Date of Award
Doctor of Philosophy (PhD)
The generation of intense, femtosecond-duration laser pulses using near-IR to IR wavelengths of light opened a new frontier of highly nonlinear physics characterized by the resolution of electronic dynamics on their natural time scale through the application of attosecond-duration coherent light. These developments were made possible through the strong-field induced phenomenon of high-order harmonic generation (HHG), which results from the tunnel ionization, propagation, and recombination of an electron wavepacket with an atomic or molecular system. By emitting a broad spectrum of coherent radiation, this process enabled the development of attosecond-duration light. Due to its fundamental dependence upon electronic dynamics ongoing within the generative system, high-order harmonic generation has promise as a spectroscopic tool capable of resolving structural and dynamical processes within molecules. In this thesis, we apply numerical methods to study the time-resolution afforded by HHG in atomic and molecular systems. We also develop and validate new methods for simulating the single-electron response of multi-electron systems in the presence of intense laser fields.
To begin, we demonstrate the capacity for high-order harmonic generation to function as a signal of the dynamics of a propagating electron wavepacket. Through the use of an isolated attosecond pulse we gate the moment of ionization, selecting for or against electron trajectories that revisit the parent ion multiple times. With this control, we identify spectral and temporal signals which conclusively demonstrate the presence of these multiple revisitations.
In addition to imaging electron dynamics during propagation, we also show that high-order harmonic generation can be used to resolve electron dynamics inside of molecules. As driving field sources become available with increasingly long wavelength, electron dynamics in large and conjugated systems show evidence of a highly nonadiabatic response. Using the model system of H2+, we demonstrate that the frequency-dependent amplitude and phase of emitted high-order harmonic generation is highly demonstrative of these dynamics. The intrinsic frequency chirp of the emitted radiation enables the translation of these spectral alterations into a time-resolved picture of the counterintuitive transient localization of the electron on alternating sides of the molecular system.
Miller, Michelle R., "Time Resolving Electron Dynamics in Atomic and Molecular Systems Using High-Harmonic Spectroscopy" (2016). Physics Graduate Theses & Dissertations. 190.