为了提高高功率激光装置光学元件的抗损伤能力，通过分析经历了上百发次高通量351 nm激光辐照的熔石英光学元件损伤的微观形貌，结合光束传输理论研究了大口径熔石英元件的紫外损伤机理。研究表明，目前加工工艺条件下引起紫外损伤的最主要原因是光学元件亚表面划痕，它能导致光学元件初始损伤阈值降低数倍甚至数十倍；损伤污染和衍射效应将导致损伤进一步加剧；小尺度自聚焦是处于终端组件后端40 mm厚度透镜体损伤的主要损伤机理，前期光学元件损伤形成的毫米和亚毫米衍射点引入的调制是导致小尺度自聚焦的根源，而输出光束的近场不均匀性导致局部光强过大，将大大增加光学元件损伤的风险。因此，改进光学元件表面加工质量，降低亚表面缺陷，对光学元件抗损伤能力的提高是非常必要的。

To improve the ultraviolet-damage threshold of the fused-quartz optics in the high-power laser facility, damage mechanism of the fused-quartz optics is investigated with the beam-transmission theory by analyzing the microscopic configuration of damage which was irradiated hundreds of times with a high-power 351 nm laser. The results show that the subsurface scratch is the mostly important factor that induces ultraviolet damage. It can lower initial damage threshold of fused-quartz optics by several times, even tens of times. The effect of beam diffraction accelerates the damage. Small-scale nonlinear self-focusing is the mostly important body damage mechanism of lens with 40 mm thickness at the end of the final optics. Modulation in the near field of the beam results in high intensity in local area and raises the risk of optics damage. Therefore, it is necessary to reform the processing technologies for the improvement of the damage threshold in the ultraviolet waveband.