Revealing non-equilibrium and relaxation in laser heated matter

Experiments creating extreme states of matter almost invariably create non -equilibrium states. These are very interesting in their own right but need to be understood even if the ultimate goal is to probe high-pressure or high -temperature equilibrium properties like the equation of state. Here, we report on the capabilities of the newly developed imaginary time correlation function (ITCF) technique [1] to detect and quantify nonequilibrium in pump -probe experiments fielding time resolved x-ray scattering diagnostics. We find a high sensitivity of the ITCF even to a small fraction of non -equilibrium electrons in the Wigner distribution. The behavior of the ITCF technique is such that modern lasers and detectors should be able to trace the nonequilibrium relaxation from tens of femto-seconds to several 10s of picoseconds without the need for a model.