Development of distributed readout imaging detectors based on superconducting tunnel junctions for UV/optical astronomy

Abstract

Superconducting tunnel junctions (STJs) have been demonstrated as photon counting detectors in the UV-NIR wavelength range. They combine a modest wavelength resolving power with fast response and high detection efficiency over a broad wavelength band. This makes this type of detector an interesting alternative to the present generation of detectors used in UV/optical astronomy, such as CCDs and micro-channel plates. Practical applications require imaging detectors with large sensitive area and good spatial resolution. While the feasibility of small arrays of closely packed STJs which are individually biased and read-out has already been demonstrated, the development of large format arrays is limited by the large number of electronics chains and wire connections to the cold detector which would be required. An alternative approach is to use a large area absorber combined with a few STJs at the edges or corners. A photon's energy as well as its absorption position in the absorber can be derived form the signal amplitudes measured in the STJs. In this paper the performance in terms of wavelength resolving power and position resolution of four different linear geometries of Ta absorbers, read out with Ta-Al STJs, is investigated and compared with single STJs. The UV and optical spectra obtained with the absorbers show resolving powers within a factor of two of the theoretical limit. In particular, a measured resolving power at (lambda) equals 300 nm of approximately 16 with a position resolution of approximately 9 micrometers is achieved with a 100 by 50 micrometers <SUP>2</SUP> absorber in between two 50 by 50 micrometers <SUP>2</SUP> STJs.