Effects of magnetic resonance on 133Cs in optical pumping with D2 light

Volume 24A, number 13

PHYSICS LETTERS

19 June 1967

EFFECTS OF MAGNETIC RESONANCE ON 133Cs OPTICAL PUMPING WITH D 2 LIGHT

IN

J. HAAS* and J. F R I C K E Physik-Department der Technischen Hochschuke M~nchen, Germany Received 19 May 1967

The dependence of the equilibrium spin polarization of 133Cs (I = I) pumped with D21ight was measured as a function of argon pressure and r.f. induced Zeeman relaxation. The results inaicate a limitation of validity for the nuclear spin zero model.

Sign and amount of alkali ground s t a t e p o l a r i zation p e r f o r m e d with c i r c u l a r l y p o l a r i z e d D 2 light depend on e x c i t e d s t a t e m i x i n g [1-3]. By m e a n s of a new t r a n s m i s s i o n technique [4] e a r l i e r m e a s u r e m e n t s of i n v e r s e ground s t a t e p o l a r i z a t i o n [2] w e r e extended. The m e a s u r e m e n t s w e r e p e r f o r m e d with a conventional o p t i c a l p u m p ing a r r a n g e m e n t [5] on 133Cs (I = ½) in an a r g o n buffer gas a t m o s p h e r e . T h e c e l l w a s wall coated. F o r c r e a c t i o n and d e t e c t i o n of spin p o l a r i z a t i o n two d i f f e r e n t light s o u r c e s w e r e used. A s t r o n g a+ p o l a r i z e d D 2 light b e a m p e r f o r m e d pumping a g a i n s t e q u i l i b r i u m . T h e weak D 1 d e t e c t i n g b e a m w a s p o l a r i z e d a l t e r n a t i v e l y a+, a - at a f r e q u e n c y of about 50 Hz [4]. The d e p e n d e n c e of the e q u i l i b r i u m spin p o l a r i z a t i o n on r . f . r e s o n a n c e p o w e r was m e a s u r e d , with the Z e e m a n t r a n s i t i o n s of F = 3 and F = 4 ground s t a t e h y p e r f i n e l e v e l s u n s e p a r a t e d . At a m a g n e t i c f i e l d of 315 m O e the r.f. p o w e r was s i n u s o i d a l l y m o d u l at ed at 0.01 Hz. The a r g o n p r e s s u r e was a l t e r e d continuously f r o m 1 to 6 T o r r within one hour. In fig. 1 pumping s i g n a l s f o r v a r i o u s buffer gas p r e s s u r e s a r e plotted a g a i n s t the r.f. power. In the s a m e f i g u r e dashed c u r v e s a r e drawn at t h r e e c h a r a c t e r i s t i c p r e s s u r e s . At pot (upper dashed c u r v e ) the signal s t r e n g t h s has z e r o d e r i v a t i v e at z e r o p o w e r . F o r p r e s s u r e p~ (middle dashed c u r v e ) the s i g n a l goes to z e r o at z e r o r.f. p o w e r . P r e s s u r e p v (lower dashed c u r v e ) i s the l a r g e s t p r e s s u r e f o r which the s i g nal i s n e v e r p o s i t i v e , p ~ and p r define a p r e s s u r e r a n g e , in which the n u c l e a r spin z e r o m o d el i s o b v i o u s l y not a p p l i c a b l e b e c a u s e this m o d e l p r e d i c t s no z e r o s o r e x t r e m a l p o i n t s * * . In the * This work is part of Ph.D. thesis work presently being carried out.

c a s e of Cs (I = ~) e x p e r i m e n t a l r e s u l t s a r e P a ~ 4.2 T o r , p~ ~ 2.5 T o r r and p~ ~ 1.4 T o r r f o r a bulb t e m p e r a t u r e of 18oc a n d ' m a x i m u m a v a i l a b l e pumping intensity. 10

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C15 1 r.f.- power (arbitrary units)

Fig. 1. Optical pumping signals versus r.f. power at various argon pressures. Dashed lines determine the char acteristic pressures Pot, P~ and p~. ** A nuclear spin zero treatment [3] including ground state relaxation shows that the three characteristic curves in fig. 1 degenerate to the zero signal axis. 757

Volume 24A. number 13

PHYSICS L E T T E R S

r a m e t e r . The c u r v e fo is for z e r o r.f. power and f ~ for s a t u r a t e d r.f. r e s o n a n c e i.e. v a n i s h i n g sign a l s , w h e r e a s m a r k s i n t e r m e d i a t e v a l u e s of r.f. power. The detection of optical pumping only with the r.fo induced a b s o r p t i o n change of cr+ light yields a signal which i s p r o p o r t i o n a l to (fo-f). This s i g nal v a n i s h e s at the buffer gas p r e s s u r e p~ if the r.f. r e s o n a n c e i s s a t u r a t e d and at about p~ if the r.f. power i s weak. The c u r v e s f c r o s s the abciss~ ( f ~ between p~ and Pfl. Such shifts of s i g n a l z e r o s have p r e v i o u s l y been detected, with p u m p ing light i n t e n s i t y and Cs vapor p r e s s u r e v a r i e d [3]. For I = 0 all t h e o r e t i c a l c u r v e s c r o s s at

6

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19 June 1967

0

P =Pa :P~ =p~" -2

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rf-power as parameter {arbitrary units) • 0.96 o O.&l o 0.20 ÷ 0.10 ° 0.05 o 0

-12

In addition to .Pfl [3] the v a l u e s of Pa and Py m a be a f u r t h e r t e s t for excited state m i x i n g models. Computer c a l c u l a t i o n s c o n c e r n i n g optical pure I ing p r o c e s s e s with a+ p o l a r i z e d D 2 light subject to p a r t i a l m i x i n g within the excited Pz - s t a t e (under the a s s u m p t i o n of m j / r a n d o m i z a t i o n ) and s u b j e c t to Z e e m a n r e l a x a t i o n in the ground state yield the s a m e r e s u l t . The a u t h o r s wish to thank P r o f e s s o r Dr. E. Lfischer for e n c o u r a g e m e n t and c l a r i f y i n g d i s c u s s i o n s . Also they a r e indebted to Dr. F. A. F r a n z and Dr. J. G a r d n e r for helpful c o m m e n t s .

References I

i

i

1

2

4 pressure (Torr)

Fig. 2. Optical pumping signals versus argon pressure at various strengths of r.f. power. Each point means an average value. In fig. 2 the m e a s u r e d s i g n a l s a r e drawn v e r sus buffer gas p r e s s u r e with r.f. power as a p a -

758

1. F.A.Franz a n d J . R . F r a n z , Phys.Rev. 148 {1966) 82. 2. J. Fricke und J. Haas, Z. Naturforsch. 21a {1966) 1319. 3. J. Fricke, J.Haas E. Lllscher and F.A. Franz, to be published. 4. J. Haas, J. Fricke und E. LUscher, to be published. 5. W.W. Holloway Jr,, E. Ltischer and R. Nowick, Phys.Rev. 126 (1962} 2109.