A low-noise 2.5 THz superconductive Nb hot-electron mixer

We report on the development of a quasioptical Nb hot-electron bolometer mixer for a 2.5 THz heterodyne receiver, The devices are fabricated from a 12 nm thick Nb film, and have a 0.3 mu mx0.15 mu m in-plane size, thus exploiting diffusion as the electron cooling mechanism, The rf coupling was provided by a twin-slot planar antenna on an elliptical Si lens. A specially designed 2.5 THz system, using a CO2-pumped FIR laser as local oscillator (LO), with rf hot/cold loads enclosed in vacuum to avoid atmospheric absorption, was used in the experiment The experimentally measured double sideband (DSE) noise temperature of the receiver was as low as less than or equal to 3000 K, with an estimated mixer noise temperature of approximate to 750 K. These results demonstrate the operation of the diffusion-cooled bolometer mixer above 2 THz.