arXiv subjects

Georgios Petros Katsoulis

Publications and source records attributed to Georgios Petros Katsoulis.

10 recordsLinked to original sources

arXiv2026

Enhanced nondipole momentum offsets in triple ionization of atoms driven by mid-infrared laser fields

We investigate the dependence on wavelength of nondipole effects in triple ionization of Ne driven by intense infrared and mid-infrared laser pulses using a three-dimensional semiclassical model that fully accounts for nondipole effects and the Coulomb singularity in the electron-core interaction. We find in triple ionization of strongly driven Ne a large positive average momentum offset along the direction of laser propagation, which vanishes in the dipole approximation. This positive momentum offset significantly increases with increasing wavelength of the laser pulse. This increase is present for all triple ionization events as well as for the main direct and delayed pathways of triple ionization. We attribute the increase of the momentum offset to the contribution of the effect of the magnetic field of the laser pulse on the bound electrons. This contribution counterbalances the decrease of electron-electron correlation in recollisions with increasing wavelength. We find that 1200 nm is an ideal wavelength for experimentally measuring the momentum offset related to correlated three-electron escape.

physics.atom-ph↗

arXiv2026

Extracting inter-nuclear distances in the oxygen molecule interacting with an XFEL-pulse: a fundamental system for understanding Coulomb explosion imaging

We investigate the interaction of O$_{2}$ with an X-ray Free Electron laser (XFEL) pulse of short duration. We consider a photon energy of 570 eV, which allows for the formation of molecular states with up to two core holes. We compute the sum of the final kinetic energies, i.e. the kinetic energy release (KER) of the atomic fragments for different fragmentation channels. We demonstrate that with the knowledge of the potential energy curves the equilibrium inter-nuclear distance of O$_{2}$ is best extracted from the O$^{+}$+O$^{+}$ channel and not from higher-charged channels such as O$^{2+}$+O$^{2+}$. This challenges our current understanding of Coulomb explosion imaging, where from just applying quasi-classical dynamics one expects that the equilibrium inter-nuclear distance of molecules is best extracted from higher-charged fragmentation channels. On the other hand, we show that the KER of the O$^{+}$+O$^{+}$ channel is inconsistent with the one obtained by just calculating the Coulomb repulsion of the atomic fragments resulting from molecular dissociation.

physics.atom-ph↗

arXiv2026

Multielectron ionization in O$_2^+$ driven by intense infrared laser pulses

We extend a recently developed three-dimensional semiclassical model [\href{https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.033106}{Phys. Rev. \textbf{A} 109, 033106 (2024)}] to study multielectron ionization and the formation of highly excited Rydberg states in O$_{2}^+$ driven by intense infrared laser pulses. Our model fully accounts for the Coulomb interaction between all particles, except for the Coulomb repulsion between bound electrons which is replaced by effective potentials. This replacement overcomes the hurdle of artificial autoinization. In addition, the multielectron motion is treated on an equal footing with nuclear motion, that is, electrons and nuclei are both allowed to move at the same time. We focus on triple and double ionization as well as frustrated triple and double ionization. For these processes, we identify and explain the main features of the sum of the kinetic energies of the final ion fragments resulting from the break-up of O$_{2}^+$. We also describe a physical mechanism that underlies frustrated triple ionization.

physics.atom-ph↗

arXiv2025

Multielectron ionization of three-electron strongly driven Ne at high intensities

We extend a recently developed three-dimensional semiclassical model to study double and triple ionization of Ne driven by infrared laser pulses at various intensities. This model fully accounts for the Coulomb singularity of each electron with the core, as well as for the interaction of a recolliding electron with a bound electron. The model avoids artificial autoionization by employing effective Coulomb potentials to describe the interaction between bound electrons. Using the extended effective-Coulomb-potential for bound-bound electrons (ECBB) model, we compute triple and double ionization spectra. For instance, we compute the distributions of the sum of the final momenta along the laser field of the escaping electrons. Taking focal volume averaging into account, we find very good agreement with experimental results, particularly for triple ionization. Also, we identify the main pathways of triple and double ionization and explain how these pathways give rise to the main features of the triple and double ionization spectra.

physics.atom-ph↗

arXiv2023

A general model and toolkit for the ionization of three or more electrons in strongly driven molecules using an effective Coulomb potential for the interaction between bound electrons

We formulate a general three-dimensional semiclassical model for the study of correlated multielectron escape during fragmentation of molecules driven by intense infrared laser pulses, while fully accounting for the magnetic field of the laser pulse. We do so in the context of triple ionization of strongly driven HeH$_{2}^{+}$. Our model fully accounts for the singularity in the Coulomb potentials of a recolliding electron with the core and a bound electron with the core as well as for the interaction of a recolliding with a bound electron. To avoid artificial autoionization, our model employs effective potentials to treat the interaction between bound electrons. We focus on triple and double ionization as well as frustrated triple and frustrated double ionization. In these processes, we identify and explain the main features of the sum of the kinetic energies of the final ion fragments. We find that frustrated double ionization is a major ionization process, and we identify the different channels and hence different final fragments that are obtained through frustrated double ionization. Also, we discuss the differences between frustrated double and triple ionization.

physics.atom-ph↗

arXiv2023

Nondipole electron momentum offset as a probe of correlated three electron ionization in strongly driven atoms

