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A parametric study of a transverse gas flow TEA CO2 laser Laidley, Thomas Edward 1973

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A PARAMETRIC STUDY OF A TRANSVERSE GAS FLOW TEA  C0 2 LASER by  THOMAS E. LAIDLEY B.Sc., M e m o r i a l  University  o f Newfoundland,  1971  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in  the  Department of PHYSICS  We a c c e p t required  this  thesis  as c o n f o r m i n g  to  standard  THE UNIVERSITY  OF BRITISH COLUMBIA  June,  1973  the  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y  a v a i l a b l e f o r r e f e r e n c e and  I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e f o r s c h o l a r l y purposes may by h i s r e p r e s e n t a t i v e s .  copying of t h i s  be g r a n t e d by the Head of my  thesis  Department or  I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l  g a i n s h a l l not be a l l o w e d w i t h o u t  written permission.  Department o f The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada  Date  study.  my  ABSTRACT  A t r a n s v e r s e gas flow TEA C0 2  laser  has been  c o n s t r u c t e d and the use of a p e r f o r a t e d hollow rod to serve s i m u l t a n e o u s l y as the cathode of the d i s c h a r g e and the gas i n l e t vessel was s u c c e s s f u l l y The e l e c t r i c a l typically  demonstrated.  e f f i c i e n c y of the l a s e r i s  3% with peak powers of 40 kw being emitted on  the P ( 2 0 ) , P(18) and P(16) l i n e s of the C0 2  spectrum.  A parametric study of peak power, gas p r e s s u r e , gas comp o s i t i o n , time delay of the l a s e r pulse and the i n t e r dependence of these q u a n t i t i e s  was  undertaken.  TABLE OF CONTENTS  Page ABSTRACT  i i  LIST OF TABLES  v  LIST OF FIGURES  vi  ACKNOWLEDGEMENTS  ,  viii  Chapter 1  2  3  INTRODUCTION  1  1.1  P r o p e r t i e s of C0 2 Lasers  1  1.2  Arrangement of T h e s i s  5  ELECTRODE DESIGN AND LASER CONSTRUCTION . . . .  7  2.1  E l e c t r o d e Design  7  2.2  Laser C o n s t r u c t i o n  . . . . .  2.2.1  Reaction  tube  2.2.2  Electrodes  2.2.3  Gas supply  2.2.4  Laser c a v i t y  13 13 14  and e x t r a c t i o n  17 18  CARBON DIOXIDE LASERS  21  3.1  21  Vibrational  Energy L e v e l s of C0 2  i ii  Chapter  4  Page 3.2  E x c i t a t i o n and I n v e r s i o n i n C0 2  24  3.3  Present  28  S t a t e of the A r t  CHARACTERISTICS OF LASER  31  4.1  A l i g n i n g C0 2 Laser  31  4.2  Operating  34  4.3  Conditions  4.2.1  The e l e c t r i c a l  system  .  4.2.2  E f f e c t of gases and p r e s s u r e . . . .  34 36  P r o p e r t i e s of System  40  4.3.1  Power decay i n a c l o s e d system. . .  40  4.3.2  Electrical  42  4.3.3  Time delay of pulse  45  4.3.4  Spectral analysis  48  efficiency  5  CHEMICAL  LASER. . .  6  CONCLUSIONS AND FUTURE IMPROVEMENTS  REFERENCES  50 55 58  APPENDICES A  INFRARED DETECTORS  62  B  SPECTRAL ANALYSIS  74  i v  LIST OF TABLES  Tab! e I  Page Induced V i b r a t i o n a l R e l a x a t i o n Rates of the C0 2 v and v Modes i n the Presence of Other Gases at 300°K  26  Gas Mixtures and Operating C o n d i t i o n s f o r Chemical Laser  51  A-l  C h a r a c t e r i s t i c s of I n f r a r e d D e t e c t o r s  67  B-I  Spectral  3  II  2  Lines Used f o r Spectrometer  Calibration  77  B-II  Raw  79  B-IH  I d e n t i f i c a t i o n of C0 2  B-IV  C0 2  Data from S p e c t r a l A n a l y s i s Lines  Laser T r a n s i s t i o n s  v  . . .  81 82  LIST OF FIGURES  Figure  Page  1.  Gas Flow i n C0 2  Lasers  4  2.  C r o s s - S e c t i o n Through C y l i n d r i c a l Test Chamber and Schematic View of Discharge Circuit  8  3.  Spark Channels i n Text Chamber  10  4.  Multiframe Exposure to Test ofDischarge  13  5.  Reproducibility  Brewester Angle Mount and Gas  Inlet  Coupling  15  6.  Cross-Sectional  7.  Electrical  8.  Vacuum System  19  9.  Vibrational  21  10.  View of Reaction Tube  System  16 17  Modes of C0 2  Energy Level Diagram f o r C0 2 and N 2 (showing only those v i b r a t i o n a l l e v e l s important f o r C0 2 l a s e r s )  23  11.  Rotation-Vibration Transistions  24  12.  Alignment System  31  vi  Figure 13.  Page M u l t i p l e Lasing with Low Net Round TripGain  33  14.  C0 2 Pulse Shape Parameters  33  15.  Spark Channels and Laser Pulses  35  16.  C0 2 Laser Pulse with Gas A d d i t i v e s  37  17.  Peak Power v s . T o t a l  39  18.  Power Decay i n Closed System  41  19.  Electrical  E f f i c i e n c y Curve  44  20.  Time Delay  v s . Total  46  21.  Modulation  of C0 2 Laser Pulse  A-l  Photoconductive  A-2  Au-Ge Detector C i r c u i t ; Output v i a 50ft Cable Response of I n f r a r e d D e t e c t o r s to a  68  C0 2  69  A-3  Pressure  Pressure. . .  Detectors  48 64  Laser Pulse  A-4  Au:Ge Power Detector Output  70  A-5  Near F i e l d  72  B-l  Spectrometer  B-2  S p e c t r a l A n a l y s i s Arrangement  R a d i a t i o n P a t t e r n of Laser Calibration  vi i  Curve  76 78  ACKNOWLEDGEMENTS  I would l i k e to take t h i s o p p o r t u n i t y to Dr. Boye Ahlborn f o r suggesting and  patiently  thank  supervising  the t o r t u r o u s course of t h i s work. On more than one o c c a s i o n my  s a n i t y has  been  preserved by Dr. Shigeo Mikoshiba and o t h e r members of the Plasma Physics group and to  extend my  heartiest  Many thanks his  to these people I would  thanks. a l s o go out to Mr. Dick Haines f o r  workshop i n s t r u c t i o n  and  assistance.  I would a l s o l i k e to thank  Frances f o r p u t t i n g  up with me when things went bad, f o o t i n g telephone b i l l s  like  those  large  and not c a r r y i n g out her t h r e a t of  divorce. The  final  p r e p a r a t i o n of t h i s t h e s i s was  p l e t e d with Dale Stevenson  at the d r a f t i n g  Shari H a l l e r at the t y p e w r i t e r Financial Council  table  com-  and  keyboard.  a s s i s t a n c e from the N a t i o n a l Research  is gratefully  acknowledged.  T h i s work i s supported by a grant from the Atomic Energy  Board of Canada.  vi i i  Chapter  1  INTRODUCTION  This t h e s i s C0  2  l a s e r c a r r i e d out  in the not  d e s c r i b e s a parametric study of a to a c q u i r e knowledge and  o p e r a t i o n of molecular l a s e r s and  previously  o b t a i n the  lasers for future  use,  as chemical a c t i v a t i o n  and  Infrared  2  the  aim  reasons:  maximum of 41%  * is  application  of  such  to design a l a s e r as  well  possible.  Lasers  lasers  The  In order to  study of e l e c t r i c a l  have a t t r a c t e d  in communications, plasma physics and several  detectors,  approach with modest means as  high average l a s e r powers as  P r o p e r t i e s of C0  i n the  i t was  c a v i t y which would allow the  1.1  infrared  studied in t h i s laboratory.  highest f l e x i b i l i t y  experience  strong  spectroscopy  e f f i c i e n c y i s high  ) because the  interest  energy of the  for  (theoretical upper l a s e r  Quantum e f f i c i e n c y of 00°l-02°0 t r a n s i s t i o n  41%.  1  2  level  i s only ~ 1/3 ev above the ground l e v e l .  d i f f e r e n c e between the upper l a s e r l e v e l lower l a s e r l e v e l length  ( 0 0 ° 1 ) and the  ( 0 2 ° 0 ) i s a l s o r a t h e r small  (10.6u) f a l l s  The energy  so the wave-  i n the 8-13u r e g i o n where there i s  an atmospheric window making the C02 l a s e r a t t r a c t i v e f o r communications purposes.  The long wavelength of i n f r a r e d  radiation  i s a l s o d e s i r a b l e and b e n e f i c i a l  for inter-  ferometry  i n l a s e r s c a t t e r i n g experiments and the produc-  t i o n of plasmas. Laser emission both  continuous  lation  inversion  by e l e c t r o n expansion (N 2  from C0 2 has been obtained i n  wave (cw) and pulsed o p e r a t i o n . necessary  The popu-  f o r l a s e r a c t i o n can be obtained  impact ( e l e c t r i c a l  d i s c h a r g e s ) , supersonic  (Laval n o z z l e s ) and resonant  energy  transfer  or D F ) . For the case of e l e c t r o n  impact the parameter  E/N governs the e f f i c i e n c y of the l a s e r porportional  i n an e l e c t r i c  with n e u t r a l p a r t i c l e d e n s i t y N. f o r any e l e c t r i c a l l y  field  E,  In theory E/N may be  e x c i t e d C02  p r a c t i c e t h i s has only been achieved  l a s e r but i n  i n TEA ( T r a n s v e r s e l y  E x i t e d at Atmospheric P r e s s u r e s ) l a s e r s . configuration  E/N i s  to the energy e l e c t r o n s a c q u i r e , on the  average, between two c o l l i s i o n s  optimized  [1,2].  Such a TEA l a s e r  c o n s i s t s o f a m u l t i s p a r k d i s c h a r g e at r i g h t  3  angles  to the l a s e r r e s o n a t o r a x i s , as w i l l  be d e s c r i b e d  l a t e r i n more d e t a i l .  This type of l a s e r has  to  i n v a r i o u s chemicals  obtain laser action  reactions  [4]-[7].  at the end  TEA  of the present The  several  The  f i r s t C02  t o r r and  l a s e r stands  by  chemical  in another  development of C 0 2  l a s e r s operated  been used  respect  lasers.  at pressures  used r . f . or a.c. e x c i t a t i o n  of  between  e l e c t r o d e s at o p p o s i t e ends of a glow d i s c h a r g e tube. the l a s e r had  a f l o w i n g gas  system the input and  exhaust  ports were i n v a r i a b l y at o p p o s i t e ends of the tube so gas  flow was  l o n g i t u d i n a l , Figure 1 ( a ) .  pumping systems t h i s arrangement had tages:  Dissociation  products  itself  definite  o p e r a t i o n and  the f l e x i b i l i t y  as well as chemical  in most devices with  longitudinal  r a t e i s not very high and  one  in c o n s t r u c -  of being able to activation.  flow the gas  et al.  [ 7 ] with t r a n s v e r s e gas  the ground e l e c t r o d e improves t h i s the cost of a r a t h e r complicated 1 (c).  However,  exchange  cannot expect a high  r a t e or high average powers, F i g u r e 1 ( b ) .  by Ahlborn  disadvan-  the heating of the  arrangements combine s i m p l i c i t y  obtain e l e c t r i c a l  tion  For low c a p a c i t y  reduces the gain of the l a s e r [ 1 0 ] . TEA  t i o n and  the  formed i n the d i s c h a r g e were  not removed q u i c k l y enough [ 8 , 9 ] and gas  two  If  flow  repeti-  A device through  s i t u a t i o n , but only at  c o n s t r u c t i o n , Figure  Figure (a) (b) (c) (d)  1.  Gas  Flow  i n C0  2  Lasers.  longitudinal flow, longitudinal discharge longitudinal flow, transverse discharge transverse flow, transverse discharge s i m p l i f i e d v e r s i o n of (c) t e s t e d i n t h i s t h e s i s  5  The with  aim  of t h i s  t r a n s v e r s e gas  construction:  [ 7 ] and  with  small  Figure 1 ( d ) , activating holes  flow but with  gas  the c o n t e n t i o n  being  i n l e t tubes of bar  the pin e l e c t r o d e s ,  that the e x c i t i n g  would i s s u e e x a c t l y from  i n the ground e l e c t r o d e and was  laser  a greatly simplified  i n l e t holes o p p o s i t e  the replacement gas  1.2  a TEA  r e p l a c i n g them by a hollow ground  t r a n s v e r s e sparks  where i t was  to design  e l i m i n a t i n g the 200 gas  reference very  t h e s i s was  hence guarantee  f l o w i n g e x a c t l y i n t o the  or the  that region  needed.  