Two-photon double ionization of helium in the region of photon energies 42-50 eV

We report the total integrated cross-section (TICS) of two-photon double ionization of helium in the photon energy range from 42 to 50 eV. Our computational procedure relies on a numerical solution of the time-dependent Schr\"odinger equation on a square-integrable basis and subsequent projection of this solution on a set of final states describing two electrons in continuum. Close to the threshold, we reproduce results previously known from the literature. The region 47-50 eV seems to have been previously unexplored. Our results suggest that TICS, as a function of the photon energy, grows monotonously in the region 42-50 eV. We also present fully resolved triple differential cross sections for selected photon energies.Comment: 12 pages, 3 figure

MURE : MCNP Utility for Reactor Evolution - Description of the methods, first applications and results

PACSInternational audienc

Molten salt reactors and possible scenarios for future nuclear power deployment

PAC

Accurate numerical method for the calculation of doubly excited states in atoms

We report in this paper computed values of the energy positions and widths of the lowest 1Po singlet doubly excited states of the helium atom. The results are obtained by a direct numerical solution of the time-independent Schrödinger equation using a discretization technique with B-spline functions combined with complex rotation method. The present approach has the numerical advantage to generate accurate energy positions and widths in a single calculation. The computed data are in very good agreement with results from other theoretical approaches. Nous reportons dans cet article nos résultats concernant les positions et largeurs énergétiques des états singulets doublement excités de symétrie 1Po de l’atome d’hélium. Nos résultats sont obtenus par la résolution numérique directe de l’équation de Schrödinger indépendante du temps avec une technique de discrétisation basée sur les fonctions B-splines avec une méthode de rotation complexe. Notre méthode numérique a pour avantage de générer de façon très précise les positions et largeurs énergétiques en un seul calcul. Nos résultats sont en très bon accord avec les résultats issus d’autres approches théoriques.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Dynamics of two-photon double-ionization of helium at the attosecond scale

We study two-photon double ionization of helium. We demonstrate that attosecond pulses can be used to probe in the time-domain the electron dynamics within the atom. The interaction of helium with attosecond pulses whose duration is close to the correlation time provides information about the relaxation of the residual ion after the first electron ejection. Here, we show that such interaction of attosecond pulses with helium also modifies the double ionization probability in a non-trivial way. We examine the situations where sequential double ionization is permitted (omega >= 2 au) and where only the direct two-photon double ionization is allowed (omega < 2 au). All the calculations rely on both a model and the numerical solution of the time-dependent Schrodinger equation in its full dimensionality

Probing electron-electron correlation with attosecond pulses

We study two-photon double ionization of helium in its ground state at sufficiently low laser intensities so that three and more photon absorptions are negligible. In the regime where sequential ionization dominates, the two-photon double ionization one-electron energy spectrum exhibits a well defined double peak structure directly related to the electron-electron correlation in the ground state. We demonstrate that when helium is exposed to subfemtosecond or attosecond pulses, both peaks move and their displacement is a signature of the time needed by the He+ orbital to relax after the ejection of the first electron. This result rests on the numerical solution of the corresponding non-relativistic time-dependent Schrodinger equation

The helium atom and helium-like ions' interaction with XFEL radiation

We study double electron ejection with one- and two-photon absorption in He and He-like ions. We use two different numerical methods aimed at solving the time-dependent Schro "dinger equation for two-active electron systems interacting with a strong and short XUV laser pulse. The two approaches, which are relevant to the Configuration Interaction (CI) method, are based on an expansion of the wave function on either B-splines or Sturmian functions for the radial part and bipolar spherical harmonics for the angular part. We treat first double electron ejection with one photon in helium. Then the case of double electron ejection with two photons is studied along the isoelectronic series of He. We calculate the total probabilities for double ionization as well as the energy distribution of the electrons in the double continuum. Emphasis will be put on the role of the correlations along the He isoelectronic series. The pertinence of the distinction between direct and independent-particle (sequential) models for double ionization will be discussed in the context of short pulses

MURE : MCNP Utility for Reactor Evolution - Description of the methods, first applications and results

PACSInternational audienc