We show that the cross-spectral density in the far zone of a homogeneous spherical source can be described as a low-pass filtered version of that existing across the source surface. We prove that, to an excellent approximation, the corresponding filter with respect to a (normalized) spatial frequency has a functional structure of the form , for . The cases of spatially incoherent and Lambertian sources are treated as significant examples.
© 2012 Optical Society of America
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