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Variable TC Hot-Electron Mixers

I. Siddiqi

Superconducting hot-electron bolometers used in astronomy for heterodyne detection at THz frequencies are currently limited in sensitivity by fluctuations in electron temperature. A reduction in critical temperature (TC) increases sensitivity but also increases the susceptibility to saturation from background photons. Using various superconductors, we have verified the reduction in thermal fluctuation noise achieved by lowering TC, and have characterized the different saturation effects which limit mixer sensitivity. Using a bilayer material system (Nb-Au) which uses the superconductor-normal metal proximity effect to tune TC, we have demonstrated devices which should achieve an optimum balance between sensitivity and saturation.