We studied the influence of foams on laser produced
shocks. Experiments were performed at LULI using a Nd laser
converted to second harmonic, and at MPQ (Max Planck Institut
für Quantenoptik) using the iodine Asterix laser converted
to third harmonic. In both cases, sub-ns lasers with pulse
energies of several tens of joules were focused on large
focal spots (hundreds of microns) to reduce 2D effects.
The laser beams were optically smoothed with 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 visible 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.
Using the well known SESAME Al equation of state, we determined
shock pressure. A stronger pressure increase was measured
when foam was present, compared 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.