On the development of superconducting tunnel junctions as photon counting spectrometers for application in astrophysics

The current state of development of superconducting tunnel junctions as pho ton counting spectroscopic detectors is reviewed and their application to a broad range of astrophysical problems discussed. Arrays of tantalum based junctions have now reached a state of maturity such that serious astronomic al applications can be considered over the wavelength range from 0.5 nm to 2 mu m. The agreement between the theoretical resolution, as defined by the tunnel limited resolution, and measurements over this waveband, for both n iobium and tantalum based devices, provides a good indication that lower cr itical temperature elemental superconductors may provide an even improved r esolution in the near future. Such devices based on hafnium with a critical temperature of similar to 130 mK are already under development. (C) 1999 E lsevier Science B.V. All rights reserved.