RADIATING ATOMS IN CONFINED SPACE - FROM SPONTANEOUS EMISSION TO MICROMASERS

Radiation of excited atoms is the fundamental mechanism of physical phenomena as important as, for instance, laser radiation. Spontaneous emission is ultimately responsible for the quantum fluctuations of a conventional laser field, and it is frequently considered an inescapable fate. In mirror cavities, electromagnetic fields are reflected and act back onto the atomic source of radiation. Depending on the circumstances, the spontaneous emission rate may be enhanced or decreased, in extreme cases even completely suppressed. Cavity induced modifications further include dispersive energy shifts and modifications of radiative forces. In a micromaser the field radiated from atoms is stored in a low-loss cavity. The radiation energy may be emitted and reabsorbed many times. Micromaser fields have nonclassical properties and present a simple illustration of the quantum theory of measurement.