Transparent Phase Images in Photoactivated Liquid Crystals

Photoactivated electric field effects in nematic liquid crystals serve as reversible nearly real-time techniques for recording phase-type holograms. In a sandwich-type cell, a photoconductive coating separates one conductive electrode from the liquid-crystal layer, which is operated below the threshold voltage for dynamic scattering. In CdS cells, transient first-order diffraction efficiencies of 10–30% are obtained within 0.1–0.2 sec from visible light exposures of less than 1 μJ/cm2. A 10-μW/cm2 Ar-ion laser interference pattern of 40 cycle/mm produced a steady-state first-order diffraction efficiency of 8% in a 13-μm thickness of MBBA in a cell operated at 4-V dc. Resolutions up to 100 cycle/mm are observed for this thickness of liquid crystal.