When the interparticle distance of a gas of atoms is small compared with the spontaneous radiation wave length, the photon emitted by one atom may be absorbed by other atoms and may thus be trapped in the gas. The number of photons that are emitted is therefore reduced, as compared to the incoherent radiation of a gas of widely separated atoms. This photon trapping effect on the natural linewidth of the radiation is calculated and found to be large in certain cases. Some experimental aspects of observing such an effect are also discussed.

• Received 26 August 1968

DOI:https://doi.org/10.1103/PhysRev.183.147