Automated interferometric technique for express analysis of the refractive indices in isotropic and anisotropic optical materials

This paper deals with the technique for the refractive index measurements based on the interferometry of a rotated parallel plate (IRPP). The device consists of the Michelson interferometer, the sample rotation system and the optoelectronic registration system. A refractive index of parallel plates is determined by their rotation through measuring simultaneously a shift of interference fringes. Although the IRPP technique is known from long ago [Shumate MS. Appl Opt 1966;5:327] several considerable improvements have been done in order to improve the accuracy of the method. The measuring process is completely automated. The method has been tested on the model crystals of the lithium niobate giving the magnitudes for ordinary and extraordinary refractive indices as n₀=2.2865±0.0007 and n_e=2.2034±0.0007. A considerable increase of accuracy is reached in our case by an automation of the measuring procedure, development of a new software as well as implementing the interferometric method for a precise determination of a sample zero position. The automated refractometer is offered for use in research laboratories and industry.