| Summary: | Electron-electron correlation, excitation and quantum interference are generally important in attosecond physics, especially for imaging of atoms and molecules. These are the main topics addressed in this thesis, in the context of laser-induced nonsequential double ionization (NSDI). Excitation is the most extensive topic of this work and is addressed within a rigorous, semi-analytic study of the recollision-excitation with subsequent tunneling ionization (RESI) mechanism in laser-induced nonsequential double ionization (NSDI). This is the most comprehensive study of this mechanism performed in the context of the strong-field approximation to the preset date. Subsequently, we investigate potential imaging applications, by computing electron momentum distributions of atoms and molecules. For atoms, we show that the RESI electron momentum distributions depends very critically on the bound state wave function. For molecules, we address the influence of the molecular orbital geometry and of the molecular alignment with respect to the laser-field polarization, by computing the electron momentum distributions of N2 and Li2. We show that the electron-momentum distributions exhibit interference maxima and minima, either due to the electron emission at spatially separated centers, or to the orbital geometry, such as nodes of the atomic wavefunction. In this latter case, we do not restrict ourself only to RESI, and we also compute the electron momentum distributions of N2 for electron-impact ionization, in which we also observe two-center interference patterns when the molecule is aligned along the laserfield polarization direction. The above-mentioned momentum constraints, together with the strong dependence of the distributions on the bound states involved, the molecular orbital geometry and the molecular alignment angle may be important for singling out the RESI mechanism in actual physical situations and using NSDI in ultra-fast imaging. In the final chapter, we present the first step taken by us in order to address the above-stated issues using an approach beyond the strong field approximation.
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