The electron-ion relaxation dynamics in warm dense iron were investigated by time-resolved x-ray absorption near-edge spectroscopy (XANES). A novel analysis, combining ab initio density functional theory (DFT) and two temperature model (TTM) simulations, was developed to calculate the x-ray absorption spectra as a function of delay time. Here we present experimental evidence of changes at the XAS L3 edge of iron that are consistent with the reduction of the electron-phonon coupling under warm dense matter conditions. The experimental results are in agreement with the model that takes both the electron ($T_e$) and the ion temperature ($T_i$) dependence of the thermophysical properties into consideration, while models where either constant electron-phonon coupling factor (G) or only $T_e$-dependent G are used do not agree with the observed relaxation dynamics of iron.

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• First-principles calculations
• Temperature
• Thermal conductivity
• Transport phenomena
• Nonequilibrium systems
• Warm-dense matter
• Femtosecond laser irradiation
• X-ray absorption near-edge spectroscopy