undisturbed) profile of the atom
L (nm)

Figure 11. Strontium saturation curves in the air-acetylene flame (â–¡)
and the induction coupled plasma (ICP) (x). The ICP had a
slightly lower E? than the flame, and therefore, a slightly
higher quantum efficiency. The log-log scale of this
figure reduces the visualization of this small change.

tí
tí
tí
cá
â–¡
â–¡
n
1 1 1— 1— 1
-3-2-1 0 1 2
log E (relative)
A

-63-
o
p(X¿) = power density of the laser (W/m-)
s 2
p (x^) = saturation power density (W/m }
The term pS(x,j) is inversely proportional to the quantum efficiency (see
Chapter 2). Therefore, the á5lexc depends upon quantum efficiency.
Saturation broadened SX are given below for strontium in the flame
and in the ICP under identical power density conditions.
Atom Cell <5Xexc (full power)
flame 0.66
ICP 1.13
The increase in SXgxc in the ICP also bears out the expected increase in
quantum efficiency in the argon atmosphere.
Hydrogen Based Flames
Hydrogen based, rather than hydrocarbon based, flames were chosen
for the major investigation of saturation because of the expected im¬
provement in saturation due to a much less complex and reactive small
molecule (quenching) mixture in the flame gas. Two inert gas diluents
were investigated to find the role they play in quantum efficiency in
flames. Nitrogen was chosen for its obvious place in any air oxidant
flame. Nitrogen is a good diatomic quencher. It is often replaced for
atomic fluorescence purposes by a monatomic species, argon, which is a
very poor excited state quencher. Therefore, it allows a higher quantum
efficiency. This yields a higher sensitivity in application of atomic
fluorescence to analysis.
Saturation curves for the two diluent gases are shown in Figure 12.
The two curves are very close in plateau values and in shape. This was
an indication that the change in flame gas had very little effect in

Figure 12.
Strontium saturation curves in two hydrogen based flames.
The flames were diluted with argon (x) and nitrogen (â–¡).
While the plotted values were ratioed to the individual maxi
mum values, the relative magnitude between the curves was
retained. The value of Ex for the data plotted here was
measured using a round (1 cm diameter) aperture.
A = A = 460.7 nm.
ex em

log Bp (relative)
ro
J
â–¡ X
â–¡ X
XI
xn
-S9-

-66-
either the atomization of strontium or the quenching of excited state
strontium atoms. Relative information was derived for Y and n^. from
this plot. Relative saturation powers (proportional to E?) were found
from the points at which the fluorescence was 50% of the maximum. The
saturation powers are proportional to 1/Y (see Chapter 2). In addition,
the slopes of the 1/Bp vs. 1/E^ curves were taken as measures of 1/Y also.
The values for Ryj and R^ were computed, and are shown below.
RYS 1,2
RYE 1'1
The plateaus of fluorescence were used as relative measures of n^
(see Chapter 2). The intercept values of the 1/Bp vs. 1/E^ curves were
used also as relative measures of nT. The values for R.1T and R,l0 are
T NI NB
shown below.
R
NI
RNB
0.91
0.87
The agreement of the two methods for finding relative Y's and n^'s
for the two flames was quite good. The percent relative error for the
Y measurement was 9%. The percent relative error for n_ was less than
c.°r
■J/O •
The errors in the ratios are probably random in nature. The percent
relative standard deviation for these measurements was about 5-10%.
Absolute Y's were measured by means of the E? method using equation
A
12 from Chapter 2 under the conditions of Figure 12, and additionally
under the conditions of Figure 13 using the flame-shielded flame and
the small slit mentioned in Appendix 1 placed in front of the photodiode.
The results are shown below. Both flame stoichiometries were the
same.

Figure 13.
Strontium saturation curve for the argon diluted flame.
The values plotted were ratioed to the highest value
observed. The values were measured using the slit
shaped aperture mentioned in Appendix 1.
ex
= X = 460.7 nm.
em

o
no
log B
X
x
x
c
m
n>
cu
r-o —
P (relative)
►—J
i
X
X
X
X
X
X
-89-
XXX X

Fluorescence Intensity
-by-
time -*•
Figure 14. Composite boxcar scan of fluorescence pulse of
strontium. The gate was halted at several delay
times (DT) to record the saturation curves seen
in Figure 15. X = X = 460.7 nm.
a ex em

-70-
Strontium Y^^in capillary burner 0.50
Strontium Y21,in flame-shielded flame 0.24
As the results indicate, careful attention must oe placed on select¬
ing a correct and representative aperture. The capillary burner, with
no flame shield, certainly had an edge effect, producing a substantially
poorer quantum efficiency. This was entirely masked, however, by the
inadequacy of the measurement of the E? caused by using an aperture
larger than the laser beam. As can be seen in equation 12, the quantum
c
efficiency is inversely proportional to E^, and therefore directly pro¬
portional to the measured laser beam cross-sectional area. The approxi¬
mately 2-fold increase of quantum efficiency corresponded in this case
to the same decrease in the estimate of E^.
Total number density was figured from the slope of the 1/Bp vs.
1/E curve after calibration of the intercept, and then the slope, under
A
12
the conditions of Figure 13. This procedure resulted in rup = 1.3 x 10
_3
cm , a very reasonable n^ for 100 ppm Sr in a hydrogen based flame. A
second value, derived from equation 10, yielded a value of n^ = 3.1 x 10^
_3
cm . This value agreed very well with the prior value. The small
discrepancy could have been due to calibration of the boxcar plug-in
module or the photometer. The boxcar module had been under repair prior
to these experiments, but had not been calibrated. Unfortunately tne
equipment required for a check of this value was not available.
A temporal scan of the fluorescence pulse from the photomultiplier
produced an interesting observation for strontium. Several overlapping
scans were taken to define the composite temporal shape shown in
Figure 14- The delay time for the boxcar was set at 4 different points
on the peak, and 4 sets of saturation measurements were taken. These

-71-
data are shown in Figure 15. As expected, the leading edge of the pulse
was not saturated. Surprisingly, however, the trailing edge of the pulse
was saturated. Normally, assuming two levels available for laser and
thermal processes, a decrease in signal could not be observed while the
system was saturated. This meant that a third, presumably photon-
induced, process was necessary to explain the phenomenon. Two possi¬
bilities existed for the explanation of these data, compound formation
and laser-induced ionization. Compound formation was rejected as a cause
of this effect, as a two body collision would be necessary. Presumably
the only suitable species available in this flame for compound formation
would be oxygen atoms or hydroxyl molecules. Even with favorable orien¬
tation of the collisions, they probably could not happen fast enough to
account for the subnanosecond phenomena which were seen here. A more
probable explanation was the absorption of a second photon of wavelength
460.7 nm, which could bring the atom within 0.3 eV of its ionization
potential. A thermal event, not so selective as a compound forming
collision, could then easily ionize the atom. Unfortunately, an experi¬
ment to measure electron current generated via laser-induced ionization
with the aid of the nitrogen pumped dye laser was unsuccessful (63).
In private communication with the investigator it was found that poor
results were attributed to laser pulse width considerations. (While
the instantaneous power produced ions, the time spread on the electron
bunch produced only a small signal. The best type of laser for this
experiment has been found to be one with a longer pulse width and
highpower, i.e., high pulse energy.)

Figure 15. Strontium saturation curves collected at several
delay times (DT). The plotted values do not contain
relative magnitude data, which can be inferred from
Figure 14. The plotted values are for DTI (x),
DT2 (P), DT3 (a), and DT4 (+). Note the substan¬
tially less saturated data from the leading edge
data (x). x = X = 460.7 nm.
ex em

2
A
tb
A $
ffl
X
X
a
x
log E (relative)
A
-1
r
o
r
l
co
“1
2

-74-
Sodium
Measurement of sodium parameters was hampered by an experimental
inconsistency. In all other measurements, the monochromator bandwidth
was narrow enough to exclude any other radiating wavelengths from the
saturated atoms. For sodium, however, both resonance lines fell within
the monochromator bandpass. Estimation of the n_ values from Bp and
rmax
continuum absorption required inclusion of both sodium resonance lines
in the theoretical treatment. The nT value for sodium was arrived at
via two different routes. A value was calculated from the saturation
plateau for the argon diluted flame by the use of equation 10 from
Chapter 2. In addition, a continuum absorption experiment was used to
give an independent measure of Op as described by DeGalan and Winefordner
(17). The lack of a suitable bandwidth monochromator (aa Sj 5 x $A . )
mono atom
in a suitable position necessitated substitution of an argon ion pumped
dye laser as a continuum source for this technique. The dye laser out¬
put bandwidth was measured by the use of a high-dispersion monochromator
(used in the second order). The optical bandwidth was 0.174 ran. As
the sodium atomic absorption linewidth was only ca. 0.005 nm (61), this
laser was considered a continuum source. The monochromator bandwidth
described in (17) was taken as the laser bandwidth. Measurements of a
(fraction absorbed) were made in both the argon and nitrogen diluted
flames. In addition, saturation curves were taken in both flames
(Figure 16). The n^'s calculated from both methods are shown below.
Method
Value (1 ppm)
continuum absorption
3.6 x 1010 cm"3
bf
max
11 -3
2.9 x 1011 cm J

Figure 16. Sodium saturation curves for hydrogen based flames.
Relative magnitude for the argon diluted (x) and the
nitrogen diluted (â–¡) flames has been preserved. The
value of Ex used for calculations has been measured
using the slit shaped aperture mentioned in Appendix 1
A = 589.0, X = includes both 589.0 nm and 589.6 nm
ex em

log E (relative)
log Bp (relative)
o *—*
-9L-

-77-
The agreement between these values was considered quite good in
light of the fact that the methods are independent, and several calibra¬
tions of different types are involved. Calibrations of absolute optical
radiances are considered to be quite difficult and error prone. An
agreement of 2-fold is considered state of the art for inexperienced
laboratories.
The value for was determined, and augmented by an R^ derived
from the continuum measurements. However, in the case of sodium in the
nitrogen diluted flame, the saturation was incomplete. Therefore, the
R^g value could not be calculated. Ratio values (R^) are given below.
The values were corrected for differing aspiration rates for the two
flames.
Method Value
R.,|, continuum absorption 0.89
Rn, intercepts 0.84
The agreement is quite good.
Since the ratios calculated by these two methods did agree so well,
the intercept ratio was used to calculate the saturation plateau value
for the nitrogen diluted flame. This enabled evaluation of the E?
parameter, which was otherwise unavailable. This allowed a second
means of determining Ry. The values are shown below.
rys
5.3
rYE
14.0
Calcium
In Figure 17, saturation curves for calcium in HOA and HON flames
are given. The Ry values for the two flames via two methods are given
below.

Figure 17. Calcium saturation curves in hydrogen based flames.
Relative magnitude for the argon diluted (x) and the
nitrogen diluted (â–¡) values has been preserved. The
value of used for calculations was measured using
the round (1 cm diameter) aperture. X = X = 422.7 nm.
' ex em

log E (relative)
log Bp (relative)
o »—1 ro
Í I I
â–¡ X
â–¡ X
â–¡ X
â–¡ X
â–¡X
â–¡ X
S3
XI
-6 L-

-80-
rys
1.81
rye
1.83
A Y value was calculated from equation 12
for the HOA flame, and is
shown below.
^HOAE
0.52
An n-j. value calculated from equation
10 is shown below.
nTH0AB
2.6 x 1011 cm-3
Values of R.. derived from the two methods are shown below.
N
rni
0.81
rnb
0.83
Indium
Indium was marginally saturated in the stoichiometric air-acetylene
flame (Figure 18), which is a highly quenching flame with respect to the
HOA flame.
In contrast with this flame Figure 19 shows the saturation curve in
the HOA flame. The much lower pcwer and much more complete saturation
shown in the resonance (A = A = 410 ran) measurement in this figure
ex em 3
indicated a much higher quantum efficiency. In addition, the observation
of a32 (451 nm) fluorescence followed the expected behavior in showing
the same saturation shape as observation. The 2+3 transition
(451 nm) could also be marginally saturated, as seen in the same figure.
The measurement of power for these curves, however, was not reliable
enough to provide anything but the relative data given above.
A more reliable power measurement was made for the data shown in
Figure 20. The values for Y and n-j- in the HOA flame given below were
arrived at by the calibration of the 1/Bp vs. 1/E^ curve.

