Year of Award

2025

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry (Physical Option)

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Kent Sugden

Commitee Members

Dong Wang, Lu Hu, Stephen Lodmell

Keywords

Generalized Pseudospectral Method, High-Order Harmonic Generation, Quantum Chemistry, Spectroscopy, Time-Dependent Density Functional Theory, Ultrafast Laser Science

Abstract

High-order harmonic generation, or HHG, is a highly nonlinear quantum optical process capable of generating X-ray/ultraviolet radiation. An atom or molecule is irradiated with a mid-IR laser at high intensity, ionizes, and then emits high-frequency light at integer multiples of the driving laser frequency when an ionized electron recollides with the molecular ion. A convenient tabletop source of coherent XUV light and a common seed for free-electron lasers, HHG can also serve as a self-probe of the source atom or molecule. In the latter case, the HHG spectrum can provide valuable insight into the structure and dynamics of the species in a strong field. Certain features, particularly minima, maxima, and lineshape, are indicative of various processes related to recombination and chemical structure. In this thesis, the calculated high-resolution HHG spectra of small molecules are explored in-depth to uncover their structure and behavior in a strong electric field. When high-resolution laser conditions are selected, molecular HHG spectra calculated using Time-Dependent Density Functional Theory with Generalized Pseudospectral Method reveal previously unobserved strong-field structural and dynamic features of the target molecules.

In Chapter 1, the concept of high-order harmonic generation is described in detail as it applies to this research; to introduce the theory in Chapter 2, Chapter 2.1 introduces the concept of density functional theory methods, which are central to the calculated results herein; Chapter 2.2 extends these principles to time-dependent density functional theory, the basis for generating HHG spectra in this work; Chapter 2.3 links the concepts in Chapter 2.2 to Generalized Pseudospectral Method, which is necessary here for the time propagation; Chapter 3 discusses the calculated HHG results for acetylene and Chapter 4 covers the results for lithium hydride; finally, conclusions and future directions are outlined in Chapter 5.

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© Copyright 2025 Christopher Michael King