Reciprocity Relations with Partially Coherent Sources

Two general reciprocity relations are formulated, relating to planar sources of any state of spatial coherence and the radiation fields they generate. One of them expresses a reciprocity between the effective coherence area of the source and the effective angular spread of the radiation. The other expresses a reciprocity between the effective intensity spread across the source and the effective angular domain subtended at the source by the coherence area of the far field. Two well-known reciprocity relations associated with coherent and incoherent sources are obtained as special cases. The general reciprocity relations take a particularly simple form when the source is quasi-homogeneous.