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High quantum efficiency (QE) X-ray absorbers are needed for future X-ray astrophysics telescopes. The Advanced Telescope for High ENergy Astrophysics (ATHENA) mission requirements for the X-ray Integral Field Unit (X-IFU) instrument dictate, at their most stringent, that the absorber achieve vertical QE > 90.6% at 7 keV and low total heat capacity, 0.731 pJ/K. The absorber we have designed is 313 µm square composed of 1.05 μm Au and 5.51 μm electroplated Bi films (Barret et al. in Exp Astron 55:373–426, 2023). Overhanging the TES, the absorber is mechanically supported by 6 small legs whose 5 μm diameter is tuned to the target thermal conductance for the device. Further requirements for the absorber for X-IFU include a > 40% reflectance at wavelengths from 1 to 20 μm to reduce shot noise from infrared radiation from higher temperature stages in the cryostat. We meet this requirement by capping our absorbers with an evaporated Ti/Au thin film. Additionally, narrow gaps between absorbers are required for high fill fraction, as well as low levels of fine particulate remaining on the substrate and zero shorts between absorbers that may cause thermal crosstalk. The Light Element Mapper (LEM) is an X-ray probe concept optimized to explore the soft X-ray emission from 0.2 to 2.0 keV. These pixels for LEM require high residual resistance ratio (RRR) thin 0.5 µm Au absorbers to thermalize uniformly and narrow < 2 μm gaps between pixels for high areal fill fraction. This paper reports upon technology developments required to successfully yield arrays of pixels for both mission concepts and presents first testing results of devices with these new absorber recipes. [ABSTRACT FROM AUTHOR]

By using a superconducting transition edge sensor (TES) to measure the thermal energy of individual decay events with high energy resolution, decay energy spectrometry provides a unique fingerprint to identify each radionuclide in a sample. The proposed measurement requires optimizing the thermal parameters of the detector for use with 5 MeV scale energy deposited by alpha decay of the sample radionuclides. The thermal performance of deep-etched silicon TES chips is examined with the use of an onboard resistive heater. With known heater power and bath temperature, the thermal conductance, heat capacity, and frame temperature are calculated and compared to theory. [ABSTRACT FROM AUTHOR]

The 2020 decadal review recognized the measurement of the polarization of the cosmic microwave background (CMB) to be a top priority for the decade. CMB experiments including POLARBEAR2/Simons Array, Atacama Cosmology Telescope/Advanced-ACT, SPT-3G, the Simons Observatory, and CMB-S4 have or will use transition edge sensor (TES) bolometer fabricated with Aluminum doped with Manganese (AlMn). AlMn is a popular material choice as the superconducting transition temperature ( T c ) and normal resistance ( R n ) of the TES can be tuned with Mn concentration, geometric patterning, film thickness, and thermal annealing. In addition the conductivity is appropriate for both time division multiplexing and frequency division multiplexing that require 10 m Ω and 1 Ω sensors respectively. In this paper we present work on the ability to tune the T c of a film based on its time and temperature thermal tuning profile combined with room temperature monitoring of film resistivity. Such control allows for the fabrication of a wide range of TES parameters from a single AlMn concentration. Scanning electron microscope (SEM) imaging shows that the AlMn film's grain boundaries are changed by thermal annealing making the film more conductive and raising its superconducting transition temperatures, and that at high enough temperatures will eventually recover the T c of bulk Al. We find that baking films at ∼ 200 ∘ C for tens of minutes yields a T c that is suitable for 100 mK base temperature experiments and we present on the thermal tune profiles of several different thicknesses of AlMn. [ABSTRACT FROM AUTHOR]

Time-division multiplexing is the readout architecture of choice for many ground and space experiments, as it is a very mature technology with proven outstanding low-frequency noise stability, which represents a central challenge in multiplexing. Once fully populated, each of the two BICEP Array high-frequency receivers, observing at 150 GHz and 220/270 GHz, will have 7776 TES detectors tiled on the focal plane. The constraints set by these two receivers required a redesign of the warm readout electronics. The new version of the standard multichannel electronics, developed and built at the University of British Columbia, is presented here for the first time. BICEP Array operates time-division multiplexing readout technology to the limits of its capabilities in terms of multiplexing rate, noise and cross talk, and applies them in rigorously demanding scientific application requiring extreme noise performance and systematic error control. Future experiments like CMB-S4 plan to use TES bolometers with time-division/SQUID-based readout for an even larger number of detectors. [ABSTRACT FROM AUTHOR]