Arrangement of T h e s i s The  o r g a n i z a t i o n of t h i s t h e s i s r e f l e c t s  purpose of the work: design  a l a s e r and  Test a new  the  electrode configuration,  study i t s performance.  Chapter 2 d i s c u s s e s p r e l i m i n a r y experiments hollow ground e l e c t r o d e s and from these  initial In order  to a p p r e c i a t e the performance of  knowledge about C 0 2  l a s e r s , which may  f o r someone j u s t g e t t i n g i n t e r e s t e d i n t h i s  and we  t r y to show the l i m i t s of the present laser.  this  have summarized in Chapter 3 some of  useful  of t h i s  derived  experiments.  newly designed l a s e r , we the standard  gives the l a s e r design  with  be field  understanding  6  Chapter 4 begins with t y p i c a l " t r i c k s of the t r a d e " and procedures and  experimental  to operate the l a s e r  then gives the parametric study of the d e v i c e operated  as a t r a n s v e r s e l y pulsed C 0 2 l a s e r . Chapter reactions and  5 d e s c r i b e s attempts  to o b t a i n  chemical  6 discusses conclusions  i n the c a v i t y and Chapter  suggestions f o r the p o s s i b l e improvement of the d e v i c e .  * Many experimental the appendices  details  are contained i n  i n order not to load the main body of the  t h e s i s with too much d e t a i l . which are standard knowledge but may save a f u t u r e i n v e s t i g a t o r much t i m e .  Chapter 2  ELECTRODE DESIGN AND LASER CONSTRUCTION  2 .1  E l e c t r o d e Design It i s attempted i n t h i s work to c o n s t r u c t a TEA  l a s e r with  t r a n s v e r s e gas flow using  the gas through holes the spark c h a n n e l s .  the idea of i n j e c t i n g  i n a hollow ground bar d i r e c t l y To a s c e r t a i n the f e a s i b i l i t y  idea a study of the behaviour of spark channels by a d i s c h a r g e  into  of t h i s  created  between a chain of r e s i s t o r pins and a  hollow ground rod with many holes was undertaken i n a small  s c a l e experiment.  For t h i s  purpose the t e s t chamber  shown i n Figure 2 was c o n s t r u c t e d . The enclosed  chamber was made e n t i r e l y of l u c i t e and  an evacuated c y l i n d r i c a l  12 cm i n d i a m e t e r . two staggered resistors. was f i x e d  r e g i o n 7 cm high and  On the top p l a t e of the chamber i n  rows of 10 were place 20, 1 kfi each,  The i n t e r e l e c t r o d e d i s t a n c e , A (see F i g u r e 2 ) , at 0.5 cm f o r each ground rod c o n s t r u c t e d and  the r e s i s t o r s were vacuum s e a l e d using Apezion Q-compound.  7  F i g u r e 2.  C r o s s - S e c t i o n Through C y l i n d r i c a l T e s t Chamber and Schematic View Discharge C i r c u i t .  of  9  The  hollow  ground bar to be t e s t e d was  chamber a f f i x e d to  to the bottom p l a t e and  the r e s i s t o r p i n s .  was  fixed  placed i n s i d e  at 2.54  The  aligned p a r a l l e l  cathode-anode s e p a r a t i o n , d,  cm f o r each ground rod t e s t e d .  Twenty  small holes were made in the top of the ground b a r , o p p o s i t e each r e s i s t o r p i n . was  two-fold:  flow.  to l o c a l i z e  Since a sharp  large e l e c t r i c f i e l d  The  purpose of these  the arcs and  edge has  a small  thus  one  holes  i n j e c t the  gas  r a d i u s of c u r v a t u r e ,  s t r e n g t h s are p r e f e r e n t i a l l y  at the l i p of the holes and  created  the d i s c h a r g e from  the  legs of the r e s i s t o r s would s t r i k e the edges of the as shown i n Figure 2.  the  holes,  At the same time i t i s p o s s i b l e to  have a flow of g a s , in t h i s case a i r , from the atmosphere, through channels through  the holes i n the hollow  ground b a r , i n t o the  a f t e r which i t i s evacuated from the chamber a hole i n the top p l a t e by a mechanical  forepump.  Photographs of the d i s c h a r g e were taken a p o l o r o i d Land camera with a close-up film  type 47, 3000 speed.  analyzed  spark  f o r u n i f o r m i t y and  charge p a t t e r n .  The  lens and  polaroid  photos were q u a l i t a t i v e l y  r e p r o d u c i b i l i t y of the  In a d d i t i o n the r e p e t i t i o n  measured using a Rogowski c o i l dual-beam o s c i l l o s c o p e .  using  and  rate  a type 551  3.  was  Tektronix  A photograph of a t y p i c a l  charge p a t t e r n i s shown in F i g u r e  dis-  dis-  Figure  3-  Spark Channels C h a m b e r a t 100  in Test Torr.  Two d i f f e r e n t hollow grounding The  rods were t e s t e d .  f i r s t was c o n s t r u c t e d of 1/32" t h i c k copper  sheet,  10 cm l o n g , which was bent and s o l d e r e d i n t o a t r a i n g u l a r cross-section.  The holes to serve as gas i n l e t s were  made by simply puncturing  the copper sheet with a n a i l ,  from the i n s i d e , so that the r e s u l t i n g directed  towards the r e s i s t o r p i n s .  cylindrical  copper pipe  sharp  The second rod was a  (3/4" i . d . , 7/8" o . d . ) , a l s o 10 cm  l o n g , with 20 holes made with #65 d r i l l The d i d indeed  spark channels  preferentially  s t r i k e the l i p s of the holes  to i n t e r f e r e with one a n o t h e r .  pins and the small Since t h i s complicated  b i t (0.035").  produced with these e l e c t r o d e s  in the ground bar but the spark channels  to some i r r e g u l a r i t i e s  had some tendency  T h i s was probably due  i n the spacing o f the r e s i s t o r  i n t e r - e l e c t r o d e d i s t a n c e , A, used.  i n t e r f e r e n c e was more n o t i c e a b l e with the more t r i a n g u l a r l y shaped ground b a r , a l l f u r t h e r  observations made here were c a r r i e d out with drically  edges were  the c y l i n -  shaped ground b a r , which i s shown i n F i g u r e 2.  11  The spark channels of  were photographed at pressures  .2, 60 and 100 t o r r , as measured by the Speedivac  gauge, with and without to be no d i f f e r e n c e s  the a i r f l o w i n g .  vacuum  There appeared  i n the symmetry of the spark  with the a i r s t a t i c and f l o w i n g at the pressures  channels used.  The e f f e c t of a i r pressure though was q u i t e pronounced. At p r e s s u r e s of .2 t o r r the e n t i r e region between the cathode and anode i s i o n i z e d and there are no d i s t i n c t spark c h a n n e l s . sparks  For pressures of 60 and 100 t o r r  are e v i d e n t with those of 100 t o r r being more  At higher pressures the number of spark channels until at  individual  t h e r e i s a s i n g l e arc and f i n a l l y  uniform.  decreases  no a i r breakdown  all. For these experiments we used the breakdown  v o l t a g e s of 14, 17 and 24 kv.  The l a r g e r the v o l t a g e the  higher the pressure a t t a i n a b l e before the a i r ceases to break down. torr.  At 24 kv the h i g h e s t pressure measured was  The negative d.c. p o t e n t i a l  160  used to break down  the a i r was a p p l i e d to the r e s i s t o r chain and a l s o to the hollow ground r o d .  However, t h i s only a f f e c t e d the  d i s c h a r g e p a t t e r n at low p r e s s u r e s .  When the high v o l t a g e  was a p p l i e d to the r e s i s t o r chain each r e s i s t o r l e g developed nected on  a corona whereas when the hollow  to the high v o l t a g e i t e x h i b i t e d  i t s surface.  rod was  con-  3 to 4 hot spots  12  The  values of R and  c i r c u i t were also v a r i e d . c a p a c i t a n c e s of 5 and of R and  0.5  C used in the d i s c h a r g i n g  R e s i s t a n c e s of 10 and nF were used.  C d i d not a f f e c t the spark  changed the d i s c h a r g e r e p e t i t i o n gap was <<  20 Mfi and  These v a r i a t i o n s  channel  rate.  patterns  Since the  but  spark  not e x t e r n a l l y t r i g g e r e d and  the d i s c h a r g e  time  the charging t i m e , the r e p e t i t i o n  r a t e i s given  by:  S.G  f = 1 - RC £n  where:  (2.1)  V. -  = breakdown v o l t a g e of spark  V0  = power supply  voltage.  The maximum r e p e t i t i o n obtained was sec.  The  260  pulses/  r e p r o d u c i b i l i t y of the d i s c h a r g e up to the  highest r e p e t i t i o n camera q u i c k l y with  r a t e was  verified  the s h u t t e r open.  p r i m i t i v e smear camera technique purposes.  gap.  The  by r o t a t i n g  This i s a rather  but adequate f o r our  photograph shown i n F i g u r e 4 was  in t h i s f a s h i o n .  the  obtained  Figure  2.2  Laser  p r e l i m i n a r y s t u d i e s of m u l t i - s p a r k  to the f o l l o w i n g 1.  Holes  the  spark channels  gas  fIow. 2.  or  M u l t i f r a m e Exposure to Test R e p r o d u c i b i l i t y of Discharge.  Construction The  led  4.  anode a t  the  bar  The  conclusions: in  the  quite  hoi low  pressures  developes  discharges  hollow  a  bar  localized  w e l l , with  and  without  transverse  ground  may  be  as  above 60  only  ground  few  rod torr.  spots  At  used  lower  if operated  cathode  pressures as  the  a node. 3. repetition  The  rates  discharge of  at  E n c o u r a g e d by laser with  a perforated  wise standard  2.2.1  Reaction  least  260  is  reproducible  Hz.  t h e s e r e s u l t s we hollow  at  bar  designed  electrode  a  i n an  TEA other-  arrangement.  tube.  A lucite was  pattern  used t o c o n t a i n  tube (2.5" the  i . d . , 3.0"  o.d.)  l a s e r ' s a c t i v e medium.  1.2  m  long  Flanges,  14 a l s o made of l u c i t e , were cemented to each end of the tube. Potassium c h l o r i d e ( K C £ ) windows  (2" <j>) were placed on  Brewster  at each end of the tube  and  angle mounted supports  were 0-ring s e a l e d by the pressure  d i f f e r e n t i a l between  the atmosphere and the gas mixture i n the tube. gas  into  the tube a brass  end  (see Figure 5 ) .  c o u p l i n g was attached  To feed to one  To ensure mechanical s t a b i l i t y the r e a c t i o n tube was secured  to a 2.13 m long s t e e l  to a 2.5 m long s t e e l  frame.  I-beam which was b o l t e d  T h i s arrangement proved to  be q u i t e adequate.  2.2.2  Electrodes. The  Allan  Bradley  parallel  anode of the d i s c h a r g e resistors  (they l a s t l o n g e r ! )  and mounted i n two staggered  top of the r e a c t i o n t u b e .  the r e a c t i o n tube through holes  5 mm  apart and are vacuum sealed with  connected i n  rows of 100 on the  The r e s i s t o r  into  and  i s composed of 200-lkfi-lw  legs  protrude  (#53 d r i l l  b i t ) spaced  S i l a s t i c TRV cement  Apezion Q-compound. Using  the r e s u l t s  of our p r e l i m i n a r y s t u d i e s a  copper rod (3/4" i . d . , 7/8" o.d.) 1.14 m long with holes The  (0.01" <|>) at i n t e r v a l s  rod was a l i g n e d p a r a l l e l  adjusted  so the r e s i s t o r  200  of 5 mm was used as the cathode. to the r e s i s t o r s  legs were o p p o s i t e  pins and  the holes i n  cn  Figure  5.  