Characterization of an Ultra-Sensitive Transition-Edge Sensor for Space-Borne Far-IR/Sub-mm Spectroscopy

We measured the noise equivalent power (NEP) of an ultra-sensitive membrane-isolated transition-edge sensor (TES) designed for the SpicA FAR Infrared instrument (SAFARI) along with several Johnson noise Thermometry Devices (JTDs) simultaneously in a “dark” experimental setup. Our goal was to characterize the dark power PD present in our experimental setup and its effect on the measured NEP. By employing resistive attenuators, filters, lossy coaxial connections, and a light-tight box, we reduced PD to 0.25 fW in our setup. For the TES, G was measured to be (325±25) fW/K at TC=78 mK giving an upper-limit expected NEP of (3.5±0.25)×10-19 W/Hz1/2. We measured an actual NEP on the TES equal to (6.5±1.5)×10-19 W/Hz1/2, which is approximately double the expected value and likely due to residual electrical dark power in our setup.