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Anne L'Huillier

Anne l'Huillier

Professor

Anne L'Huillier

Quantum interference effects in attosecond photoionization dynamics

Author

  • David Busto

Summary, in English

The interaction of extreme ultraviolet light with matter can lead to the emission of an electron in a process known as photoionization. The electron wavepacket (EWP) created in the continuum propagates on the ionic potential, resulting in a delay compared to an EWP propagating freely. The development of extreme ultraviolet attosecond light sources in recent years has opened the possibility to probe photoionization on the attosecond time scale ($10^{-18}$~s).

In this thesis, atomic photoionization is investigated in both resonant and non-resonant conditions via the attosecond photoelectron interferometric technique RABBIT (Reconstruction of Attosecond Beating By Interference of Two-photon transitions). Atoms are photoionized by an attosecond pulse train (APT), creating an EWP in the continuum. The EWP is then made to interfere with itself using a weak delayed infrared (IR) probe pulse. Recording the photoelectron signal as a function of the delay between the IR and the APT allows us to characterize the EWP in the spectral domain.

In this thesis we investigate experimentally and theoretically photoionization dynamics in various atoms (He, Ne, Ar and Xe) as well as in the N$_2$ molecule. These studies focus on understanding how the presence of multiple ionization channels affects the ionization dynamics. On the one hand, we study the situation in which different ionization channels are excited incoherently resulting in overlapping photoelectron peaks in the spectrum. In this case, we show that the RABBIT technique allows us to measure photoionization time delays with a few tens of attosecond resolution while maintaining the high spectral resolution needed to disentangle contributions from different ionization channels. On the other hand, we investigate the case where several ionization channels are excited coherently leading to interference between different quantum paths. Using the RABBIT technique, we study the interference between direct photoionization and autoionization in the vicinity of Fano resonances. Measuring the amplitude and phase of photoelectrons emitted via these resonances, we characterize the EWPs in time-frequency domain. By pushing the spectral resolution of our measurements we are able to observe signatures of quantum decoherence and to quantify it. In addition, using angle-resolved measurements, we investigate the effect of the coherent superposition of final states with different angular momenta. We show that it results in angular interference which lead to an angle-dependence of the photoionization time delays and to a modification of the photoelectron angular distribution with pump-probe delay.

Department/s

  • Atomic Physics

Publishing year

2020

Language

English

Publication/Series

Lund Reports on Atomic Physics

Document type

Dissertation

Publisher

Department of Physics, Lund University

Topic

  • Atom and Molecular Physics and Optics

Keywords

  • Attosecond
  • Photoionization
  • Interferometry

Status

Published

Supervisor

  • Anne L'huillier
  • Mathieu Gisselbrecht
  • Marcus Dahlström

ISBN/ISSN/Other

  • ISSN: 0281-2762
  • ISBN: 978-91-7895-559-6
  • ISBN: 978-91-7895-560-2

Defence date

1 January 1970

Defence time

00:59

Defence place

Lecture hall Rydbergsalen, Fysiska institutionen, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund. Join via Zoom: https://lu-se.zoom.us/j/64370769609?pwd=U3lqZms3ZVZyb3lOMGphQWFjbUdMZz09

Opponent

  • Lars Bojer Madsen (Prof.)