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Hamburg, Germany

Liu H.Y.,CFEL | Gierz I.,CFEL | Petersen J.C.,CFEL | Petersen J.C.,University of Oxford | And 14 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We use time- and angle-resolved photoemission spectroscopy in the extreme ultraviolet to measure the time- and momentum-dependent electronic structures of photoexcited K0.3MoO3. Prompt depletion of the charge-density wave condensate launches coherent oscillations of the amplitude mode, observed as a 1.7-THz-frequency modulation of the bonding band position. In contrast, the antibonding band oscillates at about half this frequency. We attribute these oscillations to coherent excitation of phasons via parametric amplification of phase fluctuations. © 2013 American Physical Society.

Kim J.,KAIST | Jung K.,KAIST | Lim J.,KAIST | Chen L.-J.,Idesta Quantum Electronics | And 4 more authors.
FEL 2013: Proceedings of the 35th International Free-Electron Laser Conference | Year: 2013

We present our recent progress in remote RF synchronization using an optical way at PAL. A 79.33- MHz, low-jitter fiber laser is used as an optical master oscillator (OMO), which is locked to the 2.856-GHz RF master oscillator (RMO) using a balanced opticalmicrowave phase detector (BOM-PD). The locked optical pulse train is then transferred via a timing-stabilized 610- m long optical fiber link. The output is locked to the 2.856 GHz voltage controlled oscillator (VCO) using the second BOM-PD, which results in remote synchronization between the RMO and the VCO. We measured the long-term phase drift between the input optical pulse train and the remote RF signals using an outof- loop BOM-PD, which results in 2.7 fs (rms) drift maintained over 7 hours. Copyright © 2013 CC-BY-3.0 and by the respective authors.

Serkez S.,German Electron Synchrotron | Kocharyan V.,German Electron Synchrotron | Saldin E.,German Electron Synchrotron | Zagorodnov I.,German Electron Synchrotron | And 2 more authors.
FEL 2013: Proceedings of the 35th International Free-Electron Laser Conference | Year: 2013

Experiments at the LCLS confirmed the feasibility of femtosecond nanocrystallography for protein structure determination at near-atomic resolution. These experiments rely on X-ray SASE pulses with a few microradians angular spread, and about 0:2% bandwidth. By indexing individual patterns and then summing all counts in all partial reflections for each index it is possible to extract the square modulus of the structure factor. The number of indexed images and the SASE bandwidth are linked, as an increasing number of Bragg spots per individual image requires an increasing spectral bandwidth. This calls for a few percent SASE bandwidth. Based on start-to-end simulations of the European XFEL baseline, we demonstrate that it is possible to achieve up to a 10-fold increase of the electron energy chirp by strongly compressing a 0.25 nC electron bunch. This allows for data collection with a 2% SASE bandwidth, a few mJ radiation pulse energy and a few fspulse duration, which would increase the efficiency of protein determination at the European XFEL. We prove this concept with simulations of lysozyme nanocrystals, with a size of about 300 nm. Copyright © 2013 CC-BY-3.0 and by the respective authors.

Toleikis S.,German Electron Synchrotron | Bornath T.,University of Rostock | Doppner T.,Lawrence Livermore National Laboratory | Dusterer S.,German Electron Synchrotron | And 29 more authors.
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2010

X-ray scattering using highly brilliant x-ray free-electron laser (FEL) radiation provides new access to probe free-electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft x-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft x-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free-electron density of (2.6 ± 0.2) × 1020 cm-3 and an electron temperature of 14 ± 3.5 eV. In pump-probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper, we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyse the data. © 2010 IOP Publishing Ltd.

Faustlin R.R.,German Electron Synchrotron | Bornath T.,University of Rostock | Doppner T.,University of California | Dusterer S.,German Electron Synchrotron | And 28 more authors.
Physical Review Letters | Year: 2010

We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state. Thomson scattering measurements using 91.8 eV photons from the free-electron laser in Hamburg (FLASH at DESY) show that the hydrogen plasma has been driven to a nonthermal state with an electron temperature of 13 eV and an ion temperature below 0.1 eV, while the free-electron density is 2.8×1020cm-3. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions. © 2010 The American Physical Society.

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