Sharp and rectified imaging of plane test objects in grazing incidence interferometers

Grazing incidence interferometry offers reduced sensitivity for the measurement of the macro-geometry of ground surfaces but suffers from unsharp imaging of the surface under test onto the detector and from undersampling along one diameter due to the anamorphic distortion caused by the grazing incidence of the probing wave field. The test of surfaces with diameters exceeding 6” is an additional challenge which makes designs necessary that require a minimum number of big-sized optical elements (lenses, gratings, prisms). Optical elements having dimensions greater than 150mm are difficult to produce and extremely expensive. Furthermore, the simultaneous test of both sides of thin wafers enables the determination of typical parameters as “bow”, “warp”, and “TTV (Total Thickness Variation)”. Solutions answering these challenges will be discussed at the example of diffractive grazing incidence interferometers.