Preparation of metastable Kr atoms in the 5s[3/2]2 level via laser-induced ionization has been achieved. The temporal evolution of the intensity of Kr atomic spectral lines at 760.15 nm, 811.29 nm, and 431.96 nm was used to elucidate the production mechanisms of metastable Kr atoms. These mechanisms primarily involve two processes: the “excitation + radiation” process, dominated by multiphoton excitation and initial plasma-induced electron impact excitation, and the “ion-electron recombination” process, governed by avalanche ionization. The decay time constants of Kr atomic spectral lines, corresponding to the “excitation + radiation” and “ion-electron recombination” processes respectively, were obtained experimentally under both strong and weak ionization conditions. The experiments revealed delay in preparations of metastable Kr atoms between these two processes. To reduce the loss of metastable Kr atoms and effectively utilize their peak concentration, we drew inspiration from metastable rare gas lasers and proposed the “cycling” idea to keep metastable Kr atoms produced by these two processes as synchronized as possible. We used 811.29 nm laser to excite metastable Kr atoms generated rapidly during the “excitation + radiation” stage to the 5p[5/2]3 level. The Kr atoms returned to the 5s[3/2]2 level through spontaneous radiation, merging with metastable Kr atoms that were slowly produced during the “ion-electron recombination” stage. We hope that the “cycling” idea can shorten the delay in preparations of metastable Kr atoms from both processes and enhance the peak concentration of metastable Kr atoms. However, the experimental results didn't meet expectations, as we observed a decrease in the 811.29 nm fluorescence after laser excitation, attributed to the accumulation of 5p[5/2]3 level Kr atoms. These atoms undergo energy pooling to populate the 4d’[3/2]1 and 5d[7/2]3 levels, followed by absorption of 811.29 nm laser energy leading to photoionization. Reducing the concentration of 5p[5/2]3 level Kr atoms helps mitigate the reionization issue.

中文翻译：

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激光诱导电离制备亚稳态氪原子的机理


通过激光诱导电离制备了 5s[3/2]2 能级的亚稳态 Kr 原子。利用 760.15 nm、811.29 nm 和 431.96 nm 处 Kr 原子谱线强度的时间演变来阐明亚稳态 Kr 原子的产生机制。这些机制主要涉及两个过程：“激发 + 辐射”过程，以多光子激发和初始等离子体诱导的电子碰撞激发为主，以及“离子-电子复合”过程，由雪崩电离控制。在强电离和弱电离条件下，分别对应“激发 + 辐射”和“离子-电子复合”过程的 Kr 原子谱线的衰变时间常数。实验揭示了这两个过程之间亚稳态 Kr 原子的制备延迟。为了减少亚稳态 Kr 原子的损失并有效利用其峰值浓度，我们从亚稳态稀有气体激光器中汲取灵感，提出了“循环”思想，以保持这两个过程产生的亚稳态 Kr 原子尽可能同步。我们使用 811.29 nm 激光激发了在 “激发 + 辐射” 阶段迅速产生的亚稳态 Kr 原子，达到 5p[5/2]3 水平。Kr 原子通过自发辐射返回到 5s[3/2]2 能级，与在“离子-电子复合”阶段缓慢产生的亚稳态 Kr 原子合并。我们希望“循环”思想可以缩短两个过程制备亚稳 Kr 原子的延迟，并提高亚稳 Kr 原子的峰浓度。然而，实验结果并未达到预期，因为我们观察到 811 有所下降。激光激发后 29 nm 荧光，归因于 5p[5/2]3 级 Kr 原子的积累。这些原子经过能量汇集以填充 4d'[3/2]1 和 5d[7/2]3 能级，然后吸收 811.29 nm 激光能量，导致光电离。降低 5p[5/2]3 级 Kr 原子的浓度有助于缓解再电离问题。