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Kinetic inductance bolometers and calorimeters, each consisting of a kinetic inductance device suspended on a membrane and embedded in a resonant circuit, are being developed for applications such as planetary science, climate science, and X-ray spectroscopy. Arrays of these resonator-bolometers, each with a unique resonance frequency, are coupled to a single feedline, allowing many bolometers or calorimeters to be multiplexed using microwave read out. We derive coupled linear differential equations describing resonator-bolometers and means for calculating responses to signal and noise sources. By employing the bolometer matrix formalism, the model compactly describes the effects of demodulation, detuning, electrothermal feedback, resonator to feedline coupling, and bolometer sensitivity to changes in temperature and bias current. Based on this theory, estimates for the bolometer response to phonon noise, Johnson noise, and microwave bias quasiparticle generation noise are derived. The model is represented in terms of accessible parameters, most of which are measurable using a network analyzer. It is applicable to other types of devices such as dielectric bolometers or alternating current biased transition edge sensors and is readily extendible to more complex bolometers or to unsuspended kinetic inductance devices. [ABSTRACT FROM AUTHOR]

Transition-edge-sensor (TES) bolometers are the chosen detector technology for the SAFARI Imaging Spectrometer on the SPICA telescope. For this mission, SRON is developing bolometers, each consisting of a TiAu TES that is weakly coupled to the thermal bath through thin legs of silicon nitride. In order to understand and optimize the bolometer and to verify our detector models, we characterize the devices using a series of complex impedance measurements. We apply equivalent bolometer analysis (EBA) in combination with model fitting to these data. From this analysis, we obtain important parameters that give us confidence in our understating of the response and noise of these sensitive detectors. [ABSTRACT FROM AUTHOR]

We have constructed a test facility for characterizing the focal plane arrays of SAFARI, the far-infrared imaging spectrometer for the SPICA satellite. SAFARI's three bolometer arrays are populated with extremely sensitive ( $\mathit{NEP}\sim 2\times 10^{-19}~\mathrm{W}/\sqrt{\mathrm{Hz}}$) transition edge sensors with a transition temperature close to 100 mK. The extreme sensitivity and low saturation power (∼4 fW) of SAFARI's detectors present challenges to characterizing them. In optimizing the SAFARI Detector System Test Facility we have paid careful attention to stray-light exclusion as well as electrical, magnetic, and mechanical isolation. We present measurements verifying the facility's performance and analyze them in terms of a two-fluid model of the TES current on the transition to investigate the background power level. We have measured a detector NEP of (5.1±0.4)×10 W Hz, showing that the facility is ready to test the SAFARI prototype arrays and is approaching the performance needed for testing the flight arrays. [ABSTRACT FROM AUTHOR]

Transition edge sensors (TES) are the chosen detector technology for the SAFARI imaging spectrometer on the SPICA telescope. The TES are required to have an NEP of $2\mbox{--}3\times 10^{-19}~\mbox{W/}\sqrt{\mathrm{Hz}}$ to take full advantage of the cooled mirror. SRON has developed TiAu TES bolometers for the short wavelength band (30-60 μm). The TES are on SiN membranes, in which long and narrow legs act as thermal links between the TES and the bath. We present a distributed model that accounts for the heat conductance and the heat capacity in the long legs that provides a guideline for designing low noise detectors. We report our latest results that include a measured dark NEP of $4.2\times 10^{-19}~\mbox{W/}\sqrt{\mathrm{Hz}}$ and a saturation power of about 10 fW. [ABSTRACT FROM AUTHOR]

SRON is developing the Frequency Domain Multiplexing (FDM) read-out and the ultra low NEP TES bolometers array for the infra-red spectrometer SAFARI on board of the Japanese space mission SPICA. The FDM prototype of the instrument requires critical and complex optimizations. For single pixel characterization under AC bias we are developing a simple FDM system working in the frequency range from 1 to 5 MHz, based on the open loop read-out of a linearized two-stage SQUID amplifier and high Q lithographic LC resonators. We describe the details of the experimental set-up required to achieve low power loading (<1 fW) and low noise ( $\mathrm{NEP}\sim 10^{-19}~\mathrm{W}/\sqrt{\mathrm{Hz}}$) in the TES bolometers. We conclude the paper by comparing the performance of a $4\times 10^{-19}~\mathrm{W}/\sqrt{\mathrm{Hz}}$ TES bolometer measured under DC and AC bias. [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]

We have characterized a thin-film Nb/Al/AlO[sub x]/Al/Nb superconducting tunnel junction (STJ) optimized for low electronic noise as an x-ray detector in the 0.2–1 keV photon energy range. The spectra measured with this junction have high spectral purity with, to the best of our knowledge, the best energy resolution ever achieved with this type of detector in this energy band. The discrepancy between the theoretical and experimental energy resolution is only about 15%. Part of this small discrepancy may be explained by the fact that our junction has electrodes made from niobium/aluminum bilayers, while the theoretical result is for electrodes made from only one material. To the best of our knowledge, this is the first time that resolution achieved with a STJ x-ray detector is in agreement with the resolution predicted from statistical fluctuations in the creation and tunneling of quasiparticles. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]