Terahertz Direct Detection Characteristics of a Superconducting NbN Bolometer

We report the terahertz direct detection characteristics of a spiral antenna coupled NbN superconducting hot-electron bolometer (HEB) at a bath temperature of 4.2 K. Thermal conductance determined from resistance transition curves with different bias currents is found to be 3×10⁻⁷ W/K. The device shows a read-out circuit limited noise equivalent power (NEP) of 4.5×10⁻¹² W/Hz^1/2 at 4.2 K with a home-made transimpedance amplifier operating at room temperature.