A new autocollimation method for refractive index measurements

Abstract We present a new autocollimation method for measuring the refractive index (RI) of transparent triangular prisms. The classical autocollimation method is simple, but due to total internal reflection it is suitable only for prisms with small angles, which limits the accuracy of RI measurements. The proposed new method makes possible the autocollimation measurements of the RI for prisms with large angles designed to implement the minimum deviation method. A comparative accuracy analysis of the proposed and classical goniometric methods of RI measurements is carried out. A reference prisms set made of Schott optical glass was studied and the measurement errors were estimated. The calculated absolute error does not exceed ±1·10-5, which proves the prospect of using the presented method for high-precision RI measurements. The autocollimation method can be used for RI measurements and to study the dispersion characteristics of triangular prisms made of optically transparent materials and liquid optically transparent substances filling a hollow triangular prism.