Correlated electron dynamics in ultrashort intense and multi-color laser fields

Electronic dynamics occurs on timescales between attoseconds (10 -18 s) and femtoseconds (10 -15 s). Although proceeding inside microscopic objects such as atoms, small molecules, clusters, biological molecules and nanostructures it defines substantially macroscopically observable effects. Electronic motion in atoms may lead to the emission of visible, ultraviolet or x-ray light; in molecules, electronic dynamics can be seen in charge transfer processes, changing chemical composition or being responsible for transporting bioinformation. To measure and even control electronic dynamics requires techniques on the same time scale. Today, electronic dynamics can be observed using either ultrashort ultraviolet light pulses (attosecond pulses) or intense few-cycle infrared laser fields. In this project, the focus is set on the interaction of intense laser fields with atoms and molecules with two active electrons such that effects of electron correlation are taken into account. The two main processes of the interaction with quantum systems in intense laser fields are excitation and ionization of the systems. Part I of the project is concentrated on driving and controlling bound electronic dynamics in molecules with and without curve crossings in the electronic structure with the constraint to keep ionization at a low level. Particularly, the systems of consideration involve correlated electronic dynamics. The motion of two electrons in intense fields is not decoupled. We will examine how the presence of a second electron affects the efficiency with which electronic motion can be steered. Part II is dealing with electronic dynamics during interaction with ultrashort, intense, high-frequency laser fields, as provided by novel last-generation light sources (free electron lasers FEL and XFEL). For a window of frequencies and intensities, such pulses lead to a suppression of ionization, or a "stabilization of the atom". We will analyze the ionization behavior of atoms and molecules in such fields focusing on the issue how correlations between electrons influence the ionization (or the stability against ionization), and how stabilization in molecular systems manifests itself.