Production of spin-polarized cold atoms by optical pumping in a magneto-optical trap

We report optical pumping of cold cesium atoms trapped in a magneto-optical trap (MOT). We use the trapping light of the MOT to pump the atoms to the 6S _1/2, F = 3 state. Another laser with either linear or circular polarization is used to pump them to either m _F = 0 or m _F = ± 3 levels, respectively. We developed a sensitive way to measure the atomic distribution among the Zeeman sublevels to find the resulting spin polarization of the sample. We can put more than 95% of the atoms into the desired state. We found that the Zeeman distribution of the MOT atoms before optical pumping was skewed to one extreme m _F level. We observed a loss of 30% of the atoms when we tried to pump them to the opposite extreme m _F state. The optical thickness of the atomic cloud dropped from 14 to 7 during the optical pumping period, which was 8 msec. Ways to reduce this time and to increase the final optical thickness are discussed.