Single-pass amplification using rod-type fibers has become a common route to pulsed laser sources around 1030 nm with high average and peak power. Average-power scaling is currently limited by the dynamic thermo-optic phenomenon of “transverse mode instability.” In comparison, double-pass amplifier configurations have not been extensively studied. Recent theoretical and experimental work has shown both static and dynamic mode degradation phenomena, including an unexpected nonlinear polarization rotation effect. Here we present new results obtained with a modified setup using polarization filtering between the first and the second pass. We obtain up to 113 W output power, i.e., more than 40 dB of amplification from a single amplifier module seeded by 10 mW of 20 ps/20 MHz/1030 nm pulses. We observe excellent beam quality and polarization extinction ratio. Finally, we investigate a wide range of seed powers and report a strong increase in the static mode deformation threshold with decreasing seed power. The experimental results are corroborated by numerical simulations.

中文翻译：

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双通杆式光纤放大器的高增益

使用棒状光纤的单程放大已成为通向1030 nm附近具有高平均功率和峰值功率的脉冲激光源的常见途径。当前，平均功率缩放受到“横向模式不稳定性”的动态热光现象的限制。相比之下，双通放大器的配置尚未得到广泛研究。最近的理论和实验工作已经显示出静态和动态模式的退化现象，包括意外的非线性极化旋转效应。在这里，我们介绍了在第一遍和第二遍之间使用极化滤波的修改设置下获得的新结果。我们从单个放大器模块获得10 mW的20 ps / 20 MHz / 1030 nm脉冲播种，从而获得高达113 W的输出功率，即超过40 dB的放大。我们观察到出色的光束质量和消光比。最后，我们研究了范围广泛的种子功率，并报告了随着种子功率的降低，静态模式变形阈值大幅增加。实验结果通过数值模拟得到了证实。