Well characterized photon number resolving detectors are a requirement for many applications ranging from quantum information and quantum metrology to the foundations of quantum mechanics. This prompts the necessity for reliable calibration techniques at the single photon level. In this paper we propose an innovative absolute calibration technique for photon number resolving detectors, using a pulsed heralded photon source based on parametric down conversion. The technique, being absolute, does not require reference standards and is independent upon the performances of the heralding detector. The method provides the results of quantum efficiency for the heralded detector as a function of detected photon numbers. Furthermore, we prove its validity by performing the calibration of a Transition Edge Sensor based detector, a real photon number resolving detector that has recently demonstrated its effectiveness in various quantum information protocols.

On the basis of simple theoretical considerations it is expected that short-lived positron emitters should be produced in fluorine, sodium, and magnesium under bombardment with 6-Mev protons. These activities have been found and ascribed to Ne 19 , Mg 23 , and Al 25 » 26 . Half-lives, positron spectra and threshold investigations have been made and found to compare very well with the theory. It is concluded that for isobars of the type (n -p) -=bl the difference in binding energy is due solely to the effect of Coulomb forces up to at least mass number 25. The half-lives are found to depend on the inverse fifth power of the upper limit of the positron spectra in agreement with the theory.

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We have investigated the optical properties of self-induced inversion-layer silicon photodiodes using spectroscopic ellipsometric measurement techniques. We report a self-consistent data set and dispersion relation for the optical constants of the thermally grown oxide layer. The oxide layer thickness and spatial uniformity of a series of custom manufactured 22 mm x 11 mm rectangular diodes are evaluated. These photodiodes are used in a light trapping arrangement and exhibit predictable quantum efficiency and thus, predictable spectral responsivity. For comparison, we report measurements of the absolute spatial uniformity of the oxide layer on commercial "S6337" and "S1337" radiometric quality photodiodes