With both radiation effects and thermal effects taken into consideration, a multiphysics thermal model concerning high-power Yb-doped fiber lasers operated with post-irradiated active fibers is established. Radiation-related parameters, including propagation losses, refractive indexes and lifetime, are considered. And, with the temperature profile of the active fiber, temperature-dependent parameters, including absorption and emission cross-sections, refractive indexes and lifetime, are updated every loop to simulate the output parameters. Simulation results show that radiation induces great changes to the thermal profiles of the active fiber. And severe performance degradation of high-power Yb-doped fiber lasers are recorded, featuring a remarkable drop in output power and an even steeper decline in the transverse mode instability threshold, which is a predominant limitation at high radiation doses. With a deposited radiation of 100 Gy, an output decline of about 50% and a mode instability threshold drop over 85% are observed. And it’s shown that, with the exploited active fiber, it’s hardly possible for the investigated fiber laser to generate stable single-mode output at kilowatt levels with accumulated radiation doses beyond 50 Gy. At low radiation doses within 20 Gy, to maintain safe and stable single-mode operation of the laser system, longer active fibers with lower absorption coefficients are preferred despite a small rollover of the output power.

中文翻译：

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高功率掺Y光纤激光器的有源光纤热模型

考虑到辐射效应和热效应，建立了一个多物理场热模型，该模型涉及用后辐照的活性纤维工作的高功率掺Y光纤激光器。考虑与辐射有关的参数，包括传播损耗，折射率和寿命。并且，利用活性纤维的温度分布，每个循环都会更新与温度有关的参数，包括吸收和发射截面，折射率和寿命，以模拟输出参数。仿真结果表明，辐射引起了活性纤维热分布的巨大变化。并记录了大功率掺Yb光纤激光器的严重性能下降，其特征在于输出功率显着下降，而横模不稳定性阈值下降幅度更大，这是高辐射剂量下的主要局限。在沉积的100 Gy辐射下，观察到输出下降约50％，模式不稳定性阈值下降超过85％。结果表明，利用所开发的有源光纤，所研究的光纤激光器几乎不可能在千瓦级产生稳定的单模输出，并且累积辐射剂量超过50 Gy。在20 Gy范围内的低辐射剂量下，为了保持激光系统的安全和稳定的单模运行，尽管输出功率的翻转很小，但具有较低吸收系数的较长的有源光纤仍是首选。使用被开发的有源光纤，被研究的光纤激光器几乎不可能在千瓦级别产生稳定的单模输出，并且累积辐射剂量超过50 Gy。在20 Gy范围内的低辐射剂量下，为了保持激光系统的安全和稳定的单模运行，尽管输出功率的翻转很小，但具有较低吸收系数的较长的有源光纤仍是首选。使用被开发的有源光纤，被研究的光纤激光器几乎不可能在千瓦级别产生稳定的单模输出，并且累积辐射剂量超过50 Gy。在20 Gy范围内的低辐射剂量下，为了保持激光系统的安全和稳定的单模运行，尽管输出功率的翻转很小，但具有较低吸收系数的较长的有源光纤仍是首选。