Efficient generation of collimated multi-GeV gamma-rays along solid surfaces

Bright gamma-ray sources are of great significance for fundamental research, medicine, and industry. However, gamma-ray pro-duction by bremsstrahlung, Compton scattering, and synchrotron radiation is often subjected to large divergence, wide size, and/or low efficiency, making it difficult to achieve high-brightness gamma-ray sources. Here, we have found an efficient mechanism to generate gamma-rays with, to our knowledge, unprecedented brilliance by use of an ultrarelativistic electron beam with nC charge incident onto a solid surface at grazing incidence. With this interaction configuration, extreme high quasistatic magnetic fields up to the gigagauss level or effective electric fields up to 1014 V/m are induced by the background electron backflows at the target surface. Subsequently, the electron beam is strongly focused by such fields by over an order of magnitude to submicrometer diameter, and its density is increased beyond the solid density; the induced effective fields are high enough to trigger quantum electrodynamics (QED) effects. These result in the produc-tion of extremely brilliant dense gamma-ray beams with photon energy reaching multi-GeV, where the electron-to-photon energy conversion efficiency can exceed 60%. This offers a promising route to push the beam-target interaction to the QED regime, leading to ultrabright gamma-ray sources for various applications. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement