Recent developments in laser science have made it possible to experimentally study ultrafast electron dynamics in atoms and molecules directly by using ultrashort pulses on the order of tens of attoseconds. It is paramount, both for current understanding and planning of future experiments and applications, that we decipher how short pulses interact with the medium. We model attosecond dynamics of multi-electron systems following three themes: (1) propagation and distortion of pulses in absorbing noble gases, (2) simulation of atoms and molecules under the effects of pump and probe pulses, (3) coherence and polarization effects on transient absorption. First, using the Kramers-Kronig relations and a fast and stable numerical algorithm based on Mobius transformations, we model the distortion of XUV pulses propagating in noble gases. Our simulations show rich features including pulse stretching, partial narrowing, partial apparent super-luminality, and tail development. Second, we deploy the density matrix formalism using Lindblad terms and the three Hilbert spaces method, incorporating multi-channel and Auger ionization compactly and consistently, to model coherence observed in pump-probe attosecond transient absorption studies of Kr II. We explain how coherent noble cation states are produced. Density matrix elements for the excited Kr II 3d_3/2 and 3d_5/2 levels caused by a resonant z-polarized 80 eV 150 as probe pulse are simulated and the resulting population densities and induced dipole moments are analyzed, including nonlinear contributions. In order to model pulse propagation, we develop absorption theory for arbitrary polarization angle and point out how coherence effects distort the Beer-Lambert law and discuss experimental implications. Third, we investigate non-adiabatic effects in attosecond dynamics in molecules driven by a laser field. We use the Algebraic Diagrammatic Construction method and Arnoldi-Lanczos TDSE programs to simulate N2 and oligocenes for 400 nm, 800 nm and 1.6 micron wavelengths with various laser intensities and polarizations. We determine the onset of non-adiabaticity in N2, benzene and naphthalene. Last, but not least, I describe my experimental contribution to the new Imperial College beamline.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:659494 |
| Date | January 2014 |
| Creators | Hung, Tsen-Yu |
| Contributors | Marangos, Jonathan |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/25522 |
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