Near-field spatial coherence of structured incoherent optical sources

Spatial coherence is a fundamental property of light with many applications. However, if a light source is spatially incoherent and structured, its near-field coherence is difficult to evaluate directly because of the complexity of the emitted random light. In this work, we propose a general approach to calculate the near-field mutual intensity and transverse coherence length of propagating radiation from a periodically structured incoherent source using optical reciprocity. If the structure period is subwavelength and much smaller than the source, the mutual intensity reduces to a Fourier transform of the angular intensity spectrum of the radiation. Tailoring the near-field spatial coherence of incoherent sources by structuring can be used, e.g., for applications in optical sensing and imaging.