It is known that the cross-correlation function (CCF) of a partially coherentvortex (PCV) beam shows a robust link with the radial and azimuthal modeindices. However, the previous proposals are difficult to measure the CCF inpractical system, especially in the case of astronomical objects. In thisletter, we demonstrate experimentally that the Hanbury Brown and Twiss effectcan be used to measure the mode indices of the original vortex beam andinvestigate the relationship between the spatial coherent width and thecharacterization of CCF of a PCV beam. The technique we exploit is quiteefficient and robust, and it may be useful in the field of free spacecommunication and astronomy which are related to the photon's orbital angularmomentum.
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