Characterization of coherent X-ray beam using Young’s double-slit experiment at PAL-XFEL

With the increasing brilliance of fourth-generation light sources, the enhanced coherence of X-rays has spasrked growing interest in coherent X-ray experiments. To ensure the reliability of such experiments, it is essential to characterize the coherence under actual experimental conditions. In this study, we measured and analyzed the spatial coherence and beam-pointing variation of femtosecond X-ray pulses generated by the Pohang Accelerator Laboratory X-ray free-electron laser (PAL-XFEL). We provide a detailed description of the measurement procedures and beam characterization techniques employed. The results offer practical guidelines for designing and conducting coherent X-ray experiments at fourth-generation light sources.