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Date: September 2009
The Space Nanotechnology Laboratory at MIT's Kavli Institute for Astrophysics and Space Research is progressing with the next generation of CAT gratings. Since their initial successful X-ray demonstrations of the CAT grating concept with large-period and lower aspect-ratio prototypes, the lab has now microfabricated 200 nm-period silicon CAT gratings comprised of grating bars with 6 micron depth, optimized for the 0.3 to 1.0 keV energy band. Preliminary analysis of recent X-ray tests has shown blazing behavior up to 1.28 keV in accordance with predictions.
Fabrication results. (a) Schematic top view of a CAT grating sample. (b) Schematic (not to scale) of CAT grating bars (white) and level I support mesh (gray). (c) Top view SEM images from sample S6B at various magnifications, showing level I support grid and CAT grating bars. (d) SEM image of cleaved cross section from sample S6A, showing the high aspect ratio of the CAT grating bars. Credit: SNL. Click the image for a larger view
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+ SPIE proceedings paperDate: September 9, 2009
The international consortium for developing Silicon Pore Optics (SPO) is making a steady progress. Recently, they have developed the next generation of the automated stacking robots. Using this robot they have built stacks with wedged plates and measured them at the BESSY synchrotron radiation facility. The stacks achieved in single reflection a half-energy width (HEW) of 7" on the first nine plates, which corresponds for a mirror module in double reflection to 10". This compares to 17" on the first four unwedged plates measured in 2007 and demonstrates the significant improvement in stacking quality. The complete first plate exhibits in single reflection a HEW of 4.2".
Stacking robot inside the class 100 clean area at cosine. The system is installed on a vibration isolated table and consists of more than 16 axes. It is fully automated and is designed to build stacks up to 100 plates high. The plates can be positioned with μm accuracy and automatically be bent into the required shape. Credit: ESA. Click the image for a larger view.
In parallel, the SPO team has developed and demonstrated stacks with patterned iridium coatings with carbon overcoatings inside the pores. The team has successfully performed the first pull tests and is now preparing environmental tests. New wedging techniques have been developed that allow meeting the requirements of IXO and methods been explored to overcome the performance limits imposed by the conical approximation.
Also, the technological issues of cleanliness and bonding have been addressed by improved assembly hardware developed in the course of the ongoing technology research program and by the steep learning curve in assembling pore optics. So far, no issue has been identified that would impede improving the performance of silicon pore optics beyond 5".
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+ Stacking of Silicon Pore Optics for IXODate: May 2009
Hard X-ray Telescope (HXMM) prototype has been tested at the PANTER Facility using the full beam illumination, with three electroformed nickel replication (ENR) mirror shells mounted. Up-to-date, ~ 30 arcsec HPD has been achieved on mounted 100-micron-thick nickel shells fabricated at MSFC.
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Hard X-ray Telescope (HXMM) prototype has been tested at Panter Facility, full beam illumination, with three mirror shells mounted. Credit: Suzanne Romaine. Click the image for a larger view. |
HXMM Optics: about 30 arcsec HPD has been achieved on mounted 100-micron-thick shells fabricated at MSFC. Credit: Suzanne Romaine. Click the image for a larger view. |
Date: April 2009
The Centre d´Etude Spatiale des Rayonnements has completed the description of the HTRS in the IXO Payload Definition Document. The instrument is based on an array of Silicon Drift Detectors (SDD), manufactured by the The Max-Planck-Institut Halbleiterlabor. The University of Geneva has designed the filter wheel for the HTRS. The filter wheel is a system to protect the detector, and to reduce the optical loading on the SDD array. It consists of a rotating disk perpendicular to the optical beam and controlled by a motor. The motor is commanded by a dedicated electronics, which allows us to select accurately a specific orientation of the filter wheel.
In parallel, the University of Tübingen and the University of Erlangen-Nuremberg have performed Monte Carlo simulations to estimate the loss of efficiency of the HTRS caused by to deadtime. The simulations assume a point source illuminating the SDD array located at an out of focus distance of 12 cm for 4 mm hexagonal pixel size. The source was assumed to have a constant count rate and a Crab-like spectrum. Photon arrival times onto the HTRS are generated according to Poisson statistics. The deadtime and energy pile-up are taken into account by discarding photons hitting a pixel within 300 ns of the previous photon. The loss of efficiency due to deadtime and pile-up is negligible up to about 10 times the intensity of the Crab.
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The top view of the HTRS detector unit (in green) and HTRS filter wheel with its 5 positions. Credit: Didier Barret. Click the image for a larger view. |
Comparison of the HTRS and the WFI count rate performance as a function of the incident count rate. The estimates for the WFI are computed for a standard mode and for the fastest window mode. The loss of efficiency due to deadtime and pile-up is negligible up to about 10 times the intensity of the Crab. Credit: Didier Barret. Click the image for a larger view. |
Photograph of 32x32 array of TES pixels on 0.3 mm pitch. Click the image for a larger view.
