Evolution of the spatial frequency spectrum of the scattering in the region of the 3S–3P transition in sodium vapor

An experimental investigation was made of the evolution of conically scattered radiation generated by excitation of sodium vapor with pump radiation in the range 16 450–17 360 cm^–1 (608–576 nm) in the region of the 3S–3P transition. It was found that the conical structure of the scattered radiation, recorded earlier in the case of near-resonant excitation, was retained in a wide range of the tunable pump radiation frequency. The conical structure observed in the vicinity of two photon resonances of the pump frequency with the 3S–5S and 3S–4D transitions was determined not only by the scattered radiation, similar to that observed in the case of near-resonant excitation, but also by the radiation due to four-photon parametric scattering in the case of full phase matching between the interacting waves.