Angular dependence of line shape and strength of degenerate four-wave mixing in a Doppler-broadened system with optical pumping

Abstract

Results of experiments investigating the effects of optical pumping and atomic motion on cw degenerate four-wave mixing in atomic sodium vapor are presented. The signal strength is found to decrease as (sin θ)⁻², where θ is the angle between the object and pump waves; however, the linewidth for generation is Doppler free and is independent of θ. Agreement is found with a simple model of the mixing process. Distortions of the atomic velocity distribution (produced in our experiments by optical pumping) are found to be essential for efficient cw generation. A new modulation scheme for the discrimination against background is used.