Date: March 2009
Goddard has recently fabricated several 32 × 32 arrays of TES pixels. These arrays have a 0.3 mm pitch instead of the previously standard pitch of 0.25 mm, to match the reference design for the XMS core array. In order to fit the array into existing test platforms, the chip size is 15 mm × 19 mm, the array scale is limited to 32 × 32 instead of the 40 × 40 of the core array, and bond pads for 256 channels (one quarter of the array) are accommodated. Nonetheless, this size array is an adequate representation of the scale needed for XMS. The first arrays produced had defects which are understood to be due to equipment failure. The equipment has been fixed and a change to the layout has been made to make future arrays less vulnerable to such equipment failure.
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+ SPIE newsroomDate: December 12, 2008
To prove the DEPFET APS concept prototype devices of 64 × 64 pixels with a pixel size of 75 μm × 75 μm and an overall area of 4.8 mm × 4.8 mm have been tested successfully. The measured parameters are fully within the WFI specifications. The noise is excellent, and the energy resolution of 126 eV (FWHM @ 5.9 keV) is dominated by the theoretical Fano limit. The devices are homogeneous and defect-free. Representative large format sensors (256 × 256 pixels, 128 × 512 pixels) have been processed, their characterization is in preparation.
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Photo of a 64 × 64 pixel DEPFET sensor prototype with readout and control front-end chips. |
Photo of a 6-inch silicon wafer with DEPFET-APS prototypes for the WFI. |
Date: December 8, 2008
The international consortium developing Silicon Pore Optics is progressing well with the 2nd generation of these X-ray optics. On the 1st generation they had demonstrated the entire production chain, resulting in 17 arcsec HEW of mounted optics in flight configuration, tested with X-rays. The next milestone is to demonstrate less than 10 arcsec by 2009. For this they have just demonstrated stacks with Ir coating and carbon overcoat inside the pores and have upgraded the fully automated stacking robots with advanced plate cleaning systems. The required wedging techniques have been demonstrated to accommodate the shorter focal length of IXO. In depth environmental testing of the mounted optics is in preparation and shall take place late in 2009.
A mirror segment in the GSFC test facility
Date: November 17, 2008
The NASA IXO mirror technology team successfully completed another X-ray test of a recently fabricated mirror pair, achieving an image quality of 16 arcsec HPD and further demonstrating the validity of the suspension mount. They are also making rapid progress in transferring mirrors from temporary suspension mounts to a permanent structure simulating a module housing. Additionally, the team has bonded a mirror in another module housing simulator (the cube) and successfully vibro-acoustic tested it to appropriate launch levels.
In addition, a parallel effort has been underway to fabricate a pair of forming mandrels to meet the 5 arcsec IXO requirements. A pair of fused quartz mandrels have been refigured to better than 5 arcsec HPD, close to meeting 2 arcsec requirements need for forming mandrels.
Scanning electron micrograph of a cross section through a 574 nm-period CAT grating prototype.
Date: November 17, 2008
The Space Nanotechnology Laboratory at MIT´s Kavli Institute for Astrophysics and Space Research has recently demonstrated a new type of diffraction grating for high resolution soft X-ray spectroscopy that combines the traditional advantages of transmission gratings (low mass, relaxed alignment tolerances) and blazed reflection gratings (high broadband efficiency, use of higher orders for higher resolution). In addition, these so-called Critical-Angle Transmission (CAT) gratings become transparent at higher X-ray energies, which allows soft X-ray spectroscopy to be performed simultaneously with spectral imaging in the 1-10 keV band using other focal plane instruments, such as the X-ray Microcalorimeter System (XMS) or the Wide Field Imager (WFI), at the telescope focus. The CAT gratings were fabricated from silicon wafers using high precision interference lithography and advanced nano-fabrication techniques (http://snl.mit.edu/) and tested with X rays at the Advanced Light Source at Lawrence Berkeley National Lab, confirming their theoretically predicted behavior.
Additional Links
+ SPIE newsroom
Grating test set-up at CU
Date: November 11, 2008
The gratings team, in the process of characterizing gratings for use in the off-plane X-ray Grating Spectrometer, have just completed efficiency testing the grating at the Gratings Test Facility at CU. The grating is a gold coated, radially grooved, type 4 holographic grating with 4500 grooves per mm. The grating itself is mounted on several linear and rotation stages allowing us to test different graze angles and incoming alpha angles. The grating is illuminated by a Manson Impact X-ray source at several energies of interest and the diffracted photons are observed via an MCP detector.
Photograph of a TES array and low-temperature read-out components. Click the image for larger view.
Date: Spring 2008
In the Spring of 2008, the Goddard Space Flight Center and National Institute of Standards and Technology collaboration used their state-of-the-art, time-division SQUID multiplexer system to demonstrate 2×8 multiplexing (16 pixels of a uniform 8x8 TES array read out with two signal channels) with modest degradation of the energy resolution. The average resolution for the 16 multiplexed pixels was 2.9 eV, and the distribution of resolution values had a relative standard deviation of 5%. Non-multiplexed, 2.3 eV resolution was obtained. The array was designed and fabricated at Goddard and the read-out system was designed and implemented at NIST.
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