Superconductive hot electron mixers for THz heterodyne receiver applications

We report on the development of quasioptical Nb hot-electron bolometer mixers for heterodyne receivers operating at 1 THz - 3 THz. The devices have submicron in-plane sizes, thus exploiting diffusion as the electron cooling mechanism. Quasioptical mixer circuits have been developed with planar double-dipole or twin-slot antennas. The measured (DSB) receiver noise temperatures are 1670 K at 1.1 THz, with an estimated mixer noise temperature of = 1060 K, and 2750 K at 2.5 THz, with an estimated mixer noise temperature of approximate to 900 K. The IF bandwidth is found to scale as the length-squared, and bandwidths as high as 8 GHz have been measured. These results demonstrate the low-noise, broadband operation of the diffusion-cooled bolometer mixer over a wide range of far-infrared wavelengths.