Dynamics of multiply charged ions in intense laser fields

S. X. Hu and C. H. Keitel
Phys. Rev. A 63, 053402 – Published 10 April 2001
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Abstract

We numerically investigate the dynamics of multiply charged hydrogenic ions in near-optical linearly polarized laser fields with intensities of order 10161017W/cm2. The weakly relativistic interaction is appropriately described by the Hamiltonian arising from the expansion of the Dirac equation up to the second order in the ratio of the electron velocity v and the speed of light c. Depending on the charge state Z of the ion, the relation of strength between laser field and ionic core changes. We find around Z=12, typical multiphoton dynamics and for Z=3 tunneling behavior, however, with clear relativistic signatures. In first order in v/c the magnetic field component of the laser field induces a Z dependent drift in the laser propagation direction and a substantial Z dependent angular momentum with repect to the ionic core. While spin oscillations occur already in first order in v/c as described by the Pauli equation, spin induced forces via spin-orbit coupling only appear in the parameter regime where (v/c)2 corrections are significant. In this regime for Z=12 ions, we show strong splittings of resonant spectral lines due to spin-orbit coupling and substantial corrections to the conventional Stark shift due to the relativistic mass shift while those to the Darwin term are shown to be small. For smaller charges or higher laser intensities, parts of the electronic wave packet may tunnel through the potential barrier of the ionic core and when recombining, are shown to give rise to keV harmonics in the radiation spectrum. Some parts of the wave packet do not recombine after ionization and we find very energetic electrons in the weakly relativistic regime of above threshold ionization.

  • Received 3 May 2000

DOI:https://doi.org/10.1103/PhysRevA.63.053402

©2001 American Physical Society

Authors & Affiliations

S. X. Hu* and C. H. Keitel

  • Theoretische Quantendynamik, Fakultät für Physik, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Straße 3, D-79104 Freiburg, Germany

  • *Present address: Department of Physics and Astronomy, University of Nebraska–Lincoln, Lincoln, NE 68588-0111. Email address: shu@unlnotes.unl.edu
  • Email address: keitel@physik.uni-freiburg.de

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Vol. 63, Iss. 5 — May 2001

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