Liquid Crystals Refractive Indices Behavior Versus Wavelength and Temperature

A new refractometer designed in our laboratory is described : it allows a 3d diagram - refractive index versus wavelength and temperature - to be experimentally obtained for any transparent material. It consists in analyzing a channelled spectrum observed in the focal plane of a spectroscope illuminated with a white light source and where the sample under study is properly inserted. The spectrum acquisition is made by means of a linear array of photosensors. The fast response time of such technology allows measurements under unstable or gently varying conditions. This opportunity has been used to measure the dispersion curve of both ordinary and extraordinary indices versus temperature for several nematic liquid crystals. Numerical processing of the data is also considered.