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Feldhaus J.,German Electron Synchrotron | Krikunova M.,TU Berlin | Meyer M.,German Electron Synchrotron | Moller Th.,TU Berlin | And 9 more authors.
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2013

Present performance and future development of the free-electron lasers (FELs) in Hamburg - FLASH for the extreme ultraviolet and the European XFEL for the soft and hard x-ray regimes - are presented. As an illustration of the unprecedented characteristics of these sources a few recent examples of experiments performed in the area of atomic, molecular and optical (AMO) physics are described. The results highlight in particular the available high photon intensities, the short pulse durations and the coherence of the FEL beam. Nonlinear processes involving for the first time inner-shell electrons, time-resolved experiments on the few femtosecond timescales, and imaging experiments on small particles have been the focus of these studies, demonstrating the unique potential of short-wavelength FELs and pointing to numerous exciting future opportunities. © 2013 IOP Publishing Ltd.

Rudek B.,Max Planck Advanced Study Group at Center for Free Electronic Laser Science | Rudek B.,Max Planck Institute for Nuclear Physics | Son S.-K.,German Electron Synchrotron | Foucar L.,Max Planck Advanced Study Group at Center for Free Electronic Laser Science | And 74 more authors.
Nature Photonics | Year: 2012

X-ray free-electron lasers provide unique opportunities for exploring ultrafast dynamics and for imaging the structures of complex systems. Understanding the response of individual atoms to intense X-rays is essential for most free-electron laser applications. First experiments have shown that, for light atoms, the dominant interaction mechanism is ionization by sequential electron ejection, where the highest charge state produced is defined by the last ionic state that can be ionized with one photon. Here, we report an unprecedentedly high degree of ionization of xenon atoms by 1.5 keV free-electron laser pulses to charge states with ionization energies far exceeding the photon energy. Comparing ion charge-state distributions and fluorescence spectra with state-of-the-art calculations, we find that these surprisingly high charge states are created via excitation of transient resonances in highly charged ions, and predict resonance enhanced absorption to be a general phenomenon in the interaction of intense X-rays with systems containing high-Z constituents. © 2012 Macmillan Publishers Limited. All rights reserved.

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