In recent years TNO has investigated and developed different innovative opto-mechanical designs to
realize advanced spectrometers for space applications in a more compact and cost-effective manner.
This offers multiple advantages: a compact instrument can be flown on a much smaller platform or as
add-on on a larger platform; a low-cost instrument opens up the possibility to fly multiple instruments
in a satellite constellation, improving both global coverage and temporal sampling (e.g. multiple
overpasses per day to study diurnal processes); in this way a constellation of low-cost instruments
may provide added value to the larger scientific and operational satellite missions (e.g. the
Copernicus Sentinel missions); a small, lightweight spectrometer can easily be mounted on a small
aircraft or high-altitude UAV (offering high spatial resolution).
Transition edge sensor (TES) is the selected detector for the SAFARI FIR imaging spectrometer (focal plane arrays covering a wavelength range from 30 to 210 μm) on the Japanese SPICA telescope. Since the telescope is cooled to <7 K, the instrument sensitivity is limited by the detector noise. Therefore among all the requirements, a crucial one is the sensitivity, which should reach an NEP (Noise Equivalent Power) as low as 3E-19 W/Hz^0.5 for a base temperature of >50 mK. Also the time constant should be below 8 ms.
We fabricated and characterized low thermal conductance transition edge sensors (TES) for SAFARI instrument on SPICA. The device is based on a superconducting Ti/Au bilayer deposited on suspended SiN membrane. The critical temperature of the device is 155 mK. The low thermal conductance is realized by using narrow SiN ring-like supporting structures. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance (G) to be equal to 1.66 pW/K. This value corresponds to a noise equivalent power (NEP) of 1E-18 W/√Hz. The current noise and complex impedance is also measured at different bias points at 25 mK bath temperature. The measured electrical (dark) NEP is 2E-18 W/√Hz, which is about a factor of 2 higher than what we expect from the thermal conductance that comes out of the IV curves. Despite using a light-tight box, the photon noise might still be the source of this excess noise. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 65 μs and a thermal capacity of 3-4 fJ/K in the middle of the transition
The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and
technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future
X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 × 5 pixel array of
TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing
(FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogenfree
cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs,
fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and
status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital
Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray
energy resolution of 1.58 eV at 250 eV and 2.5 eV @ 5.9 keV for the read-out of one TES-pixel only. Next step is
deployment of FDM to read-out the full array. Full performance demonstration is expected mid 2009.
The Simbol-X mission, currently undergoing a joint CNES-ASI phase A, is essentially a classical X-ray telescope having an exceptional large focal length obtained by formation flying technics. One satellite houses the Wolter I optics to focus, for the first time in space, X-rays above ~10 keV, onto the focal plane in the second satellite. This leads to improved angular resolution and sensitivity which are two orders of magnitude better than those obtained so far with non-focusing techniques. Tailored to the 12 arcmin field of view and ~15 arcsec angular resolution of the optics, the ~8x8 cm2 detection area of the spectro-imager has ~ 500x500 μm2 pixels, and covers the full energy range of Simbol-X, from ~0.5 to ~80 keV, with a good energy resolution at both low and high energy. Its design leads to a very low residual background in order to reach the required sensitivity. The focal plane ensemble is made of two superposed spectro-imaging detectors: a DEPFET-SDD active pixel sensor on top of an array of pixelated Cd(Zn)Te crystals, surrounded by an appropriate combination of active and passive shielding. Besides the overall concept and structure of the focal plane including the anti-coincidence and shielding, this paper also emphasizes the promising results obtained with the active pixel sensors and the Cd(Zn)Te crystals combined with their custom IDeF-X ASICs.
Operating in the 0.5-70 keV energy range, Simbol-X is a next generation hard X-ray space mission proposed by a collaboration of
European laboratories for high energy astrophysics. Simbol-X will consist of two satellites flying in formation. In the first satellite, an X-ray mirror, having a focal length of 30 m, will focus the X-rays on the second satellite containing a silicon low energy detector on top of a Cd(Zn)Te (CZT) high energy detector. The latter consists of a mosaic of ~1 cm2 elementary arrays with 256 pixels (0.5x0.5 mm2). As a first step in the development, a prototype CZT detector of 10x10x2 mm3, having one side covered with 0.9x0.9 mm2 pixels, is used. A 3-D modeling is performed of the latter. The photon interaction inside the detector is simulated. The spatial distribution of the energy deposition and the amount of charge sharing of the pixels are obtained. The results serve as input parameters for the development and choice of the detector final geometry and electronics.