Generation of Light Scattering States in Cholesteric Liquid Crystals by Optically Controlled Boundary Conditions

Abstract

Circularly polarized light was previously employed to stimulate the reversible and reconfigurable writing of scattering states in cholesteric liquid crystal (CLC) cells constructed with a photosensitive layer. Such dynamic photodriven responses have utility in remotely triggering changes in optical constructs responsive to optical stimulus and applications where complex spatial patterning is required. Writing of scattering regions required the handedness of incoming radiation to match the handedness of the CLC and the reflection bandwidth of the CLC to envelop the wavelength of the incoming radiation. In this paper, the mechanism of transforming the CLC into a light scattering state via the influence of light on the photosensitive alignment layer is detailed. Specifically, the effects of: (i) the polarization state of light on the photosensitive alignment layer; (ii) the exposure time; and (iii) the incidence angle of radiation on domain formation are reported. The photogenerated light-scattering domains are shown to be similar in appearance between crossed polarizers to a defect structure that occurs at a CLC/air interface (i.e., a free CLC surface). This observation provides strong indication that exposure of the photosensitive alignment layer to the circularly polarized light of appropriate wavelength and handedness generates an out-of-plane orientation leading to a periodic distortion of the original planar structure.

Keywords

• photoisomerization
• azobenzene
• liquid crystal
• patterning
• texture
• stimuli-responsive materials
• photoalignment
• switchable photonic bandgaps
• displays