汞原子稳定磁光阱的实现与测量
文献类型：学位论文
| 作者 | 刘亢亢 |
| 学位类别 | 博士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 王育竹 |
| 关键词 | 激光冷却 磁光阱 汞原子 光晶格钟 |
| 其他题名 | Realization and measurement of a stable magneto-optical trap of neutral mercury |
| 中文摘要 | 相比于微波钟，光晶格钟具有更高的Q因子；相比于离子光钟，光晶格钟具有更低的量子投影噪声。因此光晶格钟被认为是下一代时间基准的主要候选方案。以锶、镱为代表的光晶格钟近年在国际上取得了很大进展，其中锶光晶格钟的频率相对不确定度已经降至10-18量级，创造了原子钟领域的新纪录。与目前其他光晶格钟原子相比，汞原子光晶格钟黑体辐射不确定度小的优点，且汞原子序数高、质量大，在科研应用上具有独特的优势。实现光晶格钟的第一步是冷原子的制备。 2012年我们搭建了国内第一台汞原子冷却的磁光阱（MOT）系统，并观测到了冷原子信号。本文在此基础上开展了一系列工作，对原有系统进行了大量改进，获得了稳定的汞原子磁光阱，并测量了超冷汞原子的参数，对磁光阱参数进行了优化。具体的工作包括：对四倍频冷却光激光器进行了前馈控制改进，降低了激光器移频和稳频过程中引入的功率噪声，大大增加了频率调谐的速度和宽度，使稳频后的频率噪声在1 Hz到100 kHz范围内降低了约15 dB；改进了汞原子消多普勒调频光谱，实现了紫外冷却激光对所有高丰度汞同位素跃迁线的锁定，并保证了冷却激光在稳频状态下可快速准确移频；建立了磁光阱的时序控制系统，改进了荧光成像系统，观测到磁光阱中汞原子六个同位素的冷原子信号；利用荧光法测量了真空系统内的汞原子背景蒸气密度，对汞蒸气密度随汞源温度的变化规律做了标定；测量了磁光阱中超冷汞原子的原子数和温度等参数，以最高丰度同位素202Hg为例，测量了激光频率失谐量、激光光强和磁场梯度等参数对原子数和温度的影响；进行了压缩磁光阱的实验，获得接近多普勒冷却极限的原子温度。实验结果表明，对于玻色子202Hg，原子数约为1.7×106，冷却温度最低约170 μK。费米子199Hg是用于光晶格钟的同位素，其原子数约为1.5×106，由于存在亚多普勒冷却，其原子温度明显低于玻色子同位素，最低可以达到50 μK。 |
| 英文摘要 | Due to its higher Q factor and lower quantum projection noise, optical lattice clock is a promising candidate for the next generation of time and frequency standard. Recently, great advances have made on optical lattice clock with strontium (Sr) and ytterbium (Yb) atoms, especially a new record has been made that the relative uncertainty of Sr optical lattice clock has already reduced to 10-18 level. Compared with other optical lattice clocks, mercury (Hg) optical lattice clock has the lowest sensitivity to black-body radiation. In addition, Hg atom has large atomic number and large atom mass, which takes distinctive advantages for scientific research and application. The first step of realizing an optical lattice clock is cooling and trapping of mercury atoms. We have built up a magneto-optical trap system for laser cooling of Hg atom, and have first time observed cold atoms signal in 2012. This thesis reports a series of works based on this system. We made a lot of improvements on the original system. With these improvements, we realized stable magneto-optical trapping (MOT) for Hg atoms, measured the atom number, loading time and temperature of cold atoms, and optimized the parameters of MOT. The specific improvement listed as following: Feed forward controlling of the frequency quadruple laser system to reduce the power noise induced during the laser frequency scanning or locking, and significantly increase the frequency tuning rate and width. The frequency noise is reduced 15 dB from 1 Hz to 100 kHz during the laser frequency stabilization. We have realized laser frequency locking on all transitions of rich abundant isotopes by the modification of Doppler-free frequency modulation spectroscopy system, and ensure the laser frequency of deep-UV cooling laser can be quickly and precisely shifted when it is stabilized. We have built the time sequence control system for MOT operation, and modified the fluorescence imaging system. Cold atoms signals of six Hg isotopes were detected in the stable MOT. We measured vapor pressure of Hg atoms by fluorescence imaging method in the vacuum chamber, and calibrate the vapor pressure of Hg atoms at different temperature of Hg source. We measured the parameters of cold mercury atom, such as atom number and temperature et al., and studied the influence of MOT parameters on cold atom, such as laser detuning, laser intensity and gradient of magnetic field on the MOT. As a result, the max atom number is 1.7×106 and the lowest temperature is 170 μK for bosonic isotope 202Hg. At most 1.5×106 atoms could be trapped for fermionic isotope 199Hg, which is a good candidate of optical lattice clock. Because of the sub-Doppler cooling, the lowest temperature is about 50 μK, which is far lower than bosonic isotope. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15967]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 刘亢亢. 汞原子稳定磁光阱的实现与测量[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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