Possibility of absolute calibration of analog detectors by using parametric downconversion: a systematic study

Absolute calibration of analog detectors using stimulated parametric down conversion

“…The auto-and cross-correlation functions of the current fluctuations have almost the same form as that obtained in the case of spontaneous PDC in our earlier work [15]. This evidence shows that quantum correlations do not disappear when the emission is stimulated.…”

“…In fact, the down-converted photons are still produced in pairs, although in beam 2 the photons of the pairs are added to the bright original coherent beam propagating in the same direction. These result in the stimulated configuration, differ from the spontaneous case (both in the photo-counting and in the analog regime [15]) because of the presence of a factor two in the cross-correlation. We emphasize that this factor comes from the exact calculation which will be presented in a forthcoming paper, provided that the spontaneous emission is negligible compared to the stimulated one.…”

“…Now we introduce the quantum efficiency j of detector D j , defined as the number of pulses generated per incident photon. In [15] a real detector is modelled, as usual, with an ideal detector ( ¼ 1) preceded by a beam splitter with transmission coefficient equal to the quantum efficiency of the real detector [19]. Within this picture it is possible to take into account the quantum efficiency by the following substitutions:…”

“…Thus, this absolute technique (and others related to it [11][12][13]) exploiting PDC can be used to establish absolute radiometric standards because it relies, in principle, simply on the counting of events and involves a small number of measured quantities. After some earlier seminal work [14], in our paper [15] a detailed theoretical analysis was made into the possibility of extending the spontaneous PDC technique to higher photon fluxes, for calibrating analog detectors. Such a technique covers a large class of photodetectors from simple photodiodes, to avalanche photodiodes, to photo-multipliers, to charged coupled devices (CCDs) (see also [16]).…”

“…The special statistic of the fluctuations of the strongly correlated currents that allows calibration for small gain changes substantially when the gain increases. It can be shown that in this case one should be able to collect exactly the same number of correlated modes in two selected beams over the whole emission [15]. Since spontaneous PDC takes place with a very large spectral and spatial bandwidth, it would require accurate and wellbalanced spatial and frequency selection.…”