Inhibited spontaneous emission and electromagnetic instability of an atom in the near zone from the surface of an active medium

The back reaction field and the self-consistent dynamics of a radiating dipole atom situated near a plane boundary between two isotropic media with different values of complex dielectric constants is studied. It is shown that spontaneous emission of an excited atom is suppressed, and electromagnetic instability of the ground state is possible, if an atom is located in the vicinity of an active medium which amplifies the propagating radiation. The effect is due to the modified and phase-shifted near field of an oscillating atomic dipole, which prevails over the usual radiation reaction field related to the wave zone. The role of the nonradiative energy transfer from the medium to an atom is emphasized. The necessary conditions for the reversal of the total electromagnetic back reaction are found, and possible experimental realizations of the predicted phenomena are discussed. In particular, it is argued that an atom initially in its ground state can get spontaneously excited and emit photon when going to the upper energy level.