Toward high-energy laser-driven ion beams: Nanostructured double-layer targets

The development of novel target concepts is crucial to make laser-driven acceleration of ion beams suitable for applications. We tested double-layer targets formed of an ultralow density nanostructured carbon layer ($\ensuremath{\sim}7\text{ }\text{ }{\mathrm{mg}/\mathrm{cm}}^{3}$, $8\char21{}12\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$\char21{}thick) deposited on a $\ensuremath{\mu}\mathrm{m}$\char21{}thick solid Al foil. A systematic increase in the total number of the accelerated ions (protons and ${\mathrm{C}}^{6+}$) as well as enhancement of both their maximum and average energies was observed with respect to bare solid foil targets. Maximum proton energies up to 30 MeV were recorded. Dedicated three-dimensional particle-in-cell simulations were in remarkable agreement with the experimental results, giving clear indication of the role played by the target nanostructures in the interaction process.