Energy resolution of a superconducting quantum detector

Thin film cryogenic bolometers are widely used as integrating detectors for infrared and millimeter wave radiation. A superconducting quantum detector based on a nanometer-scaled structure may be an alternative for future applications where energy resolved single-photon detection and fast response times are simultaneously required. The mechanism responsible for the single-photon detection capability is due to the combined action of a hot-spot formation after photon absorption and a subsequent normal domain caused by an applied bias current [1]. We present recent results on energy resolution and spectral sensitivity of infrared quantum detectors made of different materials (Nb and NbN). The spectral response of the detector exhibits a pronounced threshold at a particular photon energy E0 that depends on the material and detector geometry. According to the detector model, information about the photons energy is contained in the amplitude and duration of the voltage pulse. A reasonable energy resolution is expected only for photon energies E >> E0. Preliminary experiments performed near the threshold energy have shown that the time integral of the response pulses indeed varied with the photon energy. The observed energy resolution of about 20% at 0.6 eV was not sufficient for practical applications. However, these preliminary data validate the response mechanism and support the envisaged performance at higher photon energies. [1] Semenov A D, Gol'tsman G N and Korneev A A 2001 Physica C 351 349