A study of light stimulus propagation phenomena in optical information processing media, liquid crystals

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(a) The mechanism of normally incident photoinduced current transients in homogeneous nematic samples in an applied 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 Freedericksz 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 are completely explained by the present theory.(b) Measurements of discharging current transients in nematic liquid crystals have been made at various applied voltages and temperatures. A well-marked peak in the discharging transient is observed in both nematic and isotropic phase for the first time. Computer simulation based upon a random walk method has been also carried out in order to explore the origin of such an anomalous peak. It is concluded that the occurrence of the anomalous peak is ascribed to a relaxation of an applied-electric-field-induced non-uniform distribution of space charges due to impurity ions incorporated in the liquid crystals.(c) The simulation of visual excitation (SVE) by new effect of nonlinear optical rectification in nematic liquid crystals has been reported. It is shown that this opto-electric structure is naturally similar to the real visual neurotic element. As an example, an optical parallel processing device structure using SVE is proposed for pattern recognition.