Probe beam amplification in a Kerr-like medium, e.g. a nematic liquid crystal film via 2-wave mixing is possible if it is stoke shifted relative to the pump beam. We report experiment observation of this effect and contribution from other multi-wave mixing effects.
In a highly nonlinear thin film, the presence of the diffracted beams from the pump-probe-beam-induced refractive-index grating modifies considerably the energy coupling between the pump and the probe beams. Using coupled amplitude and phase equations, the roles of various factors such as phases and phase shifts, phase modulations, pump-beam intensity, intensity ratio, interaction length, and losses in the medium in the multiwave-mixing processes are clearly identified. We also present experimental results on the dependence of the probe gain on the pump-probe-beam ratio, the pump intensity, and on the interaction length, using a nematic liquid-crystal film as the nonlinear medium.
The theory of probe beam amplification via degenerate optical wave mixing in a Kerr medium is presented. This theory includes consideration of the self-phase modulation, two-wave mixing, and multiwave mixing terms in the coupled-wave equations. Both analytical solutions, under the assumptions of a nondepleted pump beam and a transparent Kerr medium, and numerical solutions with these assumptions removed are presented. Our solutions show that under certain conditions, phase matching can be satisfied and a high probe beam gain is possible, even for a zero phase shift between the refractive index and the intensity gratings.
Further theoretical observations and a new analysis of stationary degenerate and nearly degenerate optical wave mixing effects in a Kerr-like nonlinear medium are presented. The effects of phase modulations, beam ratio, intensity, wave mixing angle and frequency differences and other physical and optical parameters in multiwave mixing mediated probe gain and their application in ring oscillation devices are analyzed in detail. New experimental studies of the intensity and the angular dependence of the probe beam amplification and side diffractions in liquid crystal provide further insights into the phenomena.