A high-power CW Yb:YAG slab laser amplifier with no adaptive optics correction has been experimentally established. At room temperature, the amplifier emits a power of 22 kW with an average beam quality (β) of less than 3 in 0.5 min. To our knowledge, this is the brightest slab laser without closed-loop adaptive optics demonstrated to date. In addition, an extracted power of 17 kW with an optical extraction efficiency of 33%, corresponding to a residual optical path difference of less than 0.5 µm, is achieved with the single Yb:YAG slab gain module. The slab gain module has the potential to be scalable to higher powers while maintaining good beam quality. This makes a high-power solid-state laser system simpler and more robust.

Optical bound states in the continuum (BICs) have recently stimulated a research boom, accompanied by demonstrations of abundant exotic phenomena and applications. With ultrahigh quality (Q) factors, optical BICs have powerful abilities to trap light in optical structures from the continuum of propagation waves in free space. Besides the high Q factors enabled by the confined properties, many hidden topological characteristics were discovered in optical BICs. Especially in periodic structures with well-defined wave vectors, optical BICs were discovered to carry topological charges in momentum space, underlying many unique physical properties. Both high Q factors and topological vortex configurations in momentum space enabled by BICs bring new degrees of freedom to modulate light. BICs have enabled many novel discoveries in light–matter interactions and spin–orbit interactions of light, and BIC applications in lasing and sensing have also been well explored with many advantages. In this paper, we review recent developments of optical BICs in periodic structures, including the physical mechanisms of BICs, explored effects enabled by BICs, and applications of BICs. In the outlook part, we provide a perspective on future developments for BICs.

高功率固体激光在先进制造、能源、信息、医疗及**等领域有广泛应用。激光陶瓷材料具有掺杂浓度均匀可控、抗激光热损伤能力强、易于制备大尺寸和复合结构等优点，被认为是高功率固体激光的重要增益材料。报道了本课题组近年来在高功率陶瓷板条激光方面的主要研究进展。采用中国科学院上海硅酸盐所制备的大尺寸Nd:YAG陶瓷板条，实现了平均功率4.35 kW的1064 nm脉冲激光输出，脉冲宽度为160 μs，重复频率为400 Hz。此外，采用中科院上海硅酸盐所制备的大尺寸Yb:YAG陶瓷板条，实现了平均功率9.8 kW的1030 nm脉冲激光输出，脉冲宽度为560 μs，重复频率为160 Hz，光光转换效率为60%。这些研究表明，激光陶瓷材料具备实现高功率、高光束质量与高效率激光的潜力。

亚纳秒激光因其对光电器件的损伤优于纳秒激光和飞秒激光，而被广泛应用于光电对抗领域。然而，在常规水冷条件下实现输出数百赫兹焦耳级亚纳秒激光还面临较大的挑战。笔者课题组面向**重大需求，结合端面泵浦微片晶体百皮秒激光产生技术和多程多级板条激光放大技术，对板条激光器的放大性能进行大量的实验研究，并提出了温控双端泵浦技术，弥补双端泵浦结构的缺陷。实现板条激光器单脉冲能量952 mJ，重复频率500 Hz的激光输出，这将为光电对抗系统所需的高重频大能量激光提供优质光源。

400 mm口径片状放大器增益性能退化是国内外惯性约束聚变（ICF）激光装置长期运行所面临的主要问题之一，直接影响激光装置的输出能力与光束质量。对造成片状放大器增益退化的因素开展了分析，建立了各因素的归一化理论分析模型，并利用2组九片长的400 mm口径4×2组合式片状放大器系统开展了实验研究，无维护策略条件下经过10年、3 000发次运行后增益性能平均退化了10.2%，符合理论预期。以此制定了大口径片状放大器的维护策略，实现了系统长期的增益性能退化率优于1.5%，满足ICF激光装置长期运行要求。

An immersed liquid cooling slab laser is demonstrated with deionized water as the coolant and a Nd:YAG slab as the gain medium. Using waveguides, a highly uniform pump beam distribution is achieved, and the flow velocity distribution is also optimized in the channels of the gain module (GM). At various flow velocities, the convective heat transfer coefficient (CHTC) is obtained. Experimentally, a maximum output power of 434 W is obtained with an optical–optical efficiency of 27.1% and a slope efficiency of 36.6%. To the best of our knowledge, it is the highest output power of an immersed liquid cooling laser oscillator with a single Nd:YAG slab.

在氙灯放电泵浦过程中, 片状放大器片腔内材料在高强度氙灯光辐照下, 存在显著的热解过程, 产生大量的μm级悬浮粒子。针对放大器在线洁净度控制，采取了包括选用有利于洁净控制的材料、消除盲孔与焊缝、深度酸洗刻蚀、高压喷淋清洗和最终的光照清洗等系列有效措施。实验研究结果表明：经过100发次光照清洗，片腔内气溶胶颗粒处于300～1000之间，接近美国国家点火装置(NIF)洁净水平；发次运行完成后，利用约0.4 m/s的氮氧混合气体对放大器腔体进行吹扫，气溶胶颗粒在2 min内可恢复至0值。