超低温条件下的Ho³⁺:YLF光学制冷性能研究

Research on the Optical Refrigeration Performance of Ho³⁺:YLF at Ultra-Low Temperatures

摘要: 在Ho³⁺:YLF晶体的光学制冷中，能量传递上转换过程与温度具有很强相关性。所以，为进一步研究Ho³⁺:YLF晶体的在超低温下的光学制冷性能，首次探讨了温度对Ho³⁺:YLF晶体制冷的影响。基于能量传递上转换理论及其能级结构，给出了Ho³⁺离子光学制冷的理论模型，并数值模拟了等效外量子效率随温度的变化规律。为探究环境温度对Ho³⁺:YLF晶体光学制冷性能的影响，数值模拟了系统制冷效率和制冷功率密度随温度和掺杂浓度的变化规律。在超低温情况下，可以通过适量增加掺杂离子浓度来提高系统的制冷效率，在接近室温时，浓度的增加会给系统制冷带来负面影响，大幅降低可实现制冷的最大温度。

Abstract: In the optical refrigeration of Ho³⁺:YLF crystals, there exists a strong correlation between the energy transfer upconversion process and temperature. Therefore, to further investigate the optical refrigeration performance of Ho³⁺:YLF crystals at ultra-low temperatures, the influence of temperature on the refrigeration process was explored for the first time. A theoretical model of optical refrigeration of Ho³⁺ ions was developed based on energy transfer upconversion theory and its level structure, and numerical simulations were conducted to analyze the variation of the equivalent external quantum efficiency with temperature. Additionally, numerical simulations were performed to investigate the impact of ambient temperature on the optical refrigeration performance of Ho³⁺:YLF crystals, including variations in system refrigeration efficiency and refrigeration power density with temperature and doping concentration. It was found that at ultra-low temperatures, the system’s refrigeration efficiency can be enhanced by moderately increasing the doping ion concentration. However, as the temperature approaches room temperature, an increase in concentration may adversely affect the system’s refrigeration, significantly reducing the maximum achievable refrigeration temperature.