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

Abstract

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.

High-order harmonic generation from molecular ions in the coherent electronic states

“…It shows that the whole second rescattering occurs after the envelope centre of the probe pulse as the white dashed line depicts, i.e., ∂I(t)/∂t < 0. Moreover, with the increase of t del , larger ionization probability of the 3dσ g state will contribute to the high nonlinear HHG process although the variation of the ionization potential is smaller [4]. So a stronger second rescattering at t del = 4.5 fs affects the HHG process shown in fig.…”

Transverse electron momentum distributions in strong-field ionization: nondipole and Coulomb focusing effects

“…However, only certain trajectories favor recollision and give birth to different strong-field processes. Even though, these models have proven to be successful for the qualitative description of the above-mentioned processes, the numerical modelling beyond these approximation is of utmost importance to properly account for the effect of Coulomb potential on the electron dynamics with a reasonable quantitative agreement.-Various theoretical approaches have been developed to treat the nondipole effects in both relativistic and non-relativistic strong field ionization for different targets and laser parameters [31][32][33][34][35][36]. In particular, to study the nondipole effects for the intense x-ray laser pulses, several nonrelativistic [37][38][39][40][41] and relativistic [42] approaches have been proposed.…”

Scaling relations of the time-dependent Dirac equation describing multiphoton ionization of hydrogenlike ions

“…These significant advances in the light-source technology have stimulated a considerable interest in the theoretical investigations of heavy one-electron ions exposed to electromagnetic radiation with extremely high frequencies and intensities. Many relativistic approaches for the description of the ion-laser interaction have been suggested recently [8][9][10][11][12][13][14][15][16][17][18][19][20]. They include simplified models based on the Coulomb-corrected relativistic strong-field approximation (SFA) [13,14] as well as various full-dimensional solutions of the time-dependent Dirac equation (TDDE) [8][9][10][11][12][15][16][17][18][19][20].…”

“…Many relativistic approaches for the description of the ion-laser interaction have been suggested recently [8][9][10][11][12][13][14][15][16][17][18][19][20]. They include simplified models based on the Coulomb-corrected relativistic strong-field approximation (SFA) [13,14] as well as various full-dimensional solutions of the time-dependent Dirac equation (TDDE) [8][9][10][11][12][15][16][17][18][19][20]. Some studies [9,11,12,15] treat the interaction of the ion with the electromagnetic field within the so-called dipole approximation where the spatial dependence of the vector potential is neglected.…”

“…The dipole approximation is a traditional approach for the infrared, visible, and ultraviolet light; in this frequency range it is usually well justified, since the wavelength exceeds by far the size of the ion. This is not necessarily the case for the hard X-ray radiation, and several attempts have been made to go beyond the dipole approximation taking into account the spatial properties of the laser pulse [8,10,[16][17][18][19][20]. If the photon energy and/or peak intensity of the laser pulse increase, the non-dipole effects become more and more important, eventually making the theoretical description beyond the dipole approximation mandatory.…”