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

Photoelectron jets and interference structures in ionization beyond dipole approximation: carrier- envelope phase effects and vortex streets

We have analyzed photoelectron jet formation in strong-field ionization using the hydrodynamic picture of quantum mechanics. We showed that von-Kármán-like vortex streets emerge in between jets in photoelectron momentum distributions. The spatial orientation of the jets can be controlled by tailoring the carrier-envelope phase of the driving laser pulse. This indicates that it is possible to experimentally measure emitted photoelectrons off the optical axis, which opens up new possibilities for high-frequency laser pulse diagnostics.

Symmetry breaking of Kramers-Henneberger atoms by ponderomotive force

It was believed that Kramers-Henneberger (KH) atoms in a linearly polarized superintense laser field exhibit the structure of "dichotomy." At large quiver amplitude, the two lowest-lying eigenstates are degenerated and both have a dichotomous symmetric structure. However, this is not a common structure for KH atoms because KH atoms practically can only exist in the focused laser field. However, in a focused laser, KH state electrons usually experience the ponderomotive force, which will lift the degeneracy and break the symmetry.

Multiphoton Ionization of One-Electron Relativistic Diatomic Quasimolecules in Strong Laser Fields

We perform a theoretical and computational study of relativistic one-electron homonuclear diatomic quasimolecules subject to strong electromagnetic fields linearly polarized along the molecular axis. Several quasimolecules with the nuclear charges 1-92 and appropriately scaled internuclear distances and field parameters are used in the calculations. The time-dependent Dirac equation is solved with the help of the generalized pseudospectral method in prolate spheroidal coordinates. We have found that employing this coordinate system makes it possible to avoid emergence of spurious states, which usually show up when solving the Dirac equation numerically. For lower carrier frequencies, interaction with the driving field is described within the dipole approximation. Relativistic effects in the multiphoton ionization probabilities are investigated with respect to the internuclear distance in the quasimolecule. For higher frequencies, the interaction with the field is described beyond the dipole approximation. Nondipole effects in the ionization probability are discussed.

Breakdown of the dipole approximation in strong-field ionization

We report the breakdown of the electric dipole approximation in the long-wavelength limit in strong-field ionization with linearly polarized few-cycle mid-infrared laser pulses at intensities on the order of 10¹³ W/cm². Photoelectron momentum distributions were recorded by velocity map imaging and projected onto the beam propagation axis. We observe an increasing shift of the peak of this projection opposite to the beam propagation direction with increasing laser intensities. From a comparison with semiclassical simulations, we identify the combined action of the magnetic field of the laser pulse and the Coulomb potential as the origin of our observations.