We measure the transverse velocity distribution in a thermal Sr atomic beamprecisely by velocity-selective saturated fluorescence spectroscopy. The use ofan ultrastable laser system and the narrow intercombination transition line ofSr atoms mean that the resolution of the measured velocity can reach 0.13 m/s,corresponding to 90$\mu K$ in energy units. The experimental results are invery good agreement with the results of theoretical calculations. Based on thespectroscopic techniques used here, the absolute frequency of theintercombination transition of $^{88}$Sr is measured using an optical-frequencycomb generator referenced to the SI second through an H maser, and is given as434 829 121 318(10) kHz.
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机译：我们通过速度选择性饱和荧光光谱法精确地测量了热锶原子束中的横向速度分布。使用超稳定的激光系统和窄的Sr原子的相互结合跃迁线意味着测得的速度分辨率可以达到0.13 m / s，相当于能量单位为90 $ \ mu K $。实验结果与理论计算结果非常吻合。基于此处使用的光谱技术，使用通过H maser指向SI秒的光频梳生成器来测量$ ^ {88} $ Sr的跃迁的绝对频率，并给出为434 829 121 318（10）kHz 。
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