High power gamma flare generation in multi-petawatt laser interaction with tailored targets

Using quantum electrodynamics particle-in-cell simulations, we optimize the gamma flare ($\gamma$-flare) generation scheme from the interaction of high power petawatt-class laser pulse with tailored cryogenic hydrogen target having extended pre-plasma corona. We show that it is possible to generate an energetic flare of photons with energies in the GeV range and total flare energy being on a kilojoule level with the efficient conversion of the laser pulse energy to $\gamma$-photons. We discuss how the target engineering and laser pulse parameters influence the $\gamma$-flare generation efficiency. High-Z targets, the oblique incidence of the laser pulse, and the effects of realistic pre-plasma obtained by hydrodynamical simulations are also discussed. This type of experimental setup for laser-based $\gamma$ source would be feasible for the upcoming high power laser facilities.