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Tantalum detector

28 March 1999

A new development in detector technology is good news for astronomers. Designed by a team in the space science department of the European Space Agency’s Science and Technology Centre, the detector saw first light earlier this spring at the William Herschel Telescope on La Palma.

The detector is based on an array of tantalum superconducting tunnel junctions (tantalum is a metal from the same family as niobium) and it operates at about 0.3 K. The instrument is interesting to astronomers because it allows single photon counting, imaging capability and the possibility to determine the energy of the incoming photon, all at the same time.

The detector has a count rate capability of 1 kHz and time tags the arrival of each photon to an accuracy of 5 µs using the Global Positioning System as reference.

In the past, astronomers used gratings to achieve high-energy resolution. However, this dispersed the light and reduced efficiency. Now they will be able to determine the energy of photons without losing light.

Testing at the William Herschel Telescope was carried out at optical wavelengths, with an array of 6 x 6 junctions, each with a field of view of 0.6 arcsec. The detector works equally well for radiation up to 1 keV X-rays, where an energy resolution of 5 eV has been obtained.

Superconducting tunnel junction (STJ) devices can also be used for building very sensitive amplifiers (SQUID circuits), and STJ] logic circuits have applications in ultrafast signal processors. They only work in zero or fixed, low magnetic fields, however.

The development is the culmination of more than 10 years of R&D in collaboration with European industry.

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