Abstract

Using both analytical and numerical techniques, we have calculated the transverse dependence of the reorientation of the director axis of a nematic liquid crystal by a linearly polarized Gaussian laser beam. The laser propagates at a small angle β with respect to the director axis direction. For this geometry, previous studies have shown that even if the optical electric field is weak in comparison with the Freedericksz field, the director axis will reorient. The reorientation gives rise to an intensity dependent phase shift. In the limit of small β and reorientation angle, the Euler equation can be solved analytically in terms of hyperbolic Bessel function integrals. A numerical evaluation of these integrals shows that, for all values of the laser beam waist compared to the thickness of the film, the transverse dependence of the reorientation has a width larger than the input laser beam waist. If the laser beam waist is comparable to or less than the thickness, the broadening is considerable (by a factor of 2 or more). We have performed quantitative experiments based on the transverse phase modulation effects. Experimental results are in excellent agreement with the theory.

© 1985 Optical Society of America