LIGHT DIFFUSION AND DIFFUSING-WAVE SPECTROSCOPY IN NEMATIC LIQUID-CRYSTALS

We present a detailed theoretical, experimental, and numerical study o f Light diffusion and diffusing-wave spectroscopy in nematic liquid cr ystals. We report on experiments showing that the transport of light e nergy is governed by an anisotropic correlation diffusion equation, an d we measure the parallel and the perpendicular components of the diff usion tensor and the diffusing-wave spectroscopy temporal decay rate. We derive theoretically the correlation diffusion equations. We then c alculate the diffusing-wave spectroscopy temporal decay rate, and we p rovide explicit approximate, yet accurate, expressions for the compone nts of the light diffusion tensor, which we evaluate numerically as a function of material parameters of nematics. Using the actual scatteri ng cross sections for a nematic, we simulate photon transport and veri fy that it is described at long times by an anisotropic diffusion equa tion with diffusion coefficients in excellent agreement with both thos e obtained experimentally and those obtained from our analytical expre ssions. (C) 1997 Optical Society of America.