TES microcalorimeter readout via transformer

Readout configuration for Transition Edge Sensor (TES) electrically coupled to a low noise warm front-end via transformer is studied. The study was aimed at the implementation of the readout involved in imaging with microcalorimeter detector arrays using frequency multiplexing technique (Appl. Phys. Lett. 81(1) (2002) 159). A model describing both TES electrothermal reaction and the readout response is investigated. Contribution of electronic noise to TES energy resolution is calculated. Prospective readout architecture with TES electrical biasing from the warm readout side is introduced. The architecture allows building of large imaging detector arrays with TES. It is shown that an unprecedented combination of imaging and spectrometry features can be achieved with TES readout via transformer.     

Analyses on the operating point dependence of the energy resolution with a Ti/Au TES microcalorimeter

We examined the performance of a single pixel Ti/Au transition-edge sensor (TES) calorimeter for incident X-ray energies of Al-K, Cr-K, and Fe-K, as a function of the TES resistance. We find that the energy resolution does not always degrade with increasing energy. The best energy resolution of 5.7±0.9 eV at 6.4 keV is obtained, which is possibly even better than the baseline width of 6.5±0.2 eV. Assuming that the noise level is determined by the noise spectrum NS(f;RR+dR(E)) considering the resistance change of dR(E), instead of NS(f;R) at the operating point, these results may be explained by the fact that the noise decreases at the higher TES resistance. The pulse variation appears to have a minimum at a certain resistance of R+dR(E)48 mΩ, and the best energy resolution for each line is obtained at such an operating point, respectively. The pulse variation could be enhanced when the fluctuation of the TES sensitivity is large at R+dR(E).     

Optimised filtering for improved energy and position resolution in position-sensitive TES based X-ray detectors

We report on a new optimal filtering algorithm for improved energy and position resolution in position sensitive Transition Edge Sensor (TES) based X-ray detectors. This algorithm takes account of the noise correlation between the detector outputs to minimise the variance on the estimated photon energy and position. Using numerical methods we show that improved energy and position resolution can be obtained than from previously published methods. Our simulations also reveal the trade-offs resulting from changes in the thermal conductances and heat capacities of the detector elements.     

Current dependence of performance of TES microcalorimeters and characteristics of excess noise

We are developing transition edge sensor (TES) microcalorimeter arrays for future Japanese astronomy missions. Although 6.6 eV energy resolution for 5.9 keV and 74 μs decay time are achieved, our energy resolution was limited by the excess noise of unknown origin. The dominant noise showed 1/R dependence and it only appeared when the current through the TES, I, is larger than 10 μA. This is explained if we assume a constant voltage noise source with a level of 2(4kT_CR_n)^1/2. We also investigated the influence of I on the TES performance and found the TES sensitivity is reduced when the ratio of current to the critical current I/I_C is large. It can explain the reduction of observed when operated without a magnetic shield. We also found a strong correlation between I_C and or the baseline width. Thus, we conclude that I_C is an essential parameter for the TES performance.     

Operation of a TES microcalorimeter cooled by a compact liquid-helium-free He-He dilution refrigerator directly coupled to a Gifford-McMahon cooler

A superconducting transition edge thermosensor (TES) microcalorimeter was irradiated with LX-ray photons emitted by an ²⁴¹Am source maintained at an operating temperature of 120 mK using a compact liquid-helium-free ³He-⁴He dilution refrigerator directly coupled to a Gifford-McMahon (GM) cooler. The first and second stages of the GM cooler were directly coupled to the first and second pre-cool heat exchangers of a stick shaped dilution unit through copper plates in a vacuum chamber. The helium-free dilution refrigerator provided a cooling power of 20 μW at 100 mK. Detection signals of LX-ray photons emitted by the ²⁴¹Am source were observed by operating the TES microcalorimeter in a severe noise environment induced by the mechanical vibrations of the GM cooler.     

Approaching the fundamental noise limit in Mo/Au TES bolometers with transverse normal metal bars

Recent efforts in the Transition Edge Sensor (TES) bolometer/calorimeter community have focused on developing detectors whose noise properties are near the fundamental limits. These include the in-band phonon noise, the out-of-band Johnson noise, and the 1/f noise. We have investigated the noise performance of Mo/Au-bilayer TES bolometers designed for infrared detectors. These detectors use normal metal regions for the suppression of excess noise, which are oriented either parallel to (“bars”) or transverse to (“stripes”) the direction of current flow. Two nearly identical detectors, one with stripes and one with bars, were fabricated at the NASA/GSFC detector development facility. Significantly lower noise is found with the normal metal regions oriented transversely. We compare the detailed noise measurement and quantitative analysis of the noise level in each device as a function of the detector resistance. Our preliminary result is that the best detector features only moderate excess noise in both the in-band region and in the out-of-band region. This noise performance is suitable for instruments with multiplexed TES arrays, such as GSFC's FIBRE and SAFIRE.     

Broadband resolution analysis for imaging with measurement noise

Resolution analysis for imaging in the presence of noise is presented. A simple definition of resolution that takes into account the effect of noise is introduced and is shown to depend also on factors such as the signal-to-noise ratio and the false-alarm rate. The striking effect of aperture-independent superresolution in imaging with broadband signals is demonstrated.     

