Voltage Controlled Self-Transparency in a Twisted Nematic Liquid Crystal Cell Bounded by Parallel Polarizers

Abstract

We report the study of non linear transparency effect given by the light induced creation of an isotropic hole in a 90° twisted nematic liquid crystal cell bounded by two parallel polarizers. The twisted structure acts as a π/2 polarization rotator so that the device is initially opaque, but becomes transparent if the twisted structure is broken, due to liquid crystal phase transition (e.g. from nematic to isotropic) or director configuration change (e.g. from twisted to homeotropic). The first, thermal, effect is driven by the impinging beam producing a nonlinear optical behaviour, while the second effect can be used to modify it. The result is a voltage controlled nonlinear thermooptical effect that presents some interest both from a fundamental and an applicative point of view. Experimental results are reported and discussed with a simple theoretical model.