Variable effective thickness of beamsplitter cube and dispersion error in white-light spectral interferometry

Abstract

A white-light spectral interferometric technique employing a Michelson interferometer with same metallic mirrors is used to measure the effective thickness of a beamsplitter cube. The thickness is measured for four different beamsplitters being in two different orientations. Moreover, it is revealed that the phase function of a thin-film structure measured by a similar interferometric technique depends on the path length difference adjusted in the Michelson interferometer. This phenomenon is due to a dispersion error of a beamsplitter cube, the effective thickness of which varies with the adjusted path length difference. A technique for eliminating the effect in measurement of the phase function is described. First, the effective thickness of the beamsplitter cube as a function of the path length difference is measured. Second, the phase function of the thin-film structure is measured for the same path length differences as those adjusted in the first case. In both cases, the phase is retrieved from the recorded spectral interferograms by using a windowed Fourier transform applied in the wavelength domain.