Independent-elementary-field model for three-dimensional spatially partially coherent sources.

The independent-elementary-source model recently developed for planar sources [Opt. Express 14, 1376 (2006)] is extended to volume source distributions. It is shown that the far-field radiation pattern is independent of the three-dimensional (3D) distribution of the coherent elementary sources, but the absolute value of the complex degree of spectral coherence is determined by the 3D Fourier transform of the weight function of the elementary fields. Some methods to determine an 'effective' three-dimensional source distribution with partial transverse and longitudinal spatial coherence properties are outlined. Especially in its longitudinal extension, this effective source volume can be very different from the primary emitting volume of the source. The application of the model to efficient numerical propagation of partially coherent fields is discussed.