Stabilization of helium in intense xuv laser fields.

We investigate the impact of electron-electron correlation on the ionization dynamics of helium in intense, high-frequency laser fields by solving the time-dependent Schrödinger equation from first principles. Although we observe a decrease in the total ionization yield at high field strengths, the hallmark of atomic stabilization, the repulsion between the electrons has a detrimental effect on the degree of stabilization, in particular for short pulses. Investigation of the ion channel yields reveals that the double ionization process is less prone to two-electron effects, and consequently exhibits the most distinct signature of stabilization. We also find that commonly used one-dimensional models tend to overestimate the effect of correlation.

Nondipole ionization dynamics of atoms in superintense high-frequency attosecond pulses.

The ionization of H(1s) in superintense, high-frequency, attosecond pulses is studied beyond the dipole approximation. We identify a unique nondipole 3rd lobe in the angular distribution of the ejected electron and show that this lobe has a well-defined classical counterpart. The ionization is likely to occur in the direction opposite to the laser propagation direction, which is fully understood from an analysis of the classical dynamics.

Strong orientation effects in ionization of H+2 by short, intense, high-frequency light pulses.

We present three-dimensional time-dependent calculations of ionization of arbitrarily spatially oriented H+2 by attosecond, intense, high-frequency laser fields. The ionization probability shows a strong dependence on both the internuclear distance and the relative orientation between the laser field and the internuclear axis. The physical features are explained in terms of two-center interference effects.

Exact nondipole Kramers-Henneberger form of the light-atom hamiltonian: an application to atomic stabilization and photoelectron energy spectra.

The exact nondipole minimal-coupling Hamiltonian for an atom interacting with an explicitly time- and space-dependent laser field is transformed into the rest frame of a classical free electron in the laser field, i.e., into the Kramers-Henneberger frame. The new form of the Hamiltonian is used to study nondipole effects in the high-intensity, high-frequency regime. Fully three-dimensional nondipole ab initio wave packet calculations show that the ionization probability may decrease for increasing field strength. We identify a unique signature for the onset of this dynamical stabilization effect in the photoelectron spectrum.