中国科学院国家授时中心光晶格锶原子光频标研究进展

Progress of strontium optical lattice clock in NTSC

介绍了中国科学院国家授时中心光晶格锶原子光频标研究的工作,主要包括锶原子的两级冷却与俘获,光晶格装载,钟跃迁探测,拉比振荡的测量以及基于光频测量的精密测量理论与技术研究。目前实验上获得温度为8.4μK,数目约1×10~5个^(88)Sr原子的一维光晶格;通过磁场混合~3P_1态与~3P_0态,扫描测量得到线宽为180 Hz的^(88)Sr钟跃迁谱线;获得拉比振荡曲线且拉比π脉冲时间为5 ms时原子跃迁几率达到65%。基于锶原子光钟研究平台,国际上首次全面测量了锶原子组间跃迁(5s^2)~1S_0–(5s5p)~3P_1所有天然同位素的跃迁频率;采用对两个外腔半导体激光器进行级联光学注入的办法,对光梳的模式进行选择和放大(重复频率250 MHz),成功实现了锶原子光钟的窄线宽冷却的689 nm光源,放大倍率达2×10~5倍,边模抑制比大于37 d B,线宽远小于240 Hz,为下一步锶原子光钟系统的简化提供了一条值得探索的途径。

The progress of strontium optical lattice clock in the national time service center is presented, which includes the two stages of cooling and trapping, optical lattice loading, clock transition detecting, Rabi oscillation measuring, and precision measurement based on optical frequency both in theory and techniques. 88Sr cold atoms with number of about 1×105 and longitudinal temperature of 8.4 μK were loaded into a one-dimensional optical lattice. By using the magnetic field-inducing 3P1 state mixing into 3P0 state, the 1S0-3P0 transition with a linewidth of 180 Hz was detected. Upon observing the Rabi oscillations, it was obtained that the atomic excitation probability is 65% for the Rabi π-pulse time of 5 ms. It was the first time in the world that the frequencies of the intercombination transition（5s2）1S0 –（5s5p）3P1 for all natural isotope strontium atoms were comprehensively measured based on the system. By adopting cascade optical injecting to two external-cavity diode lasers and using active filtering and amplification of a single mode from an optical femtosecond laser comb with mode spacing of 250 MHz, a single comb line at 689 nm was filtered and amplified to reach as high as 10 m W with 37 d B side mode suppression and a linewidth of less than 240 Hz. This method could be applied over a broad spectral band to build narrow linewidth lasers for various applications.