Uncertainty in relative energy resolution measurements

We suggest a new method for the determination of the detector relative energy resolution and its uncertainty based on spline approximation of experimental spectra and a statistical bootstrapping procedure. The proposed method is applied to the spectra obtained with NaI(Tl) scintillating detectors and ¹³⁷Cs sources.

The spectrum histogram with background subtracted channel-by-channel is modeled by cubic spline approximation. The relative energy resolution (which is also known as pulse height resolution and energy resolution), defined as the full-width at half-maximum (FWHM) divided by the value of peak centroid, is calculated using the intercepts of the spline curve with the line of the half peak height. The value of the peak height is determined as the point where the value of the derivative goes to zero. The residuals, which are normalized over the square root of counts in a given bin (y-coordinate), obey the standard Gaussian distribution. The values of these residuals are randomly re-assigned to a different set of y-coordinates where a new “pseudo-experimental” data set is obtained after “de-normalization” of the old values. For this new data set a new spline approximation is found and the whole procedure is repeated several hundred times, until the standard deviation of relative energy resolution becomes stabilized. The standard deviation of relative energy resolutions calculated for each “pseudo-experimental” data set (bootstrap uncertainty) is considered to be an estimate for relative energy resolution uncertainty.

It is also shown that the relative bootstrap uncertainty is proportional to, and generally only two to three times bigger than, , which is the relative statistical count uncertainty (N_tot is the total number of counts under the peak).

The newly suggested method is also applicable to other radiation and particle detectors, not only for relative energy resolution, but also for any of the other parameters in a measured spectrum, like peak position, shape parameters, etc.     

Ion beams with high energy resolution

The energy spread of the 350 kV cascade accelerator at Münster was found to arise predominantly from the ripple induced by the 50 kHz oscillator. When the ripple is taken into account via standard electronics, a residual energy resolution as low as 18 eV has been observed. Some applications are discussed.     

Evaluating phase noise power spectrum with variable frequency resolution

Measurement of phase noise affecting sinusoidal carriers is dealt with here. A new method is proposed, mainly intended to overcome the limits of two digital signal-processing solutions, already presented by the authors and devoted, respectively, to far-from-the-carrier and close-to-the-carrier phase noise analysis. Thanks to an original measurement procedure, the method optimizes the frequency resolution in the evaluation of phase noise power spectral density; in particular, the closer to the carrier the analysis, the finer the frequency resolution granted. It is possible to obtain accurate and reliable results in a wide range of frequency offsets with no need for heavy computational burden and expensive hardware resources of the adopted data acquisition system. The results of a number of experiments, conducted on actual sinusoidal carriers through a measurement prototype implementing the method, confirm the efficacy and reliability of the proposal.     

Large microcalorimeter arrays for high-resolution X- and gamma-rayspectroscopy

Microcalorimeter detectors provide unprecedented energy resolution for the measurement of X-rays and soft gamma-rays. Energy resolution in the 100 keV region can be up to an order of magnitude better than planar high-purity germanium (HPGe) detectors. The technology is well-suited to analysis of materials with complex spectra presenting closely spaced photopeaks. One application area is the measurement and assay of nuclear materials for safeguards and fuel cycle applications. In this paper, we discuss the operation and performance of a 256-pixel array, and present results of a head-to-head comparison of isotopic determination measurements with high-purity germanium using a plutonium standard. We show that the uncertainty of a single measurement is smaller for the microcalorimeter data compared to the HPGe data when photopeak areas are equal. We identify several key areas where analysis codes can be optimized that will likely lead to improvement in the microcalorimeter performance.     

Single-electron response and energy resolution of a Micromegas detector

Micro-Pattern Gaseous Detectors (MPGDs) such as Micromegas or GEM are used in particle physics experiments for their capability of particle tracking at high rates. Their excellent position resolutions are well known but their energy characteristics have been less studied. The energy resolution is mainly affected by ionisation processes and gain fluctuations. This paper presents a method to separately measure these two contributions to the energy resolution of a Micromegas detector. The method relies on the injection of a controlled number of primary electrons in the gas. The Micromegas has a 1.6-mm drift zone and a 160-μm amplification gap. It is operated in Ne 95%-iC₄H₁₀ 5% at atmospheric pressure. The electrons are generated by non-linear photoelectric emission derived from the photons of a pulsed 337-nm wavelength laser coupled to a focusing system. The single-electron response has been measured at different gains (3.7×10⁴, 5.0×10⁴ and 7.0×10⁴) and is fit with good agreement by a Polya distribution. From those fits, a relative gain variance of 0.31±0.02 is deduced. The setup has also been characterised at several voltages by fitting the energy resolution measured as a function of the number of primary electrons, ranging from 5 to 210. An upper limit on the Fano factor (0.37) has been estimated for 5.9 keV X-rays absorbed in a Ne 95%-iC₄H₁₀ 5% gas mixture.     