Brewester  Angle  Mount  and  Gas  Inlet  Coupling.  the  copper r o d .  ground the  The rod i s e l e c t r i c a l l y  through the brass c o u p l i n g  reaction  A cross-sectional  in Figure  used to feed  gas  into  tube.  The cathode-anode cm.  connected to  separation  was  view of the r e a c t i o n  f i x e d at d = 1 . tube i s shown  6.  Figure  6.  Cross-Sectiona1 R e a c t i o n Tube.  View o f  17  The  c i r c u i t used to i n i t i a t e  s i m i l a r to the one is  used i n our f e a s i b i l i t y  shown i n F i g u r e 7.  firing  25  the spark  gap.  M  SPARK GAP  No e x t e r n a l t r i g g e r  Figure 7.  2.2.3  Gas  supply and The  tube i s found  s t u d i e s and i s used f o r  E l e c t r i c a l System  extraction.  flow r a t e of each gas  that enters the  by making use of the P o i s e u i l l e  From i t s storage c y l i n d e r the gas tube, 5 cm  the d i s c h a r g e i s  effect.  flows through  l o n g , with the r e s u l t i n g  reaction  a capillary  pressure drop across  the tube being measured by a U-shaped manometer with 76 long arms. and  3.0  mm  Using c a p i l l a r y tubes  of r a d i i  0.5,  with n-butyl p h a t h l a t e (p = 1.047  p o s s i b l e to o b t a i n flow r a t e s from 10""  l/sec  1.0,  cm  2.0  gm/cc) i t i s to 102  i/sec.  18  The flowmeter board c o n s t r u c t e d was comprised of f o u r such manometers. From the flowmeter board the gases enter a mixing tank and then enters the r e a c t i o n mentioned  brass c o u p l i n g .  tube through the a f o r e -  A small  piece of 1/2"  polyflo  connects the brass c o u p l i n g to the copper tube used as cathode. The used gas i s e x t r a c t e d through 20 exhaust ports  (3/8" i.d.) spaced at i n t e r v a l s of 4.8 cm along the  t o p s i d e of the l u c i t e tube (see Figure 6) by a mechanical forepump. in  An o v e r a l l  view of the vacuum system i s shown  F i g u r e 8.  2.2.4  Laser c a v i t y . The 2 m long l a s e r c a v i t y , d i s c u s s e d  detail  i n S e c t i o n 4.1  coated concave m i r r o r  i n more  (see F i g u r e 1 2 ) , c o n s i s t s o f a gold (100%, R = 10 m) and a Germanium  f l a t with an e x p e r i m e n t a l l y measured t r a n s m i s s i v i t y of 8% at 10.6u. are  held  Both m i r r o r s forming the r e s o n a t o r  cavity  i n Lansing mounts (3 min of arc adjustments) and  have apertures of 2.5 cm.  Beam waist c a l c u l a t i o n s  that more than 99% of the r a d i a t i o n Germanium f l a t  f a l l s within  i n c i d e n t on the  i t s aperature.  indicate  0-760 torr SPEEDIVAC  0-100 torr SPEEDIVAC  C02 N  2  > >  HYVAC 14  He  .20 P0LYFL0 GAS EXHAUST TUBES 3/8"I.D.  99 CAPILLARIES  r MIXING TANK  LASER  FLOWMETER BOARD 200 HOLES 0.01 D.  Figure  Vacuum S y s t e m .  20  Before going of our l a s e r  i n t o d e t a i l s of the c h a r a c t e r i s t i c s  i t i s useful  knowledge of C0  2  lasers.  to summarize some of the standard A reader who  i s already f a m i l i a r  with t h i s background i n f o r m a t i o n can s k i p the next chapter and  turn to Chapter 4 where the experimental  r e s u l t s of  the t r a n s v e r s e flow t r a n s v e r s e d i s c h a r g e l a s e r are p r e sented  and d i s c u s s e d .  Chapter 3  CARBON DIOXIDE LASERS 3.1  V i b r a t i o n a l Energy Levels Carbon d i o x i d e  of CQ2  i s a l i n e a r , symmetric, t r i a t o m i c  m o l e c u l e , which can v i b r a t e i n three d i f f e r e n t modes: the  l o n g i t u d i n a l symmetric s t r e c h mode ( v i ) ( F i g u r e  the  bending or deformational mode ( v 2 ) ( F i g u r e  the  asymmetric strech mode ( v 3 ) ( F i g u r e 9 ( c ) ) . The  Wffl  (a)  f l ?  _  (b)  9 ( b ) ) , and  SYMMETRIC  { )  STRETCH  BENDING  (0,l£\0)  4fe (  •  Figure  J  ^  ASYMMETRIC STRETCH  (0,0,2/^}  9.  V i b r a t i o n a l Modes o f C 0  21  9 (a)),  2  molecule can v i b r a t e i n more than one mode at the same time and possess more than one quantum of v i b r a t i o n a l energy i n each mode.  The v i b r a t i o n a l  l e v e l s are normally  designated by four numbers r e p r e s e n t i n g the number of vibrational  quanta of each mode a s s o c i a t e d with that l e v e l  and w r i t t e n  i n the order ( v i , v i , v 3 ) , where £ r e p r e s e n t s  the  number of quanta of angular momentum a s s o c i a t e d with  the  bending mode. The C0 2 energy l e v e l s of prime importance i n  l a s e r a c t i o n are shown i n Figure 10 with t h e i r scopic c l a s s i f i c a t i o n s .  Rotation-vibration  from the ( 0 0 ° 1 ) v i b r a t i o n a l  level  spectro-  transistions  to the ( 1 0 ° 0 ) l e v e l  form the 9.6u* band and those from  ( 0 0 ° 1 ) to ( 0 2 ° 0 ) the  10.6u band, using the n o t a t i o n of [21]. The l i n e s i n a r o t a t i o n a l - v i b r a t i o n a l are  designated by P ( J ) , Q(J) and R ( J ) , where J i s the  rotational  quantum number of the 1ower l e v e l of the  transistion.  The P, Q and R branches are d e s t i n q u i s h e d  from each other by the r o t a t i o n a l  transistion  r u l e AJ = -1, 0 and +1 r e s p e c t i v e l y For  selection  (see Figure 11).  a l i n e a r , symmetric molecule l i k e C02 the r o t a t i o n -  vibration  and  spectrum  spectrum i s g r e a t l y s i m p l i f i e d .  There are no  This band a r i s e s due to mixing of the ( 1 0 ° 0 ) ( 0 2 ° 0 ) s t a t e s caused by Fermi resonance.  CARBON  10.  DIOXIDE  NITROGEN  E n e r g y L e v e l D i a g r a m f o r CO, M t u . only those v i b r a t i o n a l levelV? 9 C0 lasers). 'evels important f o r 2  d  2  C  ,  o  n  a  l  (  S  H  O  W  ?  N  3  2 I  0 O  — cvi  or Be cc  V  1  )(  l e v e l s have V  a  C0 2 's symmetry  3.2  1  Rotation-Vibration  since  Excitation  both the upper and lower  axis.  l  laser  i s the  angular momentum along  Alternate  l i n e s i n the spectrum  bands o f C0 2 are a l s o m i s s i n g because o f [11].  and I n v e r s i o n  i n C0 2  A great deal of the e a r l y can  Transistions.  = 0 ( i . e . I = Si' = 0 ) , where l  internuclear - I  ro  o_  I  component of e l e c t r o n i c o r b i t a l  of the y  OJ  SL  0  Q-branch t r a n s i s t i o n s  the  3  o_  1  11.  Figure  o — c\j ro o o o o  be a t t r i b u t e d  to C.K.N. Patel .  h i s t o r y o f C0 2  lasers  He was the f i r s t to  25  observe l a s e r emission from C0 2 mixtures  (1964  [13]  The  l a s t r e s u l t was  and  Rigden  and  (1964  C0 2 -N 2 -He mixtures  s i m u l t a n e o u s l y obtained by  originally  it  02  subsequent recombination  vibrationally excited.  C0 2  and  with the  leaving  and  d i s a g r e e d with Patel  and  d i s s o c i a t i o n of C0 2  transferred has  since  been shown by  verified  and  McKnight (1969) [20]  suggested that  was  Sobovnikov  the  CO  by  collisions. Schulz  that  Direct electron  the  -»• slow e" + C0 2 *  f o r b i d d e n ) one The  [18]  [19]  by:  .  process which  p o p u l a t i o n d e n s i t i e s because the  electron  i s l a r g e r f o r the  c a l l y allowed) l a s e r l e v e l  However  dominant e x c i t a t i o n  impact, symbolized  impact i s a r a p i d  cross-section  formed  (1968)  i n l a s e r experiments by Cheo (1967)  f a s t e" + C0 2  obtained by  was  e l e c t r o n i c a l l y excited  Boness and  mechanism i s d i r e c t e l e c t r o n  excitation  that C0 2  Sovolev and  t h i s energy to C0 2  and  the  Moeller  [16]  i n t o CO  the  [14].  believed  dissociated  by  (1965)  [15]. Patel  [17]  [ 1 2 ] , from C0 2 -N 2  than the  lower  inverts  impact  upper  (opti-  (optically  [20]. increase  in e f f i c i e n c y and  adding d i f f e r e n t gases to C0 2  l a r g e r powers can,  in  part,  26  be q u a l i t a t i v e l y e x p l a i n e d by the data shown i n Table i . In the Table I Induced  Vibrational  V 3 and v 2 Modes  Relaxation  Rates of t h e C 0 2  i n t h e Presence of Other  G a s e s a t 300°K [ 2 1 3  v3 Gas  - v2  (sec-1-  v2  torr-1)  C02  365 ± 15  Gas  N2  110+  Add i t i v e s  He  < 85  H20  3.3 ± .9 x 1 01*  D i s s o c i a t i on  CO  Products  02  ground  (sec-1  state  - torr-1)  200 ± 10  5  - 40 4 ± .8 x 1 0 3 10s  - 106  4 x 1 03  1 93 110 + 5  ~ 40  presence of other gases the p o p u l a t i o n s of the upper ( v 3 ) and  lower ( v 2 ) l a s e r l e v e l s are modified  induced  vibrational relaxation.  collisions  i s to depopulate  the v 3 l e v e l , thus a i d i n g inversion  necessary  by c o l l i s i o n  The main e f f e c t of these  the v 2 l e v e l more r a p i d l y  the formation  f o r laser emission.  than  of the p o p u l a t i o n However the e f f e c t s  of N 2 and He, the two main gas a d d i t i v e s , are not l i m i t e d to c o l l i s i o n a l  relaxation  alone.  27  Nitrogen i s a homonuclear molecule and has  a zero d i p o l e moment i n the  ground s t a t e .  therefore  Thus r a d i a -  tive rotation-vibration transistions.are s t r i c t l y  for-  bidden and  are  very long  2  v i b r a t i o n a l l y excited  lived  excitation cm )  the  [21]  (m sees.) [ 1 1 ] .  cross-section and  since  the  above the v = 1 l e v e l  f o r N2  The  total  of C0 2  there i s an  resonant t r a n s f e r of energy from the N2  to C0 2  by c o l l i s i o n s .  because of t h i s N 2 l a s e r s the the  Cw  of  affecting mean gas  C0 2  presence of N2  He,  on  the  population  efficient  cm  -1  near  v i b r a t i o n a l l y excited  usually creates repopulating  the  the  other hand, besides of the v  2  k i n e t i c temperature of the  is also The  [1].  i s only 20  a long  C0 2  tail  in  depleted 00°1  C02.  l a s e r i s increased  was  IO"16  x  l a s e r s are more e f f i c i e n t  of i t s high thermal c o n d u c t i v i t y .  tion  (3.8  impact  storage mechanism while i n pulsed  l a s e r pulse shape by  level  electron  i s very l a r g e  00°1 level  of N  l e v e l s of N2  [10]  and  the  level  profoundly also  lowers  the  d i s c h a r g e because Thus the gain  e l e c t r o n energy  of  the  distribu-  affected. importance of the  e l e c t r o n energy d i s t r i b u t i o n  t h e o r e t i c a l l y demonstrated by Nighan and  Bennett  Using e x p e r i m e n t a l l y obtained c r o s s - s e c t i o n s  computer s o l u t i o n s of the  (1969)  and  e l e c t r o n energy d i s t r i b u t i o n  28  from the Boltzman equation f o r s p a t i a l l y states  [2] they solved  the e l e c t r o n  n u m e r i c a l l y as a f u n c t i o n the  electron  o f E/N.  uniform  steady  k i n e t i c equation Their  r e s u l t s show  energy d i s t r i b u t i o n i s non-Maxwel1ian.  that Of  even more importance are t h e i r r e s u l t s f o r the f r a c t i o n a l power t r a n s f e r r e d and  from the e l e c t r o n s  e l e c t r o n i c l e v e l s of C0 2 and N 2 , as a f u n c t i o n of  — E/N and u (the average e l e c t r o n For  to the v i b r a t i o n a l  .00  energy:  — 2 I u = -5-  u  3/2  f(u)du).  an E/N value of 10~ 1 6 v-cm 2 up to 65% o f the e l e c t r o n  energy goes d i r e c t l y  i n t o the ( 0 0 ° 1 ) l e v e l  of C 0 2 * .  