Figure 18. Indium saturation curve for an air-acetylene
flame. X = X = 410 nm.
ex em

-82-

Figure 19. Indium saturation curves in the argon diluted hydrogen
flame. Aex = Xem = 410 nm (+), Aex = Xem = 451 nm (â–¡),
Xex = 410 nm - Xem = 451 nin (x). The plotted data do not
retain relative magnitudes of the three curves.

2-
>
&
â–¡
+
X â–¡
m,
CD
en
log E (relative)
A
T
0
T
1
* * é i n
O O
i
Co
4^
n
2

Figure 20. Indium saturation curve in two hydrogen based flames.
Relative magnitude of values for the argon diluted (x)
and nitrogen diluted (â–¡) flames has been retained.

log E (relative)
log Bp (relative)
-98-

-87-
' HOA
"THOA
Ú.28
2.0 x 1010 cm'3 (1 yg/ml)
An Ry value was available only from the slope method. The plateaus of
the two flames were not developed enough to find values.
A
YS
1.03
An R^ value was only available from the intercept method, and is shown
below.
R,
NI
1.05
Noise Power Density
Noise power density (W/Hz ) measurements preliminary to satura¬
tion noise power density were made under the conditions shown in Figures
21-26. Since the measurement of saturation noise power density will
only be possible in the lower frequency ranges (up to about 50 Hz, due
to repetition rate limitations on pulsed lasers), the low frequency
range (0-50 Hz) data collected were chosen for these figures. The
higher collection rate (higher frequency spread) data had no interesting
features except for harmonics of 60 Hz, and a band of discrete fre¬
quencies (centered on 6 kHz) introduced through the electronics power
supply.

Figure 21. Noise power spectrum of the OH region. Slit
width = 500 pm; X = 306 nm, no premixing of com¬
bustion gases, viewing height = 2 cm above capil¬
laries, Perkin-Elmer nebulizer and chamber, acqui¬
sition rate 100 Hz, low pass filter 3 dB point-30
Hz, DC current = 0.57 pA, no sheath, stoichiometric
air-acetylene flame.

Frequency (Hz)
RMS Current/Bandwidth172
A x 107/(0.049 Hz)1/2
o o o
o ro
-68-

Figure 22. Noise power spectrum of the OH region with sheath,
DC current = 0.8 x 10“® A, all other conditions
same as Figure 21.

RMS Current/Bandwidth^2
A x 1010/(0.049 Hz)1/2
o o o o o
-Tfi-

Figure 23. Noise power spectrum of the C2 region. X = 516.5 nm,
slit width = 250 pm, DC current = 0.38 x 10'° A, no
sheath, other conditions as Figure 21, the zeroeth
harmonic has been dropped (to expand the scale).

Frequency (Hz)
RMS Current/Bandwidth1^2
A x 10^/(0.049 Hz)1/2
-£6-

Figure 24. Noise power spectrum of the C2 region. With sheath,
DC current = 0.31 x 10"? A, slit width = 500 um,
other conditions as Figure 23.

RMS Current/Bandwidth

Figure 25. Noise power spectrum of the strontium emission.
X = 460.7, slit width = 250 pm, DC photocurrent
0.38 x 10_6 A, 20 ug/ml Sr, no sheath, zeroeth
harmonic dropped (to expand scale), other condi¬
tions same as Figure 21.

Frequency (Hz)
RMS Current/Bandwidth1/2
A x 10^/(0.049 Hz)1/2
p © o O O
o »-• ro u>
-Z6-

Figure 26. Noise power spectrum of strontium emission. Slit
width = 250 urn, DC current = 0.84 x 10"' A, with
sheath, other conditions same as Figure 25.

RMS Current/Bandwidth
«3*
O
X
c
25
Frequency (Hz)
50

CHAPTER 5
RESULTS AND DISCUSSION
Quantum Efficiency and Total Number Density
Quantum efficiency, Y, and total number density, n^, values are
notably lacking from the literature, though they are of great interest
to analytical chemists, physicists, and engineers. The reason for this
lack of literature support is the tedium of this type of measurement,
as mentioned in Chapter 1. Nevertheless, several items are available
for comparisons in flames of the type investigated here.
The quantum efficiency (or yield factor) has been previously esti¬
mated in flames very similar to the HOA and HON flames used here (64). A value
for Y for Sr in an HOA flame very close in proportions to the one in
this work was 0.16, as compared to 0.24 in this work. In addition, the
ratio of this Y to a Y evaluated in a HON flame (gas proportions some¬
what different from this work) was 2.3, as compared with 1.2 from this
work. The agreement here is very good, considering that the initial
use of laser excited saturated atomic fluorescence for these measurements
was in this work. The HOA flame Y values are remarkably similar. The
difference in the ratio values can be explained by the increased pro¬
portion of the strong quencher nitrogen in the flame used in Reference
(64).
Another source of literature data of this type is the work by
Hooymayers and Alkemade (65). Data on sodium quantum efficiency in HO
-IOC-

-101-
type flames were measured by these authors. When values for V were taken
for the two flames with gas ratios closest to those in this work, the
Ry value was 8.2. The Ry values found via two different methods in
this work were RyS = 5.3 and RyE = 14. The numerical average of these
is 9.5, which is quite close to the published value. The ratio derived
from for the two flames, 14, is based on an indirect calculation of
nTH0N from nTH0A’ as tiie P^ateau condition was not reached in the HON
flame. Therefore, the Ry^ is somewhat suspect. The RyS, 5.3, is some¬
what more substantial, and does not differ significantly from the value
in Reference (65). As the quantum efficiency is a strong function of
gas composition (even with the same diluent gas), the difference between
the slope data ratio and the published data was quite reasonable.
The absolute value of the published (65) forNa is 0.32. The value
arrived at from in the present work is 0.03. If the estimation of
power were in error for any reason, this would be reflected in the Y
value found by this method.
The quantum efficiency for calcium in the HOA flame from the pre¬
sent work, 0.52, seemed quite reasonable, in light of the quantum
efficiency seen for strontium, which should behave similarly in the
flame. No literature data were available for direct comparison,
however.
The quantum efficiency for indium was of the same order of magni¬
tude as strontium and calcium, and therefore seemed reasonable. Again,
no direct literature comparison could be made.
The Ry values seemed to be rather lower, in general, than expected.
Nitrogen was expected to be a much better quencher than argon. In addi¬
tion, the concentrations of the two diluent gases were predominant in the

-102-
flames, leading to the presumption that they would dominate the quenching
rate. In the sodium case, however, the Ry value was several times
higher, more in line with expectations. The literature available per¬
tains to sodium (64) and strontium (65). Quenching cross-sections
(a, l£) in HO type flames are given below for both atoms in Table 5.
Table 5
Quenching Cross-Sections for Sodium and Strontium
in Hydrogen Flames
Quencher
Sr l6V
0 (A)2
h2
40
21
°2
62
400
h2o
1
67
Ar
2.3
< 1
The sodium case (high Ry) seemed to fit the expectation that a
large quenching change could be expected from a change of the major
diluent (a£r/<^ = 17). The other main constituent of the burnt gases,
water, had a low a (1 Á2), and, therefore, did not affect the quenching
significantly.
In the strontium case (Ry 2 1); the a ratio is still high. Water,
however, has a larger cross-section (ca. 3-fold higher) for strontium
than nitrogen. Therefore, the influence of the change of diluent gas
will be much less than in the case of sodium. In addition, the cross-
section of oxygen was 20-fold higher than that of nitrogen. Since very
small changes in the oxidant to fuel ratio around the stoichiometric

-103-
mixture used here can grossly affect oxygen concentration, this could
greatly affect the trend caused by nitrogen.
The Rn values for this work were all quite close to 1, indicating a
very small role for nitrogen in the atomization process. It would be
expected that a large change in the flame gas composition from a
monatomic constituent (argon) to a diatomic diluent (nitrogen) should
make a gross difference in the atomization process, through thermal
equilibration. Apparently this does not happen in these flames, how¬
ever. Here again, no comparative data were available in the literature
for the two diluent gases.
Noise Power Density
A very preliminary evaluation of the results of the noise power
experiments is given below in Table 6. Experimental conditions for the
data are found in Figures 21-26. Changes in different types of noise are
indicated by arrows pointing in the direction of change.
Table 6
Noise Changes Induced by Adding an Inert Gas Sheath
Wavelength Region
Noise Types
1/f
White
Proportional
OH (306 nm)
t
l
i
C2 (516.5 nm)
—
t
f
Sr (460.7 nm)
—
t
t

-1U4-
The OH region, as was expected, exhibited a lower white noise com¬
ponent when an inert gas sheath was added. The inert sheath minimized
entrainment of O2 at the edge of the flame, producing less OH. This, in
turn, caused the white noise (shot noise) component to decrease. In¬
creased turbulence caused the 1/f noise and also the proportional noise
to increase. Proportional (or whistle) noise was nonexistent in any
case until the sheath was added. It appeared in all cases when the
sheath was added.
The region was enhanced by addition of the sheath, since a richer
atmosphere favored production. The white noise therefore increased.
The low frequency (1/f) noise remained the same, since turbulence at
the flame edge did not grossly affect production.
Strontium 1/f noise remained the same with addition of the sheath.
The lack of a change in 1/f noise could have been due to a cancellation
of two effects. The overall strontium signal was 3-fold lower when the
sheath was on. This could have resulted in lower 1/f noise, which would
have been cancelled by an increase due to increased turbulence.

CHAPTER 6
CONCLUSIONS AND FURTHER WORK
The use of a nitrogen-pumped dye laser was investigated for the
measurement of flame diagnostic parameters. The assurance that all the
conditions necessary for these measurements were fulfilled was a very
time-consuming and tedious project. The following points were especially
critical in development of the method.
System Temporal Response
The establishment of atomic fluorescence pulse widths via reliable
means (streak camera) enabled us to choose the correct measurement
system (75 ps aperture) from the choices available. The existence of a
steady state temporal plateau, while certain to occur somewhere within
the pulse, had to be long enough to measure without averaging unsaturated
portions of the pulse. The photomultiplier rise time had to be fast
enough to follow the pulse without distorting its shape unduly.
Complete Saturation
Complete saturation was desirable for several reasons. It eliminated
concern over the necessity for spatial homogeneity in illumination of the
flame volume under investigation. Complete saturation also provided
Bp and a way to find Ef for easy calculation of nT and Y. These values
hmax A T
-105-

-106-
(Br and E^) also provided confirmatory data for ratios of n_ and Y
max
in the different flames.
Measurement of Ex
Laser power, bandwidth, and area also had to be evaluated very
carefully in order to provide realistic absolute data for Y. The latter
two quantities do not affect ratios of Y, of course. As seen in the
strontium section of Chapter 5, an improper evaluation of E can easily
cause a 3-fold change in absolute Y estimation. Laser spectral band¬
width had to be evaluated in order to satisfy the requirement for a
spectral continuum for illumination, also.
Photometer Calibration
The photometer had to be calibrated in order to find B
absolute way, to get ny.
max
in an
General Considerations
Careful corrections had to be made for laser scatter into the
monochromator at high irradiances. Typically,scatter from the laser
contributed significantly to the observed signal until laser irradiance
was reduced by about 2 orders of magnitude.
The data evaluated, after these parameters were controlled, were
reasonable and generally in agreement with literature values of tiy and
Y available.
A complication arose when the discovery of a further photoinduced
process came about. Photoionization and thermally assisted photoinduced

