A detailed study on yellow conical emission observed in dense sodium vapor following near-resonant one-photon excitation of the Na 4<sup>2</sup>P levels 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 introduce self-phase modulation and induced-phase modulation as important additional nonlinear processes, explaining the nonmonotonic detuning of the wavelength of the conical radiation with the exiting laser wavelength in the vicinity of resonance transitions. The spatial evolution of emission generated via four-wave mixing is modeled by solving the two-dimensional nonlinear Schrödinger equation describing the spatial evolution of light beams in a nonlinear media. Experimental and theoretical results are presented and discussed.
© 1998 Optical Society of America
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(190.5940) Nonlinear optics : Self-action effects
(300.2570) Spectroscopy : Four-wave mixing
(300.6210) Spectroscopy : Spectroscopy, atomic
A. Dreischuh, V. Kamenov, S. Dinev, U. Reiter-Domiaty, D. Gruber, and L. Windholz, "Spectral and spatial evolution of a conical emission in Na vapor," J. Opt. Soc. Am. B 15, 34-40 (1998)