Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals

Light diffusion and temporal correlation transport are studied in an orientationally ordered multiply scattering medium. In particular, we experimentally demonstrate the anisotropic diffusion of light through a turbid nematic liquid crystal, and we measure the temporal correlations of these diffused speckle fields for the first time. The measurements are shown to provide useful information about this material, specifically the average rotational viscosity of the director. Computer simulations corroborate both the experimental observations and a more rigorous analytic theoretical formulation of this problem. (S0031-9007(96)01117-9) tocorrelation functions of the emerging speckle in several geometries, and showing that these measurements pro- vide useful information about material properties. Finally, computer simulations of light transport through nematic liquid crystals corroborate experimental observations as well as a more rigorous theoretical formulation (9) of this problem. In total, the work elucidates the importance of anisotropy for imaging and spectroscopic studies that em- ploy diffusing light probes. The dynamical results, for example, differ in an interesting way from previous DWS work in colloids, foams, and emulsions, because the same motional processes that give rise to material dynamics in nematic liquid crystal are also responsible for light scat- tering. Finally, these measurements may be useful for the investigation of hydrodynamics (10) on short time scales where single light scattering studies are ineffectual. The scattering and dynamics in nematic liquid crystals are caused by orientational fluctuations of the director n. The differential cross section for single light scattering depends on the amplitude of the director fluctuations dnsr, td, which are perpendicular to their average value n0. The differential cross section for a nematic liquid crystal with volume V is (7) ds dV › V