We employ a recently developed three-dimensional semiclassical model to identify nondipole effects in triple ionization of Ne driven by infrared laser pulses at intensities where electron-electron correlation prevails. This model fully accounts for the Coulomb interaction of each electron with the core and avoids artificial autoionization by employing effective Coulomb potentials to describe the interaction between bound electrons (ECBB). Using the ECBB model, we identify a prominent signature of nondipole effects. Namely, the component along the direction of light propagation of the average sum of the final electron momenta is large and positive. That is, we identify a positive momentum offset, absent in the dipole approximation. We find that this positive momentum offset stems mostly from the momentum change due to the magnetic field. To further understand this momentum change, we also develop a simple model for the motion of an electron inside an electromagnetic field. This simple model accounts for the effect of the Coulomb forces only as a sharp change in the momentum of the electron during recollision. We show that the momentum change due to the magnetic field is related with the sharp change in momentum during recollision for the recolliding electron as well as with the time of recollision for both the recolliding and bound electrons. Hence, we demonstrate that the final electron momentum offset probes the strength of a recollision and hence the degree of correlation in multielectron ionization.

physics.atom-ph↗

arXiv2023

Singularity in electron-core potential as a gateway to accurate multi-electron ionization spectra in strongly driven atoms

We demonstrate a general three-dimensional semiclassical model as a powerful technique for the study of correlated multi-electron escape in atoms driven by infrared laser pulses at intensities where electron-electron correlation prevails. We do so in the context of triple ionization of strongly driven Ne. We show that a drawback of other current quantum mechanical and classical models of triple ionization is that they soften the Coulomb potential of each electron with the core. The model we employ fully accounts for the singularity in the Coulomb potentials of a recolliding electron with the core and a bound electron with the core as well as for the interaction of a recolliding with a bound electron. Our model treats approximately only the interaction between bound electrons through the use of effective potentials. These effective potentials ensure that no artificial autoionization takes place as a result of the full treatment of the electron-core potential. We demonstrate the accuracy of our model by obtaining triple ionization distributions of the sum of the final electron momenta which we find to be in very good agreement with experiments. Also, we explain the main features of these momenta distributions in terms of the prevalent pathways of correlated three-electron escape in Ne. We also show that the different ionization pathways prevailing in three-electron escape in strongly driven Ne versus Ar give rise to different momenta distributions in these two atoms.

physics.atom-ph↗

arXiv2020

Signatures of magnetic field effects in non-sequential double ionization manifesting as back-scattering for molecules versus forward-scattering for atoms

For two-electron diatomic molecules, we investigate magnetic field effects in non-sequential double ionization where recollisions prevail. We do so by formulating a three-dimensional semi-classical model that fully accounts for the Coulomb singularities and for magnetic field effects during time propagation. Using this model, we identify a prominent signature of non-dipole effects. Namely, we demonstrate that the recolliding electron back-scatters along the direction of light propagation. Hence, this electron escapes opposite to the direction of change in momentum due to the magnetic field. This is in striking contrast to strongly-driven atoms where the recolliding electron forward-scatters along the direction of light propagation. We attribute these distinct signatures to the different gate that the magnetic field creates jointly with a soft recollision in molecules compared to a hard recollision in atoms. These two different gates give rise, shortly before recollision, to different momenta and positions of the recolliding electron along the direction of light propagation. As a result, we show that the Coulomb forces from the nuclei act to back-scatter the recolliding electron in molecules and forward-scatter it in atoms along the direction of light propagation.

physics.atom-ph↗

arXiv2020

Enhancing frustrated double ionisation with no electronic correlation in triatomic molecules using counter-rotating two-color circular laser fields

We demonstrate significant enhancement of frustrated double ionization (FDI) in the two-electron triatomic molecule D$_{3}^{+}$ when driven by counter-rotating two-color circular (CRTC) laser fields. We employ a three-dimensional semiclassical model that fully accounts for electron and nuclear motion in strong fields. For different pairs of wavelengths, we compute the probabilities of the FDI pathways as a function of the ratio of the two field-strengths. We identify a pathway of frustrated double ionization that is not present in strongly-driven molecules with linear fields. In this pathway the first ionization step is "frustrated" and electronic correlation is essentially absent. This pathway is responsible for enhancing frustrated double ionization with CRTC fields. We also employ a simple model that predicts many of the main features of the probabilities of the FDI pathways as a function of the ratio of the two field-strengths.

physics.atom-ph↗

arXiv2019

Fingerprints of slingshot non-sequential double ionization on two-electron probability distributions

We study double ionization of He driven by a near-single-cycle laser pulse at low intensities at 400 nm. Using a three-dimensional semiclassical model, we identify the pathways that prevail non-sequential double ionization (NSDI). We focus mostly on the delayed pathway, where one electron ionizes with a time-delay after recollision. We have recently shown that the mechanism that prevails the delayed pathway depends on intensity. For low intensities slingshot-NSDI is the mechanism that prevails. Here, we identify the differences in two-electron probability distributions of the prevailing NSDI pathways. This allows us to identify properties of the two-electron escape and thus gain significant insight into slingshot-NSDI. Interestingly, we find that an observable fingerprint of slingshot-NSDI is the two electrons escaping with large and roughly equal energies.

physics.atom-ph↗