Biphoton fields for quantum-efficiency measurements

This paper reports on an experiment performed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN), aiming at the production of biphoton fields by parametric scattering of light in a nonlinear crystal of lithium iodate. The blue line at 457,9 nm from an argon laser is used as pumping radiation, thereby resulting in a fluorescence in the visible region with degenerate pairs of photons at about 916 nm. These biphoton fields are well suited to the measurement of the quantum efficiency of photodetectors in the photon-counting regime and to the realization of an absolute source of radiation.