White-light spectral interferometry to measure the effective thickness of optical elements of known dispersion

Abstract

A spectral-domain white-light interferometric technique of measuring the effective thickness of optical elements of known dispersion is presented when a Michelson interferometer with a cube beam splitter is not dispersion balanced and when the spectral interference fringes are resolved over a wide wavelength range. The technique uses processing one of the recorded spectral interferograms by an adequate method to retrieve the unwrapped phase function, the ambiguity of which is removed by a simple procedure based on linear dependence of the optical path difference between interferometer beams on the refractive index of optical elements. The effective thickness of optical elements is given by the slope of the linear dependence. The technique is used to measure the effective thickness of a cube beam splitter alone or combined with a thin plate made of BK7 glass.