Plasma dynamics of an Al plasma in AlTi or AlAu mixtures heated by the PICO2000 ultra-intense laser pulse

The rapid cooling dynamics of thin solid foils heated by an ultra-intense ( ∼ 10 18 Wcm − 2 ) picosecond laser pulse are experimentally studied using three independent diagnostics based on a time-integrated and time-resolved x-ray emission spectroscopy as well as 2D x-ray imaging. Targets consist of plastic foils with buried Al, Al₄₂Ti₅₈, or Al₈₅Au₁₅ layers, where Al emission lines are used to infer the plasma conditions. Our measurements indicate that the Al K-shell emission occurs over a shorter duration and from a narrower region in AlTi or AlAu mixtures compared to pure Al samples, and that the average temperature is lower when increasing the atomic number of the high-Z element in the mixture. The TROLL radiation hydrodynamics code, coupled with the SAPHyR collisional radiative model, is used to infer the plasma heating conditions. This numerical platform has been able to consistently simulate the experimental results from the three diagnostics, allowing us to bypass the use of expensive PIC simulations. 2D simulations clearly show the importance of taking into account the particular 2D shape of the energy deposition, according to the measured radial laser intensity profile. The satisfactory agreement between simulations and measurements suggests that, for the relatively long laser pulse considered ( ∼ 1.3 ps ), the target bulk is primarily heated through direct collisions with fast electrons. Furthermore, simulations indicate that significant radiative cooling is observed in AlAu targets.