• Alternative gauge for the description of the light-matter interaction in a relativistic framework 

      Selstø, Sølve; Kjellsson, Tor; Lindroth, Eva; Simonsen, Aleksander; Førre, Morten (Peer reviewed; Journal article, 2017-08)
      We present a generalized velocity gauge form of the relativistic laser-matter interaction. In comparison with the (equivalent) regular minimal coupling description, this form of light-matter interaction results in superior ...
    • Breakdown of the nonrelativistic approximation in superintense laser-matter interactions 

      Førre, Morten (Peer reviewed; Journal article, 2019)
      We study the breakdown of the nonrelativistic approximation in the multiphoton ionization of atomic hydrogen by some intense x-ray laser pulse, in a regime where the dipole approximation is no longer valid. To this end, ...
    • Direct two-photon double ionization of H2 

      Simonsen, A. S.; Sørngård, Stian Astad; Nepstad, Raymond; Førre, Morten (Peer reviewed; Journal article, 2012-06-05)
      We have studied the process of direct (nonsequential) two-photon double ionization of molecular hydrogen (H2). Solving the time-dependent Schr¨odinger equation by an ab initio method, total (generalized) and singledifferential ...
    • Femtosecond-pulse-train ionization of Rydberg wave packets 

      Simonsen, Sigrid Ina; Sørngård, Stian Astad; Førre, Morten; Hansen, Jan Petter (Peer reviewed; Journal article, 2012-10-09)
      We calculate, based on first-order perturbation theory, the total and differential ionization probabilities from a dynamic periodic Rydberg wave packet of a given n-shell exposed to a train of femtosecond laser pulses. The ...
    • Ionization dynamics beyond the dipole approximation induced by the pulse envelope 

      Simonsen, Aleksander; Kjellsson, Tor; Førre, Morten; Lindroth, Eva; Selstø, Sølve (Peer reviewed; Journal article, 2016-05)
      When atoms and molecules are ionized by laser pulses of finite duration and increasingly high intensities, the validity of the much-used dipole approximation, in which the spatial dependence and magnetic component of the ...
    • Multiphoton ionization and stabilization of helium in superintense xuv fields 

      Sørngård, Stian Astad; Askeland, Sigurd; Nepstad, Raymond; Førre, Morten (Peer reviewed; Journal article, 2011)
      Multiphoton ionization of helium is investigated in the superintense field regime, with particular emphasis on the role of the electron-electron interaction in the ionization and stabilization dynamics. To accomplish this, ...
    • Probing two-center interference in H2+ using chirped pulses 

      Askeland, Sigurd; Førre, Morten (Peer reviewed; Journal article, 2013)
      The influence of intermediate resonant dissociative channels in the few-photon ionization dynamics of H+2 is demonstrated in a pump-probe scenario. Two-photon ionization of H+2 by two sequentially applied pump and probe ...
    • Semirelativistic Schrödinger Equation for Relativistic Laser-Matter Interactions 

      Kjellsson Lindblom, Tor; Førre, Morten; Lindroth, Eva; Selstø, Sølve (Peer reviewed; Journal article, 2018-12)
      A semirelativistic formulation of light-matter interaction is derived using the so called propagation gauge and the relativistic mass shift. We show that relativistic effects induced by a superintense laser field can, to ...
    • Stabilization of circular Rydberg atoms by circularly polarized infrared laser fields 

      Askeland, Sigurd; Sørngård, Stian Astad; Pilskog, Ingjald; Nepstad, Raymond; Førre, Morten (Peer reviewed; Journal article, 2011-09-29)
      The ionization dynamics of circular Rydberg states in strong circularly polarized infrared (800 nm) laser fields is studied by means of numerical simulations with the time-dependent Schr¨odinger equation. We find that at ...
    • Two-photon double ionization of helium by attosecond laser pulses: Evidence of highly correlated electron motion 

      Askeland, Sigurd; Nepstad, Raymond; Førre, Morten (Peer reviewed; Journal article, 2012)
      We apply a recently developed ab initio numerical framework to investigate the angular distributions of the emitted electrons in the immediate proximity of the threshold for the two-photon double ionization of helium. ...