KINETIC PROCESSES IN NON-HEATED COPPER VAPOUR LASER

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Submitted on 1 Jan 1979

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KINETIC PROCESSES IN NON-HEATED COPPER VAPOUR LASER

A. Ludmirsky, Ch. Cohen, Yu. Kagan

To cite this version:

A. Ludmirsky, Ch. Cohen, Yu. Kagan. KINETIC PROCESSES IN NON-HEATED COP- PER VAPOUR LASER. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-373-C7-374.

�10.1051/jphyscol:19797183�. �jpa-00219161�

JOURNAL DE PHYSIQUE ColZoque C7, supplgment au n07, Tome 40, JuiZZet 1979, page C7- 373

KINETIC

IN

A. Ludmirsky, Ch. Cohen and Yu. Kagan.

The Hebrew University of Jerusalem, fie Racah I n s t i t u t e o f Physics, JerusaZem,IsraeZ.

Copper vapour l a s e r s a t t r a c t e d a t t e n t i o n owing t o t h e i r h i g h e f f i c i e n c y i n the v i s i b l e r e g i o n o f the spectrum. I n conventional copper vapour l a s e r s , a temperature o f 150o0C i s needed t o achieve the r e - q u i r e d vapour pressure. A lower temperature (400°C -600OC) i s r e q u i r e d i n a double-pulse l a s e r s u s i n g copper ha1 ides (1.2). These temperatures a r e usu- a l l y o b t a i n e d by power d i s s i p a t i o n o f t h e a p p l i e d discharge operated a t a r e l a t i v e l y h i g h r e p e t i t i o n r a t e ( 3 ) . A p r o m i s i n g method f o r decreasing t h e working temperature o f a copper vapour l a s e r i s t h e pulsed i n t r o d u c t i o n o f vapour I n t o t h e working vo- lume of t h e l a s e r (4,5,6).

Copper vapour l a s e r w i t h i n d u c t i v e l y produced copper plasma, which i s a c c e l e r a t e d by a pulsed ma- g n e t i c f i e l d , operates a t room temperature i n a double-pulse mode (7). The magnetic f i e l d was ge- n e r a t e d by t h e discharge o f a c a p a c i t o r (0.7 pF, 30KV) through a s o l e n o i d mounted o u t s i d e a g l a s s tube (10cm bore and 175cm long) f i l l e d w i t h helium.

The p o p u l a t i o n d e n s i t i e s o f b o t h t h e ground and 2~5,2 metastable s t a t e s o f cdpper atoms were d e r i - ved from measurements o f t h e o p t i c a l a b s o r p t i o n a t 324.7nm and 510.6nm, r e s p e c t i v e l y , over a wide range o f t h e h e l i u m pressure. These measurements were made a l o n g the tube a x i s and across t h e tube t o e l i - minate the i n f l u e n c e o f t h e h e t e r o g e n e i t i e s o f t h e copper vapour moving i n t h e a x i s d i r e c t i o n a t t h e

i n s t a n t o f vapour p r o d u c t i o n .

A t r i g g e r e d xenon f l a s h tube was used as the sour- ce f o r a b s o r p t l o n measurements.

A l e n s focused t h e l i g h t o n t o t h e enterance s l i t o f a I-m monochromator equipped w i t h 10pm s l i t s and a p h o t o m u l t i p l i e r tube (PMT) a t t h e e x i t s l i t .

The PMT s i g n a l was d i s p l a y e d on an o s c i l l o s c o p e and recorded on P o l a r o i d f l lm.

Ground s t a t e and m e t a s t a b l e copper d e n s i t i e s were computed from t h e measured a b s o r p t l o n by employing

the methods described by M i t c h e l l and Zemansky (8).

The a b s o r p t i o n c o e f f i c i e n t o f the copper ground s t a - t e o r metastable s t a t e was obtained u s i n g t h e V o i g t p r o f i l e , which i n c l u d e s t h e e f f e c t s o f Doppler, na- t u r a l resonance, and Van der Waals broadening. The h y p e r - f i n e s t r u c t u r e and isotope s h i f t were taken

i n t o account i n t h e c a l c u l a t i o n .

