Single photon sources with different spatial modes

We study the correlation properties of single photons carrying orbital angular momentum (OAM) in a Hanbury Brown and Twiss (HBT) type experiment. We have characterized single photon sources obtained by pumping a nonlinear crystal with a laser beam carrying different OAM under same experimental conditions. For heralded twisted single photons carrying OAM, we calculate g(2)(0), a measurable parameter characterizing the quality of a single photon source, and observe an increment with the OAM of the single photon.