Isolated defect evolution in laser accelerated targets

Abstract

The hydrodynamic growth of pre-imposed isolated defects has been studied with varied laser drive. Targets were machined at NRL by etching narrow isolated grooves into thin polystyrene (CH) foils using femtosecond laser ablation. Two laser pulse shapes were used to drive the foils with and without a thin high-Z overcoat which produced a hybrid indirect-direct drive. The growth rate and saturation time were observed to vary with different laser drives as well as the initial perturbation depth and width. Faster growth was observed with a low adiabat drive both experimentally and in simulations. Hybrid drive reduced the apparent "closure"of defects at late time. Rear-surface structures were observed from the isolated defects, with the largest structures observed from high adiabat square pulses and the smallest from hybrid drive.