SPECTRAL AND SPATIAL EVOLUTION OF A CONICAL EMISSION IN NA VAPOR

A detailed study on yellow conical emission observed in dense sodium v apor following near-resonant one-photon excitation of the Na 4(2)P lev els was performed. The origins of conical emission are suggested to be due to Raman resonant four-wave parametric mixing processes. In order to describe spectral and spatial features of off-axis emission, we in troduce self-phase modulation and induced-phase modulation as importan t additional nonlinear processes, explaining the nonmonotonic detuning of the wavelength of the conical radiation with the exiting laser wav elength in the vicinity of resonance transitions. The spatial evolutio n of emission generated via four-wave mixing is modeled by solving the two-dimensional nonlinear Schrodinger equation describing the spatial evolution of Light beams in a nonlinear media. Experimental and theor etical results are presented and discussed. (C) 1998 Optical Society o f America.