Multilayer Laue lenses for focusing XFEL beams

X-ray optical elements in X-ray Free Electron Laser (XFEL) applications experience high thermal loads. While reflective optics can spread the incident beam over a larger area to reduce heating, refractive and diffractive optics must mitigate this by minimizing X-ray absorption, which necessitates the use of low atomic number materials. To address this challenge, we evaluated various multilayer material pairs and identified Mo₂C/SiC as the optimal choice due to its superior diffraction efficiency and thermal stability. Here, we present the novel wedged multilayer Laue lenses (MLLs) which were successfully used to focus XFEL beams at the European XFEL. A lens pair fabricated from the same Mo₂C/SiC multilayer of 100 <i>&mu;</i>m deposited thickness was characterized before and after XFEL experiment using a laboratory-based X-ray setup. The MLLs maintained stable performance throughout a week-long XFEL beamtime, with no observed degradation in focusing performance or structural integrity. These results demonstrate the robustness and suitability of MLLs for high-intensity X-ray applications.