laser pulse with H2O nano-wire targets.

ABSTRACT Compact sources of high energy protons (50-500MeV) are expected to be key technology in a wide range of scientific applications 1-8 . Particularly promising is the target normal sheah acceleration (TNSA) scheme 9,10 , holding record level of 67MeV protons generated by a peta-Watt laser 11 . In general, laser intensity exceeding 10 18 W/cm 2 is required to produce MeV level protons. Enhancing the energy of generated protons using compact laser sources is very attractive task nowadays. Recently, nano-scale targets were used to accelerate ions 12,13 . Here we report on the first generation of 5.5-7.5MeV protons by modest laser intensities (4.5 × 10 17 W/cm 2 ) interacting with H 2 O nano-wires (snow) deposited on a Sapphire substrate. In this setup, the plasma near th e tip of the nano-wire is subject to locally enhanced laser intensity with high spatial gradients, and confined charge se paration is obtained. Electrosta tic fields of extremely high intensities are produced, and protons are accelerated to MeV-le vel energies. Nano-wire engineered targets will relax the demand of peak energy from laser based sources.