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