Abstract

Optical pumping between the Zeeman sublevels of the ground state of atomic sodium provides an easily accessible nonlinear mechanism that has been widely used in degenerate four-wave mixing (DFWM) experiments in order to achieve large phase-conjugate signals even with low-power cw lasers. Since the ground-state properties of atomic sodium are a long-lived quantity, thermal diffusion severely affects the mixing process by introducing thermal wash-out, thus leading to strong saturation effects. The question arises, why this wash-out does not generally destroy the DFWM signals. One mechanism counteracting the effect of thermal wash-out, thus reestablishing locality, is the trapping of resonance radiation, as has been shown recently.¹

© 1994 IEEE