强场条件下光电子与母核的再相互作用研究
文献类型：学位论文
| 作者 | 吴艳 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 张敬涛 |
| 关键词 | 重散射 高次谐波生成 强场激光 |
| 其他题名 | Study on Re-Encounter of Photoelectron with Parent Ion in Strong Laser Field |
| 中文摘要 | 光致电离和高次谐波生成是强激光场与原子、分子相互作用中基本而重要的非线性效应，得到了广泛的研究。光电子能谱和高次谐波谱特征反映了原子、分子的结构信息。因此，对光致电离和高次谐波生成的研究不仅丰富了人们对物质与激光相互作用的了解，加深了人们对强场物理过程的认识，而且提供了一种探索物质内部信息的重要手段。 根据电离过程不同，电离可分为直接电离和重散射。在重散射过程中，束缚电子先被强激光激发到连续态，然后在反向电场和母核的共同作用下再次回到母核附近，最后与母核发生重散射而出场；若电子再次被母核俘获，同时把在光场中获得的能量以谐波光子的形式放出，这个过程就是高次谐波生成。重散射和谐波生成都属于光电子与母核的再相互作用，因此重散射光电子谱和高次谐波谱携带了更加丰富的母核信息，对它们展开深入的研究对认识靶粒子的结构、电子排布等内部信息具有重要意义。 本论文应用非微扰的量子散射理论研究了强激光场中光电子与母核的再相互作用，确定了重散射和高次谐波生成满足的标度定律。借助标度定律，本论文进一步探讨了如何应用光电子谱和谐波谱获取靶粒子信息。本论文的主要创新性研究成果如下： （1）推广了全量子的形式散射理论，得到了重散射电离率微分公式，进而研究了强激光场重散射光电子的能谱和光电子角分布。我们发现真实的重散射过程可以发生多次；高阶光电子谱的平台是由重散射过程引起的；重散射的光电子谱具有多平台结构；重散射的光电子能谱及角分布与阈上电离的光电子谱遵循相同的标度定律。应用数值求解含时薛定谔方程的方法对标度定律进行了验证。 （2）研究了母核库仑势对光电子角分布的影响。由于重散射光电子与母核再相互作用，受母核的影响比直接出场的光电子大。在光电子能谱平台区的起始区域，重散射光电子和直接电离光电子具有可比拟的产量几率幅，两者的干涉效应最明显，因此处于平台起始区的光电子角分布随母核库仑势的变化非常显著。采用Yukawa势和Gaussian势，展示了平台起始区光电子角分布随模型势参数的变化，提出应用该区域光电子角分布提取母核的势信息。 （3）推广了形式散射理论框架下的高次谐波理论，研究了氢分子离子高次谐波的双中心干涉现象。研究发现谐波生成不仅受复合过程的影响，同时也受电离过程的调制；对于单个电离通道，随着激光强度增加干涉极值位置线性地向高阶次谐波移动，移动的量与有质动力参数有关；随着分子轴与激光偏振方向夹角的增加和分子核间距的减小，谐波的干涉极值位置也非线性地向高级次谐波移动。并发现，由于多通道的谐波相干迭加，总谐波谱的极值并不明显。 （4）研究了高次谐波生成过程，提出并确立了高次谐波生成所遵循的标度定律。研究发现一个具有束缚能Eb的类氢原子被波长为λ、强度为I的激光照射产生的高次谐波谱与一个束缚能为kEb的原子，被波长为λ/k、强度为 k3I的激光照射产生的高次谐波谱形态基本相同。对于类氢原子而言，后者同阶次高次谐波产率是前者的k3倍。高次谐波生成满足与阈上电离相同的标度定律，这表明两者具有相近的物理机制 |
| 英文摘要 | Photoionization and high-order harmonic generation (HHG) are two primary and important nonlinear physical processes in the interaction of intense laser fields with atoms and molecules, which are wildly studied. Photoelectron and harmonic spectra carry the structure information of atoms and molecules, so study on them enrich our knowledge on strong field physics, and they provide important tools to learn inner information of atoms and molecules. Considering the different physical mechanisms, photoionization in strong field laser physics fall into two categories: direct ionization and rescattering. When atoms or molecules are irradiated by an intense laser field, the bound electrons will be ionized into continuum states, if the electrons are drawn back to the vicinity of the parent ions under the action of the reverse electric field and the core, then scattered by the atomic cores, finally free from the laser field, the whole process belongs to rescattering. Moreover, if the electron recombines with the parent core, meanwhile, the redundant energy which is obtained in the laser field is released as a harmonic photon, the whole process is known as HHG. In rescattering and HHG processes, photoelectrons re-encounter the parent ion, that is to say, they act with the core twice, thus the rescattering photoelectron and harmonic spectra bring out more inner information of targets, so it is more meaningful to investigate the rescattering and HHG processes in extracting the inner information. In this dissertation, using nonperturbative quantum scattering theory, we study re-encounter processes. We find that not only rescattering, but also harmonic generation obeys the same scaling law as that for above-threshold ionization (ATI). With the help of the scaling law, we study on extracting the inner information of targets. The main innovative results are as follows, (1) By developing a full quantum scattering theory of high-order above threshold ionization, we study the energy spectra and the angular distributions of photoelectrons from atoms shined by intense laser fields. We find that the real rescattering can occur many times even infinite times. The photoelectrons from the rescattering process form the broad plateau in the photoelectron kinetic-energy spectrum. We further disclose a multiple-plateau structure formed by the high-energy photoelectrons which absorb many photons during rescattering process. Moreover, we find that both the angular distributions and the kinetic-energy spectra of photoelectrons obey the same scaling law as that for the directly emitted photoelectrons. We also verify the scaling law by resolving the time dependant Schrödinger equation. (2) We study the influence of ionic potential on photoelectron distributions. The rescattered photoelectrons are greatly affected by the binding potential of the parent core, while the directly emitted photoelectrons not. They are of comparable probability amplitudes at the onset of the plateau in the kinetic energy spectra of photoelectrons, which leads to the photoelectron angular distributions varying distinctively with the binding potential of the targets. We exhibit such variations and propose that the variations can be used to extract the potential information of the target core. (3) We study the two-center interference in harmonic spectra from aligned molecules. Using the linear combination of atomic orbitals theory of molecular orbitals, we derive the HHG rate formula for molecules. Employing the formula we study the intensity dependence of the interference effect induced by the molecular structure. We find that the molecular HHG was modulated by the interference not only in the recombination process but also in the ionization process. The location of interference minimum in HHG shifts to higher energy by a quantity of the ponderomotive energy as the laser intensity increases. (4) We study the harmonic generation of atoms in intense laser fields, and establish a scaling law of HHG. The scaling law states that when the atomic binding energy Eb, the wavelength λ and the intensity I of the laser field change simultaneously to kEb, λ/k and k3I , simultaneously, the characteristics of the HHG spectrum are unchanged, while the harmonic yield is enhanced to k3 times. That HHG obeys the same scaling law with above-threshold ionization is a solid proof of that the two physical processes share a similar physical mechanism. The variation of integrated harmonic yield is also discussed. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15718]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 吴艳. 强场条件下光电子与母核的再相互作用研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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