Bray, Abbie C.; (2022) Electron Rescattering Picture in a Strong-Field Laser Regime: Diverse Initial State Geometry under Coulomb Influences. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis was nearly entitled ''The Fates of the Negatively Inclined'', alas this does not adequately convey the research on how initial state preparation of a target atom (realistic and toy models) plays a significant role in strong-field laser interaction and how Coulomb influences manifest in the electron rescattering picture. In this research, the Coulomb Quantum-orbit Strong-Field Approximation (CQSFA) model is mainly used; it is one of few semi-analytic models to account for the Coulomb potential for electrons in the continuum. Adaptations have been made by myself to further improve the CQSFA model by accounting for excited states, as well as rotational and translational elements in the initial atomic orbital. These changes better enable the assessment of how electrons of an atomic orbital behave under the influence of a laser. From this, one-electron above-threshold ionisation becomes observable, as well as copious interference patterns which are not present in classical models due to the quantum nature of the trajectories. With higher excited states and ''toy targets'', we see interesting features, such as topography, agree with other theoretical models. The key results presented here validate the importance of the inclusion of the Coulomb potential in the theoretical understanding of the quantum behaviour of electrons in the continuum. Furthermore, the fate of the electron is dissected through two definitions, recollision and recombination. We look at recollision through momentum mapping and photoelectron distributions to determine how trajectories cannot be classified only as ''direct'' or ''rescattered'', differing from other above-threshold ionisation models that use the strong-field approximation. Recombination and High Harmonic Generation are assessed through different lenses: we observe phase matching with the inclusion of Coulomb potential, and how plasmonic enhancements to the laser field can influence and control this phenomenon. This work is a novel approach to the rescattering picture of electrons from diverse initial states and regimes, or, to put it artistically: ''The Fates of the Negatively Inclined''.

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