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METASTABLE ATOMS IN GASDYNAMIC JETS :
LASER DIAGNOSTICS AND STUDIES FOR
MOLECULAR ELECTRONIC TRANSITION LASERS
U. Brinkmann, J. Kluge
To cite this version:
JOURNAL DE PHYSIQUE CoZZoque C9, suppZ6ment au nO1l, Tome 41, novembre 1980, page C9-299
METASTABLE ATOMS I N GASDYNAMIC J E T S
:
LASER D I A G N O S T I C S AND S T U D I E S FOR MOLECULAR ELECTRONIC T R A N S I T I O N LASERSU. Brinkmann and J. Kluge.
I. Physikalisches I n s t i t u t der Universitdt B Z n , 0-5000 KiiZn 41, Fed. Rep. of Germany.
RQsum6.- Nous Qtudions l'utilitQ d'une source gasdynamique pour des systsmes lasers actifs dans les transitions Qlectroniques molQculaires. Le jet transporte des atomes mstastables c o m e particules rQactives. Des atomes de Ca, Sr, Ne, Hg sont utilisQs pour ces expEriences. La densit5 et La distri- bution de la vitesse des atomes c~(~P) sont mesurges par la fluorescence produite par un laser. Les contours des bandes molQculaires de CaC1, SrCl excitges par les rQactions sont analys6s concernant une inversion de population. On ne peut pas encore dire si la source est utilisable pour le rdsultat P obtenir.
Abstract.- The utility of a gasdynamic jet carrying atoms in metastable states as reactants for an electronic transition molecular laser system is investigated Ca, Sr, Ne, Hg atoms are used. The den- sity of Ca atoms in the metastable 3~ states and their velocity distribution have been measured us- ing laser induced fluorescence. Spectral shapes of the bands belonging to the product molecules Ca Cl, SrCl are studied with respect to possible population inversion. Presently the applicability of the source for that aim is still open.
The i d e a t o g e n e r a t e c o h e r e n t r a d i a t i o n i n m o l e c u l a r e l e c t r o n i c t r a n s i t i o n s s t i l l f a s - c i n a t e s l a s e r p e o p l e . U n f o r t u n a t e l y , o u t o f t h e v a s t f i e l d o f v i s i b l e c h e m i l u m i n e s c e n t r e a c t i o n s n o n e o p e n e d t h i s p o s s i b i l i t y , s o f a r g r o u n d s t a t e r e a c t a n t s a r e u s e d . How- e v e r , t a k i n g e x c i t e d a t o m s t h e p r o d u c t m o l - e c u l e s c a n b e f o r m e d w i t h f a v o r a b l e b r a n c h - i n g i n t o e x c i t e d s t a t e s s o t h a t p o p u l a t i o n i n v e r s i o n i s o b t a i n e d . The r a r e g a s h a l i d e s
b ]
a n d Hg h a l i d e s [2,31 a r e w e l l known e x - a m p l e s . High c r o s s s e c t i o n s f o r t h e f o r m a - t i o n o f e x c i t e d p r o d u c t m o l e c u l e s h a v e b e e n f o u n d i n r e a c t i o n s o f e a r k h a l k a l i n e a t o m s i n m e t a s t a b l e s t a t e s l e a d i n g t o o x i d e sk.51
