Characterization and calibration of 2nd generation slope measuring profiler

High spectral resolution and nanometer sized foci of 3rd generation SR beamlines can only be achieved by means of ultra precise optical elements. The improved brilliance and the coherence of free electron lasers (FEL) even push the accuracy limits and make the development of a new generation of ultra precise reflective optical elements mandatory. Typical elements are wave front preserving plane mirrors (lengths of up to 1 m, residual slope errors ∼0.05 μrad (rms) and values of 0.1 nm (rms) for the micro-roughness) and curved optical elements like spheres, toroids or elliptical cylinder (residual slope error ∼0.25 μrad (rms) and better). These challenging specifications and the ongoing progress in finishing technology need to be matched by improved accuracy metrology instruments. We will discuss the results of recent developments in the field of metrology made in the BESSY-II-optics laboratory (BOL) at the Helmholtz Zentrum Berlin (HZB), by the use of vertical angle comparator (VAC) in use to calibrate the nanometer optical component measuring machine (NOM). The BESSY-NOM represents an ultra accurate type of slope measuring instruments characterized by an accuracy of 0.05 μrad (rms) for plane substrates and 0.2 μrad (rms) for significant curved surfaces.