13.5nm femtosecond laser damage behaviors of EUV multilayer mirrors

We present laser damage behaviors of a series of high reflectivity extreme ultraviolet (EUV) mirrors with radiation of 13.5 nm femtosecond laser pulses generated by Shanghai Soft X-ray Free-Electron Laser (SXFEL) facilities. Mo/Si multilayer mirrors with and without B4C barrier layer of different designs were prepared by magnetron sputtering. The reflectivity of the mirrors was tested in National Synchrotron Radiation Laboratory of China at Hefei. A FEL-EUV laser damage testing station were designed and established in SXFEL. The 10Hz pulse train was delivered and focused to target plane with about 400μm², and multi-shot damage behaviors of the witnesses were characterized. The damage morphologies were mapped comprehensively by several tools, including microscope, white light interferometer, SEM, TEM and Raman spectrum. The special bubble-like damage and compaction of multilayers were analyzed.