On the wavelength range and quantum efficiency of three-micron laser emission in concentrated Er-systems

The p rob lem o f t h r e e m i c r o n l a s e r e m i s s i o n between l e v e l s 4 1 1 1 / 2 and 4 ~ 1 3 / 2 i n c o n c e n t r a t e d E r systems gave r i s e t o c o n t r o v e r s i a l 6eba te c o n c e r n i n p t h e mechani SIT o f d e ~ o p u l a t i o n o f t h e t e r m i n a l l e v e l whose l i f e t i m e i s u s u a l l y much l a r g e r t han t h a t o f t h e e m i t t i n g l e v e l . S e v e r a l models based on E S A o f pumo r a d i a t i o n f r o m 4 ~ 1 3 / 2 and 4 ! 1 1 / 2 [ l ] , on ene rgy t r a n s f e r t o s e v e r a l r a r e e a r t h i m ~ u r ~ t i e s [2 ] o r on upconv e r s i o n p rocess TI f r om 4 1 , ~ ~ ~ [ 3 ], have been o roposed i n o r d e r t o e x p l a i n t h e absence o f s e l f s a t u r a t i o n o f l a s e r em iss i on . P a r t o f t h e up conve r t ed e x c i t a t i o n by p rocess ( 1 ) c o u l d be t hen reused f o r l a s e r e m i s s i o n . I n o r d e r t o assu re an e f f i c i e n t use o f t h e p rocess ( 1 ) a f a s t enerqy m i g r a t i o n on 41 wou ld be necessa ry and t h i s r e q u i r e s i n t u r n h i p h c o n c e n t r a t i o n o f a c t i v a t o r . U n f o r t u n a t e 1 y, a t t hese c o n c e n t r a t i o n s , d u e t o t h e r i c h ene rgy l e v e l d i ag ram o f ~ r 3 * , w i t h many c o i n c i d e n c e s o f t h e ene rgy gaps, s e v e r a l o t h e r energy t r a n s f e r p rocesses become e f f e c t i v e ( F i g u r e 1 ) . A c t i n g a l o n e o r i n c o m b i n a t i o n a l l t h e s e p rocesses reduce t h e e f f e c t o f t h e up-conversion p rocess T i . As shown i n F i g u r e 1, t h e s e p rocesses i n v o l v e a l a r g e p a r t o f t h e ene rqy l e v e l s o f Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1994477 JOURNAL DE PHYSIQUE IV