<title>Backflow effects on optical properties of nematic liquid crystals</title>

We present a model of a nematic liquid crystal cell to describe the first and final stages of the reorientation process induced by the action of an obliquely incident optical field. The presence of hydrodynamic backflows associated with the reorientation in both, a homeotropic and a planar geometry, is explicitly taken into account. We study the effect produced by the backflows on two specific optical properties of the nematic, namely, its phase change and its inverse focal length. These quantities are calculated analytically and evaluated for the nematic phase of CBOOA. It is shown that for a homeotropic arrangement, hydrodynamic backflows may produce a significant, and in principle measurable, change as high as 75% in these properties.