Radiative transfer of ultra-intense x-ray pulses

Radiative transfer of ultra-intense x-ray pulses is investigated by solving a one-dimensional radiative transfer equation. The populations of quantum states are obtained by solving a time-dependent rate equation based on collisional-radiative approximation, which are used to determine the absorption and emission coefficients. As an illustrative example. The transmission of ultra-intense x-ray pulses through a 1 um thick solid-density aluminium sample is calculated and compared with a recent experiment, where good agreement is found and saturable absorption is evidently observed.