Joseph Borel

Liquid crystal diffraction grating

Application of an electric field to a thin layer of nematic liquid‐crystal causes the formation of a lattice of cylindrical lenses within the liquid‐crystal material. An expression for the far‐field diffraction pattern of light transmitted through this lattice is derived. The observed diffraction pattern agrees with that predicted by the theory.The device comprises at least one liquid-crystal cell placed on the path of the beam and constituted by a film of liquid crystals interposed between two walls provided with electrodes between which a potential difference can be applied by suitable means. The incidence of the light beam is oblique with respect to the first wall-liquid crystal interface which is encountered. Use is made of liquid crystals for which the direction of propagation of the light beam is dependent on the potential difference applied between the electrodes.

Relations Between Liquid Crystal Order Parameter and Macroscopic Physical Coefficients-Experimental Proof

Abstract In this paper, we relate how we have determined the order parameter by measuring the diamagnetic susceptibilities of th enematic phase, and of the ordered solid state obtained by freezing a nematic “monocrystal.” Moreover, we have measured dielectric and refractive indices anisotropics, and elastic coefficients; and we have verified the theories giving the relations between the order parameter and all this physical macroscopic coefficients.

Static and Transient Electric Field Effect on Homeotropic Thin Nematic Layers

Abstract The experiments presented in this paper give a way to the determination of two elastic constants K 11 and K 33 and one viscosity coefficient y 1 of a nematic liquid crystal. ac electric field stresses applied to a thin layer of nematic liquid crystal modify its cooperative molecular alignment. So, the electrically controlled rotation of molecules induces a variable birefringence as a function of applied voltage and time. The experimental results in relation with the static and dynamic behaviour lead to the determination of these previously static and dynamic behaviour lead to the determination of these previously stated parameters. Temperature dependence of these parameters is given in the nematic range.