Since the electromagnetic field is no longer a wave, we must revise the way in which we think about this entity. The diagonal elements of the density matrix provide the probabilities of being in a particular field state, n, where n is the number of photons which inhabit this mode. Therefore, each of these amplitudes corresponds to the probability of n photons existing in the mode; so, also corresponds to the probability of counting n photons emitted from the radiation source. If is the largest amplitude, then the probability of counting a single photon is greatest, etc. This reasoning leads one to wonder if there is any pattern to this counting of photons. Suppose that one examines a field for a very long time, would one begin to see an overall pattern to the numbers of photons counted on average? Indeed, there is an overall pattern and different sources of radiation obey different patterns, i.e., statistics. This concept is the basis of photon statistics which is becoming a fascinating field, especially as more and more novel radiation sources are discovered or generated with various non--linear effects.

Wed May 17 14:34:24 EDT 1995