The possibility of absolute calibration of analog detectors by using   parametric down-conversion: a systematical study
  Accurate calibration of photodetectors both in analog and in photon-counting regime is fundamental for various scientific applications, which range from "traditional" quantum optics to the studies on foundations of quantum mechanics, quantum cryptography, quantum computation, etc. In this paper we systematically study the possibility of the absolute calibration of analog photo-detectors based on the properties of parametric amplifiers. Our results show that such a method can be effectively developed with interesting possible metrological applications. 
Giorgio Brida, Maria Chekhova, Marco Genovese, Alexander Penin, Ivano   Ruo-Berchera