Spatial uniformity of single photon 1-D imaging detectors using superconducting tunnel junctions

We have developed single-photon, one-dimensional imaging detectors based on superconducting tunnel junctions. The devices have a Ta absorber with an Al/AlOx/Al tunnel junction readout on each end. The best energy resolution is 13 eV FWHM at 6 keV in an area of 20x100 μm2. For devices with a Nb ground contact to the center of the Ta absorber, the energy resolution is worse in the center of the Ta absorber. This nonuniformity is caused by the Nb ground contact. A device with a Ta ground contact to the base electrode of one of the junctions was tested. We obtain an energy resolution of 26 eV in the large region at the center of the absorber, where this energy resolution is determined by the junction response. The diffusion constant of Ta and the loss time of quasiparticles in Ta are also studied by measuring three devices with different size absorbers