Generalized canonical statistical operator and entropy of partially coherent radiation

Using information-theoretical concepts and Glauber's correlation functions, the statistical operator of an Nth-order partially coherent radiation field is constructed. Special consideration is given to the cases N = 1 and N = 2. The entropy for N = 1 yields the early formula of von Laue. Our results for N > 1 shed new light on the relationship between thermodynamical order of a radiation field, as measured by its entropy, and optical coherence, especially in the quantum-mechanical case.