基于高性能气泡型铷原子钟的铷光谱灯脉冲光抽运研究

The lamp pumped rubidium atomic frequency standard(RAFS) have been recognized as critical equipment for the global navigation satellite systems. And the long-term frequency stability of the RAFS plays key role in determining system’s precisions, but it is primarily limitation by the light shift which caused by ac-Stark effect. At the same time, the traditional optimizing methods for reduce the light-shift coefficient can hardly get a satisfied solution. However, pulsed optically pumped method(in which the pumping, interrogation and detection phases are separated in time) can avoid light shift in theory, it has been used in optical Rubidium Frequency Standards(O-RFS) in recent years, such as POP-AFS. But, limited by poor frequency stability of the early RAFS, there are no research reports about using this method in RAFS. With the recent rapid development of RAFS technology, the high performance RAFS designed by our lab for BeiDou global navigation system, reach 5E-13/√τ of short-term frequency stability and 3E-15 of long-term frequency stability, is achieving the leading level among the same issues in the world. Then, this project intends to further reduce the light-shift coefficient of the RAFS by studying pulse lamplight pumped method base on the high performance RAFS. And study the influences on light shift and SNR of pulse lamplight pumped clock with the experimental parameters (timing sequence, temperature etc.). By optimizing the parameters, the light-shift coefficient is expected to achieve the level of 1E-12 over 10% light intensity change, while keeping high SNR. This results makes the frequency stability of the RAFS have chance to break through the limit and enter 10-16. This will bring revolutionary changes to the development of the atomic frequency standard technology.

气泡型铷原子钟是导航卫星的核心部件，其长期频率稳定度指标是决定卫星导航定位精度的关键因素。而由AC-Stark效应引起的光频移是限制铷原子钟长期稳定度的最主要因素。传统方法优化光频移已到极限（1E-11/10%），进一步改善十分困难。而近些年，在激光抽运频标领域得到运用的脉冲光抽运方法（将光抽运、微波共振和跃迁探测三者在时间上错开）理论上可以消除光频移。但是受限于早年信噪比较差，几十年来国内外都没有基于气泡型铷钟的脉冲光抽运研究的报道。随着技术发展，本实验室为北斗研制的高性能铷钟的频率稳定度（5E-13/√τ，3E-15/天）已达到国际领先水平。所以，本项目将探索在高性能铷原子钟基础上实现铷光谱灯脉冲光抽运，以减小光频移。探索时序、温度等参数对光频移和信噪比的影响，通过参数优化，在保持高信噪比的同时降低光频移系数到1E-12/10%。这将可能使铷钟频率稳定度突破极限进入E-16量级。

传统气泡型铷原子钟是导航卫星的核心部件，其频率稳定度指标是决定卫星导航定位精度的关键因素。本项目旨在探索基于铷光谱灯脉冲抽运的高性能铷原子钟可行性,并探索改善光频移问题和进一步提升铷钟性能的方法。为实现这一目标，我们研究并设计了一套高性能铷原子钟系统，其稳定度指标达到优于1.5E-13/√τ(1~100s)，为有报道的最好水平。并在此基础上探索了实现铷光谱灯脉冲光抽运技术，提出了一种实现方案，成功实现了基于铷光谱灯的毫秒量级周期的光脉冲，满足了高性能脉冲光抽运系统的必备条件。并首次成功获取了较高质量的铷光谱灯脉冲光抽运Ramsey钟跃迁信号，经过评估光频移系数也可以减小到2e-13/10%，系统频率稳定性优于8e-13/√τ。保持高性能的同时降低了光频移，为后续进一步研究进入E-16铷钟奠定了基础。