The single ionization of noble gas atoms by an attosecond pulse train assisted by an infrared laser field is theoretically investigated by means of a non-perturbative model that under certain approximations gives closed-form expressions for the angular distributions of photoelectrons. A very good agreement between our predictions and experiments is observed. Interestingly, our model allow us to interpret these angular distributions as two-center interferences where the separation between centers is governed by the infrared laser field. Finally, we provide a physical interpretation for the analogy of the two-center interferences.

Angularly resolved two-photon single ionization yields of helium resulting after the interaction with an ultrashort XUV pulse are obtained by numerically solving the full dimension time-dependent Schrödinger equation. The angular distributions reveal the underlying dominant mechanism, which depends on the effective photon energy absorbed and the pulse parameters. We specifically explore the contributions of radial and angular electron correlation terms. A single active electron picture is a qualitatively valid approach for the lowest photon energies, even in the above threshold ionization (ATI) region. Nonetheless, angular correlation plays a detectable role in the low energy region and a major role at higher energies when autoionizing states are populated. As the photon energy increases, sequential ionization-excitation dominates, therefore, the resulting probability distributions are explained as the result of two active uncorrelated electrons. This uncorrelated picture fails again for photon energies above ionization potential of the ion.

We study theoretically the photoionization of water molecules by monochromatic and linearly polarized radiation. The final state wavefunctions are given by coulomb continuum wavefunctions and the water molecule bound states are represented using linear combinations of Slater-type orbitals located on the centers of the molecule. We obtain total and differential cross sections. We compare them with more elaborated theoretical results and experiments obtaining a very good agreement in particular at enough high energies where there is a lack of predictions. We put in evidence three-center interference effects not only the total cross sections, but also show that these effects may be detected in a direct way in the angular distributions of photoelectrons corresponding to randomly oriented molecules. In particular, we find that the interference effects under certain conditions may provoke a partial suppression of the emission of photoelectrons in the classical direction given by the polarization vector.