High accuracy calibration of photon-counting detectors "On demand"

We introduce a portable, inexpensive and reliable scheme for calibration of photon-counting detectors based on our recent comparison of two independent high accuracy primary standard calibration methods. We have verified the calibration method based on two-photon correlations and its uncertainty by comparing it to a substitution method using a conventionally calibrated transfer detector tied to a national primary standard detector scale. We have reported a relative standard uncertainty for the correlated-photon method of 0.18 % (k=1) and for the substitution method of 0.17 % (k=1). Further we established, by direct comparison in a series of measurements, that the two methods agree to within the uncertainty of the comparison, with the difference being 0.14(14) %. While this experiment can be repeated in the laboratory setting, the calibration methods are not appropriate for everyday use. However, using photon-counting detector properties brought to light by our comparison of the two methods we introduce a relatively low cost calibration technique that will allow for 0.5% (k = 1) uncertainty.