Figure 1

Fig 1    Schematic of STJ detection process.  The photon is absorbed in the left-hand electrode, and its energy breaks Cooper pairs, producing single electrons with charge Q ≈ 0.6 e ( E / DTa ); E is the photon energy and e the electron charge; DTa ≈ 0.7 meV is the gap of the Ta absorber.  These quasiparticles tunnel as a current to the other superconducting electrode, and the charge is given by the integral of the current increase.  The charge Q is used to deduce the photon energy.