Stuttgart 2012 – wissenschaftliches Programm
A 11.4: Vortrag
Montag, 12. März 2012, 17:45–18:00, V47.03
Enhanced nonlinear response of Ne8+ to intense ultrafast X-rays — •Arina Sytcheva1, Stefan Pabst1,2, Sang-Kil Son1, and Robin Santra1,2 — 1Center for Free-Electron Laser Science, DESY, Germany — 2Department of Physics, University of Hamburg, Germany
We report on the possible reasons for the discrepancy between the theoretical two-photon ionization cross section (TPICS), ∼ 4 · 10−56 cm4 s, of Ne8+ obtained within the lowest nonvanishing order of perturbation theory (LOPT) for continuous light and the experimental value, 7 × 10−54 cm4 s, reported in [Phys. Rev. Lett. 106, 083002 (2011)] at a photon energy of 1110 eV and pulse bandwidth of 11 eV. We consider Ne8+ exposed to coherent and chaotic ensembles of intense X-ray pulses using the time-dependent configuration-interaction singles (TDCIS) method and LOPT, respectively. A coherent ensemble of pulses of 11-eV bandwidth centered at 1110 eV yields a TPICS enhanced by a factor of ∼ 1.25 with respect to the continuous-light TPICS, while a chaotic ensemble yields an enhancement factor of ∼ 40. This enhancement is due to the presence of the one-photon 1s2–1s4p resonance located at 1127 eV and the finite bandwidth of the X-ray pulse. Using the TDCIS approach, we also show that, for currently available radiation intensities, two-photon ionization of a 1s electron in neutral neon is much less probable than one-photon ionization of a valence electron.