Photon statistics without counting photons
  We show how to obtain the photon distribution of a single-mode field using only avalanche photodetectors. The method is based on measuring the field at different quantum efficiencies and then inferring the photon distribution by maximum-likelihood estimation. The convergence of the method and its robustness against fluctuations are illustrated by means of numerically simulated experiments. 
Andrea R. Rossi, Stefano Olivares, Matteo G.A. Paris