Coupling of terahertz radiation to a high-Tc superconducting hot electron bolometer mixer

We report on efficient coupling of THz radiation to a high-Tc superconducting hot electron bolometer that is suitable for heterodyne detection. Our quasi-optical system consisted of a planar self-complementary spiral antenna on a dielectric substrate clamped to an extended hyperhemispherical lens. The antenna was integrated into a co-planar line for broadband intermediate frequency matching. Measurements in the homodyne regime at a frequency of 2.5 THz showed a radiation pattern with a beam width of 1° and a coupling efficiency of ≊0.1. We measured, at an intermediate frequency of 1.5 GHz, an output noise temperature of ≊160 K and estimated for the device, operated in the heterodyne regime, a system noise temperature of ≊3×105 K. We also discuss possibilities of significant improvement of the sensitivity.