Measurement of curvature and thickness variations of plane surfaces by grazing incidence interferometry

In many production processes it is very important to control the parallelis m of two surfaces of technical objects. Here, a grazing incidence interfero meter is presented which allows to measure curvature and thickness variatio ns of wafer-like bodies. The set-up tests each surface at once and the two compared surfaces simultaneously. Two identical phase gratings work as beam splitters and recombiners. The incoming plane wave is the reference for th e tested object. The grating period of the gratings determines the sensitiv ity of the interferometer. The phase-shift-analysis yields the thickness va riations, the misalignment angles of the object in relation to the frame of the interferometer and a polynomial of 2(nd) order and higher describing t he curvature.