TEMPORAL INSTABILITY DUE TO COMPETING SPATIAL PATTERNS IN LIQUID-CRYSTALS IN THE LIGHT-FIELD

We unveil the physical origin of the peculiar spatio-temporal instabil ity phenomena observed in liquid crystals subject to the influence of a light wave of ordinary polarization. Our study shows that due to non -adiabatic propagation of a light beam in an anisotropic medium, the L ight polarization and, hence? the torque acting on the orientation of a nematic liquid crystal (NLC) is asymmetrically modulated over the NL C layer. The spatial pattern of the NLC reorientation that is formed a cross the NLC-layer under the influence of such a torque may become un stable in time due to competing interaction of symmetric and antisymme tric modes. The obtained results allow evaluation of the threshold int ensity and the range of the light incidence angles where the longitudi nal spatio-temporal instability is possible. (C) 1998 Elsevier Science B.V. All rights reserved.