Gaida Christian, Gebhardt Martin, Heuermann Tobias, Wang Ziyao, Jauregui Cesar, Limpert Jens
Opt Express. 2021 May 10;29(10):14963-14973. doi: 10.1364/OE.421954.
We experimentally analyze the average-power-scaling capabilities of ultrafast, thulium-doped fiber amplifiers. It has been theoretically predicted that thulium-doped fiber laser systems, with an emission wavelength around 2 µm, should be able to withstand much higher heat-loads than their Yb-doped counterparts before the onset of transverse mode instability (TMI) is observed. In this work we experimentally verify this theoretical prediction by operating thulium doped fibers at very high heat-load. In separate experiments we analyze the performance of two different large-core, thulium-doped fiber amplifiers. The first experiment aims at operating a short, very-large core, thulium-doped fiber amplifier at extreme heat-load levels of more than 300 W/m. Even at this extreme heat-load level, the onset of TMI is not observed. The second experiment maximizes the extractable average-output power from a large-core, thulium-doped, fiber amplifier. We have achieved a pump-limited average output power of 1.15 kW without the onset of TMI. However, during a longer period of operation at this power level the amplifier performance steadily degraded and TMI could be observed for average powers in excess of 847 W thereafter. This is the first time, to the best of our knowledge, that TMI has been reported in a thulium-doped fiber amplifier.
我们通过实验分析了超快掺铥光纤放大器的平均功率缩放能力。理论预测表明，发射波长在2μm左右的掺铥光纤激光系统，在观察到横向模式不稳定性（TMI）之前，应比掺镱光纤激光系统能够承受更高的热负载。在这项工作中，我们通过在非常高的热负载下运行掺铥光纤来实验验证这一理论预测。在单独的实验中，我们分析了两种不同的大芯径掺铥光纤放大器的性能。第一个实验旨在在超过300W/m的极高热负载水平下运行一个短的、非常大芯径的掺铥光纤放大器。即使在这个极热负载水平下，也未观察到TMI的出现。第二个实验使大芯径掺铥光纤放大器的可提取平均输出功率最大化。我们实现了1.15kW的泵浦限制平均输出功率，且未出现TMI。然而，在该功率水平下长时间运行期间，放大器性能逐渐下降，此后平均功率超过847W时可观察到TMI。据我们所知，这是首次在掺铥光纤放大器中报道TMI。
