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Strong field nonlinear optics in atoms and polyatomic molecules: Application of quantum mechanical methods to predict and control laser-induced processes.

机译：原子和多原子分子中的强场非线性光学：量子力学方法在预测和控制激光诱导过程中的应用。

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摘要

The central objective of this dissertation is developing new methods for calculating higher-order nonlinear optical responses of atoms, molecules, and ions, and discussing the relevant physical mechanisms that give rise to harmonic generation, Kerr effect, and higher-order Kerr effect. The applications of nonlinear optical properties in development of predictive models for femtosecond laser filamentation dynamics, photoemission spectroscopy, imaging, and design of new molecular systems have motivated the theoretical investigations in advancing methods for calculating nonlinear optical properties and finding the optimum conditions for controlling the nonlinearities.;The time-dependent nonlinear refractive index coefficient 4 n is investigated for argon and generalized for all noble gas atoms helium, neon, krypton, and xenon in the wavelengths ranging from 250 nm to 2000 nm, using ab initio methods. The secondorder polynomial fitting of DC-Kerr, electric-field-induced second-harmonic generation (ESHG), and static second-order hyperpolarizability have been performed, using an auxiliary electric field approach to obtain the corresponding fourth-order optical properties. An expression on the basis of static, DC-Kerr, DFWM fourth-order hyperpolarizability is derived, which allows the calculations of the DSWM coefficients with considerably reduced error. The results of the calculations suggest that filament stabilization is most likely to be induced by the generation of free electrons. Applications of these calculations resolve the HOKE controversy and are important for the development of predictive models for femtosecond laser filamentation dynamics.;In a series of proof-of-concept studies, the approach was employed for calculating dynamic linear and nonlinear hyperpolarizability of the radical cations. In this regard, the polarizability and second-order hyperpolarizability of nitrogen radical cation were investigated, using density functional theory (DFT) and multi-configurational self-consistent field (MCSCF) methods. The open-shell electronic system of nitrogen radical cation provides negative second-order optical nonlinearity, suggesting that the hyperpolarizability coefficient for nitrogen radical cation, in the non-resonant regime is mainly composed of combinations of virtual one-photon transitions rather than two-photon transitions. The calculations of second-order optical properties for nitrogen radical cation as a function of bond length have been investigated to study the effect of internuclear bond distance on optical process. The variation of nonlinear responses versus bond length shows the potential application in finding optimum conditions for higher values of nonlinear coefficients.;Furthermore, the computation of dynamic second-order hyperpolarizabilities for multiply ionized noble gases have been studied in the wavelength ranging from 100 nm to the red of the first multi-photon resonance all the way toward the static regime, using the MCSCF method. The results indicate that the second-order hyperpolarizability coefficients decrease when the electrons are removed from the systems. As the atoms reach higher ionization states, the second-order hyperpolarizability responses as a function of wavelength, become less dispersive. The second-order hyperpolarizability coefficients for each ionized species have also been investigated in terms of quantum state symmetries; the results suggest that the sign of the optical responses for each ionized atom depends on the spin of the quantum states defined for the ionized species. The calculations are of value for predictive models