Orientational holographic gratings observed in nematics aligned by carbon nanotube film

In this paper, we present a novel type of nematic liquid crystal cell with carbon nanotube film deposited by electrophoresis as the alignment layer. Self-diffraction was observed without applying a dc voltage across the cell under low intensity optical irradiation of a few milliwatts at 488 nm. The first-order diffraction efficiency increased and the response time of the grating decreased with the applied dc voltage increasing up to the dynamic scattering threshold voltage at 4 V (the corresponding dc electric field was 0.2 V/μm). A diffraction efficiency of ∼20%, the grating formation time of 0.5 s and an effective refractive index change coefficient of 0.14 cm²/W were obtained at 3.7 V with a writing beam intensity of 33 mW/cm². These observed phenomena were attributed to the photoactive charge layer formed at the interface of the carbon nanotube film and the liquid crystal film. PACS 42.65.Hw; 42.70.Df; 42.70.Nq; 42.40.Eq