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

Abstract

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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm P}_{\rm D}$</tex></formula> 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm P}_{\rm D}$</tex></formula> to 0.25 fW in our setup. For the TES, G was measured to be (325 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex></formula> 25) fW/K at <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm T}_{\rm C}=78\ {\rm mK}$</tex></formula> giving an upper-limit expected NEP of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(3.5\pm 0.25)\times 10^{-19}\ {\rm W/Hz}^{1/2}$</tex> </formula> . We measured an actual NEP on the TES equal to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(6.5\pm 1.5)\times 10^{-19}\ {\rm W/Hz}^{1/2}$</tex> </formula> , which is approximately double the expected value and likely due to residual electrical dark power in our setup.