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.Comment: 4 pages, 3 figure
