Redistribution of photons and frequency mixing with cross-polarized beams in sodium

The interaction of two linearly cross-polarized beams having frequencies ω₁ and ω₂ with sodium atoms leads to the generation of new waves having frequencies (2p+1)ω₁-2pω₂. The intensities of these waves are well explained by a simple model based on self-induced optical activity. The relation with the atomic cooling in a polarization gradient and with the exact resonances in multiwave mixing is pointed out.