Measurement of the coherence-orbital angular momentum matrix of a partially coherent beam

The recently introduced coherence-orbital angular momentum (COAM) matrix of a partially coherent beam [ Phys. Rev. A 103 , 023529 ( 2021 ) 10.1103/PhysRevA.103.023529 ] is experimentally measured for the first time, to the best of our knowledge. The new methodology based on Young’s interference experiment with a pair of ring-shaped slits with embedded spiral phases is thoroughly described. By introducing the phase shift of 0 and π / 2 between two ring slits, the real and imaginary parts of the elements of the COAM matrix are obtained by measuring the on-axis spectral density in the far field of the double-ring slit. We validate our protocol through measuring the COAM matrix of an elliptical Gaussian Schell-model (GSM) beam which reveals the existence of non-trivial correlations between modes with different topological indices. The experimental results agree reasonably well with the theoretical predictions.