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MICRO-WAVE DETECTION OF LASER ENHANCED IONIZATION OF METALS IN FLAMES

T. Berglind, L. Casparsson
1983 Le Journal de Physique Colloques  
Ri.sum6 -Dans et article, l a dstection h l ' a i d e de micro-ondes des signaux =sation a u g m n t e h l ' a i d e d'un l a s e r est present&. W principal avantage de l ' u t i l i s a t i o n des micro-ondes par rapport 5 une detection en courant continu est que le champ produit par ces ondes p u t &re maintenu h si bas niveau que l a cin6tique de l a f l a m e n ' e s t pas perturb&. A b s t r a c t -I n t h i s paper micro-wave d e t e c t i o n o f l a s e r enhanced i o n i z a t i o n
more » ... o n i z a t i o n s i g n a l s i s r e p o r t e d . The b a s i c advantage o f u s i n g micro-waves i n s t e a d o f u s i n g DC d e t e c t i o n i s t h a t t h e micro-wave f i e l d can be k e p t a t such low l e v e l s t h a t t h e k i n e t i c s o f t h e flame i s l e f t u n d i s t u r b e d . I n t r o d u c t i o n I n 1976 a group a t NBS, Washington, D.C., developed a new l a s e r technique f o r det e c t i o n o f small t r a c e s o f atoms and molecules i n flames. I n s t e a d o f u s i n g t h e f l u o r e s c e n c e l i g h t , t h a t atoms and molecules e m i t when e x c i t e d , t h e i o n i z a t i o n enhancement was d e t e c t e d /l/. A DC f i e l d was a p p l i e d t o t h e flame and t h e l a s e r induced i o n i z a t i o n enhancement was measured as a c u r r e n t i n c r e a s e through t h e flame. T h i s method proved t o be v e r y p o w e r f u l . D e n s i t i e s o f metal atoms down t o t h e o r d e r o f 106 atoms/cm3 have been detected. However, when s t u d y i n g t h e flame one has t o t a k e i n t o c o n s i d e r a t i o n t h a t t h e presence o f a DC f i e l d m i g h t change t h e k i n e t i c s , s i n c e t h e charges t h a t a r e c r e a t e d i n t h e flame by thermal processes a r e e x t r a c t e d from t h e flame. I n t h i s paper we p r e s e n t a d i f f e r e n t p o s s i b i l i t y t o d e t e c t l a s e r enhanced i o n iz a t i o n ( L E I ) w i t h o u t removing t h e charges from t h e flame. T h i s i s done by detect i n q t h e a t t e n u a t i o n o f a weak micro-wave f i e l d t r a v e r s i n g t h e flame. Laser enhanced i o n i z a t i o n The process o f LE1 can be described i n t h e f o l l o w i n g way: 1. Laser e x c i t a t i o n o f t h e t r a c e atom o r molecule X X t h v -p Xexc g r 2. Subsequent c o l l i s i o n a l i o n i z a t i o n : Xexc+M + X + +~-+ M where M i s a flame molecule. h, , Since t h e r e e x i s t s of t h e o r d e r e ~ more ~0 1 1 i s i o n p a r t n e r s w i t h s u f f i c i e n t energy t o i o n i z e t h e e x c i t e d atoms o r molecule, Xexc, than c o l l i s i o n p a r t n e r s w i t h s u f f i c i e n t energy t o i o n i z e t h e atoms o r molecules i n t h e ground s t a t e , Xgr, Article published online by EDP Sciences and available at http://dx.
doi:10.1051/jphyscol:1983730 fatcat:wqguh7odszgyzj3su4ng2owujq