arXiv subjects

Agapi Emmanouilidou

Publications and source records attributed to Agapi Emmanouilidou.

29 records · Page 2Linked to original sources

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↗

arXiv2018

Multiple core hole formation by free-electron laser radiation in molecular nitrogen

We investigate the formation of multiple-core-hole states of molecular nitrogen interacting with a free-electron laser pulse. We obtain bound and continuum molecular orbitals in the single-center expansion scheme and use these orbitals to calculate photo-ionization and Auger decay rates. Using these rates, we compute the atomic ion yields generated in this interaction. We track the population of all states throughout this interaction and compute the proportion of the population which accesses different core-hole states. We also investigate the pulse parameters that favor the formation of these core-hole states for 525 eV and 1100 eV photons.

physics.atom-ph↗

arXiv2010

Prevalence of different double ionization pathways and traces of three-body collisions in strongly driven Helium

We present a unified treatment of the prevalence of different double ionization (DI) pathways as a function of the sum of the final electron energies in strongly driven Helium. We do so as a function of laser frequency and intensity. At small total energy a new DI pathway prevails where both electrons are ionized with a delay after re-collision. We find that three-body collisions between the two electrons and the nucleus underly this pathway--we refer to it as triple collision (TC) pathway. At high total energy the pathway that prevails is the one where one electron is ionized with a delay following re-collision---we refer to it as Delayed pathway. Asymptotic observables that trace the prevalence of the latter pathways are identified.

physics.atom-ph↗

arXiv2009

Intensity dependence of ionization mechanisms for infrared frequencies in the strong field double ionization of diatomic molecules

Using a three-dimensional quasiclassical technique we explore the double ionization pathways of a diatomic molecule driven by an intense infrared (800nm) ultrashort laser pulse. For intensities corresponding to the tunneling regime, we find that the three main ionization mechanisms have distinct traces when considering the sum of the momenta parallel to the laser field as a function of the inter-electronic angle of escape. In addition, we find that the previously observed "finger-like" structure in the correlated momenta of the strongly driven He is also present for strongly driven diatomic molecules. We show that it is mainly due to the strong interaction, backscattering, the recolliding electron undergoes from the remaining core.

physics.atom-ph↗

arXiv2007

Initial state dependence in multi-electron threshold ionization of atoms

It is shown that the geometry of multi-electron threshold ionization in atoms depends on the initial configuration of bound electrons. The reason for this behavior is found in the stability properties of the classical fixed point of the equations of motion for multiple threshold fragmentation. Specifically for three-electron break-up, apart from the symmetric triangular configuration also a break-up of lower symmetry in the form of a T-shape can occur, as we demonstrate by calculating triple photoionization for the lithium ground and first excited states. We predict the electron break-up geometry for threshold fragmentation experiments.

physics.atom-ph↗

arXiv2007

Total quadruple photoionization cross section of Beryllium in a quasiclassical framework

In a quasiclassical framework, we formulate the quadruple ionization by single photon absorption of the Coulomb five-body problem. We present the quadruple photoionization total cross section of the ground state of Beryllium for energies up to 620 eV. Our quasiclassical results for energies close to threshold are in agreement with the Wannier threshold law for four electron escape. In addition, the agreement of our results with a shape formula provides support for the overall shape of our total quadruple cross section. Finally, we find that the photon energy where the maximum of the total photoionization cross section occurs for single, double, triple and quadruple photoionization of H, He, Li and Be, respectively, seems to follow a linear relation with the threshold energy for complete break-up of the respective element.

physics.atom-ph↗

arXiv2007

Double energy differential cross sections for the Coulomb four-body problem in a quasiclassical framework

In a quasiclassical framework, we formulate the double energy differential cross sections for the Coulomb four-body problem. We present results for the triple photoionization from the Li ground state at 220.5, 115, 50 and 3.8 eV excess energies. With the energy of one of the electrons kept fixed, the double energy differential cross sections at 220.5 and 115 excess energies are found to be of "U-shape" (unequal energy sharing), with those at 115 eV being in very good agreement with ab-initio results. At 50 eV, it seems that a transition starts taking place to more equal energy sharing configurations. Close to threshold, at 3.8 eV excess energy, the equal energy sharing configurations are the dominant ones.

physics.atom-ph↗

arXiv2006

Attosecond time-scale multi-electron collisions in the Coulomb four-body problem: traces in classical probability densities

In the triple ionization of the Li ground state by single photon absorption the three electrons escape to the continuum mainly through two collision sequences with individual collisions separated by time intervals on the attosecond scale. We investigate the traces of these two collision sequences in the classical probability densities. We show that each collision sequence has characteristic phase space properties which distinguish it from the other. Classical probability densities are the closest analog to quantum mechanical densities allowing our results to be directly compared to quantum mechanical results.

physics.atom-ph↗

arXiv2006

The Coulomb four-body problem in a classical framework: Triple photoionization of lithium

Formulating a quasiclassical approach we determine the cross section for the complete four-body break-up of the lithium ground state following single photon absorption from threshold up to 220 eV excess energy. In addition, we develop a new classification scheme for three-electron ionizing trajectories in terms of electron-electron collisions, thereby identifying two main ionization paths which the three electrons in the ground state of lithium follow to escape to the continuum. The dominant escape paths manifest themselves in a characteristic ``T-shape'' break-up pattern of the three electrons which implies observable structures in the electronic angular correlation probability. This break-up pattern prevails for excess energies so low that the Wannier threshold law $σ\propto E^α$ describes already the triple ionization cross section, whose predicted value $α=2.16$ we can confirm quantitatively.

physics.atom-ph↗

arXiv2006

Triple photoionization of Lithium near threshold

Solving the full classical four-body Coulomb problem numerically using a Wigner initial distribution we formulate a classical-quantum hybrid approach to study triple ionization by single photon absorption from the Li ground state in the threshold region. We confirm the Wannier threshold law $σ\propto E^α$ and we show that the $α$ determined in the interval between 2-5 eV deviates from the analytical threshold value of 2.16 which we find in the interval between $0.1-2$ eV.

physics.atom-ph↗

arXiv2001

Floquet Scattering and Classical-Quantum correspondence in strong time periodic fields

We study the scattering of an electron from a one dimensional inverted Gaussian atomic potential in the presence of strong time periodic electric fields. Using Floquet theory, we construct the Floquet Scattering matrix in the Kramers-Henneberger frame. We compute the transmission coefficients as a function of electron incident energy and find that they display asymmetric Fano resonances due to the electron interaction with the driving field. We find that the Fano resonances are associated with zero-pole pairs of the Floquet Scattering matrix in the complex energy plane. Another way we "probe" the complex spectrum of the system is by computing the Wigner-Smith delay times. Finally we find that the eigenphases of the Floquet Scattering matrix undergo a number of "avoided crossings" as a function of electron Floquet energy that increases with increasing strength of the driving field. These "avoided crossings" appear to be quantum manifestations of the destruction of the constants of motion and the onset of chaos in classical phase space.

physics.atom-ph↗