An interferometric technique based on Fourier fringe analysis for measuring the thermo-optic coefficients of transparent materials

We describe an interferometric technique based on temperature-dependent optical path length changes in a thin slab of transparent materials, suitable for measuring the thermal coefficient of refractive index. This technique allows an accurate determination of the fringe shift corresponding to a change in the sample temperature, by means of a two fringe pattern Fourier-transform-based processing algorithm for phase retrieval. The principle of measurement of the method and its applications to the measurements of the thermo-optic coefficients of some commercial glasses are presented and discussed.