of high-harmonic generation in multiply ionized plasma at X-ray photon energies.;This research also focuses on investigating possible mechanisms for photodissociation of polyatomic molecules (acetophenone and the substituted derivatives) ionized through strong field infrared laser pulses. In this regard, quantum mechanical methods are combined with pump-probe spectroscopy to understand and control the dissociation dynamics in strong field regime. The applications of quantum mechanical models in interpreting time-resolved wavepacket dynamics and achieving coherent control has stimulated the interest to explore the PESs and investigate the role of conical intersections in wavepacket dynamics in strong field regime.;The electronic ground and excited states for acetophenone radical cation and the substituted derivatives have been investigated to probe the resonance features observed in measurements at 1370 nm with laser intensity of 10 13 W cm-2. The ten lowest lying ionic potential energy surfaces (PESs) of the acetophenone radical cation were explored, and the three-state conical intersection was mapped onto the PES, using MCSCF model to propose a photo-dissociation mechanism for acetophenone undergoing tunnel ionization and elucidate the potential dissociation pathways for formation of benzoyl fragment ion, as well as phenyl, acylium, and butadienyl small fragment ions. Similar calculations are presented for propiophenone radical cation which support the existence of a one-photon transition from the ground ionic to a bright dissociative D2 state, where motion of the acetyl group from a planar to nonplanar structure within the pulse duration enables the otherwise forbidden transition. The wavepacket dynamics in acetophenone molecular ion is modeled using the classical wavepacket trajectory calculations, to propose the mechanism wherein the 790 nm probe pulse excites a wavepacket on the ground surface D0 to the excited D2 surface at a delay of 325 fs. The innovations of this research are used to design control strategies for selective bond-breaking in acetophenone radical cation, as well as design control schemes for other molecules.
机译：本文的主要目的是开发计算原子，分子和离子的高阶非线性光学响应的​​新方法，并讨论引起谐波产生，克尔效应和高阶克尔效应的相关物理机理。非线性光学性质在飞秒激光丝化动力学，光发射光谱学，成像和新分子系统设计的预测模型的开发中的应用激发了理论研究方法的发展，从而促进了计算非线性光学性质和寻找控制非线性的最佳条件的方法的发展。使用从头算方法，对氩气进行了时变非线性折射率系数4 n的研究，并对波长范围从250 nm至2000 nm的所有稀有气体原子氦，氖，k和氙进行了概括。已经使用辅助电场方法执行了DC-Kerr的二阶多项式拟合，电场感应的第二谐波生成（ESHG）和静态的二阶超极化性，以获取相应的四阶光学特性。推导了基于静态DC-Kerr DFWM四阶超极化率的表达式，该表达式可以计算DSWM系数，并且误差大大减小。计算结果表明，灯丝稳定最有可能由自由电子的产生引起。这些计算的应用解决了HOKE争议，对开发飞秒激光丝化动力学预测模型非常重要。；在一系列概念验证研究中，该方法用于计算自由基阳离子的动态线性和非线性超极化性。在这方面，使用密度泛函理论（DFT）和多构型自洽场（MCSCF）方法研究了氮自由基阳离子的极化性和二级超极化性。氮自由基阳离子的开壳电子系统提供负的二阶光学非线性，这表明在非共振状态下氮自由基阳离子的超极化系数主要由虚拟的单光子跃迁而不是双光子的组合组成过渡。研究了氮自由基阳离子作为键长的函数的二阶光学性质的计算方法，以研究核间键距对光学过程的影响。非线性响应随键长的变化显示了为寻找更高的非线性系数最佳条件而潜在的应用。此外，研究了在100 nm至100 nm范围内的多种电离惰性气体的动态二阶超极化率的计算。使用MCSCF方法，将第一个多光子共振的红色一直指向静态。结果表明，当电子从系统中移出时，二阶超极化系数降低。随着原子达到更高的电离态，二阶超极化率响应随波长的变化而变得不那么分散。还已经根据量子态对称性研究了每种电离物质的二阶超极化系数。结果表明，每个电离原子的光学响应的​​符号取决于为电离物质定义的量子态的自旋。该计算对于在X射线光子能量下多电离等离子体中高谐波产生的预测模型具有价值。;本研究还致力于研究通过强场红外电离的多原子分子（苯乙酮和取代的衍生物）光解离的可能机理。激光脉冲。在这方面，将量子力学方法与泵浦探针光谱法相结合，以了解和控制强场条件下的解离动力学。量子力学模型在解释时间分辨波包动力学和实现相干控制中的应用激发了人们的兴趣，探索了PES，研究了圆锥交点在强场状态下波包动力学中的作用。苯乙酮基的电子基态和激发态已经研究了阳离子和取代的衍生物，以探测在1370 nm的激光强度为10 13 W cm-2的测量中观察到的共振特征。探索了苯乙酮自由基阳离子的十个最低位的离子势能面（PESs），并将三态圆锥形相交点映射到PES上，使用MCSCF模型提出了苯乙酮经历隧道电离的光解离机理，并阐明了形成苯甲酰碎片离子以及苯基，酰基的潜在解离途径和丁二烯小碎片离子。对于丙苯酮自由基阳离子也进行了类似的计算，该计算支持从基态离子到亮解离D2状态的单光子跃迁的存在，其中乙酰基在脉冲持续时间内从平面结构到非平面结构的运动使得原本可以禁止的跃迁。使用经典波包轨迹计算对乙苯分子离子中的波包动力学进行建模，以提出机理，其中790 nm探测脉冲以325 fs的延迟将地表D0上的波包激发到激发的D2表面上。这项研究的创新成果用于设计苯乙酮自由基阳离子选择性键断裂的控制策略，以及其他分子的设计控制方案。

著录项

  • 作者

    Tarazkar, Maryam.;

  • 作者单位

    Temple University.;

  • 授予单位 Temple University.;
  • 学科 Physical chemistry.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 347 p.
  • 总页数 347
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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