量子统计权重对原子场电离效率的影响

发布时间：2018-05-15 07:21

本文选题：锂原子 + 三步光激发　；参考：《物理学报》2017年07期

【摘要】：原子能级的量子统计权重(G)是原子的重要光谱参数,但在研究原子的电离过程中通常却为了简化问题而被忽略.本文在锂原子的三步光激发(PE)+电场电离(EFI)过程中计入了其影响,并发现其对原子EFI效率的影响显著.本文精心设计了一套锂原子的PE+EFI方案:首先,采用三台不同波长的脉冲激光器分三步将原子从基态激发到某一Rydberg态上,经过一段时间延迟后再施加脉冲电场将其电离.针对原子所经历的PE、零场和EFI这三个物理过程,本文对其物理机制进行了分析并建立了服从粒子数守恒的物理模型进而导出了显含G参数的普适的速率方程组.其次,通过Matlab编程,分别针对精心选定的两条激发路径2S_(1/2)→2P_(1/2)→3S_(1/2)→25P_(1/2,3/2)和2S_(1/2)→2P_(3/2)→3D_(5/2)→25F_(5/2,7/2)开展了数值计算.研究发现:PE+EFI过程的总体效率的上限既与激光参数无关,也不依赖于G参数的绝对值,而是决定于Rydberg态的G参数的分支比.总之,通过精选激发路径可以调控PE过程各相关态的布居率,并能适当提高PE+EFI过程的总电离效率,但却因受到Rydberg态布居率的限制而很难进一步提高.
[Abstract]:The quantum statistical weight of atomic energy is an important spectral parameter of atoms, but it is usually neglected to simplify the process of atomic ionization. In this paper, the influence of the three-step photoexcited electron field ionization (EFI) of lithium atom is considered, and it is found that it has a significant effect on the atomic EFI efficiency. In this paper, a set of PE EFI scheme for lithium atoms is carefully designed. Firstly, three pulsed lasers of different wavelengths are used to excite the atoms from ground state to a certain Rydberg state in three steps, and then ionization them with a pulsed electric field after a period of delay. In this paper, the physical mechanism of PE-, zero-field and EFI processes experienced by atoms is analyzed, and a physical model of conservation of particle numbers is established, and then the universal rate equations with G parameters are derived. Secondly, through Matlab programming, numerical calculations were carried out for two carefully selected excitation paths, 2S / 1 / 2) 2P / 1 / 2) / 3s / 2) 25P, 1 / 2 / 2) and 2S / 1 / 2) 2P / 2) 2P / 2) 3 / 2) 3D / 5 / 2) 25F / 52 / 72). It is found that the upper limit of the total efficiency of the EFI process is not dependent on the laser parameters nor on the absolute value of the G parameters, but on the branching ratio of the G parameters of the Rydberg state. In a word, the population distribution of each dependent state in PE process can be controlled by the selective excitation path, and the total ionization efficiency of PE EFI process can be improved appropriately, but it is difficult to improve further because of the limitation of Rydberg distribution.
【作者单位】：天津理工大学理学院;中国科学院武汉物理与数学研究所波谱与原子分子物理国家重点实验室;
【基金】：国家自然科学基金(批准号:11174218)资助的课题~~
【分类号】：O562

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