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Effects of multi-electron correlation on multiphoton ionization and high-order harmonic generation of atomic and molecular systems in intense ultrashort laser fields.

机译：在强超短激光场中，多电子相关性对原子和分子系统的多光子电离和高次谐波产生的影响。

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摘要

The study of the electron correlation and quantum dynamics of many-electron atoms and molecules in the presence of intense external fields is a subject of much current importance in science and technology. While experimental breakthroughs constantly challenge theorists, the reverse is also true, with theorists suggesting new experimental paths and novel ways to reach exciting regimes where new physics can be explored. For example, we have recently developed ab initio methods and applications to study time dependent quantum dynamics of atoms and molecules which cannot be understood by traditional perturbation theories. Moreover, currently there exist no adequate methods capable of studying the dynamical role of the individual valence electron to the high-order harmonic generation (HHG) and multiphoton ionization (MPI) processes in strong fields. Such a study can provide insights regarding the detailed quantum dynamics and HHG mechanisms, as well as the optimal control of strong-field processes. To advance this strong-field atomic and molecular physics, this dissertation aims at the developing new theoretical formalisms and accurate computational methods for ab initio non-perturbative studies of atomic and molecular processes in intense laser fields. The new methods developed allow in-depth and precision studies of strong-field phenomena for multielectron systems.;In this dissertation we investigate the role of electron correlation in dynamics of multielectron systems subject to strong fields. We present a time-dependent density functional theory (TDDFT), with proper asymptotic long-range potential, for nonperturbative treatment of multiphoton processes of homonuclear and heteronuclear diatomic molecules in intense ultrashort laser fields. A time-dependent two-center generalized pseudospectral method is presented for accurate and efficient treatment of the TDDFT equations in space and time. The procedure allows nonuniform and optimal spatial grid discretization of the Hamiltonian in prolate spheroidal coordinates and a split-operator scheme in the energy representation is extended for the time propagation of the individual molecular spin-orbital. The theory is applied to a detailed all-electron study of multiphoton ionization (MPI) and high-order harmonic generation (HHG) processes of N 2 and CO molecules in intense laser pulses. The results reveal intriguing and substantially different nonlinear optical response behaviors for N 2 and CO, despite the fact that CO has only a very small permanent dipole moment. In particular, we found that the MPI rate for CO is higher than that of N2. Furthermore, while laser excitation of the homonuclear N 2 molecule can generate only odd harmonics, both even and odd harmonics can be produced from the heteronuclear CO molecule.;Next, we present a complex-scaling (CS)-generalized pseudospectral (GPS) method in hyperspherical coordinates (HSC) for an accurate ab initio and accurate treatment of the electron structure and quantum dynamics of two-electron systems. The six-dimensional coupled hyperspherical adiabatic-channel equations are discretized and solved efficiently and accurately by means of the GPS method. The GPS method allows non-uniform and optimal spatial discretization of the two-electron Hamiltonian in HSC with the use of only a very modest number of grid points. The procedure is applied for the precision calculation of the energies and widths of doubly-excited Rydberg resonance states as well as the ionization rates of He atoms in an external electric field.;Lastly, we present a time-dependent generalized pseudospectral (TDGPS) approach in hyperspherical coordinates for fully ab initio nonperturbative treatment of multiphoton dynamics of atomic systems in intense laser fields. The laser-driven two-electron system is described by hyperspherical close coupling scheme. A novel 6D coupled time-dependent generalized pseudospectral method approach in hyperspherical coordinates are developed for single or double ionization without the use of the conventional adiabatic channels.;In conclusion, the present dissertation provides new developments in both theoretical and computational techniques, as well as advancements in the essential understanding of strong-field atomic and molecular physics.
机译：在强烈的外场存在下对多电子原子和分子的电子相关性和量子动力学的研究是科学技术中当前非常重要的课题。尽管实验性突破不断挑战理论家，但事实却恰恰相反，理论家提出了新的实验途径和新颖方法，以达到可以探索新物理学的令人兴奋的状态。例如，我们最近开发了从头算的方法和应用来研究原子和分子的时间依赖性量子动力学，而传统的微扰理论无法理解这种动力学。此外，目前还没有足够的方法来研究价电子在强场中对高次谐波产生（HHG）和多光子电离（MPI）过程的动力学作用。这样的研究可以提供有关详细的量子动力学和HHG机理以及强场过程的最佳控制的见识。为了推动这一强场原子和分子物理学的发展，本文旨在为在强激光场中原子和分子过程从头开始进行非扰动研究开发新的理论形式和精确的计算方法。所开发的新方法可以对多电子系统的强场现象进行深入而精确的研究。本文研究了电子相关性在强场作用下的多电子系统动力学中的作用。我们提出了一种具有时间渐近性远距离潜能的时变密度泛函理论（TDDFT），用于在强超短激光场中对同核和异核双原子分子的多光子过程进行非扰动处理。为了准确有效地处理时空上的TDDFT方程，提出了一种时变两中心广义伪谱方法。该程序允许球状坐标中哈密顿量的非均匀和最佳空间网格离散化，并且在能量表示中的分裂算子方案扩展了单个分子自旋轨道的时间传播。该理论适用于在强激光脉冲中N 2和CO分子的多光子电离（MPI）和高次谐波生成（HHG）过程的详细全电子研究。结果表明，尽管CO仅具有非常小的永久偶极矩，但N 2和CO的非线性光学响应行为有趣且基本不同。特别是，我们发现CO的MPI速率高于N2的MPI速率。此外，虽然同核N 2分子的激光激发只能产生奇次谐波，但异核CO分子却可以产生偶次和奇次谐波。其次，我们提出了一种复杂的标度（CS）-广义伪谱（GPS）方法在超球坐标（HSC）中进行精确的从头算和对两电子系统的电子结构和量子动力学的精确处理。利用GPS方法离散化并有效地求解了六维耦合的超球形绝热通道方程。 GPS方法仅使用非常少量的网格点就可以在HSC中对双电子哈密顿量进行非均匀且最佳的空间离散化。该程序用于精确计算双激发里德堡共振态的能量和宽度以及氦原子在外部电场中的电离速率。最后，我们提出了一种时变的广义伪光谱（TDGPS）方法在超球坐标系中进行完全从头开始的无扰动处理强激光场中原子系统的多光子动力学。激光驱动的双电子系统通过超球面紧密耦合方案来描述。为单电离或双电离开发了一种新颖的超球面6D耦合时变广义伪谱方法，无需使用传统的绝热通道。；总而言之，本论文为理论和计算技术提供了新的发展对强场原子和分子物理学的基本理解方面的进步。

著录项

  • 作者

    Heslar, John Thomas.;

  • 作者单位

    University of Kansas.;

  • 授予单位 University of Kansas.;
  • 学科 Chemistry Physical.;Physics Atomic.;Physics Theory.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 132 p.
  • 总页数 132
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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