Laser‐induced Reorientation Nonlinear Optical Effects

Summary

Liquid crystals are optically highly nonlinear materials in that their physical properties, particularly refractive indices or birefringence, can be affected by the incident optical fields. In the isotropic phase, the liquid crystal molecules are randomly oriented owing to thermal motion, just as in conventionally anisotropic liquids. Besides molecular reorientations, an optical field could also induce nuclear orientational anisotropy. Laser‐induced molecular orientation in isotropic liquid crystals has been studied by several groups. The dynamics of molecular reorientation are described by equating all the prevailing torques acting on the director axis in the reorientation process. In many optical wave mixing processes involving the interference of two coherent co‐polarized laser beams, the resulting optical intensity imparted on the liquid crystal is a sinusoidal function. The chapter summarizes the basic theories and principal mechanisms responsible for the orientational photorefractivity in liquid crystals. Director axis reorientation in the cholesteric phase of liquid crystals was first theoretically studied.