SPIRE: Spin-Resolved Particle-in-Cell with Radiative Corrections for Extreme Laser--Plasma Interactions

Abstract

We present SPIRE, a spin- and photon-polarization-resolved particle-in-cell (PIC) code for self-consistent simulations of laser-plasma interactions in the strong-field quantum electrodynamics (QED) regime. The classical PIC framework combines a Yee-grid finite-difference time-domain Maxwell solver, a relativistic Boris particle pusher, shape-function particle-grid interpolation, Esirkepov charge-conserving current deposition, laser boundary injection, and a relativistic moving window in one, two, and three spatial dimensions. A vectorial Laguerre-Gaussian laser injector based on an angular-spectrum formulation supports tightly focused, nonparaxial optical orbital-angular-momentum modes. The strong-field QED module treats nonlinear Compton scattering and nonlinear Breit-Wheeler pair production as stochastic processes using spin- and polarization-resolved probabilities in the local constant-field approximation. Electron and positron spin evolution includes stochastic transitions, no-emission corrections, and Thomas-Bargmann-Michel-Telegdi precession with a field-dependent anomalous magnetic moment. Photon polarization is represented by the Stokes vector and evolves through nonlinear Compton scattering, pair production, vacuum birefringence, and vacuum dichroism. The implementation is verified with one-, two-, and three-dimensional benchmarks. Classical PIC results are cross-checked against SMILEI, and the spin- and polarization-resolved QED modules reproduce published results for polarized electron generation, vacuum birefringence and dichroism, and dense polarized positron production. These benchmarks verify the coupled classical PIC, strong-field QED, spin, and photon-polarization modules implemented in SPIRE.