Summary: Experimental and theoretical study of spontaneous spin polarization
and hysteresis in cesium vapor
A. Andalkar,* R. B. Warrington,
M. V. Romalis, S. K. Lamoreaux,
B. R. Heckel, and E. N. Fortson§
Department of Physics, Box 351560, University of Washington, Seattle, Washington 98195-1560
Received 8 August 2001; published 11 January 2002
We report results of measurements and theoretical modeling of spontaneous spin polarization and associated
hysteresis in an optically pumped Cs vapor. We observe hysteresis over the full range 20450 torr of N2
buffer gas pressures tested, and on two hyperfine components of the D1 transition, so long as both electronic
spin exchange and optical pumping of a resolved ground state hyperfine level take place faster than spin
relaxation. On the F 3Fe 4 transition, the spin angular momentum is gained from the linearly polarized
pump light, while on the 33 transition, it comes instead from the buffer gas during collisional quenching.
The density-matrix theoretical model we have developed includes the effects of coherence in the excited state.
It reproduces all observed features of spontaneous polarization, including hysteresis curves in quantitative
agreement with the data across a broad range of experimental parameters.
DOI: 10.1103/PhysRevA.65.023407 PACS number s : 32.80.Bx, 42.65.Pc, 34.10. x
Under certain conditions, an alkali-metal vapor illumi-
nated with unpolarized or linearly polarized light can spon-