Excited-State Mixing in the Optical Pumping of Alkali-Metal Vapors

The effect of excited-state mixing on the optical pumping of alkali-metal vapors is considered for the case where the energy separation between the ²P1/2 and ²P3/2 first excited states is relatively large, allowing the isolation of mixing effects within a particular J level. Two models for the mixing process are proposed, one a random reorientation of the total electronic angular momentum J, and the other a reorientation of J subject to the selection rule ΔmJ=0, ±2. The probabilities for mixing transitions among J-state sublevels have been calculated for an alkali atom of nuclear spin 3/2, and can be used to calculate the optical-pumping transition probabilities for a vapor subject to any degree of excited-state mixing. Several possible experiments suggested by these calculations are discussed.