We have investigated high-density Rb optical pumping in polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ 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 (${\mathit{k}}_{\mathrm{Rb}\mathrm{-}\mathrm{Rb}}$=8×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^3$/s), due to ${\mathrm{N}}_2$ (${\mathit{k}}_{\mathrm{N}2\mathrm{}\mathrm{-}}$Rb=8×${10}^{\mathrm{-}18}$ ${\mathrm{cm}}^3$/s), and due to ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, an upper limit of (${\mathit{k}}^3$He-Rb≤2×${10}^{\mathrm{-}18}$ ${\mathrm{cm}}^3$/s). The data and model presented are used to predict laser power and intensity requirements for high-density polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ targets.

• Received 18 October 1993

DOI:https://doi.org/10.1103/PhysRevA.49.3854