The temporal v a r i a t i o n o f t h e temperature i n t h e a f t e r g l o w was s t u d i e d by f a s t - s c a n i n g Fabry-Perot spectroscopy (9). The temperature o f the copper vapour was determined f tom t h e Doppler broadening o f t h e 521.8nm copper l i n e . T h i s 1 i ne was s e l e c t e d

i n o r d e r t o exclude i s o t o p e s h i f t e f f e c t s .

The tenlperature medsurements were made across o f the tube t o exclude t h e v e l o c i t y broadening e f f e c t s o f t h e moving copper vapour along t h e a x i s d i r e c t i o n .

The temporal v a r i a t i o n o f t h e temperature o f t h e copper vapour ( F i g . 1 ) was taken i n t o account f o r

l i n e p r o f i l e i n t e r p r e t a t i o n .

The s l t t - f u n c t I o n was determined w i t h t h e h e l p o f a copper hollow-cathode lamp. The s i l t f u n c t i o n was used t o c a l c u l a t e a b s o r p t i o n c o e f f i c i e n t s fro111 a

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797183

continuum r a d i a t i o n source.

The d e n s i t i e s o f b o t h t h e ground and metastable

REFERENCES

s t a t e s o f copper atoms w i t h h e l i u m a t d i f f e r e n t 1. C.I. Chen, N. Nerheim, and G. Russel

pressures a r e shown i n F i g . 2. Appl. Phys. L e t t . 23, 514 (1973)

Only measurements o f the ground-state d e n s i t i e s a t 2. 1 . Liberman, R. Babcock, C. L i n , T. George h i g h e r h e l i u m pressures a r e shown as metastable l e - and i. Weaver, Appl. Phys. L e t t . 25,334 (1974) v e l s were n o t d e t e c t a b l e . 3. A. I s a r v , M. Kazaryan and G. petrash;

The metastable l e v e l d e n s i t y decays r a p i d l y from ZhETF P i s . Red 16,40, (1972)

an i n i t i a l l y h i g h v a l u e w h i l e t h e ground-state 4. G.R. Russel. N.M. Nerheim and T . J . P i v i t o t t o , d e n s i t i e s e x i s t up t o 2ms. w i t h o u t n o t i c a b l e changes. Appl. Phys. L e t t . 21, 565 (1972)

KEY

I n our experiments a l o n g i t u d i n a l e x c i t a t i o n p u l s e from a 3500pF c a p a c i t o r charges t o 30KV was a p p l i e d 300-2000~.fSf2Cafter t h e vapour production.Lasing was o b t a i n e d o n l y w i t h low he1 ium pressure (2 t o r r ) , because o f the d i f f i c u l t y o f o b t a i n i n g a l o n g i t u d i - n a l glow discharge between e l e c t r o d e s separated by

175 cm.

The maximum l a s e r o u t p u t energy was lOr11J w i t h a p u l s e d u r a t l o n o f 150nsec. Lasing on b o t h green and y e l l o w l i n e s was detected. The mentioned l a s e r ene-

r g y was o b t a l n e d w i t h o u t o p t l m i z a t l o n o f l a s e r para- meters.

Study o f h l g h efficiency copper l a s e r s w l t h pulsed p r o d u c r l o n o f vapour i s c a r r i e d o u t by t h e authors.

5. J.F. Asmus ans N.K. Moncur, Appl. Phys. L e t t . 13,384 (1968)

6. A.M. Shukhtln, G.A. Fedotov and V.G. Mishakov, Opt. Spectroscopy 40, 237, (1976)

7. A. Ludmirsky. Laser ( f i l e p a t e n t a p p l i c . i n the USA, N889396 f rom 28/3/78).

8. A.C. M i t c h e l l and M.N. Zemanski, Resonance R a d i a t i o n and E x c i t e d Atoms (Cambridge U n i v e r s i t y Press, London

,

9. A. Ludn~lrsky, C. Cohen and Yu. M. Kagan Appl. O p t i c s , Jan 1979.