飞秒强激光场下惰性气体原子的电离动力学研究

发布时间：2018-03-16 11:48

本文选题：阈上电离　切入点：非顺序双电离　出处：《中国科学院大学(中国科学院武汉物理与数学研究所)》2017年博士论文　论文类型：学位论文

【摘要】：随着超快强激光技术的发展,飞秒强激光与物质相互作用已经成为揭示原子分子内部超快运动规律,探索极端强场条件下的原子物理新现象的重要手段。在飞秒强激光场中,光与物质相互作用进入全新的非线性、强非微扰区域,实验上发现了一系列新颖的物理现象,如多光子电离、阈上电离、非顺序双电离、高次谐波产生等。对这些新现象的研究已成为当前原子分子光物理领域的重要基础前沿,同时推动了一些新兴学科领域的诞生与发展,例如通过飞秒强激光与原子分子气体相互作用产生高次谐波的方法是获得阿秒光脉冲的首选方案,也是当前唯一实现了阿秒光脉冲的方案,直接导致了阿秒物理学的出现与蓬勃发展。本论文利用飞行时间质谱仪和冷靶反冲离子动量谱仪(COLTRIMS)等实验技术,结合半经典理论计算方法,研究了飞秒强激光与惰性气体原子相互作用的非顺序双电离以及阈上电离动力学行为。主要工作内容及取得成果如下:1.实验和理论研究了强激光场中氙原子非顺序双电离过程对激光波长的依赖。我们发现,实验上观测到的二价氙离子与一价氙离子产量比值与激光波长的关系偏离了simple-man模型的理论预测结果,具体表现为比值随波长下降的整体斜率发生了变化以及在关系曲线上出现了一系列的峰。基于包含了库仑势的半经典模型我们重现了离子产量与波长的整体依赖关系。分析表明,这种依赖关系是由自由电子的波包扩散,库仑聚焦以及与其密切相关的库仑散焦三种效应之间的相互作用导致的。2.实验和理论研究了中红外强激光场下氙原子非顺序双电离机制。我们发现当激光波长为2400nm时,随着激光光强的增加,二价氙离子动量分布从在零动量处呈现平台结构过渡到非零动量处呈现明显的双峰结构,这与实验室常用的790nm下的实验结果不同。基于再碰撞模型,我们可以得到非顺序双电离过程中碰撞直接电离(RII)和碰撞激发电离(RESI)两种通道贡献的相对比值。分析表明,随着波长和光强的增加,RII通道的贡献增大,导致离子动量分布出现双峰结构。此外,我们可以通过简单的函数拟合得到与实验结果一致的离子动量分布,并能获得对应于这两种通道的离子动量分布。3.理论研究了原子极化效应对椭圆偏振激光场中惰性气体阈上电离机制的影响。基于包含了库仑势和原子极化效应的半经典模型的理论计算结果显示,惰性气体原子Ar,Kr,Xe在椭圆偏振光下的光电子角分布几乎是一致的,这与实验结果相符。分析表明,极化效应会使电子隧穿时离母离子的距离增加,并且削弱母离子与光电子之间的库仑相互作用,这导致前向散射电子被抑制、直接电子贡献增加,从而造成Ar,Kr,Xe具有一致的光电子角分布。
[Abstract]:With the development of ultra-fast laser technology, the interaction between femtosecond laser and matter has become an important means to reveal the law of ultrafast motion in atoms and molecules, and to explore the new phenomena of atomic physics under extremely strong field. The interaction between light and matter has entered a new nonlinear, strong non-perturbation region. A series of new physical phenomena have been found experimentally, such as multiphoton ionization, suprathreshold ionization, non-sequential double ionization. The study of these new phenomena has become an important fundamental frontier in the field of atomic and molecular photophysics, and has promoted the birth and development of some new disciplines. For example, the method of producing high-order harmonics through the interaction of femtosecond intense laser with atomic and molecular gases is the first choice to obtain the attosecond optical pulse, and it is also the only current scheme to realize the attosecond optical pulse. This paper makes use of time-of-flight mass spectrometer and cold target recoil ion momentum spectrometer (COLTRIMS), combined with semiclassical theoretical calculation method. The dynamic behaviors of nonsequential double ionization and suprathreshold ionization of femtosecond intense laser interacting with inert gas atoms are studied. The main work and results are as follows: 1. Experimental and theoretical study of xenon atoms in intense laser field. The dependence of the sequence double ionization process on the wavelength of the laser. The relation between the yield ratio of bivalent xenon ion and monovalent xenon ion and the laser wavelength has deviated from the theoretical prediction result of simple-man model. It is shown that the overall slope of the ratio decreases with wavelength and a series of peaks appear on the relation curve. Based on the semi-classical model including Coulomb potential, we reproduce the global dependence of ion yield and wavelength. Relationship. Analysis shows that. This dependency is diffused by the wave packets of free electrons, 2. Experimental and theoretical studies on the mechanism of nonsequential biionization of xenon atoms in a mid-infrared intense laser field. We find that when the wavelength of the laser is 2400nm, the mechanism of nonsequential biionization of xenon atoms is investigated. With the increase of laser intensity, the bivalent xenon ion momentum distribution changes from a flat structure at zero momentum to a bimodal one at non-zero momentum, which is different from the experimental results at 790 nm, which is based on the recollision model. We can obtain the relative ratios of the contribution of collision direct ionization (RII) and collision-excited ionization (RESI) in the process of non-sequential double ionization. The analysis shows that the contribution of RII channel increases with the increase of wavelength and light intensity. In addition, we can get the ion momentum distribution which is consistent with the experimental results by simple function fitting. The ion momentum distribution corresponding to these two channels can be obtained. 3. The effect of atomic polarization on the mechanism of upper threshold ionization of inert gas in elliptical polarization laser field is theoretically studied. The theoretical results of semiclassical model show that, The angular distribution of the photoelectron of the inert gas atom Arn Krn Xe in elliptically polarized light is almost consistent with the experimental results. The analysis shows that the polarization effect increases the distance between the electron tunneling and the parent ion. The Coulomb interaction between the parent ion and the photoelectron is weakened, which leads to the suppression of the forward scattering electrons and the increase of the direct electron contribution, which leads to the consistent photoelectron angular distribution of Arn Krn Xe.
【学位授予单位】：中国科学院大学(中国科学院武汉物理与数学研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O562

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