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Theoretical and Experimental Studies of XUV Multielectron (Auto-)Ionization Dynamics in Helium and Molecular Hydrogen


Borisova,  Gergana Dimitrova
Division Prof. Dr. Thomas Pfeifer, MPI for Nuclear Physics, Max Planck Society;

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Borisova, G. D. (2017). Theoretical and Experimental Studies of XUV Multielectron (Auto-)Ionization Dynamics in Helium and Molecular Hydrogen. Master Thesis, Ruprecht-Karls-Universität, Heidelberg.

This work consists of two parts: theoretical studies of laser-intensity dependent ionization processes in the helium atom and experimental attosecond transient-absorption spectroscopy studies of the (auto-)ionization dynamics of the Qn resonances of molecular hydrogen. In an experiment, motivating the simulations of ionization processes in helium, abrupt ionization of doubly excited states above a certain critical NIR-laser intensity was observed. Numerically solving the quantum-mechanical one-dimensional time-dependent Schrödinger equation for two electrons, the time-dependent population of relevant atomic states during the laser-pulse interaction is directly accessed. With respect to the theoretical results, an ionization mechanism for the doubly excited states is suggested, where non-sequential double ionization, arising due to electron– electron interaction, plays an important role. The investigations of the (auto-)ionization processes of doubly excited states in the hydrogen molecule concentrated on measuring timeand energy-dependent XUV absorption signals to separate the autoionization effects from the overall continuum absorption of H2. First results of (auto-)ionization effects in the hydrogen molecule were obtained in a technically challenging absorption spectroscopy study.