  The excitation of atomic levels due to interaction with electromagnetic waves
became of interest in accelerator physics in relation to high efficiency charge
exchange injection into rings for high beam power applications. Usually, the
beam density is so small that its influence on the wave is completely
neglected. Here we consider the case of dense beams - the beam dimensions are
large as compared to light reflection length. This paper shows that the waves
can be trapped in the medium under these conditions. Moreover, the atoms with
induced dipole moments start to interact strongly with each other, leading to
possibility to create some atomic patterns when the medium is relatively cold.
