MULTIPLE RAMAN SCATTERING SCHEME FOR XUV GENERATION

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MULTIPLE RAMAN SCATTERING SCHEME FOR XUV GENERATION

V. Papanyan, M. Bertolotti

To cite this version:

V. Papanyan, M. Bertolotti. MULTIPLE RAMAN SCATTERING SCHEME FOR XUV GENERA- TION. Journal de Physique Colloques, 1986, 47 (C6), pp.C6-121-C6-127. �10.1051/jphyscol:1986616�.

�jpa-00225859�

JOURNAL DE PHYSIQUE,

CoAloque C6, supplement au n o 10, Tome 47, octobre 1986

MULTIPLE RAMAN SCATTERING SCHEME FOR XUV GENERATION

V.O. PAPANYAN" and M. BERTOLOTTI

Sezione Fisica, Dipartimento di Energetics, Universitd di Aoma

"La Sapienza", Via Scarpa, 14, 1-00161 Roma, Italy

REsum6

-

On propose un systsme avec double scattering stimul6 de Raman et un resonateur 2 multipass pour la radiation IR. Le sys- tsme est fondg sur la conversion dans la r&gion XUV utilisant des niveaux quartetmetastable dans l'afterglow d'une discharge He-K.

On peut avoir des impulsions XUV 2 64nm avec 6nergie 1,2uJ en utilisant un laser 2 colorant 2 404nm de 14MW, 6ns avec une ef f icience ^tv 1 . 7 ~ 1 0 - ~

-

Abstract

-

^A scheme with double stimulated Raman scattering and multipass resonator for intermediate radiation is proposed based on up-conversion into XUV region by quartet metastable level of potassium atoms excited in a He-K discharge afterglow. 64nm wavs length XUV output pulse with 1 2 U J energy may be obtained with 404nm dye-laser input power of 14MW and 6ns duration withoverall efficiency

-

1 . 7 x 1 0 - ~ .

I

-

INTRODUCTION

Stimulated anti-Stokes Raman scattering (SASRS) processes have been found of some interest for achieving laser action in the VUV and XUV spectral regions / I / . Up-conversion of existing powerfull lasers' radia tion to a shorter wavelength by SASRS on metastable atomic states was proposed long ago / 2 / , but only recently interesting experimental re- sults were reported / 3 , 4 / . The problem is to find a suitable medium with a metastable level which can be pumped easily to achieve popula- tion inversion between the initial and the terminal levels. A tunable pump laser must be used to obtain resonance enhancement of SASRS / 5 / .

An attractive scheme was proposed by S. Harris / 1 , 6 / in which a termi- nal level may be selected which is not the ground a t o m k state. Inthis aproach a high-lying quartet metastable state of an alkali metal atom i.s populated by direct electron impact excitation in a discharge and the pump laser radiation is tuned to an intermediate doublet autoioni- zation quasi-metastable state from which the lasing transition takes place terminating on an usual excited level of the alkali atom.However it turned out to be difficult to obtain the required initialmetastable density in a pulsed discharge / 7 / . This difficulty may be overcome by using collisional energy transfer from rare gas atom metastable states to the quartet state of an alkali metal /8,9/. One of the proposedreac_

tions is the following ^*

*on l e a v e from I n s t i t u t e f o r P h y s i c a l Research Armenian Academy o f S c i e n c e s . 378410. USSR

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986616

JOURNAL DE PHYSIQUE

with energy defect 0.04eV. Recent spectral measurements of 60-80nm wa- velength emission from He-K discharge showed effective excitation of the potassium quartet states /lo/. A powerful source of tunable IR

(A,=

=1.20gPm) radiation is needed to pump SASRS in resonance withpotassium quartet ("storage" level)

-

intermediate transition :

3p53d4s 4~ 5/2

-

^{3p5 (4s4p 3~ )} 2 ~ 3 / 2 1 (Fig. I and /9/)

.

