  We study multi-photon effects in quantum electrodynamics in lepton
photo-production on heavy nuclei and nuclear medium at high energies. We are
interested in energy, charge density and nuclear geometry dependence of the
cross sections. We use the impact parameter representation that allows us to
reduce the problem of photo-production to the problem of propagation of
electric dipoles in the nuclear Coulomb field. In the framework of the Glauber
model we resum an infinite series of multiphoton amplitudes corresponding to
multiple rescattering of the electric dipole on the nucleus. We find that
unitarity effects arising due to multi-photon interactions are small and
energy-independent for scattering on a single nucleus, whereas in the case of
macroscopic nuclear medium they saturate the geometric limit of the total cross
section. We discuss an analogy between nuclear medium and intense laser beams.
