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

This study proposes a simple alternative purely linear optical approach based on noise scattering and speckle analysis to extract aligned liquid crystal diffusion length and director relaxation time. This method relies only on noise induced director fluctuations and does not use any voltage or optical driving nor nonlinear effects that can give optical response times in place of director relaxation time. In the experiments, a 50 μm thick layer of Merck E₇ homeotropically oriented LC has been irradiated by a 532 nm frequency doubled YVO₄ laser with a beam waist of 1.5 mm. Moreover, this method also gives access to liquid crystal splay/bend elastic constants. Practically the accuracy of the measurement depends on the calibration of the position of the imaging plane for the near-field and on the relevance of the model chosen for describing propagation inside the LC.