Proceedings Volume 7021

High Energy, Optical, and Infrared Detectors for Astronomy III

David A. Dorn, Andrew D. Holland
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Proceedings Volume 7021

High Energy, Optical, and Infrared Detectors for Astronomy III

David A. Dorn, Andrew D. Holland
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 7 August 2008
Contents: 9 Sessions, 73 Papers, 0 Presentations
Conference: SPIE Astronomical Telescopes + Instrumentation 2008
Volume Number: 7021

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7021
  • Visible Detectors I
  • Visible Detectors II
  • Infrared Detectors I
  • Infrared Detectors II
  • High Energy Detectors I
  • High Energy Detectors II
  • High Energy Detectors III
  • Poster Session
Front Matter: Volume 7021
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Front Matter: Volume 7021
This PDF file contains the front matter associated with SPIE Proceedings Volume 7021, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
Visible Detectors I
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Teledyne Imaging Sensors: silicon CMOS imaging technologies for x-ray, UV, visible, and near infrared
Teledyne Imaging Sensors develops and produces high performance silicon-based CMOS image sensors, with associated electronics and packaging for astronomy and civil space. Teledyne's silicon detector sensors use two technologies: monolithic CMOS, and silicon PIN hybrid CMOS. Teledyne's monolithic CMOS sensors are large (up to 59 million pixels), low noise (2.8 e- readout noise demonstrated, 1-2 e- noise in development), low dark current (<10 pA/cm2 at 295K) and can provide in-pixel snapshot shuttering with >103 extinction and microsecond time resolution. The QE limitation of frontside-illuminated CMOS is being addressed with specialized microlenses and backside illumination. A monolithic CMOS imager is under development for laser guide star wavefront sensing. Teledyne's hybrid silicon PIN CMOS sensors, called HyViSITM, provide high QE for the x-ray through near IR spectral range and large arrays (2K×2K, 4K×4K) are being produced with >99.9% operability. HyViSI dark current is 5-10 nA/cm2 (298K), and further reduction is expected from ongoing development. HyViSI presently achieves <10 e- readout noise, and new high speed HyViSI arrays being produced in 2008 should achieve <4 e- readout noise at 900 Hz frame rate. A Teledyne 640×480 pixel HyViSI array is operating in the Mars Reconnaissance Orbiter, a 1K×1K HyViSI array will be launched in 2008 in the Orbiting Carbon Observatory, and HyViSI arrays are under test at several astronomical observatories. The advantages of CMOS in comparison to CCD include programmable readout modes, faster readout, lower power, radiation hardness, and the ability to put specialized processing within each pixel. We present one example of in-pixel processing: event driven readout that is optimal for lightning detection and x-ray imaging.
Design of prototype scientific CMOS image sensors
We present the design and test results of a prototype 4T CMOS image sensor fabricated in 0.18-μm technology featuring 20 different 6.5 μm pixel pitch designs. We review the measured data which clearly show the impact of the pixel topologies on sensor performance parameters such as conversion gain, read noise, dark current, full well capacity, non-linearity, PRNU, DSNU, image lag, QE and MTF. Read noise of less than 1.5e- rms and peak QE greater than 70%, with microlens, are reported.
Mapping electrical crosstalk in pixelated sensor arrays
S. Seshadri, D. M Cole, B. R. Hancock, et al.
Electronic coupling effects such as Inter-Pixel Capacitance (IPC) affect the quantitative interpretation of image data from CMOS, hybrid visible and infrared imagers alike. Existing methods of characterizing IPC do not provide a map of the spatial variation of IPC over all pixels. We demonstrate a deterministic method that provides a direct quantitative map of the crosstalk across an imager. The approach requires only the ability to reset single pixels to an arbitrary voltage, different from the rest of the imager. No illumination source is required. Mapping IPC independently for each pixel is also made practical by the greater S/N ratio achievable for an electrical stimulus than for an optical stimulus, which is subject to both Poisson statistics and diffusion effects of photo-generated charge. The data we present illustrates a more complex picture of IPC in Teledyne HgCdTe and HyViSi focal plane arrays than is presently understood, including the presence of a newly discovered, long range IPC in the HyViSi FPA that extends tens of pixels in distance, likely stemming from extended field effects in the fully depleted substrate. The sensitivity of the measurement approach has been shown to be good enough to distinguish spatial structure in IPC of the order of 0.1%.
Results from the Pan-STARRS Orthogonal Transfer Array (OTA)
John L. Tonry, Barry E. Burke, Sidik Isani, et al.
The Pan-STARRS project has completed its first 1.4 gigapixel mosaic focalplane CCD camera using 60 Orthogonal Transfer Arrays (OTAs). The devices are the second of a series of planned development lots. Several novel properties were implemented into their design including 4 phase pixels for on-detector tip-tilt image compensation, selectable region logic for standby or active operation, relatively high output amplifier count, close four side buttable packaging and deep depletion construction. The testing and operational challenges of deploying these OTAs required enhancements and new approaches to hardware and software. We compare performance achieved with that which was predicted, and discuss on-sky results, tools developed, shortcomings, and plans for future OTA features and improvements.
Characterization of prototype LSST CCDs
P. O'Connor, J. Frank, J. C. Geary, et al.
We present characterization methods and results on a number of new devices produced specifically to address LSST's performance goals, including flatness, QE, PSF, dark current, read noise, CTE, cosmetics, and crosstalk. The results indicate that commercially produced, thick n-channel over-depleted CCDs with excellent red response can achieve tight PSF at moderate applied substrate bias with no evidence of persistent image artifacts. We will also report ongoing studies of mosaic assembly techniques to achieve chip-to-chip co-planarity, high fill factor, and thermal stability.
