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Abstract of [Sytcheva12]

Enhanced nonlinear response of Ne8+ to intense ultrafast X-rays

Arina Sytcheva, Stefan Pabst, Sang-Kil Son, and Robin Santra

DPG Spring Meeting of the Section AMOP
(German Physical Society, Stuttgart, Germany, March 12-16, 2012)

[bib][BibTeX][link]http://www.dpg-verhandlungen.de/year/2012/conference/stuttgart/part/a/session/11/contribution/4

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 бн 1.25 with respect to the continuous-light TPICS, while a chaotic ensemble yields an enhancement factor of бн 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.


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