-107-
ionization were discussed as possible explanations for these data. Two
photons of the same wavelength (460.7 nm) were enough to bring strontium
close to ionization (0.3 eV from the ionization potential). For indium
two photons (410 nm) were enough to exceed the ionization potential.
Further work by another student found recombination ion lines upon
scanning the emission monochromator while illuminating indium with the
laser. The current theory does not include the processes of ionization
or recombination. At laser powers of the order necessary for saturation
of some elements these effects may have to be considered in the future.
The possibility exists, with the advent of the excimer laser, that
peak powers can be had at visible and ultraviolet wavelengths to com¬
pletely ionize atoms in a reasonable volume in a flame. If this power,
and the longer pulse widths of this type of laser, can completely and
selectively ionize a given atomic population, good sensitivity and a
certain immunity to kinetic (recombination) factors should result. This
type of saturation should readily avail itself of theoretical calibra¬
tion via geometric collection efficiency factors.
A second possibility for measurement of Py in three-level atoms is
to use two dye lasers to saturate both transitions and to thereby
equalize populations (according to their degeneracies). This would
allow measurement with no assumptions about kinetic quenching constants.
Noise Power Density
Since only preliminary noise power spectra have been measured so
far, much work remains. The expected reduction in noise during satura¬
tion has yet to be observed. Further characterization remains to be

-108-
done on the temporal behavior of the different atoms under laser excita¬
tion. It is hoped that the application of saturation to noise power
spectra measurement will allow real progress to come about in the critical
areas of nebulization and burner design.
General Comments
Saturated atomic fluorescence has been developed and critically
evaluated as a tool for flame diagnostic measurements. It promises to
be more straightforward and less tedious than other methods of arriving
at values for Y and n-p Hopefully saturated atomic fluorescence will
enable the evaluation of noises basic to design features in atomic
analytical instrumentation.
Spatial and temporal information obtainable through the means of
saturated atomic fluorescence are available by no other means.

APPENDIX 1
SUBSIDIARY MEASUREMENTS
Since the measurement system used in these studies was to be used
for the measurement of fast signals, it was necessary to characterize
its response on a very short (ns) time scale. The temporal response
of the system was investigated in several ways, using several auxiliary
systems to the one mentioned previously. The points which needed to
be investigated were
1. PMT pulse response,
2. laser pulse width,
3. atomic fluorescence pulse width.
Photomultiplier Pulse Response
The response of the photomultiplier tube and base combination
was measured by the use of a small laboratory-built nitrogen-pumped
dye laser. The laser pulse duration had previously been measured at
about 600 ps. This pulse was directed through the same collection
system used for the saturation measurements. For all practical pur¬
poses, this represented an impulse of light to the photomultiplier
tube. The pulse time response of the PMT was then measured by
scanning a 75 ps gate across the output pulse. The result, shown
in Figure 27, was a pulse response width of 2.9 ns.
-109-

-110-
3 ns
H
Figure 27. Boxcar temporal scan of photomultiplier pulse
response. Laser input pulse width was ca. 600 ps.
Photomultiplier response width was 2.9 ns.

-111-
Laser Pulse Width
The temporal features of the laser output were checked in two
independent ways. The output of a calibrated vacuum photodiode
(risetime i 500 ps) was scanned using the 75 ps gate (Figure 28). The
data collected in this manner were checked against the manufacturers
calibration via the use of a borrowed joulemeter. The joulemeter
response indicating pulse energy could be reconciled with peak power
measurements, made via connection of the output of the photodiode
through a 50 n load to a fast oscilloscope (Type 454, Tektronix,
Portland, OR). The pulse energy and peak power could be related if a
pulse shape and pulse width were found. Pulse width from the photo-
diode-boxcar measurements did not agree with the manufacturer's
calibration data, using the peak energy found with the joulemeter.
However, using a variety of other sources, pulsed and continuous
wave, the diode calibration was upheld. Therefore, a need to further
investigate the laser temporal distribution was expressed, as the laser
pulse width and time response of the PMT to the fluorescence caused by
the pulse needed to be understood thoroughly.
Manufacturer's literature (66) and several publications featuring
the use of this laser list the duration of the dye laser pulse width
as 4-5 ns. The joulemeter data indicated times ranging from 3DC ps
to approximately 2 ns as pulse widths for different dyes. As these
were considered somewhat nonsensical for this laser system, it was
decided to use a very fast response system for time dependence of the
dye laser pulses. A Hamamatsu streak camera (Temporal Dispersor,
Hamamatsu, Middlesex, NJ) was used in conjunction with a microprocessor

-112-
Figure 28. Boxcar temporal scan of photodiode pulse response.
Laser input pulse width was ca. 600 ps. Photodiode
response width was 2.2 ns.

li>
based data collection and display system (Temporal Analyzer, Hamamatsu, Mid¬
dlesex,'NJ). This system could trigger the laser and the streak camera
with the use of suitable delay lines and trigger generators to ensure
overlap of the camera firing and the laser pulse. The laser was
directed through suitable neutral density filters (to avoid damage to
the very sensitive streak tube) and into a monochromator via two
front surface mirrors. The exit slit of the monochromator was focused
by streak camera optics on the streak camera entrance slit. Several
streaks were observed to find the general temporal shape for the given
dye. As these experiments were done during the daytime, severe
triggering jitter existed. Only 10® or so of the streaks collected
were usable. Several representative streaks were collected. Each of
these was recorded via a digital to analog converter and a strip chart
recorder (Model SRG, Sargent-Welch, Cleveland, OH). The results
for several dyes are shown in Figures 29-32. The results indicated
that the dye laser system used here was either producing much shorter
and more temporally complicated pulses than expected, or a serious
systematic error was being committed. Therefore, the temporal output
of a second dye laser (DL2000, Lambda-Physik, Interactive Radiation,
Northvale, NJ), an oscillator-amplifier configuration, was also in¬
vestigated. This laser was expected to give a temporal pulse width
in the same 4-5 ns range. The streak results are shown in Figure 33.
This result was as expected, and the other results were therefore
trusted. The calibration of the photodiode via the joulemeter could
then be reconciled with the manufacturer's calibration.*
*Note: Further data collected since experimental work for this disser¬
tation was finished indicate that variations ir. pulse width and jitter
of the laser depend strongly on repetition rate and gas flow velocity.

-114-
Figure 29. Streak of Molectron dye laser scatter (7D4MC),
1.5 ns per inch.

-115-
Figure 30. Streak of Molectrondye laser scatter (DPS), 1.5 ns
per inch.

-116-
Figure 31. Streak of Molectron dye laser scatter (R6G) , 1.5 ns
per inch.

-117-
Figure 32. Streak of Molectron dye laser scatter (bis-MSB),
1.5 ns per inch.

-110-
Completeness of Saturation
The completeness of saturation was shown for the several atomic
species chosen by the plateau region in the plot of fluorescence
radiance vs. laser irradiance (Figures 9-20). In addition, this
provided proof that the precautions against spatial laser beam in-
homogeneity were working.
Laser Power Measurement
Laser power (peak power) was measured by the use of the above-
mentioned vacuum photodiode. This was placed in front of the laser
with a large enough calibrated neutral density filter to provide a
signal still linear with respect to the power (typically 4.0 neutral
density). The output was connected through a 50 a attenuator, and the
peak voltage was read on the oscilloscope. The laser power could be
arrived at after consultation of the manufacturer's calibration table.
Laser Bandwidth
The laser bandwidth calibration was approached in two separate
ways. When the first bandwidth data were taken, a suitable mono¬
chromator (high resolution) was not accessible for direct measurement
of the bandwidth of the laser output. Inasmuch as saturation of an
atomic transition can give a larger fluorescence excitation bandwidth
than the naturally occurring bandwidth, an experiment was undertaken
to find the excitation bandwidth of the laser. After a transition
was found, a wavelength scan of the laser output was made. The

-119-
Figure 33. Streak of Lambda-Physik dye laser scatter (704MC),
8.7 ns per inch.

-120-
fluorescence, collected by the same low-resolution monochromator was
that of the integrated emission bandwidth. A suitable theory was
developed in Omenetto et al. (62) to understand this manifestation of
saturation broadening in terms of the laser wavelength spread and laser
power density. The low power limit of the excitation band¬
width vs. laser power, phenomena turns out to be the laser bandwidth,
as might be surmised. Plots of excitation bandwidth low and high
power limits are shown for the dyes used in this study (Figures 34-37).
In order to confirm the low power limits as a source of laser
bandwidths, a suitable monochromator (HR1000, Jobin-Yvon, Instruments
SA, Inc., Metuchen, NJ) was used. Resolution (bandwidth) of the mono¬
chromator was found by wavelength scanning a mercury line from a low
pressure pen lamp source in the second order. This resulted in a
0.12 Á bandwidth for the monochromator. The dye laser outputs for
the pertinent atomic transitions were scanned directly (with suitable
neutral density filters). These scans were done with the use of the
scanning attachment for the Molectron dye laser, as this was easier
than monochromator scanning. The bandwidth results for both measure¬
ments are shown in Table 7.* In several years of use the anti-
reflective coating of the dye laser cells had apparently been
destroyed. This allowed the development of a second laser cavity,
coupled to the front surface of the dye cell, which resonated at a
different wavelength, and with a different temporal position. This
*Note: An anomalous side-lobe structure is seen in the results of both
monochromator scan and saturation broadening bandwidth for the dye
7D4MC. This structure is probably related to the anomalous second
pulse seen in some temporal scans of this dye.

-121-
Figure 34. Excitation broadening of strontium. Relative atomic
fluorescence (vertical axis) vs. wavelength (horizontal
axis), obtained by scanning the dye laser wavelength past
the atomic wavelength (460.7 nm), while continuously
recording the atomic fluorescence signal (7D4MC dye).
a. low power limit--represents laser bandwidth.
b. high power 1 inrit--represents broadened
sensitivity under saturation conditions.

-122-
a
Figure 35. Excitation broadening of indium. Relative atomic
fluorescence (vertical axis) vs. wavelength (horizontal
axis) (DPS dye, center wavelength, 410 nm).
a. low power limit--laser bandwidth.
b. high power limit.

-123-
Figure 36. Excitation broadening of sodium. Relative atomic
fluorescence (vertical axis) vs. wavelength (horizontal
axis) (R6G dye, center wavelength, 589.0 nm).
a. high power limit.
b. low power limit--laser bandwidth.

124-
Figure 37. Excitation broadening of calcium. Relative atomic
fluorescence (vertical axis) vs. wavelength (horizontal
axis) (bis-MSB dye, center wavelength, 422.7 nm).
a. low power limit--laser bandwidth
b. high power limit

-125-
Table 7
Excitation Profile vs. Scanned Laser 3andwidth
6X (A)
Element
Direct
Measurement
Fluorescence
Excitation Profile
Ar/02/H2
n2/o2/h2
Ca
0.23
0.20
0.20
Sr
0.23
0.42
0.23
Na
0.36
0.23
0.40
In
0.24
0.19
0.28

- 126-
observation was further born out by the abbreviated pulse width of the
other dyes, and the limiting spectral bandwidths exhibited. These were
approximately three times those specified by the manufacturer. The
further evidence of some temporal mode structures on most of the
dyes' output seemed to concur with the above. The times between maxima
of the temporal modes corresponded to a distance of about 1 cm, the
width of the dye cell. This indicated a strong coupling within the
cell with an additional coupling to the entire cavity. Further ex¬
periments will be done with a new dye cell to confirm this line of
reasoning. In the meantime, the sensitivity of the temporal width to
tuning of the cavity invites the goal of very short laser pulses from
a commercial system not designed for this type of work. In atomic
spectroscopy, this invites the study of rate constants of quenching,
etc.
Laser Cross-Section
The evaluation of the cross-section involved in the excitation
of atoms in the viewing area was purely based on the geometry of
collection. The vertical distance was the slit width, as the mono¬
chromator was fixed on its side. The horizontal distance was assumed
to be the width of the inner (seeded) flame, which was somewhat smaller
than the laser beam. Therefore a mask was placed over the face of the
photodiode before peak power was measured. The aperture measured
0.5 mm by 4 mm, and was centered in the laser beam, which had been
centered at the correct vertical and horizontal displacement during
alignment. The homogeneity of the laser beam is discussed in the
following section.

