Temperature and Field Hysteresis of the Pitch Variations in Thin Planar Layers of Cholesterics

Abstract

Temperature hysteresis of the cholesteric pitch in planar cholesteric layers was observed in [1,2]. A similar hysteresis of the cholesteric pitch in planar layers has to take place in the applied electric (magnetic) field. The restriction on the sample characteristics and strength of the surface anchoring potential are found which ensure defectless mechanism of the pitch field and temperature variations (jumps in the pitch value). The equations describing temperature and field pitch variations are presented and analysed. For weak field an universal character of the pitch variations, similar to those for the temperature variations and dependent on the value of some parameter only, is revealed. In the frame of Rapini model anchoring potential the field and temperature dependencies of the pitch variations and the hysteresis in the pitch jumps for specific values of the mentioned parameter are calculated. Transmission optical spectra of the layer for normal incidence of light are calculated at the points of pitch jumps.