Highly efficient γ-ray generation by 10 PW-class lasers irradiating heavy-ion plasmas

10 PW-class lasers irradiating overcritical plasmas in the quantum electrodynamics regime promise to generate ultrabright γ-ray sources in the laboratory. Here using two-dimensional particle-in-cell simulations, we report highly efficient γ-ray generation in the parameter regime of 10 PW-class lasers at an intensity level of 10²³ W cm^–2 interaction with heavy-ion plasmas which have large-scale preplasmas. The laser-to-γ-ray (> 1 MeV) energy conversion efficiency reaches close to 60% with an above 10¹⁴γ-photons/pulse. The average γ-photon energy is about 14 MeV with the highest photon energy exceeding 1 GeV. The high-energy γ-photons are mainly directed in the forward direction. We also find that plane target geometry is efficient enough for high power γ-ray radiation, which is beneficial for easing the difficulty of complex target manufacturing and alignment in experiments.