We investigate the role of the source coherence length in the two alternative definitions, [Phys. Rev. E 66, 016615 (2002)] and [Opt. Commun. 248, 333 (2005)], respectively, on the degree of polarization of a three-dimensional near field emitted by a random planar source. It is demonstrated that for the wide variety of statistically homogeneous sources, there are regimes where both definitions are identical. In particular, this occurs for fields from -correlated, such as thermal sources. Further, we discuss how the excitation of surface waves influence whether those two definitions coincide.
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