Method and apparatus for detecting and measuring the refractive index of an optical disc substrate

摘要

A light beam linearly polarized is incident on a substrate for a disc not a right angle, but at an an oblique angle with respect to the substrate surface, while holding constant an angle kappa between the plane of polarization of the linearly polarized light and the incident plane, and the intensity of the leaked light passing through an analyzer set in a crossed Nichol state with respect to the linearly polarized light is measured while changing an angle (azimuth angle PSI ) between the incident plane and a reference line, such as a line extending in the radial direction of the disc substrate. These measured values are compared with the calculated values derived from the theoretical formula for determining the respective magnitudes of the three refractive indices.