Reorientational optical nonlinearity of nematic liquid-crystal cells near the nematic-isotropic phase transition temperature.

We address the reorientational optical nonlinearity of homogeneously aligned neamtic liquid-crystal (NLC) cells. The propagation of light in NLC cells depend strongly on temperature. At a temperature approaching the clearing point, an undulating beam and multifocal points are observed in the NLC cell by use of a polarizing optical microscope. Using a conoscopic technique, we observed novel consecutive concentric and parabolic patterns projected onto a screen. Optical energy is considered to compete with thermal energy to affect NLC's orientation and to generate singularities in the steady state. A model of the configuration of the liquid crystal's orientation is proposed.