Spectral and spatial evolution of a conical emission in Na vapor

Abstract

A detailed study on yellow conical emission observed in dense sodium vapor following near-resonant onephoton excitation of the Na 4 2 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.

Multichannel conical emission and parametric and nonparametric nonlinear optical processes in ytterbium vapor

“…7 illustrates, if one generated frequency occurs off-axis from the incident laser light then at least one other must do so as well. This behavior was predicted for CE in Na [9], but emission for wavelengths corresponding to transitions between excited states has not been observed (see Refs. [9,10]).…”

“…Conical emission in multilevel systems has been commonly interpreted to be a result of photon momentum conservation (phase-matching) in parametric 4WM (see, e.g., Refs. [9,10,12]).…”

“…We measure spatial profiles of emission at different wavelengths and total emission energies as a function of incident light frequency and observe distinct behavior for light generated by parametric and nonparametric processes. Several features of this experiment, such as observation of CE near-resonant with transitions between excited atomic states, distinguish it from previous, closely-related work in sodium vapor employing one-photon excitation [6,8,9,10,11,12,13]. The nonparametric nonlinear processes investigated in this work may be useful in a new scheme to measure atomic parity nonconservation (PNC) in Yb [19].…”

“…[6,7,8] and references therein). Under certain conditions, the generated light can be emitted in hollow cones [6,8,9,10,11,12,13,14,15,16].…”

“…Such conical emission (CE) has been observed at wavelengths near that of the incident laser light (see, e.g., [13,14,15,16,17] and references therein) and also at wavelengths corresponding to other atomic transitions [9,10,11,12]. Collimated light (light emitted in a filled-in cone with relatively small angle of divergence compared to CE) can be generated in both the forward and backward directions with respect to the propagation direction of incident laser light (see, e.g., [1] and references therein).…”