Coherence-induced population redistribution in optical pumping.

Abstract

We present experimental and theoretical investigations of the ground-state levels of the Cs cycling transition. We show that in such multilevel nondegenerate systems, the populations of the extreme Zeeman sublevels, under optical pumping, can have asymmetric (``dispersive'') line shapes as a function of laser frequency. A density-matrix model which takes into account optical, Zeeman, and hyperfine coherences, and allows for a fluctuating laser field, correctly predicts the experimental observations. A comparison of the density-matrix model with a rate-equation model demonstrates the role of coherences in the population distribution. Investigation of the effect theoretically and experimentally for \ensuremath{\sigma} and \ensuremath{\pi} laser polarizations is presented in the paper.