Intra- and intercycle interference of electron emissions in laser-assisted XUV atomic ionization

Abstract

We study the ionization of atomic hydrogen in the direction of polarization due to a linearly polarized XUV pulse in the presence a strong field IR. We describe the photoelectron spectra as an interference problem in the time domain. Electron trajectories steming from different optical laser cycles give rise to intercycle interference energy peaks known as sidebands. These sidebands are modulated by a grosser structure coming from the intracycle interference of the two electron trajectories born during the same optical cycle. We make use of a simple semiclassical model which offers the possibility to establish a connection between emission times and the photoelectron kinetic energy. We compare the semiclassical predictions with the continuum-distorted wave strong field approximation and the ab initio solution of the time dependent Schrödinger equation. We analyze such interference pattern as a function of the time delay between the IR and XUV pulse and also as a function of the laser intensity.

Electron emission perpendicular to the polarization direction in laser-assisted XUV atomic ionization

“…However, Bivona et al envisaged non-zero emission for XUV ionization of hydrogen by short intense pulses [33]. Therefore, in the present paper, we extend our previous work [34] for LAPE from H(1s) to study the emission in the direction perpendicular to the polarization axis of both XUV and laser fields. In contrast to the case of forward emission, we find that transversal emission has relatively low probabilities, i.e., the PE energy range is highly reduced.…”

“…(19) which gives the positions of the different sidebands. We see that the energy difference between two consecutive sidebands is 2ω L and not ω L as for the emission in the direction parallel to the polarization axis [34]. From Eq.…”

“…(13)] giving rise to destructive interference between the contribution of the two electron trajectories of the first half cycle with the corresponding to the second half cycle of every optical cycle during the time interval that the XUV pulse is on. Contrarily, for emissions in the parallel direction, whereas the ionization during one of the two half cycles contributes to emissions in one direction (forward or backward), the other half cycle will contribute to the opposite direction [34]. Therefore, no interference is produced for parallel emissions allowing to all peaks separated by ω L .…”

“…A quick analysis of equations (8) and (9) indicates that the periodicity for the solution of Eq. (9) is π/ω L , which is half of that corresponding to the parallel emission case [34]. Therefore, the sum over the emission times can be performed alternatively over 2N half cycles with two emission times in each of them.…”

“…In the present work, we restrict the photoelectron momentum k = k zẑ + k ρρ (in cylindrical coordinates) to the direction perpendicular to the polarization axis, i.e., k z = 0 and k ρ ≥ 0. The case of emission parallel to the polarization axis, i.e., k ρ = 0, was studied recently in [34].…”