Two-photon double ionization of atoms in attosecond x-ray radiation fields

Journal Article · Tue Jun 15 04:00:00 EDT 2010 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.81.063424· OSTI ID:21437933

Chuluunbaatar, Ochbadrakh; Bachau, Henri; Popov, Yuri V; Piraux, Bernard; Stefanska, Kamila ^[1]

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1. Joint Institute for Nuclear Research, Dubna, Moscow region 141980 (Russian Federation)

We consider two-photon double ionization of helium with 100, 200, and 400 eV excess energy for the two ejected electrons, corresponding to photon energies of 89.5, 139.5, and 239.5 eV, respectively. We focus on the case of ultrashort pulses (two oscillations of the field) and develop an approach to calculate the two-photon transition matrix elements within the lowest order of the time-dependent perturbation theory. One of the major difficulties in calculating such amplitudes is the infinite summation over a complete set of intermediate states. In the subfemtosecond regime, however, this summation can be performed accurately by means of the closure approximation. This results in a simple expression for the two-photon amplitude that contains a dipole term and a quadrupole term. The dipole term can be clearly associated to a process in which each electron absorbs a photon whereas the quadrupole term is associated to a process in which one electron absorbs two photons and ejects the second one by collision. We analyze in detail how the relative weight of both processes influences the behavior of the electron energy and angular distributions. In particular we study how the shape of these distributions changes with the amount of electron correlations taken into account in both initial and final states. For 100 eV excess energy, our results for the electron energy distribution are compared with those obtained by solving the time-dependent Schroedinger equation. All these results unveil the crucial role of electron correlations in this transient regime of ionization which is neither sequential nor direct.

• OSTI ID: 21437933
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 6 Vol. 81; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
AMPLITUDES
ANGULAR DISTRIBUTION
APPROXIMATIONS
ATOM COLLISIONS
ATOMS
BOSONS
CALCULATION METHODS
COLLISIONS
CORRELATIONS
DIFFERENTIAL EQUATIONS
DIPOLES
DISTRIBUTION
ELECTROMAGNETIC RADIATION
ELECTRON CORRELATION
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY RANGE
ENERGY SPECTRA
EQUATIONS
EV RANGE
FERMIONS
FLUIDS
GASES
HELIUM
IONIZATION
IONIZING RADIATIONS
LEPTONS
MASSLESS PARTICLES
MATRIX ELEMENTS
MULTIPOLES
NONMETALS
PARTIAL DIFFERENTIAL EQUATIONS
PERTURBATION THEORY
PHOTON COLLISIONS
PHOTON-ATOM COLLISIONS
PHOTONS
RADIATIONS
RARE GASES
SCHROEDINGER EQUATION
SPECTRA
TIME DEPENDENCE
WAVE EQUATIONS
X RADIATION