Spectral variation of the birefringence, group birefringence and retardance of a gypsum plate measured using the interference of polarized light

Polarized white light interferometry is used to characterize the wavelength dependence of the birefringence, group birefringence and retardance of a gypsum crystal. Two different calculation schemes are used to extract values of the birefringence across the whole visible spectrum. In the spectral range 435 nm–642 nm, the variation of the gypsum birefringence is fitted to the two terms Cauchy formula and to a fourth order dispersion function. The gypsum birefringence is found to be inversely proportional with wavelength. The experimental method used gives a relative error in finding the gypsum birefringence of an order of 6×10−4. The wavelength dependence of gypsum group birefringence is also calculated with a relative error of order 5×10−4. In the same spectral range, the retardance changes by 28π and the gypsum plate introduced halfwave retardance 15 times.