Laser optical pumping of high-density Rb in polarized He3 targets

We have investigated high-density Rb optical pumping in polarized He3 targets and present measurements of collisional relaxation rates and studies of diffusion-driven wall relaxation of the Rb polarization. We show that a boundary layer resides in the vicinity of the cell walls within which a polarization gradient is established by diffusion. Absorption of the incident laser radiation within this layer leads to a striking decrease in optical-pumping efficiency for resonant light but has little effect for off-resonant light. Our theory introduces polarization-dependent slowing of optical pumping rates due to the Rb nuclear spin. We have observed a strong frequency dependence of the optical-pumping efficiency, consistent with our theoretical predictions. We report the following rate constants for collisional relaxation of Rb polarization: due to Rb (kRb-Rb=8×10-13 cm3/s), due to N2 (kN2-Rb=8×10-18 cm3/s), and due to He3, an upper limit of (k3He-Rb≤2×10-18 cm3/s). The data and model presented are used to predict laser power and intensity requirements for high-density polarized He3 targets.