Date of this Version
PHYSICAL REVIEW A 82, 033408 (2010); DOI: 10.1103/PhysRevA.82.033408
We have studied the optical pumping of mixtures of Rb vapor and N2 buffer gas by laser light tuned to the D1 transition having a spectral width of ∼500 MHz. The Rb densities are of the order of 1013 cm−3, while the buffer-gas pressures range from 0.1 to 10 torr. As the frequency of the right-hand circularly polarized laser is varied across the D1 absorption profile, the electron spin polarization of the Rb is found to take on negative values for small negative values of pump detuning from the absorption profile center. This occurs for N2 pressures below ∼1 torr; at 10 torr the electron spins consistently point in the same direction as the angular momentum of the pump light. The spin-reversal effect can be understood in terms of populations of the F = 2 (85Rb) and F = 1 (87Rb) states caused by small unpolarized fractions in the pump beam and its elimination in terms of pressure broadening caused by the N2 buffer gas. We speculate that this effect could be used for fast Rb spin modulation.