In the perspective of building a solid state cryocooler based on optical refrigeration, it is strategic to develop high purity crystals and to have a full understanding of the mechanisms that can reduce cooling efficiency. In this paper we highlight two loss mechanisms that can hinder the optical refrigeration performance of a Yb:YLF monocrystal: the presence of impurities and fluorescence reabsorption. We show how the presence of impurities can be inferred by measuring the mean lifetime of the Yb optical transition. We measure how a few ppms of other rare earth ions can be detrimental for optical refrigeration by exciting a cooling Yb:YLF sample with two laser sources. We also report the first practical demonstration of the negative effect of fluorescence reabsorption on the cooling performance.

中文翻译：

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晶体冷却效率的损失过程

从构建基于光学制冷的固态低温冷却器的角度来看，开发高纯度晶体并充分了解降低冷却效率的机制具有战略意义。在本文中，我们重点介绍了可能阻碍 Yb:YLF 单晶光学制冷性能的两种损耗机制：杂质的存在和荧光重吸收。我们展示了如何通过测量 Yb 光学跃迁的平均寿命来推断杂质的存在。我们通过用两个激光源激发冷却的 Yb:YLF 样品来测量几 ppm 的其他稀土离子对光学制冷的不利影响。我们还报告了荧光重吸收对冷却性能的负面影响的首次实际证明。