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Summary: VOLUME 76, NUMBER 13 P H Y S I C A L R E V I E W L E T T E R S 25 MARCH 1996
Observation of Spontaneous Spin Polarization in an Optically Pumped Cesium Vapor
W. M. Klipstein, S. K. Lamoreaux, and E. N. Fortson
Department of Physics, University of Washington, P.O. Box 351560, Seattle, Washington 98195
(Received 20 November 1995)
We have observed spontaneous atomic spin polarization of a Cs vapor undergoing rapid spin
exchange in a cell when illuminated with plane-polarized 894 nm (D1) light. The spin polarization
shows marked hysteresis in switching between two stable orientations, fully aligned parallel or
antiparallel to an external magnetic field, as the circular polarization of the pump light is varied
about zero. We show that our observations agree with theoretical expectations and point out possible
applications of spontaneous polarization.
PACS numbers: 42.65.Pc, 32.80.Bx
We have made the first observation of spontaneous
atomic spin polarization in an alkali metal vapor optically
pumped with plane-polarized light. Such polarization
has been predicted to occur when optical pumping and
electronic spin exchange take place faster than spin
relaxation [1]. In our experiment, Cs vapor contained
in a cell along with a nitrogen buffer gas becomes fully
spin polarized when illuminated with linearly polarized
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