Role of ionization dynamics on copper ion acceleration driven by intense short pulse laser and ultra-thin film interaction

Abstract

Summary form only given. Acceleration of copper ions from ultra-thin targets by a short pulse laser (30fs) with intensity of 10²⁰ W/cm² were systematically studied using two-dimensional relativistic Particle-in-Cell code EPOCH2D¹, which includes an ionization module. It was found that ionization dynamics play an important role in heavy ion acceleration, particularly in the generation of quasi-mono-energetic ion bunches. These bunches were generated from the both sides of target and accelerated by the sheath fields on the surfaces, being attributed from ionization dynamics and Target Normal Sheath Acceleration (TNSA)^2,3. In study of 20 nm copper target, higher charge state ions Cu⁺²⁶ and Cu⁺²⁷ were generated by the laser pulse directly from the target front side. On the target rear side, we detected quasi-mono-energetic Cu⁺²⁰, Cu⁺²¹, Cu⁺²², Cu⁺²³, Cu⁺²⁴ and Cu⁺²⁵ ion bunches. The peak energy increased with ion charge number from 82 MeV (Cu⁺²⁰) to 157 MeV (Cu⁺²³), and the particle number was around 4.5×10⁸ ~ 7×10⁸ for each ion species. A scan of target thickness was made to find an optimum thickness for ion acceleration for the given laser parameters, which was 10 nm. The effect of impurities was also considered in which quasi-mono-energetic O⁺⁷ and O⁺⁸ ion bunches were obtained with O⁺⁸ bunches accelerated to a peak energy of 85 MeV. In this work, it is clear that much more information of ions was obtained than normal PIC simulations, which further helped us to understand the whole interaction process to improve ion acceleration experimental design.