Diffusion-cooled superconducting hot electron bolometer heterodyne mixer between 630 and 820 GHz

We report on heterodyne mixing experiments between 630-820 GHz using a diffusion-cooled superconducting hot electron bolometer at intermediate frequencies from 1-2 GHz. The niobium bolometer which is cooled by diffusion of the hot electrons into a normal conductor has dimensions of 0.3 mu m x 0.15 mu m and was fabricated at KOSMA with a two-step electron beam lithography process. The film thickness of the device is 30 nm with T-c of 6.1 K and Delta T-c of 0.7 K. The mixing experiments are performed with a tunerless waveguide mixer block previously used for very low-noise SIS receivers. At 2.2 K physical temperature they result in receiver noise temperatures at 666 GHz of 1500 K at 1.0 GHz intermediate frequency, increasing rapidly above 1.5 GHz. The dissipated local oscillator power is evaluated to be 65-90 nW.