Detecting photons: Properties and challenges

This paper reports on work being carried out on detector characterisation at the National Physical Laboratory in the UK. It focuses on the development of a new technique based on correlated photons produced via parametric downconversion which can be used to directly measure the quantum efficiency of photon counting detectors. The main drivers for these measurements are the wide uptake of few photon optical technologies and the rapidly progressing field of quantum information processing which operates in the photon counting regime. Photodetection in the fields of biology, nuclear physics and astrophysics will also benefit from this work. The potential of this technique for realising primary radiometric scales will also be briefly discussed.