Partial coherence: A nonstatistical approach, and some basic microwave experiments.

The basic concepts of second-order coherence theory are introduced, followed by a nonstatistical development of the coherence equations. The various possible generalizations of scalar second-order coherence are briefly described. Microwave experiments are reported in which incoherent as well as partially coherent radiating sources are simulated by suitable arrangements of noise tubes. Two effects in particular are examined: the factorization of the coherence function into space- and time-dependent factors under conditions of "spectral purity," and the spectral modulation of two superposed beams that have a large path delay between them (Alford and Gold effect).