Proton acceleration from ultrahigh-intensity short-pulse laser-matter interactions with Cu micro-cone targets at an intrinsic ∼10-8 contrast

Abstract

In this paper, we report on experiments comparing various geometries of conical Cu targets to Cu flat foils, which were performed on the 200 TW Trident laser (∼80 J, 600 fs, ∼7 μm spot size, S-polarization and ∼1.5×1020 W/cm2) at an intrinsic (to the system's regenerative amplifier) ASE contrast of 10-8. The current work builds on previous results obtained on Trident (∼20 J, ∼14 μm spot size, P-polarization, ∼1019 W/cm2, also at the intrinsic contrast of 10-8) demonstrating enhanced proton energies and laser-proton conversion efficiencies (η) using Flat Top Cone (FTC) targets [1]. An electron spectrometer and a Cu Kα imaging diagnostic were added to respectively assess the electron population, and determine the characteristics of laser absorption in FTCs. Results indicate a linear correlation between electron temperatures and proton energies, as well as laser absorption taking place in a preplasma filling the cone, preventing the previously observed enhancement in proton energies. © 2010 IOP Publishing Ltd.