Measurement of the refractive indices of a ferroelectric liquid crystal

Abstract

Optical excitation of half‐leaky guided modes has been used to determine the refractive indices of a ferroelectric liquid crystal (Merck‐SCE13) in a homeotropically aligned state. The uniform homeotropic alignment is realized, with no surface treatment, by the application of an in‐plane dc electric field. This applied field, of the order of 5×10⁵ V m⁻¹ is sufficient to fully unwind the S^*_c helix giving a uniformly tilted homeotropic monodomain for optical characterization. Analytic and numerical modeling results indicate that, for a slab with its optic axis tilted in a plane orthogonal to the plane of incidence, two distinct critical angles appear in the half‐leaky guided mode response. These independently relate simply to the ordinary and extraordinary refractive indices of the S^*_c material. By fitting theoretical angle dependent reflectivities to those recorded experimentally the two refractive indices have been obtained for a range of temperatures in both the S^*_c and S_A phases.