Visible Detectors II
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Characterization of DECam focal plane detectors
H. Thomas Diehl, Robert Angstadt, Julia Campa, et al.
DECam is a 520 Mpix, 3 square-deg FOV imager being built for the Blanco 4m Telescope at CTIO. This facility instrument will be used for the "Dark Energy Survey" of the southern galactic cap. DECam has chosen 250 μm thick CCDs, developed at LBNL, with good QE in the near IR for the focal plane. In this work we present the characterization of these detectors done by the DES team, and compare it to the DECam technical requirements. The results demonstrate that the detectors satisfy the needs for instrument.
The 123 mm 8kX3k e2v/Ohio State CCD231-68 for MODS
As is only fitting, the largest Optical/Infrared Telescope (the Large Binocular Telescope, LBT) has the two largest telescope-mounted spectrographs (MODS) and the MODS's have the four largest scientific CCDs. We describe herein the design, fabrication and early use of the e2v CCD231-68 8k × 3k 15 micron back-illuminated detector designed specifically for low and intermediate resolution multi-object spectroscopy on large telescopes. The 123 mm length of the CCD231-68 is the largest of any scientific CCD. The device can be read out in full frame mode to cover the whole 6 arc-min slit length of MODS, in full frame mode for multi-object spectroscopy with short slits, or in split frame transfer mode to allow readout while integrating subsequent exposures. The four very low noise (<2 e- RMS at 100 kPixels/second) outputs are located at the ends of the four 4k serial registers. Excellent CTE (five-9s5 per Pixel) insures good photometric accuracy across the device. Backthinned red and blue optimized variants are used on the corresponding channels of both MODS.
VIRUS-P: camera design and performance
We present the design and performance of the prototype Visible Integral-field Replicable Unit Spectrograph (VIRUS-P) camera. Commissioned in 2007, VIRUS-P is the prototype for 150+ identical fiber-fed integral field spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment. With minimal complexity, the gimbal mounted, double-Schmidt design achieves high on-sky throughput, image quality, contrast, and stability with novel optics, coatings, baffling, and minimization of obscuration. The system corrector working for both the collimator and f / 1.33 vacuum Schmidt camera serves as the cryostat window while a 49 mm square aspheric field flattener sets the central obscuration. The mount, electronics, and cooling of the 2k × 2k, Fairchild Imaging CCD3041-BI fit in the field-flattener footprint. Ultra-black knife edge baffles at the corrector, spider, and adjustable mirror, and a detector mask, match the optical footprints at each location and help maximize the 94% contrast between 245 spectra. An optimally stiff and light symmetric four vane stainless steel spider supports the CCD which is thermally isolated with an equally stiff Ultem-1000 structure. The detector/field flattener spacing is maintained to 1 μm for all camera orientations and repeatably reassembled to 12 μm. Invar rods in tension hold the camera focus to ±4 μm over a -5-25 °C temperature range. Delivering a read noise of 4.2 e- RMS, sCTE of 1-10-5 , and pCTE of 1-10-6 at 100 kpix/s, the McDonald V2 controller also helps to achieve a 38 hr hold time with 3 L of LN2 while maintaining the detector temperature setpoint to 150 μK (5σ RMS).
LCOGT Imaging Lab
Joseph R. Tufts, Rich Lobdill, Benjamin J. Haldeman, et al.
The Las Cumbres Observatory Global Telescope Network (LCOGT) is an ambitious project to build and operate, within 5 years, a worldwide robotic network of 50 0.4, 1, and 2 m telescopes sharing identical instrumentation and optimized for precision photometry of time-varying sources. The telescopes, instrumentation, and software are all developed in house with two 2 m telescopes already installed. The LCOGT Imaging Lab is responsible for assembly and characterization of the network's cameras and instrumentation. In addition to a fully equipped CNC machine shop, two electronics labs, and a future optics lab, the Imaging Lab is designed from the ground up to be a superb environment for bare detectors, precision filters, and assembled instruments. At the heart of the lab is an ISO class 5 cleanroom with full ionization. Surrounding this, the class 7 main lab houses equipment for detector characterization including QE and CTE, and equipment for measuring transmission and reflection of optics. Although the first science cameras installed, two TEC cooled e2v 42-40 deep depletion based units and two CryoTiger cooled Fairchild Imaging CCD486-BI based units, are from outside manufacturers, their 18 position filter wheels and the remainder of the network's science cameras, controllers, and instrumentation will be built in house. Currently being designed, the first generation LCOGT cameras for the network's 1 m telescopes use existing CCD486-BI devices and an in-house controller. Additionally, the controller uses digital signal processing to optimize readout noise vs. speed, and all instrumentation uses embedded microprocessors for communication over ethernet.
ULTRASPEC: an electron multiplication CCD camera for very low light level high speed astronomical spectrometry
Derek Ives, Nagaraja Bezawada, Vik Dhillon, et al.
We present the design, characteristics and astronomical results for ULTRASPEC, a high speed Electron Multiplication CCD (EMCCD) camera using an E2VCCD201 (1K frame transfer device), developed to prove the performance of this new optical detector technology in astronomical spectrometry, particularly in the high speed, low light level regime. We present both modelled and real data for these detectors with particular regard to avalanche gain and clock induced charge (CIC). We present first light results from the camera as used on the EFOSC-2 instrument at the ESO 3.6 metre telescope in La Silla. We also present the design for a proposed new 4Kx2K frame transfer EMCCD.