-127-
Laser Beam Homogeneity
The necessity of a spatially homogeneous laser beam for meaningful
diagnostic measurements has been discussed at length previously (67)•
In order to use the data from these experiments, it was necessary to
prove the homogeneity via direct sampling, as well as by the results
of the diagnostic experiments. The laser beam, suitably filtered as
previously described was measured at the edge of the flame cell farthest
from the laser. The same vacuum photodiode as used previously was
masked with a 100 ym pinhole and suitable neutral density filters.
It was then translated through the beam in two dimensions via a
laboratory-built screw translator mechanism. The output of the
photodiode was measured with the boxcar system using the 164 plug-in.
The resulting voltage was recorded on a strip chart recorder. These
data were then entered manually into a digital computer. The data
were plotted using a three-dimensional plotting routine developed by
the author (see Appendix 2). These results are shown in Figure 38.
The homogeneity in the central portion was quite good. This central
portion (0.5 mm by 4 am) was the portion directly exciting the field
of view.
Self-Absorption
Self-absorption was proved to be negligible for all measure¬
ments by introducing a 10-fold higher concentration of analyte into
the flame with a 1.0 neutral density filter inserted between the
flame and the PMT. In all cases, this produced the same size signal
as the 10-fold lower concentration. The lower concentration was used,

Relative Intensity
Figure 38. Laser intensity as a function of X-Y position.
Retouched to eliminate hidden lines.
-128-

-129-
however, for the measurements because of the tendency for higher con¬
centrations to reduce the degree of saturation (68).
Spectral Continuum
The laser bandwidth of approximately 0.25 Á was assumed to be a
continuum despite the possibility of a saturation broadened absorption
profile. Power broadening should not be present at these laser power
levels.
Achievement of Steady State
The achievement of a steady state in the population of the ex¬
cited state is necessary to measure a meaningful quantum efficiency
or total number density. While steady state could be achieved
in at least two ways, only one of these was suitable for these
measurements. The first steady state has been predicted (67) as a
condition in which (in a three-level system) the populations of the
ground state and the highest excited state are equalized by the fast
rising edge of a laser pulse. This steady state relaxes to a second
steady state plateau involving the second level. It is this feature
which accurately reflects the quantities that we are interested
in. As a means of determining that such a steady state exists, a
temporal scan (streak) was made of the fluorescence of the highest
excited state of indium as a function of laser excitation tuning.
The tuning, as mentioned before, strongly affected the pulse width
of the dye used. Fluorescence corresponding to excitation
and X23 excitation are shown in Figures 39 and 40. In order to

-130-
Figure 39. Streak of indium atomic fluorescence. Excitation
wavelength 410 nm (see streak in Figure 41). Emission
wavelength 451 nm. Concentration 1000 ug/ml. 19 ns
per inch.

-131-
Figure 40. Streak of indium atomic fluorescence. Excitation
wavelength 451 nm (see streak in Figure 33). Emission
wavelength 410 nm. Concentration 1000 yq/ml. 19 ns
per inch.

-132-
Streak of Solectron dye laser scatter (DPS), 8.7 ns per
inch.
Figure 41.

-133-
collect these streaks a very high (ca. 1000 pg/ml) concentration
solution was necessary. In addition, the non-resonance transition
had to be used, as scatter was too high for resonance measurements.
This transition also had to be in steady state for the measurements
to be meaningful. No evidence of peaking in the highest excited state
was found. It was evident that the temporal width of the fluorescence
was far longer than that of the laser, and that a significant plateau
existed at the top of the pulse. The steady state was quite evident.
It was also evident that either the threshhold of saturation had to
be quite low on the laser excitation pulse or that the combined
decay rate connecting the third excited state with the other states
had to be very low. If the latter were true, the plateau would be
much shorter than it is, as the laser drops off with quite a fast
fall time compared to the length of the plateau (see Figure 41).
Therefore, it can be considered that saturation occurred quite early
in the pulse. Although there is no data representing the relative
timing of the leading edges of the laser and the fluorescence pulses,
it could be assumed that if the laser shape were not changed grossly
that the falling edge of the atomic fluorescence pulse represented a
relaxation of the excited state population. A later section on rate
constants discusses this possibility.
Coherence Effects
Coherence effects (population changes synchronous with the
electric field of the laser output) would destroy the approach used
in the theoretical section to find quantum efficiency and total number
density. These effects are not expected to be seen in high pressure

-134-
environments at the power levels used here, as collisions of the
dephasing type are quite frequent (47).
Measurement of Fluorescence Depth
Since the laser beam exceeded the width of the inner (seeded)
flame, the fluorescence collection depth was taken as the width of the
flame in the collection axis, 4 mm.
„Calibration of Photometer
A DC calibration procedure was used for calibration of the
photometer used for collection of pulsed data. Pulsed calibration
procedures and calibrated sources are not available. A tungsten strip
lamp (GE pyrometer 6818, S6, GE, Nela Park Cleveland, OH) calibrated
against a National Bureau of Standards calibrated strip lamp (EPUV
1068, National Bureau of Standards, Washington, D.C.) was placed at
the focus of the optical system for fluorescence collection. The
lamp was operated at the standard 35 A current (AC) specified, and
allowed to stabilize for 1/2 hour, shielded on all sides by drop
cloths. Measurement of output current was made under the experimental
conditions at the wavelengths specified in the lamp calibration table.
The resulting data are shown in Figure 42.
Quenching Rate Constants
The atomic fluorescence streak data exhibit the plateau mentioned
in the Steady State section of this appendix. This feature means that
if the saturating pulse is short enough, yet intense enough to populate

X
ai
XI
E
E
4->
OJ
LO
E
O
4->
O
X
x
X
J r
350 400
X
—1 1
450 500
Wavelength (nni)
Figure 42. Photometer calibration curve.
X
X
—t-
550
-»
600
-135-

-136-
substantially the highest state, that a combined quenching and
radiative lifetime for that level could be found from streak data.
The signal to noise ratio of the present data is quite poor, but if
a smoothed decay profile were used, it could establish an upper limit
for a decay lifetime. The problem with this approach is that the
laser temporal response cannot be seen with enough amplitude resolu¬
tion (with the present equipment) to determine if some response to
the tail of the pulse is determining the observed decay. In addi¬
tion, with the jitter problems as they stand, no temporal relationship
could be established between onset of lasing and onset of fluor¬
escence, although they should coincide closely. A computer acqui¬
sition of several temporal streaks of the laser, and then the fluor¬
escence, followed by alignment of the leading edges has been tried
by one author (69) to eliminate problems of this sort. In the
present case, this was out of the question, as the jitter was far
too large.
Noise Power Density Measurement
The system used to collect these data has been used before (69),
but will be described here briefly. Figure 43 depicts the system.
The source of the noise for the spectra collected was an ordinary
laboratory flame (nebulizer and spray chamber: Perkin-Elmer Corpora¬
tion, Norwalk, Conn.) with a laboratory-built capillary burner
(Haraguchi et al. (70)) and an inert gas sheath (laboratory-built).
A stabilized gas flow system similar to the one mentioned previously
was used. Emission signals were collected by a simple point to point
lens system at the slit of a medium resolution monochromator

Figure 43. Noise power density collection system. Component symbols
are as follows: F = flame, L = lens, MO = monochromator,
PMT = photomultiplier tube, PS = power supply, R = load
resistor, ACA = AC amplifier, C = blocking capacitor,
A/D = analog to digital converter, D/A = digital to
analog converter, MC = minicomputer, 0 = oscilloscope,
X-Y = X-Y recorder, T = terminal.

-138-

-139-
(EU-700, McPherson Instrument Co., Acton, Ma.). A 1P28 PMT (RCA,
ElectroOptics and Devices Di'v., Lancaster, Pa.) was used at -700 V
(Model 240, High Voltage Supply, Keithley, Cleveland, OH). The
output current was converted to a voltage with one of two load
resistors (1 kn or 16.2 kn). An AC amplifier was used to block the
DC voltage and amplify the AC or noise signal, in order to best use
the dynamic range of the data acquisition system. The output of this
amplifier was taken, after suitable adjustment of an upper cut-off
RC filter, through another blocking capacitor (1 pF, mylar, used to
block DC offset from the amplifier) to an analog to digital converter
(LPS-11, Digital Equipment Corporation, Maynard, Mass.). This ADC
was interrogated by the computer at programmable intervals to collect
2048 samples of noise voltage. These were Fourier transformed. The
average of 100 Fourier transforms at a given acquisition rate were
converted to a power spectrum, which could be displayed in several
ways (see Figure 43). The digital data were transferred in a
parallel fashion to another digital computer (PDP-11/20, Digital
Equipment Corporation). These data were stored in binary fashion
for fast acquisition by a sequential data plotting program (see
Appendix 2).

APPENDIX 2
COMPUTER PROGRAMMING AND PLOTTING
A useful and necessary function of a computer system is the ability
to express the results of its computations in a way which is intel¬
ligible to the programmer and the user. It has been said that man,
since he lives in a three-dimensional world, has a limited ability to
visualize in higher dimensions. Mechanical considerations limit his
ability to display data in more than two. At best, he can produce
a pseudo-three-dimensional display.
The PDP 11/20 system used for some of this research has lacked
for many years even the most rudimentary display system. A need was
established for plotted data from several sources, of two types,
sequential (or channel) type data, and paired X-Y data. Both types lend
themselves to two and (pseudo-)three-dimensional plotting. Therefore,
a project was undertaken to produce a stepping motor plotter to ful¬
fill the need for this type of display and for creation of simple
diagrams.
An old X-Y analog plotter chassis was scavenged for the bed and
pen movement. Stepping motors were attached via gears and belts.
Driving cards were installed, as well as end of travel micro¬
switches.
As our computer had no general digital input-output function, a
request was made to local software support specalists to install and/or
-140-

-141-
modi fy existing routines as part of the group’s BASIC language package.
This included a stepper drive command capable of addressing eight
separate motors. This enabled the plotter to be programmed in a
somewhat wasteful way from BASIC. A modular program of providing
plotting packages was commenced at that time. The basis of the total
package was a 45 line subroutine which plotted a best line between two
points on the plotter. No provision was made for runoff, so scaling
and manipulation of data had to provide for the plotter size internal
to a driving program utilizing the best line routine. The routine
could have been made shorter, but included the following points neces¬
sitated by the present form of BASIC:
1. software integerization to provide symmetry in the function,
2. skip-out to delta X-delta Y change when the pen is up,
3. skip-out to single axis call when only one axis is changed,
4. mini-vector approximation with correction after each
mini-vector in only one dimension.
The basic best-line routine has been used as the core of several
data-plotting routines:
1. sequential—e.g., optical multichannel analyzer, noise
power spectra, or streak camera data,
2. X-Y format—e.g., scans of intensity vs. a single dimension,
as in profiling cuts of a flame or a plasma,
3. X-Y-Z format—e.g., scans of intensity vs. two dimensions,
as in multidimensional profiling, wavelength-intensity-time
profiles, etc.
These programs were used on various types of computer files, as suited
each program, and type and volume of data.

