High-power ultrafast laser amplification based on a non-polarization maintaining fiber chirped pulse amplifier is demonstrated. The active polarization control technology based on the root-mean-square propagation (RMS-prop) algorithm is employed to guarantee a linearly polarized output from the system. A maximum output power of 402.3 W at a repetition rate of 80 MHz is realized with a polarization extinction ratio (PER) of > 11.4 dB. In addition, the reliable operation of the system is verified by examining the stability and noise properties of the amplified laser. The M² factor of the laser beam at the highest output power is measured to be less than 1.15, indicating a diffraction-limited beam quality. Finally, the amplified laser pulse is temporally compressed to 755 fs with a highest average power of 273.8 W. This is the first time, to the best of our knowledge, that the active polarization control technology was introduced into the high-power ultrafast fiber amplifier.

基于产生3 μm中红外激光的Er³⁺能量转换过程与能级体系，建立了掺铒氟化物光纤激光器的速率方程和传输方程，系统地研究了泵浦结构和光纤长度对输出功率、斜率效率以及腔内泵浦和激光功率分布的影响，为后续的实验提供理论依据。仿真确定了小泵浦功率的光纤激光器理想的光纤长度为4~8 m，最终实验选择4.7 m光纤完成了中红外掺铒氟化物光纤激光器连续激光输出光路的搭建， 在泵浦功率为5 W、中心波长为2.797 μm处实现了最大功率1.038 W、斜率效率20.4％的连续激光输出。

基于多纵模振荡种子源的窄线宽光纤激光器具有光路简单、结构紧凑、可靠性高、成本低等特点，在实际工程应用以及在空间受限的载荷平台上有着显著优势，是高功率光谱合成的理想子束模块。受自脉冲效应的影响，多纵模振荡种子源的时域特性较差，导致放大过程中会产生较强的光谱展宽与受激拉曼散射效应。这限制了其输出功率的进一步提升并降低了其光谱纯度。本文首先介绍了4种常见的窄线宽种子源，并重点分析了多纵模振荡种子源中自脉冲效应产生的机理及抑制方法，对优化多纵模振荡种子源和放大器的关键技术进行了详细介绍，归纳总结了近几年的技术突破与研究成果，对未来的发展方向进行了展望分析。本文研究对基于多纵模振荡种子源的窄线宽激光器的功率提升和光谱优化提供一定思路。

We report a high-stability ultrafast ultraviolet (UV) laser source at 352 nm by exploring an all-fiber, all-polarization-maintaining (all-PM), Yb-doped femtosecond fiber laser at 1060 nm. The output power, pulse width, and optical spectrum width of the fiber laser are 6 W, 244 fs, and 17.5 nm, respectively. The UV ultrashort pulses at a repetition rate of 28.9 MHz are generated by leveraging single-pass second-harmonic generation in a 1.3-mm-long BiB₃O₆ (BIBO) and sum frequency generation in a 5.1-mm-long BIBO. The maximum UV output power is 596 mW. The root mean square error of the output power of UV pulses is 0.54%. This laser, with promising stability, is expected to be a nice source for frontier applications in the UV wavelength window.

锥形光纤能够有效兼顾非线性效应抑制和模式控制，具备实现高功率、高光束质量光纤激光的潜力。近期国防科技大学研制了锥形掺镱光纤，采用1018 nm光纤激光后向级联泵浦实现了20.2 kW 激光输出，光束质量β因子平均值优于2，拉曼抑制比为33 dB。研究结果展示了锥形光纤在实现万瓦级高光束质量激光方面的优势。

A whispering gallery mode resonator (WGMR) filter can narrow laser linewidth while significantly changing the output power characteristics of fiber laser system. It is found that traditional laser output power model is invalid. We report a correction model of a narrow linewidth fiber laser filtered with a WGMR to analyze its power. We believe that the loss of the laser system and the threshold gain increase caused by the WGMR filter lead to the predominate amplified spontaneous emission during the original laser period. According to that, we assume the correction coefficient is an exponential decay related to the Er-doped fiber length in the large loss situation, and we verify it experimentally. As a result, the correction model is valid for WGMR-filtered fiber laser.

搭建了基于半导体可饱和吸收镜（SESAM）锁模的全保偏皮秒脉冲光纤激光器，对比分析了以多量子阱和体材料作为可饱和吸收层的SESAM对锁模激光器输出特性的影响。实验结果表明，多量子阱和体材料SESAM均可实现稳定的自启动锁模。随着量子阱周期数的增加，SESAM调制深度增大，激光器输出脉冲宽度变窄，具有更高的输出功率和更大的锁模区间。但量子阱周期数过高的SESAM具有较大非饱和损耗，使得相同泵浦功率下输出功率降低。在相同调制深度下，体材料SESAM的非饱和损耗偏大，降低了输出功率和光光转化效率，但对脉冲的窄化作用更显著。SESAM对输出脉冲的波长和光谱宽度无显著影响，主要受光纤布拉格光栅（FBG）控制。本文对SESAM的设计与选型具有一定指导意义。