Using noise speckle pattern for the measurements of director reorientational relaxation time and diffusion length of aligned liquid crystals

A purely optical approach using noise as a perturbation source and speckle analysis is used to measure the diffusion length and the director reorientational relaxation time of an aligned nematic liquid crystal. This method gives a direct measure of the intrinsic director relaxation time without any voltage or optical driving nor nonlinear effects contrarily to previous approaches. The obtained values of the diffusion length and relaxation time are in excellent agreement with those calculated from the liquid crystal elastic and rotational viscosity constants.