^{In this} way /1YHv=64nm 5 3 2

radiation may be produced in resonance with 3p (4s4p P) P3,2-

r

-

-

~P'~P'P~/~, I /2. The optical oscillator strength of the pumping tran- sition is f =I. 2

-

^{1 o - ~ ,} and of radiating transitions f =0.05 for j=3/2

si ie

terminal sublevel and 0.02 for j=1/2 /11/. Application of the pump ra- diation in afterglow conditions, i.e. delayed by 50-150ns from an ac- tual discharge pulse, results in a decrease of the terminal 4 2 ~ level population due to its radiation and an increase of the He 23s metasta- ble density due to recombination processes, thus achieving the popula- tion inversion needed for SASRS. In this paper we consider a new possi- bility to obtain

/I,

=1.209pm radiation for SASRS pumping by means of preliminary Stokes %aman scattering (SRS) in the same He-K discharge.

In this way the preliminary step is the stimulated SRS from He 2 3 ~ le- vel which in a strong violet radiation field ( p=404nm) undergoes a transition to He 3 3 ~ level producing / f t R =I .209,um in resonance with He . 5 3 ~ level (detuningx80cm-1): The measured density of initial He 2 3 ~ a-

toms in pulsed discharge of [ ~ e ] : [KJ =4:1 mixture is high enough 1012cm-3 /12/.

Fig.1- Energy level diagram for the proposed double Raman scattering scheme in the He-K system.

The second main point is to use high-quality IR mirrors foramultipass Raman cell /13,14/ so achieving a conversion efficiency from p=404nm to IR up to 20-30%. Calculations show that overall conversion efficien- cy of the double Raman process from the violet to XUV can reach several percents according to focusing geometries choosen.

I1

-

INFLUENCE OF FOCUSING ON UP-CONVERSION OF THE I R RADIATION I N T O THE XUV

The i n t e n s i t y of l o w - s i g n a l SRS r a d i a t i o n from t h e n o i s e l e v e l i s expo- n e n t i a l l y growing w i t h d i s t a n c e x a s exp ( g ~ s x ) . The plane-wave g a i n c o e f f i c i e n t f o r t h e r e s o n a n t SRS i n a t h r e e l e v e l s y s t e m i s g i v e n b y /5/:

g A S = d R N~ IS (cm-l ^I ( 2 )

where N S i s t h e s t o r a g e 4p512 s t a t e d e n s i t y , IS ( W ~ m - ~ ) i s t h e pump wa- v e i n t e n s i t y ( S t o k e s

A

s = l .20 lpm wave i n ourscheme)

,

and

where

C = P . I . ~ O - ~ * W " ,

( a l l a n g u l a r f r e q u e n c i e s a r e g i v e n i n cm-1) ;buAsis d e t u n i n g from t h e i n t e r m e d i a t e l e v e l , which i n t h e e x a c t r e s o n a n c e c a s e must b e r e p l a c e d by t h e Doppler l i n e w i d t h . Three t y p i c a l o p t i c a l f o c u s i n g c o n f i g u r a t i o n s a r e h e r e c o n s i d e r e d f o r t h e same c e l l of o v e r a l l l e n g t h L=80cm, and-po- t a s s i u m v a p o r c o n f i n e d i n t h e medium r e g i o n l e n g t h 1=40cm. For c a l c u l a - t i o n s we c o n s i d e r a t y p i c a l p o t a s s i u m atom d e n s i t y N ~ = I o ~ ~ c ~ - ~ w i t h a helium b u f f e r g a s p r e s s u r e of 4 T o r r ( s e e / 5 / , p . 1 5 4 ) . I t seems r e a s o - n a b l e t o f o c u s t h e I R beam i n t h e middle of t h e l e f t s u b c a v i t y a t a d i - s t a n c e 10cm from t h e l e f t m i r r o r i n o u r c a s e . The first process of SRS from p=404nm t o

