Picosecond radiography combined with other techniques to investigate microjetting from laser shock-loaded grooves

Abstract

Debris ejection upon shock breakout at a rough surface is a key issue for many applications, including pyrotechnics and inertial confinement fusion. For a few years, we have used laser driven shocks to investigate microjetting in metallic samples with calibrated grooves in their free surface. Fast transverse optical shadowgraphy, time-resolved measurements of both planar surface and jet tip velocities, and post-shock analysis of recovered material have provided data over ranges of small spatial and temporal scales, short loading pulses (ns-order) and extremely high strain rates. The new experiment presented here involves two laser beams in a pump-probe configuration. Picosecond laser irradiation of a thin copper wire generates x-rays which are used to radiograph the microjets expanding from single grooves in tin and copper samples shock-loaded by a longer, nanosecond laser pulse. Such ultrashort radiography can be used to infer the density gradients along the jets as well as inside the samples deep beneath the grooves. Thus, combining this x-ray probe with the other experimental techniques mentioned above provides a more complete insight into the physics of microjetting at very high loading rates and the ballistic properties of the resulting ejecta.