Purcell effect

The Purcell effect, named after Edward Mills Purcell, stating that the probability of spontaneous emission can be increased by the fact that the source is placed in a resonator. The emission rate grows while at the Purcell factor

Wherein the wavelength of the emitted radiation, and the goodness, the mode volume of the resonator and the refractive index in the respective medium are. The Purcell effect is in particular used in the construction of single photon sources.