Electronic structure investigation of highly compressed aluminum with K edge absorption spectroscopy.

The electronic structure evolution of highly compressed aluminum has been investigated using time resolved $K$ edge x-ray absorption spectroscopy. A long laser pulse (500 ps, I$_L$ $\approx$ 8 X 10$^{13}$ W/cm$^2$) was used to create a uniform shock. A second ps pulse (I$_L$ $\approx$ 10$^{17}$ W/cm$^2$) generated an ultrashort broadband x-ray source near the Al $K$ edge. The main target was designed to probe aluminum at reshocked conditions up to now unexplored (3 times the solid density and temperatures around 8 eV). The hydrodynamical conditions were obtained using rear side visible diagnostics. Data were compared to ${ab}$ ${initio}$ and dense plasma calculations, indicating potential improvements in either description. This comparison shows that x-ray-absorption near-edge structure measurements provide a unique capability to probe matter at these extreme conditions and severally constrains theoretical approaches currently used.