The L3Vision CCD220 with its OCam test camera for AO applications in Europe
Philippe Feautrier, Jean-Luc Gach, Philippe Balard, et al.
ESO and JRA2 OPTICON have jointly funded e2v technologies to develop a custom CCD for Adaptive Optic Wave Front Sensor (AO WFS) applications. The device, called CCD220, is a compact Peltier-cooled 240×240 pixel frametransfer 8-output back-illuminated sensor. Using the electron-multiplying technology of L3Vision detectors, the device is designed to achieve sub-electron read noise at frame rates from 25 Hz to 1,500 Hz and dark current lower than 0.01 e-/pixel/frame. The development has many unique features. To obtain high frame rates, multiple EMCCD gain registers and metal buttressing of row clock lines are used. The baseline device is built in standard silicon. In addition, two speculative variants have been built; deep depletion silicon devices to improve red response and devices with an electronic shutter to extend use to Rayleigh and Pulsed Laser Guide Star applications. These are all firsts for L3Vision CCDs. These CCD220 detectors have now been fabricated by e2v technologies. This paper describes the design of the device, technology trade-offs, and progress to date. A Test Camera, called "OCam", has been specially designed and built for these sensors. Main features of the OCam camera are extensively described in this paper, together with first light images obtained with the CCD220.
A DSP-based infrared and optical bidimensional detectors controller
Arturo Iriarte, Luis A. Martínez, Fernando Ángeles, et al.
The Institute of Astronomy at the Universidad Nacional Autonoma de México have developed and tested a CCD controller based on Texas Instruments Digital Signal Processor (DSP) TMS30C31@50MHz. Images are temporally stored in a 2MB static RAM attached to the DSP and transferred to the host computer running under Linux. Both tasks, acquisition and timing, are programmable so it can be conditioned to control any bidimensional detector. Analog voltage for bias, offsets and gains are fully programmable also. The system has been tested on an infrared Hawaii detector and fast Marconi 80x80 pixels CCD.
Infrared Detectors I
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Teledyne Imaging Sensors: infrared imaging technologies for astronomy and civil space
James W. Beletic, Richard Blank, David Gulbransen, et al.
Teledyne Imaging Sensors develops and produces high performance infrared sensors, electronics and packaging for astronomy and civil space. These IR sensors are hybrid CMOS arrays, with HgCdTe used for light detection and a silicon integrated circuit for signal readout. Teledyne manufactures IR sensors in a variety of sizes and formats. Currently, the most advanced sensors are based on the Hawaii-2RG (H2RG), 2K×2K array with 18 μm pixel pitch. The HgCdTe detector achieves very low dark current (<0.01 e-/pixel/sec) and high quantum efficiency (80-90%) over a wide bandpass. Substrate-removed HgCdTe can simultaneously detect visible and infrared light, enabling spectrographs to use a single focal plane array (FPA) for Visible-IR sensitivity. The SIDECARTM ASIC provides focal plane electronics on a chip, operating in cryogenic environments with very low power (<11 mW). The H2RG and SIDECARTM have been qualified to NASA Technology Readiness Level 6 (TRL-6). Teledyne continues to advance the state-of-the-art and is producing a high speed, low noise array designed for IR wavefront sensing. Teledyne is also developing a 4K×4K, 15 µm pixel infrared array that will be a cost effective module for the large focal planes of the Extremely Large Telescopes and future generation space astronomy missions.
Development of non-hybridised HgCdTe detectors for the next generation of astronomical instrumentation
The superb image quality that is predicted, and even demanded, for the next generation of Extremely Large Telescopes (ELT) presents a potential crisis in terms of the sheer number of detectors that may be required. Developments in infrared technology have progressed dramatically in recent years, but a substantial reduction in the cost per pixel of these IR arrays will be necessary to permit full exploitation of the capabilities of these telescopes. Here we present an outline and progress report of an initiative to develop a new generation of astronomical grade Cadmium Mercury Telluride (HgCdTe) array detectors using a novel technique which enables direct growth of the sensor diodes onto the Read Out Integrated Circuit (ROIC). This technique removes the need to hybridise the detector material to a separate Silicon readout circuit and provides a route to very large monolithic arrays. We present preliminary growth and design simulation results for devices based on this technique, and discuss the prospects for deployment of this technology in the era of extremely large telescopes.
A theory for image persistence in HgCdTe photodiodes
Roger M. Smith, Maximilian Zavodny, Gustavo Rahmer, et al.
Image persistence can produce systematic errors, which remain significant in some applications even when buried in noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward bias. For several Teledyne 1.7 μm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal range. We characterize the temporal response, and examine the dependence of charge emission time constants on total stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the superposition of the decay curves from multiple stimuli.
Calibration of image persistence in HgCdTe photodiodes
Roger M. Smith, Maximilian Zavodny, Gustavo Rahmer, et al.
Image persistence can produce systematic errors, which remain significant in some applications even when buried in noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward bias. For several Teledyne 1.7 μm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal range. We characterize the temporal response, and examine the dependence of charge emission time constants on total stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the superposition of the decay curves from multiple stimuli.
