First- and second-order Freedericksz transitions in nematic liquid crystals subjected to static and optical-electromagnetic fields

The electric-field-induced Freedericksz transition in a nematic liquid crystal is always second order, with or without an additional electric or magnetic field. However, with an additional optical field, the transition can become first order and bistable in both planar parallel and homeotropic nematic cells. The first-order transition condition and criterion are obtained. There exists a critical optical intensity above which the first-order transition can be obtained from an otherwise second-order transition, and in general, the critical intensity is smaller for a parallel cell than for a homeotropic cell.