TRANSVERSE SHADOWGRAPHY AND NEW RECOVERY TECHNIQUE TO INVESTIGATE DYNAMIC FRAGMENTATION OF LASER SHOCK‐LOADED METALS

With the development of high energy laser facilities dedicated to inertial confinement fusion, the question of debris ejection from metallic shells subjected to intense laser irradiation has become a key issue. We have used two diagnostics to investigate this phenomenon. Transverse shadowgraphy is an optical time‐resolved diagnostic. It provides successive images that allow characterizing the motion of fragments generated by processes such as microjetting and spallation. Quasi‐instantaneous pictures of the debris clouds are obtained and mean ejection velocities can be derived. Complementary data are provided by post‐shock analysis of recovered fragments. Such recovery can be achieved in aerogels, but their brittleness and low transparency make the analysis difficult. Instead, we have used a new technique, based on a highly transparent gel of density $0.9 g/cm3,$ which allows soft recovery and easy observation of the fragments sizes, shapes and penetration depths, with a spatial resolution of μm‐order.