Precision quantum efficiency measurements on 1.7 micron near infrared devices
M. Schubnell, M. G. Brown, A. Karabina, et al.
High detector quantum efficiency (QE) can greatly improve speed and performance of wide field instruments that strive for fast precision photometry. SNAP, a proposed satellite mission dedicated to exploring the nature of the dark energy will employ a very large focal plane instrumented with about equal number of CCD and NIR sensors totaling more than 600 million pixels covering roughly 0.7 square degrees on the sky. To precisely characterize the NIR detector QE, the SNAP project has put in place a test set-up capable of measuring absolute QE at the 5% level with the goal of ultimately reaching a precision better than 2%. Illumination of the NIR detectors is provided by either a quartz tungsten halogen lamp combined with a set of narrow band filters or a manually tunable monochromator. The two light sources feed an integrating sphere at a distance of roughly 60 cm from the detector to be tested and a calibrated InGaAs photodiode, mounted adjacent to the NIR detector provides absolute photon flux measurements. This paper describes instrumentation, performance and measurement procedures and summarizes results of detailed characterization of the QE on several SNAP devices as a function of wavelength.
Development of a focal plane module for JWST/MIRI
Kalyani G. Sukhatme, Michael P. Thelen, Hyung Cho, et al.
We present the development of a Focal Plane Module (FPM) for the Mid-Infrared Instrument on JWST. MIRI will include three FPMs, two for the spectrometer channels and one for the imager channel. The FPMs are designed to support the detectors at an operating temperature of 6.7 K with high temperature stability and precision alignment while being capable of surviving the launch environment. The flight units will be built and will undergo a rigorous test program in the first half of 2008. This paper includes a description of the full test program and will present the results.
Infrared Detectors II
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Performance of the JWST/MIRI Si:As detectors
Michael E. Ressler, Hyung Cho, Richard A. M. Lee, et al.
The Mid-Infrared Instrument (MIRI) is a 5 to 28 micron imager and spectrometer that is slated to fly aboard the JWST in 2013. Each of the flight arrays is a 1024×1024 pixel Si:As impurity band conductor detector array, developed by Raytheon Vision Systems. JPL, in conjunction with the MIRI science team, has selected the three flight arrays along with their spares. We briefly summarize the development of these devices, then describe the measured performance of the flight arrays along with supplemental data from sister flight-like parts.
Performance evaluation, readout modes, and calibration techniques of HgCdTe Hawaii-2RG mosaic arrays
Gert Finger, Reinhold J. Dorn, Siegfried Eschbaumer, et al.
Recently ESO has commissioned the HAWK-I camera which is equipped with a 2×2 mosaic of λc~ 2.5 µm HAWAII-2RG arrays. The arrays have high quantum efficiency and achieve photon shot noise limited performance on the telescope. Using reference pixels it can be shown that the readout noise for most arrays is limited by the MBE grown HgCdTe material and not by the multiplexer or the data acquisition chain. Results obtained with the guide window of the HAWAII-2RG multiplexer will be presented. Inter-channel crosstalk and fringing in the detector substrate will be discussed. The dynamic range of detectors can be expanded by applying threshold limited integration (TLI) to the follow-up-the-ramp nondestructive sampling scheme. For substrate removed arrays a calibration technique based on the X-ray emission of Fe55 will be discussed.
Evaluation of the Teledyne SIDECAR ASIC at cryogenic temperature using a visible hybrid H2RG focal plane array in 32 channel readout mode
Reinhold J. Dorn, Siegfried Eschbaumer, Donald N. B. Hall, et al.
Teledyne Imaging Sensors (TIS) has developed a new CMOS device known as the SIDECAR application-specific integrated circuit (ASIC). This single chip provides all the functionality of FPA drive electronics to operate visible and infrared imaging detectors with a fully digital interface. At the last SPIE conference we presented test and performance results of a Teledyne 2K×2K silicon PIN diode array hybridized to a Hawaii-2RG multiplexer, the Hybrid Visible Silicon Imager (HyViSI). This detector was read out with the ESO standard IR detector controller IRACE, which delivers detector limited performance. We have now tested the H2RG HyViSI detector with the new TIS SIDECAR ASIC in 32 channel readout mode at cryogenic temperatures. The SIDECAR has been evaluated down to 105 Kelvin operating temperature and performance results have been compared to those obtained with external electronics. We find that the SIDECAR ASIC provides performance equal to optimized external electronics.
Cold performance tests of blocked-impurity-band Si:As detectors developed for DARWIN
Stephan M. Birkmann, Jutta Stegmaier, Ulrich Grözinger, et al.
We report first results of laboratory tests of Si:As blocked-impurity-band (BIB) mid-infrared (4 to 28 μm) detectors developed by IMEC. These prototypes feature 88 pixels hybridized on an integrated cryogenic readout electronics (CRE). They were developed as part of a technology demonstration program for the future Darwin mission. In order to be able to separate detector and readout effects, a custom build TIA circuitry was used to characterize additional single pixel detectors. We used a newly designed test setup at the MPIA to determine the relative spectral response, the quantum efficiency, and the dark current. All these properties were measured as a function of operating temperature and detector bias. In addition the effects of ionizing radiation on the detector were studied. For determining the relative spectral response we used a dualgrating monochromator and a bolometer with known response that was operated in parallel to the Si:As detectors. The quantum efficiency was measured by using a custom-build high-precision vacuum black body together with cold (T ~ 4K) filters of known (measured) transmission.
