原子喷泉频标:原理与发展

介绍了喷泉频标的原理与发展.喷泉频标是一项近20年来发展起来的原子钟技术,它以激光冷却技术为基础,利用该技术实现了冷原子介质的俘获与上抛.冷原子介质在上抛下落过程中首先完成原子态制备,然后两次通过微波谐振腔实现Ramsey作用,在两次作用之间原子经历自由演化,最后原子经过探测区,通过双能级荧光探测法探测原子跃迁概率得到鉴频的Ramsey干涉条纹,并实现频率锁定,其中心条纹的线宽在1Hz左右.频率稳定度和频率不确定度是喷泉频标的两个重要指标.影响喷泉钟频率稳定度的因素主要有量子投影噪声和电子学噪声,目前喷泉钟的短期稳定度为(10~(-13)—10~(-14))τ~(-1/2),长期稳定度在(10~(-16)—10~(-17))量级.喷泉频标的频率不确定度主要受二阶塞曼频移、黑体辐射频移、冷原子碰撞频移以及与微波相关的频移等的影响.目前喷泉钟的不确定度在小的10~(-16)量级.作为基准频标,喷泉钟的工作介质主要是~(133)Cs,~(87)Rb.国际各大计量机构都研制了喷泉频标,它在各地协调世界时的建立、国际原子时的校准等方面发挥着越来越重要的作用.此外,喷泉频标还用于研究高精度时频基准和时间比对链路、验证基本物理理论等.

Atomic fountain frequency standard: principle and development

The principle and development of fountain frequency standard are introduced in this paper. Fountain frequency standard is an atomic clock technology developed in recent 20 years. It is based on laser cooling technology, and realizes the trapping and projection of the cold atom medium with laser cooling technology. In the process of launching upward and falling back, the cold atom medium first completes the preparation of atomic state, then passes through the microwave cavity twice to achieve the Ramsey interaction; between the two interactions it undergoes free evolution, and finally the Ramsey interference fringes are obtained by detecting the atomic interference probability with the two-level fluorescence detection method in the detection region, and the frequency is locked with a line width of the central fringe being about 1 Hz. The stability and uncertainty of the frequency are two important indexes of the fountain frequency standard. The factors influencing the stability of the fountain clock frequency mainly are quantum projection noise and electronic noise. At present, the short term stability of the fountain clock is (10^-13-10^-14)τ^-1/2, and the long term stability is (10^-16-10^-17). The frequency uncertainty of the fountain frequency standard is mainly influenced by the two-order Zeeman frequency shift, the blackbody radiation frequency shift, the cold atom collisional frequency shift, and the frequency shift relating to the microwave. The uncertainty of the fountain clock is around 10^-16 currently. As a reference frequency standard, the working media of the fountain clock mainly are ¹³³Cs and ⁸⁷Rb. All international metrology institutions have been developing the fountain frequency standard, and it plays a more and more important role in establishing the coordinated universal time and the calibration of the international atomic time. In addition, the fountain frequency standards are also used to study high-precision time-frequency reference and time comparison chain, and verify basic physical theories.