中文摘要：

模式不稳定效应会影响高功率激光输出的光束质量,成为高功率光纤激光器定标放大过程中获得近衍射极限光斑的主要限制因素。基于模式耦合理论建立描述模式不稳定现象的半解析模型。理论模型的计算结果表明与正向抽运结构相比,反向抽运和双向抽运结构具有更高的模式不稳定阈值。通过实验对理论结果进行验证,发现反向抽运光纤激光器的模式不稳定阈值至少比正向抽运结构高50%。实验中搭建反向抽运光纤激光器,实现了2kW窄线宽高光束质量激光输出。

英文摘要：

Mode instability has become the major limitation for power scaling of fiber lasers with nearly diffraction- limited beam quality. Based on mode coupling theory, we establish a semi-analytical model to simulate mode instability effect. Compared with co-pumped fiber laser, counter-pumped and bi-pumped fiber lasers reveal mode instability threshold enhancement in our theoretical model. Compared with that of the co-pumped scheme, the experimental mode instability threshold of the counter-pumped fiber laser is enhanced by at least 50G. Moreover, we demonstrate a kW high power narrow-linewidth counter-pumped fiber laser with high beam quality.