Experimental protocol for single-shot irradiation studies on optical materials at the SXFEL facility

Abstract

Ultra-intense and ultra-short x-ray free-electron lasers (XFELs) impose rigorous requirements on the damage resistance of optical materials. The investigations of interactions between XFELs and optical materials are vital for both evaluating the durability of optical components applied in XFEL beamlines and elucidating the fundamental physics of light–matter interaction under extreme conditions. In this paper, we report an experimental protocol for single-shot irradiation studies on optical materials at the Shanghai Soft X-ray Free-Electron Laser (SXFEL) facility, including detailed descriptions of the XFEL beamline layout, experimental setup, incident angle calibration, pulse-energy measurement, focused FEL spot size characterization, and irradiation procedures. Following this experimental protocol, single-shot irradiation was performed on a Si wafer at the SXFEL under normal incidence. A damage threshold of 0.22 ± 0.06 J/cm2 was determined at a photon energy of 517 eV. It is in good agreement with the fluence calculated based on the melting dose of Si, confirming thermal ablation as the dominant damage mechanism.