Although the output power of commercial fiber lasers has been reported to exceed 500 kW, the heat generated within fiber gain-media has limited the generation of higher laser powers due to thermal lensing and melting of the gain-media at high temperatures. Radiation-balanced fiber lasers promise to mitigate detrimental thermal effects within fiber gain-media based on using upconverted, anti-Stokes photoluminescence to extract heat from the optical fiber’s core. In this paper, we experimentally demonstrate that Yb(III) ions within $ {\text{YLiF}_4} $ (YLF) microcrystals are capable of cooling the cladding of optical fibers. We also present a design for radiation-balanced fiber lasers using a composite fiber cladding material that incorporates YLF nanocrystals as the active photonic heat engine. YLF crystals have the potential to form composite cladding materials to mitigate thermal gradients within the core and cladding based on anti-Stokes photoluminescence. Analytical models of heat transfer within the fiber are presented where the electric-field amplitude within the fiber core is responsible for both the heating of the core and the excitation of Yb(III) ions for anti-Stokes laser refrigeration in the cladding.

中文翻译：

---

光学活性复合材料在辐射平衡光纤激光器中的设计

尽管据报道商用光纤激光器的输出功率超过500 kW，但是由于增益透镜在高温下的热透镜化和熔化，光纤增益介质内产生的热量限制了较高激光功率的产生。辐射平衡的光纤激光器有望利用上转换的抗斯托克斯光致发光技术从光纤纤芯中吸收热量，从而减轻光纤增益介质中有害的热效应。在本文中，我们通过实验证明了$ {\ text {YLiF} _4} $内的Yb（III）离子（YLF）微晶能够冷却光纤的包层。我们还提出了一种辐射平衡光纤激光器的设计，该光纤激光器使用了掺有YLF纳米晶体作为有源光子热机的复合纤维包层材料。YLF晶体有可能形成复合覆层材料，以减轻基于反斯托克斯光致发光的纤芯和覆层内部的热梯度。给出了光纤内部传热的分析模型，其中光纤纤芯内的电场幅度既负责纤芯的加热，又负责激发包层中的抗斯托克斯激光致冷的Yb（III）离子。