A superconducting film with a tunable low transition temperature (Tc) is required in high-resolution Transition-Edge Sensor (TES) detectors, which have applications including dark matter detection, low threshold coherent elastic neutrino nucleus scattering measurement, and X-ray spectroscopy. We have been investigating a new approach to tune the Tc of superconducting thin films fabricated by co-sputtering Iridium and Platinum. The effects of Pt concentration and deposition parameters on the films' structural, electrical, and superconducting properties have been studied. AFM and XRD techniques and low temperature resistance measurements have been utilized for film characterization. By varying the Pt concentration and deposition parameters when co-sputtering, we have successfully achieved controllable tuning of Tc in the range of 30–200 mK. The experimental results demonstrate co-sputtering as a viable method for controlling the Tc of Ir-based thin films that can be applied to fabricating high-resolution TESs. [ABSTRACT FROM AUTHOR]

We are developing a low-Tc TES-based large-area and low-threshold detector targeting a variety of potential applications. The detector consists of a 50.8-mm-diameter Si wafer as the substrate and radiation absorber, a single Ir/Pt bilayer TES sensor in the center, and normal metal Au pads added to the TES to strengthen the TES–absorber thermal coupling. Tight TES–absorber thermal coupling improves detector sensitivity and response uniformity. Here, we report on the electron–phonon (e–ph) coupling strengths for the Ir/Pt bilayer and Au that are measured with our prototype detectors and TES devices. We found that a second weak thermal link besides the one due to e–ph coupling in Ir/Pt or Au was required to explain our data. With the effects of the second weak link accounted for, the extracted e–ph coupling constant Σ for Ir/Pt bilayer in the Tc range between 32 and 70 mK is 1.9×108WK-5m-3, and Σ’s for Au at 40 mK and 55 mK are 2.2×109WK-5m-3 and 3.2×109WK-5m-3, respectively.

Many applications require monitoring of increasingly high neutron flux levels. Pre‐neutron characterization is performed of a superconducting transition edge bolometric device, sensitive to neutrons by an enriched boron carbide (10B4C) layer. Heat from the absorption of neutrons is simulated using an attenuated laser, while the detector is cooled to the critical temperature, Tc. Frequency dependent (4–25 Hz) and constant input power measurements are performed on a 10B4C‐coated and a non‐coated pixel. Results are used to fit a two lumped element thermal model. The effective specific heat is highly dependent on the input pulse duration due to the interconnected stack structure. For modulated pulses, the active volume in the thermal circuit is the full depth of the substrate in the area under the pixel. For constant power input, a large portion of the substrate is heated and the interface conductivities to the cold finger are found to be important. The detectivity is D* = 3.5 × 108 cmHzW−1${{\rm cm}} \sqrt {{\rm Hz}}\,{{\rm W}^{-1}}$, and is only slightly lower than similar detectors. Understanding the dynamics of the detector better and using neutron excitation, it is expected that optimizations can lead to an equally good detector for cold to thermal neutrons at flux levels >106 n cm−2s−1. [ABSTRACT FROM AUTHOR]

The Background Imaging of Cosmic Extragalactic Polarization (BICEP)/Keck (BK) collaboration is currently leading the quest for the highest-sensitivity measurements of the polarized cosmic microwave background (CMB) anisotropies on a degree scale with a series of cryogenic telescopes, of which BICEP Array (BA) is the latest Stage-3 upgrade with a total of ∼ 32,000 detectors. The instrument comprises 4 receivers spanning 30–270 GHz, with the low-frequency 30/40 GHz deployed to the South Pole Station in late 2019. The full complement of receivers is forecast to set the most stringent constraints on the tensor-to-scalar ratio r. Building on these advances, the overarching small-aperture telescope concept is already being used as the reference for further Stage-4 experiment design. This paper describes the development of the BICEP Array 150 GHz detector module and its fabrication requirements, with highlights on the high-density time division multiplexing (TDM) design of the cryogenic circuit boards. The low-impedance wiring required between the detectors and the first stage of superconducting quantum interference device amplifiers is crucial to maintaining a stable bias current on the detectors. A novel multi-layer FR4 Printed Circuit Board with superconducting traces, capable of reading out up to 648 detectors, is detailed along with its validation tests. An ultra-high-density TDM detector module concept we developed for a CMB-S4-like experiment that allows up to 1920 detectors to be read out is also presented. TDM has been chosen as the detector readout technology for the Cosmic Microwave Background Stage-4 (CMB-S4) experiment based on its proven low-noise performance, predictable costs, and overall maturity of the architecture. The heritage for TDM is rooted in mm- and sub-mm-wave experiments dating back 20 years and has since evolved to support a multiplexing factor of 64x in Stage-3 experiments. [ABSTRACT FROM AUTHOR]

