高功率固体激光装置的负载问题是制约装置建设与运行的瓶颈问题。在高通量紫外纳秒激光辐照下，熔石英后表面的损伤不断产生和增长，严重限制了装置的负载能力。在提升熔石英抗损伤性能的基础上修复既有损伤，循环使用光学元件，是现阶段提升装置负载能力的主要手段。主要介绍了国内外近年来在熔石英损伤的规律与机制、光学元件循环处理的支撑技术以及提升负载能力的新材料与新技术方面所取得的重要进展。

In this work, a confined-doped fiber with the core/inner-cladding diameter of 40/250 μm and a relative doping ratio of 0.75 is fabricated through a modified chemical vapor deposition method combined with the chelate gas deposition technique, and subsequently applied in a tandem-pumped fiber amplifier for high-power operation and transverse mode instability (TMI) mitigation. Notably, the impacts of the seed laser power and mode purity are preliminarily investigated through comparative experiments. It is found that the TMI threshold could be significantly affected by the seed laser mode purity. The possible mechanism behind this phenomenon is proposed and revealed through comprehensive comparative experiments and theoretical analysis. Finally, a maximum output power of 7.49 kW is obtained with the beam quality factor of approximately 1.83, which is the highest output power ever reported in a forward tandem-pumped confined-doped fiber amplifier. This work could provide a good reference and practical solution to improve the TMI threshold and realize high-power high-brightness fiber lasers.

针对现有小尺寸集群损伤修复及检测技术仍不完善的问题，重点研究亚表面缺陷多模态原位检测方法，从损伤样件表面损伤数量和尺寸、典型小尺寸损伤的形貌、光热吸收、荧光面积等多项指标进行了系统测量和分析，并开展了磁流变修复研究。研究结果表明：熔石英小尺寸损伤内部的吸收性杂质是影响元件性能的主要因素，在磁流变缎带接触到损伤底部前，损伤的整体吸收和荧光分布呈上升趋势；高重频激光对磁流变修复后的损伤辐照过程是一个由慢变快、由杂质到本体、由边缘逐渐向外扩张的过程，能够有效对磁流变修复后的表面进一步起到修复作用，可作为组合修复工艺的第三道工序。研究结果对光学元件检测表征体系的构建提供参考。

To determine whether a potassium dihydrogen phosphate (KDP) surface mitigated by micro-milling would potentially threaten downstream optics, we calculated the light-field modulation based on angular spectrum diffraction theory, and performed a laser damage test on downstream fused silica. The results showed that the downstream light intensification caused by a Gaussian mitigation pit of 800 μm width and 10 μm depth reached a peak value near the KDP rear surface, decreased sharply afterward, and eventually kept stable with the increase in downstream distance. The solved peak value of light intensification exceeded 6 in a range 8–19 mm downstream from the KDP rear surface, which is the most dangerous for downstream optics. Laser damage sites were then induced on the fused silica surface in subsequent laser damage tests. When the distance downstream was greater than 44 mm with a downstream light intensification of less than 3, there were no potential damage threats to downstream optics. The study proves that a mitigated KDP surface can cause laser damage to downstream optical components, to which attention should be paid in an actual application. Through this work, we find that the current manufacturing process and the mitigation index still need to be improved. The research methods and calculation models are also of great reference significance for related studies like optics mitigation and laser damage.