arXiv subjects

R. Taïeb

Publications and source records attributed to R. Taïeb.

8 recordsLinked to original sources

arXiv2026

Photoelectron interferometry with spectrally shaped polychromatic infrared pulses

Laser-assisted photoelectron interferometry is a cornerstone of attosecond science, first used to characterize attosecond pulse trains and later to study photoionization dynamics. Extending this method to spectrally shaped polychromatic infrared probe fields enables encoding of information across multiple interferometric pathways within the photoelectron spectrum. Here, we experimentally demonstrate laser-assisted photoelectron interferometry using a spectrally shaped polychromatic infrared probe field composed of five distinct spectral components forming a Golomb ruler in the frequency domain. The measured interferograms exhibit multiple beating frequencies that agree with theoretical calculations, demonstrating the simultaneous encoding of multiple laser-assisted quantum beats in a single measurement. A quantitative analysis of the beating amplitudes shows that the strongly modulated temporal profile of the polychromatic probe introduces intensity- and delay-dependent distortions of the quantum beats that cannot be explained by second-order perturbation theory. These results establish the conditions required for the quantitative interpretation of polychromatic photoelectron interferometry and highlight the opportunities offered by spectro-temporal engineering of the probe field for future developments in attosecond science.

physics.atom-ph↗

arXiv2025

Strong-field ionization in particle-in-cell simulations

The inclusion of the process of multiple ionization of atoms in high-intensity electromagnetic fields into particle-in-cell (PIC) codes applied to the simulation of laser-plasma interactions is a challenging task. In this paper, we first revisit ionization rates as given by the Perelomov-Popov-Terent'yev formulas within the paradigm of sequential tunnel ionization. We analyze the limit of validity and possible inconsistencies of this approach. We show that a strongly limiting factor to a precise description of ionization is the competing contribution of different sequential ionization processes. To solve this an algorithm is proposed that allows to find the dominant nonsequential path of tunnel ionization, and significantly improves the precision in simulations. This novel procedure is implemented in the PIC code SMILE, and includes the dependence of the ionization rates on the magnetic quantum number of the level. The sensitivity to variations in the ionization model is studied via full simulations of the ionization of an argon target by an incident high-intensity laser pulse. Finally, we analyze generalizations of the Perelomov-Popov-Terent'yev rate developed to describe the barrier suppression ionization in high fields and discuss the necessity and possibility of including these extensions in PIC simulations.

physics.plasm-ph↗

arXiv2023

Production of positronium chloride: A study of the charge exchange reaction between Ps and Cl$^{-}$

We present cross sections for the formation of positronium chloride (PsCl) in its ground state from the charge exchange between positronium (Ps) and chloride (Cl$^-$) in the range of 10 meV - 100 eV Ps energy. We have used theoretical models based on the first Born approximation in its three-body formulation. We simulated the collisions between Ps and Cl$^-$ using ab-initio methods at both mean-field and correlated levels extrapolated to the complete basis set limit. We have investigated Ps excited states up to ${n=4}$. The results suggest that the channel Ps(${n=2}$) is of particular interest for the production of PsCl in the ground state, and shows that an accurate treatment of the electronic correlation leads to a significant change in the global shape of the PsCl production cross section with respect to the mean-field level.

physics.chem-ph↗

arXiv2022

Phase-resolved attosecond near-threshold photoionization of molecular nitrogen

We photoionize nitrogen molecules with a train of extreme ultraviolet attosecond pulses together with a weak infrared field. We measure the phase of the two-color two-photon ionization transition (molecular phase) for different states of the ion. We observe a 0.76 $π$ shift for the electrons produced in the ionization channels leading to the X$^2 Σ_g^+$, $v'=1$ and $v'=2$ states. We relate this phase shift to the presence of a complex resonance in the continuum. By providing both a high spectral and temporal resolution, this general approach gives access to the evolution of extremely short lived states, which is hardly accessible otherwise.

physics.atom-ph↗

arXiv2019

Attosecond dynamics through a Fano resonance: Monitoring the birth of a photoelectron

Amplitude and phase of wavepackets encode the dynamics of quantum systems. However, the rapidity of electron dynamics on the attosecond timescale has precluded their complete measurement in the time domain. Here, we demonstrate that spectrally-resolved electron interferometry reveals the amplitude and phase of a photoelectron wavepacket created through a Fano autoionizing resonance in helium. Replicas obtained by two-photon transitions interfere with reference wavepackets formed through smooth continua, allowing the full temporal reconstruction, purely from experimental data, of the resonant wavepacket released in the continuum. This in turn resolves the buildup of the autoionizing resonance on attosecond timescale. Our results, in excellent agreement with ab initio time-dependent calculations, raise prospects for both detailed investigations of ultrafast photoemission dynamics governed by electron correlation, as well as coherent control over structured electron wave-packets.

physics.atom-ph↗

arXiv2017

Laser-induced distortion of structural interferences in high harmonic generation

We study theoretically the two-center interferences occurring in high harmonic generation from diatomic molecules. By solving the time-dependent Schroedinger equation, either numerically or with the molecular strong-field approximation, we show that the electron dynamics results in a strong spectral smoothing of the interference, depending on the value and sign of the driving laser field at recombination. Strikingly, the associated phase-jumps are in opposite directions for the short and long trajectories. In these conditions, the harmonic emission is not simply proportional to the recombination dipole any more. This has important consequences in high harmonic spectroscopy, e.g., for accessing the molecular-frame recombination dipole in amplitude and phase.

physics.optics↗

arXiv2012

Theory of attosecond delays in laser-assisted photoionization

We study the temporal aspects of laser-assisted extreme ultraviolet (XUV) photoionization using attosecond pulses of harmonic radiation. The aim of this paper is to establish the general form of the phase of the relevant transition amplitudes and to make the connection with the time-delays that have been recently measured in experiments. We find that the overall phase contains two distinct types of contributions: one is expressed in terms of the phase-shifts of the photoelectron continuum wavefunction while the other is linked to continuum--continuum transitions induced by the infrared (IR) laser probe. Our formalism applies to both kinds of measurements reported so far, namely the ones using attosecond pulse trains of XUV harmonics and the others based on the use of isolated attosecond pulses (streaking). The connection between the phases and the time-delays is established with the help of finite difference approximations to the energy derivatives of the phases. This makes clear that the observed time-delays is a sum of two components: a one-photon Wigner-like delay and an universal delay that originates from the probing process itself.

physics.atom-ph↗

arXiv2010

Probing single-photon ionization on the attosecond time scale

We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the $3s^2$ and from the $3p^6$ shell, at different excitation energies ranging from 32 to 42 eV. The determination of single photoemission time delays requires to take into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using an universal formula and is found to account for a substantial fraction of the measured delay.

physics.atom-ph↗