Analysis of laser-driven shocks in confined and unconfined geometries

Pulsed lasers are convenient generators of shocks in materials. The efficacy of laser shock generation depends on several factors including laser-target coupling, laser pulse temporal shape and intensity, and the resultant pressure profile generated at the target surface. Target coupling is a dynamic mechanism that changes as the target surface evolves due to heating, ionization and ablation during laser irradiation. Confining a metal target surface using a transparent 'tamper' material can increase the impulse transferred to the target, but also can cause decoupling of the laser energy from the target as the heated tamper begins to move the laser absorption region away from the metal surface. We have analyzed this process using the radiation hydrodynamics code Lasnex in an attempt to simulate experiments using planar targets and determine the coupling efficiency versus tamper material properties. Good agreement with experimental measurements of the shock pressure in Al and PMMA were obtain using laser absorption values of 40%. Dielectric tamping of the laser absorption increased the shock pressures by factors of 2 to 3. Further increases in pressure into the megabar regime were obtained inside the tamping dielectric as a radiatively-coupled ionization wave propagated back toward the laser