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Optimal extraction of pulses of constant known shape from a time series with stationary noise is well understood and widely used in detection applications. Applications where high resolution is required over a wide range of input signal amplitudes use much of the dynamic range of the sensor. The noise will in general vary over this signal range, and the response may be a nonlinear function of the energy input. We present an optimal least squares procedure for inferring input energy in such a detector with nonstationary noise and nonlinear energy response.

We are developing superconducting transition-edge sensor (TES) microcalorimeters for astronomical x-ray spectroscopy. We have obtained very high energy resolution (2.4 eV at 1.5 keV and 3.7 eV at 3.3 keV) in large, isolated TES pixels using Mo/Au proximity-effect bilayers on silicon-nitride membranes several mm wide. In order to be truly suitable for use behind an x-ray telescope, however, such devices need to be arrayed with a pixel size and focal-plane coverage matched to the telescope focal length and spatial resolution. For the Constellation-X mission, this requires fitting the TES, its thermal link, and contact wiring into a 0.25 mm square, a far more compact geometry than has previously been investigated. We have demonstrated that the weak thermal link can be restricted to a narrow (∼10 micron) perimeter of membrane around the TES and still provide a thermal conductance in the acceptable range. Varying the size and placement of slits in that nitride perimeter, we can tune that value.

We present an overview of our efforts in fabricating Transition-Edge Sensor (TES) microcalorimeter arrays for use in astronomical x-ray spectroscopy. Two distinct types of array schemes are currently pursued: 5×5 single pixel TES array where each pixel is a TES microcalorimeter, and Position-Sensing TES (PoST) array. In the latter, a row of 7 or 15 thermally-linked absorber pixels is read out by two TES at its ends. Both schemes employ superconducting Mo/Au bilayers as the TES. The TES are placed on silicon nitride membranes for thermal isolation from the structural frame. The silicon nitride membranes are prepared by a Deep Reactive Ion Etch (DRIE) process into a silicon wafer. In order to achieve the concept of closely packed arrays without decreasing its structural and functional integrity, we have already developed the technology to fabricate arrays of cantilevered pixel-sized absorbers and slit membranes in silicon nitride films. Furthermore, we have started to investigate ultra-low resistance throug...

In the X-ray astrophysics community, the desire for wide- field, high-resolution, X-ray imaging spectrometers has been growing for some time. We present a concept for such a detector called a Position-Sensing Transition-edge sensor (PoST). A PoST is a calorimeter consisting of two Transition- Edge Sensors (TESs) on the ends of a long absorber to do one dimensional imaging spectroscopy. Comparing the rise time and energy estimates obtained from each TES for a given event, the position of that event in the PoST is determined. Energy is inferred from the sum of the two signals on the TESs. We have designed 7, 15, and 32 pixel PoSTs using our Mo/Au TESs and bismuth absorbers. We discuss the theory, modeling, operation and readout of PoSTs and the latest results from our development.

Our detectors are superconducting transition edge sensors (TESs) optimized for the wide band detection of individual photons from the mid infrared, through the optical, and into the near ultraviolet. We typically achieve an energy resolution of 0.15 eV FWHM over this range with timing resolution of 100 ns. We have measured photon events with sub- microsecond rise times and 3 microsecond fall times allowing count rates as high as 30 kHz without significant degradation in energy resolution. Such characteristics along with the predicted high quantum efficiency (10% in IR to 50% in optical-UV) make our TES detectors very appealing for low-flux applications which have energy and timing requirements, such as fast spectrophotometry for observational astronomy. We present results from our recent observation of the Crab Pulsar (PSR BO531 + 21) which demonstrate the ability of our sensors to extract wide band phase-resolved spectroscopic information of the pulsar using the student-class 24 inch telescope on the campus of Stanford University. We present a description of the optical system and an analysis of the single pixel energy response.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

COnstellation-X is a cluster of identical observatories that together constitute a promising concept for a next- generation, high-throughput, high-resolution, astrophysical x-ray spectroscopy mission. The heart of the Constellation-X mission concept is a high-quantum-efficiency imaging spectrometer with 2 eV resolution at 6 keV. Collectively across the cluster, this imaging spectrometer will have twenty times the collecting efficiency of XRS on Astro-E and better than 0.25 arc minute imaging resolution. The spectrometer on each satellite will be able to handle count rates of up to 1000 counts per second per imaging pixel for a point source and 30 counts per second per pixel for an extended source filling the array. Focal plane coverage of at least 2.5 arc minutes X arc minutes, comparable to XRS but with a factor of thirty more pixels, is required. This paper will present the technologies that have the potential to meet al these requirements. It will identify the ones chosen for development for Constellation-X and explain why those were considered closer to realization, and it will summarize the results of the development work thus far.

