<title>Refractive index evaluation using reflectometry: accuracy analysis</title>

Abstract

Modern optical design requires measurement of the refractive index of optical glass to the sixth or the seventh decimal place. Reflectometry represents an interesting option to go beyond the fifth decimal place, since from the literature we know that this technique can work to the fifth decimal place. In addition to that, this method does not use a large area of the sample, a condition that helps to increase the contribution of systematic errors. The techniques used to determine the refractive index of optical materials include transmission and reflection methods. The highest accuracy transmission techniques used in refractometry are: minimum deviation and critical angle goniometry, moire deflectometry, and interferometry. The main systematic errors that limit the measuring accuracy of each of these techniques are mentioned. The techniques used for the determination of the refractive index of optical materials from measurements of the ratio of the reflectance coefficients of its surface are widely used. Many of these methods rest on simplifications of Fresnel equations at specific angles of incidence. The geometries used include: normal incidence, 45 degree(s), Brewster angle, and other angular positions related with the specific sample to be evaluated. The analyses reported in the literature contain just the parameters present in the simplified formulas obtained for the Fresnel coefficients of each specific configuration. In this work a more complete analysis of these techniques is presented.