Multi-photon Emission

When an electron drops from an excited state why does it only emit one photon? (Why can't it emit multiple photons with the sum of the energies of the photons being equal to the change in energy of the electron)
- Bob (age 25)
Seattle, WA, USA

Those multi-photon processes can and do happen. However, except when some selection rule forbids the single-photon process, they're much less common. The reason is essentially that the coupling between the charges and the photon field is not very strong. It's characterized by the dimensionless fine-structure constant, 2πe²/hc, where e is the electronic charge, h is Planck's constant, and c is the speed of light. This number is about 1/137, which means that generally the probability of many-photon processes is low.

Mike W.

(published on 10/14/2012)