Influence of an electrostatic field on the permittivity of dense and cold atomic ensembles

The permittivity tensor of dense and cold atomic ensembles exposed to an electrostatic field has been calculated in the microscopic quantum-mechanical approach. The anisotropic properties and dispersion of the systems under consideration have been analyzed. It has been shown that the electro-optical effects in dense ensembles are manifested in an essentially different manner than in diluted ones, where the resonant dipole-dipole interaction between atoms can be neglected. The discovered features have been explained by the influence of the electric field on the character of collective effects, which affect considerably the optical properties of the ensembles of interacting atoms.