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Title: Atomic electron dynamics in intense laser fields
Author: Robinson, David Jonathan
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2015
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Electron dynamics in laser-driven one- and two-electron atoms and ions are probed through numerical integration of the full -dimensional, time-dependent Schro"dinger Equation. Physical observables, such as ionization rates and the spectrum of harmonics generated by the system, are extracted from the wavefunction. For an atom in a one-colour, linearly polarized laser field, wavepackets ejected at certain times will recoillide with the core, generating harmonics of the driving field. The harmonic spectrum is calculated using HELIUM and used to benchmark those from the time-dependent R-matrix (TDRM) method and a single-active-electron (SAE) code. HELIUM and TDRM results agree to within 20% while SAE calculations agree in the high-frequency region of the spectrum. The two-photon double ionization (TPDI) cross section of helium is calculated for frequencies 40 eV<ω< 54 a.u. In this frequency range, sequential ionization requires the absorption of three photons while non-sequential ionization is a two-photon process so that the latter mechanism is dominant for fields with low intensity. The cross section is shown to be sensitive to pulse duration, especially near the 54 eV threshold. Calculations using the HELIUM code provide TPDI cross sections accurate to a few percent across the whole frequency range. Extension of the method to treat one-electron atoms and ions in orthogonally polarized, two-colour laser fields are described. An orthogonally polarized, two-colour field will steer ionized wavepackets in the continuum. The likelihood of recollision, and the recolliding wavepackets velocity are significantly changed. These effects can be seen in the harmonic spectrum. Such a two-colour scheme has been proposed as a way to image complex molecular orbitals. The harmonic spectrum from model atomic systems in such fields is calculated. It is observed that the harmonic spectrum is sensitive to the symmetry of the electron orbitals. Thus, for the 2p state even harmonics are significantly stronger than those in the 2s case.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available