Phase refractive index measurement of thick glass plates with a spectrally resolved interferometer

Measurements of phase refractive indexes of thick objects by using fitting method have been reported in many papers, but the fitting method produces errors in the fitted coefficients of a fitting function. In this paper it is made clear that the thickness of object, for which the phase refractive index can be measured exactly, is limited by the errors. Phase refractive indexes of three kinds of glass plates of 1 mm thickness are measured directly from spectral phases detected with a spectrally resolved interferometer. Instead of using the fitting method, the 27t phase ambiguity contained in a detected spectral phase is determined by using an assumption that an actual refractive index measured in experiment is almost the same as well-known data of the refractive index. The actual refractive indexes measured with an error less than 8 x 10-5 are slightly different from the well-known data about the slope and the constant value in the distributions.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement