ACCELERATION-DECELERATION PROCESS OF THIN FOILS CONFINED IN WATER ANDSUBMITTED TO LASER-DRIVEN SHOCKS

An experimental, numerical, and analytical study of the acceleration a nd deceleration process of thin metallic foils immersed in water and s ubmitted to laser driven shocks is presented. Aluminum and copper foil s of 20 to 120 mu m thickness, confined on both sides by water, have b een irradiated at 1.06 mu m wavelength by laser pulses of similar to 2 0 ns duration, similar to 17 J energy, and similar to 4 GW/cm(2) incid ent intensity. Time resolved velocity measurements have been made, usi ng an electromagnetic velocity gauge. The recorded velocity profiles r eveal an acceleration-deceleration process, with a peak velocity up to 650 m/s. Predicted profiles from numerical simulations reproduce all experimental features, such as wave reverberations, rate of increase a nd decrease of velocity, peak velocity, effects of nature, and thickne ss of the foils. A shock pressure of about 2.5 GPa is inferred from th e velocity measurements. Experimental points on the evolution of plasm a pressure are derived from the measurements of peak velocities. An an alytical description of the acceleration-deceleration process, involvi ng multiple shock and release waves reflecting on both sides of the fo ils, is presented. The space-time diagrams of waves propagation and th e successive pressure-particle velocity states are determined, from wh ich theoretical velocity profiles are constructed. All characteristics of experimental records and numerical simulations are well reproduced . The role of foil nature and thickness, in relation with the shock im pedance of the materials, appears explicitly. (C) 1997 American Instit ute of Physics.