The so-called “optimal filter” analysis of a microcalorimeter's x-ray pulses is statistically optimal only if all pulses have the same shape, regardless of energy. However, the shapes of pulses from a nonlinear detector can and do depend on the pulse energy. A pulse-fitting procedure that we call “tangent filtering” accounts for the energy dependence of the shape and should, therefore, achieve superior energy resolution. We take a geometric view of the pulse-fitting problem and give expressions to predict how much the energy resolution stands to benefit from such a procedure. We also demonstrate the method with a case study of K-line fluorescence from several 3d transition metals. The method improves the resolution from 4.9 to 4.2 eV at the Cu K $\alpha$ line (8.0 keV).
AbstractSuperconducting Quantum Interference Device (SQUID)‐based instruments have proven to be the most sensitive measurement techniques for not only magnetization measurements but also for a number of other electrical measurements. Their device noise (well below 1 mK), flat frequency and phase response that extends from DC to above 10 GHz, and low drift permit electromagnetic measurements at levels far superior to conventional techniques. SQUID instruments consist of a SQUID amplifier or sensor and a detection circuit that transforms the signal of interest into a magnetic flux that is detected by the SQUID sensor. Associated control electronics transform this signal into a room temperature voltage that is available for additional signal processing if needed. The SQUID amplifier and the detection coils are superconducting devices that are kept at cryogenic temperatures. Various types of SQUID sensors and materials (low‐temperature and high‐temperature superconductors) are discussed along with a wide variety of applications, including laboratory, geophysical, nondestructive test and evaluation along with specific examples of medical applications.
Binary Nb-Sn thin film samples were fabricated and characterized in terms of their composition, morphology, and superconducting properties. Nb-Sn was magnetron-sputtered onto heated R-plane sapphire substrates at 700°C, 800°C, and 900°C, using a custom-built heater assembly. Samples were cut into strips, where each strip has a unique composition. For a subset of the samples, Nb-Sn was selectively etched away at an etching rate of 6 ± 1 nm/s using an aqueous solution of 3 vol.% hydrofluoric and 19 vol.% nitric acid. The sample composition was investigated with a scanning electron microscope with an X-ray energy dispersive spectroscopy detector. Surface and cross-section morphologies were investigated using scanning electron microscopy and scanning transmission electron microscopy, revealing a dense columnar poly-crystalline grain structure. X-ray diffraction measurements indicate a highly textured film that is (100) oriented out-of-plane and random in-plane. The critical temperature Tc (ranging from 9.8 to 17.9 K), critical magnetic field μ0Hc2 (ranging from 12.5 to 31.3 T), residual resistivity ratio (RRR), and normal state resistivity ρ0 were measured and found to be broadly consistent with literature data on bulk Nb3Sn.
Having developed a transition-edge-sensor (TES) calorimeter design that enables high spectral resolution in high fill-factor arrays, we now present array-scale results from 32-pixel arrays of identical closely packed TES pixels. Each pixel in such an array contains a Mo/Au bilayer with a transition temperature of 0.1 K and an electroplated Au or Au/Bi xray absorber. The pixels in an array have highly uniform physical characteristics and performance. The arrays are easy to operate due to the range of bias voltages and heatsink temperatures over which solution better than 3 eV at 6 keV can be obtained. Resolution better than 3 eV has also been obtained with 2x8 time-division SQUID multiplexing. We will present the detector characteristics and show spectra acquired through the read-out chain from the multiplexer electronics through the demultiplexer software to real-time signal processing. We are working towards demonstrating this performance over the range of count rates expected in the observing program of the Constellation-X observatory. We mill discuss the impact of increased counting rate on spectral resolution, including the effects of crosstalk and optimal-filtering dead time.
The microwave surface resistance (R/sub s/) of YBCO films sputtered simultaneously on both sides of CeO/sub 2/ coated sapphire wafers of 3 inch diameter was measured using the disk resonator technique at a frequency of 1.92 GHz. Gold layers were deposited on the unpatterned side of the resonator, and the microwave losses were measured in the Au-contacted YBCO films. Although the Au layer was not directly exposed to the microwave power, it dramatically increased the effective R/sub s/ of the YBCO film, while leaving the effective surface reactance (X/sub s/) almost unchanged. The R/sub s/-enhancement was examined experimentally and theoretically in terms of the impedance transformation approach as a function of the Au and YBCO film properties. Furthermore, the technique appeared suitable for the determination of the absolute value of the London penetration depths (/spl lambda//sub L/) in the double-sided YBCO films. The resulting temperature dependencies of /spl lambda//sub L/ were in a good agreement with those estimated by the conventional frequency-shift technique.
We have made Radio-Frequency Single-Electron Transistors (RF-SETs) with large input gates, and tested performance and modes of operation with the goal of using such devices as on-chip amplifiers for a variety of high impedance cryogenic photodetectors. We achieved /spl ap/100 kHz of closed-loop bandwidth for charge-locked-loop and transimpedance amplifier feedback configurations, and have combined amplifier outputs using a form of wavelength division multiplexing. With our choice of SET junction resistance, a 0.5 fF input gate capacitance gave a cotunneling-degraded charge noise of 1/spl times/10/sup -4/ e//spl radic/Hz, but a fairly low input voltage noise of 30 nV//spl radic/Hz.
We report on high quality planar junctions fabricated from well characterized c-axis quasi-homoepitaxial NdBa2 Cu3O7−δ/PrBa2Cu3O7−δ/NdBa2Cu3O7−δ multilayers. C-axis tunneling spectroscopy investigations provide evidence of quasiparticle tunneling that is commonly observed for superconductor-insulator-superconductor (SIS) junctions. We observed a temperature dependent BCS like gap giving 2Δ/KBTc=6. The tunneling conductance dI/dV of the junctions in parallel magnetic field reveals an anomalous splitting of the superconducting quasiparticle density of states. The magnitude of the splitting can be related to the magnetic moment of the quasiparticles.
We have measured the switching current distributions out of the zero-voltage state of Josephson junctions in nonstationary conditions, obtained by means of fast sweeping of the current bias (≌100 kHz) resulting in a dI/dt up to 25 A/s. In this way we have analysed the effects of the levels quantization on the escape rate out of the zero voltage state in conditions where the occupancy probability of the energy levels is far from being in equilibrium.