Abstract Many applications require monitoring of increasingly high neutron flux levels. Pre‐neutron characterization is performed of a superconducting transition edge bolometric device, sensitive to neutrons by an enriched boron carbide (10B4C) layer. Heat from the absorption of neutrons is simulated using an attenuated laser, while the detector is cooled to the critical temperature, Tc. Frequency dependent (4–25 Hz) and constant input power measurements are performed on a 10B4C‐coated and a non‐coated pixel. Results are used to fit a two lumped element thermal model. The effective specific heat is highly dependent on the input pulse duration due to the interconnected stack structure. For modulated pulses, the active volume in the thermal circuit is the full depth of the substrate in the area under the pixel. For constant power input, a large portion of the substrate is heated and the interface conductivities to the cold finger are found to be important. The detectivity is D* = 3.5 × 108 cmHzW−1, and is only slightly lower than similar detectors. Understanding the dynamics of the detector better and using neutron excitation, it is expected that optimizations can lead to an equally good detector for cold to thermal neutrons at flux levels >106 n cm−2s−1.

Gamma-ray transition edge sensors (TESs) are intensively studied not only to measure isotopic composition of nuclear materials but to monitor transuranic radionuclides inside the human body. We have recently proposed a thick-trilayer membrane as an alternative to silicon-nitride (Si x N y ) single-layer ones. It consists of silicon dioxide (SiO 2 ), Si x N y , and SiO 2 layers. Their total thickness is 6.9 μ m and exhibits almost the same thermal conductance as conventional Si x N y ones with 1- μ m thickness. The thick-trilayer membrane is expected to have better mechanical strength against implementing heavy-bulk absorbers. In this paper, the gamma-ray TES with the thick-trilayer membrane is used to carry out the spectroscopy for the nuclear radiation source. Neptunium-237 and its decay product Protactinium-233 emit 86.5 and 86.6-keV lines, respectively, and they are clearly resolved by four pixels with the full-width-half-maximum (FWHM) resolution of ( 43.7 ± 0.9 ) eV. Furthermore, their intensity ratio agrees with the radioactive equilibrium between the two nuclides. Our experimental results predict that a vast array of pixel formats will reduce the statistical uncertainty in less measuring time. [ABSTRACT FROM AUTHOR]

We present on the status of POLARBEAR-2 A (PB2-A) focal plane fabrication. The PB2-A is the first of three telescopes in the Simons Array, which is an array of three cosmic microwave background polarization-sensitive telescopes located at the POLARBEAR site in Northern Chile. As the successor to the PB experiment, each telescope and receiver combination is named as PB2-A, PB2-B, and PB2-C. PB2-A and -B will have nearly identical receivers operating at 90 and 150 GHz while PB2-C will house a receiver operating at 220 and 270 GHz. Each receiver contains a focal plane consisting of seven close-hex packed lenslet-coupled sinuous antenna transition edge sensor bolometer arrays. Each array contains 271 dichroic optical pixels, each of which has four TES bolometers for a total of 7588 detectors per receiver. We have produced a set of two types of candidate arrays for PB2-A. The first we call Version 11 (V11) uses a silicon oxide (SiOx) for the transmission lines and crossover process for orthogonal polarizations. The second we call Version 13 (V13) uses silicon nitride (SiNx) for the transmission lines and cross-under process for orthogonal polarizations. We have produced enough of each type of array to fully populate the focal plane of the PB2-A receiver. The average wirebond yield for V11 and V13 arrays is 93.2% and 95.6%, respectively. The V11 arrays had a superconducting transition temperature (Tc) of 452±15 mK, a normal resistance (Rn) of 1.25±0.20Ω, and saturation powers of 5.2 ± 1.0 pW and 13 ± 1.2 pW for the 90 and 150 GHz bands, respectively. The V13 arrays had a superconducting transition temperature (Tc) of 456 ± 6 mK, a normal resistance (Rn) of 1.1±0.2Ω, and saturation powers of 10.8 ± 1.8 pW and 22.9 ± 2.6 pW for the 90 and 150 GHz bands, respectively. Production and characterization of arrays for PB2-B are ongoing and are expected to be completed by the summer of 2018. We have fabricated the first three candidate arrays for PB2-C but do not have any characterization results to present at this time.

