Ultracold Bose atoms in intense laser fields: intensity- and density-dependent effects

Starting from the first principles of nonrelativistic QED we have derived the system of Maxwell-Schr\"odinger 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 gas are studied: formula for the refractive index has been derived and the polariton spectrum of a condensate interacting with an intense laser field has been investigated.