Simple model of energy deposition by suprathermal electrons in laser-irradiated targets

Abstract

Energy deposition (preheat) by suprathermal electrons in laser-irradiated targets is described using a model based on Spencer's electron transport calculation. Approximate analytical, as well as numerical, solutions are found for the specific energy deposition ${\mathcal{E}}_{\mathrm{dep}}\left(\frac{J}{g}\right)$ and fraction $f$ of energy transmitted beyond a given depth, measured in curvilinear ranges. Example calculations are presented for homogeneous targets of gold, aluminum, and carbon. The application of the model to treat multilayer composite targets is briefly considered. The parametric dependence of these results reveal that the most significant parameter by far is the source temperature $T_h$ of the hot or suprathermal electrons. The predictions of the preheat model are shown to be in good agreement with experimental data on gold and aluminum disks irradiated by Nd-glass laser pulses at the ${10}^{15}$ W/${\mathrm{cm}}^2$ level. Included in the theory-data comparison are predictions for these experiments based on several other simple models and large code simulations of the experiments. Future aluminum disk experiments in which $T_h$ is accurately measured could provide a sensitive test for the theories.