Single-laser scheme for reaching strong field QED regime via direct laser acceleration

Abstract

We investigate a single-laser scheme for reaching the strong-field QED regime based on direct laser acceleration (DLA) of electrons followed by their head-on collision with the same laser pulse reflected from an overdense foil. In this configuration, electrons are first accelerated inside an underdense plasma by a relativistic laser pulse and subsequently interact with the reflected laser field, emitting high-energy photons via nonlinear Compton scattering which decay into electron-positron pairs through the nonlinear Breit-Wheeler process. Using analytical scalings supported by quasi-3D particle-in-cell simulations including QED effects, we demonstrate that a laser pulse with power as low as 2 PW is sufficient to reach the quantum regime characterized by $\chi_e> 1$ . For higher powers, we observe a rapid nonlinear increase in the number of generated positrons, reaching more than 2 nC for a 10 PW laser pulse with energy of approximately 1.1 kJ. A semi-analytical model is employed to estimate the positron yield, showing good agreement with simulation results. We further study the influence of laser depletion and the positioning of the reflecting foil on the efficiency of pair production. The presented scheme provides an experimentally feasible platform for probing strong-field QED effects using currently available multi-petawatt laser systems.