  The scattering of photons off photons at the one-loop level is investigated.
We give a short review of the weak field limit, as given by the first order
term in the series expansion of the Heisenberg-Euler Lagrangian. The dispersion
relation for a photon in a radiation gas is presented. Based on this, a wave
kinetic equation and a set of fluid equations is formulated. These equations
describe the interaction between a partially coherent electromagnetic pulse and
an intense radiation gas. The implications of the results are discussed.
