A simple interferometric technique was used for measuring the absolute
birefringence of an anisotropic material. The sample has constant thickness. It
was placed between crossed polarizers and illuminated with a parallel beam of
monochromatic light. The resulting interferograms were analyzed to deduce the
birefringence and its dispersion across the visible spectrum. A Cauchy formula
was applied to fit the experimental data. The same technique was used for a
variable thickness with constant rate (a wedge form) of the same sample.
Interference fringes was formed in the photographic plate. The value of the
birefrengence was also measured.