Quantum electrodynamics in intense laser fields
A very intense laser field polarizes the virtual electron-positron pairs that populate the vacuum. This provides for a coupling between different modes of the electromagnetic field, giving rise to effects such as scattering of light by light, a refractive index of the vacuum, vacuum birefringence, etc. Given enough energy in a sufficiently small spacetime region, the virtual pairs can become real, which leads to pair production in the intense field under the action of a third agent. These, as well as related effects, are summarized with respect to their orders of magnitude and conditions under which they might become accessible to experiment. Some other processes that are normally mentioned in this context, such as Thomson (Compton) scattering at high intensities, are considered, too, even though they are unrelated to the vacuum structure of quantum electrodynamics.
