Optical photon counting using superconducting tunnel junctions

Abstract

Abstract We demonstrate the feasibility of optical photon counting using a superconducting substrate in combination with an array of widely spaced superconducting tunnel junctions of lower energy gap. In the proposed device, a photon impinging on the substrate generates quasiparticles within it, and these are channelled towards, and are detected by, the nearest four elements of the junction array. We show that certain substrate/junction combinations generate sufficient numbers of quasiparticles per incident photon to permit pulse counting and positional encoding, whilst resulting in a quasiparticle number density which is low enough to prevent significant recombination within the relevant diffusion and tunnelling timescales. A combination of Al junctions with a Nb or Sn substrate provides the basis for a large area detector with very high sensitivity to individual optical and UV photons, high intrinsic time-resolution, and moderate energy resolution.