A simple technique is presented for estimating the thickness of a transparent plate. Using a laser source and detector, the transmitted light is measured as a function of angle of incidence. With prior knowledge of the refractive index of the plate at the laser wavelength, the observed fringes can be processed to estimate the plate thickness. The technique works with a modest degree of wedging, as long as fringes are discernible. Formal estimates of the error budget indicate the accuracy of this method is approximately 1 μm. If fringes are measured versus both angle and wavelength, it should be possible to estimate both thickness and refractive index.
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A 1995 study studied this question.