Phase Control of Nonlinear Breit-Wheeler Pair Creation

Prolific e^-e⁺ pair creation in the laboratory will enable the study of collective effects of electron-positron plasma, which is relevant for understanding the physics of extreme astrophysical environments (e.g. magnetosphere of pulsars and magnetars). One way to generate pairs on Earth consists of colliding a relativistic electron beam with a high-intensity laser pulse. In this method, the electrons emit high-energy photons while crossing the pulse through non- linear Compton scattering. These photons then decay into pairs via the nonlinear Breit-Wheeler process. Although experimental observation of pairs produced by these processes has already occurred, only ∼100 positrons were observed experimentally due to limitations in laser intensity which modern state-of-the-art facilities can surpass. Conventionally, the electron-positron pairs co-move after being born and require separation for diagnosis. Here we demonstrate that by using a laser pulse and its second harmonic, it is possible to impart transverse momenta to the pairs such that each species drifts in opposite asymptotic angles after leaving the pulse. This process separates electrons from positrons facilitating experimental detection and diagnosis of these species [1].