Target normal sheath acceleration by fs laser and advanced carbon foils with gold films and nanoparticles

Abstract

Thin foils of graphene oxide (GO) are irradiated by a fs titanium sapphire laser at an intensity of about 1019 W/cm2 in high vacuum. The produced plasma in the forward direction accelerates ions in a regime of target-normal-sheath-acceleration, thanks to the relativistic electron emission from the target surface and to their emission from the rear foil surface, generating a high electric field pulse with the positive target. The ion acceleration is measured mainly using SiC detectors in the time-of-flight configuration. Adding gold as nanoparticles or as a thin coverage film, the ion acceleration is enhanced as a result of a higher plasma electron density. The optimal acceleration is reached by varying the GO thickness, the Au nanoparticle concentration, the thin Au film thickness, and the irradiation conditions. Particularly important is the laser focal position with respect to the target surface, which is responsible for different acceleration values. In the used experimental conditions, a maximum proton energy of 2.6 MeV was obtained and the best modality to add Au atoms to the target is discussed.