NONLINEAR EFFECTS OF RADIATION TRAPPING IN GROUND-STATE ORIENTED SODIUM VAPOR

Effects of radiation transport in the interaction of a laser beam with sodium vapor in an argon atmosphere are reported. Investigations of t he temporal and spatial evolution of ground-state orientation, which i s produced by optical pumping with a circularly polarized near-resonan t laser beam, reveal a strong deviation from the expected pure diffusi ve behavior. Transverse profiles are narrowed considerably with increa sing sodium density as well as with increasing pump intensity. The tem poral decay of orientation is also drastically altered. A simplified n onlinear and nonlocal theoretical model of radiation trapping gives ex cellent qualitative agreement with the observations and allows an intu itive interpretation.