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MULTIPHOTON EXCITATION OF THE XENON NEAR THE 6s’ |1/2|1 RESONANT STATE AND
THIRD-HARMONIC GENERATION
Y. Salamero, A. Birot, H. Brunet, Jean Galy, P. Millet, J. Teyssier, J.
Foulquier
To cite this version:
Y. Salamero, A. Birot, H. Brunet, Jean Galy, P. Millet, et al.. MULTIPHOTON EXCITATION OF THE XENON NEAR THE 6s’ |1/2|1 RESONANT STATE AND THIRD-HARMONIC GENERA- TION. Journal de Physique Colloques, 1987, 48 (C7), pp.C7-565-C7-567. �10.1051/jphyscol:19877134�.
�jpa-00226954�
JOURNAL DE PHYSIQUE
Colloque C7, supplbment au n012, Tome 48, decembre 1987
MULTIPHOTON EXCITATION OF THE XENON NEAR THE 6s111/21, RESONTINT STATE AND THIRD-HARMONIC GENERATION
Y. SALAMERO, A. BIROT, H. BRUNET, J. GALY, P. MILLET, J.L. TEYSSIER and J.N. FOULQUIER
DBcharges dans les Gaz, Centre de Physique Atomique, Universit6 Paul Sabatier, UA-277, 118, Route d e Narbonne, F-31062 Toulouse Cedex, France
The r e s u l t s obtained i n a multiphotonic excitation o f xenon near t h e 6s111/21, state b y a tunable pulsed d y e laser are presented. A t low p r e s s u r e t h e l p l reson- n a n t state o f xenon i s created b y 3-photon resonnant absorption. When t h e pressu- r e increases, t h e excitation spectra widen and s h i f t towards s h o r t e r wavelengths.
We explain t h i s phenomenon b y an excitation o f t h e Xeq molecules i n t h e g r o u n d state O'g towards molecular excited state correlated t o l p l state. A spec- t r a l analysis showed t h e presence in t h e luminescence o f the f i r s t and second conti- nuum o f xenon. We demonstrated t h a t t h e third-harmonic generation o f t h e incident laser beam intervenes in t h e excitation process. T h i s radiation was detected and h i s pressurg: dependance studied. The phase matching parameter C x e and t h e non- linear susceptibility were measured.
Experimental Set-up :
It has been described i n previous paper (1,2). The excitation i s achievied b y a tunable laser pulsed beam (50 Hz). The dye used i n t h e present experiment i s t h e B.B.Q. centered a t 388 nm. T h e e n e r g y o f t h e laser pulses can be adjusted between 10 and 80 p J . The bandwith o f t h e beam i s about 0.8 cm-l a t 388 nm.
T h i s beam i s focused i n t h e gaz b y a 40 mm focal l e n g t h lens. The luminescence i s observed b y a extremely solar b l i n d P.M. set t o detect single photon i n a lateral direction t o t h e incident laser beam. The t h i r d harmonic generation i s detected i n t h e f r o n t a l observation.
Lateral observation-Excitation and Emission Spectra :
A t low pressure ( p x e < l t o r r ) excitation spectra a r e v e r y narrow and cente- r e d on t h e wavelength(hlr=388.7 nm) corresponding t o t h e 3-photon resonnant exci- t e d l P l state ( f i g u r e 1 ) . When the pressure increases the excitation spectra widen and s h i f t towards shorter wavelengths. Some failures appear i n t h e excitation spec- t r a ( f i l t e r e d a t 129 ; 145 and 168 nm) a t several reproductible incident beam wave
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2
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3827 387,9 389 3883 3685 n m laser
F i g u r e 2 - Excitation spectrum o f Xenon
3885 3886 3687 - luminescence a t 168 nm.
F i g u r e 1 - Excitation spectrum o f Xenon luminescence a t 128 nm.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19877134
C7-566 JOURNAL DE PHYSIQUE
lengths ( f i g u r e 2). T h i s i s i n t e r p r e t e d b y a molecular excitation o f t h e free o r bound dimers in t h e g r o u n d state towards t h e excimers l u ( l ~ l ) a n d l o r O & ( ~ P ~ ) . As t h e third-harmonic generation (T.H.G.) i s present, these levels can be excited e i t h e r b y 1-VUV photon o r 3-laser photon. O u r r e s u l t s a r e i n agreement w i t h Miller and Compton experiment (3) who simultaneously detected T . H .G. and induced ionisation b y t h e incident laser beam. T h e failures i n t h e excitation spectra can be attribuated, as shown b y Aron and Jonhson (4) a t a &-photon excitation process which increases t h e ionisation phenomenon. The f o u r t h photon absorption intervenes p r o b a b l y between excited molecular states. Emission spectra shown o n l y the f i r s t a n d sedond continuum o f Xenon respectively centered a t 150 a n d 170 nrn. T h e i r ,
p r e s s u r e dependance is identical t o t h a t obtained b y a selective excitation near t h e 6s resonnant state 3Pl ( l ) o r b y o t h e r excitation means ( 5 ) .
The presence o f t h e 145 nm emission f o r pressures so weak t h a n 1 t o r r , whi- le t h e i n i t i a l excitation i s nearly resonnant w i t h t h e state, traduces t h a t a v e r y q u i c k process leads t o t h e creation o f t h e T h e 6p11121 1 and 6s'I 1/21 1 states are s t r o n g l y coupled by r a d i a t i v e de- sexcitation o f t h e f i r s t conduces t o creation o f t h e 6s states (6).
The temporal analysis o f t h e 145 and 170 nm emissions shows t h e participation of t h e 6s 11 11212 ( 3 ~ 2 ) metastable state t o t h e creation o f the molecular state res- ponsible o f the second continuum emission.
