Antenna-coupled niobium bolometers for terahertz spectroscopy

We report characterizations of antenna-coupled hot electron bolometers designed for laboratory-based terahertz spectroscopy. These direct detectors combine sub-nanosecond response, high sensitivity, and the ability to operate below saturation when viewing a room temperature background. The optimum small-signal responsivity is 4.4 X 10(4) V/W, measured at a bath temperature T-b approximate to 0.9T(c). The corresponding saturation power is 7 nW. The saturation power increases and the small-signal responsivity decreases as the bath temperature is lowered. The measured noise equivalent power is 2.0 x 10(-14) W/(Hz)(1/2), near the predicted thermal fluctuation limit. The noise is white from approximately 100 Hz to 100 MHz.