Protons accelerated in the target normal sheath acceleration regime by a femtosecond laser

L Torrisi,J Wołowski,A Torrisi,M Cutroneo,J Badziak,L Silipigni,P Parys,A Zaraś-Szydłowska,G Costa,M Rosinski

doi:10.1103/physrevaccelbeams.22.021302

Abstract

Advanced targets based on thin films of graphene oxide covered by metallic layers have been irradiated at high laser intensity ($\ensuremath{\sim}{10}^{19}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) with 40 fs laser pulses to investigate the forward ion acceleration in the target normal sheath acceleration regime. A time-of-flight technique was employed with silicon-carbide detectors and ion collectors as fast on-line plasma diagnostics. At the optimized conditions of the laser focus position with respect to the target surface was measured the maximum proton energy using Au metallic films. A maximum proton energy of 2.85 MeV was measured using the Au metallization of 200 nm. The presence of graphene oxide facilitates the electron crossing of the foil minimizing the electron scattering and increasing the electric field driving the ion acceleration. The effect of plasma electron density control using the graphene oxide is presented and discussed.

Highlights

In the ambit of laser-driven ion acceleration in solid targets using the target normal sheath acceleration (TNSA) regime [1], let us remember that energetic ions are accelerated not directly by the laser fields but by the plasma field
The plasma fields are formed due to the laser heated electrons; plasma electrons can mediate the forces of laser fields on ions by generating quasistatic electric fields which rise from a local charge separation generated in the rear side of the laser irradiated foil
The role of the relativistic electron crossing the foil is of primary importance, to this we proposed to use a foil of graphene oxide (GO) with a micrometric thickness, covered by metallic films, in order to reduce the electron energy loss in the low density foil [5], the electron scattering and the laser reflections

Summary

Introduction

In the ambit of laser-driven ion acceleration in solid targets using the target normal sheath acceleration (TNSA) regime [1], let us remember that energetic ions are accelerated not directly by the laser fields but by the plasma field. The plasma fields are formed due to the laser heated electrons; plasma electrons can mediate the forces of laser fields on ions by generating quasistatic electric fields which rise from a local charge separation generated in the rear side of the laser irradiated foil. The quasistatic field varies on a timescale comparable to the laser pulse duration and can be of the same magnitude as that of the fast oscillating laser fields, giving the ions significantly longer time to accelerate [2]. The laser energy can be transferred to the plasma electrons by various mechanisms leading to the different ion acceleration regime depending on the laser parameters, the irradiation conditions, and the target properties.

Methods

Results

Conclusion