Single optical photon detection with a superconducting tunnel junction

A niobium-based superconducting tunnel junction (STJ) is useful in detecting individual photons at rates up to 2.5 kHz in the wavelength range 200-500 nm. The STJ detects the photons with an intrinsic spectral resolution of 45 nm and at a quantum efficiency of nearly 50%. The device eliminates the limitations of charge-couple devices which provide linear response to photons. The device may be able to attain the limiting theoretical resolution of nearly 20 nm at 350 nm if the electronic noise is further reduced.