As an important characterization method for beamline optics, at-wavelength metrology technology based on wavefront measurements has been developed for many years. However, the previous studies on at-wavelength metrology of reflective mirrors is limited to the indirect method. So, the accurate surface information of the mirror under test would normally be inaccessible because of lack of experimental deconvolution between the mirror and any backgrounds from upstream optics. In this study, an absolute metrology method is developed based on the speckle scanning technique. Using this method, the surface profile of the mirror can be extracted exactly from the mixed information of the entire upstream beamline. At the same time, data acquisition time can also be significantly reduced by the processing algorithm introduced in this study without sacrificing the angular sensitivity.

A speckle-based method for the X-ray crystal diffraction wavefront measurement is implemented, and the slope errors of channel-cut crystals with different surface characteristics are measured. The method uses a speckle scanning technique generated by a scattering membrane translated using a piezo motor to infer the deflection of X-rays from the crystals. The method provides a high angular sensitivity of the channel-cut crystal slopes in both the tangential and sagittal directions. The experimental results show that the slope error of different cutting and etching processes ranges from 0.25 to 2.98 μrad. Furthermore, the results of wavefront deformation are brought into the beamline for simulation. This method opens up possibilities for new high-resolution applications for X-ray crystal diffraction wavefront measurement and provides feedback to crystal manufacturers to improve channel-cut fabrication.