Theoretical calculations of K-edge absorption spectra in warm dense Al

Abstract

Theoretical calculations of the shape of an absorption edge in a warm dense simple material such Al are described. The calculations include the XAFS (x-ray absorption fine structure) features above the edge. The shape of these modulations relates to the atomic spatial distribution and to the electronic density of states (DOS) in the continuum. The underlying warm dense plasma model is based on a density-functional neutral pseudoatom approach which gives the radial distribution function (RDF) and the electron density around one specific site. Combined with a full multiple-scattering (MS) approach giving the final free wavefunction in a photoionization process, the model is used to predict the shape of photoabsorption K edges over a range of compression ratios from 0.5 to 3 and temperatures from 0.1 to 10 eV. It is found that XAFS structures are intense enough to be observable for densities of the order of (and above) the solid density and that dynamic or static absorption spectroscopy measurements could provide interesting information on the warm dense matter regime.

Temperature and density dependence of XANES spectra in warm dense aluminum plasmas

“…Moreover, the author uses the Slater's transition state method to evaluate the 1s energy orbitals. 6 The density effect on this energy orbitals is less pronounced in this case. While the calculation presented here provides a consistent description of the plasma state and the x-ray response, the lack of agreement with the experimental data at this highest density calls for further measurements along the shock compressed Hugoniot.…”

“…2,3 From the theoretical side, several attempts have been made to combine electronic structure calculations with plasma models of varying degree of sophistication to provide a description of the near-edge absorption spectra or K-edge photoionization position. [4][5][6] All these models suffer, however, from an inconsistency between the two treatments as these calculations make use of various assumptions to model the electronic or the ionic structures. These two quantities are difficult to obtain, especially in the dense plasma regime where a self-consistent description of the ionic and electronic structures is needed.…”

Isochoric heating of solids by laser-accelerated protons: Experimental characterization and self-consistent hydrodynamic modeling

“…For thick targets, the measurements can give us access to the transitions from solid to plasma, whereas for thin targets, e.g., 0.5 mm thick Al, measured XANES structure allows one to measure the correlation factor of neighbour ions. X-ray photoabsorption data thus allow study of the ion distribution and open the possibility that one could benchmark different models [20,33,34].…”

Absorption X près des seuils (XANES, EXAFS) pour l'étude de la matière dense et tiède

“…Toutes ces méthodes donnent accès à des états de la matière plus ou moins chauds et denses et permettent ainsi d'aborder différentes dynamiques jusqu'à la matière dense et tiède (état Warm Dense Matter, WDM). Parallèlement, des spectres XANES théoriques de l'aluminium dense et tiède [16] nous permettent d'attendre des modifications nettes des structures XANES lors de la transition solidematière dense et tiède.…”