But  f o r an E/N of 10" 1 5 v-cm 2 t h i s f i g u r e i s only about 20% with most o f the e l e c t r o n  energy being used to e x c i t e  the  e l e c t r o n i c l e v e l s o f C0 2 and N 2 .  the  energy t r a n s f e r i s the more non-Maxwellian the e l e c t r o n  energy d i s t r i b u t i o n becomes, f a l l i n g  The more e f f i c i e n t  o f f f a s t e r at higher  energies than the Druyvesteyn d i s t r i b u t i o n .  3.3  Present State of the A r t In s p i t e of t h i s b a s i c  u l a r processes i n C0 2 l a s e r s  understanding of the molec-  i t i s however not p o s s i b l e to  * For a TEA l a s e r at atmospheric pressure with a cathode-anode s e p a r a t i o n of 2.541 6 cm and an a p p l i e d v o l t a g e o f 20 kv, E/N = 3.2 x 1 0 ~ v - c m 2 .  29 predict  the  quantitative  quantitative  analysis  is precisely  the  d i s c h a r g e as  a function  performance of a C0 2  would r e q u i r e  electron  c u r r e n t d e n s i t y , 2)  how  N2,  3)  how  radiation  electron  vibrational  "temperature"  l e v e l s of  p a r t i c l e s and, excited  4)  how  p o p u l a t i o n of  and  narrow a m p l i f i c a t i o n  be  small  electron  gain c u r v e .  with a c t i v e  and  as  1 nsec with peak power of ~ 1 Mw  (1972)  the  i n c r e a s e the  to do  Never-  achieved  Pulse widths have been  [22].  number of e l e c t r o n s ,  obvious way  elements.  for  longitudinal  been attempted and  passive o p t i c a l  C0 2  make i t s u i t a b l e  number of  f i t t e d w i t h i n the  t h e l e s s , mode-locking has  To  the  bandwidth of the  S e c t i o n 4.3.3) does not  modes that can  reported  C02.  i t s non-Maxwel1ian  concept of mean  mode-locking because of the  short as  C0 2  coherent  experimental measurement of  of the  electrons  questionable.  The (see  use  from  and  energy r e l a x e s because  energy d i s t r i b u t i o n e x i s t s  form makes the  lasers  gas  1) what  composition  energy i s t r a n s f e r r e d  i n t e r a c t s with the To-date no  a knowledge of:  of p r e s s u r e , gas  this vibrational  of c o l l i s i o n s of the  A  energy d i s t r i b u t i o n in a pulsed  in a pulsed discharge to the and  laser.  l a s e r output one n f i l i n the  has  discharge.  t h i s , namely to i n c r e a s e the  to The  increase most  current,  30  does not work, s i n c e to a higher gas  ng  current  processes.  Two  at NRC  the 100  j o u l e s at s e v e r a l  has  have obtained  gigawatts.  an  Daugherty into  obtained 2000 j o u l e s with almost  of power. The  the e x t e n s i v e  l a c k of a comprehensive theory i n v e s t i g a t i o n of any  different features.  To  parameters as p o s s i b l e properties of our  elaborate  used e l e c t r o n beams to i n j e c t e l e c t r o n s  a c t i v e medium and Mw's  increases  Firstly,  have used  techniques to p r e i o n i z e the gases and output of 300  which  lead  other methods f o r i n -  however have been s u c c e s s f u l .  Richardson et al. (1973) [23]  (1973) [24]  density w i l l  temperature in the d i s c h a r g e ,  the d e a c t i v a t i o n creasing  increased  of the  new  this  end  new  one  C0 2  l a s e r with  should vary as many  in order to understand device.  l a s e r are presented  The  in the  necessitates  the  experimental next c h a p t e r .  studies  Chapter 4  CHARACTERISTICS OF LASER 4.1  Aligning Any  CQ2  Laser  l a s e r work s t a r t s with the f r u s t r a t i n g  o p e r a t i o n of a l i g n m e n t . emitted by a C0 2  Since the wavelength of r a d i a t i o n  l a s e r i s i n the i n f r a r e d some of the  optical  components used are opaque to r a d i a t i o n  visible  spectrum.  i n the  Thus to a l i g n the l a s e r c a v i t y  i t is  necessary to i n t r o d u c e the alignment beam used i n a roundabout way.  100% GOLDCOATED MIRROR  The set-up i s shown i n Figure  * PLATE*  12.  K C I  I I i l i |I I I I l i R = IOm  ^-i  O Au=Ge  /  DETECTOR  GERMANIUM FLAT 8 % TRANSMISSION  SILVERED MIRROR  Figure 12.  Alignment System,  Removed a f t e r i n i t i a l 31  alignment.  32  One  should not be s u r p r i s e d  a l i g n m e n t , no l a s e r a c t i o n  i s observed.  the change i n the r e f r a c t i v e  careful  T h i s i s due  been observed  and  the pulsed d i s c h a r g e .  i n low  pressure  C0 2  l a s e r s , He-Ne l a s e r s and most r e c e n t l y by F o r t i n et (1971) [25] i n a h e l i c a l lens e f f e c t was  TEA  attributed  C0 2  This e f f e c t causes the alignment  occurs.  Thus f o r alignment  cm  al.  l a s e r where a d i v e r g i n g  to each p i t c h of the  s u r f a c e of the m i r r o r s ~ 0.5  to  index of the l a s e r medium  because of the heating of the gas Such an e f f e c t has  i f ,after  helix.  beam to "jump" on  the  each time the d i s c h a r g e  purposes i t i s b e t t e r to note  * the p o s i t i o n of the beam while the d i s c h a r g e i s on. Once the l a s e r has  been a l i g n e d the KC1  plate i s  removed because i t i s a source of l o s s i n the c a v i t y affects  the pulse shape and  delay time.  Quite f r e q u e n t l y  m u l t i p l e p u l s i n g occurs with some pulses being over 20 usee a f t e r the i n i t i a t i o n Figure 13).  T h i s behaviour  operating of  at low gas  i s i n general  (see  the case i f  be caused  by  p r e s s u r e s , a s l i g h t misalignment  c a v i t y m i r r o r s or l o s s e s  are d i s c u s s e d f u r t h e r  emitted  of the d i s c h a r g e  the round t r i p gain i s s m a l l , which may  and  i n the c a v i t y .  These p o i n t s  i n S e c t i o n 4.3.3.  * D i f f e r e n t beam displacements due to d i f f e r e n c e in index of r e f r a c t i o n f o r 10.6y (C0 2 ) and 6328A (He-Ne) may be n e g l e c t e d .  5.68  kw/div  5 usec/d i v  Figure  13. M u l t i p l e L a s i n g w i t h Round T r i p Gain.  The m e c h a n i c a l  rigidity  o f t h e l a s e r was s u c h  t h a t o n c e t h e l a s e r was a l i g n e d o n l y were n e c e s s a r y f o r s u c c e s s f u l  Low N e t  slight  operation  adjustments  on a d a y - t o - d a y  basis. The u s u a l Figure  14 w i t h  C02pulse  thepulse  shape o b t a i n e d  shape parameter  i s shown i n  measured  i n this  P  P = PEAK POWER  i1  T = PULSE WIDTH AT  HALF POWER  n -  or  TIME DELAY  >  p  V*T  1  0'* 1| | H ' " 2 y  7*  pA  Figure  14.  3  '^  5  6  7  TIME (microseconds)  C 0 Pulse 2  Shape  Parameters.  8  34  chapter  as i n d i c a t e d .  to  the spark  fire  Since no e x t e r n a l t r i g g e r was  used  gap no great e f f o r t was made to e l i m i -  nate the e l e c t r i c a l  n o i s e . On the c o n t r a r y , the noise  was  used to t r i g g e r the o s c i l l o s c o p e so that x ^ measures the elapsed  time between the s t a r t of the c u r r e n t pulse and  the beginning  4.2  of the l a s e r  Operating  4.2.1  Conditions  The e l e c t r i c a l Of course  Does the hollow  pulse.  system.  the f i r s t  question  ground rod a c t u a l l y work?  found a f t e r s e v e r a l weeks of f r u i t l e s s How well  to be asked i s : The answer,  adjustment, i s y e s .  i t works though depends upon the i n t e r e l e c t r o d e  d i s t a n c e , A, used, as can be seen i n F i g u r e 15. Using  a l l 200 r e s i s t o r s c r e a t e s a d i s c h a r g e  p a t t e r n that shows the sparks c o u p l i n g with one another. of and  channels i n t e r f e r i n g  and  By d i s c o n n e c t i n g one chain  r e s i s t o r pins the i n t e r e l e c t r o d e d i s t a n c e i s doubled the discharge  pattern i s quite  uniform.  However, the power from the 200 r e s i s t o r s i s l a r g e r than that with only 100 r e s i s t o r s . is  the reduced height of the t a i l  Also  of the C0 2  means the energy of the pulse i s l e s s  significant  pulse.  This  (but not by a f a c t o r  35 Spa r k  Channels  Laser  200  Pulses  resistors  A = 0.5  100  cm  resistors  A = 1.0  P  =  140  torr  11.4  kw/div  C02:N2:He  Figure  of  15.  2) b e c a u s e l e s s  resistors thus  Spark  N2  =  Channels  1  ysec/div  2:1:10  and  Laser  i s being e x c i t e d .  With  Pulses.  a l l 200  i n use more volume o f t h e g a s i s e x c i t e d  the energy content of the pulse i s l a r g e r .  reason  cm  t h e l a s e r was o p e r a t e d  using  and  For t h i s  200 r e s i s t o r s .  36 Throughout the experiment r e p e t i t i o n 1 pulse/sec and  were used.  the power supply  tition  By v a r y i n g  voltage  r a t e agreed with  the spark gap s e t t i n g  i t was v e r i f i e d  equation  r a t e s of  that the repe-  2.1 ( S e c t i o n 2 . 1 ) .  The  c h o i c e of 1 Hz was n e c e s s i t a t e d by the need to apply a reasonable  v o l t a g e to the d i s c h a r g e  overheating  of the 1 watt r e s i s t o r s  In a d d i t i o n there was the very noise from the d i s c h a r g e frequent  and avoid  excessive  used as the anode.  human problem of e l e c t r i c a l  and spark gap which brought  (1 Hz ?) complaints  from f e l l o w students  was e v e n t u a l l y s o l v e d by simply  setting  and  the spark gap at  a lower v o l t a g e , namely 16 kv.  4.2.2  E f f e c t of gases and p r e s s u r e . As  explained  other gases a l t e r s laser.  i n S e c t i o n 3 . 2 , the presence of  the power and energy output of a C0 2  The o s c i l l o g r a m s shown i n F i g u r e 16 v e r i f y  statements.  With no gas a d d i t i v e s ( F i g u r e 16(a)) the  l a s e r pulse shows a very  f a s t r i s e and decay t i m e .  rapid risetime i s attributed the f a s t e x c i t a t i o n  situation  by Beaulieu  The  (1970) [ 3 ] to  caused by the short c u r r e n t  T h i s causes a r a p i d b u i l d switching  these  pulse.  up i n gain which c r e a t e s a g a i n -  giving rise  to a g i a n t  pulse.  37  co  2  N  2  He  kw d iv  Pressure (torr)  (a)  1  0  0  70  5.68  (b)  2  1  0  1 00  5.68  (c)  1  0  5  1 20  11  Figure  16.  C02  The a d d i t i o n  A  Laser Pulse  of N  2  does  much b u t i n c r e a s e s t h e e n e r g y o f t h e p u l s e  as e v i d e n t by  the  When He i s  tail  added but  i n the C02 pulse  (Figure 16(b)).  to C02 (Figure 16(c))  t h e peak power i s a l m o s t d o u b l e d  t h e p u l s e s h a p e i s t h e same as w i t h o n l y C 0 2  Oscillograms  w i t h a l l three gases present  F i g u r e 15 and e x h i b i t  t h e same p u l s e  and N 2 a l o n e  t h e peak powers  but w i t h  present.  a r e shown i n  s h a p e as t h a t o f C 0 2 o f C 0 2 and He.  38  The of  volume r a t i o of gases used throughout most  the experiment were 10 parts He:l  This r a t i o for  C0 2  is typical  lasers.  creasing  the  of the values  Some work was  part N2:2 cited  parts  i n the  literature  done on the e f f e c t of i n -  He content in the gas mixture and  i t was  found that f o r r a t i o s up to 25:1:2 the peak power i n c r e a s e d ~ 30%. obtaining  C02.  This l a r g e r gas  r a t i o was  the spectrum of the l a s e r  used when  (see Appendix  Although more He gives more power, He  was  B).  