Ideally, this would require diffraction-limited X-ray optics with high numerical aperture (NA) that are at the same time stable in the intense XFEL pulses 1. Creating small and intense X-ray beams is crucial to confine the beam and concentrate the radiation onto the sample. Modern synchrotron radiation sources and X-ray free-electron lasers (XFELs) provide highly brilliant X-ray beams that allow studying the structure and dynamics of matter from atomic distances and a few femtoseconds to macroscopic dimensions and seconds.