Infrared absolute calibrations down to 10 fW in low-temperature environments at NIST
The Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST) is responsible for absolute IR radiometric calibrations (SI traceable) in low-background temperature (below 80 K) environments. IR radiometric test hardware that needs to be operated in cryogenic environments is calibrated in cryogenic vacuum chambers maintained by the facility to create environments that simulate the low-temperature background of space. Transfer radiometers have also been developed to calibrate IR radiometric test hardware this is too large to ship to NIST from their own IR test facilities. The first generation transfer radiometer, the BXR, is a filter-based radiometer that uses an As-doped Si Blocked Impurity Band detector, and can calibrate IR test chambers to a total uncertainty of less than 3 % (1 σ ) at powers as low as to 10-14 W/cm2. The BXR has evaluated 9 chambers and the performance of a subset of these chambers will be discussed to a limited extent to demonstrate the need for calibrating IR test chambers. The second generation transfer radiometer, the MDXR, and new primary standards allowing absolute calibrations as low as 10-15 W/cm2 are in the final stages of development. The MDXR will have all the functionality of the BXR and it will have a cryogenic Fourier transform spectrometer (FTS) for high resolution spectral capability. Performance specifications and test results from development activity on the new primary standards will be discussed.
Characterization of a megapixel mid-infrared array for high background applications
A. K. Mainzer, Henry Hogue, Maryn Stapelbroek, et al.
Our group has developed the first 1024×1024 high background Si:As detector array, the Megapixel Mid-Infrared array (MegaMIR). MegaMIR is designed to meet the thermal imaging and spectroscopic needs of the ground-based and airborne astronomical communities. MegaMIR was designed with switchable capacitance and windowing capability to allow maximum flexibility. We report initial test results for the new array.
Count rate dependent non-linearity and pixel size variations in 1.7 micron cut-off detectors
Wolfgang Lorenzon, Robert Newman, Michael Schubnell, et al.
Over the past decade scientists have collected convincing evidence that the content of our universe is dominated by a mysterious dark energy. Understanding the nature of dark energy is a very difficult task, and requires a variety of independent experimental approaches. Most of these approaches rely on photometric calibrations over a wide range of intensities using standardized stars and internal reference sources, and hence on a complete understanding of the linearity of the detectors. The SNAP near infrared (NIR) instrument team has performed a comprehensive study of precision photometry on 1.7 micron cut-off HgCdTe detectors. Among those studies are the count rate dependent detector non-linearity that was recently discovered with the NICMOS array on the Hubble Space Telescope, and possible pixel size variations seen in quantum efficiency (QE) data. The nonlinearity on NICMOS exhibits an unexpected behavior, where pixels with high (low) count rates detect slightly more (less) flux than expected for a linear system. To test this count rate dependent non-linearity a dedicated setup was built that produces a known amount of light on a detector, and measures its response as a function of light intensity and wavelength. If the pixel response variations seen in QE data are due to pixel area variations, standard flat-fielding will degrade photometry precision for point sources in an undersampled telescope. Studies have been performed to estimate the magnitude of pixel area variations.
Performance and evaluation of the infrared AO sensor CALICO
Leander H. Mehrgan, Siegfried Eschbaumer, Gert Finger, et al.
The CALICO sensor is a pathfinder for the development of the future infrared high speed low noise detectors for AO. Low readout noise at high readout speed is accomplished by high gain and signal processing circuitry under each pixel. The high gain makes the detector very susceptible to instability if the system noise is too high. Lnpix3, the most promising structure, has a pixel gain of 400. In this paper we will report on test results and different measures we had to take getting the detector to work.
Characterization of flight detector arrays for the wide-field infrared survey explorer
Amy Mainzer, Mark Larsen, Maryn G. Stapelbroek, et al.
The Wide-field Infrared Survey Explorer is a NASA Midex mission launching in late 2009 that will survey the entire sky at 3.3, 4.7, 12, and 23 microns (PI: Ned Wright, UCLA). Its primary scientific goals are to find the nearest stars (actually most likely to be brown dwarfs) and the most luminous galaxies in the universe. WISE uses three dichroic beamsplitters to take simultaneous images in all four bands using four 1024×1024 detector arrays. The 3.3 and 4.7 micron channels use HgCdTe arrays, and the 12 and 23 micron bands employ Si:As arrays. In order to make a 1024×1024 Si:As array, a new multiplexer had to be designed and produced. The HgCdTe arrays were developed by Teledyne Imaging Systems, and the Si:As array were made by DRS. All four flight arrays have been delivered to the WISE payload contractor, Space Dynamics Laboratory. We present initial ground-based characterization results for the WISE arrays, including measurements of read noise, dark current, flat field and latent image performance, etc. These characterization data will be useful in producing the final WISE data product, an all-sky image atlas and source catalog.
High Energy Detectors I
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New DEPFET structures: concepts, simulations, and experimental results
G. Lutz, S. Herrmann, P. Lechner, et al.
Two new DEPFET concepts are presented motivated by potential applications in adaptive optics and in synchrotron radiation experiments at the future Free Electron X-ray Laser (XFEL) in Hamburg. The gatable DEPFET structure allows the selection of signal charges arriving in a predefined time interval. Charges produced outside this gate interval are lead to a sink electrode while charge collected already is protected and kept for later delayed readout. In synchrotron radiation experiments one faces the challenge of being sensitive enough for single X-ray photons in some parts of the detector while on other regions a very large charge due to the superposition of many X-rays has to be measured. A DEPFET with strongly non-linear characteristics combines naturally excellent energy resolution with high dynamic range, large charge handling capability and high read out speed.
