RELATION BETWEEN THE STRIATION AND THE STIMULATED EMISSION IN A He-Ne LASER

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RELATION BETWEEN THE STRIATION AND THE STIMULATED EMISSION IN A He-Ne LASER

Hiroko Amemiya, T. Dote, S. Kawamoto

To cite this version:

Hiroko Amemiya, T. Dote, S. Kawamoto. RELATION BETWEEN THE STRIATION AND THE STIMULATED EMISSION IN A He-Ne LASER. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-389-C7-390. �10.1051/jphyscol:19797191�. �jpa-00219170�

JOURNAL DE PHYSIQUE ColZoque C7, strppldment au n07, Tome 40, JuiZZet 1979, page C7- 389'

RELATION BETWEEN THE STRIATION AND M E STIMULATED EMISSfON IN A He-Ne LASER

H. Amemiya, T. Dote and 5. ~awamoto'.

*Ins ti t u t e of Physical and Chemical Research Hirosma, Wakoshi, Saitama, Japan.

Sai tama U n i v e r s i t y , Saitama, Japan.

1. I n t r o d u c t i o n

The i n f l u e n c e o f d i s c h a r g e n o i s e such a s t h e s t r i a t i o n on t h e gas l a s e r p e r - f ormance h a s been s t u d i e d . ( 1 ) - ( 5 ) ~ n e o b j e c t of t h e p r e s e n t work i s t o reexamine i f t h e s t r i a t i o n would have always a damaging e f f e c t on t h e g a s l a s e r and t o s e a r c h a l a s i n g domain f r e e from such a wave.

Another o b j e c t i s t o s t u d y t h e i n f l u e n c e o f s t i m u l a t e d e m i s s i o n on t h e s t r i a t i o n . We t a k e up a He-Ne g a s l a s e r f o r t h e p u r p o s e o f t h i s i n v e s t i g a t i o n .

2.Experimental Apparatus

A p y r e x l a s e r t u b e o f 4mm~,L=80cm l o n g w i t h B r e w s t e r q u a r t z windows was used f o r

l a s e r o s c i l l a t i o n s a t 6328A and 3 . 3 9 ~ . A s a c a v i t y , c o n c a v e m i r r o r s w i t h i n d e x of r e f l e c t i o n r=0.99 and 1 n e a r r e d and t h e c u r v a t u r e r a d i u s R=2m were used f o r t h e v i s i b l e l i g h t w h i l e a concave m i r r o r w i t h r=0.90 n e a r 3 ~ and R = l m and an Au f l a t m i r r o r w i t h r-1 were used f o r t h e i n f r a r e d beam.The l a s e r i n t e n s i t y was d e t e c t e d by a p h o t o m u l t i p l i e r o r a l i q u i d N 2 c o o l e d Au-Ge semiconductor t h r o u g h a monochro- m e t e r a s a f u n c t i o n o f t h e d i s c h a r g e current.An o p t i c a l f i b e r was d r i v e n by a motor a l o n g t h e l a s e r t u b e t o p i c k up t h e s i d e l i g h t and o b t a i n an i n t e r f e r o m e t r y o f t h e s t r i a t i o n . The f l u c t u a t i o n i n t h e d i s - c h a r g e was measured by a spectrum a n a l y z e r and an a u t o c o r r e l a t o r .

3.Experimental R e s u l t s

F i g . 1 shows t h e o u t p u t i n t e n s i t y o f 6328A and 3 . 3 9 ~ l a s e r s a g a i n s t t h e d i s - c h a r g e c u r r e n t Id f o r some t o t a l p r e s s u r e s p ( T o r r ) , t h e p r e s s u r e r a t i o o f H e and Ne b e i n g 5 : l and 8 : l r e s p e c t i v e l y . C i r c l e s i n d i c a t e c r i t i c a l c u r r e n t s above which t h e

s t r i a t i o n was o b s e r v a b l e on t h e s p e c t r u m a n a l y z e r . The c r i t i c a l c u r r e n t s s h i f t e d t o a h i g h e r v a l u e a s p d e c r e a s e d . F o r 6328A, t h e o n s e t of s t r i a t i o n c o i n c i d e d w i t h t h e c u r r e n t g i v i n g t h e maximum i n t e n s i t y o f l a s e r o u t p u t between p=1.3 and 1 . 6 T o r r , b u t d e v i a t e d from i t a t lower and h i g h e r v a l u e s o f p . I n t h e r a n g e o f Id where t h e l a s e r e m i s s i o n was p r e s e n t , t h e s t r i a t i o n was w e l l r e g u l a r . W i t h i n c r e a s e o f I d , t h e 6328A e m i s s i o n d i s a p p e a r e d . C o n t r a r y t o t h e v i s i - b l e l a s e r , t h e o u t p u t c h a r a c t e r i s t i c o f 3.39

p l a s e r showed a more g r a d u a l v a r i a t i o n w i t h Id.Even a f t e r t h e s t r i a t i o n i n c r e a s e d i t s i n t e n s i t y and.became t u r b u l e n t , t h e l a s e r o s c i l l a t i o n p e r s i s t e d w i t h a s l i g h t d e c r e a s i n g tendency w i t h Id.

