Many optical applications requires often totally polarized light. However there are an other applications, such as optical spectrum analyzer, in which incident polarized light is undesirable. Insertion of depolarizer in such devices may stabilize the optical signal of the measured light, in order to reduce offsets in measurements. Liquid crystal are functional materials possessing anisotropies originating from their inner molecular alignment. A vertically aligned nematic liquid crystal with zero pretilts in the off state is isotropic for light impinging at normal incidence. However, the liquid crystal orientation upon electric switching is undefined; therefore the cell usually generates disordered birefringent medium related to undefined switching direction of molecules which produce random polarization of the transmitted light by liquid crystal cell, therefore depolarization effect is produced. In this work, the treatment of problems involving depolarization of incident polarized light beam passing through a depolarizing medium and general physical phenomena associated with it, will be investigated at the speckle scale. A suitable tool for this treatment will be real time Young’s interferometer constructed with a new principle including the possibility to control the fringe pattern in real time with objective to study the dynamics of speckle fluctuation. Modulation of depolarization control with an applied voltage are reported, also.
Low viscosity high birefringence nematic liquid crystalline compounds and mixtures are described. They belong to the families of 4'-alkyl-3-fluoro-4-isothiocyanatobiphenyls, 4"-alkyl-3,5-difluoro-4-isothiocyanatoterphenyls, 4'-alkyl-3-fluoro-4-isothiocyanatotolanes and 4'-(4-alkylphenyl)-3,5-difluoro-4-isothiocyanatotolanes.
Several linearly conjugated isothiocyanato (NCS) tolanes, biphenyl-tolanes and bistolanes were synthesized and their properties evaluated. Eutectic mixtures compromising these compounds were formulated. The temperature dependent birefringence, visco-elastic coefficient and figure-of-merit were measured. These isothiocyanato tolane mixtures exhibit a favorably high figure of merit at elevated temperatures. Potential applications of these mixtures for laser beam steering, tunable-focus lens and telecom variable optical attenuator are emphasized.
We report the synthesis procedures, phase transition temperatures, optical and dielectric properties of the fluoro and chloro -- substituted two rings and three rings isothiocyanatotolanes. Three eutectic mixtures comprising of these isothiocyanatotolane compounds showing a wide nematic range, low viscosity and high birefringence (~0.4) are formulated.
The synthesis, mesomorphic properties and visible spectra of 4'-substituted alkyl-, alkoxy-, alkylcyclohexyl and alkylcyclohexylethy1-4-isothiocyanatotolanes have been described. Multicomponent mixtures with birefringence higher than 0.4 and low viscosity have been formulated.