1. I n t r o d u c t i o n The i n f l u e n c e of 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 perf 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 gas 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 of s t i m u l a t e d e m

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... s s i o n on t h e s t r i a t i o n . W e t a k e up a He-Ne gas l a s e r f o r t h e purpose of t h i s i n v e s t i g a t i o n . 2.Experimental Apparatus A pyrex l a s e r t u b e of 4mm~,L=80cm l o n g w i t h Brewster 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 index 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 N2 cooled Au-Ge semiconductor through a monochrometer a s a f u n c t i o n of 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 of 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 scharge 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 of 6328A and 3 . 3 9~ l a s e r s a g a i n s t t h e d i scharge 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 spectrum 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 . For 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 of p. I n t h e range 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 of I d , t h e 6328A emission d i s a p p e a r e d . Contrary t o t h e v i s ib 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 -F i g . l a Fig. lb F i g . 2 a shows frequency 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 parameter. 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 frequency spectrum v a r i e d from monochromatic t o multimode and t h e n t o a broad 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 peaks a s Id was r a i s e d . I n s p i t e of t h e s i d e l i g h t modulation by t h e wave,the amplitude modu-Article published online by EDP Sciences and available at http://dx.