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 μm-thick Al foils in the relativistic regime (up to 5 × 1020 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 × 109 protons/shot) with respect to uncoated foils (9.5 MeV, 1 × 109 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.