Nonlinear optics of nematic, smectic and cholesteric liquid crystals

Summary form only given, as follows. Recent advances in nonlinear optics of liquid crystals (LC) are related to optically induced collective molecular reorientation processes, which account for non-resonant but huge nonlinearities. Those processes exhibit such spectacular features as propagation-induced reorientation, self-oscillations, etc. Jumps and hysteresises of LC´s orientational state with changing incidence angle and intensity of light provides new schemes for optical bistability and opto -optical modulation. In certain circumstances, direct orientational interaction may be conquered by absorption-induced effects. Among several mechanisms to transform the energy of absorbed light beam into molecular reorientation, the strongest one utilizes generation of hydrodynamic motions. In this way, e.g., infrared-visible modulation turns out to be possible at microwatt power level. Thermally induced reorientation in cholesteric LC (CLC), resulting in its helix pitch change, is able to lead to a new effect of light wave tunneling through CLC´s Bragg reflection region. A nonlinear resonator can be designed with intensity dependent reflection coefficients of CLC-mirrors. Thermal indexing itself can have remarkable contribution to nonlinear optics of LC. It provides, in particular, the effect of stationar energy exchange between two equal-frequency light waves through media with local and instantaneous nonlinear response. Thus degenerate wave mixing and beam cleaning turns out to be possible with only two incidence beams.