The ability to generate fast protons from small and relatively inexpensive systems is of great importance to many applications such as medical radiation treatment and others. Target structuring is considered as one of the possible ways towards this goal. Nano-structured solid or quasi-solid targets attract significant attention. The presented scheme of using H₂O “snow” nano-wires can relieve the demand for very high laser intensities, thus reducing the size and the cost of laser systems.

Usually ultra high intensity laser beams produce protons above the MeV energy level when the multi –terawatt scale laser facility provides intensity on the target which is at least 10¹⁸ – 10¹⁹ W/cm² and the beam irradiates targets such as thin-foils or gas jets. In this study, we examined the ability to achieve the same proton energy range with use of relatively modest laser intensity (10¹⁷ W/cm²) and a nano-structured H₂O target.

In this present experiment, we used frozen H₂O deposited on Sapphire, which were shaped as nanometer sized elongated wires with characteristic diameter in the range of 10-100 nm and length of several µm. In this setup, the plasma near the tip of the nano-wire is subject to locally enhanced laser intensity with high spatial gradients, and confined charge separation is obtained. Electrostatic fields of extremely high intensities are produced, and protons are accelerated to MeV-level energies.  Nano-wire engineered targets will relax the demand of peak energy from laser based sources.

[1] A. Zigler , T. Palchan , N. Bruner , E. Schleifer , S.Eisenmann Z. Henis, M. Botton, S.A. Pikuz, A.Y. Faenov Jr, D. Gordon, P.Sprangle, arXiv:1011.0632v1 [physics.plasm-ph]

[2] T. Palchan, S. Pecker, Z. Henis, S. Eisenmann, and A. Zigler,  Appl. Phys. Lett. 90 041501 (2007)

[3] T. Palchan, Z. Henis, A. Y. Faenov, A. I. Magunov, S. A. Pikuz, S. V. Gasilov, I. Yu. Skobelev, and A. Zigler, Appl. Phys. Lett. 91 251501 (2007)