从长度米到时间秒: 稳频激光-铯喷泉钟-飞秒光梳-锶光晶格钟

报道了近年来中国计量科学研究院(NIM)在时间频率基准领域的研究进展: 稳频激光波长实际实现国际单位制(SI)的长度单位米(m); NIM5 铯喷泉钟以不确定度2×10^-15 复现时间单位秒(s); 飞秒光学频率梳建立光学频率与微波频率的相干联系, 以优于4×10^-14 的不确定度实现光学波长向标准微波频率的溯源标定; 以及正在研制的锶原子光晶格钟, 为应对未来修改秒定义做准备. 另外, 文中还提出飞秒光梳是从动跟踪系统, 描述其性能的指标应当是它的跟踪精度; 估计了“吸收室 - 原子束 - 原子喷泉 - 原子/离子存储”四种频率参考方案可能达到的不确定度极限.

From meter to second at NIM: Stabilized lasers-Cs fountain clocks-fs optical frequency combs-Sr lattice clock

In this paper we report the recent progresses on the time and frequency primary standards at the National Institute of Metrology (NIM) China: stabilized lasers for practical realization of the length unit (meter) of the International System of Units (SI); the cesium fountain clocks to realize the SI time unit (second) with an uncertainty of 2×10^-15; the femto-second optical frequency combs, establishing the coherent connection between microwave frequency and optical frequency, to calibrate the optical wavelengths traceably to the microwave standard frequency with uncertainty better than 4×10^-14; and the construction of a Sr lattice optical clock as a candidate of possible future redefinition of the second. We also describe: (1) fs optical combs are serve-locking systems and the specification to characterize their performance should be their tracking precision; (2) the estimated uncertainty limitations of sample cell - atom beam - cold atom fountain - trapped atom/ion frequency reference techniques.