Two-color Thomson scattering at FLASH

We propose a two-color pump–probe Thomson scattering experiment at the FLASH facility in Hamburg to characterize warm dense matter states. The fundamental free electron laser wavelength of 40.5 nm is used to pump a liquid hydrogen jet that is subsequently probed with the third harmonic at 13.5 nm. We have considered the laser–target interaction in the pump and probe phase by using the radiation hydrodynamics code HELIOS. The calculation of the Thomson scattering spectrum is based on the Chihara formula which is evaluated using the Born–Mermin approximation for the free electron dynamic structure factor and the Debye–Hückel static structure factor for the elastic scattering part. We consider the full density- and temperature-dependent Thomson scattering cross section throughout the inhomogeneous target. The results indicate that the electron–ion equilibration rate can be extracted by measuring the electron and ion feature with varying time delays between the pump and the probe pulse.