Ultrafast imaging of transient states and non-equilibrium dynamics in clusters with x-ray laser based pump-probe techniques

Summary form only given. Free-electron lasers are a new class of x-ray sources that deliver extremely intense, coherent x-ray flashes with femtosecond pulse length. The unprecedented brightness of these x-ray lasers opens the door for single shot imaging and non-linear spectroscopy approaches involving core-level states [1]. We have employed ultrafast imaging in the soft x-ray regime and ultrafast hard x-ray scattering to investigate optically and x-ray induced dynamics in nanometer-scale samples. Already with single x-ray pulses tuned to resonances, ultrafast scattering can be used to gain information about transient electronic states in highly excited nanoplasmas, in addition to obtaining their geometric information [2]. Extending the single pulse investigations to two-pulse two-color x-ray/x-ray pump/probe experiments we can follow the structural changes of massively excited systems at the solid-to-plasma interface [3]. The combination of optical with x-ray lasers opens door for studying dynamically evolving systems with femtosecond time and nanometer spatial resolution [4]. In parallel to the experimental efforts we have developed massively parallel Monte Carlo Molecular Dynamics codes that allow us to model the x-ray induced processes in clusters, or more generally, nanoscale samples and predict the limitations of ultrafast x-ray imaging [5].