Recently, there is a demand for a single-photon detector in the mid-infrared wavelength. For that reason, we fabricated an optical transition edge sensor with an Ir–Au bilayer and demonstrated the behavior of this device. There is a possibility to improve the energy resolution of this device by lowering superconducting transition temperature and reducing heat capacity. In addition to this, because of the chemical stability of Iridium, the Iridium-based devices are easy to fabricate, and they tend to have long-term stability. We also etched a silicon wafer to match the inner diameter of an optical fiber sleeve. This process helped us improve the accuracy of alignment with the core of optical fiber and a sensitive area of this optical transition edge sensor. Consequently, we found that the superconducting transition temperature was estimated to be approximately 175 mK and developed an Ir–Au optical transition edge microcalorimeter with an energy resolution of 0.68 eV full-width at half-maximum for the pulse laser at 850 nm. This result will contribute to the measurement of photons. [ABSTRACT FROM AUTHOR]

Experiments deploying large arrays of transition-edge sensors (TESs) often require a robust method to monitor gain variations with minimal loss of observing time. We propose a sensitive and non-intrusive method for monitoring variations in TES responsivity using small square waves applied to the TES bias. We construct an estimator for a TES's small-signal power response from its electrical response that is exact in the limit of strong electrothermal feedback. We discuss the application and validation of this method using flight data from SPIDER, a balloon-borne telescope that observes the polarization of the cosmic microwave background with more than 2000 TESs. This method may prove useful for future balloon- and space-based instruments, where observing time and ground control bandwidth are limited. [ABSTRACT FROM AUTHOR]

We report the first calorimetric detection of individual He2∗ excimers within a bath of superfluid 4He . The detector used in this work is a single superconducting titanium transition edge sensor (TES) with an energy resolution of ∼1eV , immersed directly in the helium bath. He2∗ excimers are produced in the surrounding bath using an external gamma-ray source. These excimers exist either as short-lived singlet or long-lived triplet states. We demonstrate detection (and discrimination) of both states: In the singlet case the calorimeter records the absorption of a prompt ≈15eV photon, and in the triplet case the calorimeter records a direct interaction of the molecule with the TES surface, which deposits a distinct fraction of the ≈15eV , released upon decay, into the surface. We also briefly discuss the detector fabrication and characterization.

The Any Light Particle Search (ALPS II) is a light shining through a wall (LSW) experiment searching for axion-like elementary particles in the sub-eV mass range, which are motivated by astrophysics and cosmology and fulfill the requirements for being dark matter. ALPS II aims to measure an axion-to-photon coupling of , which is several orders of magnitude better than that of previous LSW experiments and will thus investigate a new parameter range. The increased performance is achieved by enhancing the magnetic field interaction length to m and by amplifying the signal in an optical cavity on each side of a light-tight barrier. The expected signal is in the order of 1 photon per day, which will be measured by photon detectors with very low dark count rates of . This article gives a technical overview on the experiment design, previous and ongoing investigations, and the current status with focus on the single photon detection. [ABSTRACT FROM AUTHOR]

We report gamma-ray spectroscopy measurements of trinitite samples and analogous samples obtained from detonation sites in Nevada and Semipalatinsk, as well as in situ measurements of topsoil at the Trinity site. We also report the first isotopic composition measurements of trinitite using the novel forensics technique of decay energy spectroscopy (DES) as a complement to traditional forensics techniques. Our gamma spectroscopy and DES measurements are compared to other published results. [ABSTRACT FROM AUTHOR]

