title: Recoil-ion momentum distributions for two-photon double ionization of He and Ne by 44 eV free-electron laser radiation.
abstract: Recoil-ion momentum distributions for two-photon double ionization of He and Ne (variant Planck's over omega=44 eV) have been recorded with a reaction microscope at FLASH (the free-electron laser at Hamburg) at an intensity of approximately 1 x 10(14) W/cm2 exploring the dynamics of the two fundamental two-photon-two-electron reaction pathways, namely, sequential and direct (or nonsequential) absorption of the photons. We find strong differences in the recoil-ion momentum patterns for the two mechanisms pointing to the significantly different two-electron emission dynamics and thus provide serious constraints for theoretical models.
authors.affiliation: Max-Planck Advanced Study Group at CFEL, Notkestrasse 85, 22607 Hamburg, Germany.
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authors.lastname: Rudenko
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authors.lastname: Voitkiv
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authors.lastname: Treusch
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authors.lastname: Moshammer
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