A,*

=I .209 urn t a k e s p l a c e i n t h e whole d i s c h a r g e l e n g t h

L

,

and t h e second SASRS from t o /\*uu=64nm o n l y i n t h e p o t a s s i u m f i l l e d r e g i o n o f l e n g t h 1. T h i s p a r t of t h e c e l l i s e n l i g h t e n e d by a qone of I R r a d i a t i o n w i t h v e r t e x a n g l e 28. F o r example w e g i v e h e r e t h r e e f o c u s i n g c a s e s : t i g h t f o c u s i n g w i t h c o n f o c a l p a r a m e t e r = L /40

( d - c a s e )

,

medium w i t h

#

= ,& / 4 (/3) and weak f o c u s i n g w i t h

g

= L

(6) .

Here a s u s u a l l y

g

=2zg2/,4 = 2 ~ , ~ / ~ $ ~ where UT, i s t h e g a u s s i a n beam w a i s t r a d i u s i n t h e focus!R Gain c a n b e c a l c u l a t e d now u s i n g e g s ( 2 ) and

( 3 ) w i t h dW=O.~cm-1 b e c a u s e we h a v e e x a c t r e s o n a n c e w i t h i n t e r m e d i a t e l e v e l and Doppler w i d t h must b e u s e d , and

f

=0.05cm-1 i s t h e Raman w i d t h ( s e e / 5 / f o r d i s c u s s i o n ) . Then t h e number o f XUV photons i s

n * u r = a ~ ( A e f l ) f o r n * u v < n x e v ( s a t ) = - ( 4 ) where PIR i s t h e power of AIA=1 .209/c(m r a d i a t i o n and

6.5 MW-1 f o r ( d ) 4-1012 ( A )

32 MW-I f o r $3)

63 MW-I f o r

( 8 )

2 . 2 . 1 0 ~ ~

(4)

The s a t u r a t e d number of XUV p h o t o n s h e r e i s t a k e n e g u a l t o t h e o v e r a l l number of s t o r a g e m e t a s t a b l e K** (3p5 3d4s 4 ~ 0 5 , 3 ) atoms i n t h e SASRS

- 1 -

cone c a l c u l a t e d w i t h t h e i r d e n s i t y N**=8-1 011cm-3 which i s a v a i l a b l e on t h e p r e s e n t s t a t e o f a r t of t h e p u l s e d d i s c h a r g e /9/. T h i s d e n s i t y i s v e r y i m p o r t a n t b e c a u s e i t i s l i m i t i n g t h e XUV o u t p u t . A s it c a n b e s e e n from t h e T a b l e t h e s a t u r a t i o n i n p u t power i s v e r y n e a r t o t h r e s h o l d . XUV o u t p u t p u l s e e n e r g y t h r e s h o l d i s takenlo-$3 a s u s u a l l y f o r stimu- l a t e d Raman p r o c e s s e s ( / 5 / p.94)

.

I11

-

DOUBLE RAMAN SCATTERING SCHEME

A s it w a s shown i n t h e p r e v i o u s s e c t i o n I R pump power more t h a n 0.35MW ( s e e t h e T a b l e ) w i t h l i n e w i d t h l e s s . t h a n 0.05cm-1 i s needed t o a c h i e - v e 64nm g e n e r a t i o n i n t h e He-K d i s c h a r g e a f t e r g l o w . Because t h e a b s o l u - t e v a l u e s o f e n e r g i e s o f t h e p o t a s s i u m qaartets a r e n o t measured w i t h

C6-124 JOURNAL DE PHYSIQUE

a good a c c u r a c y /15/ t h a n t u n a b i l i t y 100cm-1 of pumping r a d i a t i o n i s needed. We a n a l y s e i n t h i s s e c t i o n t h e p o s s i b i l i t y t o u s e t h e same He- K d i s c h a r g e f o r r e c e i v i n g t h i s I R c o h e r e n t r a d i a t i o n . The most conve-

n i e n t was found t o b e SRS from H e 1 ~ 2 i n i t i a l l e v e l t o 1~ 3 ~ ~ f i n a l 3 ~ ~ ~ l e v e l w i t h I s 5 d 3 ~ i n t e r m e d i a t e s t a t e ( F i g . I )

.

