Spectral Invariance and Non-Invariance of Light Generated by Partially CoherentSources

摘要

A basic formula is derived for the spectrum of the field generated by a planarsource of any state of spatial coherence. The formula shows clearly the contribution due to diffraction and due to source correlations. The distinction between these two contributions has not been appreciated in some previous publications. Examples are presented illustrating the effect of source correlations on the spectrum of the far field. A brief preliminary account is also presented of a recent investigation by H. Chen and E. Wolf which has shown that it is possible to produce a source whose degree of coherence will act on the spectrum of the source as a low pass filter with a sharp frequency cut off.