DEPFET based x-ray detectors for the MIXS focal plane on BepiColombo
J. Treis, O. Hälker, L. Andricek, et al.
DEPFET Macropixel detectors, based on the fusion of the combined Detector-Amplifier structure DEPFET with a silicon drift chamber (SDD) like drift ring structure, combine the excellent properties of the DEPFETs with the advantages of the drift detectors. As both device concepts rely on the principle of sideways depletion, a device entrance window with excellent properties is obtained at full depletion of the detector volume. DEPFET based focal plane arrays have been proposed for the Focal Plane Detectors for the MIXS (Mercury Imaging X-ray Spectrometer) instrument on BepiColombo, ESAs fifth cornerstone mission, with destination Mercury. MIXS uses a lightweight Wolter Type 1 mirror system to focus fluorescent radiation from the Mercury surface on the FPA detector, which yields the spatially resolved relative element abundance in Mercurys crust. In combination with the reference information from the Solar Intensity X-ray Spectrometer (SIXS), the element abundance can be measured quantitatively as well. The FPA needs to have an energy resolution better than 200 eV FWHM @ 1 keV and is required to cover an energy range from 0.5 keV to 10 keV, for a pixel size of 300 x 300 μm2. Main challenges for the instrument are the increase in leakage current due to a high level of radiation damage, and the limited cooling resources due to the difficult thermal environment in the mercury orbit. By applying an advanced cooling concept, using all available cooling power for the detector itself, and very high speed readout, the energy resolution requirement can be kept during the entire mission lifetime up to an end-of-life dose of ~ 3 × 1010 10 MeV p / cm2. The production of the first batch of flight devices has been finished at the MPI semiconductor laboratory, and first prototype modules have been built. The results of the first tests will be presented here.
The low energy detector of Simbol-X
P. Lechner, L. Andricek, U. Briel, et al.
Simbol-X is a French-Italian-German hard energy X-ray mission with a projected launch in 2014. Being sensitive in the energy range from 500 eV to 80 keV it will cover the sensitivity gap beyond the energy interval of today's telescopes XMM-Newton and Chandra. Simbol-X will use an imaging telescope of nested Wolter-I mirrors. To provide a focal length of 20 m it will be the first mission of two independent mirror and detector spacecrafts in autonomous formation flight. The detector spacecraft's payload is composed of an imaging silicon low energy detector in front of a pixelated cadmium-telluride hard energy detector. Both have a sensitive area of 8 × 8 cm2 to cover a 12 arcmin field of view and a pixel size of 625 × 625 μm2 adapted to the telescope's resolution of 20 arcsec. The additional LED specifications are: high energy resolution, high quantum efficiency, fast readout and optional window mode, monolithic device with 100 % fill factor and suspension mounting, and operation at warm temperature. To match these requirements the low energy detector is composed of 'active macro pixels', combining the large, scalable area of a Silicon Drift Detector and the low-noise, on-demand readout of an integrated DEPFET amplifier. Flight representative prototypes have been processed at the MPI semiconductor laboratory, and the prototype's measured performance demonstrates the technology readiness.
Hard x-ray and gamma-ray imaging and spectroscopy using scintillators coupled to silicon drift detectors
P. Lechner, R. Eckhard, C. Fiorini, et al.
Silicon Drift Detectors (SDDs) are used as low-capacitance photon detectors for the optical light emitted by scintillators. The scintillator crystal is directly coupled to the SDD entrance window. The entrance window's transmittance can be optimized for the scintillator characteristic by deposition of a wavelength-selective anti-reflective coating. Compared to conventional photomultiplier tubes the SDD readout offers improved energy resolution and avoids the practical problems of incompatibility with magnetic fields, instrument volume and requirement of high voltage. A compact imaging spectrometer for hard X-rays and γ-rays has been developed by coupling a large area (29 × 26 mm2) monolithic SDD array with 77 hexagonal cells to a single non-structured CsI-scintillator of equal size. The scintillation light generated by the absorption of an energetic photon is seen by a number of detector cells and the position of the photon interaction is reconstructed by the centroid method. The measured spatial resolution of the system (≤ 500 μm) is considerably smaller than the SDD cell size (3.2 mm) and in the order required at the focal plane of high energy missions. The energy information is obtained by summing the detector cell signals. Compared to direct converting pixelated detectors, e.g. CdTe with equal position resolution the scintillator-SDD combination requires a considerably lower number of readout channels. In addition it has the advantages of comprehensive material experience, existing technologies, proven long term stability, and practically unlimited availability of high quality material.
Development of an ASIC for multi-readout x-ray CCDs
We have developed application specific integrated circuits(ASICs) for multi-readout X-ray CCDs in order to improve their time resolution. ASICs with the size of 3mm × 3mm were fabricated by employing a Taiwan Semiconductor Manufacturing Company(TSMC) 0.35 μm CMOS technology. The number of channels is 4 and the each channel consists of a preamplifier, 5-bit DAC and delta-sigma analog-to-digital converters (ADCs). The measured equivalent input noise at the pixel rate of 19.5 kHz and 625 kHz are 36 μV and 51 μV, respectively. The power consumption is about 110 mW/chip at 625 kHz pixel rate, which is about 10 times lower than that of our existing system. We now expect to employ an ASIC as the readout system of X-ray CCD camera onboard the next Japanese X-ray astronomy satellite. We tested the readout of the prototype X-ray CCDs by using ASICs and the total-dose effects of ASICs. We describe the overview of our ASICs and test results.
