Experiments at Large-Scale Facilities
We perform experiments exploring high energy density matter with laser systems in Dresden and at various other facilities around the globe. Currently, we are focussing on planning and performing first experiments with the HIBEF infrastructure at the High Energy Density instrument of European XFEL, Germany's largest resarch instrument. Moreover, we use other X-ray Free Electron Laser facilities for these studies, e.g. the Linac Coherent Light Source of SLAC National Accelerator Laboratory in California or the SACLA facility at the Spring-8 science campus in Japan. Furthermore, we perform experiments at large optical high-energy laser facilities including the National Ignition Facility of Lawrence Livermore National Laboratory and the PHELIX laser system of GSI Helmholzzentrum für Schwerionenforschung. We also support the commissioning and further development of the High-Power Laser Facility at the Eurpean Synchrotron Radiation Facility (ESRF) in Grenoble.
Non-Equilibrium Warm Dense Matter
We perform first principle quantum simulations for equilibrium warm dense matter to obtain quantities like the equation of state, opacity, conductivity, dielectric functions, (dynamic) structure of electrons and ions, ionization potential depression, and temperature relaxation times. We use real time Green's functions for the description of non-equilibrium warm dense matter states, in particular their time dependent structure and relaxation processes. Using these results, we build effective models that allow a simulation of x-ray spectra of warm dense matter as obtained in experiments allowing excellent and accurate comparison with measured quantities.
During short pulse high power laser solid matter interactions, a significant fraction of laser pulse energy is absorbed to generate an intense beam of fast electrons with relativistic kinetic energies near the critical density surface. The transport of the intense fast beam into the solid target is of fundamental importance to many complex dynamics such as plasma oscillation, heating, ionization, instability, electric field and magnetic field generation, photon emission etc. We focus on numerically investigating the ultrafast plasma dynamics for ion heating in buried layer targets, bulk electron heating, collisional ionization, transport instability and quasi-static magnetic generation from PIC simulations. In order to connect the complex plasma dynamics seen in PIC simulations with experiments, we further study the role of in situ synthetic diagnostics that mimic experimental environments. As one key example we propose to use X-Ray Free Electron Lasers for probing the density modulations and ionization dynamics in the bulk target by small angle X-ray scattering which allows for femtosecond and nanometer resolution of transient plasma processes. We also investigate the feasibility to probe self-generated MegaGauss magnetic fields associated with the transport instability of the laser accelerated hot electrons using Faraday rotation. This diagnostic technique can also be used to detect the vacuum birefringence and thus is highly attractive for both high energy density community and quantum electrodynamics community. With these techniques, probing fundamental plasma properties will allow for direct comparison to simulations, challenging state of the art theoretical modeling of collisions, ionizations.
Laser-matter interactions generate a very large amount of high-energetic particles. In a typical highintensity short-pulse experiment, about 1010 bremsstrahlung photons with energy up to tens of MeV are generated in a single shot. The spectrum of these photons is directly related to the electron temperature in the plasma. We are developing an active, single-shot, high-repetition rate calorimeter to measure this spectrum. Additionally, the high number of photons presents a challenge for the detectors used to diagnose the interaction. Our group is developing new techniques based on silicon photomultipliers with a fast power switching that allows the detector to be switched on immediately after the main MeV-photon pulse has passed avoid saturation. This will open the field to current standard nuclear experiment techniques.