We present spectroscopic measurements focusing on a detailed investigation of temperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gain medium. Measurements are carried out in the 78–300 K range, but we especially targeted our attention to the 78–150 K interval, which is the desired working range of liquid nitrogen cooled cryogenic Yb:YLF lasers/amplifiers. A tunable (770–1110 nm) Cr:LiSAF laser with around 100 mW continuous-wave output power and sub-0.2 nm bandwidth is used as an excitation source. The average power of the Cr:LiSAF laser is low enough to prevent heating of the sample, and its spectral flux (W/nm) is high enough to enable large signal-to-noise ratio measurements. Measured absorption data is used to cross-check the validity of the emission measurements, while the measured temperature dependent small-signal gain profile provided a second independent confirmation. The acquired absorption cross section curves match the previous literature quite well, whereas the measured strength of c-axis emission is stronger than some of the earlier reports. Direct measurements of small signal gain confirmed the emission cross section data, where single pass gain values above 50 have been measured for the 995 nm transition of E//c axis at 78 K. We further provide simple analytic formulas for the measured temperature dependence of absorption and emission cross section. We hope the presented results to be useful for the development of next generation of cryogenic Yb:YLF laser and amplifier systems.

中文翻译：

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详细研究78–300 K范围内Yb：YLF的吸收，发射和增益

我们目前的光谱测量重点在于对单轴Yb：YLF激光增益介质中吸收，发射和增益的温度依赖性的详细研究。测量在78–300 K的范围内进行，但我们尤其将注意力集中在78–150 K的间隔，这是液氮冷却的低温Yb：YLF激光器/放大器的理想工作范围。具有约100 mW连续波输出功率和小于0.2 nm带宽的可调（770–1110 nm）Cr：LiSAF激光器用作激发源。Cr：LiSAF激光器的平均功率低到足以防止样品发热，并且其光谱通量（W / nm）高到足以进行大的信噪比测量。测得的吸收数据用于交叉检查排放测量的有效性，而与温度相关的小信号增益曲线则提供了第二个独立的确认。所获得的吸收截面曲线与以前的文献非常吻合，而测得的c轴发射强度比某些早期报道要强。直接测量小信号增益证实了发射横截面数据，其中在78 K下针对E // c轴的995 nm跃迁测量了大于50的单程增益值。我们进一步提供了简单的解析公式，用于测量吸收和发射截面。我们希望提出的结果对下一代低温Yb：YLF激光器和放大器系统的开发有用。所获得的吸收截面曲线与以前的文献非常吻合，而测得的c轴发射强度比某些早期报道要强。直接测量小信号增益证实了发射横截面数据，其中在78 K下针对E // c轴的995 nm跃迁测量了大于50的单程增益值。我们进一步提供了简单的解析公式，用于测量吸收和发射截面。我们希望提出的结果对下一代低温Yb：YLF激光器和放大器系统的开发有用。所获得的吸收截面曲线与以前的文献非常吻合，而测得的c轴发射强度比某些早期报道要强。直接测量小信号增益证实了发射横截面数据，其中在78 K下针对E // c轴的995 nm跃迁测量了大于50的单程增益值。我们进一步提供了简单的解析公式，用于测量吸收和发射截面。我们希望提出的结果对下一代低温Yb：YLF激光器和放大器系统的开发有用。其中在78 K下测量了E // c轴的995 nm跃迁的大于50的单程增益值。我们进一步为吸收和发射截面的温度相关性提供了简单的解析公式。我们希望提出的结果对下一代低温Yb：YLF激光器和放大器系统的开发有用。其中在78 K下测量了E // c轴的995 nm跃迁的大于50的单程增益值。我们进一步为吸收和发射截面的温度相关性提供了简单的解析公式。我们希望提出的结果对下一代低温Yb：YLF激光器和放大器系统的开发有用。