Improved energy resolution of x-ray single photon imaging spectrometers using superconducting tunnel junctions

We present measurements of the energy resolution of improved single-photon imaging x-ray spectrometers based on superconducting tunnel junctions. The devices have a Ta film absorber with an Al/AlOx/Al tunnel junction on each end. Recent device designs optimized for better quasiparticle cooling in th e Al trap obtain an energy resolution of 13 eV full width at half maximum f or a photon energy E=5.9 keV, an improvement of a factor of two over earlie r devices. We also determined that the niobium contact used in previous dev ices degraded the energy resolution in the center section of the absorber. With a different contact configuration, we have eliminated this spatial bro adening. (C) 2001 American Institute of Physics.