  Reconstruction of photon statistics of optical states provide fundamental
information on the nature of any optical field and find various relevant
applications. Nevertheless, no detector that can reliably discriminate the
number of incident photons is available. On the other hand the alternative of
reconstructing density matrix by quantum tomography leads to various technical
difficulties that are particular severe in the pulsed regime (where mode
matching between signal an local oscillator is very challenging). Even if
on/off detectors, as usual avalanche PhotoDiodes operating in Geiger mode, seem
useless as photocounters, recently it was shown how reconstruction of photon
statistics is possible by considering a variable quantum efficiency. Here we
present experimental reconstructions of photon number distributions of both
continuous-wave and pulsed light beams in a scheme based on on/off avalanche
photodetection assisted by maximum-likelihood estimation. Reconstructions of
the distribution for both semiclassical and quantum states of light (as single
photon, coherent, pseudothermal and multithermal states) are reported for
single-mode as well as for multimode beams. The stability and good accuracy
obtained in the reconstruction of these states clearly demonstrate the
interesting potentialities of this simple technique.
