Development of Energy-dispersive UV Superconducting Tunnel Junction Detectors

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We developed and fabricated Superconducting Tunnel junction (STI) detectors for one-photon ultraviolet spectroscopy by applying the fabrication process developed for fabricating STJ detectors for X-ray spectroscopy. We introduced the following new processes for the energy-dispersive detection of ultraviolet photons1.the process to remove the covering SiO2 layers accumulated to avoid the damage2.the anodization process of the junction edge to suppress the leakage current3.the increase of the thickness of Al-trapping layers.No.1 caused the direct illumination of ultraviolet photons without absorption by the covering layer. No.2 made it possible to reach down to the leakage current of lnA for the junctions with the critical current of 1 kA/cm^2. No.3 caused the amplification of the signal charges by more than a factor of 5. We succeeded to detect one photon in energy of 47-280 eV by the detector. The energy resolution was 18 eV at 55 eV. In addition, we clarified that the energy resolution of the detector became worse due to the high capacitance of readout stainless coaxial wires. After replacing them, we confirmed that the energy resolution reduced to 1/4. Moreover, we trided to detect optical photons. We succeeded the detection and estimated the energy resolution of 2.4 eV at 13 eV (λ/Δλ〜5) by using the multi-photon events (2-5 photons per event).