Sensitivity, noise, and resolution in QCM sensors in liquid media

The use of quartz-crystal oscillators as high-sensitivity microbalance sensors is limited by the frequency noise present in the circuit. To characterize the behavior of the sensors, it is not enough to determine their experimental sensitivity, but, rather, it is essential to study the frequency fluctuations in order to establish the sensor resolution. This is fundamental in the case of oscillators for damping media, because the level of noise rises due to the strong decline of the quality factor of the resonator. In this paper, a comparative study of noise and resolution is presented with respect to the frequency and the quality factor. The study has been made using four oscillators designed to be used in quartz-crystal microbalance sensors in damping media. The four circuits have been designed at increasing frequencies in order to improve the sensitivity or frequency change per unit of measurand. Also, the present theoretical resolution limit or best resolution achievable with a microbalance oscillator using an AT resonator is determined, since this does not depend on frequency. However, when operating in liquid, the damping of the resonator makes the resolution diminish due to a worsening of the quality factor. The relationship between the resolution limit and the frequency and characteristics of the liquid medium is determined. The resolution worsens when the density and viscosity of the liquid is increased. However, in this case, an increase in frequency implies a small increase in resolution. Therefore, we find that when working below the maximum quality factor, for similar values, the resolution can be improved by elevating the work frequency.     

A determination of the energy resolution at LANSCE

The energy resolution of the white neutron source at the Manuel Lujan, Jr. Neutron Scattering Center (LANSCE) was determined in the energy range from approximately 1 eV to 100 keV by comparing measurements with resolution-broadened theoretical resonance shapes. It was found that the LANSCE resolution function could be well described by a skewed Gaussian having a width in agreement with the sum of the known contributions from the incident proton pulse width, the moderation width, the channel width, and Doppler broadening. In addition, to obtain a good fit to the data it was necessary to use an energy-dependent skew parameter.     

Imaging resolution and properties analysis of super resolution microscopy with parallel detection under different noise,detector and image restoration conditions

Parallel detection, which can use the additional information of a pinhole plane image taken at every excitation scan position, could be an efficient method to enhance the resolution of a confocal laser scanning microscope. In this paper, we discuss images obtained under different conditions and using different image restoration methods with parallel detection to quantitatively compare the imaging quality. The conditions include different noise levels and different detector array settings. The image restoration methods include linear deconvolution and pixel reassignment with Richard–Lucy deconvolution and with maximum-likelihood estimation deconvolution. The results show that the linear deconvolution share properties such as high-efficiency and the best performance under all different conditions, and is therefore expected to be of use for future biomedical routine research.     

Understanding dissipative tip-molecule interactions with submolecular resolution on an organic adsorbate

Three-dimensional force spectroscopy measurements on 3,4,9,10-perylene-tetra-carboxylic dianhydride adsorbed on Ag(111) are combined with first-principles calculations to characterize the dissipative tip-molecule interactions with submolecular resolution. The experiments reveal systematic differences between the energy dissipation at the end groups and the center of the molecules that change with the tip-sample distance. Guided by the strength of the experimental conservative forces, an Ag-contaminated Si tip is identified as the likely tip termination in the experiments. Based on this tip configuration, the energy dissipation in the tip-sample contact is determined from the approach and retraction force curves calculated as a function of distance for different molecule sites. These calculations provide an explanation for the experimental trends in terms of the competition between localized dissipation mechanisms involving the quite mobile oxygen atoms on the sides of the molecule, and global molecular deformations involving the more rigid perylene core. The results confirm that the observed dissipation can be explained in terms of adhesion hysteresis and show the power of combined experimental-theoretical spectroscopy studies in the characterization of the underlying microscopic mechanisms.     

Optimization and Analysis of Code-Division Multiplexed TES Microcalorimeters

We are developing code-division multiplexing (CDM) systems for TES arrays with the goal of reaching multiplexing factors in the hundreds. We report on x-ray measurements made with a four-channel prototype CDM system that employs a flux-summing architecture, emphasizing data-analysis issues. We describe an empirical method to determine the demodulation matrix that minimizes cross-talk. This CDM system achieves energy resolutions of between 2.3?eV and 3.0?eV FWHM at 5.9?keV.     

Signal rise times and energy resolution in radial semiconductor drift chambers

The risetimes expected in a semiconductor drift chamber (SDC) incorporating a constant drift field component to the electric field have been calculated. The combined influence of systematic risetime broadening and the random broadening processes has been determined and applied to some hypothetical test cases. It is predicted that the resolution of a 50 mm diameter SDC at 300 K will be limited by straggle in the dead layer for alpha particle spectrometry. The same detector could also detect 10 keV X-rays with an anticipated σ of 1.4 keV, limited by the electronic noise.     

The e/h ratio and energy resolution of hadron calorimeters

The e/h ratio and the energy resolution for a variety of experimental test setups are compared with Monte Carlo calculations, using the GHEISHA/EGS hadronic and electromagnetic cascade code. The compensation mechanism in uranium calorimeters is discussed. The dependence of the e/h ratio and the energy resolution on the absorber and detector material, on the sampling thickness and the thickness of the detector material is studied in detail. Solutions for uranium calorimeters with equal response to electrons and hadrons are investigated for different readout techniques.