Electron-positron pair generation using a single kJ-class laser pulse in a foam-reflector setup

TL;DR

The paper proposes and analyzes a single-shot, foam-based laser–matter setup to access strong-field QED, where direct laser acceleration in a near-critical foam generates high-energy electrons that, upon reflection from a cone-shaped reflector, experience a counterpropagating field that drives nonlinear Compton scattering and Breit-Wailer pair production. Using 3D PIC simulations with Monte Carlo QED and sub-sampling to improve statistics, complemented by 2D parameter scans, the authors map how foam channel parameters and reflector geometry affect pair yield. They find that maximizing field amplification at the reflector and optimizing the foam channel (density and width) can yield up to ~ $10^{11}$ electron-positron pairs from a 1.5 kJ laser, with a 3D case reaching $\chi \sim 10$ and pair spectra extending to the GeV scale. Pre-pulse structure can dramatically alter results, underscoring the need for precise pulse shaping, but the single-stage approach remains a practical route to study SF-QED dynamics and dense pair plasmas in the laboratory.

Abstract

We investigate the process of creating electron-positron pairs from laser-matter interaction in pre-ionised foam targets using particle-in-cell simulations. A high-intensity laser pulse drives electrons via direct laser acceleration up to a cone-shaped reflector. The high-energy electrons interact with the reflected laser pulse, generating abundant pairs. The effects of the plasma-channel shape on the propagation of the laser pulse and subsequent pair production is studied. The results show that the number of Compton emission and Breit-Wheeler pair creation events is highly sensitive to the diffraction of the laser due to its interaction with the foam.

Figures (7)

• Figure 1: Visualisation of the laser pulse propagating through the pre-ionised foam inside a cone-shaped cavity within a solid reflector target. The laser expels electrons transversely, forming a channel structure (green). Once the laser pulse is reflected at the cone target, a region with high $\chi$-parameter is generated (blue).
• Figure 2: Longitudinal (blue) and perpendicular(red) momentum of a particle with the $B_z$ (grey) field it experiences.
• Figure 3: Total kinetic energy of high-energy ($E_\mathrm{kin} > 0.5$ GeV) electrons over time (top) for different plasma channel parameters and the maximum $B_z$ field for different parameters. Results from a 2D simulation with $n_0 = 0.3 n_c$ , $n_1 = n_c$ and $\sigma = 10\lambda$ unless stated otherwise.
• Figure 4: Amplification of the field amplitude for different opening angles $\alpha$ and positions $x_0$ of the reflector target.
• Figure 5: Maximum $\gamma_{e^-}$ (top), maximum $B_z$ (middle) and total pairs created (bottom) against the length of the foam pre-plasma, from 2D simulations.