Efficient Laser-Driven Proton And Bremsstrahlung Generation From Cluster-Assembled Foam Targets

The interaction between intense 30 fs laser pulses and foam-coated 1.5 mu m-thick Al foils in the relativistic regime (up to 5 x 10(20) W cm(-2)) is studied to optimize the laser energy conversion into laser-accelerated protons. A significant enhancement is observed for foam targets in terms of proton cut-off energy (18.5 MeV) and number of protons above 4.7 MeV (4 x 10(9) protons/shot) with respect to uncoated foils (9.5 MeV, 1 x 10(9) protons/shot), together with a sixfold increase in the bremsstrahlung yield. This enhancement is attributed to increased laser absorption and electron generation in the foam meso- and nanostructure.