Ultrabright GeV photon source via controlled electromagnetic cascades in laser-dipole waves

Abstract

Electromagnetic cascades have the potential to act as a high-energy photon source of unprecedented brightness. Such a source would offer new experimental possibilities in fundamental science, but in the cascade process radiation reaction and rapid electron-positron plasma production seemingly restrict the efficient production of photons to sub-GeV energies. Here, we show how to overcome these energetic restrictions and how to create a directed GeV photon source, with unique capabilities as compared to existing sources. Our new source concept is based on a controlled interplay between the cascade and anomalous radiative trapping. Using specially designed advanced numerical models supported with analytical estimates, we demonstrate that the concept becomes feasible at laser powers of around 7 PW, which is accessible at soon-to-be-available facilities. A higher peak power of 40 PW can provide 109 photons with GeV energies in a well-collimated 3-fs beam, achieving peak brilliance 9 × 1024 ph s-1 mrad-2 mm-2=0.1%BW.