Abstract
We have observed the diffusion constants of a dye in several liquid crystals by forced Rayleigh scattering. In a liquid crystal which has a standard phase sequence of N-SA-SC, the diffusion anisotropy changes at the N-SA phase transition and increases with decreasing temperature in SA and SC phases. The diffusion constants exhibit a rather smooth decrease with decreasing temperature except an anomaly at the SA-Sc phase transition. In a liquid crystal which has the antiferroelectric SCA phase, however, the diffusion constants show discontinuous increase and decrease at the SA-Sc and the Sc-ScA phase transition temperatures, respectively: the diffusion constant in SC is larger than that in the higher temperature SA phase. Anomalous signal increase and profile were observed at the phase transition temperatures, and were ascribed to the complementary transient grating due to the coexistence of two phases.