APPLICATION OF RF DISCHARGE WITH ROTATING ELECTRIC FIELD FOR EXCITATION OF CO2-LASER

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APPLICATION OF RF DISCHARGE WITH ROTATING ELECTRIC FIELD FOR EXCITATION

OF CO2-LASER

B. Kuteev, A. Smirnov, A. Zhilinsky

To cite this version:

B. Kuteev, A. Smirnov, A. Zhilinsky. APPLICATION OF RF DISCHARGE WITH ROTATING

ELECTRIC FIELD FOR EXCITATION OF CO2-LASER. Journal de Physique Colloques, 1979, 40

(C7), pp.C7-395-C7-396. �10.1051/jphyscol:19797194�. �jpa-00219173�

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JOURNAL DE PHYSIQUE CoZZoque C7, supptdment au n07, Tome 40, JuiZZet 1979, page C7- 395

APPLICATION OF RF DISCHARGE WITH ROTATING ELECTRIC FIELD FOR EXCITATION OF C02-LASER

B.V. Kuteev, A.S. Smirnov and A.P. Zhilinsky.

KaZinin Po ZytechnicaZ Ins t i t u t e , RadiophysicaZ Department, Leningrad/U. S. S . R.

I t ' s w e l l known, t h a t t h e r m a l i n s t a - b i l i t y l e a d s t o t h e c o n s t r i c t i o n of glow d i s c h a r g e and r e s t r i c t s t h e i n c r e a s i n g of g a s p r e s s u r e i n GO2-lasers. E x t e r n a l i o n i s a t i o n by e l e c t r o n beam i s one of t h e most e f f e c t i v e methods of d i s c h a r g e sta- b i l i s a t i o n

[I]

. However s e a r c h of a n o t h e r methods of i n s t a b i l i t y damping i s not

stopped. I n r e c e n t t h e o r e t i c a l i n v e s t i g a - t i o n s E2,3] i t was shown t h a t e l e c t r i c f i e l d r o t a t i o n w i t h frequency exceeding t h e i n s t a b i l i t y growth r a t e may l e a d t o t h e s t a b i l i s a t i o n of glow d i s c h a r g e . T h i s

The o u t p u t power of each a m p l i f i e r e x c i - ded

1

kl. Phase s h i f t between a m p l i f i e r s i g n a l s was v a r i e d from 0 t o 180°. Ref.

p u l s e d u r a t i o n was 5 msec, i t s p e r i o d 1.6 s e c . Gas m i x t u r e of C02:N2;He (1:6:12 by molar c o n c e n t r a t i o n ) have been i n v e s t i g a -

t e d . The main d i s c h a r g e p a r a m e t r e s were v a r i e d i n f o l l o w i n g ranges:

g a s p r e s s u r e p=1+250 T o r r s p e c i f i c power W= 1 +50 W/cm 3 ' e l e c t r i c f i e l d E=10+30 V/cm T o r r c u r r e n t d e n s i t y j=5+60 mA/cm

²

-Gain of t e s t C02-laser r a d i a t i o n a t e f f e c t h a s been e x p e r i m e n t a l l y observed h = 1 0 . 6 ~ ~ was measured a f t e r s i n g l e p a s s i n s t a t i o n a r y r . f . d i s c h a r g e 141. I n t h i s of d i s c h a r g e volume. T y p i c a l dependance corm~unication vie d e s c r i b e t h e e x c i t a t i o n

of C02-laser m i x t u r e s i n p u l s e d r e f . d i s - charge w i t h l i n e a r and c i r c u l a r e l e c t r i c f i e l d p o l a r i s a t ion.

