强激光场中原子HATI类共振增强的研究

发布时间：2018-03-08 03:33

  本文选题：强激光场　切入点：阂上电离　出处：《西南交通大学》2015年硕士论文　论文类型：学位论文

【摘要】：超短超强激光场与原子、分子相互作用的研究是目前国际上非常活跃的前沿研究领域之一。在该极端物理条件下原子、分子会呈现出许多新奇的非微扰现象,包括多光子电离(Multiphoton ionization, MPI)、阈上电离(above threshold ionization, ATI)、隧穿电离(Tunneling ionization, TI)、非序列双电离(Nonsequential double ionization, NSDI)以及高次谐波的产生(High-order harmonic generation, HHG)等。其中阈上电离现象自被发现以来一直是强激光场原子、分子物理研究的重点和热点。由于强激光场与原子、分子相互作用过程的复杂性,目前对于一些阈上电离实验现象背后的物理机制尚未形成共识,其中之一就是高阶阈上电离光电子能谱中出现的类共振增强结构,还有待进一步的理论研究。另一方面,近年来由于可调谐中红外波段的超强超短激光技术的突破性发展,使得强场原子、分子物理的研究逐步由近红外波段向中红外波段扩展。目前,中红外强激光场物理的前沿性研究已在世界上引起广泛的关注。本文利用量子S-矩阵理论,借助“统一近似(uniform approximation)”方法,研究了近红外以及中红外波段的强激光场下氩原子高阶阂上电离光电子能谱上的类共振增强结构。研究表明,在近红外和中红外波段的强激光场下,阈上电离光电子能谱中均会出现类共振增强结构,即当激光强度仅仅增加几个百分比的时候,平台上的一系列峰就会表现出明显的增强现象。而出现的光强正好满足通道关闭条件,因而进一步证实了类共振增强的通道关闭机制解释。另外,我们还发现随着激光波长和光强的增加,光电子能谱中类共振增强和抑制会交替出现。该现象出现的可能原因是电子的不同次返回“量子轨道”间的相干叠加,利用它可以解释实验观察到的长波长下出现的类共振增强能量范围展宽的现象。同时,研究表明在中红外波段的强激光场下,也会出现与近红外波段下类似的type-Ⅰ和type-Ⅱ类共振增强结构。
[Abstract]:The study of the interaction of ultrashort and ultra-strong laser fields with atoms and molecules is one of the most active frontier research fields in the world at present. Under this extreme physical condition, atoms and molecules will present many novel non-perturbation phenomena. These include multiphoton ionization, multiphoton ionization, threshold ionization above threshold ionization, ATIN, tunneling ionization, tir, nonsequential double ionization nonsequential double ionizationand high order harmonic generation of high-order harmonics, in which suprathreshold ionization has been a strong laser field atom since its discovery. Because of the complexity of the interaction process between intense laser fields and atoms and molecules, there is no consensus on the physical mechanism behind some experimental phenomena of suprathreshold ionization. One of them is the resonant enhanced structure in high order suprathreshold ionization photoelectron spectroscopy, which needs further theoretical study. On the other hand, in recent years, due to the breakthrough development of ultra-strong ultrashort laser technology in tunable mid-infrared band, Therefore, the study of strong field atom and molecular physics has gradually expanded from near infrared band to mid infrared band. At present, the research on the frontier of high intensity laser field physics in mid infrared field has attracted wide attention in the world. In this paper, quantum S- matrix theory is used. By means of the uniform uniform approximation method, the resonant enhanced structures of photoelectron spectra on the high order barrier of argon atoms in near infrared and mid infrared intense laser fields are studied. The results show that, in the near infrared and middle infrared bands, the resonant enhancement structures on the ionization photoelectron spectra on the high order barrier of argon atoms are obtained. Resonance-like enhancement structures appear in the suprathreshold ionization photoelectron spectroscopy, that is, when the laser intensity increases by only a few percent, A series of peaks on the platform will show obvious enhancement phenomenon, and the light intensity will satisfy the channel closing condition, which further confirms the explanation of the channel closing mechanism of the resonance like enhancement. In addition, We also find that with the increase of the wavelength and intensity of the laser, the resonance like enhancement and suppression will occur alternately in the photoelectron spectroscopy. The possible cause of this phenomenon is the coherent superposition between the "quantum orbits" returned by the electrons in different order. It can be used to explain the phenomenon of broadening the energy range of resonance like enhancement observed in experiments at long wavelength. At the same time, it is shown that under the intense laser field in the mid-infrared band, Similar type- 鈪，

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