The AdvancedAtacama Cosmology Telescope Polarimeter (AdvACT) is an upgrade for the Atacama Cosmology Telescope using Transition Edge Sensor (TES) detector arrays to measure cosmic microwave background (CMB) temperature and polarization anisotropies in multiple frequencies. The low frequency (LF) array was deployed early 2020. It consists of 292 TES bolometers observing in two bands centered at 27 GHz and 39 GHz. At these frequencies, it is sensitive to synchrotron radiation from our galaxy as well as to the CMB, and complements the AdvACT arrays operating at 90, 150 and 230 GHz. We present the initial LF array on-site characterization, including the time constant, optical efficiency and array sensitivity. [ABSTRACT FROM AUTHOR]

Precise knowledge of the energy and lifetime of 229mTh isomeric state has notable importance as a basis for a nuclear clock. Such a clock would be capable to extend precision on the oscillator frequency by up to four orders of magnitude compared to the presently best atomic clocks. However, the technique proposed for the clock requires that the isomeric state energy is accessible with existing laser systems. Previous measurement placed this state at ∼8 eV (150 nm), in the Vacuum Ultra Violet (VUV) range of the electromagnetic spectrum. A precise direct measurement of the energy of this state is necessary to determine whether the nuclear clock can be made using existing laser technology. We are developing a cryogenic microcalorimeter to measure the energy and lifetime of the 229mTh isomeric state directly. The experiment will use a 233U source whose alpha-decay will populate the 229mTh isomeric state with 2% probability. The subsequent decay of 229mTh will be measured by a Transition Edge Sensor (TES) with <1 eV resolution. Such a technique will allow to observe all possible types of decays of 229mTh in the range of energy from 3 to 50 eV and lifetimes >5 microseconds. The single-photon TES has sufficient resolving power combined with high efficiency in the whole energy band for this experiment. Here we present a prototype of TES based on a 200 nm thick iridium-gold (Ir/Au) film which was tested with a pulsed laser source and demonstrated ∼0.8 eV energy resolution and 5.8 ± 2.1 μs signal recovery time. [ABSTRACT FROM AUTHOR]

We are currently developing transition edge sensors (TES) for the gamma-ray spectroscopy using a single gold bump post to connect the bulk metal absorber to the superconducting thin film. In order to develop a multi-pixel TES array for the gamma-ray spectroscopy, a stable and feasible method of mounting gamma-ray absorbers is indispensable. However, mounting gamma-ray absorbers on a single gold bump post is difficult from a structural stability and process development perspective. To overcome this problem, we have established a method to improve the structural stability in mounting gamma-ray absorbers by using 4 gold bump posts. We developed a TES array coupled with a Sn absorber which was mounted with our newly established method and used it to collect gamma-ray spectrum from an Am241 source. The rise time of the signal waveform was shorter than 200 μs and showed a favorable energy resolution considering the high transition temperature of the Ir/Au superconducting film. This new method to mount gamma-ray absorbers on TES will contribute to the development of multi-pixel TES arrays using bulk metal for gamma-ray absorbers. [ABSTRACT FROM AUTHOR]

Low Temperature Detectors have been used to measure embedded radioisotopes in a measurement mode known as Decay Energy Spectroscopy (DES) since 1992. DES microcalorimeter measurements have been used for applications ranging from neutrino mass measurements to metrology to measurements for safeguards and medical nuclides. While the low temperature detectors have extremely high intrinsic energy resolution (several times better than semiconductor detectors), the energy resolution achieved in practice is strongly dependent on factors such as sample preparation method. This review seeks to present the literature consensus on what has been learned by looking at the energy resolution as a function of various choices of detector, absorber, and sample preparation methods. [ABSTRACT FROM AUTHOR]

The origin and the evolution of the universe are concealed in the evanescent diffuse extragalactic background radiation (DEBRA). To reveal these signals, the development of innovative ultra-sensitive bolometers operating in the gigahertz band is required. Here, we review the design and experimental realization of two bias-current-tunable sensors based on one dimensional fully superconducting Josephson junctions: the nanoscale transition edge sensor (nano-TES) and the Josephson escape sensor (JES). In particular, we cover the theoretical basis of the sensors operation, the device fabrication, their experimental electronic and thermal characterization and the deduced detection performance. Indeed, the nano-TES promises a state-of-the-art noise equivalent power (NEP) of about 5 × 10 − 20 W / Hz , while the JES active region is expected to show an unprecedented NEP of the order of 10 − 25 W / Hz . Therefore, the nano-TES and JES are strong candidates to push radio astronomy to the next level. [ABSTRACT FROM AUTHOR]

