Spectral narrowing in coherent rayleigh scattering

Spectral narrowing of the coherent Rayleigh scattering line shape in a room temperature CO2 gas (2.5×1023m-3) with intense fields in the 1015Wm-2 range is observed. The line shape saturates to a width of approximately half that observed at low pump intensities and indicates a transition from scattering primarily from untrapped molecules to that from both trapped and untrapped molecules that are localized by the deep (60 K) optical potentials produced by the pump beams. At higher densities (5×1024m-3), collisions between the trapped and untrapped molecules broaden the spectral profile.