Material Ejection from Surface Defects in Laser Shock-Loaded Metallic Foils

Ejecta production upon the breakout of a shock wave at a rough surface has been the subject of extensive research work for about six decades. For a few years, we have investigated how laser-driven shocks could provide original, complementary data on this issue, over specific ranges of very high loading pressures, very short pulse durations (ns-order), small dimensions (tens of mu m) and extremely high strain rates. Here, selected results are presented in two metals (Cu and Sn), with either single triangular grooves of controlled depths and sharp angles or periodic, quasi-sinusoidal perturbations of different amplitudes. Experimental data combine measurements of jet velocities, using both optical shadowgraphy and Photonic Doppler Velocimetry, with ultra-fast laser based X-ray radiography to estimate mass ejection. Results are briefly compared with the predictions of analytical models and data obtained by other teams from explosive-based experiments, at lower pressure and over much larger temporal and spatial scales. Thus, both interest and limitations of laser shocks for this particular field of shock physics are illustrated and discussed.