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 P_D 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 P_D to 0.25 fW in our setup. For the TES, G was measured to be (325±25) fW/K at T_C=78 mK giving an upper-limit expected NEP of (3.5±0.25)×10^-19 W/Hz^1/2. We measured an actual NEP on the TES equal to (6.5±1.5)×10^-19 W/Hz^1/2, which is approximately double the expected value and likely due to residual electrical dark power in our setup.