<title>Optical glass refractometry using holographic interferometry</title>

Abstract

The refractive index of optical glass is typically measured using techniques based on the change of the direction light experiences after traveling through the sample; that is, using deflectoruetric methods such as: minimum deviation goniometry, critical angle procedures, moire deflectometry, etc. , (Ref.l) . On the other hand, interferometry has been used to evaluate the optical homogeneity of optical glass, as well as to determine the refractive index variation with temperature. In this work it is presented a method to measure the refractive index of optical glass samples using a holographic interferometer. This is an indirect technique in which the refractive index of the glass samples is measured by comparison with the refractive index of a reference liquid in which the sample is immersed. The presence of the reference fluid is used as well, to get higher values for the flatness tolerance on the working faces of the sample, and less precision in the measurement of the wedge angle. The values of the useful wedge angles depend on the fringe spacing value and the ruatching between the refractive index of the immersion fluid and the refractive index of the glass sample. The necessity of iaeasuring along a raininuirn distance given by the detector spacing and the accuracy needed for the measurement of fringe spacing, is discussed.