Temperature-dependent radiative lifetime of Yb:YLF: refined cross sections and potential for laser cooling

We revisit the spectroscopic characterization of ytterbium-doped LiYF4 (Yb:YLF) for the application of laser cooling. Time-dependent fluorescence spectroscopy reveals a temperature dependence of the radiative lifetime which we explain by the Boltzmann distribution of excited ions in the upper Stark levels. The emission cross sections of Yb:YLF from 17 K to 440 K are revised using the temperature-dependent radiative lifetimes from fluorescence spectra. We provide fit equations for the peak values of important transitions as a function of temperature, which is also useful for the design of Yb:YLF laser oscillators and amplifiers operated at cryogenic temperatures. Based on our spectroscopic data, we show the prerequisite crystal purity to achieve laser cooling below liquid nitrogen temperatures. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

By revisiting the spectroscopic characterization of ytterbium-doped LiYF4 (Yb:YLF), it was found that the emission cross sections and radiative lifetimes are temperature-dependent, which can be used for laser cooling application design. Fit equations for important transition peak values as a function of temperature were provided, while the necessary crystal purity for achieving laser cooling was also emphasized based on the spectroscopic data.