Electron-Photon Interaction in Microcavities

Spontaneous emission is a physical phenomenon observed not only in laboratories but also in daily life where various materials emit light spontaneously. The typical phenomenon is the fluorescence of materials excited in some way. Spontaneous emission is known as an elementary process which is required, together with the process of stimulated emission, to establish thermal equilibrium between matter and a light field. In free space, spontaneous emission is an irreversible process, i.e., once a photon is emitted by an atom, it never returns to the emitting atom and, ultimately, escapes to remote space or is dissipated in obstacles. Spontaneous emission occurs when an atom is excited to a high-lying level and then releases the energy in the form of light. The emission of light is accompanied by a decay to a lower-lying level.