-142-
In addition, the best-line routine served the etch-a-sketch or
box diagram routine via a very simple language containing a number of
symbols for commonly used figures in spectroscopic diagrams. This
was useful for slide and figure preparation for talks and journal
articles.
A third utilization of this routine was for the character genera¬
tion module. This type of programing has generally been done in
assembly language to facilitate speed. In this case, the generation
has all been done in BASIC with approximately a ten times reduction
in speed from a commercial system. All of the letters and numbers
and several of the ASCII symbols have been provided for labelling of
charts, etc., created by the other programs. In some cases, the
character generation module has been integrated with other graphics
modules.
Specifics follow for the best-line routine and programs utilizing
it.
Best-Line Routine
Lines 5000-5020
This is a set-up section. It saves current position (C is the X
axis position, D is the Y axis position) in Cl and Dl. Flags J and K
are set to indicate the sign of change for each axis, for the purpose
of the software integerization.
Line 5025
This line transfers to a short form when the pen is raised (i.e.,
when B(0) = 1). The short form (lines 5900-5915) steps off the X axis
change first, then the Y axis change, to save time.

-143-
Lines 5028, 5029
These lines transfer control to short form sections when only one
axis is changed, again to save time.
Lines 5520-5530
The Y axis only is changed.
Lines 5500-5520
The X axis only is changed.
Lines 5030-5050
These lines decide whether the greater change is in the X axis
or the Y axis and steers the program to the correct subroutine. In
addition, a true slope is computed and the best integer approximation
(absolute value) is found.
Lines 5600-5665
This is the best line generator for a change in X axis larger
than a change in Y axis.
Lines 5800-5870
This subroutine generates the best line for the opposite case,
change in the Y axis larger than the change in the X axis. The in¬
verse of the original slope is computed, and the integer of the
absolute value is found. The integerized slope is a minivector, when
used in conjunction with the direction flags J and K. This minivector
is the closest approximation to the real line that can be made by

-144-
discrete steps. At every repetition, it is correct in the dimension
on the bottom of the slope (in this case the X axis change) since
steps of unit size are always taken on this axis. On the other axis,
if the correct position is kept track of, a correction can be made
whenever the correction amounts to at least one step (as computed in
lines 5830-5850). If the minivector is repeated as many times as there
are steps between the points on the lower axis (X in this case), the
best line has been plotted. This is the basis of all the graphics
functions. New position is provided to the subroutine in XI and Yl.
The change in terms of steps is computed from the present position,
C and D. A variable list can be found in Table 8.
Sequential Data Plots
0P1.3AS Lines 1-4 and 1000-2000
A virtual data file must be provided with values ranging from 0
to 35,565. Scaling is done at the keyboard to provide for expansion.
The file is searched for the maximum integer value.
Line HOP
The actual working value is assigned to this integer.
Line 1105
The expansion is decided here by the actual largest value to be
displayed. All values topping this value are limited to it (cropped)
in a subroutine (lines 1600-1610). The X axis is treated similarly,
except no cropping is provided. Therefore, care must be taken when
expanding via lines 1070-1090.

-145-
Table 8
Variable List for Best-Line Routine
Cl Saves present X position
D1 Saves present Y position
C Present X position
D Present Y position
J Delta X sign flag
K Delta Y sign flag
XI New X position
Y1 New Y position
B Digital output matrix for word 1
51 Actual slope
52 Integerized absolute slope
P9 Loop variable for best-line
56 Actual pen position
57 Difference between actual and correct pen positions
M Sign flag for S7 for X/Y
L Sign flag for S7 for Y/X

-146-
Lines 1110-1390
These lines provide for axis drawing and tic marks on either axis
or both. The position of the tic marks is remembered for later
labelling.
Lines 1400-1500
These lines provide for actual plotting, using the best-line
routine and either placing dots or drawing lines between each data
point.
Axis Labelling and Numbering
0P1.BAS Lines 2Q0-760
Lines 200-351
These lines allow numbering at remembered tic mark positions and
multiple line labellingfor the X axis.
Lines 355-465
The same function is performed for the Y axis.
Lines 500-760
This is the caption section subroutine, which services the
labeling and numbering sections. It cuts up the caption into in¬
dividual ASCII characters, finds out the size of the caption, and
steps back half of this length to center it. The captions can be
plotted horizontally or vertically, and character size is at the

-147-
operator's choice. This routine makes use of the best-line routine
via the character generation routine.
Character Generation Subroutine
Lines 4400-4456
This is the look-up table which provides the look-up in variable
J8 for the character minivectors. This variable accesses a binary
virtual data file containing the mini vectors and pen up-down commands
comprising the 57 ASCII characters and special symbols. These symbols
were coded and converted into the binary virtual file via the program
LEDAT.BAS. The file name is LEI.DAT. The data file may be output in
an intelligible manner by running VFP1.BAS, and referring to the
character sort section of this subroutine.
The manner in which the virtual data file is used is straight¬
forward. The file is arranged as follows:
Item l--the number of symbols contained in the file.
Item 2--the number of symbols plus one--the beginning number
of the minivector data for the corresponding symbol.
Items through the end of the file-symbol minivector tables as
follows:
the first item in each table is the number of vectors
in the symbol, starting at the lower left corner of a
7 by 7 dot matrix, and ending at the lower right
corner. The following items are minivector com¬
ponents by threes,
1. Pen up (0) or down (I) bit

-148-
2. X change in steps
3. Y change in steps.
The character routine uses the BASIC table to find the virtual
file element pointing to the minivector set. A loop is run through
the correct number of times (specified by the first element), each
time using the pen set routine and scaling the minivector as desired
before calling the best-line section to draft the pen stroke. At the
finish of the letter, the pen is moved a space corresponding to half
a letter. Then, the loop is used for the next letter.
Data Passage Between Computers
Passage of sequential data files from the PDP 11/34 in a parallel
fashion to the PDP 11/20 was accomplished via the PSTRN program (11/34)
and the REC program (11/20). The only formality necessary for com¬
munication in this fashion is the handshake routine. This was per¬
formed on the 11/34 end with "peek" and "poke" commands. The 11/20
used the augmented BASIC commands "INPB" and "PLSB." A 1000 by 16
bit word transfer takes about 1/2 minute, which is not very spectac¬
ular, but quite easy to program. The major holdup was in BASIC,
which was quite slow. An assembly language program transferring to
the 11/34 from a hardware device ran about an order of magnitude
faster. The ease of use of this method balanced the time consumed.
The transfer of ten or more files at a stretch would be accomplished
with no intervention.
Passage the other way has not been developed in great detail
yet. Test programs have run with only hardware-caused errors.

-149-
Plans are underway for bit-parallel character-serial passage
of ASCII files as a completely general method of exchange for programs
and data files. BASIC (on the 11/20) has ASCII coding and decoding
statements for alphanumeric sending and receiving. Fortran (on the
11/34) does not have these features. However, a look-up table
should suffice.

-150-
Best-line routine-- This subroutine serves all plotting
functions.
5000 C1=C\B1=D
5005 J=1
5010 IF CXl-Ci:-=OPO 10 5010 \J--1
5015 K=1
5020 IF -OGO TO 5025 \K -.1.
5025 If 8(0)=1 GO TO 5022
5026 GO SUB 5900 \RE1 U 22
5023 IF X1-CGO TO 5520
5029 IF Y1 =BGO 10 5500
5030 51 -- ( X1 ~ C ) / < Y 1 - O ) \ C 2=.1N 7 ( ft B S <{il) >
50-10 IF APS(S1 )>" 1G0 TO 5600
5050 GOSUB 5000 \G0 TO 5400
5400 RETURN
5500 CALL, ‘STEP* < INT (ABS(Xl-C) :>#J>50»1)
5505 C=C+INT ( hL 3 ( X1 --C) ) t J
5510 GO TO 5400
5520 CALL 1 STEP • ( INT ( AITS ( Y1 -I') ) ":K , 50,0 )
5525 ri=It+INr(ABS(Yl-») )*K
5530 GO TO 5400
5600 FOR P9-1 TO ABS 5610 CALL ■STEP *(82*J r SO >1>\CALL "STEP* 50»0)
5625 C=C+S2*J\D-D • F K
5630 S 6 = 1-'9? A »5 (51 ) # J i C1
5640 S7---S6--C
5644 N-l
5645 IF S7>=OCiO TO 5650 \M=~J
5650 CALL ' ST EP ’ < IN T (APS (S7 ) ' Yh, 50 » 1. )
5655 C=C+INT < ALTS ( 57) ) 7M
5660 NEXT P?
5665 GO TO 5400 '
5800 81=1/S1\S2“INT(APS(SI>)
5305 FOR I"'9=1 10 AÍTS < XI-C)
5810 CALL -STEP"(57YK,50,0>\CALL "ST L!'“ (J,50■1)
5320 C = C + J \ IT â–  - BiS 2 â– !' K '
5330 S6=P9>TAVS ( SI) YK'-vPi
5840 S7=S6-P
5344 L=1
5045 IF S7>-0C0 10 5550 \L~-1
5850 CALL * S IT P" C j ;•»! (AUG < S7 ) ) YL - 50 • t >
5355 Li-D-i INT (iTkl (S/) > M L.
5860 NEXT P9
5870 RETURN
5900 CALL ’ SHIP* (INT CABS CM1-C) ) Y J • 50» 1 )\C=C! INT< ABS (Xl-C) )#J

-151-
0.1.BAS--A section of the program dealing with sequential plottinq
Í Dili K( 1 5) ,¡¡£410) »■£< 10)
2 DEF FNA(fl*»#C)=rt!Srh:200/C
3 df:f fnb (u,x»i! ■) -w-i-Xi y/:;
4 n E F F N c f ri * E r Ci * I-1) ~ 11 f E *: IV- G 111)
5 GO TO 1000
1000 PRINT TILE NAURU FOR INPUT MUST BE A BASIC VIRTUAL INTEGER PILE.
1001 PRINT ‘(UP TO 1024 INTEGERS!; VALUES 0 TO ,45335) ‘
1005 A = 0
loto p pint * f 11. r: n 11111 \ t m p 11 r 7 i-
1020 OPEN It* PUR JNPl.IT OP MU. VI 1.1. U02J.)
1025 PRINT • I! OF Pi.iTMlS TO PUT T " ; \ i API) Y ;<:t
1030 FOR J6--0 TO X3-1
1040 ] F V r 1 ( J 6 ) < - A 0 0 T(.J 10 6 0
1050 A = VF1Í.JÓ)
1060 NeXT J6
1070 PRINT •* UP STEPS BET WEEN X POINTS" i \.INPUT X2
1080 PRINT * MAXIMUM X VALUE INPUT COT: RESPONDS TO" ¡VtNPlJl X5
1090 PRINT ‘MAXIMUM X VALUE ON AXLlt1' ? VTNPUT XÓ
1095 PRINT "Y AXIS SCALE 1100 PRINT ‘MAXIMUM Y VALUE INPUT CORRESPONDS TO* 5 V1NPUT Y5
1105 PRINT ‘MAXIMUM Y VALUE ON AXIS“5XINUJT Y4
1110 PRINT ‘DRAW AXES (Y 0R N)‘J\1NPU T 14f
1120 IF Y4$^*N*0# TO 1400
1130 30SUB 4900
1140 X1*FNB 1145 Y1=0\G03UB 5000
1150 XI=-50
1160 GCSIJD 5000
1170 Y1=FNA(Y2» Y6?'(6)
1130 CALL 1 STEP" ( Y1 , liO . 0)
1190 C ALL ‘ S T E P “ < - Y 1 > 3 0,0 )
1200 GOSUP 4950
1250 PRINT ‘TIC MARKS (Y OR N)‘>\INPUT ft
1260 IF T*=‘N‘GO TO 1400
1265 P=1
1270 PRINT ‘X VALUE”J\INPUT X7
1275 IF X7=-99960 TO 1.340
1280 X1 = FNB (X2 • X3 fX7fX5) \ Y1 ==0
1285 R 1290 GOSLJB 5000
1295 GOSUB 4900
1300 CALL ‘STEP"(-20t30 - 0)
1310 GOSUB 4950
1320 CALL 'STEP*(20,30■0.«
1325 1 — f' -J- .1
1330 GO TO 1270
1340 0=1
1350 P RIN T ‘ Y V A l. UI “ ? M N | U T Y 7
1355 IF Y7 = --9?>Gi.i TO 1 -100
1340 Yl=*F Nft ( Y2 , Y 7 . Y6 ) \X J - -50
1365 S(Q) = Yl
1370 GOSUB 5000 SPOSU»; 4900