i s expensive!  Enough  s a i d about t h a t ! The  v a r i a t i o n of peak power with gas  shown i n F i g u r e error  bars  17.  represent  In this  graph,  the rms  error  The  curve has  due  to s e v e r a l e f f e c t s .  with  as in all of five  The  initial  i s created by an  per u n i t volume.  shots  I f no other  and  pressure.  the c o l l i s i o n a l  itself  i s reduced by d e - a c t i v a t i n g c o l l i s i o n s Also above 5.2  However,  [26].  to  Thus the i n v e r s i o n at  t o r r the l i n e width of  broadened [26] and  this  high C0 2  homogeneous broaden-  i n c r e a s e s the t h r e s h o l d f o r l a s i n g  the e x t r a c t a b l e l a s e r power.  the  relaxation rates also i n -  l i n e a r l y with  ing  pressure  energy  mixture are due  crease  collision  each.  e f f e c t s were important  d e - e x c i t a t i o n mechanisms i n the gas  is  the  i n c r e a s e i n power  i n c r e a s e in the  power would i n c r e a s e l i n e a r l y with  pressures.  others,  an approximate p a r a b o l i c shape which i s  pressure  collisions  pressure i s  and  thereby reduces  40  A s i m i l a r graph was of 15:1:2.  This graph had  a l s o obtained with gas  the same p a r a b o l i c shape  the optimum pressure occurred at 150 140  torr  t o r r with the 10:1:2 gas m i x t u r e .  thus  T h i s i s reasonable by  collisions  i n c r e a s e s the p o p u l a t i o n  even though the t h r e s h o l d i n c r e a s e s with the band  inversion  increasing  width. Using  these r e s u l t s  a pressure of 140  torr  the l a s e r was  operated  at  (10:1:2 gas mixture) when studying  other p r o p e r t i e s of the  4. 3  but  i n s t e a d of the  s i n c e He c l e a r s out the lower l a s e r l e v e l (see Table 1) and  ratios  laser.  P r o p e r t i e s of System  4.3.1  Power decay i n a c l o s e d system. The  most important  i s the l a s e r r e a c t i o n t h i s v e s s e l had  component i n the vacuum system  tube which i s made of l u c i t e .  over 200  holes d r i l l e d  i n i t f o r the  r e s i s t o r p i n s , exhaust p o r t s , e t c . , i t was surprising  e f f e c t the vacuum leaks had vacuum pump was gas was  not  too  t h a t the lowest vacuum (?) o b t a i n a b l e  200 microns as measured with a McLeod  gauge.  c l o s e d from the r e a c t i o n  was  To see what  upon the l a s e r output  s u p p l i e d to the t u b e .  Since  tube and  the no  fresh  Thus the graph shown i n  POWER (Normalized Units)  F i g u r e 18 was o b t a i n e d .  Since the vacuum leak was at a  r a t e of 5 torr/min some gas was p e r i o d i c a l l y from the system to maintain torr.  a constant  pressure of 140  At a leak r a t e of 5 t o r r / m i n , a f t e r  250 t o r r of a i r w i l l making the p a r t i a l pressure  have leaked  50 min some  i n t o the r e a c t i o n  Even with  i n the r e a c t i o n  this  l a r g e amount of  tube the l a s e r s t i l l  but only at 30% of the power i t s t a r t e d with  4.3.2  Electrical The  tube  pressure of a i r some 60% of the t o t a l  i n the tube.  impurities  evacuated  lases  initially.  efficiency.  electrical  e f f i c i e n c y of a l a s e r  i s defined  as the r a t i o of the energy of the l a s e r pulse to the electrical  energy i n p u t .  l a s e r the e f f i c i e n c y  In a r e s i s t i v e l y  is typically  loaded TEA  5% [ 2 8 ] ,  To o b t a i n t h i s measurement i t i s necessary to know the v o l t a g e , V , a p p l i e d to the r e s i s t o r chain from the spark  gap.  The e l e c t r i c a l  energy input i s the energy  s t o r e d by the c a p a c i t o r s which i s ( i ) C V 2 . due to the r e s i s t i v e l y The  loaded  The I 2 R l o s s e s  anode are u s u a l l y n e g l e c t e d .  v o l t a g e across the c a p a c i t o r bank can be obtained by  calibrating  e i t h e r the spark gap o r , because there i s no  e x t e r n a l l y a p p l i e d t r i g g e r pulse to the spark gap, the power s u p p l y .  Since the e l e c t r o d e s of the spark gap  43  d e t e r i o r a t e with use used.  The  Tekronix  the l a t t e r of the two  power supply was  calibrated  methods  was  using a compensated  high v o l t a g e probe (30 kv max.). The  energy content  of the l a s e r pulse was  found  by measuring the area under the curve of the power pulse shapes from the Au:Ge d e t e c t o r (see Appendix A ) . The 19.  To  e f f i c i e n c y curve obtained  i n t e r p r e t t h i s graph i t i s necessary  the work of Nighan and [2].  fractional  it  - IO  N the t o t a l  ionization - 6  ,  and  i s necessary  the gas m i x t u r e .  may  Nighan  (1970)  t r a n s f e r of power  v i b r a t i o n a l l e v e l s of C0 2  dent upon the value of E/N, s t r e n g t h and  to look at  Bennett (1969) [1] and  They found t h a t the f r a c t i o n a l  to the e l e c t r o n i c and  10" 8  i s shown i n F i g u r e  and  N2  where E i s the e l e c t r i c  are depen-  field  neutral p a r t i c l e d e n s i t y .  The  of the gases i s q u i t e s m a l l , t y p i c a l l y be i g n o r e d .  To f i n d E ( i . e . E =  v'/d)  to know the net v o l t a g e , v', a p p l i e d to T h i s i s the v o l t a g e a p p l i e d across  the  e l e c t r o d e s by the power supply minus the cathode f a l l v o l t a g e drop across the anode r e s i s t o r s . drops have been estimated than  by Lyon  used here.  less  s i m i l a r to that  Thus f o r a cathode-anode s e p a r a t i o n d = 1.8  at a pressure of 140 used r e p r e s e n t s E/N to 22.5  These p o t e n t i a l  (1973) [26] to be  2 kv i n a l a s e r with a gas mixture  and  t o r r the values of the input energy values  x 10"16v-cm2.  i n the range 9.2  x 10~ 1 6 v-cm 2  From these c o n s i d e r a t i o n s the  cm  ELECTRICAL INPUT ENERGY Figure  19.  Electrical  (joules)  Efficiency  Curve.  45  increase in e f f i c i e n c y of E/N (3.5  i s not  e.v.)  i s so high that most of the C0 2  is e l e c t r o n i c a l l y e x c i t e d . ( i . e . energy) l e s s C0 2 tional^  and  and  is directly  excited  illustrate  that one  understand a l l f a c e t s of C0 2  lasers.  Time delay of  vibra-  to assume  still  does  between the beginning  the s t a r t of the c u r r e n t pulse  by l o s s e s in the  l a s e r c a v i t y and  the gain  a l r e a d y mentioned in S e c t i o n 4.1  alignment and  operating  (< 30 t o r r ) .  The  [30].  the l a s e r at low  gas  the  with during  pressures time  delay  pressure.  If the time delay was would expect the delay  of  This  i n connection  graph in Figure 20 shows t h i s  as a f u n c t i o n of t o t a l  pressure  not  i s governed  the m u l t i p l e p u l s i n g caused by the K C £ p l a t e used  we  voltage  pulse.  time d e l a y , x^,  l a s e r pulse and  was  N2  N2  decreased.  These r e s u l t s  The  and  With i n c r e a s i n g a p p l i e d  t h e r e f o r e i t would be reasonable  the e f f i c i e n c y was  4.3.3  values  used i n d i c a t e that the average e l e c t r o n energy  - 4.5  fully  e x p l a i n a b l e s i n c e the  due  to c o l l i s i o n  effect  to decrease with i n c r e a s i n g  because the c o l l i s i o n a l  r e l a x a t i o n rates  d i r e c t l y p o r p o r t i o n a l to the t o t a l  pressure.  The  are influence  Figure  20.  Time  Delay  vs.  Total  Pressure.  47  of l o s s e s may be excluded losses  a l s o s i n c e the only  i n t r o d u c e d by i n c r e a s i n g the pressure  l o s s e s which are n e g l i g i b l e . of the g a i n .  additional as a b s o r p t i o n  T h i s leaves only the e f f e c t  I t has been found by Gerry  [27] that above 5.2 t o r r C0 2 i s c o l l i s i o n  et al. (1966) broadened  with  a bandwidth i n c r e a s e of 6.5 MHz/torr.  T h e r e f o r e , as the  pressure  l a r g e r and broader  i n c r e a s e s the gain curve  gets  thus i n c r e a s i n g the t h r e s h o l d f o r l a s i n g . length of 2 m the frequency modes i s 75 MHz  With a c a v i t y  s e p a r a t i o n between a x i a l  ( i . e . Af = c / 2 L ) .  Thus, at a pressure  of 20 t o r r there are at most two a x i a l  modes w i t h i n the  gain curve whereas at 240 t o r r there are 21 modes The  i n c r e a s e i n the time delay may be caused by c o u p l i n g  between these modes with one mode saying " A f t e r you" and the othermode r e p l y i n g  to the other  "No, a f t e r you!"  It i s a l s o known by those more f a m i l i a r * C0 2  present.  lasers  with  that the c u r r e n t pulse plays q u i t e an important  r o l e with C0 2 l a s e r s and i s a f f e c t e d by the d i s c h a r g e which i n turn i s p a r t i a l l y  determined by the p r e s s u r e .  Another i n t e r e s t i n g o b s e r v a t i o n pressures  i s that up to  100 and 120 t o r r the C0 2 pulse i s modulated.  This modulation was much more pronounced i n mixtures of j u s t C0 2 and N 2 and i s shown i n F i g u r e 21.  *  By r e f e r r i n g  P r i v a t e communications with Dr. A.A. O f f e n b e r g e r . i  48  C02 : N  = 2:1 100 t o r r 5.68 kw/dlv 0 .5 usec/d i v  Figure  to  Figure  sures  21.  20 one w i l l  that the delay  starts  Modulation  of  note t h a t  C02  Pulse.  i t i s around these  t i m e no l o n g e r  to i n c r e a s e with  Laser  2  pressure.  remains constant This  t h e s e two phenomena a r e r e l a t e d .  pres-  This  suggests  but  that  modulation, with  p e r i o d T ~ 70 n s e c , i s n o t c a u s e d by m o d e - l o c k i n g  effects  and a t t e m p t s t o e x p l a i n i t as l a s e r  s p i k i n g by t h e S t a t z -  De Mars e q u a t i o n  [ 1 4 ] . Once a g a i n  to  the e f f e c t s  taining ring  have p r o v e n f u t i l e  of the c u r r e n t  non-negligible inductance  and t h u s pump t h e l a s e r  effect.  For a c i r c u i t  the current  level  to p r o v i d e  i n Figure  the p o s s i b l e  will  p o s s i b l y causing  this  21 a p p e a r s  discharge  t o be t o o  explanation.  Measurements of the h a l f - w i d t h o f the p u l s e , x , show no v a r i a t i o n  4.3.4  con-  pulse  However, the r i n g i n g f r e q u e n c y of t h e  w h i c h can a l s o be s e e n slow  pulse.  we  with  laser  pressure.  Spectral a n a l y s i s . The s p e c t r u m o f t h e l a s e r was  investigated with  a J a r r e l - A s h 0.5 m s p e c t r o m e t e r e q u i p p e d w i t h  a 148 l/mm  return  49  grating.  The alignment of t h i s  instrument caused some  d i f f i c u l t i e s which were f i n a l l y piece of untreated  overcome by using a small  s t e e l which was s u f f i c i e n t l y  by the l a s e r pulses  heated  to evaporate the grease on i t s s u r f a c e  * and  emitting a f a i n t , v i s i b l e The  flash.  