惰性气体原子以及双原子分子在飞秒强激光场中的里德堡态激发

发布时间：2018-01-01 06:42

本文关键词：惰性气体原子以及双原子分子在飞秒强激光场中的里德堡态激发　出处：《吉林大学》2015年博士论文　论文类型：学位论文

【摘要】：随着现代科技的发展，超快激光与原子分子相互作用产生了许多新的强场物理过程，如高次谐波发射，阈上电离和非序列双电离等。其中强场下的中性里德堡态激发作为一个新的强场物理现象，不仅被认为是三步重散射模型的重要补充，而且是中性粒子有效加速的一种可能手段，近年来受到了大量理论和实验工作者的关注。尽管从2008年开始至今已有许多关于强场中里德堡态激发的研究被发表，仍然存在一些问题亟待进一步的深入研究予以解决。例如，强场中原子里德堡态激发的物理机制；里德堡态激发与其他强场物理过程的竞争关系；中性分子的里德堡态激发；各种激光参数（如激光波长，椭偏率，光强）的影响，以及原子和分子的里德堡态激发过程对比等。本论文中，我们使用脉冲电场电离里德堡态的方法结合飞行时间质谱，研究了不同原子和分子的里德堡态激发现象。通过测量强场电离和里德堡态激发的几率随激光参数（光强和椭偏率）的变化关系，，并比较原子的里德堡态激发和非序列双电离，相同电离限的原子和分子的里德堡态激发过程，以及红外和紫外激光场下里德堡态激发过程的区别，讨论了原子和分子在红外和紫外激光场下的里德堡态激发机制，分析了里德堡态激发与其他强场物理过程的竞争关系。获得了以下主要的研究结果： 1）测量了惰性气体原子（He，Ar，Xe）在800nm飞秒激光场中里德堡态激发的产量，及其随激光参数（光强，椭偏率）的变化关系，同时作为比较，实验中也测量了原子的非序列双电离过程。研究发现，里德堡态激发和非序列双电离呈现相似的现象，如随着原子序数的增加，其产率都增加，椭偏率依赖的程度随之减小；相比于非序列双电离，所有原子的里德堡态激发的产率较大，对激光椭偏率的依赖更弱。结合已有的研究报道和相关理论，我们分析并讨论了800nm强激光场中原子里德堡态激发的内在物理机制，即受挫的隧穿电离机制。 2）首次在实验上观测到分子在飞秒激光场下的里德堡态激发现象。对比研究了双原子分子N2和O2与其同伴原子Ar和Xe里德堡态激发几率。研究发现，与强场电离类似，N2分子表现为与原子Ar类似的里德堡态激发几率，而与原子Xe相比，O2分子的里德堡态激发几率明显被抑制，且里德堡态激发的抑制比强场电离抑制更为明显。量子计算定性的重现了实验结果。分析表明，不同分子的轨道结构导致的出射电子角分布的不同是决定里德堡态激发几率的重要因素。 3）研究了红外和紫外飞秒激光中NO的里德堡态激发现象。首次观测到了紫外飞秒强激光场中的里德堡态激发现象。实验发现NO*在800nm和400nm波长下对激光椭偏率的依赖不同，结合之前的实验结果和理论模型，认为NO分子在紫外光场中的里德堡态激发机制为多光子共振激发过程。
[Abstract]:With the development of modern technology, the interaction of ultrafast laser with atoms and molecules to produce many new high field physics process, such as harmonic emission, threshold ionization and non sequential double ionization. The neutral Rydberg states of strong field excitation as a new high field physics phenomenon, not only is considered to be an important supplement of the three step heavy scattering model, and is a possible means of neutral particles effectively accelerated, in recent years has been a large number of theoretical and experimental researchers.
Although from the beginning of 2008 has been many studies on excited Rydberg states in the strong field was published, there are still some problems need to be solved further study. For example, the physical mechanism of atomic Rydberg states excitation magnetic field; Rydberg state excitation competitive relationship with other strong field physics; Rydberg states of neutral molecules excited; various laser parameters (such as laser wavelength, ellipticity, intensity) effect, and Rydberg states of atoms and molecules of the excitation process of contrast.
In this paper, we use the method of pulsed field ionization of Rydberg states with time-of-flight mass spectrometry, studied the phenomenon of different excitation Rydberg states of atoms and molecules. The probability of measuring strong field ionization and excitation of Rydberg states with laser parameters (intensity and ellipticity) changes, and compare the Rydberg atom and non excitation sequential double ionization of Rydberg atoms and molecules, the same ionization limit the excitation process, and the difference between Rydberg states of infrared and ultraviolet laser field excitation, excitation mechanism of atoms and molecules in the infrared and ultraviolet laser field of the Rydberg States discussed the Rydberg state excitation in competition with other strong field physics. Analysis obtained the following main results:
1) inert gas atoms (He, Ar, Xe measurement) excited Rydberg states in 800nm femtosecond laser field in production, and with the laser parameters (intensity, ellipticity) changes, at the same time as the comparison experiment also measured in non sequential double ionization process of atoms. The study found the Rydberg states the excitation and non sequential double ionization showed similar phenomena, such as the atomic number increases, the yield increased, the ellipticity dependence decreases; compared to the non sequential double ionization of Rydberg states of all atoms excited by the yield greater dependence on laser ellipticity is weaker. Combined with the existing research reports and the related theory, we analyzed and discussed the intrinsic physical mechanism of excited atomic Rydberg states of 800nm in strong laser field, which frustrated the tunneling ionization mechanism.
2) the first observation of the Rydberg molecules in femtosecond laser field in the experiment. A comparative study of the phenomena of excitation of diatomic molecules N2 and O2 and its companion Ar and Xe atomic Rydberg states excitation probability. The study found that similar strong field ionization, N2 molecule is similar to Fort Reed state of atom Ar excitation probability. Compared with the Xe atom, Rydberg O2 molecule excitation probability was obviously inhibited, and the inhibition of the Rydberg state excitation inhibition was more obvious than the strong field ionization. Quantum computation qualitatively reproduce the experimental results. The analysis shows that different track structures lead to different molecular electron angular distribution is an important factor in determining Rydberg States excitation probability.
3) on the phenomenon of the Rydberg state excitation infrared and ultraviolet femtosecond laser in NO. The first observation of the Rydberg state UV intense femtosecond laser field excitation phenomenon. The experimental results showed that NO* dependent bias rate of laser elliptical in 800nm and 400nm wavelength under different experimental results and combined with the previous theoretical model, think the Rydberg NO molecule in the UV field excitation mechanism for multiphoton resonance excitation process.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O562

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