Production of highly polarized vapors using laser optical pumping with velocity-changing collisions

Experiments have shown the novel combination of laser optical pumping and velocity-changing collisions (between active- and buffer-gas atoms) to be very effective in producing vapors with high atomic or nuclear polarizations. This paper presents a theory which has proven successful in analyzing these experiments. The theory predicts the amount of polarization attainable for particular experimental conditions and establishes the general criteria for optimum polarization. The theory is based on sets of coupled rate equations, which contain terms describing the pumping process (i.e., stimulated absorption or emission), radiative branching, relaxation, and velocity-changing collisions. The collision terms are written in the strong-collision approximation, which assumes that a single collision, on average, thermalizes the velocity distribution. Expressions are derived for the polarization and level populations