镱原子光钟晶格激光频率稳定系统的实验研究

发布时间：2018-09-18 08:26

【摘要】：基于中性镱原子的光晶格钟在千秒的平均时间内不稳定度已经可以进入小系数E-18的量级,并且已经被确定为成为SI二级秒定义的候选原子光钟体系。光晶格场的提出,对于基于中性原子的光钟是一个里程碑性质的贡献,它可以有效地提高原子光钟的信噪比同时抑制原子间的相互作用。由于光晶格原子钟的光晶格场存在一个魔数波长,使得钟跃迁上下能级在光晶格场中发生相同大小的移动,这个对光晶格钟获得更高的稳定度和精确度至关重要,所以对光晶格场的线宽和频率稳定性的控制就成为一项重要的关键技术。围绕这一关键技术,我在研究生期间,设计并实现了一整套基于光学传输腔的稳频系统,实现了对759nm光晶格场的线宽和长期频率漂移的控制,本文总结我的主要研究工作内容如下:1)搭建了基于85Rb D2跃迁的调制转移谱(MTS)锁频系统,得到一个波长为780nm稳定的频率参考源。通过两套完全独立的锁定系统进行拍频,实验结果显示,此锁定系统在1s平均时间下具有小于1kHz的Allan标准差;2)制作了基于殷钢合金的光学传输腔,并通过Pound-Drever-Hall方法(PDH)将误差信号反馈到此参考腔PZT上,实现了参考腔对780nm的频率参考源的锁定;实验结果显示,此传输腔的自由光谱区是375MHz,分别对应于780nm和759nm激光的精细度为236和341;3)设计制作了多套抑制剩余幅度调制(RAM)的反馈系统。通过对电光调制器的温度反馈控制,使得RAM产生的频率起伏受到压窄。实验结果显示,在759nm PDH环路中的RAM噪声最差不超过2.3kHz;在0.1Hz以下,开环信号中的RAM贡献在传输腔锁定后可以得到有效的抑制;而在0.1Hz以上,传输腔锁定与否对于RAM的影响不大;4)通过已锁定的传输腔,实现了 759nm光晶格场的线宽压窄和长期频率漂移控制。可以实现至少连续10个小时的无跳模锁定。与光梳拍频的结果显示,稳频后晶格激光在1s的平均时间下具有6kHz的Allan标准差;长期漂移所产生的Allan标准差最大为261kHz(200s平均时间下)。在研究生期间,我设计实现的传输腔稳频系统可以保证晶格光能以600kHz的步长进行频率扫描,为后续的魔数波长确定和锁定打下基础,锁定后的频率漂移特性可以确保镱原子光晶格钟的不稳定度小于10-17的量级。
[Abstract]:The instability of optical lattice clock based on neutral ytterbium atom has reached the order of small coefficient E-18 in the average time of kilosecond, and has been identified as a candidate atomic clock system defined by SI second-order second. The optical lattice field is a landmark contribution to the optical clock based on neutral atom. It can effectively improve the SNR of the atomic clock and suppress the interaction between atoms. Due to the existence of a magic wavelength in the optical lattice field of the optical lattice atomic clock, the upper and lower energy levels of the clock transition move in the same size in the optical lattice field, which is crucial to the higher stability and accuracy of the optical lattice clock. Therefore, the control of the linewidth and frequency stability of the optical lattice field has become an important key technology. Focusing on this key technology, I designed and implemented a set of frequency stabilization systems based on optical transmission cavities during my graduate study, and realized the control of the linewidth and long-term frequency drift of the 759nm optical lattice field. The main work of this paper is summarized as follows: 1) A modulation transfer spectrum (MTS) frequency locking system based on 85Rb D2 transition is built, and a frequency reference source with stable wavelength of 780nm is obtained. Through two totally independent locking systems, the experimental results show that the locking system has a Allan standard deviation of less than 1kHz in the average time of 1 s. (2) the optical transmission cavity based on Yin steel alloy has been fabricated. The error signal is fed back to the reference cavity PZT by the Pound-Drever-Hall method (PDH), and the frequency reference source of the 780nm is locked by the reference cavity. The experimental results show that, The free spectral region of the transmission cavity is 375MHz and the fineness of the 780nm and 759nm laser are 236 and 341m3 respectively. Several sets of feedback systems are designed and fabricated to suppress the residual amplitude modulation (RAM). By controlling the temperature feedback of the electro-optic modulator, the frequency fluctuation produced by RAM is reduced. The experimental results show that the RAM noise in the 759nm PDH loop is the worst less than 2.3 kHz, under 0.1Hz, the RAM contribution in the open loop signal can be effectively suppressed after the transmission cavity is locked, but above 0.1Hz, Whether the transmission cavity is locked or not has little effect on the RAM. 4) through the locked transmission cavity, the narrow linewidth of the 759nm optical lattice field and the long-term frequency drift control are realized. Can achieve at least 10 consecutive hours of mode-free locking. The results show that the lattice laser has the Allan standard deviation of 6kHz at the average time of 1 s, and the maximum standard deviation of Allan caused by long-term drift is 261kHz (under the average time of 200s). During the post-graduate period, the transmission cavity frequency stabilization system I designed and implemented can ensure that the lattice light energy can be scanned with the step size of 600kHz, which will lay the foundation for the subsequent determination and locking of the magic number wavelength. The frequency drift characteristics after locking can ensure that the instability of Yb atomic optical lattice clock is less than 10-17.
【学位授予单位】：中国科学院大学(中国科学院武汉物理与数学研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O562.3

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