Yang Fan, Wang Xinliang, Fan Sichen, Bai Yang, Shi Junru, Liu Dandan, Zhang Hui, Guan Yong, Hao Qiang, Ruan Jun, Zhang Shougang
National Time Service Center, Chinese Academy of Sciences, Xi'an, Shaanxi 710600, China.
Rev Sci Instrum. 2022 Apr 1;93(4):044708. doi: 10.1063/5.0082708.
A cryogenic cesium atomic fountain clock is a novel clock with the microwave cavity and atomic free flight region placed in liquid nitrogen. On the one hand, the blackbody radiation shift is reduced at cryogenic temperature. On the other hand, the vacuum in the atomic free flight region is optimized, and the background gas collision shift reduced. The microwave resonant cavity is the most important unit in a cryogenic cesium atomic fountain clock. Through theoretical and simulative investigation, this study designs the configuration and dimensions for an optimized microwave cavity. Concurrently, experiments reveal the effects of temperature, pressure, humidity, and other factors on the resonant frequency of the microwave cavity. Combining the theoretical and experimental study, we obtain the resonant frequency difference between the microwave cavity in a cryogenic vacuum and at room temperature and ambient pressure. By subtracting this frequency difference, we adjust the microwave cavity for room temperature and ambient pressure, then vacuumize and immerse it in liquid nitrogen for verification and fine tuning. Finally, we determine that the microwave cavity resonant frequency deviation from the clock transition frequency is 10 kHz with an unloaded quality factor of 25 000, which meets the application requirements of the cryogenic cesium atomic fountain clock.
低温铯原子喷泉钟是一种新型时钟，其微波腔和原子自由飞行区域置于液氮中。一方面，在低温下黑体辐射频移减小。另一方面，原子自由飞行区域的真空得到优化，背景气体碰撞频移降低。微波谐振腔是低温铯原子喷泉钟中最重要的单元。通过理论和模拟研究，本研究设计了优化微波腔的结构和尺寸。同时，实验揭示了温度、压力、湿度等因素对微波腔谐振频率的影响。结合理论和实验研究，我们得到了低温真空和室温及常压下微波腔的谐振频率差。通过减去这个频率差，我们对微波腔进行室温及常压调整，然后抽真空并浸入液氮中进行验证和微调。最后，我们确定微波腔谐振频率与时钟跃迁频率的偏差为10 kHz，无载品质因数为2500０，满足低温铯原子喷泉钟的应用要求。
