[show abstract][hide abstract] ABSTRACT: We describe quasi-optical SIS mixers operating in the submillimeter band (500-750 GHz) which have very low noise, around 5 hν/k<sub>B</sub> for the double-sideband receiver noise temperature. The mixers use a twin-slot antenna, Nb/Al-Oxide/Nb tunnel junctions fabricated with optical lithography, a two-junction tuning circuit, and a silicon hyperhemispherical lens with a novel antireflection coating to optimize the optical efficiency. We have flown a submillimeter receiver using these mixers on the Kuiper Airborne Observatory, and have detected a transition of H<sub>2</sub><sup>18</sup>O at 745 GHz. This directly confirms that SIS junctions are capable of low-noise mixing above the gap frequency.
IEEE Transactions on Appiled Superconductivity 07/1995; · 1.20 Impact Factor