Anomalous photocurrent transients in nematic liquid crystals: The nonlinear optical Pockel’s effect induced by the Fréedericksz transition

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Abstract
The mechanism of the normally incident photoinduced current transients in homogeneous nematic samples in an applied dc voltage has been studied theoretically and experimentally. Explicit expressions for the photovoltaic emf are derived using the nonlinear optical Pockel’s effect induced by the Fréedericksz transition. The current transient is elucidated by the effect of dc field-induced ion drift to electrodes based on an equivalent circuit. The experimental results [briefly reported in Phys. Rev. Lett. 63, 555 (1989)] are completely explained by the present theory. According to the theoretical prediction, two methods to enhance the photoinduced current in liquid crystals, light exposure and dye doping, have been found and implemented.