The calculation of photoelectron spectra (PES) in the field of strong laser-matter interaction is a great challenge for theoretical physics. For several decades now the strong-field approximation (SFA) has proven to be quite successful in that respect. Additionally, thanks to its formulation in terms of quantum trajectories, it provides deep insight into the dynamics of the ionization process. However, in the plain SFA the influence of the Coulomb potential on the emitted electron is neglected. With more and more sophisticated experimental techniques this approximation leads to more and more features being missed by the SFA even on a qualitative level.
In this work we investigate different extensions of that theory to analyze spectral features beyond the scope of the plain SFA. We consider different systems where additional forces influence the emitted electron. The collective field of a laser-driven metal cluster is observed to cause strong acceleration of emitted electrons near resonance. The Coulomb potential of the parent ion can for certain parameters lead to unexpectedly high yield around the cutoff energy for direct ionization. And finally the magnetic Lorentz force which appears when dropping the dipole approximation can cause asymmetries with respect to the laser propagation direction even for non-relativistic laser parameters.
Appropriate methods are derived for each of these systems and used to calculate PES. The results are compared on a qualitative level to the time-dependent Schrödinger equation or reference results from the literature and analyzed in terms of quantum trajectories which allow us to understand the underlying physical mechanisms leading to the effects under consideration.