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We fabricated and characterized a low thermal conductance (G) transition edge sensor (TES). The device is based on a superconducting Ti/Au bilayer deposited on a suspended SiN membrane. The critical temperature of the device is 155 mK. The low thermal conductance is realized by using narrow SiN ring-like supporting structures. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance (G) to be equal to 1.66 pW/K. This value corresponds to a noise equivalent power (NEP) of 1\times 10^-18\ W/\surdHz. The current noise and complex impedance are also measured at different bias points at 25 mK bath temperature. The measured electrical (dark) NEP is 2\times 10^-18\ W/\surdHz, which is about a factor of 2 higher than what is expected from the thermal conductance that comes out of the IV curves analysis. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 62 \mus and a thermal capacity of 3 fJ/K. [ABSTRACT FROM AUTHOR]

Complex impedance measurements are widely used to characterize superconducting transition edge sensors (TESs) in bolometers and microcalorimeters. Typically, models are fit to impedance data to find parameters which pertain to the performance of these detectors. After the parameters are determined, the models are then used to compute the response and noise of these devices. In this paper, we present general relationships between the measured impedance, the thermal response to power in the TES, and noise. We describe a method for measuring \alphaI and \betaI of the superconducting phase transition, which does not require model fitting. We find bolometer response is determined from the impedance provided that the absorber is strongly coupled to the TES electron system. We also demonstrate how to calculate upper and lower limits on the noise directly from the impedance data without modeling. Additionally, the relations can be used to check the validity of the models and to understand what information can and cannot be obtained from measurements of impedance, response, and noise. [ABSTRACT FROM AUTHOR]

Results of study optical performance of single pixel transition edge sensor (TES) bolometer presented at wavelength band 30–60 \mum are presented. FIR radiation is coupled into a multimode horn with entrance aperture of 450 \mum, length 4.5 mm and exit aperture of 45 \mum, which feeds a metal integrating cavity containing the detector. The radiation band is defined by a pair of lowpass and highpass mesh filters in front of the horn. Here we present measurements of optical noise equivalent power (NEP), optical efficiency, dynamic range and time constant. The results show that measured TES detectors are close to meeting the requirement of the “Band S” of SAFARI FTS imaging instrument [1] on the SPICA mission [2]. [ABSTRACT FROM AUTHOR]

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\pm25) fW/K at TC=78\ \rm mK giving an upper-limit expected NEP of (3.5\pm 0.25)\times 10^-19\ W/Hz^1/2. We measured an actual NEP on the TES equal to (6.5\pm 1.5)\times 10^-19\ W/Hz^1/2, which is approximately double the expected value and likely due to residual electrical dark power in our setup. [ABSTRACT FROM AUTHOR]

We highlight the progress on NbN hot electron bolometer (HEB) mixers achieved through fruitful collaboration between SRON Netherlands Institute for Space Research and Delft University of Technology, the Netherlands. This includes the best receiver noise temperatures of 700 K at 1.63 THz using a twin-slot antenna mixer and 1050 K at 2.84 THz using a spiral antenna coupled HEB mixer. The mixers are based on thin NbN films on Si and fabricated with a new contact-process and—structure. By reducing their areas HEB mixers have shown an LO power requirement as low as 30 nW. Those small HEB mixers have demonstrated equivalent sensitivity as those with large areas provided the direct detection effect due to broadband radiation is removed. To manifest that a HEB based heterodyne receiver can in practice be used at arbitrary frequencies above 2 THz, we demonstrate a 2.8 THz receiver using a THz quantum cascade laser (QCL) as local oscillator. [ABSTRACT FROM AUTHOR]