Magnetic impurities in metallic superconductors are important for both fundamental and applied sciences. In this study, we focused on dilute Mn-doped aluminum (AlMn) films, which are common superconducting materials used to make transition edge sensors and other superconducting devices. We developed a multi-energy ion-implantation technique to make AlMn films. Compared with frequently used sputtering techniques, ion-implantation provides more precise control of the Mn doping concentration in the AlMn films. It enables us to fabricate reliably AlMn films with a different superconducting transition temperature (Tc) that can match a variety of application needs. We also found that the superconducting transition temperature drops with increasing film thickness for samples with the same nominal concentration of Mn dopants. The dependence of Tc on the film thickness is attributed to the increasing implantation energy. By quantitatively analyzing the curves of Tc versus the Mn doping concentration, we propose that Mn dopants act as magnetic impurities and suppression of superconductivity is counteracted by the antiferromagnetic Ruderman–Kittel–Kasuya–Yosida interaction among Mn dopants, which is influenced by the defects induced in the ion-implantation process. [ABSTRACT FROM AUTHOR]

We are developing an imaging capability ("Hyperspectral X-ray Imaging") for mapping chemical information (molecular formula, phase, oxidation state, hydration) that is based on ultra-high-resolution X-ray emission spectroscopy with large transition-edge sensor microcalorimeter arrays in the scanning electron microscope. By combining microcalorimeter arrays with hundreds of pixels, high-bandwidth microwave frequency-division multiplexing, and fast digital electronics for near real-time data processing, our goal is to enable measurements using laboratory-scale instrumentation rather than synchrotron beamlines. Our application focus here is on mapping the chemical form of uranium compounds on the nanoscale. We will present our approach to developing the Hyperspectral X-ray Imaging capability, progress toward a 128-pixel microwave multiplexed X-ray fluorescence instrument at LANL, and the path to high-throughput nanoscale chemical mapping. [ABSTRACT FROM AUTHOR]

We have measured the energy of each charged particle in carbon ion beam using a transition edge sensor (TES). The TES was irradiated by carbon ion beam of 100 MeV/u in Heavy Ion Medical Accelerator in Chiba. We have measured the energy of each charged particle in the carbon ion beam. This will contribute to the establishment of a new dosimetry method of carbon ion beam for radiotherapy. [ABSTRACT FROM AUTHOR]

The Simons Observatory is building both large (6 m) and small (0.5 m) aperture telescopes in the Atacama Desert in Chile to observe the cosmic microwave background CMB radiation with unprecedented sensitivity. Simons Observatory telescopes in total will use over 60,000 transition edge sensor (TES) detectors spanning center frequencies between 27 and 285 GHz and operating near 100 mK. TES devices have been fabricated for the Simons Observatory by NIST, Berkeley, and HYPRES/SeeQC corporation. Iterations of these devices have been tested cryogenically in order to inform the fabrication of further devices, which will culminate in the final TES designs to be deployed in the field. The detailed design specifications have been independently iterated at each fabrication facility for particular detector frequencies. We present test results for prototype devices, with emphasis on NIST high frequency detectors. A dilution refrigerator was used to achieve the required temperatures. Measurements were taken both with 4-lead resistance measurements and with a time-domain Superconducting Quantum Interference Device (SQUID) multiplexer system. The SQUID readout measurements include analysis of current versus voltage (IV) curves at various temperatures, square wave bias step measurements, and detector noise measurements. Normal resistance, superconducting critical temperature, saturation power, thermal and natural time constants, and thermal properties of the devices are extracted from these measurements. [ABSTRACT FROM AUTHOR]

The SPICA-SAFARI instrument requires extremely sensitive transition edge sensor (TES) arrays with a noise equivalent power of 2 × 10 - 19 W/ Hz and a readout system with an output noise that is dominated by the detector noise. It is essential to ensure the frequency domain multiplexing (FDM) readout system in SAFARI meets the noise requirement. The FDM system in SAFARI consists essentially of LC filters, a superconducting quantum interference device, a room-temperature low-noise amplifier (LNA), and a demultiplexer. Here we present a noise study of the LNA from a laboratory amplifier chain. We found the equivalent current and voltage noise of the LNA to be 5.4 pA/ Hz and 315 pV/ Hz , respectively, which are low enough to read out SAFARI's TES arrays. [ABSTRACT FROM AUTHOR]

