Fabrication of ZnO-nanowire-coated thin-foil targets for ultra-high intensity laser interaction experiments

The coupling of ultra-intense, ultra-short laser pulses with solid targets is heavily dependent on the properties of the vacuum-solid interface and is usually quite low. However, laser absorption can be enhanced via micro or nanopatterning of the target surface. Depending on the laser features and target geometry, conditions can be optimized for the generation of hot dense matter, which can be used to produce high-brightness radiation sources or even to accelerate particles to relativistic energies. In this context, ZnO nanowires were grown on metallic, thin-foil targets. The use of a thin-foil substrate was dictated by the need to achieve proton acceleration via target normal sheath acceleration at the rear side. The chemical process parameters were studied in-depth to provide control over the nanowire size, shape, and distribution. Moreover, the manufacturing process was optimized to provide accurate reproducibility of key parameters in the widest possible range and good homogeneity across the entire foil area.