Laser plasma proton acceleration experiments using foam-covered and grating targets

A. Sgattoni, T. Ceccotti, V. Floquet, A. Bigongiari, M. Raynaud, C. Riconda, F. Baffigi, L. Labate, L. A. Gizzi, L. Vassura, J. Fuchs, O. Klimo, M. Kveton, F. Novotny, M. Possolt, J. Prokupek, J. Proska, J. Psikal, L. Stolcova, A. Velyhan, M. Bougeard, P. Martin, I. Prencipe, A. Zani, D. Dellasega, A. Macchi, M. Passoni

Proceedings of SPIE: LASER ACCELERATION OF ELECTRONS, PROTONS, AND IONS II; AND MEDICAL APPLICATIONS OF LASER-GENERATED BEAMS OF PARTICLES II; AND HARNESSING RELATIVISTIC PLASMA WAVES III, vol. 8779, Article Number: UNSP 87790L, (2013).

Abstract

Experimental results are reported for two different configurations of laser driven ion acceleration using solid foils with a structured layer on the irradiated side, aiming to improve the laser-target coupling by exploiting engineered surfaces. Two experimental campaigns have been performed exploiting a 100TW 25fs Ti:Sa laser capable of maximum intensity of 4.10(19) W/cm(2). "Grating" targets have been manufactured by engraving thin mylar foils (0.9, 20 and 40 mu m) with a regular modulation having 1.6 mu m period and 0.5 mu m depth. The periodicity of the grating corresponds to a resonant incident angle of 30 degrees for the excitation of surface waves. Considering a target of 20 mu m and changing the angle of incidence from 10 degrees to 45 degrees, a broad maximum in the proton energy cut-off was observed around the resonant angle (about 5 MeV) which was more than a factor two higher than the case of planar target. "Foam" targets have been manufactured by depositing a porous 10 mu m nanostructured carbon film with an average density of 1-5 mg/cm(3) on a 1 mu m thick aluminium foil. At maximum focalization the foam targets gave a maximum proton energy similar to the case of bare aluminium target (about 6 MeV), while educing the intensity the presence of the foam enhanced the maximum proton energy, obtaining about 1.5MeV vs. 500KeV at an intensity of 5. 10(16) W/cm(2). 2D Particle-In-Cell simulations have been used to support the intepretation of the experimental results.