Rear surface isolated defect evolution in laser accelerated targets

The hydrodynamic growth of pre-imposed isolated rear-surface defects, specifically 9–20 μm deep by 8–20 μm wide laser-machined grooves on planar polystyrene foils, was investigated using the NIKE krypton-fluoride laser facility at the U.S. Naval Research Laboratory. High-resolution monochromatic x-ray radiography was employed to capture streaked face-on and two-dimensional side-on images of the defect evolution. The observed interfacial dynamics are consistent with the key characteristics of isolated-defect-triggered hydrodynamic perturbation growth first observed with front-surface defects by Zulick et al. [Phys. Rev. Lett. 125, 055001 (2020)] and Zulick et al. [Phys. Plasmas 27, 072706 (2020)]. These characteristics include an inherently multi-mode, phase-locked perturbation development, a monotonic increase in the lateral dimension of the perturbed region, and the oblique ejection of spikes during the nonlinear growth phase. Initially, material accelerated into the rear-surface groove forms a jet, which is subsequently overtaken by multi-mode bubble and spike Rayleigh–Taylor growth at the front surface. Experimental results demonstrated good agreement with both high-resolution fastrad3d simulations and analytical theoretical predictions.