We have observed very large probe beam gain (up to 600 percent) in a thin film (100 μm) of nematic liquid crystal for a low pump beam intensity on the order of 2 W/cm2. The effect is nonlinearly dependent on the pump intensity and the wave mixing angle.
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.
We report several recently observed optical wave mixing effects in thin films of nonlinear materials, such as liquid crystals and silicon. Kerrlike local and nonlocal and diffusive nonlinear resonses are studied. The presence of the diffracted beam is, theoretically and experimentally, shown to have a pronounced effect on the amplification of the probe beam in pump–probe wave mixing. The diffracted beam also drastically alters the phase conjugation reflection of the probe beam, phase conjugation self-oscillation threshold, and aberration correction characteristics.