泵浦跃迁对多千瓦级掺铥光纤激光器热效应的影响
Influences of pump transitions on thermal effects of multi-kilowatt thulium-doped fiber lasers
摘要：
热效应是制约高功率掺铥光纤激光器发展的关键因素。在本文中，我们数值研究了在不同的泵浦跃迁的时间延迟线光纤的激光和热特性。我们的研究结果表明，广泛使用的泵浦跃迁$^3H_6\rightarrow^3H_4$，利用高功率高效率的激光二极管在$\sim$ 0.8 $μ$ m的优势，可能不是一个更好的选择，直接输出数千瓦的2 $μ$ m，因为严重的热问题。同时，利用其他泵浦跃迁产生的2- $μ$ m辐射，特别是带内泵浦跃迁$^3H_6\rightarrow^3F_4$，将在很大程度上减少产生的热量。通过优化增益光纤的功率填充因子，发现在1.9 $μ$ m泵浦下，2- $μ$ m TDFL包层的激光器斜率效率接近其量子效率（95%）。这种诱导的超低量子缺陷对功率缩放具有重要意义。因此，我们提出了在高功率下减少热量的串联泵浦TDFL，并讨论了相关的设计问题。此外，我们还探讨了激光和超荧光工作时热特性的差异，这将有助于加深对高功率掺铥光纤放大器中热效应的理解。
英文摘要：
Thermal effects are critical constrains for developing high-power thulium-doped fiber lasers (TDFLs). In this paper, we numerically investigate the lasing and thermal characteristics of the TDFLs under different pump transitions. Our results show, the widely-used pump transition $^3H_6\rightarrow^3H_4$, taking advantages of high-power high-efficiency laser diodes at $\sim$0.8 $μ$m, may not be a superior choice for directly outputting multi-kilowatt at 2 $μ$m because of severe thermal problems. Meanwhile, using other pump transitions resulting 2-$μ$m emissions, especially the in-band pump transition $^3H_6\rightarrow^3F_4$, will decrease the generated heat to a large extent. By optimizing the power filling factor of the gain fiber, we find a 2-$μ$m TDFL cladding-pumped at 1.9 $μ$m will lead to the laser slope efficiency close to its quantum efficiency (95\%). The induced ultra-low quantum defect would be of great importance for power scaling. We thus propose tandem-pumped TDFLs for reducing the heat at high powers and discuss the related issues of design. Besides, we also explore the differences of the thermal characteristics between laser and superfluorescent operations, which will contribute to deepening the understanding of the thermal effects in high-power thulium-doped fiber amplifiers.
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