CALCULATION OF EXAFS IN SHOCK-COMPRESSED MATTER

Extended X-ray absorption fine structure (EXAFS) in shock-compressed matter have been investigated theoretically. EXAFS may be a way to determine the density behind the shock front, giving the second parameter needed for equation-of-state measurements. First experimental data on EXAFS in laser-compressed aluminum were obtained by Hall et al [1]. The critical issue is the temperature dependence, since increasing temperature fends to wash out the EXAFS signal. Strong shocks turn the solid probe into strongly coupled plasmas, the regular lattice structure is changed into a plasma fluid with strong ion-ion correlations. Ion-ion potentials are obtained using the Thomas-Fermi model for a quasimolecule, and fluid theory is applied to calculate the correlation function. The photoelectron mean free path, which also reduces the EXAFS signal, is determined from a dielectric approach. Finally, results for dense Al-plasmas are presented, also showing the change along the principle Hugoniot.