Hannover 2013 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 27: Visualizing Ultrafast Dynamics in atoms, molecules, and clusters

A 27.4: Hauptvortrag

Mittwoch, 20. März 2013, 15:30–16:00, E 415

Clusters in intense x-ray pulses — •Christoph Bostedt — SLAC National Accelerator Laboratory, Stanford CA (USA)

Free-electron lasers deliver extremely intense, coherent x-ray flashes with femtosecond pulse length, opening the door for imaging single nanoscale objects in a single shot. All matter irradiated by these intense x-ray pulses, however, will be transformed into a highly-excited non-equilibrium plasma within femtoseconds. During the x-ray pulse complex electron dynamics and the onset of atomic disorder will be induced, leading to a time-varying sample.

We have performed experiments about intense x-ray pulse -- matter interaction at both, the FLASH and LCLS x-ray free-electron lasers using atomic clusters. Imaging experiments with xenon clusters in the soft x-ray regime have revealed power-density dependent changes in the scattering patterns. The data show that the scattering signal carries information about transient charge states in the cluster. Single-shot single-particle experiments with keV x-rays reveal that for the highest power densities an highly excited and hot cluster plasma is formed for which recombination is suppressed. Studying the ionization dynamics of smaller clusters shows that the energy absorption depends on the particle size which is attributed to changing Auger rates in the x-ray induced nanoplasma. Recent single-shot experiments with hard x-rays yield insight into the crystalline order of the particles.