物理学报2016，Vol.65Issue(13)：130201-1-130201-7,7.DOI:10.7498/aps.65.130201
中性汞原子磁光阱装载率的优化∗
Optimization of the loading rate of magneto-optical trap for neutral mercury atom
摘要
Abstract
Optics lattice clock is a hot topic in the researches of frequency standard and metrology. Neutral mercury atom is one of the most promising candidates for optical lattice clock. Due to its large atomic number, mercury atom is insensitive to black body radiation, which is the severe limitation for developing the optical lattice clocks. To realize the optical lattice clock of neutral mercury atoms, the first step is to implement laser-cooling and trapping of neutral mercury atoms. The cooling transition of mercury atom is 1S0–3P1 transition. The wavelength is 253.7 nm, the line width is 1.27 MHz, and the saturation intensity is 10.2 mW/cm2. Quantum projection noise (QPN) is an important parameter that affects optical lattice clock. Increasing the loading rate of magneto-optical trap (MOT) can help lower the QPN, thereby improving the performance of optical lattice clock. In this work, we calculate the scattering force of deep UV cooling laser, which is exerted on mercury atom in our single chamber MOT, and numerically simulate the one-dimensional motion of the atom in the MOT. It gives us the capture velocity under optimized parameters of the MOT. Then we calculate the loading rate of three-dimensional MOT by a high efficient random sampling method. According to the rate equation of MOT, the loading rate is proportional to the atom number of the steady state, which is the accessible parameter in the experiment. An experimental setup of MOT is established with a high vacuum system and a frequency quadrupled semiconductor laser system. The fluorescence imaging on an EMCCD gives the atom number in the MOT. We also calibrate the vapor density of background mercury gas in the vacuum, and measure the atom number in a steady MOT. We numerically simulate and experimentally study the influences on the atom number on the parameters of MOT, such as laser intensity, laser detuning and magnetic field gradient. The calculated results are in consistent with the experimental results. We also find the optimized parameters to maximize the loading rate. The numerical simulation also gives some results beyond current experimental condition, especially for laser intensity. From the simulations we obtain the optimized MOT parameter and relation for laser cooling of neutral mercury atom. Especially, current deep UV cooling laser with 20 mW of power does not have enough power to enhance the loading rate. These results are rather valuable for designing the next generation of optical lattice clocks for neutral mercury atoms.关键词
汞原子/磁光阱/光晶格钟/激光冷却Key words
mercury atom/magneto-optical trap/optical lattice clock/laser cooling引用本文复制引用
苟维,刘亢亢,付小虎,赵儒臣,孙剑芳,徐震..中性汞原子磁光阱装载率的优化∗[J].物理学报,2016,65(13):130201-1-130201-7,7.基金项目
国家自然科学基金(批准号:91436105,11547251)资助的课题.* Project supported by the National Natural Science Foundation of China (Grant Nos.91436105,11547251) （批准号:91436105,11547251）
