Generation of quasimonoenergetic positron beams in chirped laser fields

High energy photons can decay to electron-positron pairs via the nonlinear Breit-Wheeler process when colliding with an intense laser pulse. The spectrum of produced particles is broadened because variation their effective mass in course Applying a suitable chirp pulse narrow distribution generated electrons and positrons. We present scenario where high-energy electron beam collided chirped generate quasi-monoenergetic $\gamma$-photons, which then second chirped, UV produce source