An X-ray photon-counting imaging spectrometer based on a Ta absorber with four superconducting tunnel junctions

We present the first results obtained with a two-dimensional X-ray imaging spectrometer consisting of a 200×200 μm2 Ta absorber and read out by four Ta/Al superconducting tunnel junctions (STJs). A preliminary image reconstruction algorithm allows the visualisation of the diffraction pattern from a 5 μm pinhole illuminated with 10 keV X-rays. The image suggests a spatial resolution better than 10 μm. The algorithm does not take into account quasi-particle losses in the absorber. Hence, the pulse-height reconstruction is not optimal and the energy resolution varies significantly across the absorber. The best energy resolution is obtained for a 20×20 μm2 area in the centre of the absorber, and amounts to ∼77 eV at a photon energy of 5895 eV, with a 70 eV electronic noise contribution.