Experimental demonstration of the van Cittert-Zernike theorem for random electromagnetic fields

In scalar coherence theory, the van Cittert-Zernike theorem plays an importance role for studying the propagation processes of partially coherent fields. In the past few years, a lot of work has been done to describe an extension of the van Cittert-Zernike theorem in terms of the 2x2 matrix to examine coherence and polarization properties of the field generated by a partially polarized incoherent electromagnetic beam. In this paper, we would like to experimentally demonstrate the unified theory of coherence and polarization of random electromagnetic beams by a modified radial shearing interferometer, which may be regarded as a tensor version of van Cittert-Zernike theorem. The experimental results show that the mutual intensity matrix of the electromagnetic field produced by a polarized incoherent source increases on propagation whereas the degree of the polarization remains unchanged.