Role of Statistics of Primary Excitations in Optical Coherence
We examine the coherence properties of stationary light obtained by the superposition of nonstationary emissions, occurring at random space-time points. The positions of the points are uniformly distributed over the volume of the source. The emission times fluctuate in accordance with a stationary renewal point process. This process admits super-Poissonian, sub-Poissonian, or Poissonian behavior. The individual emissions are assumed to be in a coherent, chaotic, or n-state. The statistical nature of the random emission space-time points plays an important role in determining the coherence properties and photon statistics of the total field. This is manifested in the normalized secondorder correlation function, which turns out to have the usual form for chaotic light with two additional terms. The first is determined by the statistical nature of the individual emissions (it is positive for coherent or chaotic, but negative for n-state emissions). The second term is governed by the statistics of the primary excitations (it is positive for super-Poissonian, negative for sub-Poissonian, and zero for Poissonian excitations). Both additional terms become very small for light with a high degeneracy parameter (high number of total photons per emission lifetime).