Ab initio simulations and measurements of the free-free opacity in aluminum

The free-free opacityin dense systems is a property that both tests our fundamental understanding of correlated many-body systems, and is needed to understand the radiative properties of high energy-density plasmas. Despite its importance, predictive calculations of the free-free opacityremain challenging even in the condensed matter phase for simple metals. Here we show how the free-free opacitycan be modelled at finite-temperatures via time-dependent density functional theory, and illustrate the importance of including local fieldcorrections, core polarization and self-energycorrections. Our calculations for ground-state Al are shown to agree well with experimental opacitymeasurements performed on the Artemis laser facility across a wide range of extreme ultravioletwavelengths. We extend our calculations across the melt to the warm-dense matterregime, finding good agreement with advanced plasma modelsbased on inverse bremsstrahlung at temperatures above 10,eV.