Critical Pitch in Thin Cholesteric Films with Homeotropic Boundaries

Abstract

Calculations of the planar cholesteric texture with homeotropic boundary conditions are presented. At a constant film thickness there is a critical twist t0c below which the planar texture has transformed into a homeotropic one. The additional influence of an external field is discussed for positive and negative anisotropy and with field orientations parallel or normal to the film plane. A general solution of the director field has been found for a normal orientation of the field. A properly adjusted twist t0 obtained by dilution of an optically active material in a nematic matrix opens a possibility to reduce the critical voltage in technical devices.