Phase conjugate Fizeau interferometer: testing of laser beam collimation, spherical surfaces, and determination of refractive index

Abstract

An improved technique of collimation testing using a phase conjugate interferometer with a self-pumping BaTiO3 crystal is presented. The degree of collimation is better than existing techniques. A Fabry-Perot etalon is introduced between the focus and collimating lens of the phase conjugate interferometer to measure its refractive index. Noncollimation of the beam is indicated by the appearance of circular fringes. The collimation is again obtained by displacing the lens in such a way that the straight fringes are obtained in the field of view. By measuring the displacement of the lens, the refractive index of the F.P. etalon is calculated from a simple relation with an accuracy of 0.0001. This is a nondestructive technique specially useful for measuring the refractive indices of Fabry- Perot etalons without damaging their dielectric multilayer coatings. This technique is also useful for determining the refractive index of liquids.