procedure used and d i f f i c u l t i e s  i n o b t a i n i n g the i n f r a r e d Appendix B.  light  involved  spectrum are d e s c r i b e d i n  Only three P branch t r a n s i s t i o n s were observed:  the P ( 2 0 ) , P(18) and P(16) l i n e s . s h i f t and other  These l i n e s d i d not  l i n e s d i d not appear when the pressure  was v a r i e d from 40 to 200 t o r r and spark gap s e t t i n g s of 17.4 and 15 kv were used. The and  P(20) l i n e was by f a r the most i n t e n s e  using P a t e l ' s [10] a n a l y s i s o f the gain  f o r P-branch t r a n s i s t i o n s population mizing f o r  was  N  N  ratio  00ol^N02o0  ^001^020  w i t n  =  J  l'H>  +  T n i s  "  1 = 20 . f°  r  a  w a s  The r e s u l t  r e s u l t s obtained  ° y maxi-  obtained  k i n e t i c temperature of 3 0 0 ° K .  t i o n as a t r a n s v e r s e l y p u l s e - i n i t i a t e d  by means of chemical  d o n e  r e s p e c t to J and s o l v i n g  Having s u c c e s s f u l l y operated  on to the more d i f f i c u l t  coefficients  i t i s p o s s i b l e to determine the  the gain c o e f f i c i e n t with  001 y ' N 020  line  the l a s e r c o n f i g u r a C0 2 l a s e r we moved  task of o b t a i n i n g l a s e r  pumping.  are d i s c u s s e d  emission  The gas mixtures used and i n the next  chapter.  * effect.  Alcohol  cleaned  s u r f a c e s d i d not show the same  Chapter 5  CHEMICAL LASER Laser emission by means of chemical first  s u c c e s s f u l l y accomplished  (1965) [30] i n a f l a s h chlorine explosion. spark-initiated CO  photolytically  lasers  atmosphere.  time gas mixtures c o n t a i n i n g hydrocarbons a l s o produced in  hydrogen/  transversely  have been operated using  [ 5 ] , [31,33], produced  a c t i o n s up to pressures of one  was  Pimentel  initiated  In the past three years  chemical  [ 4 ] , [7] and HF  by Kasper and  pumping  i n chemical During  re-  this  [33-35] have  l a s e r a c t i o n but only at very low pressures  discharge tubes. Attempts to o b t a i n  produced  i n chemical  gas mixtures Table  l a s e r emission from  molecules  r e a c t i o n s were not s u c c e s s f u l .  The  and o p e r a t i n g c o n d i t i o n s used are shown i n  II. To o b t a i n maximum s e n s i t i v i t y with the Au:Ge  d e t e c t o r a KC& r a d i a t i o n was  lens  ( f = 9.4  cm)  was  used  to ensure a l l  focused on the d e t e c t o r element and  50  no 50Q  51  Table I I Gas M i x t u r e s  and O p e r a t i n g Chem i c a I  Gas  Mixture  #1  C 2 H 2 + C 0 2 + N 2 + He  #2  C2H2  N 2 + He  #3  C2H2  + He + A i r  #4  C2H2 + C02 + 02  #5  C 2 H 2 + He + 0 2  #6  +  Conditions f o r  Laser  Gas R a t i o s by Volume  P  4.5:2:1:10  30-50  T0TAL (torr)  Laser Act ion Yes  1:25:60  5-25  No  1:4.2:1.7  5-75  No  45  No  <l:5:40*  5  No  C2 H 2 + 0 2  * < 1 : 1: 5 * 1 :2  5-60  No  #7  SF6  + C 2 H 2 + He  12:1:233  1 5-40  No  #8  SF6  + H2+  1.7:1  1 0-40  No  #9  H 2 + C 0 2 + He  1:1.7:8.6  #10  SF6  Laser  + C 0 2 + He  emission  Gas r a t i o s  1:2:10  has been r e p o r t e d  by p a r t i a l  50-80  pressures.  in these  Yes  40  mixtures.  No  52  t e r m i n a t o r was  used with  the d e t e c t o r .  would enable d e t e c t i o n of powers as low distorting due  These two as 50 mw  the power pulse shape because of the  to the l a r g e RC  time constant  of the BNC  although integration  cable-oscillo-  scope input impedance network (see Figure A-4). attempting  to d e t e c t l a s e r emission  #7  electrical  and  #8)  noise was  pulse i s c r e a t e d ~ 100  from HF  a problem.  steps  When  (mixtures The  HF  nsec a f t e r the i n i t i a t i o n  of  d i s c h a r g e which would bury i t amid the e l e c t r i c a l from the d i s c h a r g e .  the  noise  A f t e r u n s a t i s f a c t o r y attempts to  reduce the noise a delay cable the s i g n a l  laser  (3 usee) was  used to delay  from the d e t e c t o r thus s i d e s t e p p i n g the  noise  problem. The #6  and  #8.  gas mixtures of primary i n t e r e s t are  These mixtures have p r e v i o u s l y been  to produce l a s e r emissions molecules r e s p e c t i v e l y .  from CO  The  and  C02,  CO  #3,  reported and  HF  other gas mixtures were used  to study what e f f e c t the gases of the primary mixtures ( i . e . #'s  3, 6 and  8) had  known to work i n our observations  of these  The v i o l e n t quires  on a l a s e r mixture which i s  laser.  In s h o r t , the c o n c l u s i o n s  and  s t u d i e s are: nature of C 2 H 2 + 02  t h e use o f low o p e r a t i n g  mixture produced f l a m e - l i k e  pressures.  reactions r e The C 2 H 2 + 0 2  r e a c t i o n s , w h i c h a r e known t o  53 suppress Using  laser  action,  low p r e s s u r e s ,  versely  2  excited  + C0 CO2.  soon  as H  This  type  4  2  gain  and 0  H  2  2  readily  breakers C0  2  it  indicates  from  level  + N2 +  been  H  as  the active  discussed  2  He  electrically  into  that C  C0  the reaction  absorbing  quenches  and H  2  medium.  in Chapter decrease  2  what C 0  2  2  stopped  tube.  This  adds  "insult  radiation  used  (see Table I ) .  inversion  to  injury"  arcs  For  in circuit  f o r Q-switching  i s deleterious to laser  the population  when  isn't too  i s emitted.  t o quench  S t u d i e s on t h e d i s s o c i a t i o n 2  immediately  electrons available for  and t h e n  SF6 h a s b e e n  that 0  destroys  laser  introduced  and a s a s a t u r a b l e a b s o r b e r  lasers.  indicate  produced  has a l r e a d y  emission  entered  reasons  C2H2 + CO2  laser.  excitation  these  were  13) a n d  C0 by  in the mixtures  multiple pulses  of the  2  pattern.  mixtures  s i n c e SFe  and N  resulting  These  surprising 2  because of the  trans-  to  of behaviour  2  laser  to a  torr.  c a n be a t t r i b u t e d  Laser SF6  o f 50  + He  and C  2  (see Figure  the  action  in excess  i s deterimentaI  of the discharge  Laser H  however,  spark-initiated  non-uniformity  and  at pressures  of  products  of C0  emission  because  2  by d e p l e t i n g t h e u p p e r  54  Although l a s e r emission not detected reaction  this  tube i s inadequate f o r the t a s k . help to achieve  l a s e r are d e s c r i b e d and discussed.  pumping  does not n e c e s s a r i l y mean that the  improvements t h a t may  are  by chemical  was laser  In Chapter 6  an o p e r a t i n g  chemical  p o s s i b l e experiments f o r the f u t u r e  Chapter 6  CONCLUSIONS AND FUTURE IMPROVEMENTS A t r a n s v e r s e gas has  been c o n s t r u c t e d  e x c i t e d CO2  laser.  and The  f l o w , t r a n s v e r s e l y pulsed  operated  e f f i c i e n c y of the l a s e r  other r e s i s t i v e l y  loaded  TEA  are not as l a r g e .  characteristics  C0 2  lasers  cm,  1.0  be f i x e d  thus maximizing the  e f f i c i e n c y and  proved by o p t i m i z i n g E/N criteria.  the  the  between  l a r g e enough to prevent c o u p l i n g  the spark channels and The  the powers  lasers.  improve the performance of the l a s e r  0.5  volume used.  was  l a s e r system were  t h e o r i e s of C0 2  s e p a r a t i o n , A, should  and  although  Some measurements of  interelectrode cm  cathode  i s comparable to  of the l a s e r pulse and  not e x p l a i n a b l e by present To  discharge  demonstrated.  The  obtained  electrically  i n n o v a t i o n of using a hollow ground  rod f o r t r a n s v e r s e gal flow and successfully  as an  laser  to Nighan and  This would r e q u i r e l a r g e r  55  excitation  power output may  according  of  be  im-  Bennett's  v o l t a g e s but would  56  also  i n c r e a s e the optimum pressure thus reducing  problems  with the vacuum system. Experimental  r e s u l t s by Mikoshiba  (1973) [36] i n d i c a t e that the power may optimizing  Ahlborn  i n c r e a s e d by  the l a s e r c a v i t y using a v a r i a b l e f o c a l  gold-coated m i r r o r . mizing  be  and  Some r u l e of thumb guides  length  for opti-  the t r a n s m i s s i v i t y of the output m i r r o r are given  i n an a n a l y s i s by Meneely (1965) [37] f o r high power  C0 2  lasers. For o p e r a t i o n as an e l e c t r i c a l l y l a s e r the Brewster removed and  C0 2  angle mounted KCl windows should  the m i r r o r s forming  mounted d i r e c t l y on the r e a c t i o n are a source of l o s s chemical  excited  the r e s o n a t o r tube.  be  cavity  These KC£ windows  i n the c a v i t y but should be used f o r  l a s e r o p e r a t i o n because of the p o s s i b l e damage  to good q u a l i t y m i r r o r s by the chemicals  formed.  Another small item of p o s s i b l e value i s a mixing tank with f a c i l i t i e s  f o r p r e - c o o l i n g of the gas  This would lower the gas  k i n e t i c temperature and  mixture. thus  i n c r e a s e the l a s e r ' s g a i n . Failing  to f i n d  l a s e r a c t i o n with  pumping, gain measurements would be u s e f u l if  any  v i b r a t i o n a l l y e x c i t e d molecules  the d i s c h a r g e .  chemical to a s c e r t a i n  are produced i n  57  The design  use of t r a n s v e r s e gas flow makes t h i s  s u i t a b l e f o r studying  rates on the power o u t p u t . the vacuum system reaction  the e f f e c t of gas replacement This would r e q u i r e improving  ( i . e . place anode r e s i s t o r s  inside  tube) to e l i m i n a t e i m p u r i t i e s and c o n s t r u c t i n g  a fast repetition  r a t e high v o l t a g e  In c o n c l u s i o n t h i s  were detected  supply.  l a s e r v e s s e l has l i v e d  some but not a l l our e x p e c t a t i o n s . emissions  to allow o p e r a t i o n  from chemical  pumping  as an e l e c t r i c a l l y  processes  to e s t a b l i s h  the techniques and  infrared  in this  discharges  excited C 0 2 l a s e r ,  under v a r i o u s c o n d i t i o n s of f l o w , pressure helped  up to  Although no l a s e r  the arrangement d i d produce adequate t r a n s v e r s e  it  laser  and gas mixture  l a b , f o r the f i r s t  time,  of d e t e c t i o n and measurement of C 0 2 l a s e r s radiation.  REFERENCES Nighan, W.L. and J.H. 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" S e l e c t i v e E x c i t a t i o n Through V i b r a t i o n a l Energy T r a n s f e r and O p t i c a l Maser A c t i o n i n N 2 -C0 2 ." Phys. Rev. L e t t . , 1_3 ( 2 1 ) : 617-619.  14.  P a t e l , C.K.N., P.K. Tien and J.H. McFee. 1965. "CW High-Power C0 2 -N 2 -He Laser." A p p l . Phys. L e t t . , I (1 1 ): 290-292 .  15.  M o e l l e r , G. and J.D. Rigden. 1965. "High Power Laser A c t i o n i n C0 2 -He M i x t u r e s . " A p p l . Phys. L e t t . , I (10):274-276.  16.  P a t e l , C.K.W. 1964. "Continuous-Wave Laser A c t i o n on V i b r a t i o n a l - R o t a t i o n a l T r a n s i s t i o n s o f C0 2 ." Phys. Rev., 1_36 (5a): Al 1 87-A11 93.  17.  S o b o l e v , N.N. and V.V. Sokovikov. 1966. "A Mechanism Ensuring Level P o p u l a t i o n I n v e r s i o n i n C0 2 Lasers." Sov. Phys. - JEPT, 4:204-206.  18.  Boness, M.J.W. and G.J. S c h u l z . 1968. " V i b r a t i o n a l E x c i t a t i o n o f C0 2 by E l e c t r o n Impact." PHys. Rev. L e t t . , 21 (5):1031-1034.  19.  Cheo, P.K. 1967. " E f f e c t s of C 0 2 , He and N 2 on the L i f e t i m e s of the 0 0 ° 1 and 1 0 ° 0 C0 2 Laser L e v e l s and Pulsed Gain a t 10.6u." J . Appl. Phys., 38 (9):3563-3568.  