All-optical measurement, based on director axis fluctuations, of the three elastic constants K 11 , K 22 , and K 33 of nematic liquid crystals and of the spatial and temporal relaxation constants of the director

We developed an all-optical technique for the precise measurement at the same time of the three elastic constants K11, K22 and K33 of nematic liquid crystals. The measurements were performed with a unique wall alignment (homeotropic) under the same environmental conditions. The method is based on the analysis of the optical speckle pattern induced by the director axis fluctuations observed for the optical beam that passes through the liquid crystal sample. Analysis of the output optical speckle pattern provides the values of the relaxation time and spatial diffusion lengths of the director, from which the elastic constants K11, K22 and K33 are calculated. The results are given with confidence intervals, which are rarely the case. The validity of the method was demonstrated for the E7 nematic and showed very good agreement with the values found in the literature.