Infra-red divergences in plane wave backgrounds
  We show that the emission of soft photons via nonlinear Compton scattering in a pulsed plane wave (laser field) is in general infra-red divergent. We give examples of both soft and soft-collinear divergences, and we pay particular attention to the case of crossed fields in both classical and quantum theories. 
Victor Dinu, Thomas Heinzl, Anton Ilderton
hep-ph hep-th