100 MeV protons from nanostructured hemispherical target using PIC simulations

Abstract

The improvement of laser-driven proton energy with the use of nano-structured hemispherical targets of 100 nm thickness over conventional flat foil has been reported in this work. The curvature of the target is found to result in focussed particle density at the center of the hemispherical target followed by emergence of energetic ions due to combined action of sheath electric field and ambipolar expansion. The presence of nano-rods on the curved hemispherical target further increases the laser energy absorption by the electrons, thus resulting in increase in the maximum proton energy. Use of hemispherical target embedded with nanorods is possibly reported here for the first time that may generate protons with energy 92 MeV by using linearly polarised laser of intensity 1021 W cm−2 and pulse duration of 30 fs. At this laser intensity, the energy gain by the protons is much higher compared to the conventional flat foil targets. The maximum proton energy can be increased further to 103 MeV by using truncated hemispherical target of similar parameter.