Superconducting single-photon detector for the visible and infrared spectral range

We present results on dark count rates and spectral sensitivities of superconducting single-photon detectors in the visible and near-infrared spectral range. The active detector element is a nanometre-sized (a few nanometres thick and less than 100 nm wide) meander line carrying a supercurrent. The superconducting materials are NbN and Nb, respectively. The NbN detector exhibited a flat spectral sensitivity up to about 2.4 μm. Fluctuations of the superconducting order parameter are considered as a major source of dark count events. A simple model and its limitations to explain the observed dark count rates is discussed.