Electron-Positron Pair Production Driven by Laser-Accelerated Electrons and Isolated Bremsstrahlung Gamma-Rays

We report on the generation and characterization of relativistic electron-positron beams from two distinct laser-driven schemes. First, in an electron-driven scheme, a 100 TW laser generated a laser-wakefield accelerated (LWFA) electron beam that directly irradiated solid converters (Fe, Zn, W, and Pb) [1]. This approach produced up to 3×10⁸ positrons per shot with a peak leptonic density of 4×10¹² cm^-3 and established that normalizing the converter thickness by its radiation length (L_R) ensures consistent yields across materials. Second, a gamma-ray-driven scheme utilized a multi-PW laser to generate a GeV-scale electron beam, which produced intense bremsstrahlung photons in a primary target [2]. These photons were magnetically separated from charged particles and then directed onto a secondary converter. This method produced pair beams that were uniquely charge-neutral across a broad energy spectrum from 10 MeV to 1.8 GeV, a feature achieved regardless of the converter thickness. These findings demonstrate powerful and distinct methods for generating high-energy pair beams, offering valuable insights for designing future laboratory astrophysics experiments.