Multiple transitions in atom optics: Intensity- and density-dependent effects

Starting from the first principles of nonrelativistic QED we have derived the system of Maxwell-Schrödinger equations which can be used for theoretical description of atom optical phenomena at high densities of atoms and high intensities of the laser radiation. The role of multiple atomic transitions between ground and excited states in atom optics has been investigated. Nonlinear optical properties of interacting Bose gases are studied and an equation for the refractive index has been derived. We have investigated the role of light-induced and collisional nonlinearities in the diffraction of an ultracold atomic beam from an intense standing laser wave in the Raman-Nath and in the Bragg regimes.