RECENT DEVELOPMENTS IN SUPERCONDUCTING TUNNEL-JUNCTIONS FOR ULTRAVIOLET, OPTICAL AND NEAR-INFRARED ASTRONOMY

Some recent results associated with the development of tantalum based photon counting superconducting tunnel junctions (STJ) suitable for us e as broadband low resolution spectrometers for optical and ultraviole t astronomy are presented. A 20 x 20 mu m square tantalum based STJ; o perated at a temperature of 0.3 K, lias demonstrated a limiting resolu tion of similar to 8 nm at 200 nm and similar to 80 nm at 1000 nm. The device is extremely linear in response with photon energy, and covers the waveband from 200 nm to 2 mu m while measuring the individual pho ton wavelength and arrival time. The short wavelength limit is current ly constrained by the current experimental configuration (a fibre opti c) as well as to some extent the sapphire substrate. The estimated qua ntum efficiency for single photons is over similar to 50% between 200 and 700 nm with a maximum of similar to 75% at 550 nm. Such all STJ wh en packaged into an array could contribute significantly to many field s of near infrared, optical and ultraviolet astronomy being able to pr ovide efficiently and simultaneously the broad band spectrum and photo n arrival time history of every single object in the field over a very wide dynamic range.