To produce >,A =I - 2 0 9 ~ m

pumping p=404nm must b e u s e d , which i s e a s i l y a v a i l a b l e from a power- f u l l and good beam q u a l i t y d y e - l a s e r . Using r e l a t i o n s ( 2 ) and ( 3 ) w i t h d e t u n i n g ~ ~ = 8 l c m - l , Raman l i n e w i d t h

r

=~.Olcm-1 and o s c i l l a t o r s t r e n g h t s fsi=0.0738, f i e = 0 . 0 4 7 4 / I 6 1 w e h a v e d ~ = 4 . 5 - 1 0 - ~ ~ W-lcm4. A s t h e measured d e n s i t y of H e ( 2 p 3 ~ ) s t a t e s i n He-K p u l s e d d i s c h a r g e s u i - t a b l e p r e s s u r e ( 4 T o r r ) i s Np=1012cm-1 /12/ t h e S t o k e s plane-wave g a i n c o e f f i c i e n t i s

5. g s = d s N p = 4 . 5 . 1 0 - 5 c m / ~ ~ ( 5 )

To have low S t o k e s SRS t h r e s h o l d an i n t e r n a l s p h e r i c a l r e s o n a t o r must be u s e d t h u s a c h i e v i n g h i g h c o n v e r s i o n e f f i c i e n c y /13,14,17/. The l o s - s e s a r e s m a l l b e c a u s e good q u a l i t y m i r r o r s a r e a v a i l a b l e f o r t h e n e a r I R . The number of p a s s e s i n t h e a c t i v e medium i s n = c Z / L , where C i s t h e pumping p u l s e d u r a t i o n which must b e l e s s t h a n 100ns which i s d u r a - t i o n of p o p u l a t i o n i n v e r s i o n i n t h e a f t e r g l o w of He-K d i s c h a r g e . The maximum p o s s i b l e c o n v e r s i o n e f f i c i e n c y ( r e l a t i o n o f t h e I R o u t p u t p o w e r t o t h e p=404nm i n p u t power:

2

'PIR/P ) i s

2

^{= (} w s / ) ~~ n - 1

,

where R i s t h e m i r r o r r e f l e c t i v i t y . ~ n o u r c a B c u l a t i o n s r e f l e c F i v i t y i s t a k e n e q u a l t o 99%. F o r a f o c u s e d Gaussian beam, g a i n p e r p a s s G I i s i n f a c t n o t a f u n c t i o n of pump i n t e n s i t y b u t o f pump power Pp and i s g i v e n by /13,17/:

were gs i s g i v e n by ( 5 ) and b i s t h e c o n f o c a l p a r a m e t e r . The o v e r a l l g a i n c o e f f i c i e n t f o r n p a s s e s i s

Conversion e f f i c i e n c y v e r s u s t h e number of p a s s e s , w i t h pump d e p l e t i o n and m i r r o r r e f l e c t i v i t y t a k e n i n t o a c c o u n t / 1 7 / c a n b e w r i t t e n i n a s i m p l e form

where r i s t h e r a t i o of s p o n t a n e o u s S t o k e s n o i s e power P s a t ~ t h e i n p u t pump power P p r P s c b h V s d V s . With a S t o k e s Raman l i n e w i d t h of t h e s a - me v a l u e a s u s e d b e f o r e (0.Olcm-1) p s o - 5 . 1 0 - g ~ and f o r an i n p u t power -5MW we have r-10-16. C a l c u l a t i n g Gn from ( 7 ) and

