High-order harmonic generation by H$_2^+$ in super-intense xuv ultrashort laser pulses

Abstract

Dynamics of the two-dimensional H + 2 under 30-and 40-cycle xuv (45 and 90 nm) laser pulses is investigated by numerical solution of the time-dependent Schrödinger equation beyond the dipole and Born-Oppenheimer approximations for two orientations (θ = 0 • and θ = 90 • referenced to the molecular axis) of the laser polarization. Dynamics of the electron and nuclei are treated in quantum and classical approaches, respectively. The ground, first and second excited states of H + 2 are considered as initial states for different laser field intensities in the range of (4×10 16 -4×10 19 W cm −2 ). For parallel orientation (θ = 0 • ), a negligibly small difference is seen for high-order harmonic generation (HOHG) spectra obtained with the dipole and non-dipole Hamiltonians for all three electronic states. While, for the perpendicular orientation (θ = 90 • ), non-dipole forces attenuate the HOHG spectra for the initial ground and the second excited states. For the initial first excited state and orientation θ = 90 • , the motion of nuclei considerably increases the HOHG yield within the dipole approximation, but decreases it partially beyond dipole approximation. It is shown that contribution of the motion of nuclei to the HOHG yield depends on the extent of the increase in the separation between nuclei.

High harmonic generation from pre-ionized H2in ultrashort intense laser fields

“…In the present study, we have focused on pre-ionization regions. In the next steps of this series of works, we will work on the ionized regions of the H 2 system, and investigate their contributions to the overall HHG structure [29].…”

“…The effect of the motion of nuclei on this evolution and its consequent HHG are investigated semiclassically. In this report and in the following work [29], effects of the intensity and frequency of the laser pulse on the H 2 -ultrashort laser pulse interaction are investigated in order to develop a realistic setup for prospective time-resolved experiments on two-electron systems exposed to ultrashort laser pulses.…”