We use a comprehensive model of cooling by anti-Stokes fluorescence in a single-mode fiber that includes the effects of fiber loss, concentration quenching, mode profiles, and amplified spontaneous emission to analyze the trends of cooling in single-mode Yb-doped ZBLANP fibers. Simulations demonstrate that heat extraction varies significantly along the fiber. There is an optimum pump power (58 mW at 1015 nm for the modeled fiber) for which the maximum heat extracted per unit length is at the start of the fiber. Launching more power moves the coolest point further down the fiber. At substantially higher powers, ASE has a significant heating effect, and coupled with the heating due to absorptive loss, the entire fiber warms up. For a given fiber length, the total extracted heat is maximized for a different pump power (430 mW for a 20-m length). The temperature change is then negative along the entire fiber, and the total extracted heat is 7.12 mW (1.65% cooling efficiency). When the fiber absorptive loss is negligible, this value increases to 30.5 mW for a 2-W pump, giving a 3.48% cooling efficiency, only slightly below the quantum limit (3.7%). The optimum dopant concentration has a similar trade-off: the total extracted heat is maximized for a Yb concentration of 2 wt.%, and the cooling efficiency for 0.5 wt.%. A model of ASF cooling in fiber lasers is also described and exploited to investigate how to select the fiber laser parameters to extract the most power output from a radiation-balanced fiber laser. It shows that increasing the cavity length increases cooling at the expense of laser efficiency, and that a low output coupler reflectivity enhances ASF cooling. Simulations predict that a large-mode-area fiber laser should produce 12.7 W of output power at 63% efficiency, a performance limited by the fiber’s absorptive loss, the core diameter (30 μm), and concentration quenching.
Jenny Knall, Mina Esmaeelpour, and Michel Digonnet, "Model of anti-Stokes cooling in a Yb-doped fiber," Proc. SPIE 10550, Optical and Electronic Cooling of Solids III, 105500K (Presented at SPIE OPTO: January 31, 2018; Published: 22 February 2018); https://doi.org/10.1117/12.2288616.
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