-152-
137S caí .i. * p rr.p • (-20»30 r i) \nof¡ui: 1950
litio CALL "ti I i 20 • 30» J >
1385 B-CM-1
1390 GO TO 1300
1 TOO X1=0\Y1=0\G0SUB 3000
1405 PRINT "LINTS Olí HOTO 1406 IF l_£ = ' I.i ’ GO TO RI O
140 7 Y 1 -FNO ('.'F1 ( O > , Y 2 « Y5 . A,. Y6 > *700
.14 00 CUOUli lo O O MiOSUl,.' 3000
1409 GOñIJI'i 4900
1410 TUR JR I TO X3-1
14 20 Y1 - F N C C V F J ( J 6 ) , Y 2 y Y 5 y A . Y > 12 O O
1430 X1.--J6*X2
1435 GOSUlí J 600
1440 COSIN'! 3000
1450 IF Lt~"L“GO TO 1500
1460 GOSUJ? 4900 \GOStU-! 4950
1500 NEXT J6
1510 GD-UB 4950
1520 X1“O\Y1=O
1530 ü03Lit; 5000
1535 CLOSE VF1
1540 PRINT ‘REPLOT (Y OR H) ■ ?\IMPIJT ZOi
1550 IF ZSía'Y'GO TO 1000
1560 PRINT ’CAPTION ( Y OR N)*í\INPUT 23$
1570 IF 205='N'GO TO 2000
1580 GO TO 10
1600 IF Y1<=Y2*200G0 TO 1610
1605 Y1. -Y21200
1610 RETURN
2000 F NIT

-153-
OP T .SAS —A subsection of this program dealing with axis
labelling and generation is shown here.
200 PRINT 'X'JMNPUT XI
210 PRINT 'Y"»\INPUT Y1
220 GOSUB 5000
230 RETURN
250 PRINT “GRACE BETWEEN X AXIS AND NUMBERS“Í\INPUT U4
255 Yl=-H4
260 FOR Pl-=1 TO P-1
270 XI =R(PI)
230 GOSUB 5000
270 GOSUB 500
300 NEXT PI
301 GO TO 3.1.0
305 PRINT “ANOTHER I.TNE OF X AXIS LABEL (Y CP N)"»\INPUT V*
306 IF V$<>"Y“GO TO 355
310 PRINT “SPACE BETWEEN X AXIS AMU X AXIS LABEL'» MNPUT W4
320 Yl=-W4
330 Xl=rHB(X?.X3■XótX5)/2
340 GOSUB 3000
350 GOSUB 500
351 GO TO 305
355 PRINT "SPACE BETWEEN Y AXIS AND NUMBERS“> MNPUT U4
360 XI=-W4~50
370 FOR Pl = l TO 0-1
380 Y1=S
390 GOSUB 5000
400 GOSUB 500
410 NEXT PI
411 00 TO 420
415 PRINT “ANO I HER LINE OF Y AXIS LABEL 416 IF 060 “ Y “ GO TO 4VO
420 PRINT “SPACE BETWEEN Y AXIS AND Y AXIS LABEL’» MNPUT W4
430 XI = -114-50
440 Y1 =FNA(Y2»Y6tY6)/2
450 GOSUB 5000
460 GOSUB 500
465 GO TO 415
490 X1= O\Yi- 0\G0SUB 5000
495 RETURN
500 PRINT “POSITION PEN AT CENTER POINT CP CAPTION"
505 P6=0
510 L'i =C\I!2-'H
520 PRINT “HORIZONTAL (II) OR VERTICAL ('.») LETTERING*»MNPUT LI
530 PRINT \PRINT \PRINT
540 PRINT “LETIEN SIZE (ABOUT 200 STEPS PER INCH)“fMNPUT CS
550 PRINT “CAPTION" r MNPUT Olí

-154-
551 S4-Ü
555 GCl BUB 700
5¿0 IF L1 $ - ’ O ” Lit) TO 5yo
56? Y.1-H
570 XI =C- ( S4/2) - (OS/2 ) T (LEN ( C1$ ) -1) /2
575 GOSUB 5000
5SO GO TO 600
590 XI-C
591 Y1 --D — ( 84/2) - < CU/2) T ( LEW ( C1. ) -1 )/2
595 GOG'.IB 5000
600 FOR' 09=1. TO LEM < C J.Í )
610 A2f SEGí < C1 $ » 09,0? )
620 GOSUB 4-100
630 NEXT 09
640 X1*U1\Y1=W2\G05UB 5000
650 RETURN
700 P6---1.
710 FOR 09-= 1 TO LEM (Cl Í )
720 A 2 â–  -- S E 0 $ ( C1V-, 0 ?. 0 v)
725 F6=]
730 GOSUB 4400
735 P6=C
740 NEXT 09
760 RETURN

-155-
0P1.BAS--A subsection of the program dealing with
character generation is shown here.
•MOO
IF
A2'f<>
■"A‘GO
10
4401
\Jti-3 \G0
i0 4457
-J-IOl
IF
" R' GO
TH
4 402
\ JO-r:\GO
TO 4457
4402
IF
A2*<>
â–  â–  C * Gil
TO
4403
\j>j=3\ea
i0 4457
A A 03
IF
A 2 SO
" D “ GO
TO
4 404
\tl8=4\C>0
TO 4457
A 404
IF
A 2 SO
■"E’GÜ
TO
4405
\J0=5\G0
TO 4457
4405
IF
A 2 SO
" F a GO
TO
4 4 06
\JG=A\Gn
10 4457
4406
IF
A2$<>
* G" GO
TO
4407
\J8-~7\GC
TO 4457
4 407
IF
" H “ GO
TO
4 4 00
\JiOSXGO
10 4457
4408
IF
A2S O'
* I â–  GO
TO
44 09
\J8=?\G0
TO 4457
4409
IF
A 2 CO
â–  J â–  60
TO
4410
\J8=10\G0
TO 4457
4410
IF
A 2 SO
’ K11 ÜÜ
TO
4411
\JB--=11\0C
7 ü 4 4 5 7
4413.
IF
A 2 SO
" L “ GO
TO
4 412
\J0=12\b0
TO 4457
4412
IF
A 2 SO
• * rf * GO
TO
4413
\J3=13\G0
10 4457
4413
IF
A 2
â–  H "GO
TO
4 4 1 4
\J8=14\G0
TO 4457
4414
IF
A 2 50
■"0“GO
TO
4415
\JS-15\G0
¡ J 4 4 5 7
4415
IF
A 2 í O
■ P ”00
TO
A A 1 o
\JS---16 \ G 0
TO 4457
4 416
IF
A2SO
■ “Q * GO
TO
4417
.\JS-17\G0
TO 4457
4417
IF
A2SO
•“ R ’ GO
TO
4418
\J8~1S\00
TO 4457
4418
IF
A 21 O
” S ” G 0
TO
4 419
\JC-19\G0
TJ 4457
4419
IF
,-¡2 40
■T‘C-0
TO
4420
\ J 3 - â–  .2 0 \ b G
Til 4457
4420
IF
A2ÍO
“ U ” GO
T 0
4 421
\J0=21\G0
TQ 4457
4421
IF
A2$<>
“ V" GO
TO
.0 S S’ ’ }
\J8=22\00
10 4457
4422
IF
A2-ÍO
â–  W" GO
TO
4423
\J8-23\GU
TO 4457
4423
IF
ft 2 SO
“ X" GO
TO
4424
\J8 -24\G0
TO 4437
4424
i r-
J. I
A2S<>
“ Y" G 0
TO
4425
\ J&--25NG0
10 4457
4 425
IF
02 SO
“ Z" GO
TO
4 4.26
\JG~26\GC)
”0 4137
4426
t r:
A 2 SO
u 3. 3 GO
TO
4 4 2 7
\J3=27\G0
TO 4457
4427
IF
A 2 v < >
‘ 2 “ GO
TO
4 4 20
\ J!70 \ G'l
TO 4457
4428
1F
A 2 -- O
• 3 “ GO
TO
4 429
\ JCJ-- -WOO
TO 4457
4 429
IF
A 2 i- <>
"A" G 0
TO
4 4 3 0
019-30700
TO 4457
4 430
i r
A 2 SO
“ 5 ‘ GO
10
4431
\JG-3i\G0
TO 4457
4431
It-
A 2-0
“ 6" GO
TO
r £ s
\J8-32\G0
TO 4457

156-
4-132
IF
A 2 S <'
> “ 7"GO
TO 4433
,\JS-33XG0
TO 4457
4 433
IF
A 2 SC
" 8 1 GO
TO 4434
\J8“34\G0
TO 4457
4434
1 F
A 2 SC
“ 9 " GO
TO 4 435
\J3--35\G0
TO 4457
4435
IF
a:.’sc
>* 0”GO
TO 4434
\J3-36\G0
10 4457
4 436
IF
A 2 SC
" ( " GO
TO 4437
\ ..10-37X00
TO 4437
4437
IF
A 2 SC
‘ ) "CO
TO 4430
XJ8-3SXG0
TO 4457
443S
IF
A 2 SC
>‘-•00
TO 4439
\J03V\Gfi
TO 4457
4439
IF
A 2 SC:
■■ • . “ GO
TO 4440
XJ3-40X00
TO 4-137
4440
IF
A2SC
>â– . 1 GO
TO 4441
XJ8=--41XG0
TO 4487
4441
1 F
A 2 SC:
;• “ " GO
TO 4442
\jn-42\60
JO 4457
4442
] F
A 2 $ <
1 / * GO
TO 4443
X58-43XG0
TO 4457
444 3
IK
r2s<:
“3 "GO
TO 4144
XJS-44X00
TO 4457
44 44
IF
A2SC
>= r:“on
TO 4445
XJÍ5-45XG0
TO 4457
4445
1 F
A 2 S C
>â– "=â– 'GO
fU 4 4 6
XJ8-46XÜ0
TO 4457
4446
IF
A 2 SC
>*>* 00
lb 4447
XJ3---4 7X00
TO 4457
4 447
IF
A ' S ''
“ < " GO
TO 4448
X JO-4 0X00
TO 4457
4448
.1 f-
A 2 SC:
HE “ GO
TO 4949
kjO--19X00
TO 4-15
4449
ir
A2$ “ HU *00
TO 4150
X JS--50XG0
TO 44 5:
4 450
IF
A2S-C
CGI "GO
TO 4451
XJO“51X00
TO 445
4451
IF
A 2 SC
.-■LA‘GO
TO 4452
\ 5 03 2 X G ( 3
TO 4 45
4452
IF
A 2 S â– â– 
;• “ F' I * 0 0
TO 4453
XJS-53XC0
TO 115
4453
IF'
A 2 SC:
- “Cl"GO
TO 4154
XJB=o4XG0
TO 445'
4 454
I!
47 SC
- “ N 1. ‘ GO
TO 4455
X 2 S — 5 5 X G 0
TO 4 15
4455
i r-
A 2 SC:
.■•111' GO
TO 4453
\J3~56\G0
TO 445"
4456
IF
•If: SC
â– "F"GO
TO 4457
XJ3-57XG0
TO 4457

