Fast scaling of energetic protons generated in the interaction of linearly polarized femtosecond petawatt laser pulses with ultrathin targets

Abstract

Laser-driven proton/ion acceleration is a rapidly developing research field attractive for both fundamental physics and applications such as hadron therapy, radiography, inertial confinement fusion, and nuclear/particle physics. Laser-driven proton/ion beams, compared to those obtained in conventional accelerators, have outstanding features such as low emittance, small source size, ultra-short duration and huge acceleration gradient of similar to 1 MeV mm(-1). We report proton acceleration from ultrathin polymer targets irradiated with linearly polarized,30-fs, 1-PW Ti: sapphire laser pulses. A maximum proton energy of 45 MeV with a broad and modulated profile was obtained when a 10-nm-thick target was irradiated at a laser intensity of 3.3 x 10(20) W/cm(2). The transition from slow (I1/2) to fast scaling (I) of maximum proton energy with respect to laser intensity I was observed and explained by the hybrid acceleration mechanism including target normal sheath acceleration and radiation pressure acceleration in the acceleration stage and Coulomb-explosion-assisted free expansion in the post acceleration stage. (C) 2014 Elsevier B.V. All rights reserved.