Ultra-bright GeV photon source via controlled electromagnetic cascades   in laser-dipole waves
  One aim of upcoming high-intensity laser facilities is to provide new high-flux gamma-ray sources. Electromagnetic cascades may serve for this, but are known to limit both field strengths and particle energies, restricting efficient production of photons to sub-GeV energies. Here we show how to create a directed GeV photon source, enabled by a controlled interplay between the cascade and anomalous radiative trapping. Using advanced 3D QED particle-in-cell (PIC) simulations and analytic estimates, we show that the concept is feasible for planned peak powers of 10 PW level. A higher peak power of 40 PW can provide $10^9$ photons with GeV energies in a well-collimated 3 fs beam, achieving peak brilliance ${9 \times 10^{24}}$ ph s$^{-1}$mrad$^{-2}$mm$^{-2}$/0.1${\%}$BW. Such a source would be a powerful tool for studying fundamental electromagnetic and nuclear processes. 
A. Gonoskov, A. Bashinov, S. Bastrakov, E. Efimenko, A. Ilderton, A.   Kim, M. Marklund, I. Meyerov, A. Muraviev, and A. Sergeev
physics.plasm-ph