-10/-
IEDAT.BAS--A program to create a binary vector file for
the generation of characters and symbols.
1005 OPEN ' Hi LI I LEI ' FOR OUTPUT AS FILE UFlX.f 1500 )
1010 READ B
1015 F=B+1
1020
FOR 1=2 TO F
1030
READ l.i
1040
UF1 ( D-tHf
1050
NEXT I
1060
v r i < i
1070
0--OF1 (F)
1075
G=Gil
1 000
FOR J-F+l
TU u
1090
READ E
1100
0F1 (J )=•■[■£
1 1 10
NEXT J
1120
READ H
1130
OF 1 (CM .1.) =!-
1
114 0
FOR K=iM2
TO (3*H+G+2)
1150
READ I
1160
OF 1 (K) ---1
1170
NEXT K
1180
CLOSE UF1
1200
END
1900
If A1 A 57
1905
DATA 1íi7v
5-1 ? 82 ? 104-126 ? 1
45,179,198,217
1910
DATA 236 »252,262,275,288,
319,341,375,400
1915
DATA 4)0-4
56 â– ?478 -49.1. ,510?
523,542,555,571,602
1920
DATA 633*6
46,677-708?718-
/ 7 5,0 0 • 1, !:■ 3 8, D 5 4,0 6 7,
877
1925
DATA 892,912,928,935>943,
764,980,9'-0 ? 1000,1 OR
8
1930
DATA 1047?
1.072,1.091 ? 1117?
1.1.35,1.1.54? 1.1.73
2000
DATA 5•1? 3
» 6 ? 1 • 3! - 6 >■ 0 ? -■ J. ,
2,1 , — 4,0, (1 > 5 ? — 2
2010
DATA 12?1,
0,6,1 > 4,0 ? 1 ? 2 > -
1. -1 v 0,-1,1,-2,-1
2013
DATA 1?-4 ?
0,0,4,0,1,2? --1. ?
1,0,-1,1,-2,-1
2016
I.i ATA 1 >• A f 0 r 0 ? 6 ? 0
2020
DATA 9-0?6
, .1,1. ,-1,-1. 1,-4
,0,1,-1,1 ,1,0,4,1,1,
1
2025
DATA 1? 4 ? 0
T 1 f 1 9 ~ J. 9 0 f 0 V * " 5
2050
DATA 7?1.0
t 6 H • *1 7 0 9 :L y 2 v -1
,1,0,-4,1.-2,-1,1?-4
, 0,0 ? 6? y 0
2060
D A f A / ? 0 7 á 7 ó J 1 y - 6 y 0 ? 1 ? 0 ? —
6 , j,6,0,0, — 2,3,1,—A,
0,0,6,-3
2070
DATA 6 .* 0 r A
, 6,1 ?--6?0 ? 1 • 0 ? -
6,0,4,3,1. — 1,0,0,6,-
3
2080
DATA 11/0?
6,5 , 1 , -Í ? 1 > .1. , -A
,0,1,-1,-1,1,0,-4,i,
1,-1
2083
DATA l-4,o
,1,1,1. ,1,0,1,1. ?
-2,0,0,2,-2
2100
DATA 6 ?1? 0
,6,0,6,0,1,0,-6
, 0? 0,3,1,-6,0,0,6?-3
2110
DATA 6 ?1?4
? 0? 0>0,6,1,-4 ?C
r 0 < 2,0,1,0 t -6 • 0 ? 2,0
2120
DATA 6-0,0
, 2,1,2,-2,1?2,0
, 1., 2,2,1., 0,4,0,0, — 6?
2130
DATA 5?1.0
,6,0,6,0,1, - 6 ,
3» 0» 2 > 1 ,14 y -4
2140
DATA 3-0,0
. 6,1 ? 0 ? - 6 , J • 4 ? 0
2150
D A T A 4 ? 1 ? 0
,6,1,3, -3,1,3 3
, .1 >0,-6
2160
DATA 1?1.0
,6,1,6,-6,1,0,6
,0r0,-A

-158-
2170 DATA 10,0,1,0,1,-1,1,1,O,4.1,1,1,1,4,0
2175 DATA 1 »1,-1 ,:!. « 0 , -4 , 1 ,-I »-1 , 1 ,-4 > 0 , 0»5 , 0
2190 DAT A 7 , 1, 0 , ó > 1 , A , 0,1,2» -1 , 1 , 0 , -1 , .!. , -2 , -1 , 1 t -A » 0 » O» 6 ,
2200 DATA 11,0 ? 5,0,1 , -4 , 0,1, -1 , 1 » 1 » 0 , -T,1 > 1 , 1 , 1 ,4 » 0
2205 DATA 1,1,-1,1,0»-4,1,-1»-1 » 0.-1» 2,1, 2»-2
2220 DATA 8,1.0»ó»1,4»0»1»2 »-1,1,0»-1,1,~2»~1,1,-4»0
2225 DATA 0,3,0,1,3,-3
2230 DATA 13 , 0 » 6 » 5, 1 » — 1 y 1 , 1 » —4 , 0 * ,1. , —1 , --1 , 1, 0» —1
2235 DATA 1 , 1» -1 ,1 , 4,0,1. , .1. . -1 • 1.0.-1 , 1 • - ' --1
2237 DATA 1,-4,0,1,-1,1,0, ó,-1
2260 DATA 5 - 0 , 3 .< 0 , 1 » 0 , 6 > 0 • -3 » 0»1 ■ 6,0,0,0,-6
2270 DATA 7 y 0 , 0 , 6»1» 0.-4,1»2,-2,1-2»0»1,2.2 ,1,0»4,0,0,-6
2200 DATA 4,0,0,&, 1 ,3,-6,1 ,3,6,0,0,-6
2290 DATA 6,0,0,6? 1,1, -6,1,2,3,1 , 2, -3 , .1 , 1 , 6,0,0 - /
2300 DATA 4 , 0,3 , ,9 , 1 , -6 ,-6,0 • 0 • é , 1.6 ,-6
2310 DATA 6,0,0,6,1,3,-3,1,0,-3,0,0,3,1,3-3,0,0,-6
2320 DATA A,0,0,6,1,6,0,1,-6,-6,1,6,0
2330 DATA 5,0,0,4 ,.1. * 2,2 , 1 , 0? -6 » 0, -2 « 0 , .1.4,0
2340 DATA 10,0,0 j 5,1 > 1,1 » 1 > 4 y O1.M1 -1 ? 1. ? '■ • -1 > 1» ~ 1 > -1
2345 DATA 1»-4 r 0•1r-1»-1r1,0,-2,l,6,0
2360 DATA 3 (>. 0,0,6? 1,6,0,1 » - 6.-3.1,5 • 0. ■■ : : ,• -1
2365 DATA l r O . -1 r 1 .-1 » -1 r 1. . -4 ? 0 , J-1 , 1 « 0 --1
2380 DATA A,0,6,2,1,-6,0,1,ó,A,1,0,~6
2390 DATA 10 * 0,0.. 1 .. 1 .. 1-1 • 1 > 4,0 j 1.1 . .1. • 1 y 0.2 » 1 >■ -1 > 3.
2395 DATA 1 .• -5.. 0 y 1,0,2,1 , & , 0.0,0 ,-6
2410 DATA 10j0.4,¿,1,-A,-4,1,0,-1,1,1,-1,1,A,0
2415 DATA 1 , 1 r 1 .1,0» 1 ,1,-1 y 1 , T . -4,0,0,‘1,-3
2430 DATA 3,1,6,6,1,-6,0,0,6,—6
2440 DATA 18.0.1,0,1 , -1, 1 • 1 , O , 1 , 1 . 1,1,1 , A , 0,1 ? .1.« 1
2445 DATA i.0rlfl»-l»l,1»-4,0>1 ,~1 ,~lr1>6,-1,1,1»-l
2447 DATA C , A , 0,1 , 1 , -1 r 1,0 . -1 y 1 , - 1 ,-1 ,1 , -4,0,0, E ,• 0
2470 DATA 10y0,2,0 y 1,4,A,1■0,1,1,-1.1•1 --4,0>1s-1,-1
2475 DATA 1 ? 0 ?-1 > J. , 1 , -1. , 1,4 » 0 ? 0,1 >-3
2490 DATA 11tO,1,0,1,-1,1,1,0,A,1,1,1,1,4,0,1,1,-1
2495 DATA 1,0» —1 r 1 , -1 ..-1,1, -4 * 0,1,4,0,0,1» ~6
2510 DATA 5-0,2,0,1,-2,2,1,0»2,1,2,2,0,0,-6
2520 DATA 4.1,2,2,1 :• 0»2»1»-2,2,0,2,-6
2530 DATA 3,0.0»3,1,6,0»0y0,-3
2540 DATA 5» 1 ,0»1,1,1,0»1,0,-1»1,-1,0,0»1»0
2550 DATA 6,0,1 »0,1, -.1,0,1 0 ,M.J.Crl ,0,-2,0,0» 1
2560 DATA 5,0,0,3 , I. ,6,0.0 . -3 • -3 »1,0 • 6» 0 » 3 « -6
2570 DATA 2,1»6»6,0,0,-6
2580 DATA 4,1,2,0,1,0,,'.. 1 , -2,0 , O , 2 ,-6
2590 DATA 5?0,2,0,1,-7,0,1,0»6,1,2»0,0,0»-6
2600 DATA 5,0,0»2,1,6,0,0,0»2»1,-6•0,0,6,-4
2610 DATA 3,1,6,3,1,-6»3,0»6»-6
2620 DATA 3,0,6,6»1»-6,-3,J *6,-3
2630 DATA V,0,3» 1 »1»-.1 ,1 »1»-1 »-l»1 »1 ,-1,3 ,1.1,1,0,2
2635 DATA 1,3,2,1» t,0>0,1,-5
2640 DATA 6.0-1 ,2,1,1,0,1,1, -7,3,1,3 , .1 .1,0,0» 1 » -3
2650 DATA V . 0,4,0,1,0,7,1 ,-2 • 0, .1. - 0 » - 2,1; 2 » 0, 1,0» -7

-159-
2653
DATA
1,-2,
0,
2660
DA 1 A
6,0,2
.6
2670
DATA
9,0,1
, 2
2675
DATA
0,-2,
0 ,
2680
DATA
3,0.6
,0
2690
DATA
A , 0.2
, 0
2710
DATA
6,0,2
, 3
2720
DATA:
? ,0,2
, 2
2725
DATA:
1 - 2 , -
2 • i
- 1
1.1.1» 2» O
.. ^. r¡. ,1
í, 0. ■ 1.2.:!. . -1. 2.0.3 . O
I » I y 1 .Oí-i.-l .1.0.3
» 1 . — 2 » O y.!.» O y .2.1 y 2 . O » 0 y 2 ? — 2
f .1 y O y 3 • O y O y - 1 . 1 » 2.0.1.0» “2.0.2.0
» 1 . O y -5 , O .0.2. .!. y 2 y O y 1 y O . -2.0.2.0
y 1.2.2,0 y 0.-1 y 1 , 2.0.0,0.1
O y — 1 y O y I. , O ,2,0.3" ~~4

