Quantitative study of optical pumping in the presence of spin-exchange relaxation

We have performed quantitative measurements of the variation of the on-resonance absorption coefficients k(0) of the four hyperfine components of the Cs D-1 transition as a function of laser power P, for pumping with linearly and with circularly polarized light. Sublevel populations derived from rate equations assuming isotropic population relaxation (at a rate gamma(1)) yield algebraic k(0)(P) dependences that do not reproduce the experimental findings from Cs vapor in a paraffin- coated cell. However, numerical results that consider spin-exchange relaxation (at a rate gamma(se)) and isotropic relaxation fit the experimental data perfectly well. The fit parameters, viz., the absolute value of k(0), the optical pumping saturation power Psat, and the ratio gamma(se)/gamma(1), are well described by the experimental conditions and yield absolute values for gamma(1) and gamma se. The latter is consistent with the previously published Cs-Cs spin-exchange relaxation cross section.