Laser-driven proton acceleration via excitation of surface plasmon polaritons into TiO <sub>2</sub> nanotube array targets
G. Cristoforetti, F. Baffigi, F. Brandi, Giuseppe D’Arrigo, A. Fazzi, Lorenzo Fulgentini, D. Giove, P. Koester, L. Labate, G. Maero, Daniele Palla, M. Romé, R. E. Russo, Davide Terzani, P. Tomassini, L. A. Gizzi
Abstract
Abstract In this paper we report the measurement of laser-driven proton acceleration obtained by irradiating nanotube array targets with ultrashort laser pulses at an intensity in excess of 10 20 W cm −2 . The energetic spectra of forward accelerated protons show a larger flux and a higher proton cutoff energy if compared to flat foils of comparable thickness. Particle-In-Cell 2D simulations reveal that packed nanotube targets favour a better laser-plasma coupling and produce an efficient generation of fast electrons moving through the target. Due to their sub-wavelength size, the propagation of e.m. field into the tubes is made possible by the excitation of Surface Plasmon Polaritons, travelling down to the end of the target and assuring a continuous electron acceleration. The higher amount and energy of these electrons result in turn in a stronger electric sheath field on the rear surface of the target and in a more efficient acceleration of the protons via the target normal sheath acceleration mechanism.