QED vacuum effects in intense laser fields

Two quantum electrodynamical processes occurring in the presence of a strong laser field and involving the polarization of quantum vacuum are discussed. First, the process of photon splitting in a laser field is examined and the possibility of its experimental observation is investigated. In particular, it is seen that envisaged progress in the generation of high-flux monochromatic gamma ray beams by employing Compton backscattering by electrons coming from an undulator could lead to an experimental observation of this process. Then, the laser photons merging due to vacuum polarization in the collision of a strong laser field and a proton beam is studied. It is shown that this process allows, in principle, the possibility of observing for the first time non-perturbative refractive vacuum polarization effects primed by a strong laser beam.