Abstract

A system using correlated photons for radiometric purposes has been set up at the National Institute of Standards and Technology (NIST). Correlated photons are produced by using the process of parametric downconversion which allows, within a nonlinear medium, the conversion of individual photons from a pump beam into pairs of photons. Because both photons of a downconverted pair are created virtually simultaneously, the detection of one photon indicates the existence of the other. In addition, a measurement of the direction and the energy of one photon of the pair determines the direction and the energy of the other photon. We have used the properties of such photon pairs to determine the absolute efficiency of photon-counting detectors without the need to tie the measurement to any externally calibrated standard detector. Detector- efficiency measurements made by using this method have been compared to conventional measurements to verify the correlated technique.

© 1995 Optical Society of America