Caliste 64: detection unit of a spectro imager array for a hard x-ray space telescope
A. Meuris, O. Limousin, F. Lugiez, et al.
In the frame of the hard X-ray Simbol-X observatory, a joint CNES-ASI space mission to be flown in 2014, a prototype of miniature Cd(Zn)Te camera equipped with 64 pixels has been designed. The device, called Caliste 64, is a spectro-imager with high resolution event time-tagging capability. Caliste 64 integrates a Cd(Zn)Te semiconductor detector with segmented electrode and its front-end electronics made of 64 independent analog readout channels. This 1 × 1 × 2 cm3 camera, able to detect photons in the range from 2 keV up to 250 keV, is an elementary detection unit juxtaposable on its four sides. Consequently, large detector array can be made assembling a mosaic of Caliste 64 units. Electronics readout module is achieved by stacking four IDeF-X V1.1 ASICs, perpendicular to the detection plane. We achieved good noise performances, with a mean Equivalent Noise Charge of ~65 electrons rms over the 64 channels. Time resolution is better than 70 ns rms for energy deposits greater than 50 keV, taking into account electronic noise and technological dispersal, which enables to reject background by anticoincidence with very low probability of error. For the first prototypes, we chose CdTe detectors equipped with Al-Ti-Au Schottky barrier contacts because of their very low dark current and excellent spectroscopic performances. So far, three Caliste 64 cameras have been realized and tested. When the crystal is cooled down to -10°C, the sum spectrum built with the 64 pixels of a Caliste 64 sample results in a spectral resolution of 664 eV FWHM at 13.94 keV and 841 eV FWHM at 59.54 keV.
The CALET mission on the ISS
S. Torii, M. Hareyama, N. Hasebe, et al.
We are developing the CALorimetric Electron Telescope, CALET, mission for the Japanese Experiment Module Exposed Facility, JEM-EF, of the International Space Station. Major scientific objectives are to search for the nearby cosmic ray sources and dark matter by carrying out a precise measurement of the electrons in 1 GeV - 20 TeV and gamma rays in 20 MeV - several 10 TeV. CALET has a unique capability to observe electrons and gamma rays over 1 TeV since the hadron rejection power can be larger than 105 and the energy resolution better than a few % over 100 GeV. The detector consists of an imaging calorimeter with scintillating fibers and tungsten plates and a total absorption calorimeter with BGO scintillators. CALET has also a capability to measure cosmic ray H, He and heavy ionsi up to 1000 TeV. It also will have a function to monitor solar activity and gamma ray transients. The phase A study has started on a schedule of launch in 2013 by H-II Transfer Vehicle (HTV) for 5 year observation.
Optically sensitive MCP image tube with a Medipix2 ASIC readout
We present the first results from the successful fabrication of an optical imaging tube consisting of a pair of MCPs read out by a CMOS application specific integrated circuit (ASIC) developed for x-ray imaging called the Medipix2. The Medipix2 is an array of 256×256 pixels, each of which amplifies and counts individual photon stimulated events amplified by the MCPs. A multi-alkali photocathode installed in proximity focus above the MCP is used for conversion of incoming photons into photoelectrons.. The Medipix2 integrates these detected photons, and the binary values of these counters is read fast (~ 1kHz frame rate) and without readout noise. Initial imaging tests of this tube, including QE, resolution, background, dynamic range and microsecond shutter operation are presented..
Position sensitive x- and gamma-ray scintillator detector for new space telescopes
C. Labanti, M. Marisaldi, F. Fuschino, et al.
The instruments on board the latest gamma observatories (INTEGRAL, SWIFT, AGILE, GLAST) combines technologies based on solid state and on scintillator detector, the first one being favorite when a low energy threshold and a good energy resolution is required, the latter being more convenient for large volume when worse performance are still acceptable. With the developments achieved both with the new scintillator material and even more with new low-noise light readout devices the differences between the two techniques are narrowing and for some application the cheaper scintillator detector can compete with solid state devices. Starting from the techniques used in INTEGRAL-IBIS and AGILE a new generation position sensitive X and gamma ray detector based on scintillator with Silicon Drift Chamber readout has been developed and tested. The ASIC read-out electronics make it suitable for replication in a large scale when a great number of pixel is needed. The performance of the detector as well as its applications in new generation space telescopes are presented and discussed.
A new family of swept charge devices (SCDs) for x-ray spectroscopy applications
In this paper we discuss the design and performance of a new family of swept charge devices intended for X-ray spectroscopy. The devices were designed to combine large area with good detection efficiency over the 0.5-10 keV band, and, importantly, to be capable of operation at "warm" temperatures, e.g. room temperature. Three types of device have been manufactured ranging in detection area from 5-420 mm2 and the paper discusses the initial characterisation of the detectors over a range of temperatures. Whilst the device leakage current scales with detector area, we demonstrate that the smallest detector is capable of yielding Fano-limited X-ray spectra at room temperature, whereas the largest requires modest cooling down to -20°C to achieve this resolution.
High Energy Detectors II
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Physics of reverse annealing in high-resistivity Chandra ACIS CCDs
After launch, the Advanced CCD Imaging Spectrometer (ACIS), a focal plane instrument on the Chandra Xray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. An effect of the damage was to increase the charge transfer inefficiency (CTI) of the front illuminated CCDs. As part of the initial damage assessment, the focal plane was warmed from the operating temperature of -100° C to +30° C which unexpectedly further increased the CTI. We report results of ACIS CCD irradiation experiments in the lab aimed at better understanding this reverse annealing process. Six CCDs were irradiated cold by protons ranging in energy from 100 keV to 400 keV, and then subjected to simulated bakeouts in one of three annealing cycles. We present results of these lab experiments, compare them to our previous experiences on the ground and in flight, and derive limits on the annealing time constants.