20.  McKnight, W.B. 1969. " E x c i t a t i o n Mechanisms i n C0 2 L a s e r s . " J . A p p l . Phys., 40 (7):2810-2816.  D. van  60  21.  Y a r i v , Annon. Advances New York, 1967.  i n Quantum E l e c t r o n i c s .  Wiley,  22.  D a v i s , D.T., D.L. Smith and J . S . K o v a l . 1972. "Generation of S i n g l e 1-ns Pulses at 10.6um." IEEE J . Quantum E l e c t r o n . , QE-8:846-848.  23.  R i c h a r d s o n , M.C, A . J . A l c o c k , K. Leopold and P. B u r t y n . 1973. "A 300-J M u l t i g i g a w a t t C0 2 Laser." IEEE J . Quantum E l e c t r o n i c s , QE-9 (2):236-243.  24.  Daugherty, J.D. 1972. " E l e c t r o n Beam-Sustainer C0 2 Lasers." Presented at 7th I n t . Quantum E l e c t r o n i c s Conf., M o n t r e a l , Canada.  25.  F o r t i n , R., M. Gravel and R. Tremblay. 1971. "Helical TEA-C0 2 L a s e r s . " Can. J . Phys., 49:1783-1793.  26.  Lyon, D.L. 1973. "Comparison of Theory and E x p e r i ment f o r a T r a n s v e r s e l y E x c i t e d High-Pressure C0 2 Laser." IEEE J . Quantum E l e c t r o n i c s , QE-9 (2):139-153.  27.  G e r r y , E.T. and D.A. Leonard. 1966. "Measurement of 10.6u C0 2 Laser T r a n s i s t i o n P r o b a b i l i t y and O p t i c a l Broadening Cross S e c t i o n . " A p p l . Phys. L e t t . , 8 (9):227-229.  28.  B e a u l i e u , A . J . 1971. "High Peak Power Gas L a s e r s . " P r o c . of IEEE, 59 (4):667-674.  29.  G a r s i d e , B.K., E.A. B a l l i k and J . R e i d . 1972. "Pulse Delays i n TEA C0 2 L a s e r s . " J . A p p l . Phys., 43 (5):2387-2390.  30.  Kasper, J.V.V. and G.C. P i m e n t e l . 1965. "HCl Chemical Laser." Phys. Rev. L e t t . , 14 (10):352-354.  31.  J a c o b s o n , T.V. and G.H. K i m b e l l . 1971. " T r a n s v e r s e l y Pulse I n i t i a t e d Chemical L a s e r s : Atmospheric Pressure Operation of an HF Laser." J . Appl. Phys., 42 (9):3402-3405.  61  32.  Pummer, H. , W. B r e i t f e l d , H. W e o l l e r , G. Klement and K.L. Kompa. 1973. "Parameter Study of a 10-J Hydrogen F l u o r i d e Laser." A p p l . Phys. L e t t . , 22 (7):319-320.  33.  B a r r y , J.D. and W.E. Boney. 1971. "Laser Emission From He-Air-CHu and H e - A i r - C 3 H 8 M i x t u r e s . " A p p l . Phys. L e t t . , 1_8 (1):15-16.  34.  B a r r y , J.D. and W.E. Boney. 1972. "CO Laser A c t i o n by C 2 H 2 O x i d a t i o n . " A p p l . Phys. L e t t . , 20 ( 7 ) : 243-244.  35.  Boney, W.E., J.D. Barry and J . E . B r a n d e l i k . 1973. "CO and C0 2 Laser A c t i o n by Organic Molecule Oxidation." IEEE J . Quantum E l e c t r o n i c s , QE-9 (1):246-247.  36.  M i k o s h i b a , S. and B.A. A h l b o r n . 1973. "Laser M i r r o r with V a r i a b l e Focal Length." Rev. S c i . I n s t r . , 44 (4):508-51 1 .  37.  Meneely, C T . 1967. "Laser M i r r o r T r a n s m i s s i v i t y O p t i m i z a t i o n i n High Power O p t i c a l C a v i t i e s . " A p p l . Opt. , 6 (8):1434-1436.  38.  S t a n l e y , C.R. 1971. " I n f r a r e d Detectors f o r the Range 1.5-30um." O p t i c s and Laser T e c h . , August, 1971:144-149.  39.  P u t l e y , E.H. 1971. " I n f r a r e d A p p l i c a t i o n s of the Pyroelectric Effect." O p t i c s and Laser T e c h . , August, 1971:150-156.  40.  G i b s o n , A.F. and M.F. Kimmitt. 1972. "Photon Drag Detection." Laser Focus, August, 1972:26-8.  41.  Siegman, A.E. An I n t r o d u c t i o n to Lasers and Masers. McGraw-Hill, 1971 .  APPENDIX A  INFRARED DETECTORS The d e t e c t i o n of r a d i a t i o n infrared  i n the i n t e r m e d i a t e  range T.5u to 3 0 u [ 3 8 , 3 9 ] i s l i m i t e d  by  background  n o i s e , s i n c e at room temperature the peak of the black body r a d i a t i o n curve f a l l s radiation limits  this  near l O u .  l i m i t a t i o n may  the number of u s e f u l  For i n t e n s e  be bypassed but t h i s  Thermal  also  detectors.  There are three main types of i n f r a r e d t h e r m a l , p h o t o e l e c t r i c and  laser  detectors:  pyroelectric.  Detectors Thermal  d e t e c t o r s depend upon the heating p r o -  p e r t i e s of the r a d i a t i o n  to produce a temperature  rise  and hence i n v o l v e s a change i n the bulk p r o p e r t i e s of the d e t e c t o r element. wide s p e c t r a l  Although these d e t e c t o r s have a very  range they a l s o have very slow response times  and low power a b s o r p t i o n c a p a b i l i t i e s .  Thermocouples,  t h e r m o p i l e s , Golay c e l l s and c a l o r i m e t e r s have been used  62  63  to measure the power output of low but are too  slow f o r pulsed  C02  power cw  lasers.  C02  lasers  Thermal  detectors  are normally operated at room temperature.  Photoelectric  Detectors  Photoelectric detectors on  semiconductor m a t e r i a l s  action  between the  r e l y on a quantum  r a d i a t i o n and  tion creates a voltage or photoconductive  and  are e x c l u s i v e l y based  the d e t e c t o r .  interThe  radia-  s i g n a l by e i t h e r a p h o t o v o l t a i c  effect.  In d e t e c t o r s the r a d i a t i o n m o d i f i e s  based on  the p h o t o v o l t a i c  effect  the j u n c t i o n b a r r i e r p o t e n t i a l  between d i f f e r e n t i a l l y - d o p e d semiconductor m a t e r i a l s . Two  types of photoconductive d e t e c t o r s  are i n  use:  Intrinsic  Vino to conductive  Detectors  With these undoped semiconductor m a t e r i a l s radiation  i s detected  by  the a l t e r a t i o n  c o n d u c t i v i t y by d i r e c t e x c i t a t i o n band gap,  Eg  (see Figure A - l ( a ) ) .  of the  electrical  of e l e c t r o n s across Radiation  the  of energy  l e s s than Eg does not cause i n t r i n s i c a b s o r p t i o n Eq  the  but  since  i s a f u n c t i o n of temperature i t i s p o s s i b l e to decrease  CONDUCTION 4 BAND hi/  (a) INTRINSIC PHOTOCONDUCTIVE VALENCE /  BAND  e '  CONDUCTION BAND (b) N-TYPE EXTRINSIC PHOTOCONDUCTIVE  E ,  hi/  n 9  VALENCE BAND  CONDUCTION BAND (c) P-TYPE EXTRINSIC PHOTOCONDUCTIVE  hi/  VALENCE  Figure A - l .  BAND  Photoconductive Detectors.  65  Eg  by c o o l i n g the d e t e c t o r element thus  detector's  s p e c t r a l range.  increasing  the  PbS and InSb are two examples  of p h o t o c o n d u c t i v e d e t e c t o r m a t e r i a l s .  Both are o p e r a t e d  at room t e m p e r a t u r e w i t h the l a t t e r a l s o b e i n g used at 77°K ( l i q u i d  N ). 2  Extrinsic  Photo conductive  Detectors  These d e t e c t o r s are almost e n t i r e l y made of doped Germanium. tivity  In n - t y p e d e t e c t o r s  a conduc-  change o c c u r s w i t h e x c i t a t i o n of e l e c t r o n s from a  donor l e v e l is  (Figure A - l ( b ) )  i n t o the c o n d u c t i o n band.  When the  excitation  from the v a l e n c e band i n t o an a c c e p t o r l e v e l  the band gap ( F i g u r e A - l ( c ) )  we have a p - t y p e  within  detector.  Some dopants produce l e v e l s which are c l o s e to the upper l i m i t of the v a l e n c e band and as thus by thermal e x c i t a t i o n at room t e m p e r a t u r e .  It  filled is  there-  f o r e n e c e s s a r y to " f r e e z e o u t " these l e v e l s to have an e f f e c t i v e d e t e c t o r and reduce the background n o i s e . t e m p e r a t u r e s are commonly u s e d , 77°K ( l i q u i d (liquid  He).  N ) 2  Two  and 4°K  66  Pyroelectric  Detectors  The p y r o e l e c t r i c  detector  i s composed of a f e r r o -  e l e c t r i c m a t e r i a l which possesses a temperature permanent e l e c t r i c p o l a r i z a t i o n . the d e t e c t o r  i s converted  R a d i a t i o n absorbed by  i n t o heat which a l t e r s  l a t t i c e s p a c i n g of the f e r r o e l e c t r i c .  Below the  temperature a change i n e l e c t r i c p o l a r i z a t i o n from these l a t t i c e  the Curie  results  alterations.  Unlike other i n f r a r e d detectors signal  dependent  generated i s p o r p o r t i o n a l  the  voltage  to the time r a t e of change  of the temperature and thus the d e t e c t o r does not come i n t o e q u i l b r i u m w i t h the r a d i a t i o n .  Pyroelectric  are a l s o c a p a c i t i v e r a t h e r than r e s i s t i v e thus e s s e n t i a l l y an i n f i n i t e e l e c t r i c a l f r e q u e n c y  having  response.  During the c o u r s e of t h i s experiment i n f r a r e d d e t e c t o r s were u s e d :  devices  three  a g o l d doped Germanium  (Au:Ge) power d e t e c t o r , which i s a p - t y p e i n t r i n s i c conductive detector, a pyroelectric  a pyroelectric  energy m e t e r .  photo-  power d e t e c t o r and  Table A - i g i v e s  the  pertinent  data f o r each d e t e c t o r . The d e t e c t o r elements w i t h the n e c e s s a r y circuits  detector  are p r o v i d e d f o r by the m a n u f a c t u r e r s i n the  Gentec and M o l e c t r o n p y r o e l e c t r i c f o r the Au:Ge d e t e c t o r  it  detectors.  However,  i s n e c e s s a r y to c o n s t r u c t a  Tab Ie A - I C h a r a c t e r i s t i c s of  Detector A r e a (cm 2)  Detector Au :Ge  3.14 *  1.0  x x  10"2 10" 2  Respons i v i t y 1 .35 1.5  v/kw v/kw  Mo 1 e c t r o n 3.6  8.1  r i s e t i m e are  variable.  v / j 0 u1e  Gentec Responsivity t  and  When t e r m i n a t e d  with  I Mfl.  t  Infrared  Detectors  O p e r a t i ng Temperatu re  R i s e t i me  77°K  30  nsec  293°K  50  nsec  '293°K  5 msec  Recovery T i me  0.3  sec  68  circuit  f o r the d e t e c t o r  (Figure A-2)  r a t i o n f o r c o o l i n g the d e t e c t o r d e s i g n i s mounted i n a vacuum. to couple r a d i a t i o n i n t o the  100  A-2.  Figure  and a dewar  configu-  e l e m e n t , which i n our * A CaF window i s used 2  detector.  K  IJJF  Au:Ge D e t e c t o r O u t p u t v i a 50ft  Circuit; Cable.  To compare the responses of the d e t e c t o r s C0  2  l a s e r p u l s e a KCJl c o n v e r g i n g  lens  (f  = 9 . 7 cm, <> ) =  2 cm) was used to f o c u s r a d i a t i o n on the d e t e c t o r and mylar sheets were used as a t t e n u a t o r s  to a  elements  to p r e v e n t damage  to the d e t e c t o r s .  F i g u r e A - 3 shows t y p i c a l  o b t a i n e d w i t h each  detector.  oscillograms  The energy of the p u l s e i s found by o b t a i n i n g the peak v o l t a g e  from the Gentec o s c i l l o g r a m and knowing  the r e s i s t a n c e used to t e r m i n a t e the c o - a x i a l  *  Experimentally by f a c t o r of 0 . 4 2 .  cable  found to a t t e n u a t e l a s e r  the  pulse  69  (a)  (b)  (c)  Gentec Energy Meter  0.05 10  v/div msec/d i v  Au:G e Powe r Detector  2 0.5  usec/d i v  Molectron Power Detector  0.2  v/div  0.5  ysec/div  Figure  A-3•  Response to a C02  of Infrared Laser Pulse  v/div  Detectors  70  manufacturer's c a l i b r a t i o n joule. of  Terminating  curve  gives the number of v o l t s / the 1 Mft input impedance  the cable with  the o s c i l l o s c o p e gives a c a l i b r a t i o n  f i g u r e of 8.1  v/joule. When using the power d e t e c t o r s i t i s necessary to  terminate  the cable with  the RC time constant  a 50ft t e r m i n a t o r .  