A HOME MADE PULSED DYE LASER INDUCES VERY NUMEROUS LASER LINES IN THE TELLURIUM MOLECULE 130TE2

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A HOME MADE PULSED DYE LASER INDUCES VERY NUMEROUS LASER LINES IN THE

TELLURIUM MOLECULE 130TE2

P. Dupre

To cite this version:

P. Dupre. A HOME MADE PULSED DYE LASER INDUCES VERY NUMEROUS LASER LINES

IN THE TELLURIUM MOLECULE 130TE2. Journal de Physique Colloques, 1987, 48 (C7), pp.C7-

581-C7-583. �10.1051/jphyscol:19877138�. �jpa-00226958�

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JOURNAL DE PHYSIQUE

C o l l o q u e C7, supplement au n012, Tome 48, d 6 c e m b r e 1 9 8 7

A HOME MADE PULSED DYE LASER INDUCES VERY NUMEROUS LASER LINES IN THE TELLURIUM MOLECULE TE,

P. DUPRE

Service National des Champs Intenses, CNRS and Greco Celphyra, BP 166 X , F-38042 Grenoble Cedex, France

Abstract : We have b u i l t a pulsed dye l a s e r , pumped by t h e t h i r d harmonic of a pulged Nd:YAG l a s e r , t h e beam q u a l i t i e s of which (averaged r e s o l u t i o n : 1.3 GHz

(FWHM), obtained without t h e use of an i n t r a c a v i t y e t a l o n , low divergence

<

I mrad (FWHW) ) , a r e e s s e n t i a l . We have noted t h e p o s s i b i l i t y of a mono mode operating. W have used t h i s l a s e r t o pump Tellurium molecule and we have obser- e ved t h a t very numerous l e v e l s of t h e molecule g i v e rise t o l a s e r t r a n s i t i o n s above 890 K q u a s i spontaneously f o r a p u l s e energy of about 40 p.J ( p u l s e dura- t i o n : 6 n s ) .

The dye l a s e r i s made up of t h r e e stages. The o s c i l l a t o r s t a g e which re- ceived 1 . 5 ,% of t h e t o t a l energy of Nd:YAG l a s e r (40 m J a t 355 nm. 20 Hz). A l a r g e g r a t i n g (3600 gr/mm, 102 mm long) t o g e t h e r with a quad prism beam expander ( G

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^{2 0 ) ,} i s used i n double pass t o obtaine t h e desired s p e c t r a l linewidth, y i e l d -- 1 %. I n a r e c e n t paper [I] we have j u s t i f i e d t h i s choice by t h e o r e t i c a l arguments ( i n c l u d i n g t h e "opening a n g l e " ) , comparing t h e r e s o l u t i o n given by t h r e e types of arrangements of t h e d i s p e r s i v e device (1, 2 o r 3 passes on t h e g r a t i n g ) and t a k i n g i n t o account t h e optimun l e n g t h of t h e g r a t i n g and of t h e mirror ( i f z i s the d i s t a n c e between t h e d i s p e r s i v e device and L, t h e Rayleigh l e n g t h , t h e lowest s p e c t r a l linewidth i s obtained f o r z

=

1.2 L , ) . The experi- mental c h a r a c t e r i s t i c s of t h e l a s e r beam a r e p a r t i a l l y i n agreement with t h e t h e o r e t i c a l model. We d i s c u s s a l s o t h e double p a s s arrangement t h e optimun place of t h e d i s p e r s i v e device a s a f u n c t i o n of t h e s p e c t r a l r e s o l u t i o n and of t h e beam divergence. The a n a l y s i s of t h e s p e c t r a l l i n e w i d t h shows t h a t we have a mono mode s t r u c t u r e f o r 90 % o f t h e s h o t s , t h e averaged l i n e w i d t h (due t o t h e shot t o s h o t i n s t a b i l i t i e s ) i s roughly t h e r e s u l t of t h e f l u c t u a t i o n s over two modes.

The a m p l i f i e r s t a g e g a i n i s about 30 and we have noted t h a t they g i v e a decrease of t h e divergence from 2.5 t o 1 mrad (FWHM). The y i e l d of t h e complete dye l a s e r can reach 10 % with coumarine dye.

To know t h e wavelength of t h e dye l a s e r beam we have used t h e Tellurium spectrum a s r e f e r e n c e [2] by comparing t h e s p e c t r a but we had t h e s u r p r i s e t o observe t h a t over a l a r g e s p e c t r a l range (440

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470 nm) l a s e r l i n e s were emitted from t h e Tellurium oven under c e r t a i n c o n d i t i o n s of p r e s s u r e and pump energy

C31.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19877138

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JOURNAL DE PHYSIQUE

The Tellurium c e l l (100 mm long) i s placed i n s i d e a d i f f e r e n t i a l heating oven ( f i g u r e 1) t h e two temperatures of which a r e a d j u s t a b l e (between 300 K and 1050 K ) , t h e lowest temperature f i x e s the Tellurium pressure and t h e highest one t h e l e v e l population.

