Shift of the first ionization threshold of Sm atom in electric field
doi: 10.37188/CO.2020-0071
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摘要: 为了获得Sm原子的第一电离阈，将Sm原子多步激发产生的光电离、自电离和场电离信号进行了区分，并研究了不同磁量子数Rydberg态Sm原子对第一电离阈的影响。首先，结合多步共振激发和偏振组合技术，将稀土Sm原子激发到第一电离阈附近具有特定磁量子数的自电离或束缚Rydberg态。接着，通过反向静电场将光电离和自电离等过程产生的离子推出作用区。然后，通过施加延时脉冲电场对束缚Rydberg态Sm原子进行探测。最后，通过改变静电场强度获得了Sm原子第一电离阈随着静电场强度的变化情况，拟合确定了零场下不同磁量子数Sm原子的第一电离阈。实验结果表明：Sm原子的第一电离阈为45519.69±0.17 cm−1；该结果与用其它方法获得的结果进行了比较。实验验证了延时场电离探测技术用于测量Sm原子第一电离阈的有效性。Abstract: In order to obtain the first ionization threshold of Sm atom, the photoionization signal, autoionization signal and field ionization signal generated by the Sm atom under multi-step excitation were distinguished, and the influence of the Rydberg state of the Sm atom with different magnetic quantum numbers on the first ionization threshold was studied. At first, by use of multi-step resonance excitation combined with polarization technology, the rare-earth Sm atoms were excited to the autoionization or bound Rydberg state with a specific magnetic quantum number near the first ionization threshold. Then the ions generated by photoionization and autoionization were pushed out of the action zone by the reverse electrostatic field, and a delayed pulsed electric field was applied to detect the Sm atoms of bound Rydberg state. Finally, the relationship between the first ionization threshold of Sm atom and the varying intensity of electrostatic field was acquired, and the first ionization threshold of the Sm atom with different magnetic quantum numbers under zero field was determined by fitting. The experimental results show that the first ionization threshold of Sm atom is 45519.69±0.17 cm−1, which has been compared with the results obtained by other methods. The effectiveness of the delayed field ionization technique in measuring the first ionization threshold of Sm atom has been verified.
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图 2 Sm原子的多步激发路径示意图
Figure 2. Schematic diagram of multistep excitation path of Sm atom
图 3 零场和电场下Sm原子在第一电离阈附近的光谱图
Figure 3. Spectra of the Sm atom near the first ionization threshold under zero and electric fields
图 4 td=38.5 μs时，在零场和电场下Sm原子第一电离阈附近的光谱图
Figure 4. Spectra of the Sm atom near the first ionization threshold under zero and electric fields at td=38.5 μs
图 5 Sm原子在静电场为1.9993 V·cm−1时的光谱图
Figure 5. Spectra of Sm atom under the electrostatic field of 1.9993 V·cm−1
图 6 三步激光不同偏振组合下，Sm原子第一电离阈随静电场强度改变而移动的规律图。(a) π + π+ π; (b) π + π+ σ; (c) σ+ + σ+ + σ+
Figure 6. Diagram of the first ionization threshold of Sm atom shifting with the change of electrostatic field intensity under different polarization combinations of three-step lasers. (a) π + π+ π; (b) π + π+ σ; (c) σ+ + σ+ + σ+
表 1 Magnetic quantum numbers of Sm atom in 4f66snk state excited by different polarization combinations of λ1, λ2 and λ3
Table 1. Magnetic quantum numbers of Sm atom in 4f66snk state excited by different polarization combinations of λ1, λ2 and λ3
Combination
组合Polarization state
偏振状态Magnetic quantum number
磁量子数λ1 λ2 λ3 m 1 π π π 0 2 π π σ ±1 3 σ+ σ+ σ+ 3 
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表 2 Fitting results of the first ionization threshold of the Sm atom with different magnetic quantum numbers
Table 2. Fitting results of the first ionization threshold of the Sm atom with different magnetic quantum numbers
Combination
组合Magnetic quantum number, m
磁量子数mIonization threshold/ cm−1
电离阈/ cm−11 0 45519.67±0.21 2 ±1 45519.46±0.18 3 3 45519.95±0.11
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