Time-resolved x-ray imaging of high-power laser-irradiated underdense silica aerogels and agar foams

Abstract

This article presents the results of experiments in which a high‐power laser was used to irradiate low density (4–9 mg/cm3) silica aerogel and agar foam targets. The laser–solid interaction and energy transport through the material were monitored with time‐resolved imaging diagnostics, and the data show the production and propagation of an x‐ray emission front in the plasma. The emission‐front trajectory data are found to be in significant disagreement with detailed simulations, which predict a much more rapid heating of the cold material, and the data suggest that this discrepancy is not explainable by target inhomogeneities. Evidence suggests that energy transport into the cold material may be dominated by thermal conduction; however, no completely satisfactory explanation for the discrepancies is identified, and further experimental and theoretical research is necessary in order to resolve this important problem in laser–plasma interaction physics.