We present, what is to our knowledge, the first detailed set of experiments comparing different in situ optical temperature estimation methods for Yb:YLF (Yb:LiYF4) crystals used in cryogenic laser applications. The proposed temperature estimation methods are based on the temperature dependence of emission spectra of Yb:YLF in E//c axis, and looks at either the variation of the spectral intensity ratio of different wavelengths, or to the full-width half-maximum (FWHM) of the emission lines, or to the overall absolute integrated spectral change with respect to a reference temperature (also known as Differential Luminescence Thermometry: DLT). We have shown that by using the DLT method we can estimate the temperature of Yb:YLF crystals in the 78-300 K range with an accuracy better than ±1 K. The other methods work well in the 78-150 K range, and provide a fast temperature estimation with ±2 K accuracy. The benefit of the proposed technique has been demonstrated via evaluation of thermal contact quality of different Yb:YLF crystals, where we have seen that, a temperature estimation accuracy of ±5 K is feasible even for samples under nonhomogeneous thermal load. We hope the findings presented in this work to be useful to laser engineers and scientists working with cryogenic Yb:YLF systems.

中文翻译：

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低温 Yb:YLF 不同原位光学温度探测技术的比较

据我们所知，我们展示了第一组详细的实验，比较了低温激光应用中使用的 Yb:YLF (Yb:LiYF4) 晶体的不同原位光学温度估计方法。提出的温度估计方法基于 Yb:YLF 在 E//c 轴上的发射光谱的温度依赖性，并着眼于不同波长的光谱强度比的变化，或全宽半最大值（ FWHM），或相对于参考温度的整体绝对积分光谱变化（也称为差示发光温度法：DLT）。我们已经证明，通过使用 DLT 方法，我们可以估计 78-300 K 范围内 Yb:YLF 晶体的温度，精度优于 ±1 K。其他方法在 78-150 K 范围内工作良好，并提供 ±2 K 精度的快速温度估计。通过评估不同 Yb:YLF 晶体的热接触质量，已经证明了所提出技术的好处，我们已经看到，即使对于非均匀热负载下的样品，±5 K 的温度估计精度也是可行的。我们希望这项工作中提出的发现对使用低温 Yb:YLF 系统的激光工程师和科学家有用。