Degenerate multiwave mixing and optical phase conjugation in semiconductor silicon are reexamined both theoretically and experimentally. It is found that, in general, the often neglected diffracted beams influence considerably both the forward as well as the backward phase conjugated signal gain.
We present a detailed theory and experiment on degenerate-multiwave-mixing-mediated beam amplification in the semiconductor silicon. The theory accounts for several important factors, such as coupling to higher-order diffractions, intensity-dependent self- and mutual-phase modulations, losses, phase matchings, intensity ratio among the input beams, etc. In the silicon case under study, involving the generation of electron-hole pairs by 1.06-\ensuremath{\mu}m laser pulses, the intensity-dependent absorption loss and the temporal and/or spatial intensity profile of the input laser beam are also explicitly accounted. The experimental results for probe-gain dependences on several parameters are in good agreement with the theory. The important role played by the side diffractions in mediating the amplification of the probe is also apparent in our experiment on phase conjugation of the probe beam, where a strong dependence of the phase-conjugation reflection on the pump- to probe-beam ratio is observed, similar to the probe-gain dependence.
Optical phase conjugation through nearly degenerate four-wave mixing (NDFWM) in semiconductor lasers has attracted considerable attention in recent years since being first demonstrated by Nakajima and Frey[ 1 ]. Such interest arises due to the very high conjugate reflectivity of order 30-40dB which can be achieved owing to the amplifying effect of the semiconductor gain medium and cavity enhancement of mixing process. However, most previous experimental and theoretical work has placed emphasis on the weak signal case, where the injection signal acts only as a small perturbation of free-running laser diode. It is only very recently that a theoretical analysis of NDFWM in a semiconductor laser subject to strong probe injection power has been presented[2].
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.