积分球冷原子钟性能优化
文献类型：学位论文
| 作者 | 王秀梅 |
| 文献子类 | 博士 |
| 导师 | 刘亮 |
| 关键词 | 积分球冷原子钟，频率稳定度，噪声分析，性能优化 ISCAC, frequency stability, noise analysis, performance improvement |
| 其他题名 | Improvement on the performance of the integrating sphere cold atom clock |
| 英文摘要 | 积分球冷原子钟是一种使用漫反射激光冷却和分离振荡场技术的小型化原子钟。本学位论文的主要内容包括作者在攻读博士学位期间的两项工作：第一项是积分球冷原子钟的性能分析工作，第二项是积分球冷原子钟的性能优化工作。 在第一项工作中，首先模拟了积分球内的光场分布。建立了积分球的二维模型，将其内表面设置成为服从标准正态分布的随机边界，并利用有限元分析法模拟仿真出了球形积分球和柱形积分球在不同打光方式下内部光场的分布，这对积分球冷原子钟物理系统的设计提供了指导。频率稳定度和频率准确度是原子钟性能的重要指标。根据Dick效应，结合目前钟时序分析了本地振荡器和频率综合器的相位噪声对钟频率稳定度的影响。理论推导出探测光噪声对钟频率稳定度影响的关系式。结合实验测量到的探测光强度噪声和频率噪声，分析出了探测光噪声对钟频率稳定度的影响。基于分析结果，对每一种分析出来的噪声贡献都给出了实验解决方案。除了分析频率稳定度，本文还分析了一些影响频率准确度的因素。 积分球冷原子钟的性能优化是在性能分析工作的基础上展开的。为了减小反馈噪声和提高反馈电压分辨率，搭建了一套数字电压反馈链路。该链路代替了之前的板卡直接反馈链路。理论研究发现Dick效应是影响积分球冷原子钟频率稳定度的一个重要因素。为了减小Dick效应，我们选用了一个新的超低相噪的5MHz晶振作为本地振荡器。基于该晶振搭建了自制频率综合器，为此Dick效应可降低至是2.5E-13*tao^-1/2。闭环锁定新晶振，积分球冷原子钟的频率稳定度被提高到了4.6E-13*tao^-1/2。积分球冷原子钟将冷原子的吸收光强作为钟信号，因此冷原子数的涨落会直接影响钟信号的信噪比。为了降低冷原子数的涨落，本文提出了一种积分球冷原子钟中冷原子数稳定的新方法。该方法通过周期性地监测冷原子的吸收信号，反馈控制冷却光声光调制器的衍射效率，改变冷却光功率，实现冷原子数的稳定。稳定后的冷原子数涨落优于正负0.1%（3个小时），其功率谱密度在频率0.001 Hz到0.2 Hz范围内，最大抑制约30 dB。冷原子数稳定之后，由原子数涨落引起的频率稳定度可降低至7E-14*tao^-1/2。 微波腔是积分球冷原子钟的核心部件。在圆柱形波导的基础上，设计了一种可应用于星载原子钟的重入式均匀场微波腔。该腔采用重入式结构和双缝耦合的微波注入方式，具有中心轴线区域微波场均匀范围大的特点，可提高钟信号的信噪比和钟的频率稳定度。; The Integrating Sphere Cold Atom Clock（ISCAC）is a compact cold atom clock which uses diffuse laser cooling and Ramsey microwave interrogation technologies. The main content of this thesis includes two parts: one part is the noise source analysis on the ISCAC, and the other is the improvement on the performance of the ISCAC. For the first part, the laser intensity distribution in the integrating sphere is simulated. A two-dimensional integrating sphere model is established and its inner faces are set to be the random edges which obey to the standard normal distribution. The laser intensity distribution in the spherical integrating cavity and cylindrical cavity are simulated by the finite element method, which gives advice to the design of physical package of the ISCAC. The frequency stability and accuracy are the two important parameters of the ISCAC. According to the theory of Dick effect, the impact of phase noise contributed from local oscillator and microwave synthesizer on the clock frequency stability are evaluated in present time sequence. The impact of probe laser noise on the frequency stability is estimated based on the measured probe laser intensity noise and frequency noise. The experiment schemes for reducing the impact of these noise sources are presented. Apart from the frequency stability, some factors limiting the frequency accuracy are also evaluated in this paper. We made several performance improvement in experiment based on the theoretical analysis. To reduce the feedback electronics noise and improve the feedback voltage resolution，a digital voltage feedback system is built in house. This system replaces the previous circuit board. It is found that the Dick effect is an important factor limiting the clock frequency stability. To reduce the Dick effect, a new 5 MHz local oscillator with ultra-low phase noise is selected. The new microwave synthesizer is built based on this new oscillator and the Dick effect is reduced to 2.5E-13*tao^-1/2.So the frequency stability of ISCAC is improved to 4.6E-13*tao^-1/2 when the new oscillator is used. The clock signal is detected with the light absorption method in the ISCAC, and therefore the fluctuations of cold atom number affect the signal to noise ratio of clock signal. To reduce the fluctuations of cold atom number, a new method of cold atom number stabilization is proposed. This method is to stabilize the absorption signal of cold atoms by adjusting the diffraction efficiency of the cooling laser’s acoustic optical modulation (AOM) periodically. The normalized fluctuation of the stabilized cold atom number is better than 0.1%（3 hours）, and the noise suppression in power spectral density is about 30 dB in the range of 0.001 Hz to 0.2 Hz. After stabilization, the limit of short-term frequency stability induced by the fluctuations of cold atom number is decreased to 7E-14*tao^-1/2. The microwave cavity is the key part in the ISCAC. On the basis of cylindrical wave guide, a uniform filed microwave cavity is designed which can be applied in space borne atom clock. The reentry structure and the double slits microwave injection method lead to the large uniform field in the center axis region, which can improve the signal to noise ratio of clock signal and the frequency stability of atom clock. |
| 学科主题 | 光学 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/30982]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 王秀梅. 积分球冷原子钟性能优化[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。