High energy density matter generation using a focused soft-X-ray laser for volumetric heating of thin foils

We report on time-resolved transmission measurements of a 21.2 nm X-ray laser through thin Al and polyimide foils in the intensity range 1010–1012 Wcm−2. Absolute time-integrated and relative time-dependent transmission measurements indicate significant differences with cold opacity data, due to the heating, leading to partially ionized states with temperatures of 0.5–20 eV. The transmission data are compared with simulations that qualitatively reproduce the time-dependent transmission measurements and demonstrate the importance of including detailed atomic absorption processes in the warm dense matter regime.