Optical-field-enhanced and static-field-induced first-order Fréedericksz transitions in a planar parallel nematic liquid crystal

It is shown that the purely static (magnetic or electric) field-induced Fréedericksz transition in a planar parallel oriented nematic-liquid-crystal cell is always second order. But with an additional optical field, the magnetic-field-induced Fréedericksz transition can become first order and bistable. For the electric field, if 9/4>w>0, the electric-field-induced first-order transition can be enhanced by the optical field, where =(nc/no)2-1, w=?/μ-1, no and nc are the ordinary and extraordinary indices of refraction, μ and μ? are the dielectric constants perpendicular and parallel to the local nematic director. The exact and small-angle approximate solutions describing the nematics orientation are obtained. The first-order transition enhancement tricritical optical field intensity and criterion are also given. © 1986 The American Physical Society.