INVESTIGATION OF NON-THERMAL ELECTRON DYNAMICS IN SHORT-PULSE, LASER-SOLID INTERACTIONS

Investigated here is the dynamics of non-thermal heat transport in solid materials driven by ultrafast, high-intensity lasers. The primary context is buried-layer experiments where multi-keV electrons uniformly heat a tamped layer of mid-Z material, such as iron sulfide, allowing for accurate measurements of emitted x-ray spectra and consistent inference of material opacities under HED conditions. Femtosecond to picosecond time-scale laser-plasma interactions give rise to complex energy spectra that are difficult to quantify as strictly thermal, i.e., keV, or hot, i.e., MeV. Traditionally, the thermal population is exclusively considered as the primary means to heat the buried layer. Low-density, hot electrons do not interact much with the dense core but are "long-lived" and recirculate around the target for several 10s of picoseconds, moderating that assumption. Likewise, a "warm" population of intermediary energy electrons that are not neatly described by a thermal distribution are present and can contribute to heating. Using ensembles of 1D and 2D particle-in-cell simulations, both collisionless as well as collisional, we investigate how electron dynamics evolve and thermally equilibrate to hydrodynamic conditions necessary to allow modeling of target materials with standard radiation hydrodynamic tools. These ensembles serve as the database for developing machine learning models for rapid exploration of parameter space and identification of salient latent space features.