Speckle analysis as a characterization tool for the focusing properties of diamond X-ray lenses

The availability of intense X-ray beams at megahertz repetition rate allows for new scattering and imaging experiments using the unique pulse train structure of the European X-ray Free-Electron Laser (EuXFEL). However, the resulting heat load can pose challenges for X-ray optics and potentially limit the efficiency. In this context, X-ray optics made of diamond emerge as a promising solution better suited for the extreme beam conditions at EuXFEL. In this article, we demonstrate a simple speckle analysis to determine the size of the focused beam in a caustic scan. The lenses are 1D planar diamond lenses and experiments were performed at the Materials Imaging and Dynamics (MID) station of EuXFEL. We find a minimum beam size of 630 nm and compare the speckle method with the more conventional method of wire scanning.