Enhanced Energy Localization and Heating in High ContrastUltra-Intense Laser Produced Plasmas via Novel ConicalMicro-Target Design

摘要

We report new experiments showing enhanced laser-target coupling and energyrnlocalization using nano-fabricated micro-conical Cu targets performed at the 100 TW CPArnlaser at LULI. A comparison was made between 1ω (λ = 1.057 μm, I = 1019 W/cm2) and 2ω (λrn= 0.53 μm, I = 4-8×1018 W/cm2) irradiation to determine the effect of ASE induced preformedrnplasma filling the cone, using as principal diagnostics 2D Cu Kα imaging (transversernand rear-side), and high-resolution conical crystal spectroscopy of the Cu Kα bands. The 2ωrnirradiation exhibits laser absorption up to 50 μm deeper into the cone tip (versus at 1ω), with arncommensurately smaller Kα emission zone. Spectroscopy indicates a higher average chargernstate for the Cu emission at 2ω, with some shots exhibiting up to at least O-like emission. Werndeduce that micro-cone targets have similar performance in terms of material heating as a 50rnμm diameter reduced mass target, despite a 900-fold larger mass. The observed enhancementrnin energy localization and heating in the cone geometry is supported by 2D collisional PICrnsimulations which indicate the presence of self-generated resistive magnetic field structures (≥rn10 MG) which confine the energetic electrons to the tip region