Accuracy analysis of the refractive index measurements by modifed prism methods

Abstract

Goniometric methods of measuring the refractive index of optically transparent materials based on the refraction of light by a triangular prism are considered. Modified method of the minimum deviation and 3 modified constant deviation methods are considered, which allows determining the refractive index of triangular prisms with unknown apex angles. According to modified methods, the angles of light deviation by a prism are measured with goniometer, and the refractive index of the material and the prism angles are determined from solving the systems of equations. Thus, there is no need for preliminary measurement of the prism angles, which requires the use of special autocollimation goniometers. In addition, the modified methods do not use radiation reflected from the faces of the prism, which makes it possible to extend the spectral range of measurement of the refractive index to the infrared and ultraviolet regions. A comparative accuracy analysis of the considered methods for a prism with a refractive index of 1.5 and an angle of 60° as example is carried out. It is shown that the modified methods can be used for high-precision measurements of the refractive index in cases if the apex angles of the prism are unknown or their measurement is associated with technical difficulties. The considered methods can be used to measure the refractive index of triangular prisms made of optically transparent materials, as well as liquids poured into hollow prisms with plane-parallel transparent windows. The practical implementation of such a methods can be useful in the optical, chemical and food industries to control the composition and properties of optically transparent substances.