a n d h a l i d e s b,7]. T h e r e f o r e e f f o r t s t o a c h i e v e l a s i n g i n t h e s e s y s t e m s a r e r e a s o n - a b l e . An a t t r a c t i v e f e a t u r e o f b o t h t h e r a r e g a s a n d Hg h a l i d e s y s t e m s i s t h a t l a s i n g f o l - l o w s e f f e c t i v e l y t h e f o u r - l e v e l s c h e m e ( c . f . f i g . 3 b . c ) . G e n u i n e cw l a s i n g h a s n o t y e t b e e n a c h i e v e d , b u t l o n g - p u l s e l a s e r a c - t i o n w a s o b s e r v e d i n some c a s e s [ 8 , 9 ] . I n o r d e r t o s u s t a i n cw l a s e r a c t i o n a n e f f i - c i e n t e x c i t a t i o n t e c h n i q u e i s i n d i s p e n s a b l e . F o r t h i s r e a s o n a s o u r c e o f a l k a l i n e e a r t h a t o m s i n m e t a s t a b l e s t a t e s w a s d e v e l o p e d w h i c h c o m b i n e s e f f i c i e n t e x c i t a t i o n o f t h e a t o m s i n d i s c h a r g e s a n d t h e i r c o l l i m a t i o n i n a g a s d y n a m i c j e t [10,11]. B r i e f l y , a r a r e g a s j e t i s f o r m e d by a n o z z l e ( i n n e r d i a m e t e r a c c o r d i n g t o o p e r a t i n g c o n d i t i o n s 2 - 4 mm 1 . I t p a s s e s a h o l l o u c a t h o d e i n t o w h i c h t h e m e t a l a t o m s d i f f u s e , a n d e x p a n d s i n t o t h e r e c i p i e n t c a r r y i n g e x c i t e d a t o m s . An a d d i t i o n a l d i s c h a r g e i s b u r n t a l o n g t h e j e t t o e n h a n c e e x c i t a t i o n . R e a c t i v e g a s e s a r e a d m i x e d w i t h t h e r e s u l t t h a t b r i g h t mo- l e c u l a r s p e c t r a o f CaC1. S r C l a r e e m i t t e d c 2 ] . The s p e e d o f t h e j e t c a n b e made s u - p e r s o n i c s o t h a t a l t e r n a t e e x p a n s i o n a n d c o m p r e s s i o n z o n e s become v i s i b l e fi0,13]. T h e s e p r o p e r t i e s s u p p o r t t h e h o p e s t i m u l a - t e d e m i s s i o n t o b e r e a l i z a b l e . I n t h i s c o n t r i b u t i o n we r e p o r t o n s t u d i e s t o e x p l o i t t h i s e x c i t a t i o n s c h e m e f o r cwc9-300 JOURNAL DE PHYSIQUE m o l e c u l a r e l e c t r o n i c t r a n s i t i o n l a s e r s . We r e f e r t o a r e c e n t a n a l y s i s o f t h e j e t b y l a s e r i n d u c e d f l u o r e s c e n c e
fi
l ] , d e s c r i b e t h e e x c i t a t i o n o f C a C l a n d S r C l i n t h e j e t , a n d t h e s e t - u p f o r HgCl c u r r e n t l y u n d e r i n - v e s t i g a t i o n . I . L a s e r d i a g n o s t i c s o f t h e j e t A p r e r e q u i s i t e o f a n y l a s i n g i s t h e s t o r a g e o f s u f f i c i e n t e n e r g y i n a r e s e r v o i r s t a t e , f o r i n s t a n c e i n t h e m e t a s t a b l e 3~ s t a t e s o f C a . L a s e r i n d u c e d f l u o r e s c e n c e ( L I F 1 a n d l a s e r beam a b s o r p t i o n . h a v e b e e n u s e d t o t r a c e t h e v e l o c i t y d i s t r i b u t i o n a n d s t a t e 3 d e n s i t y o f C a ( P ) a l o n g t h e j e t 11-
.
W i t h a s i n g l e - m o d e R h o d a m i n l a s e r p 4 1 t h e l i n e s i n t h e 4 s 4 p 3 ~ - 4 s 5 s 3~ m u l t i p l e t c a n b e e x - c i t e d . T h e s e t - u p i s s h o w n i n f i g . 1 .(
dye loser beamin the elctronic ground state of HgBr has [g] now been realized [19]. Therefore favorable
conditions are met for cw lasing.
Cl
01F
fl
The support of this work by the OeutscheForschungsgemeinschaft is gratefully
F
23ac knoledged.
E
31[ l ] For a review see Ch.K. Rhodes, Topics
D
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