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Abstract

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 Q_n 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.