| Popis: |
An experimental set-up based on correlated photons has been developed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) for the absolute measurement of the quantum efficiency and dead time of single-photon counting photodiodes. The overall accuracy is improved with respect to previously reported results, by using a thin and highly transmitting non-linear crystal. For comparison, a conventional set-up has been developed at 632.8 nm with a He-Ne laser, a trap detector and calibrated neutral-density filters. Measurements at different count levels have been performed with both techniques and results are compared for the quantum efficiency in the limit of zero count, η0, and for the dead-time measurement, tD. Contributions to the final uncertainty are analysed for both techniques. The results obtained are η0 = 0.3372 (standard uncertainty u(η0) = 0.0016) and tD = 33.8 ns (u(tD) = 2.0 ns) in the case of the two-photon technique and η'0 = 0.3376 (u(η'0) = 0.0036) and t'D = 31.7 ns (u(t'D) = 5.4 ns) in the case of the conventional technique. |