2 ,

from ( 8 ) we ob- t a i n Ps=fnPp a s a f u n c t i o n of n o r i n o t h e r words a s a f u n c t i o n of t h e pumping p u l s e d u r a t i o n . Here r e c t a n g u l a r pump p u l s e i s c o n s i d e r e d w i t h s l o p e s l e s s t h a n h a l f d u r a t i o n of one p a s s i n t h e r e s o n a t o r , which i s e q u a l t o 2 . 7 n s . Then u s i n g ( 4 ) we c a n o b t a i n a n t i - S t o k e s SRS g a i n and XUV o u t p u t e n e r g y WXuV=hVXUV nxv". T h i s e n e r g y f o r t h e t h r e e f o c u s i n g c a s e s we a r e s t u d y i n g i s g i v e n I n F i g . 2 a s a f u n c t i o n of t h e d y e - l a s e r i n p u t power. I n t h e T a b l e main p a r a m e t e r s o f t h e t h r e e f o c u s i n g c o n f i - g u r a t i o n s a r e summarized. The d - c a s e h a s t h e l o w e s t power t h r e s h o l d f o r t r a v e l l i n g - w a v e e x c i t a t i o n b e c a u s e it i s t h e c a s e of t i g h t f o c u s i n g . But f o r i n t r a r e s o n a t o r enhanced a n t i - S t o k e s wave t h e l o w e s t t h r e s h o l d i s f o r t h e 8 - c a s e ( o n l y 1.5MW). Also t h e s a t u r a t i o n i s r e a c h e d e a r l i e r f o r

# ,

b u t t h e o u t p u t e n e r g y v a l u e i s t h e l o w e s t d u e t o t h e s m a l l pum- ping cone volume. I n t h e t i g h t f o c u s i n g c a s e 4 , t h e o u t p u t i s h i g h

enough up t o ^12.3vJ p e r p u l s e . A l s o t h e h i g h e s t e f f i c i e n c y : 2.10-~'without r e s o n a t o r may be a c h i e v e d , b u t i n t h i s c a s e t h e i n p u t power must b e ve- r y h i g h

-

22MW. I t can b e reduced by i n t r a r e s o n a t o r SRS. For L=80cm r e - s o n a t o r l e n g t h t h e optimum p u l s e d u r a t i o n i s c a l c u l a t e d t o b e 5.4ns1 and pump power r e d u c e s t o 13.8Mli: e f f i c i e n c y i s t h e n I . 7 x l 0 - ~ . ~ h e s h o r t c o - ming of t i g h t f o c u s i n g i s h i g h pump-power i n t e n s i t y i n t h e f o c u s which can l e a d t o some unwished e f f e c t s . T h i s i n t e n s i t y i s a minimum i n t h e

8

- c a s e . Pumping power (hp=404nm) a s a f u n c t i o n of pumping p u l s e dura- t i o n i s g i v e n i n F i g . 3 . I t may b e s e e n t h a t a l l t h e c u r v e s have minima t h a t means optimum pumping p u l s e d u r a t i o n .

I n t h i s p a p e r t h e a n t i - S t o k e s Raman l a s e r based on c o l l i s i o n a l e n e r g y t r a n s f e r from ~ e ( 2 s 3 ~ ) m e t a s t a b l e atoms e x c i t e d i n a d i s c h a r g e a f t e r - glow t o q u a r t e t m e t a s t a b l e 3$3d4s 4 ~ 5 / 2 s t a t e o f p o t a s s i u m i s a n a l y s e d f o r d i f f e r e n t pumping beam f o c u s i n g p a r a m e t e r s . A new method i s propo- s e d t o produce t h e needed I R r a d i a t i o n f o r t h e a n t i - S t o k e s o p e r a t i o n i n t h e same d i s c h a r g e medium, by s t i m u l a t e d SRS of a c o n v e n i e n t v i s i b l e d y e - l a s e r l i g h t , a l s o u s i n g I R r e s o n a t o r f o r t h i s S t o k e s r a d i a t i o n . P r i n c i p a l r e s u l t s a r e shown i n t h e T a b l e and s e v e r a l c o n c l u s i o n s c a n b e drawn :

1 . The l o w e s t t h r e s h o l d f o r ~ ~ ~ J ~ ~ ' 6 4 n m g e n e r a t i o n may be a c h i e v e d by u s i n g 0.35MW r a d i a t i o n a t =1.209,um by f o c u s i n g it i n t o t h e p o t a s s i u m v a p o r column (1=40cm) w i t h s t o r a g e 3d5 3d4s4 P5/2 atoms c o n c e n t r a t i o n N**= 8.1011cm-~ and l o n g f o c u s i n g ( =80cm, 8 - f o c u s i n g c a s e )

.

