Deflectometric Measurements of Synchrotron-Optics for Postprocessing

The technological limits to the beam quality of modern synchrotron-radiation sources are set by the geometrical accuracy of the optical components. The fabrication of these components is limited by the measuring technique. The exactly measured topography of the surface under test (SUT) allows postprocessing (e.g. ion beam etching). For form components of the SUT this is possible between its whole length and some millimeters. Present measurement technologies such as long-trace profilers, reach slope uncertainties down to 50 milli-arcsec rms. Their height uncertainty corresponds to several tens of nanometers for a synchrotron mirror 1 m in length. The parabolic and long-wave contributions of form in particular might differ due to systematic errors of the slope measurement. In the context of a cooperative research project initiated by BESSY, two profilers have been set up at the PTB - one for the absolute definition of flatness, the second presented here is faster and more robust. They operate with commercial autocollimators implementing the ESAD method. Only angle differences are used to reconstruct the topography of the SUT. This completely rejects common errors of angle measurement as guide errors and whole body movements of the SUT. This deflectometric method works without a lateral straightness reference and is capable of measuring free-form surfaces. We show results with a slope reproducibility of up to some milli-arcsec and a length of up to 88 cm