The d i s c h a r g e t a k e s p l a c e i n c y l i n d - r i c a l g l a s s t u b e w i t h i n n e r d i a m e t e r 1.3 cm and l e n g t h

50

cm, Four e l e c t r o d e s 27 cm i n l e n g t h and 0,7 cm i n width were a d j u s t e d on e x t e r n a l s u r f a c e a l o n g t h e tube. E l e c t r o d e s were c u t from t h e b r a s s t u b e w i t h i n n e r d i a m e t e r 1.5 cm equal t o t h e g l a s s t u b e e x t e r n a l diameter. R.f.

o f g a i n c o e f f i c i e n t K v e r s u s time t o b t a i n e d i n d i s c h a r g e w i t h c i r c u l a r pola- r i s a t i o n of e l e c t r i c f i e l d i n gas pres- s u r e 250 T o r r i s shown i n fig.1. I n i t i a l g a i n i n c r e a s i n g i s due t o s e t up o f d i s - charge parametres. Subsequent g a i n de- c r e a s e can be e x p l a i n e d by g a s h e a t i n g . Energy i n p u t Q h a s been e s t i m a t e d u s i n g time

C

e q u a l t o p o s i t i v e g a i n d u r a t i o n and s p e c i f i c power

V! .c

Q I

----

P

power supply of I MEGC f r e q u e n c y from

f

- g a s d e n s i t y

two s e p a r a t e a m p l i f i e r s was f e d t o each I n experiments w i t h l i n e a r e l e c t r i c p a i r of o p p o s i t e l l y placed e l e c t r o d e s . f i e l d p o l a r i s a t i o n only one p a i r of e l e c -

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797194

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trodes and one amplifier were used, The dependance of maximum gain coefficient

%ax versus gas pressure is sholvn in fig.2 (curve I), When p exceeded 100 Torr dis- charge arced and luminous region occupied 1/3+1/5 of the tube length. This being.

the case gain vanished. Discharge was com- pletely uniform when gas pressure was less then 30 Torr. When 3 0 4 p

4100

Torr strea- mers

0.1

cm in diameter parallel to dis- charge current were observed. Their origin is apparently connected with ionisation of metastable molecules [ 5 ] . The strea- mers

didn't

effect strongly on gain coef-

f icient .

In case of circular electric field polarisation discharge arcing wasn't ob- served-in the whole range of gas pressure.

The dependance of gain coefficient versus p is shown in fig.2 (curve 24. Sometimes

discharge. Efficiency of linear polarisa- tion discharge is lower, Nevertheless the the Kmax values achived are of practical interest

The results presented indicate that the rotating field discharge can be suc- cesfully used for GO2-laser excitation, This method may be useful for another gas laser excitation both alone and in combi- nation with the external ionisation, References:

1. E.P.Velikhov, V.D.Pismenny, A,T. Rak- himov. UFI?, -- ¹²² ⁴¹⁹ ^, ¹⁹⁷⁷

^e

2.

G.I.Shapiro. Pisma v ZhTF, 2 , ^189,1976

3. A,V.Kuteev, A.S.Smirnov. Pisma v ZhTF

4, ^111,

^1978.

4. A.P,Zhilinsky et al. ZhTP, $3,2260,1978 5. A.P.I?apartovitch, A.H.Star0sti.n.

Fisika Plasmy, 2 , ^{5, 1976.}

larger values of K , , , nave been achieved.

Values of W, 5 , ^,

^Q,

^, ^, ^[ ^I obtained with a 1

maximum gas pressure are presented in

table

1.

Energy input Q was approximately i equal to 500

j/g,

This values are close to the theoretical limit and to the data achieved in electron beam controlled dis- charge. Theoretical values of sax ^were

calculated in assumption that 50"J of to- tal discharge power is spent to high-ly- ing laser level excitation and gas tempe- rature is equal to 300 OK. For discharge with circular polarisation calculated values of sax are in a good agreement with the experimentally observed ones. It indicates a high homogeniety and effici- ency of power input in ro'mting field

Table

1,

"v5b ^Fig, ^I

Polari- sation linear circular

1

Î Î Î ^B

0

50

100

150 200 p, Torr h g . 2

TJ

W/cm3

19 50

P Torr

100 250

ms 2

2

Q

j i g

500 500

%ax