New spectral representation of random sources and of the partially coherent fields that they generate

It is shown that, contrary to general belief, it is possible to construct a statistical ensemble of monochromatic oscillations, all of the same frequency, that yields rigorously the spectral and cross-spectral densities of a fluctuating, statistically stationary source and of the field that the source generates. New mode representations are also introduced. The modes may be interpreted as natural oscillations of sources and fields of any state of coherence.