Preferential enhancement of laser-driven carbon ion acceleration from optimized nanostructured surfaces

High-intensity ultrashort laser pulses focused on metal targets readily generate hot dense plasmas which accelerate ions efficiently and can pave way to compact table-top accelerators. Laser-driven ion acceleration studies predominantly focus on protons, which experience the maximum acceleration owing to their highest charge-to-mass ratio. The possibility of tailoring such schemes for the preferential acceleration of a particular ion species is very much desired but has hardly been explored. Here, we present an experimental demonstration of how the nanostructuring of a copper target can be optimized for enhanced acceleration of carbon ions over protons or Cu-ions. Specifically, a thin (≈0.25 μm) layer of 25-30 nm diameter Cu nanoparticles, sputter- deposited on a polished Cu-substrate, enhances the carbon ion energy almost 10-fold at a laser intensity of 1.2 x 10(18) W/cm2. However, particles smaller than 20 nm have an adverse effect on the ion acceleration. Particle-in-cell simulations provide definite pointers regarding the size of nanoparticles necessary for maximizing the ion acceleration.