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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, Kavli Institute of Nanoscience, Applied Sciences

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 2–3 × 10?19 W/? Hz to take full advantage of the cooled mirror. SRON has developed TiAu TES bolometers for the short wavelength band (30–60 ?m). 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 4.2×10?19 W/? Hz and a saturation power of about 10 fW., Kavli Institute of NanoScience, Applied Sciences

We describe the design of a focal plane array assembly incorporating transition edge superconducting bolometers (TES) for the SAFARI instrument aboard the SPICA satellite. SPICA consists of a 3.5 metre telescope actively cooled to a temperature of < 7 K, designed to be diffraction limited at a wavelength of 3 μm. The active cooling of the telescope reduces its emission to a level below the astrophysical background power level over the entire wavelength range of operation (~4 – 210 μm). This represents a reduction in loading at far-infrared (FIR) wavelengths of more than a factor of 10,000 over the 50 K HERSCHEL telescope. SAFARI is a proposed FIR instrument for SPICA consisting of an imaging Fourier Transform Spectrometer (FTS) covering The wavelengths from 34 – 210 μm with science goals of furthering our understanding of planetary system formation, the life cycle of dust and gas in the galaxy and the formation of galaxies. The SAFARI wavelength coverage is divided into 3 bands in the focal plane covering the wavelength ranges from 35 – 60 mm, 60 – 110 μm, and 110 – 210 μm. Each band requires a 2D focal plane array of 0.5 fλ spaced pixels covering a 2' x 2' field of view. The total number of pixels in all three bands is approximately 6000. In order to take advantage of the reduction in background power provided by the cooled telescope, SAFARI requires detectors with a combination of low optical NEP (~ 2 x 10-19 W√ x Hz) and high optical efficiency. There are several detector technologies that have been under development to meet these requirements including Kinetic Inductance Detectors (KIDs), Transition Edge Superconducting bolometers (TES), Silicon bolometers, Ge:Ga photoconductors and Quantum Well detectors. We describe the conceptual design of a TES focal plane array including the detector array, coupling optics, cold electronics and interconnections and mechanical and thermal design. We also describe the results of measurements of performance of single pixel pro

How structures of various scales formed and evolved from the early Universe up to present time is a fundamental question of astrophysics. EDGE1 will trace the cosmic history of the baryons from the early generations of massive stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing gravitational collapse by dark matter (the so-called warm hot intragalactic medium). In addition EDGE, with its unprecedented capabilities, will provide key results in many important fields. These scientific goals are feasible with a medium class mission using existing technology combined with innovative instrumental and observational capabilities by: (a) observing with fast reaction Gamma-Ray Bursts with a high spectral resolution (R - 500). This enables the study of their (star-forming) environment and the use of GRBs as back lights of large scale cosmological structures; (b) observing and surveying extended sources (galaxy clusters, WHIM) with high sensitivity using two wide field of view X-ray telescopes (one with a high angular resolution and the other with a high spectral resolution). The mission concept includes four main instruments: a Wide-field Spectrometer with excellent energy resolution (3 eV at 0.6 keV), a Wide-Field Imager with high angular resolution (HPD 15") constant over the full 1.4 degree field of view, and a Wide Field Monitor with a FOV of 1/4 of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part of the Cosmic Vision call. We will briefly review the science drivers and describe in more detail the payload of this mission.

We demonstrate that the performance of NbN lattice cooled hot electron bolometer mixers depends strongly on the interface quality between the bolometer and the contact structure. We show experimentally that both the receiver noise temperature and the gain bandwidth can be improved by more than a factor of 2 by cleaning the interface and adding an additional superconducting interlayer to the contact pad. Using this we obtain a double sideband receiver noise temperature TN,DSB = 950?K at 2.5 THz and 4.3 K, uncorrected for losses in the optics. At the same bias point, we obtain an IF gain bandwidth of 6 GHz., Kavli Institute of Nanoscience, Applied Sciences

Superconducting tunnel junctions (STJs) are promising as high energy resolution x-ray detectors. However, the theoretical limit of the energy resolution of STJs has not yet been reached for several reasons. In many cases quasiparticle losses limit the energy resolution. We have investigated STJs with different multilayer structures by means of low temperature scanning electron microscopy. By measuring the quasiparticle lifetime of Nb junctions with and without Ta passivation at the surface, we have identified quasiparticle losses at the surface of nonpassivated junctions as the dominant loss process. The temperature dependence of the quasiparticle lifetime gives information about the loss mechanism. The influence of quasiparticle traps on the effective quasiparticle lifetime is discussed. © 1999 American Institute of Physics.