Skin-depth resolved surface plasma dynamics of laser-excited solids by grazing incidence X-ray surface scattering using X-ray free-electron laser

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The interaction of high-intensity lasers with solids creates high-density, warm-to-hot temperature plasmas involving a wide range of nonlinear physics phenomena. Such plasmas are not only of great relevance to astrophysics and inertial confinement fusion but also hold promise for the generation of bright, coherent light sources and for bright particle beams including ions. Here, efficiently depositing laser energy into plasmas is a key. Laser coupling into dense plasmas occur within the skin depth of the overcritical plasma, where the laser wave is evanescent. Innumerable theoretical studies suggest that the nanometer scale density structure plays a dominant role in laser-plasma coupling, but it has never been tested experimentally in a direct way. Our project aims at visualizing the density evolution of dynamically changing dense surface plasmas with nanometer (or skin-depth) resolution employing X-ray free electron lasers. We will perform grazing incidence small angle X-ray scattering experiments (GISAXS) and grazing incidence diffraction experiments (GID) from the laser excited solid density surface. This will not only allow obtaining a complete picture of the laser-plasma coupling and the subsequent energy transport into the bulk, including testing and benchmarking of simulations, but also allow researchers to optimize the laser-plasma interaction in a well-controlled way eventually opening new unexplored ultrafast processes. The high-resolution measurements also yield quantitatively assess to assumptions made in various theoretical codes.For this project we bring together the expertise of plasma physics (Nakatsutsumi) with expertise in X-ray reflectivity and coherent X-ray scattering (Gutt). The project is accordingly organized in work packages adapted to the different expertises of the groups involved.