Downloaded By: [Universiteit Gent] At: 11:04 6 February 2007 Ferroelectrics, 344:225–231, 2006 Copyright © Taylor & Francis Group, LLC ISSN: 0015-0193 print / 1563-5112 online DOI: 10.1080/00150190600968348 Lateral Light Propagation in SSFLC Devices and Thermal Optical Nonlinearities JEROEN BEECKMAN, ∗ KATARZYNA CHA LUBI ´ NSKA, AND KRISTIAAN NEYTS Liquid Crystals & Photonics Group, Department of Electronics and Information Systems, Ghent University, Sint-Pietersnieuwstraat 41, Gent 9000, Belgium Optical nonlinearities in ferroelectric liquid crystals are investigated experimentally by launching a laser beam laterally into a surface stabilized ferroelectric liquid crystal cell. Our set-up allows measuring both the propagation of the beam inside the cell and the changes induced in the liquid crystal layer. The first is possible due to scattering of light in the liquid crystal layer and the latter by using polarization microscopy. The observed effects are related to thermal optical nonlinearities. Keywords Optical nonlinearity; lateral light propagation; surface stabilized ferroelec- tric liquid crystal cells Introduction Liquid crystals are partially ordered fluids, in such way that molecules are oriented along a certain direction. These materials are widely used nowadays in flat panel displays because of their extraordinary electro-optical properties. They also exhibit a number of optical nonlinearities with different origin. These nonlinear effects can be divided into two types: electronic and nonelectronic nonlinearities [1]. The electronic nonlinearities are very fast and are similar to nonlinear effects in other materials originating from a perturbation of the electronic wave functions of the molecules. The nonelectronic nonlinearities affect the temperature, molecular orientation, density, . . . of the liquid crystal and they are in general much slower, but require an optical power which is substantially lower. In nematic liquid crystals these nonelectronic nonlinearities are well investigated and are mainly focused on the generation of holographic gratings [2]. Here, the light travels through the liquid crystal cell as in a display, perpendicular to the glass plates (i .e. tranverse light propagation). In this work light travels laterally in the cell, so parallel to the glass plates. This configuration was used to generate spatial solitons in nematic liquid crystals using either thermal or reorientational nonlinear effects. In the thermal case, the soliton can be captured in an isotropic channel [3] or due to thermal indexing [4]. In the other case molecules are reoriented by the electric field of the light and this way it is possible to generate solitons of several millimeters with a few milliwatts of light power [5, 6]. The generation of these solitons is unfortunately very slow [7]. Received September 12, 2005. ∗ Corresponding author. E-mail: jeroen.beeckman@elis.ugent.be [469]/225