Abstract

An applied electric field changes the local symmetry of isotropic dielectrics thus making them uniaxial, what is the Kerr effect. In case of the uniaxial anisotropic materials, such as nematic liquid crystals (LCs), the situation becomes more interesting; in addition to enhancing their uniaxial order, the field also induces the local biaxial order. At the same time, the electric field affects the macroscopic orienational fluctuations of the optic axis (the director ñ) of LC. These fluctuations pose an experimental challenge to detect a local change of symmetry. We used an approach of the dielectric tensor at optical frequencies (optic tensor) to demonstrate the contribution of each of these processes. Using oblique light propagation geometry, we eliminated the effect of the director fluctuations. The remaining effects were caused by electric field induced modification of the order parameters (EMOP). Experimentally we demonstrated these two processes have characteristic times 30 ns and less than 2 ns for both field on and field off driving. We attribute these two processes respectively to the uniaxial and biaxial contributions to the EMOP effect. The EMOP effect opens possibilities of using LC’s for designing, engineering, and manufacturing electro-optic liquid crystal devices where the nanosecond response time is required, such as fast optical modulators, switches, shutters, optical limiting, and other applications.

© 2013 Optical Society of America