Optical/UV single-photon imaging spectrometers using superconducting tunnel junctions

We present preliminary test results of optical/UV single-photon imaging spe ctrometers using superconducting tunnel junctions. Our devices utilize a la teral trapping geometry. Photons are absorbed in a Ta thin film, creating e xcess quasiparticles. Quasiparticles diffuse and are trapped by Al/AlOx/Al tunnel junctions located on the sides of the absorber. The Ta/Al interface does not overlap the junction area. Imaging devices have tunnel junctions o n two opposite sides of the absorber. Position information is obtained from the fraction of the to tal charge collected by each junction. We have fabr icated high-quality junctions with a ratio of subgap resistance to normal s tate resistance greater than 100000 at 0.22 K. We have measured the single- photon response of our devices. For photon energies between 2 and 5 eV, we measure an energy resolution between 1 and 1.6 eV. We can estimate the numb er of pixels the device can resolve from the energy resolution. We find tha t these early devices have as many as 4 pixels per strip. (C) 2000 Publishe d by Elsevier Science B.V. All rights reserved.