Excitation of convective motions in isotropic and anisotropic liquids by light

The possibility of excitation of convective motions of the Rayleigh – Benard and Marangoni type in isotropic liquids and nematic liquid crystals upon absorption of light with a spatially periodic intensity distribution is demonstrated theoretically and experimentally. It is shown that gravitational and thermocapillary surface hydrodynamic waves are observed in the case of a running interference pattern. The possibility of control and the stability of convective motions are investigated. Benard cells become unstable when the light intensity is high. These instabilities are of thermal origin because the Prandtl number for the medium under investigation is considerably larger than unity. The competition between the gravitational and thermocapillary mechanisms of photohydrodynamic reorientation of the nematic liquid crystal director is also studied. The effect of convective motions on the thermodynamic phase transition is observed and explained.