Third-harmonic generation : (T. H.G.) . When a laser beam i s focused i n a gaz w i t h a wavelength X i , t h e third-harmonic generation &3=A 113) i n t h e ran- ge o f t h e negative phase mismatch ( A k<O) i s possible. The power o f t h i s VUV ra- diation generated is, s t a r t i n g from t h e expression o f Ward and New (7) o f h i s elec-
t r i c f i e l d : 2
E () (x2+y2) 112 ~ ~ I d r
we can w r i t e : 2
p ( 3 w ) = 8.204.10-l6 N~.P:' F ( b A k, b / L , f1L) (3XO3l4
P i and P(3w) a r e t h e incident a n d generated powers i n Wlcm 2 , b t h e confocal pa- rameter, f the position o f t h e focal p o i n t i n t h e medium, L t h e l e n g t h o f t h e me- dium, N i s i n a t / ~ m ~ , x ( ~ ~ ) i n erg-l.cm6 (u.e.s.1.
I n t h e present ex eriment A k is negative i n t h e b l u e side o f t h e resonnance line a t 129.6 nm (lP1-fSq t r a n s i t i o n ) . We have found b y a calculation t h a t t h e non-linear process i s p o s s ~ b l e between 126.6 and 129.6 nm b y application o f t h e Sellmeir formula. We v e r i f i e d i n t h e f r o n t a l d i r e c t i o n the presence o f t h i s VUV tu- nable radiation. T h e VUV i n t e n s i t y is, l i k e t h e luminescence, linear w i t h t h e cube
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h l . \ i i h 5 1 1 Y c,Z
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I
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F i q u r e 3 - T.H.G. i n t e n s i t y X /- 12p.o 124s I I l z e g 128s -17
(129.10 nm) versus Xenon 7"')
pressure.
' ~ i g u r e 4 - Theoretical and experimental variation o f C x e w i t h VUV Wavelength.
o f t h e i n c i d e n t laser beam e n e r g y . H i s b a n d w i t h i s v e r y n a r r o w , less t h a n 1 0 - ~ n m . T h e p r e s s u r e dependance o f t h e T.H.G. i n t e n s i t y , f o r a laser e x c i t a t i o n wavelength, p r e s e n t s a maximum s i t u a t e d a t t h e optimal p r e s s u r e ( f i u r e 3 ) . T h e e x p e r i m e n t a l p o i n t s a r e s u i t e d by t h e t h e o r e t i c a l low g i v e n b y t h e P a W ) e x p r e s s i o n :
T h e full c u r v e o f t h i s f i g u r e i s i n good agreement w i t h e x p e r i m e n t a l p o i n t s . From t h e d e t e r m i n a t i o n o f t h e optimal p r e s s u r e (bA k =-4) we f o u n d t h e phase mat- c h i n g parameter C x e = A k / N . T h e f i g u r e 4 r e p r e s e n t s t h e o r e t i c a l v a r i a t i o n a n d expe- r i m e n t a l r e s u l t s o f C x e v e r s u s VUV w a v e l e n g t h r a d i a t i o n . T h e desagreement in t h e w a v e l e n g t h r a n g e u n d e r 128.8 nm i s p r o b a b l y d u e t o a r e a b s o r p t i o n o f t h e VUV ra- d i a t i o n when t h e p r e s s u r e increases ans by t h e i n t e r v e n t i o n o f molecules i n t h e g r o u n d s t a t e whose p o p u l a t i o n augments l i n e a r w i t h t h e s q u a r e o f t h e p r e s s u r e . T h e e x p e r i m e n t a l d e t e r m i n a t i o n o f x f 3 ) h a s been possible b y a p p l i c a t i o n o f P ( ~ ) e x p r e s s i o n . In table 1, we r e p p o r t s e v e r a l values o f x ( 3 f o r d i f f e r e n t wave- lengths. A b s o l u t e e r r o r i s a b o u t 100 % b u t t h e v a r i a t i o n w i t h t h e w a v e l e n g t h i s si- g n i f i c a n t . T h e measurements o f t h e t h i r d - o r d e r non-linear s u s c e p t i b i l i t y o f Xenon in t h i s r a n g e a r e n o t f r e q u e n t .
T a b l e 1 - D i f f e r e n t values o f third non-linear s u s c e p t i b i l i t y x (a)(-- w,w, w ) o f Xenon v e r s u s T . H. G. wavelength.
BIBLIOGRAPHIE.
' Y . Salamero, H. Asselman, A. B i r o t , H. B r u n e t , J. Galy a n d P. Millet, J. Phys.
B 3, 2971, (1983).
'Y. SalamBro, A. B i r o t , H. B r u n e t , J. Galy a n d P. Millet, J. Chem. P h y s . 8 0 , 4774, (1984).
3 ~ . ~ . M i l l e r a n d R.N. Compton, Phys. Rev. A - 25, 4, 2056, (1982).
4 ~ . A r o n a n d P.N. Johnson, J. Chem. Phys., 67, 5099, (1977).
'J.P. Millet, A. B i r o t , H. B r u n e t , J. Galy, B . Pons-Germain e t J.L. T e y s s i e r , J. Chem. Phys., e? 92, (1978).
6 ~ . Sadeghi a n d J. Sabbagh, Phys. Rev. A.16, 6, (1977).
7 ~ . ~ . Ward a n d G.H.C. New, Phys. Rev., 135, 57, (1969).
x (cm6.erg-'I
1.3 1 .0 6.7 4.9 2.8 2.0
&
A laser(""')
388.5 388.35 388.2 387.9 387.3 387.0
A raser
A V U V = 7
129.5 129.45 129.4 129.3 129.1 129.0
P X e ( t o r r )
15 28 5 7 95 165 200
