Abstract: A method for measuring the refractive index of a material with Bragg gratings includes the emission of a collimated radiation beam (9) from a radiation source (4) with a large spectrum and orientation thereof along a direction normal to the material (2) to be examined, the propagation of the collimated radiation beam (9) entering the material (2), then a Bragg diffraction grating (3) that is obliquely placed to the direction of the collimated radiation beam (9), and again the material (2), the subjection to spectral analysis of the collimated radiation beam exiting the material (2), the grating (3) producing a minimum in the spectrum subjected to the spectral analysis in accordance with Bragg's law, and the calculation of the refractive index of the material (2) from the measure of the wavelength corresponding to the minimum in thus spectrum. A relevant apparatus is described.

Abstract: A method for measuring the refractive index of a material with Bragg gratings includes the emission of a collimated radiation beam (9) from a radiation source (4) with a large spectrum and orientation thereof along a direction normal to the material (2) to be examined, the propagation of the collimated radiation beam (9) entering the material (2), then a Bragg diffraction grating (3) that is obliquely placed to the direction of the collimated radiation beam (9), and again the material (2), the subjection to spectral analysis of the collimated radiation beam exiting the material (2), the grating (3) producing a minimum in the spectrum subjected to the spectral analysis in accordance with Bragg's law, and the calculation of the refractive index of the material (2) from the measure of the wavelength corresponding to the minimum in thus spectrum. A relevant apparatus is described.

Abstract: A liquid crystal device for continuous rotation of the selective polarization of monochromatic light is provided by a cholesteric mixture with positive dielectric anisotrophy contained between a pair of glass plates which are conductive on the surface in contact with the mixture and have received a surface treatment to provide planar orientation for the mixture. A voltage is applied between the two glass plates and an input light polarizer is applied to one of the two glass plates. The device preferably uses a cholesteric mixture comprising cholesteryl chloride (31.2%), cholesteryl oleyl carbonate (47.7%) and cholesteryl nonanoate (21.1%) and is advantageously employed in laboratory polarization rotators and colored display units.