Radiation-balanced lasers are lasers where the heat generation in the gain medium is compensated by optical refrigeration due to anti-Stokes fluorescence emission. To investigate the feasibility of RBL operation in an optical fiber, a diagnostic test and a comprehensive model are essential. The model presented here is based on a two-level system and includes the intensity saturation effect, which has been usually neglected in bulk materials. We will show that for a material with a very low dopant area such as a single mode fiber (SMF) in which the saturation power is easily attainable, there is an optimum power at which the best cooling efficiency is obtained. The effect of the dopant density on the cooling power is investigated to find the maximum cooling efficiency which can be extracted for the material. We also present data for the extraction efficiency and other parameters of commercial Yb:ZBLAN glass and Yb:Silicate SMFs to discuss their cooling feasibility. Due to the structural defects, a double exponential behavior is usually observed in the fluorescence decay of the fibers that includes an slow and a fast decay channels. Some of the ions usually reside in the fast decay side and cause a large decrease in the heat extraction efficiency. Using our model, we will first analytically show that there is a maximum limit for the fast decay lifetime below which the cooling can still be functional and secondly discuss the effect of the measured decay lifetimes on the cooling efficiency.
Esmaeil Mobini, Mostafa Peysokhan, Behnam Abaie, and Arash Mafi, "Strategies for laser cooling of Yb-doped ZBLAN and silica single-mode optical fiber (Conference Presentation)," Proc. SPIE 10550, Optical and Electronic Cooling of Solids III, 105500P (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289580.5751548055001.
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