Ding Xinyi, Li Haobo, Zeng Lingfa, Wu Hanshuo, Zhang Hanwei, Wang Xiaolin, Ning Yu, Xi Fengjie
Opt Lett. 2025 Jan 1;50(1):125-128. doi: 10.1364/OL.546745.
Transverse mode instability (TMI) significantly limits the power scaling of ytterbium-doped fiber lasers. In this Letter, what we believe to be a novel TMI mitigation strategy is proposed and demonstrated in a bidirectional output fiber laser. On the basis of the continuous wave (CW) pump, integrating a quasi-continuous wave (QCW) pump can effectively improve the TMI threshold of the system. In the experiment, a QCW pump with a repetition rate of 1 kHz and a duty cycle of 10% was injected into a CW-pumped fiber laser oscillator, which successfully broke the power limit and alleviated the beam quality degradation. Moreover, when applying a pump modulation depth of approximately 68%, the TMI threshold was notably increased from 624 W in the free-running condition to 1093 W at end B, which is a 469 W (75%) improvement. At this time, the beam quality factor M at end B is approximately 1.48, and the stimulated Raman scattering suppression ratio is about 28 dB. Compared to conventional TMI mitigation methods, this approach provides active control in the time domain of fiber lasers, without compromising the optical structures, thereby effectively mitigating TMI and offering broad application prospects.
横向模式不稳定性（TMI）显著限制了掺镱光纤激光器的功率缩放。在本信函中，我们提出并在双向输出光纤激光器中演示了一种我们认为新颖的TMI缓解策略。在连续波（CW）泵浦的基础上，集成一个准连续波（QCW）泵浦可以有效提高系统的TMI阈值。在实验中，一个重复频率为1 kHz且占空比为10%的QCW泵浦被注入到一个连续波泵浦的光纤激光振荡器中，成功突破了功率限制并缓解了光束质量退化。此外，当施加约68%的泵浦调制深度时，TMI阈值显著从自由运行条件下的624 W提高到末端B处的1093 W，提高了469 W（75%）。此时，末端B处的光束质量因子M约为1.48，受激拉曼散射抑制比约为28 dB。与传统的TMI缓解方法相比，该方法在光纤激光器的时域中提供了主动控制，而不影响光学结构，从而有效缓解了TMI并具有广阔的应用前景。