-160-
PSTRN.FOR --A program to send sequential data files to
the 11/20 comouter.
:■ iiit.fi::;cut-; i:om cÍÍ2-!: .. „t..t< .1.0.:o :■
LOGICAL
f< 0
II0 3 O r I 1 » 1 0
i Li; A ' i \ 12 0 10 1 ' .
TVPC 10
i.o füuaatí' cue;! fill,- to ¡re?; c;v' •
tv pi:: so
20 F"'i;.:ili-,T( ' ¡GP L.! V;:'; THAI: if. FILLC..: CM TCP ' C ' !■
PciCPT :;o» m : ;■ s- ; !.v:
30 FC.!-:;i.';V (ivY.l;
ir ¡T-;: m
so ccctitje
coo rvrc no
no ru,w-;AT< * Fit.r;mí.; tc
DO j 20 >â–  I - .i. > M
120: T ,122-1 w Li !¡ , - I i v J • . :
1. i r 0!; i i A r \ ' 11 ? i- i.!.)
Fit 130
130 i At :0 1 ’ 21‘■ t f. i-. PC i lCF: f )
i i..i 2 0 0 - On CO
200 F 22: FAT Cl A 4;
1 . L r-i l C.t iliL > M f ¡ ' ) U 2 i C 2
TV PC 2J. C
210 FCTAATi - l CF D.'iTfi PTS< PER FILE'.'
ACCEPT 2201 NPF
220 FüÁiirnT i 17)
HU 10C0»MuM-i if!
hi 230- 1=1 r It
230 - FLiVTPIrr'UF)
L i ■; i. I. ¡ CIA ‘i . V. )
C. ACL \ VC I L 1 : \ -. X....2 i
Ci" L i' * U.': ... ■■■ TYCO; - ' ijLIi ' i , h .CC •GCI. V. I :..! .2CjX'...V 1
DC. 26\>: !■ = .! »;:o
230 :. ' o
pi ...oc-i ;G00«[ i'Ti-rcoo) l_;r ( j ; ;> cvr :■
300 FCi-ilATfC. 3,3)
p.i. oscaiiii i =■■■■; tuc; ccrv- • cap;
E-i.ii= i.i-LT â– . 1 )
pc v-o •• v ijcr-r
ir < pig . it; . tVi'.ur f. i;â–  > r.i.; <â– 
L‘ 11 * ■ iM í .i; 1.i.'
too ct'ci c11::
re 0 G :■ i-i »cc:
t â– â– â–  I ; :..l UI i i / j ' .i Li' i xl / Ui *
•reo i:. fj ;• ja : ¡ • ttt
Lift. J V L, i I.' * 11 : t . 1 !
i .i ;■ •: o. Men
900 r CCmVff ' FILL ' AC ' j G C OT

Pi i3
> 3>IQ.JI I i:.'j
,:jí !:■: i. J.:;
.t i • - i - n r 1
•' : I » > ':; O ,-i I IT,'3
r,f p ■ fin ' i * ;y~ ’ oc'j_;■;!j)
L‘; I -OCIXÜ
( t ..- - >n:iodT ití:j
tit:•• s]. \ ■" i„ 1 :"¡': o ■! x rvrj
•y n'; i j t‘ci:-r op.lxü)-:i
â–  â– . . r:i i.; i -/j';;.
f!1 TO -‘001 f:G
'0, i„ ' r.W.II '! T.'J
;:!■ • I ,!•; i.',i1 3"UI
a:- ¡íi:fi :> jo i ::i ‘in í.iioooms
Oí: J
• afino.f ir)3, .jpjic
, IA:! , J'lJLG
on I,13.1 id 0 j
0 l T
00 OS
000 T
-I9I-

-162-
EC.BAS--A program to
computer and
receieve sequential data from the 11/34
store it in a binary data file.
•OOO PRINT * TRANSFERRING DEC 11/34 DATA FILES TO DEC 11/20 DIR i UAL DATA*
010 PRINT "FILES < MAXIMUM VALUE 32767» MINIMUM VALUE 0)."
015 PRINT *1023 VALUES MAXIMUM TO BE 1RANSFERRED. *
020 PRINT \PRINT
030 PRINT * Hull MANY FILLS TO PC TRANSFERRED ’ * \ INPUT Ml
050 FOR 1=1 ro Ml
060 PRINT 'FILE t * 5IÍ * IS * 5MNPUT L4 < I)
070 PRINT Lid) J * * í “OK CY OR M)*i\INPUT GT
080 IF 04 = * M * GO TO 9060 \NEXT I
100 FOR 1=3 TO N1
105 At- * RL1 : 1 81.4 < I) 8 * . DT *
110 OPEN At FOR OUTPUT AS FILE VF1%<1023>
120 GC3UB 10000
130 CLOSE vl-'l
140 PRINT ‘FILE I d? 8 IS DONE!» 0
100 NEXT I
250 PRINT CRRÍ(7)
100 END.
>000 GO TO 10010
)0.10 ¡1=0
,020 DIM A(15)â– B <15)
3040 CALL *INPB* )050 IF B<1) = 100 TO 10050
)055 IF B (2) = 3.GO TO 10200 \G0 TO 10040
)060 CALL *DIRA*(IsCrZ)
1064 VF1 (N)--C
1065 N=N+1
>070 A í 1) =1\CALL “ PI.SB * (A)
'080 CALL * INPBdR)
085 IF B< 1 ) = 100 TO 10000
090 Ad ) = 0\CALL *PLSB " < A)
100 GO TO 10040
200 PRINT N
250 N=0
300 RETURN

OUTPLT.BAS —A program to plot X-Y data
1 DIM B<15)
2 22=250
5 DEF FNA000/4.75
20CO DIM X(256)>Y(256>
2010
PRINT
*i• i» frame* ; \tnput 39$
2020
UFEN ¿
'?$ FOR I NT'! I !' AS FILE â– ! 1
2030
INPUT
tl t 7.n$ , 7? / X7 i XA r Y7 y Y6
20---0
PRINT
ZÃœi v 7 9 :â–  X7 . X6, Y7 , Y6
2050
FOR 1 =
â– 1 TO 7.9
20ft0
INPUT
u:xu)fY(I)
2110
NEXT I
2120
CLOSE
«- •<
2130
A$ = ' I '
SGÃœSUB 4000
2140
PRINT
■x SPAN IS "ÍX7--X6
2150
PRINT
•Y SPAN IS *;Y7-Y6
2155
PRINT
* LO’v'ES f X V11LUL * yXó
2156
PRINT
â–  LOSES i" Y VALUE ' ? Y6
2160
PRINT
■NOftrlAI 17.E X SPAN TO HUM MANY INCHES" Í \INPUT
C4
2170
PRINT
’NORMALIZE Y SPAN TO HQU MANY INCHES*5\INPUT
04
2210
PRINT
•BRAN AXL S">\INPUT A9$
nOOQ
IF A??
Y “ GO TO 2240
2222
60S U 3
4 900 \ X1 F U A <1.2 5 í C 4 ) \ G 0 S ü B 5000
2225
X1=0\S
OSIJB 4950 \G05UB 5000
2220
GO SUB
4900 \Y1.----FNA (.1. .25*04>\GOSUB 5000
2232
Y1*0\G0£U?: 4 950 \GOSUD 3000
22X0
PRINT
â– OFFSET X HOW MANY INCHES"j\INPUT XI
2242
PRINT
•OFFSET Y HOW MANY INCHES*?\INPUT Y1
2244
XI -'FNA
< a 1 ) \ Y1 = FNA < Y J. )
2246
GOSUB
5000
2247
C6=C\Dó=0
2250
PRINT
* SYMBOL CHOICE?0
2260
PRINT
•AVAILABLE SYMBOLS AREi■
2270
PRINT
"SÃœUARE "
2275
PR 1 NT
“CIRCLE 2280
PRINT
• 1 Fv3 A.NGI. 1.-'. UP < T1 ) “
276Í"*
PRINT
’ TRIANGLE DOWN 2 2 y f,
PRINT
â– TRIANGLE RIGHT 2 2 9 f;
PRINT
â– TRIANGLE LED < T-1) *
2300
PRINT
•CROSS (CR)'
2305
PRINT
L- 1.
2310
PRINT
■STAR < S r ) “
2315
PRINT
"DOT (D >‘
2320
PRINT
"CHOICE ‘ > \ .I NTT IT A'E
2325
PRINT
■WHAT IS THE DTMENS 10! 1 “> yINPUi 02<1>\Q2<2>=02<11
2330
FOR T=
1 TO 79
734 0
X1 = < X <
1 >-X6mn.‘: 2350
Y J . = ( Y a ■> - Y6 ) HA (Ui)/< Y 7-Y6 H RÓ

-164-
2360 COSUB 5000
2370 GOSUB -1000
2380 NEXT T
2385 CALL 'SI EP"<-C» 30 »1)\CALL ‘STEP*<-D>30*0)
23SÓ C=0\D=0
2390 PRINT 'WOULD YOU LIKE TIC MARKS'Í\INPUT V9*
2400 IF V9Í-0 “ Y “GO TO 2430
2410 PRINT “X VALUE (-999 FOR Y VALUES>"?\1NPUT MS
2411 IF K8--999GÜ TO 2430
2415 Y1 = O\X1 - < M8-X6 ) *F'NA (C4 ) / ( X7-X6 ) -! C&
2416 GOSUB 5000 \G03UB 4900 \X1= C\Y1~-20\G0SU3 5000
2417 GOSUB 4950 \Y1=0\G0SUB 5000
2418 GO TO 2410
2430 PRI NT *Y VALUE (-999 FOR CONTINUE>*5\INPUT NO
2431 IF NO--999GQ TO 2470
2435 X1 ~0\Y1. - (N8-Y4 > í'FNA (D4 ) /( Y7-Y6 ) +.06
2436 GOSUB 5000 \GOSUB 4900 \Y1 =D\X:L = -2O\G0SUB 5000
2437 GOSUP 4950 \X1=0\GOSUB 5000
2438 GO tO 2430
2470 X1=0\Y1=0\GOSUD 5000
2480 PRINT ‘ANOTHER PLOT (Y OR N> *?\INPUT A9$
2490 IF A9*“ * Y ‘ GO- TO 2010
2500 END
This section is followed by the best-line routine.

-165-
LASPLT . BAS--A program to
pseudo-three
plot laser intensity
dimensional manner.
i n a
900 DIM 11(15)
1000
r-R T NT
â– x SIZE " r M NI-'LJT
1005
PKi NT
•Y SIZE* íMí.T'UT
1010
FT,! N T
•z GI/K* ; Mill TIT
1015
PR T N 1
“ANGLE”> MNP LIT
1030
GO SUB
4900
1035
Xl=2«>
I5\803UB 5000
10-10 XI---'O\GOSlJi-': 5000
1045 Yl-2*Z5\Gl)5UB 5000
1050 Yl=0\G08Ut: 5000
1055 XI =-:.># x5
105é ¡VW?5S2*3.14159/360
1057 Y1=aj*SIN
1060 (iOSUB 5000
1065 50SUB 4950
1100 YO-O
1300 FOR T8 = 1 TO ¿>8
13 .a 0 R : A I.i X i Y - Z
1350 IF Y= YOGO 10 1400
1360 G OS LIB 4950
1400 Yi~(Y*SIH 1450 X1 - ( Y*COS< A5&2*3.14.1.59/360) *Y5/12) 1 XSX5/12
1460 YG~Y
1500 GCiSUB 5000
1510 GGSUB 4900
1520 NOT TO
1530 GOSUB 4950
1550 X1 -'0\Y.1 -0\• 0SUB 5000
1600 END

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BIOGRAPHICAL SKETCH
James Neill Bower was born March 30, 1950, in Ithaca, New York.
After graduating from the local excuse for a high school, he attended
Cornell University, there learning several important lessons in
abnormal psychology. After holding several jobs, including one at
Cornell University, he returned to school at U.F., where he learned
a good deal about bureaucracy (as well as a good deal about analytical
chemistry).
-170-

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
8 D
Dr.^J.D. Winefoy'aner, Chairman
Graduate Research Professor of
Chemistry
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Associate Professor of Chemistry
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.

I certify that I have read this study and that iri my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Dr. P. Urone
Professor of Environmental Engineering
Sciences
This dissertation was submitted to the Graduate Faculty of the Department
of Chemistry in the College of Liberal Arts and Sciences and to the
Graduate Council, and was accepted as partial fulfillment of the re¬
quirements for the degree of Doctor of Philosophy.
December 1979
Dean, Graduate School

UNIVERSITY OF FLORIDA
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