Abstract

The absolute determination of the shape errors of an optical flat is a classic problem in the interferometric measuring technique. The use of the surface of a liquid as a flatness reference is only practicable in exceptional cases /1/. Various authors have therefore proposed further solutions /2,3,4/ in which, however, the error curve is either only obtained along a section (with the traditional three-flat method) or in terms of a polynomial approximation, e.g. by Zernike polynomials. In the measurements of high spatial resolution made possible by electronic phase shifting interferometry, preference should be given to a local interpolation method over the global polynomial interpolation in order to ensure that the original information density of the raw data is also retained in the subsequent evaluation.

© 1986 Optical Society of America