2. The maximum XUV o u t p u t i s l i m i t e d by s a t u r a t i o n d u e t o t h e l i m i t e d number of q u a r t e t K** m e t a s t a b l e s i n s i d e t h e pumped volume. Thisnumber may b e r i s e d , i n c r e a s i n g K** c o n c e n t r a t i o n by o p t i m i z i n g d i s c h a r g e con- d i t i o n s ( e l e c t r i c power, d u r a t i o n , e t c . ) o r by i n c r e a s i n g t h e pumped volume.

3.

3

p=404nm pump r a d i a t i o n may b e used t o produce t h e needed I R r a d i a - t i o n I n t h e same c e l l by S t o k e s SRS, from t h e H e 3p 3~ l e v e l s e x c i t e t i n t h e same d i s c h a r g e . Large o v e r a l l c o n v e r s i o n e f f i c i e n c y and h i g h o u t p u t ( 12PJ ) may b e a c h i e v e d i n t h e t i g h t f o c u s i n g c a s e (dl. But t h e pump i n t e n s i t y i n t h e f o c u s i s v e r y h i g h i n t h i s c a s e . On t h e c o n t r a r y f o r a l o n g c o n f o c a l p a r a m e t e r ( ] - c a s e ) pump i n t e n s i t y i n t h e f o c a l p l a - ne i s low.

4 . To r e d u c e t h e d y e - l a s e r pump power an I R r e s o n a t o r may b e u s e d . Be- c a u s e h i g h q u a l i t y m i r r o r s i n t h i s wavelength r e g i o n a r e a v a i l a b l e , t h a n m u l t i p a s s g a i n may be a c h i e v e d . Thus t h e 404nrn pump t h r e s h o l d may b e lowered down t o 1.5MW f o r 8ns p u l s e r a d i a t i o n i n t h e ,j'-case.Maximum XUV o u t p u t , e q u a l t o 1 2 . 3 ~ J

,

i s r e a c h e d f o r a 3.8MW1 5.4ns d y e - l a s e r pumping p u l s e i n t h e &-case, w i t h o v e r a l l e f f i c i e n c y 1 . 7 ~ 1 0 - ~ .

REFERENCES

/ I / S.E. H a r r i s : Opt. L e t t .

5 ,

1 (1980)

/ 2 / A.V. Vinogradov and E . A . Ukov: Sov. Phys.-JETP. L e t t . 1 6 , 4 4 7 ( 1 9 7 2 ) j 3 / J . C . White: IEEE J . Quant. E l e c t r o n . QE-20, 185 (1984)-

/ 4 / K . Luderwight, H . Schmidt, R . D i e r k i n g and B. Wellegehausen: Opt.

L e t t .

10,

606 (1985)

/ 5 / D.C. Hanna, M.A. Y u r a t i c h and D . C o t t e r : " N o n l i n e a r O p t i c s Of F r e e Atoms and M o l e c u l e s " , S p r i n g e r - V e r l a g , 1979

/ 6 / J.E. Rothenberq and S.E. H a r r i s : IEEE J . Q u a n t . E l e c t r o n . QE-17,

. .

418 (1981)

/ 7 / R.G. Caro, J . C . Wang, R.W. F a l c o n e , J.F. Young and S.E. H a r r i s : Phys. Rev.

el

1407 (19843

/8/ A.E. M a r t i r o s y a n and V.O. Papanyan: Sov. J . Quantl E l e c t r o n .

