Photon polarisation in electron-seeded pair-creation cascades

An electromagnetic pair-creation cascade seeded by an electron or a photon in an intense plane wave interacts in a complicated way with the external field. Many simulations neglect the vector nature of photons by including their interaction using unpolarised cross-sections. After deriving rates for the tree-level processes of nonlinear Compton scattering and pair creation with an arbitrary linearly-polarised photon in a constant-crossed field, we present results of numerical simulations that include the photon's vector nature. The simulations of seed electrons in a rotating electric field of optical frequency on the one hand support the approximation of using unpolarised cross-sections for tree-level processes, which predicts the same number of created particles when using polarised cross-section to within around 5 percent. On the other hand, these simulations show that when the polarisation of the photon can be influenced by its environment, the asymmetry in the polarisation distribution could be used to significantly increase the rates of each process.