In the past grazing incidence interferometry has been applied for plane, cylindrical, acylindrical and general rod-like surfaces using diffractive beam splitters. Here, we demonstrate that also rough convex steep rotational symmetric aspherics can be measured along one meridian in a single step using diffractive beam splitters and phase shifting techniques. Especially, rough surfaces can be measured with this method due to the large effective wavelength (here about 10μm) of the test. The extension to the whole surface can be attained by successive meridional measurements of the surface under test by azimuthal adjustments. The principle of the method is given, first simulated and experimental results are presented. The occurrence of the interferogram is discussed and the experimental evaluation on a single meridian including the unwrapped phase are shown. Furthermore the simulated results of aberrations caused by object misalignment and the first results for the elimination of adjustment aberrations are presented.
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