Gamma-ray flash in the interaction of a tightly focused single-cycle ultra-intense laser pulse with a solid target

We employ the $λ ³$ regime where a near-single-cycle laser pulse is tightly focused, thus providing the highest possible intensity for the minimal energy at a certain laser power. The quantum electrodynamics processes in the course of the interaction of an ultra-intense laser with a solid target are studied via three-dimensional particle-in-cell simulations, revealing the generation of copious $γ$-photons and electron-positron pairs. A parametric study of the laser polarisation, target thickness and electron number density shows that a radially polarised laser provides the optimal regime for $γ$-photon generation. By varying the laser power in the range of 1 to 300 PW we find the scaling of the laser to $γ$-photon energy conversion efficiency. The laser-generated $γ$-photon interaction with a high-$Z$ target is further studied using Monte Carlo simulations revealing further electron-positron pair generation and radioactive nuclide creation.