  Joint photocount distributions of a weak twin beam acquired by an iCCD camera
are analyzed with respect to the beam spatial correlations. A method for
extracting these correlations from the experimental joint photocount
distributions is suggested using a suitable statistical model that quantifies
the contribution of spatial correlations to the joint photocount distributions.
In detail, the profile of twin-beam intensity spatial cross-correlation
function is revealed from the curve that gives the genuine mean photon-pair
number (both photons from a pair are detected) as a function of the extent of
the detection area. Also, the principle of reducing the noise in
photon-number-resolving detection by using spatial correlations is
experimentally demonstrated.
