Shock impedance matching experiments in foam-solid targets and implications for "foam buffered ICF"

We studied the influence of foams on laser produced shocks. Experiments wer e performed at LULI using a Nd laser converted to second harmonic, and at M PQ (Max Planck Institut fiir Quantenoptik) using the iodine Asterix laser c onverted to third harmonic. In both cases, sub-ns lasers with pulse energie s of several tens of joules were focused on large: focal spots (hundreds of microns) to reduce 2D effects. The laser beams were optically smoothed wit h phase zone plates (PZP) and directly focused on layered targets made of a foam layer on the laser side and a stepped Al layer on the other side. A v isible streak camera was used to detect shock breakthrough at the base and at the step of the Al target, allowing shock: velocity to be determined. Us ing the well known SESAME Al equation of state, we determined shock pressur e. A stronger pressure Increase was measured when foam was present, compare d to what was obtained by focusing the laser beam directly on the Al target . This was due-to the,impedance mismatch effect at the Al-foam interface.