Multi-PW laser-driven proton acceleration using a plasma-lens target.

We investigate laser-driven proton acceleration using state-of-the-art multi-petawatt laser technology and a double-layer target design. The front layer is composed of homogenised near-critical density carbon, which enhances the laser pulse through relativistic self-focusing, effectively acting as a lensing medium. This layer is paired with a solid plastic rear layer that serves as the primary acceleration medium. The thicknesses of both layers and the density of the front layer are optimised to maximise acceleration efficiency of the solid layer protons. These protons are accelerated up to 550 MeV through a synergistic interplay of acceleration mechanisms, with hole boring and light sail radiation pressure acceleration playing dominant roles. These mechanisms are further enhanced by target normal sheath acceleration, which benefits from increased laser-to-electron coupling, especially in the front near critical density part. Additionally, proton acceleration is accompanied by the generation of γ-ray radiation via nonlinear inverse Compton scattering. Our investigation employs fully resolved 3D particle-in-cell simulations, providing comprehensive insights into the underlying dynamics. Detailed technical aspects of the simulation setup are discussed.