Dynamical instabilities of spectroscopic transitions in dense resonant media

We consider the influence of the near dipole-dipole interaction, underlying the local field, on the dynamics of two-level and V-type three-level atoms exposed to cw-laser radiation. The dipole-dipole interaction between the V-type three-level atoms is shown to give rise to the Poincar\'e-Andronov-Hopf bifurcation in steady-state solution of the equations of motion. As a result, the populations of the energy levels periodically vary in time. In the framework of the two-level model, dynamical instabilities are proved to be impossible.