Absolute calibration of photon-number-resolving detectors with an analog   output using twin beams
  A method for absolute calibration of a photon-number resolving detector producing analog signals as the output is developed using a twin beam. The method gives both analog-to-digital conversion parameters and quantum detection efficiency for the photon fields. Characteristics of the used twin beam are also obtained. A simplified variant of the method applicable to fields with high signal to noise ratios and suitable for more intense twin beams is suggested. 
Jan Perina Jr., Ondrej Haderka, Alessia Allevi, Maria Bondani
quant-ph