We report the detection of γ-ray emission coincident with three supernova remnants (SNRs) using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. W41, G337.7-0.1, and MSH 17-39 are SNRs known to be interacting with molecular clouds, as evidenced by observations of hydroxyl (OH) maser emission at 1720 MHz in their directions and other observational information. SNR shocks are expected to be sites of cosmic-ray acceleration, and clouds of dense material can provide effective targets for production of γ-rays from π[superscript 0]-decay. The observations reveal unresolved sources in the direction of G337.7-0.1 and MSH 17-39 and an extended source coincident with W41. We model their broadband emission (radio to γ-ray) using a simple one-zone model, and after considering scenarios in which the MeV-TeV sources originate from either π[superscript 0]-decay or leptonic emission, we conclude that the γ-rays are most likely produced through the hadronic channel., United States. National Aeronautics and Space Administration (Fermi grant NNX10AP70G), Smithsonian Astrophysical Observatory (Contract SV3-73016)

The Micro-X sounding rocket program will fly a 128-pixel array of transition-edge-sensor microcalorimeters to enable high-resolution X-ray imaging spectroscopy of supernova remnants. To match the angular resolution of the optics while maximizing the field-of-view and retaining a high energy resolution (2-4 eV at 1 keV), we have designed the pixels using 590 × 590 μm2 Au/Bi absorbers, which overhang 140 × 140 μm2 Mo/Au sensors. Here we report experimental results from flight-candidate arrays, including measurements of energy resolution, uniformity, and absorber thermalization. We describe the reduction in pixel-to-pixel crosstalk afforded by an angle-evaporated Cu backside heatsinking layer, which provides Cu coverage on the four sidewalls of the silicon wells beneath each pixel. In addition, we present measurements of devices that have an identical pixel architecture but were fabricated with thin (sub-micron) all-Au absorbers.

We present results on phonon quasidiffusion and Transition Edge Sensor (TES) studies in a large, 3 inch diameter, 1 inch thick [100] high purity germanium crystal, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare calibration data with results from a Monte Carlo which includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels. The phonon energy is then parsed into TES based phonon readout channels and input into a TES simulator.

Weakly Interacting Massive Particles (WIMPs) are a strong candidate for the Cold Dark Matter of the Universe. CDMS-II is a direct-search WIMP search experiment, operating at 50 mK and housed at the Soudan mine, Minnesota. The 250 gram Ge detectors utilize athermal phonon sensors where tungsten transition edge sensors are operated in negative electrothermal feedback. The search at Soudan is ongoing with an expected final reach of CDMS-II by the end of 2008 of a WIMP-nucleon cross-section sensitivity of 2.1 x10-44 cm2, at a WIMP mass of 60 GeV/c2. To proceed further, we have proposed the SuperCDMS program.

We present measurements of high fill-factor arrays of superconducting transition-edge x-ray microcalorimeters designed to provide rapid thermalization of the x-ray energy. We designed an x-ray absorber that is cantilevered over the sensitive part of the thermometer itself, making contact only at normal metal-features. With absorbers made of electroplated gold, we have demonstrated an energy resolution between 2.4 and 3.1 eV at 5.9 keV on 13 separate pixels. We have determined the thermal and electrical parameters of the devices throughout the superconducting transition, and, using these parameters, have modeled all aspects of the detector performance.

An x-ray microcalorimeter consists of an absorber and a thermometer connected to each other, and to a heat sink, via well defined thermal conductances. The standard theoretical derivation of energy resolution treats the absorber and thermometer as point elements that are internally isothermal. In reality, the finite size and internal diffusivity of the absorber and thermometer prevents these elements from instantly achieving a uniform temperature, leading to a variation in observed pulse shapes as a function of the interaction’s position within the absorber. These variations result in a distortion of the detector response and a subsequent degradation of the energy resolution. This paper presents diffusivity measurements for x-ray microcalorimeters fabricated at the NASA/GSFC. Using a diffusion model we developed, we show quantitatively how a 2eV Gaussian response is distorted into a non-Gaussian profile roughly 12eV wide at an energy of 6keV for an absorber diffusivity of 104μm2∕μs. We then present a meth...

We present a general formalism for calculating the linear response, noise spectrum, and energy resolution of complex calorimeters. Using this formalism calorimeters with arbitrary numbers of distinct linked heat capacity systems and/or coupled thermometers can be analyzed. We use this formalism to derive the theoretical resolution of an imaging microcalorimeter called a position- sensitive transition-edge sensor.

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years., 66 pages, 15 figures, 3 tables. Workshop website and agenda: http://www-conf.slac.stanford.edu/darksectors2016/ https://indico.cern.ch/event/507783/ Editors: J. Alexander, M. Battaglieri, B. Echenard, R. Essig, M. Graham, E. Izaguirre, J. Jaros, G. Krnjaic, J. Mardon, D. Morrissey, T. Nelson, M. Perelstein, M. Pyle, A. Ritz, P. Schuster, B. Shuve, N. Toro, R. Van De Water

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017., Comment: 102 pages + references