Fizeau interferometers for surfaces with different reflectivity

Intensities of the interferences of common Fizeau interferometers, in this example calculated for a reference surface with a reflectivity of 0.5 and test sample surfaces with varying reflectivity between 0 and 100% and a variation of the distance d between test sample and reference piece over a wavelength (λ = 633 nm). The new method avoids the strong dependence of the intensity profile and the contrast on the reflectivity of the test sample's surface. Credit: PTB