3 . 3 9 ~

1

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F i g . l a Fig. lb

F i g . 2 a shows f r e q u e n c y s p e c t r a of s i d e l i g h t w i t h Id a s a p a r a m e t e r . According a s Id i n c r e a s e d , t h e a m p l i t u d e o f s t r i a t i o n i n c r e a s e d and t h e f r e q u e n c y spectrum v a r i e d from monochromatic t o multimode and t h e n t o a b r o a d spectrum. F o u r i e r t r a n s f o r m a t i o n o f t h e a u t o c o r r e l a t i o n o f s t r i a t i o n showed a change from a s i n g l e peak t o m u l t i p l e p e a k s a s Id was r a i s e d . I n s p i t e o f t h e s i d e l i g h t modulation by t h e w a v e , t h e a m p l i t u d e modu-

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l a t i o n o f 6328A and 3 . 3 9 ~ l a s e r s by t h e i n t h e c a v i t y t o l o c k - i n d e t e c t any v a r i - s t r i a t i o n was v e r y s m a l l , a l t h o u g h t h e low a t i o n o f Id a s s o c i a t e d w i t h 3.391.1 e m i s s i o n f r e q u e n c y n o i s e l i k e l / f power s p e c t r u m b u t t h e change was t o o s m a l l t o e x p l a i n Af was w e l l o b s e r v a b l e . F i g . 2 b shows i n t e r - b y A I, from F i g . 3.

f e r o m e t r i e s of t h e wave a t e a c h v a l u e o f Id. I t i s s e e n t h a t t h e s p a t i a l c o h e r e n c e o f t h e s t r i a t i o n becomes s m a l l e r w i t h a n i n c r e a s e o f T -.

s p e c t r a o f s i d e l i g h t

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w h i l e t h e wave

l e n g t h i n c r e a s e d F i g . 3 s l i g h t l y w i t h Id.

F i n a l l y , t o i n v e s t i g a t e t h e e f f e c t of s t i m u l a t e d e m i s s i o n o n s t r i a t i o n t h e d i s - c h a r g e c u r r e n t was s e t a t a v a l u e where b o t h monochromatic s t r i a t i o n and 3.3911 e m i s s i o n were p r e s e n t . When t h e l a s e r was s p o i l e d by i n s e r t i n g a n o b s t r u c k i o n i n t h e c a v i t y , a f r e q u e n c y s h i f t - a £ o c c u r r e d i n t h e s t r i a t i o n s p e c t r u m and o c c a s i o n a l l y s i d e bands a p p e a r e d , a s shown i n F i g . 4 a . F i g . 4 b shows t h e f r e q u e n c y s h i f t A f v s . l a s e r o u t p u t I o f 3 . 3 9 ~ 1 a t p=0.92 T o r r . I t i s s e e n t h a t A f h a s a t f i r s t a l i n e a r de- pendence on I b u t t h e n r e a c h e s a c o n s t a n t v a l u e a t a l a r g e r 1 . A chopper was i n s e r t e d

0.92 T o r r

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F i g . 4b 2kHz/div.

4 . ~ i s c u s s i o n and C o n c l u s i o n

One c a n s e e from F i g . 1 t h a t f o r 6328A i t i s p o s s i b l e t o s e e k a l a s i n g domain f r e e from t h e s t r i a t i o n and a n y s i g n i f i - c a n t o u t p u t d r o p , a l t h o u g h t h e s i t u a t i o n i s less f a v o r a b l e f o r 3 . 3 9 ~ . The r e a s o n why, w h i l e t h e l / f power n o i s e a p p e a r b o t h i n

t h e s i d e l i g h t and t h e l a s e r , t h e s t r i a t i o n a p p e a r s much l e s s i n t h e l a t t e r may b e a s f o l l o w s . The l a s e r beam p a s s e s a l t e r n a t e l y t h r o u g h p a r t s w i t h l a r g e and s m a l l i n v e r - s i o n s whose wave l e n g t h i s a b o u t lcm(<<L) t o c a n c e l t h e m o d u l a t i o n e f f e c t . F u r t h e r , t h e f r e q u e n c y i s h i g h e r t h a n t h e i n v e r s e l i f e t i m e o f He(2S) and N e ( 1 s ) , e t c .

On t h e o t h e r hand, t h e l a s e r c a u s e s a f r e q u e n c y s h i f t o f t h e s t r i a t i o n , which i s n o t a r e s u l t o f a change o f Id a s s u g g e s t - e d by F i g . 3, b u t may b e d u e t o a change o f l e v e l d e n s i t i e s i n t h e r a t e e q u a t i o n . Thus a L a s e r t u b e may become a u s e f u l t o o l f o r a m i c r o s c o p i c s t u d y o f t h e d i s c h a r g e . R e f e r e n c e s

l.A.Garscadden:Appl.Phys.Lett.8 ( ' 6 6 ) 85 2.A. Z e o t s e v e t al:Sov.Phys. (T.P) 14 ( ' 6 9 ) 575 3.T.Suzuki:Jap.J.Appl.Phys.9 ( ' 7 0 ) 309 4.YuG. Zakharenko: O p t - S p e c t . 37 ( ' 7 4 ) 990 5.L.A.Malenikov e t a l : i b i d . 3 8 ( ' 7 5 ) 791 6.L.N.Guskov e t a 1 ^: i b i d . 4 0 ( ' 7 6 ) 1 7 0 ,

39 ( ' 7 4 ) 528