Glauber Effect

Does a standard incandescent light bulb emit single photons? Paired photons? Triplets?

Answer

Yes, a standard incandescent light bulb does emit single photons, and sometimes there are photon pairs, and triplets, and so on. In the ideal chaotic photon source a hot, incandescent wire that has physical dimensions smaller than a wavelength of the emitted light, for example the first spontaneously emitted photon can stimulate the emission of a second photon from a nearby atom, and the two can stimulate the emission of a third photon, and so on. In principle, the photons arriving at the receptor can be single, double, triple, and so on, the actual photon state depending on how many stimulated photons were picked up before escaping the light source. The receptor receives a different energy burst with each absorption. Since the probability for stimulated emission into the same final state is proportional to the number of photons in that state already, these multiple photon processes occur quite readily.

Real light sources such as incandescent bulbs have huge physical dimensions compared to the wavelength of light. There will be numerous ideal chaotic sources along the filament wire simultaneously and randomly emitting photons toward the detector. These photons tend to arrive in bunches, with the photons within any one bunch coming from several places in the source. Very seldom does one find a steady stream of photons with nearly equal time spacing arriving from the light bulb when one looks on the nanosecond time scale.