The blue l a s e r beam goes d i r e c t l y across t h e Tellurium c e l l . A photode- t e c t o r i s used t o measure t h e absorption l i g h t and another one t o measure t h e emitted l a s e r l i n e . The f i r s t observation of t h e phenomenom was s t r a n g e because we d i d n o t b u i l d a l a s e r c a v i t y and. i n f a c t t h e r e f l e c t i o n c o e f f i c i e n t of t h e q u a r t z windows ( 4 ,%) i s enough t o give r i s e t o a round t r i p of the emitted l i g h t and t o its p o s s i b l e amplification.

We have recorded f o r s e v e r a l temperatures ( o r Tellurium p r e s s u r e ) : 875 K , 895 K, 980 K ( f o r example) t h e absorption and l a s e r s p e c t r a (dye l a s e r pulse energy

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⁴⁰^{p J ) .} ^{A t 875}K we a r e s l i g h t l y above t h e l a s e r threshold and around 21320 cm-l o n l y few l a s e r l i n e s appear. A t 980 K ( s e e f i g u r e 2 ) , i n t h e o t h e r hand, very numerous l e v e l s g i v e rise t o l a s e r emissions ; only few percent of t h e i n c i d e n t p u l s e energy i s c o l l e c t e d after the pass inside the c e l l . Above t h i s temperature t h e l a s e r l i n e i n t e n s i t y decreases. W have noted t h a t t h e r e e i s no c o r r e l a t i o n between t h e maximum absorption of t h e pump l a s e r beam ( i n f a c t t h e a b s o r p t i o n is s a t u r a t e d ) and t h e l a s e r l i n e emission. Figure 3 shows an un- s a t u r a t e d spectrum ( p u l s e energy 0.4 p J ) which i s t o t a l l y d i f f e r e n t from the one obtained with e n e r g i e s hundred times g r e a t e r ( f i g u r e 2 ) .

A quick a n a l y s i s o f t h e emitted l a s e r l i n e s ( i n t h e v i s i b l e range) shows t h a t i n most of t h e cases (depending on t h e Tellurium p r e s s u r e ) t h e emitted spectrum is c o n s t i t u t e d of few l i n e s which s i g n a v i b r a t i o n a l progression i n which doublets g e n e r a l l y appear (R and P l i n e s ) . The emitted l i n e s p e c t r a i s do- minated by one t r a n s i t i o n which g i v e s t h e colour t o t h e l a s e r t r a n s i t i o n . This colour i s f u n c t i o n of t h e wavelength e x c i t a t i o n and permits t o recognize regula- r i t i e s i n s i d e t h e emission l a s e r s p e c t r a notably a t high temperature.

U n t i l now t h e assignment of t h e l e v e l s which are involved i n t h e l a s e r t r a n s i t i o n s i s unknown, t h e numbering of t h e e x c i t e d l e v e l s is required and t h i s work i s i n progress.

We can n o t e t h e extreme s i m p l i c i t y of t h e emission l a s e r s p e c t r a a t 875 K f o r example compared t o the complexity o f t h e ones obtained by Fourier Transform spectroscopy.

[I] P. DUPRE A q u a s i unimodal tunable pulsed dye l a s e r a t 440 nm : t h e o r e t i c a l development f o r u s i n g a quad prism bean expander and one o r two g r a t i n g s i n a pulsed dye l a s e r o s c i l l a t o r c a v i t y ; Appl. Opt. 26 (1987). 860.

[2] P. LUC and J. CARIOU A t l a s du s p e c t r e d ' a b s o r p t i o n de l a mol6cule de t e l l u - r e ; Laboratoire Aim6 Cotton, CNRS il 91405 ORSAY (1980).

[3] P. DUPRE Very numerous r o v i b r a t i o n a l l e v e l s of t h e t e l l u r i u m vapor ( 1 3 0 ~ e 2 ) induce l a s e r t r a n s i t i o n s ; i n Opt. Commun. (1987).

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Therrnic insulator

/

\ ~ e l l u r i u m

cell

Figure 1 : The differential heating oven.

Figure 2 : Absorption (uppest curve) and laser emission (lowest curve) spectra of '3O~e, at 975 K (1005 K) , pulse energy "

40

N.

Figure

3

: Absorption spectrum of '3OTe2 at 860 K (885 K), pulse energy 0.4