Laser-driven flyer experiments: analogy with Gurney high explosive plate acceleration model

Abstract. The sustainability of satellites is threatened by the growing number of space debris in low-Earth orbit, which can collide and damage them. Understanding the mechanisms involved in such hypervelocity impacts (HVI) is essential to improving space shielding technologies. To experimentally investigate HVI, double-stage launchers can be used, propelling millimetric projectiles at very high velocities, reaching up to 8 to 10 km/s. Alternatively, high-power lasers may replicate similar characteristics of HVI, such as target craterization and debris cloud ejection, but with firing rates and equivalent speeds far superior to those of launchers. The laser sources can also be employed to launch small projectiles at very high speeds by an ablation process or to generate local severe pressure states useful in the determination of equations of state under shocks. This work aims to investigate the hypervelocity fragment ejection generated after a laser ablation. The conducted experiments employ the BELENOS facility at ENSTA Bretagne, France, having 1064 nm Nd: YAG pulsed laser generator with a full width at half maximum pulse duration of 7.5 ns ± 0.5 that can deliver a maximum energy of 3 J ± 0.05. The target is made of pure aluminum with two different thicknesses, respectively of 40 and 100 micrometers. Using a laser fluence from 10 to 50 J/cm2 with a 3.5 mm focal spot, the ejection reaches a velocity range of 1200 to 1600 m/s for the first sample, and a range of 400 to 800 m/s for the second one. The material velocity of the flyer's rear surface over time is captured by a Photonic Doppler Velocimeter (PDV) and is correlated with recordings from an ultra-high-speed camera. Fracture morphology of the specimen is then analyzed to identify specific patterns. Finally, since high explosives are also an alternative way to propel plates, an analogy is made with the Gurney's plate acceleration model.