2ND SOUND AND NONLINEAR-OPTICAL PHENOMENA IN SMECTIC-A LIQUID-CRYSTALS

We investigated theoretically the nonlinear phenomena (a self-focusing , a self-trapping, stimulated light scattering and four-wave mixing) i n smectic A liquid crystals (SA) caused by a new physical mechanism of cubic nonlinearity determined by the propagating mode of a layer norm al displacement, or the so-called second sound. A nonlinear part of a refractive index caused by a layer normal deformation which is respons ible for a self-focusing effect, and a gain coefficient in the case of a stimulated light scattering (SLS) on the second sound are one or tw o orders of magnitude greater than the similar quantities for isotropi c organic liquids. The light-induced dynamic grating of layer deformat ions generates a high-frequency longitudinal electric field due to the flexoelectric effect. The light-induced dynamic grating of layer norm al displacement ultimately excites a rotational hydrodynamic how with a considerable velocity. Using the slow varying amplitude approximatio n we calculated the light wave and second sound wave amplitudes explic itly for some important cases.