120-pixel array of superconducting tunnel junctions as spectrophotometer for optical astronomy

Superconducting tunnel junctions (STJs), applied as photon counting detectors, combine intrinsic energy resolution with good detection efficiency and high count rate capability in a wide energy range, from the near infrared to the X-ray. The Science Payload and Advanced Concepts Office of the European Space Agency (ESA), is developing S-Cam: a cryogenic camera for ground-based optical astronomy exploiting an array of Ta STJs. The first generations of this instrument (S-Cam1–2), using a 6×6 pixel array, have undergone four campaigns at the 4.2 m William Herschel Telescope at La Palma (Spain). The goals for S-Cam3, presently under development, are to increase the field of view of the instrument from 4×4″ to 11×9″, to optimize IR rejection, to extend the ‘red’ response and to increase the electronics readout speed. The camera will use a 10×12 array of Ta/Al STJs. Results are presented on the performance of these larger arrays.