Measurement techniques to improve the accuracy of x-ray mirror metrology using stitching Shack–Hartmann wavefront sensors

We describe the development of specific measurement protocols to improve the accuracy of surface metrology of x-ray mirrors using a dedicated commercial instrument based on wavefront sensing techniques. This instrument, SHARPeR, uses measurements from a Shack–Hartmann wavefront sensor combined with a sub-aperture stitching method to provide two-dimensional maps of the surface slope errors and can measure curved mirrors above 1 m radii. In this paper, we describe the results of measurement methods developed on a SHARPeR system installed at the European Synchrotron (ESRF) to reduce the contribution of systematic errors to measurements of strongly curved spherical and aspherical x-ray mirrors with intrinsic slope errors of the order of 100–200 nrad rms. We demonstrate how this commercial integrated instrument can provide measurements of these mirrors with comparable accuracy to those measured with a long trace profiler.