Nanoscale subsurface dynamics of solids upon high-intensity laser irradiation observed by femtosecond grazing-incidence x-ray scattering

TL;DR

This study uses femtosecond grazing-incidence x-ray scattering to observe nanoscale subsurface dynamics in solids caused by high-intensity laser irradiation, revealing new insights into ultrafast laser-matter interactions.

Contribution

It demonstrates a novel application of picosecond GISAXS with XFELs to measure depth-resolved subsurface dynamics during laser irradiation.

Findings

Surface ablation and subsurface density changes measured with nanometer resolution

Data challenges existing models of matter under extreme conditions

Method opens new avenues for laser material processing and high-energy-density science

Abstract

Observing ultrafast laser-induced structural changes in nanoscale systems is essential for understanding the dynamics of intense light-matter interactions. For laser intensities on the order of $10^{14} \, \rm W/cm^2$, highly-collisional plasmas are generated at and below the surface. Subsequent transport processes such as heat conduction, electron-ion thermalization, surface ablation and resolidification occur at picosecond and nanosecond time scales. Imaging methods, e.g. using x-ray free-electron lasers (XFEL), were hitherto unable to measure the depth-resolved subsurface dynamics of laser-solid interactions with appropriate temporal and spatial resolution. Here we demonstrate picosecond grazing-incidence small-angle x-ray scattering (GISAXS) from laser-produced plasmas using XFEL pulses. Using multi-layer (ML) samples, both the surface ablation and subsurface density dynamics are measured with nanometer depth resolution. Our experimental data challenges the state-of-the-art modeling of matter under extreme conditions and opens new perspectives for laser material processing and high-energy-density science.