A free-electron laser (FEL) is a robust tool for studying the interaction of intense X-rays with matter. In this study, we investigate the damage threshold and morphology of fused silica irradiated by extreme ultraviolet femtosecond pulses of a FEL. The experimental results indicate the superiority of the FEL processing. The FEL-damage threshold of fused silica at a wavelength of 13.5 nm is 0.17 J/cm2, which is 20 times lower than that of a near infrared (NIR) femtosecond laser. The relationship between the crater depth and laser fluence reveals that the effective absorption length is αeff -1 = 58 nm. The damage threshold and the absorption length are the key values for smooth crater formation. In addition, the formation of rim structures and microcracks, which are usually the critical issues in NIR laser processing, cannot be found in the interaction region. The hole diameter is maintained below the beam size at the exit.
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