Photoinduced helical inversion in cholesteric liquid crystal cells with homeotropic anchoring

Abstract

Structural changes caused by the optically induced helical inversion in the cholesteric liquid crystal cells with homeotropic anchoring are studied. In a one-step exposure, a sequence of structural transformations "lying left-handed helix - unwound homeotropic state - lying right-handed helix" is realized. In this process, smooth expansion of a left-handed helix, transition to an unwound state, emergence and smooth compression of a right-handed helix was observed. The unwound state was maintained over a rather wide range of exposures. Well-oriented and highly periodic fingerprint textures capable of the above mentioned structural changes were obtained by rubbing the aligning substrates. This allowed for obtaining photo-tunable diffraction gratings and using them to demonstrate new beam steering principle. Also, pitch reversal suggested new options for optical recording, in particular contrast reversal and edge enhancement.