Otherwise  of the cable and o s c i l l o s c o p e  input  impedance network i s of the order of 50 usee and the o s c i l l o s c o p e would d i s p l a y the time i n t e g r a t i o n of the power d e t e c t o r ' s o u t p u t , which i s the energy  (see Figure  A-4) .  a) O u t p u t w i t h Figure  50ft t e r m i n a t o r . A-**.  Au:Ge  b ) O u t p u t w i t h , no t e r m i n a t o r  Power  Detector  Output.  Comparison of the pulse shapes obtained the Au:Ge and Molectron p y r o e l e c t r i c Molectron detail  power d e t e c t o r s show that the d e t e c t o r does not give as much  of the pulse shape as the photoconductive  detector.  with  Au:Ge  The f a s t r i s e t i m e of the pulse i s e v i d e n t i n  both o s c i l l o g r a m s but the Molectron  gives i n c r e a s e thus  71  cutting off  the t a i l of the l a s e r p u l s e .  Therefore i t  not p o s s i b l e to make e s t i m a t e s of the energy of the p u l s e u s i n g the M o l e c t r o n  is  laser  detector.  The c a l i b r a t i o n of the d e t e c t o r s was s e l f - c o n s i s t e n t l y v e r i f i e d u s i n g a 2 w cw C 0  2  laser.  The  radiation  was chopped at a f r e q u e n c y of 50 Hz and f o c u s e d on the d e t e c t o r elements u s i n g the KC£ l e n s .  Assuming t h a t  b r a t i o n of the Gentec energy meter was c o r r e c t ,  the  c u l a t e d r e s p o n s i v i t i e s of the Au:Ge and M o l e c t r o n  calical-  detectors  agreed w i t h the m a n u f a c t u r e r ' s v a l u e s to w i t h i n 10%. The d e t e c t o r used throughout  the experiment was  the l i q u i d n i t r o g e n c o o l e d Au:Ge d e t e c t o r . r e s u l t s have shown t h a t the s h o t - t o - s h o t is  Experimental  power  the same w i t h and w i t h o u t the KCJt l e n s .  variation  Therefore,  because the KCZ l e n s i s h y d r o s c o p i c and d e t e r i o r a t e s when exposed to the atmosphere, i t was d e c i d e d to make power measurements w i t h o u t the l e n s .  When u s i n g the l e n s  peak power i s i n c r e a s e d by a f a c t o r of 3 . 2 2 . c e r t a i n t h a t the l e n s  We are  (2 cm d i a m e t e r ) would cover  i m p o r t a n t p a r t s of the c r o s s - s e c t i o n of the l a s e r  (see F i g u r e  fairly  the tube  having measured the near f i e l d r a d i a t i o n p a t t e r n of laser  the  the  A-5).  Using the v a l u e of 1.35 v/kw f o r the  responsivity  and t a k i n g i n t o account the a t t e n u a t i o n by the C a F  2  window  2.5  2.3  2.1  1.9  1.7  1.5 X-AXIS  Figure  A-5.  Near  Field  1.3  I.I  0.9  (cm)  Radiation  Pattern.  ro  and the power i n c r e a s e i f  the l e n s was p r e s e n t a c a l i b r a -  t i o n f i g u r e of 5.68 kw/v was used to c a l c u l a t e the peak powers w i t h the Au:Ge d e t e c t o r .  APPENDIX B  SPECTRAL ANALYSIS The s p e c t r a l o u t p u t of the l a s e r was a n a l y z e d u s i n g a J a r r e l - A s h 0.5 m Ebert s p e c t r o m e t e r  (Model 82-010).  The g r a t i n g used was b l a z e d f o r 5.0u a t 21.6° w i t h a r u l e d area 52 x 52 mm s and had 148 Z/mm. 1  With t h i s  grating o  the l i n e a r d i s p e r s i o n a t t h e e x i t The e n t r a n c e and e x i t  s l i t was 128 A/mm.  s l i t s were both s e t a t 400u s l i t  width. The manual d r i v e of t h e s p e c t r o m e t e r was originally  c a l i b r a t e d w i t h a g r a t i n g of 1180 l/mm.  This  corresponds to a d i a l m u l t i p l i c a t i o n f a c t o r o f 1.0 and o  a maximum d i a l r e a d i n g of 8600 A .  With the 148 l/mm  g r a t i n g t h e maximum measureable wavelength was 6.85u which falls  s h o r t of the 10.6u r e g i o n n e c e s s a r y to study C02  radiation.  I t was t h e r e f o r e n e c e s s a r y to r e l e a s e the  g r a t i n g h o l d e r from the g r a t i n g p i v o t mount and r o t a t e the g r a t i n g by hand.  By f i r s t  o b s e r v i n g t h e zero  of the spectrum o f the c a l i b r a t i n g l i g h t  order  source and c o u n t i n g  the o r d e r s o f the s p e c t r a as the g r a t i n g was r o t a t e d 74  there  75  was no d i f f i c u l t y the 10.6u  i n p o s i t i o n i n g the g r a t i n g f o r use i n  region.  sources.  The s p e c t r o m e t e r was c a l i b r a t e d u s i n g  three  A He G e i s s l e r t u b e , a He-Ne a l i g n m e n t  laser  and a mecury (Hg)  lamp.  sodium i m p u r i t y and i t s  The mecury lamp c o n t a i n e d a spectrum e x h i b i t e d  d o u b l e t b e s i d e s the g r e e n , y e l l o w  the sodium D  and v i o l e t  Hg l i n e s .  When working i n the i n f r a r e d c a r e must be taken when o b t a i n i n g measurements of wavelength  s i n c e the  variation  of wavelength due to the changes i n the r e f r a c t i v e  index o  of a i r i s n o n - n e g l i g i b l e . f o r 10.6u.  It  A l l wavelengths  are those measured i n a i r . used f o r c a l i b r a t i n g the  i s of the o r d e r of 29 A  used w i t h the Table B-I  calibration  shows the  lines  spectrometer.  A s m a l l e r v e r s i o n of a t y p i c a l cruve i s shown i n F i g u r e B - l .  calibration  For wavelengths  greater  than ~ 10.6u the graph d i s p l a y s a n o n - l i n e a r i t y . i s not s u r p r i s i n g  because of the u n u s u a l l y  the g r a t i n g makes to the i n c i d e n t for correcting  non-linearities  large  radiation.  The  This angle procedure  of the s i n e bar d r i v e was  c a r r i e d out but t h e r e was no n o t i c e a b l e change and the non-linearity  remained.  The c a l i b r a t i o n data was a l s o a n a l y z e d by computer and l e a s t squares f i t s were o b t a i n e d .  A linear  3350  3530  3710  3890  4070  4250  SPECTROMETER DIAL SETTING Figure B - l . Spectrometer Calibration  Curve.  T a b l e B-I Spectral  Lines  Used  f o r Spectrometer  X  Source  o  nX  Order  (A)  Used  Calibration  Colour  o  (A)  Hg  lamp  5461  1 9  103,759  Green  Hg  1 amp  5790  1 8  104,220  Yellow  Hg  lamp  4358  24  104,592  B 1 ue  5875.6  1 8  105,761  Ye 1 1ow  6328  1 7  1 07,576  Red  5461  20  1 09,220  Green  Ge i s s 1 e r He-Ne Hg  tube  laser  1 amp  l e a s t squares f i t was done u s i n g o n l y t h e f i r s t of t h e c a l i b r a t i o n d a t a , w i t h the r e s u l t  four  points  shown below:  Y = (86896 ± 12) + (5.1289 ± .003)X  where, Y = wavelength X = dial  o  in A  s e t t i n g of spectrometer.  A quad r a t i c l e a s t  squares f i t  was a l s o  u s i n g a l l s i x data p o i n t s , w i t h the r e s u l t  being,  tried  Y = (84876 ± 55) + (6.2414 ± .029)X -  ( 0 . 1 5 x 10""* ± . 0 0 0 ) X  For o b t a i n i n g the s p e c t r a l was a l i g n e d as shown i n F i g u r e B - 2 .  2  o u t p u t the a p p a r a t u s The s p e c t r o m e t e r  SPECTROMETER  Figure  B-2.  Spectral  Analysis  Arrangement.  a l i g n m e n t was g r e a t l y f a c i l i t a t e d by u s i n g a s m a l l of u n t r e a t e d s t e e l which developed v i s i b l e l i g h t when h i t by the l a s e r r a d i a t i o n . was a l s o found to be e f f e c t i v e  piece  f l a s h e s of  Knurled  brass  i n a l i g n i n g the s p e c t r o m e t e r .  79  To compensate f o r t i o n and s c a t t e r i n g  the l o s s of power due to  the l a s e r power was i n c r e a s e d by  d o u b l i n g the amount of helium i n the gas m i x t u r e Section 4.2.2)  absorp-  so the volume r a t i o of He:N : C 0  When i d e n t i f y i n g  2  (see was  20:1:2.  l i n e s the s p e c t r o m e t e r d i a l was  a d j u s t e d to o b t a i n maximum peak power.  All  lines  were o  measureable to an a c c u r a c y of ± 1 d i a l d i g i t  or ~ ± 5 A.  The r e s u l t s o b t a i n e d are shown i n Table B - I I . T a b l e B-II Raw  Data  Mode o f Measu rement 2 slits exit  No  +  slit  slits  Peak Vo1tage  lens +  from S p e c t r a l  lens  + lens  Analysis  Dial S e t t i ng  Width o f * L i n e (A*)  1 .2 v  3706  45  1 .2 v O.I5v 0.02 v  3706 . 3669 3633  45 5 5  Range o f v a l u e s 3 5 4 5 - 3 7 7 1 , b u t not peaks d i s c e r n i b l e .  W i d t h o f l i n e i s r a n g e o v e r w h i c h any power o u t p u t i s obtained. I t i s n o t t h e h a l f power w i d t h .  The r e s u l t s  o b t a i n e d w i t h both s l i t s and the  l e n s are c o n s i d e r e d v a l i d d a t a . the e n t r a n c e s l i t  The data o b t a i n e d  removed i s a l s o c o n s i d e r e d v a l i d  with because  t h e r e was no n o t i c e a b l e i n c r e a s e i n the peak v o l t a g e the 3706 d i a l s e t t i n g .  at  T h i s i n d i c a t e s t h a t the KC£ l e n s  80  is effectively l e n s a c t s as i f the l a s e r beam.  f o c u s e d on the e n t r a n c e i t was the e n t r a n c e  slit.  slit  The data taken w i t h  2  s h o u l d be taken w i t h a g r a i n of s a l t . t h i s case i s e f f e c t i v e l y  by c o l l i m a t i n g  no s l i t s  i n d i c a t i o n of the p o s s i b l e range of C 0  Thus the  lines  gives  an  lasing,  The e x i t s l i t  the d i a m e t e r of the Au:Ge  element which i s 2 mm and thus the p o s s i b l e number  The r e s u l t s shown i n Table  of o  ± 256 A (2 mm x 128 A/mm).  o b t a i n e d w i t h no e n t r a n c e s l i t  B - i n . I n d e n t i f i c a t i o n of l i n e s  comparison w i t h s t a n d a r d C 0  2  spectra  (see Table  the l i n e P(12) -»• P(22) are a l s o  are  i s based upon B-iv ) .  From the c a l i b r a t i o n graph the data taken w i t h no indicates  in detector  o  l i n e s may be measured to w i t h i n  but  slits  present.  The s p e c t r o m e t e r was a l s o scanned i n the 9.6u r e g i o n but no l i n e s were  detected.  Table Identification  co  Graph  2  (A)  Linear  Y-P(J )  B-III of  C0  2  Lines  Fit  Quadratic  F i t  L i ne  Y  P(20)  1 05,940  - 1  105,904  ± 16  -37  105,878  ±121  -63  P ( 1 8)  1 0 5 , 748  +6  105,714  ± 16  -28  105,690  ± 120  -52  P( 1 6)  1 0 5 , 555  +8  105,529  ± 16  - 1 8  105,506  ±119  -4 1  Y  CA)  Y-P(J)  Y CA)  Y-P(J )  82  Table B - I V C02  Wavelengths rections Ed.),  from  Patel  C I 6 ] and c o r -  from C.R.C. Rubber B i b l e (50  A l l wavelengths  T r a n s i s t ion  in a n g s t r o m s .  Wave l e n g t h in Vacuum  C o r r e c t i on Wave 1ength Due t o A i r in A i r  •PC 1 8 ) PC20) PC22) PC24) PC26) PC28) PC30) PC32) PC34) PC36) PC38)  105,135 105,326 105,518 105,713 105,912 106,1 18 106,324 106,534 106,748 106.965 107,194 107,415 107,648 107,880  28.66 28.71 28.77 28.82 28.88 28.93 28. 99 29 .04 29. 1 0 29. 1 6 29.22 29.28 29.35 29 .4 1  PC22) PC24) PC26) .PC28) PC30) P (3,2) PC34)  95,691 95,862 96,063 96,211 96,391 96,576 96,762  26.09 26. 1 4 26. 1 9 26.23 26.28 26.33 2 6 . 38  P( 1 2 )  P( 1 4) PC 1 6)  00°I - I0°0  Transistions  i n vacuum  fora i r calculated  p . E-233  00°I-02°0 Band  Laser  105,163.7 105,354.7 105,546.7 105,741.8 105,940.8 106,146.9 106, 352. 9 106,563.0 1 06,777.1 106,994.1 107,223.2 107,444.3 107,677.3 107,909.4 95,717.1 95,888. 1 96,089.2 96,237.2 96.417.3 96,602.3 96,788.4  

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