next previous
Up: Superconducting tunnel junctions

6. Conclusion

We have shown that superconducting tunnel junctions based on niobium or hafnium may have considerable potential as photon counting optical and ultraviolet detectors. The basic experimental feasibility has now been demonstrated, and the key features of such a detector can be summarised as follows: (a) photon counting operation with no readout noise, and with minimal dark current contribution; (b) an inherent spectroscopic capability at ultraviolet, optical, and infrared wavelengths, with tunnel noise-limited resolutions ranging from tex2html_wrap_inline1309 at 100 nm and tex2html_wrap_inline1311 at 500 nm for materials with tex2html_wrap_inline1313 from tex2html_wrap_inline1315; (c) high quantum efficiency of 50 per cent or more over the range tex2html_wrap_inline1317. A higher efficiency over a more restricted waveband could be achieved through the introduction of appropriate anti-reflection coatings; (d) high speed, limited primarily by the processing electronics, leading to a high count-rate capability, and high resolution time datation (sub-ms) of individual photon events; (e) inherent discrimination against background events through the application of energy and risetime discrimination.

An illustrative list of astronomical applications for which such a detector could play a major role, either at optical wavelengths from the ground (tex2html_wrap_inline1319 nm), or at ultraviolet and optical wavelengths (tex2html_wrap_inline1321 nm) from space, would be: (a) faint object broad-band spectroscopy which, if coupled to a panoramic imaging capability, would lead to the direct determination of the spectral energy distribution and redshift of every object detected in the field either through the observation of continuum discontinuities (Lyman edge) or through the observation of line centroids; (b) highly efficient spectrophotometry of variable objects, with time resolution well below 1 ms; (c) order separation when coupling a strip of STJs to a high resolution echelle-type spectrograph; (d) speckle imaging, speckle spectroscopy, adaptive optics, interferometric fringe detection, and other atmospheric correction techniques requiring high time resolution.

An STJ array is already being considered as a possible European-contributed camera for Hubble Space Telescope (STECF 1995), and the benefits of the time and energy resolution for a space interferometer have also been considered (Perryman & Peacock 1995).

Acknowledgements

The authors acknowledge the technical support of A. van Dordrecht (ESTEC), R. Venn of Cambridge Microfab Ltd (UK) and D. Goldie of Oxford Instruments Ltd (UK).


next previous
Up: Superconducting tunnel junctions

Copyright by the European Southern Observatory (ESO)
web@ed-phys.fr