Directionality and Spatial Coherence

The same directionality properties as a laser field or, indeed, as any coherent field can be obtained with sources that are nearly spatially incoherent. This has been proved by Collett and Wolf. Here, it is shown that such a result can be made clear intuitively by realizing that suitable superpositions of mutually uncorrelated spatially coherent contributions can drastically reduce the spatial coherence of the resulting field without affecting the far-zone intensity distribution. Practical methods for obtaining such superposition fields starting from spatially incoherent sources are discussed.