(a) The twin focusing system comprising two sets of vertically and horizontally focusing mirrors (VFM and HFM) made of Si crystal blocks with the indicated dimensions (in mm). Half of each mirror surface is coated with Ru/Pt bilayers (colored in green) for enhanced reflectivity of high-energy X-rays; the other half remains bare Si surface (yellow). (b) Calculated X-ray reflectivity of the bare Si surface and Pt/Ru-coated surfaces of the focusing mirrors. (c) Simulated beam size and divergence (FWHM) over the whole beam path. (d) Measured evolution of the beam size from the sample position to the beam focus, using a 10 keV DCM beam and the Eiger X 9M detector. The beam size 280 µm (H) × 50 µm (V) extrapolated (solid line) to the focus position is consistent with the simulated one shown in (c). Note that the beam size at the 52 m focus could not be measured due to a length limit (14 m) of the data transmission cables of the Eiger X 9M detector in vacuum.