SUPERCONDUCTING TUNNEL-JUNCTIONS AS DETECTORS FOR ULTRAVIOLET, OPTICAL, AND NEAR-INFRARED ASTRONOMY

We discuss the capabilities of superconducting tunnel junctions as det ectors for ultraviolet, optical, and near-infrared astronomy. Such jun ctions have recently been shown to allow the detection oi: individual optical and ultraviolet photons with an inherent spectral resolution r elated to the critical temperature of the absorbing superconductor. Li miting resolutions at 500 nm ranging from 5 - 40 nm (for materials wit h critical temperatures between 0.1 to 10 K) should be achievable. The se detectors should have a high quantum efficiency (> 50 per cent) ove r a very broad wavelength range from the ultraviolet to the near infra red (100 - 2000 nm). The overall efficiency is limited by reflection f rom the superconducting film, and should be improved significantly by appropriate anti-reflection coatings. The devices function at very hig h incident photon rates-with count rates of order 10 kHz or higher bei ng feasible, and photon arrival time datation possible to microsec-lev el accuracy. It is realistic in the future to envisage that these devi ces, of a size typically 20 - 50 mu m(2), could be packaged into imagi ng arrays. These key characteristics imply that many areas of optical and ultraviolet astronomy could benefit significantly from their furth er development.