X-Ray Grating Interferometry - Applications in Metrology and Wave Front Sensing

X-ray grating interferometry was first developed in context with x-ray phase contrast imaging. Here we focus on applications where 1- and 2-dimensional grating interferometers are used to measure the distortions of x-ray wave fronts with extreme sensitivity. This allows for the in-situ and at wavelength characterization on x-ray optics such as mirrors and refractive lenses. Angular sensitivities down to the 10 nrad range can be obtained. We point out some specific concerns when using the technique in context with metrology. A precise rotational alignment is essential for accurate, absolute measurements of the local wavefront radius of curvature. Moreover, in many cases no flat-field image can be recorded, therefore the gratings need to fulfill very stringent requirements with respect to distortions.