激光冷却双原子分子中的超精细结构及其Zeeman效应的理论研究

分子的复杂内部能级结构使激光冷却双原子分子存在巨大挑战，选择合适的候选分子是激光冷却的一个首要问题。前期理论研究表明碱土金属氢化物双原子分子(MH, M = Be、Mg、Ca、Sr、Ba)初步满足激光冷却条件：1)高对角分布的Franck-Condon因子；2)较短的激发态辐射寿命；3)没有中间电子态终止冷却循环。为进一步研究激光冷却MH分子的可行性，超精细结构及其Zeeman效应对磁光阱中分子的冷却和陷俘必不可少。本项目拟以MH分子基态X2Σ+和第一激发态A2Π1/2较低振转能级的超精细结构及其Zeeman效应为研究内容。利用从头算和编写程序计算MH分子X2Σ+和A2Π1/2的超精细结构及其Zeeman效应。根据跃迁选择定则，确定可能的冷却循环能级，提出冷却方案。通过本项目的研究，揭示MH分子的超精细能级分裂及其随磁场强度变化的定量关系，为磁光阱中MH分子的冷却过程提供理论上的支持。

Laser cooling of diatomic molecule has a big challenge due to the complex internal level structure, the primary problem in laser cooling is the selection of appropriate diatomic molecules. A preliminary theoretical study on the electronic structure of the alkaline-earth-metal monohydrides (MH, M = Be、Mg、Ca、Sr、Ba) shows that these molecules meet certain criteria to be potential laser cooling candidates. Briefly, these criteria include (1) a highly-diagonal distributed Franck-Condon factors, (2) a shorter excited-state lifetime, and (3) no intervening electronic states to which the upper state could terminate the cycling transition. The hyperfine structure and the Zeeman effect in an external magnetic field, which are essential for laser cooling and magneto-optical trapping (MOT) of the alkaline-earth-metal monohydrides. This project will focus on the hyperfine structure and the Zeeman effect of lower ro-vibrational levels of ground state X 2Σ+ and first excited state A 2Π1/2 of MH molecules. The hyperfine structure and Zeeman effect can be evaluated numerically, which can be computed via ab initio and a computer program. According to the selection rule of the transitions, we will propose an optical cycling scheme for laser cooling of the MH molecules. The hyperfine splitting and Zeeman shift can be obtained. This project will lay the foundation for the process of laser cooling of these diatomic molecules in a MOT.