UV to IR photon detection using superconducting tunnel junctions

Superconducting Tunnel Junctions have been investigated in the past as particle and X-ray detectors. We report here on results obtained illuminating Nb-Al-AlOx-Nb junctions with radiation covering the UV to IR (250 – 1100 nm) at 0.30 K. In the presence of continuous illumination, an increase of the subgap current is observed, while the change is found to be consistent with the amount of energy supplied to the junction. Several measurements have been performed in a pulsed mode, showing the detection of pulses containing about 100 photons each, at =850 nm. These results have allowed a determination of the mean energy required to create a single charge carrier in Nb, which agrees well with theoretical predictions. Such results open new possibilities for the fabrication of optical photon counting cameras based on Josephson junctions.