Variable wavelength interferometry of birefringent retarders

A new interferometric procedure is proposed for testing birefringent retarders. The procedure uses monochromatic light with a continuously variable wavelength and two parallel pointer lines localized at a distance from each other in the fringe interference field of a double-refracting interferometer. The zero-order fringe of the empty interference field is brought into coincidence with one pointer line, and higher-order interference fringes displaced by an object under study are next brought into consecutive coincidence with the other pointer line as the wavelength of the monochromatic light is continuously varied.