Mode distortion induced by stimulated Raman scattering (SRS) has become a new obstacle for the further development of high-power fiber lasers with high beam quality. Here, an approach for effective suppression of the SRS-induced mode distortion in high-power fiber amplifiers has been demonstrated experimentally by adjusting the seed power (output power of seed source) and forward feedback coefficient of the rear port in the seed source. It is shown that the threshold power of the SRS-induced mode distortion can be increased significantly by reducing the seed power or the forward feedback coefficient. Moreover, it has also been found that the threshold power is extremely sensitive to the forward feedback power value from the rear port. The influence of the seed power on the threshold power can be attributed to the fact that the seed power plays an important role in the effective length of the gain fiber in the amplifier. The influence of the forward feedback coefficient on the threshold power can be attributed to the enhanced SRS configuration because the end surface of the rear port together with the fiber in the amplifier constitutes a half-opening cavity. This suppression approach will be very helpful to further develop the high-power fiber amplifiers with high beam quality.

中文翻译：

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有效抑制高功率光纤放大器中受激拉曼散射引起的模式失真

受激拉曼散射（SRS）引起的模式畸变已成为进一步发展高光束质量高功率光纤激光器的新障碍。在这里，通过调整种子功率（种子源的输出功率）和种子源后端口的前向反馈系数，实验证明了一种有效抑制高功率光纤放大器中 SRS 引起的模式失真的方法。结果表明，通过降低种子功率或前向反馈系数可以显着提高 SRS 引起的模式失真的阈值功率。此外，还发现阈值功率对来自后端口的前向反馈功率值极为敏感。种子功率对阈值功率的影响可以归因于种子功率对放大器中增益光纤的有效长度起着重要作用。前向反馈系数对阈值功率的影响可归因于增强的 SRS 配置，因为后端口的端面与放大器中的光纤一起构成半开口腔。这种抑制方法将有助于进一步开发具有高光束质量的大功率光纤放大器。前向反馈系数对阈值功率的影响可归因于增强的 SRS 配置，因为后端口的端面与放大器中的光纤一起构成半开口腔。这种抑制方法将有助于进一步开发具有高光束质量的大功率光纤放大器。前向反馈系数对阈值功率的影响可归因于增强的 SRS 配置，因为后端口的端面与放大器中的光纤一起构成半开口腔。这种抑制方法将有助于进一步开发具有高光束质量的大功率光纤放大器。