We are developing a transition edge sensor (TES) microcalorimeter array based on a Ti/Au superconducting bilayer, as a backup option for the X-IFU instrument on the Athena X-ray observatory. The array is read out by a frequency-division multiplexing readout system using a 1–5 MHz frequency band. Extensive research collaborations between NASA/Goddard and SRON have led to new design rules for microcalorimeters such as low resistivity of the superconductor bilayer, moderately high ohmic resistance of the TES by changing the aspect ratio and no extra metal strips. We have improved our detector fabrication process according to these design principles and produced TES arrays. Although single-pixel characterizations of these arrays are ongoing, the best energy resolution of 2.0 eV for 5.9 keV X-ray has been observed with a 120 × 20 μm2 TES with a normal resistance of 150 mΩ, biased at 2.2 MHz frequency. This shows that our Ti/Au TES array has a potential to fulfill the detector requirements of the X-IFU instrument. [ABSTRACT FROM AUTHOR]

X-ray absorbers of the X-ray Integral Field Unit (X-IFU) microcalorimeters are required to provide high quantum efficiency (QE) for incident X-rays and high reflectivity to longer wavelength radiation. The thickness of the electroplated Au and Bi layers of the absorber is tuned to provide the desired pixel heat capacity and the QE. To calculate the QE precisely, in addition to filling factor, we have included the effects of surface roughness, edge profile of the absorbers and the effects of the different angles of incidence of the incoming X-rays from the X-IFU optic. Based on this analysis, it is found that thickness of the Bi layer needs to be adjusted by 4.3% to achieve the X-IFU QE requirements. To enhance the absorber's rejection of low-energy radiation, a second thin layer of Au is sputter-deposited on top of the Bi layer. Optical measurements in the wavelength range 0.3–20 μm show a significant increase in reflectivity compared to a bare Bi layer. [ABSTRACT FROM AUTHOR]

Photon imaging technology is applied in various research fields such as quantum information communication and biological imaging. We have been developing photon-counting devices using optical transition edge sensors (TES). We demonstrated a single-photon spectroscopic imaging system comprising an optical TES and a scanning microscope. However, a great number of TES pixels are required to increase the field of view in the imaging system. To read out the TES array, output signals need to be multiplexed. Microwave SQUID multiplexer (MW-Mux) is a kind of frequency multiplexing method with a carrier wave having a frequency of several GHz, and it can be used to widen the frequency band. In this paper, we report the first demonstration on readout of an optical TES with MW-Mux. [ABSTRACT FROM AUTHOR]

Low Temperature Detectors have been used to measure embedded radioisotopes in a measurement mode known as Decay Energy Spectroscopy (DES) since 1992. DES microcalorimeter measurements have been used for applications ranging from neutrino mass measurements to metrology to measurements for safeguards and medical nuclides. While the low temperature detectors have extremely high intrinsic energy resolution (several times better than semiconductor detectors), the energy resolution achieved in practice is strongly dependent on factors such as sample preparation method. This review seeks to present the literature consensus on what has been learned by looking at the energy resolution as a function of various choices of detector, absorber, and sample preparation methods.

The aim of this research work was to model the behaviour of a transition edge sensor (TES) bolometer by applying curve fitting methodology on empirical data. Data obtained from the experiments were used to plot characteristic curves to find resistance-temperature (R-T) and current-voltage (I-V) relations. The measurements were taken by using a cryogenic-free 3He refrigerator with a least temperature of 320 mK. Least-squares curve fitting technique was used to devise the equations of the experimentally obtained data. Similarly, the empirical data and estimated curves were validated using the parameters of R-squared, sum of squares due to error (SSE), adjusted R-squared, and root-mean-squared error (RMSE). By comparing the plot of the empirical data and estimated behaviour curves showed high degree of similarity, and hence it was established that these equations could be used to estimate the bolometer's operating behaviour for different ambient conditions with minimal percentage error. We also studied etched (TES device suspended on SiN) and non-etched (Si substrate based device) samples of bolometers. It was concluded that bolometers made up of etched sample of TES are appropriate for use in millimetre and submillimeter waves, especially for cosmic microwave background polarization detection. [ABSTRACT FROM AUTHOR]