Surface dynamics of solids upon high-intensity laser irradiation investigated by grazing incidence X-ray scattering

The excitation of solids by ultrafast, intense lasers creates high-density plasmas relevant for astrophysics, inertial confinement fusion, various practical applications including laser processing, realization of compact sources of coherent XUV to X-ray radiation and bright particles including ions. Obviously, a comprehensive understanding of laser coupling and subsequent energy transport into dense-plasma is of key importance. Up to now, the current lack of appropriate methods observing complex density dynamics with sufficient spatial resolution prevented us from a quantitative understanding of the underlying physics and benchmarking existing models. This thesis demonstrates for the first time the feasibility of single pulse grazing incidence X-ray diffuse scattering experiments from laser excited condensed matter employing single XFEL pulse of 7 fs pulse duration. The experiments, performed at the Japanese FEL facility SACLA, reveal the ultrafast evolution of the electron density in the vicinity of the surface. We deduce the dynamics of the density and surface profiles on ultrafast time scales.
The retrieved density information infers the electronic heat conduction velocity and surface ablation dynamics caused by electrostatic ablation or electron-ion collisions. As the dynamics of the multilayer sample is caused by particle penetration and pressure balance between adjacent layers, our new tool will play a central role in benchmarking various models including particle collisions and the equation of states.
The results can be anticipated to be useful for various applications that rely on transient dynamics of high-density states: material processing, isochoric heating, laser dynamic compression and relativistic laser matter interaction. Our new technique will play an important role towards long-awaited quantitative benchmark of various models that have been suffered from lack of precise experimental data.
Additionally, grazing-incidence X-ray scattering provides also information on lateral and vertical correlation and roughness properties at the surface upon laser excitation. With this surface roughness and ripples changing upon laser excitation, surface plasma instability dynamics and spatial homogeneity of shock wave with sub-μm resolution can be investigated.
Bringing together X-ray scattering techniques and high energy density science opens a complete new field in understanding the fundamental processes in laser-plasma interaction.