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

高强度激光与固体的相互作用产生高密度、从暖到热的等离子体，涉及广泛的非线性物理现象。这种等离子体不仅与天体物理学和惯性约束聚变有很大的相关性，而且还有望产生明亮的相干光源和明亮的粒子束，包括离子。在这里，有效地将激光能量沉积到等离子体中是关键。激光耦合到致密等离子体发生在过临界等离子体的皮肤深度内，在那里激光波是消失的。无数的理论研究表明，纳米尺度的密度结构在激光等离子体耦合中起着主导作用，但从未在实验中直接测试过。我们的项目旨在利用x射线自由电子激光器，以纳米（或皮肤深度）分辨率可视化动态变化的致密表面等离子体的密度演变。我们将在激光激发固体密度表面进行掠入射小角x射线散射实验（GISAXS）和掠入射衍射实验（GID）。这不仅可以获得激光等离子体耦合和随后的能量传输到体的完整图像，包括模拟的测试和基准测试，而且还允许研究人员以良好控制的方式优化激光等离子体相互作用，最终开辟新的未开发的超快过程。高分辨率的测量还对各种理论代码中的假设进行了定量评估。在这个项目中，我们将等离子体物理学（Nakatsutsumi）的专业知识与x射线反射率和相干x射线散射（Gutt）的专业知识结合在一起。因此，该项目被组织成工作包，以适应所涉及的小组的不同专业知识。

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.