General Theorem of Spatial Coherence:

INTRODUCTION The Michelson stellar interferometer (MSI) (also known as long-baseline interferometer) is used for measuring the shape of planar objects that emit quasi-monochromatic, spatially incoherent light. Its principle of operation is based on recording interference patterns in the far field obtained by a two-pinhole Young interference configuration. The fringes' visibility and phase versus the separation between the pinholes are equal to the complex degree of coherence in the plane of the pinholes. According to the Van Cittert--Zernike theorem, the complex degree of coherence is proportional to the Fourier transform of the source's (planar) intensity distribution. Thus measuring the complex degree of coherence versus pinhole separation and performing inverse Fourier transformation yield the image distribution of the source. The resolution of this imaging method is proportional to the maximum distance between the pinholes. Thus the resolution of an MSI with a maximum pinho