be detected in the field free region. These photons can be considered as emitted from the vacuum subjected to the space-time dependent macroscopic laser field – whose microscopic composition in terms of laser photons is not resolved – enabling and stimulating the emission process. Of course, this scenario can alternatively be interpreted in terms of microscopic laser photon scattering and deflection in the collision of two laser pulses. From this perspective, the emitted photons correspond to the outgoing photons carrying the imprint of the collision process, i.e., outgoing photons whose properties (in particular their polarization characteristics and propagation directions) differ from the incident laser photons brought into collision. However, we believe that viewing laser pulse collision processes in terms of a stimulated emission process, i.e., viewing the laser pulses as macroscopic fields, rather than in terms of the constituting laser photons, allows for a particularly intuitive and elegant theoretical treatment. In this framework it is easy to vary detector sizes and ask for the number of photons carrying the signature of vacuum nonlinearity to be registered in any given solid angle interval, which is not so straightforward in other approaches. In addition, and in contrast to previous studies, e.g., [@King:2012aw; 