Population-grating transfer in cold cesium atoms

Optical-pumping-induced population-grating transfer between hyperfine levels of the cesium $D_2$ line is observed through four-wave mixing in a sample of cold atoms. Diffraction efficiencies of order of 1% have been measured for a large range of angular apertures. We have studied the angular dependence of the diffracted signal in the limit of small atomic velocities and discussed its application for a nondestructive diagnostic of the trap dynamic. Image processing with nearly degenerate frequency conversion was also demonstrated using this specific mechanism.