13,

99 (1983)

/ 9 / V.O. Papanyan, A.E. M a r t i r o s y a n and F.K. T i t t e l : IEEE J . Q u a n t . E- l e c t r o n . QE-19, 1835 (1983)

C6-126 JOURNAL D E PHYSIQUE

Fig.3

-

Pumping power of A,, =404nm pulse needed

for achieving XUV genera- tion threshold (dotted lines) and saturation

(full lines) versus pum- ping pulse duration. d

,P

/3 and

d/

are for corre- sponding focusing parame- ters.

/lo/ Yu.K. Gabrielyan, A.E. Martirosyan, G.C. Nersisyan and V.O. Papa- nyan: Phys. Lett.

=,

198 (1984)

/11/ A.V. Kuplyauskene and Z.I. Kuplyauskis: Optics and Spectroscopy (USSR)

58,

821 (1985)

/12/ A.E. Martirosyan and V.O. Papanyan: Zhournal Prikladnoi Spectro- skopii

43,

383 (1985) (Russian)

/13k W.R. Trutna and R.L. Byer: Appl. Opt.

19,

301 (1980)

/14/ W. Schmidt and W. Appt: IEEE J. Quant. Electron. QE-17, 509 (1981) /15/ M.W.D. Mansfield and T.W. Ottley: Proc. Roy. Soc. London:

s,

413 (1979)

/16/ W.L. Wiese, M.W. Smith and B.M. Miles: "Atomic Transition Probabi- lities", Washington DC, US Government Printing of- fice, 1969

/17/ R.T.V. Kung: IEEE J. Quant. Electron. QE-17, 509 (1981)

WX,,

Fig.2

-

Output pulse e-

I O - ~ ~ J ' I

-

0 3 ;

0.01

nergy at

A

=64nm as a a function of ~umping vio-

let h,=404nm power with IR resonator used and pumping pulse duration 8ns for d

,

^{40ns for} P and 48ns for $'-case; an

ff?

initial quartet metasta-

ble potassium atom den-

I ^Y I

sity of 8-lollcm-3 (full

I

-- --- ----

curves) or 4 ^a 1

o1

I cm-3

B'

(dotted curves and pri-

,

!

- - - 4 med letters).

Y'

0

.

5 10

TABLE. XUV GENERATION PARAMETERS

P a r a m e t e r Unit Focusing cases d

2 13 4 . 1 0 ~ ~

6 . 5 ~ 1 0 ~ 3 . 4

20.8 1 0 . 5

8

P I C

' 0 1 " ~

4 4 . 1 0 ~ ~ 2.2'10'~

6.5-lo9 1 .2.101°

0.68 0.35 2 2 . 6 36.7

2.3 1.5

40 4 8

cm mrad

cm-3

tIW

M\V

ns

UJ

MW

MW

ns

o - ~

.

!2!!

c m 2 Confocal parameter (b)

XUV beam divergence (2 8 )

K*

*

atoms pumped optically

for a density ~ * * = 8 9 7 0 ~ ~ c r n - ~

xuv

threshold (pulse energy

1

o - ~

k l ~ )

0.07

0.42 37 .O 1.7 40 1.23

4 . 5

21.3 13.8 Minimum density N**

Minimum IR power

0.12

0.83 2 2 . 7

2.5 Minimum

J p =404nm

pump power

Maximum XUV pulse energy (at saturationr

2.1 1.7 176

114 Travelling wave

Resonator

Max.

xuv

pulse energy

(satu- ration)

C

Pulseduration formin. power

5.4

0.2 0.2

18.8

I

^2.1

Minimum,IR power needed for saturation

3 2

0.07 0 . 1 2 7 . 7 0.36 Minimum

J p =404nm

pump power

Travelling wave Resonator Pulse duration for min. power

overall maximum conversion efficiency

Pump beam intensity in the fo-

Travelling wave (pulse duration 2.7n.s)

Resonator Travelling wave

c a l planc

1

^Resonator