The holographic investigation of diffusion of azo-dye in liquid crystals host

The diffusion of azo-dye (DR-1) in a planar liquid crystals host (5CB) at various temperatures has been investigated by laser-induced holographic grating relaxation technique. The decay of the diffraction intensity provides information about the diffusion of photoexcited azo-dye molecules. The relaxation time constants can be derived from the time dependence of the diffraction intensity fitted by a single exponential function. Thus, the diffusion coefficients parallel and perpendicular to the director of liquid crystals at various temperatures can be obtained from the plots of the reciprocal of the relaxation time versus the square of the grating vector. From the analysis of the holographic grating relaxation, the diffusion is faster along the molecular director than for the perpendicular case, and the diffusion increases with rising temperature either parallel or perpendicular to the nematic director of liquid crystals.