  We have studied correlations in the speckle patterns generated by the
scattering of perfect optical vortex (POV) beams and used them for producing a
new-class of coherence functions, namely Bessel coherence functions. Higher
(zeroth) order Bessel coherence functions have been realized in cross
(auto)-correlation between the speckle patterns generated by the scattering of
perfect vortex beams of different orders. We have also studied the propagation
of produced Bessel coherence functions and characterized their divergence with
respect to the radius of their first ring for different orders m=0--4. We
observed that the divergence varies linearly with the order of the coherence
function. We provide the exact analytical expression for the auto-correlation
as well as cross-correlation functions for speckle patterns. Our experimental
results are in good agreement with the analytical results.
