<title>Electro-optic response of a thin liquid-crystal layer in the pretransitional regime</title>

Abstract

In this work, the electro-optic response of 6CB liquid crystal is studied using a sensitive differential technique. The liquid crystal layer is held at a temperature just above the nematic to isotropic (N-I) phase transition. Transverse magnetic (p) polarized light incident on the cell is coupled to guided modes in the liquid crystal layer using either grating or prism coupling. In both cases the modes manifest themselves as sharp resonances in the reflectivity as the angle of incidence is scanned. When a low frequency sinusoidal voltage is applied to the cell the resonance shapes and positions are altered at a frequency which is twice that of the applied field, resulting in a modulation of the reflectivity for a given angle of incidence. By carefully observing the modulated signal, and comparing the data with modelling generated from multilayer optics theory, two effects are quantified. The first of these is an induced birefringence, (delta) n, varying quadratically with applied voltage, which is well understood and can be expressed in terms of Landau De Gennes theory. The second is a field induced perturbation in the imaginary part of the optical permittivity, (delta) (epsilon) i, which implies a modification of the light scattering properties of the liquid crystal. The measurement of the latter effect is, as far as we know, a novel one, being only made possible by the remarkable sensitivity of the synchronous differential technique.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.