Rook, Thomas;
(2025)
Symmetries and catastrophes in
strong-field photoelectron physics.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
In this thesis, we explore the effect of symmetry and the benefit of a catastrophe theory perspective in strong-field photoelectron physics. There is a focus on understanding and further developing the Coulomb Quantum-orbit Strong Field Approximation (CQSFA) theory [1]. After having derived the CQSFA transition amplitude, in an almost complete manner, taking a tour through path integral theory and saddle-point approximations of integrals, from the exact quantum mechanical transition amplitude, we begin with a systematic study of Above Threshold Ionization (ATI) in tailored bichro- matic fields. The symmetry perspective allows us to make general statements about how certain field configurations can lead to the enhancement or suppression of various features of the photoelectron momentum distributions (PMDs), in particular, the contrast and relative prominence of holographic interference patterns. Developments of the CQSFA theory are introduced, which extend the theory to be more general and to incorporate additional saddle point solutions. These advancements are validated, finding improved agreement with numerical solutions of the Time-Dependent Schrödinger Equation (TDSE), demonstrating the robustness of the CQSFA in predicting and disentangling com- plex strong-field phenomena. The hugely complicated set of solutions to the Saddle Point Equations (SPEs) presents a tremendous task. In order to use the new solutions, we work to find different approaches for extracting and classifying trajectories in a systematic comparison with the results of the Strong Field Approximation (SFA), and make progress towards a detailed understanding the structure of the sets of solutions by taking a catastrophe theory perspective. In the process, we ob- serve and interpret the influence of dynamical symmetries on the CQSFA model and the underlying physics. This work provides a solid platform for future studies, through the introduction of a con- ceptual paradigm which connects initial to final momentum mappings with catastrophe theory. This has the potential to provide value to any future work which utilises semi-classical trajectory based methods such as (and including) the CQSFA. These are invaluable for understanding and working towards the goals of measurement and manipulation of electron dynamics by ultrafast lasers.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Symmetries and catastrophes in strong-field photoelectron physics |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10213388 |
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