Radiation study of swept-charge devices for the Chandrayaan-1 X-ray Spectrometer (C1XS) instrument
The Chandrayaan-1 X-ray Spectrometer (C1XS) will be launched as part of the Indian Space Research Organisation (ISRO) Chandrayaan-1 payload in September 2008, arriving at the Moon within 7 days to begin a two year mission in lunar orbit conducting mineralogical surface mapping over the range of 1 - 10 keV. The detector plane of the instrument consists of twenty four e2v technologies CCD54 swept-charge devices (SCDs). Such devices were first flown in the Demonstration of a Compact Imaging X-ray Spectrometer (D-CIXS) instrument onboard SMART-1 [4, 5]. The detector plane in each case provides a total X-ray collection area of 26.4 cm2. The SCD is capable of providing near Fano-limited spectroscopy at -10°C, and at -20°C, near the Chandrayaan-1 mission average temperature, it achieves a total system noise of 6.2 electrons r.m.s. and a FWHM of 134 eV at Mn-Kα. This paper presents a brief overview of the C1XS mission and a detailed study of the effects of proton irradiation on SCD operational performance.
Gallium nitride photocathode development for imaging detectors
Recent progress in Gallium Nitride (GaN, AlGaN, InGaN) photocathodes show great promise for future detector applications in Astrophysical instruments. Efforts with opaque GaN photocathodes have yielded quantum efficiencies up to 70% at 120 nm and cutoffs at ~380 nm, with low out of band response, and high stability. Previous work with semitransparent GaN photocathodes produced relatively low quantum efficiencies in transmission mode (4%). We now have preliminary data showing that quantum efficiency improvements of a factor of 5 can be achieved. We have also performed two dimensional photon counting imaging with 25mm diameter semitransparent GaN photocathodes in close proximity to a microchannel plate stack and a cross delay line readout. The imaging performance achieves spatial resolution of ~50μm with low intrinsic background (below 1 event sec-1 cm-2) and reasonable image uniformity. GaN photocathodes with significant quantum efficiency have been fabricated on ceramic MCP substrates. In addition GaN has been deposited at low temperature onto quartz substrates, also achieving substantial quantum efficiency.
Silicon drift detectors array coupled to scintillators operated with pulse shape discrimination technique: a 1 keV - 1 MeV position sensitive gamma-ray detector
Francesco Perotti, Claudio Labanti, Martino Marisaldi, et al.
Silicon Drift Detectors (SDD) can work both as direct X-ray detectors, exhibiting excellent spectroscopic capabilities in the 1-30 keV energy range, and as photodetectors for scintillators readout. Both these detector concepts can be combined in a single compact device by means of the Pulse Shape Discrimination (PSD) technique. A complete detection system based on a monolithic 20-channels SDD array coupled to CsI(Tl) scintillating pixels operated with PSD technique has been realized. The instrument description and performance will be presented and discussed, as well as its possible applications as a detection plane for a wide field monitor for forthcoming gamma-ray burst search missions.
Improved energy resolution of a superconducting single-photon detector
A. D. Semenov, P. Haas, H.-W. Hübers, et al.
We demonstrated successful operation of an NbN single photon detector in the temperature range from 6 K to 1.2 K using a 3He sorption refrigerator combined with a pulse-tube mechanical cooler. The detector was read out either by microwave amplifiers or by a broadband SQUID-amplifier that limited the maximum counting rate to 107 counts per second. This counting rate was only one third of the maximum rate provided by the detector. Besides an increase in the quantum efficiency in the visible and near-infrared spectral range with the decrease of the operation temperature, we found a more than twofold improvement in the energy resolution as compared to earlier demonstrated 1 eV at 6.5 K. The noise equivalent power estimated at 4.2 K for visible light was better than 10-18 W Hz-1/2. We verified that the lowest achieved dark count rate was still caused by the harsh electrical conditions in the mechanical cooler.
High Energy Detectors III
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Application of double-sided silicon strip detectors to Compton cameras
We have developed a Compton camera with a double-sided silicon strip detector (DSSD) for hard X-ray and gamma-ray observation. Using a DSSD as a scatter detector of the Compton camera, we achieved high angular resolution of 3.4° at 511 keV. Through the imaging of various samples such as two-dimentional array sources and a diffuse source, the wide field-of-view (~ 100°) and the high spatial resolution (at least 20 mm at a distance of 60 mm from the DSSD) of the camera were confirmed. Furthermore, using the List-Mode Maximum-Likelihood Expectation-Maximization method, the camera can resolve an interval of 3 mm at a distance of 30 mm from the DSSD.
A phenomenological explanation of TES excess noise
L. Ferrari, D. Bagliani, E. Celasco, et al.
The evidence of excess noise in the power spectrum of many natural systems that span over the mHz to the THz, such as biological system, superconductors at dendritic regime, Barkhausen noise of magnetic system and plasma emission from nanometric transistors, was observed and related to a class of statistical models of correlated processes. Intrinsic or induced fluctuations of the elementary processes taking place in transport phenomena couple each other giving rise to time-amplitude correlated avalanches. TES sensors for X-ray microcalorimeters have shown a clear evidence that this excess noise has typical spectral behavior spanning from 100 Hz to 10 kHz. We present an analysis of the excess noise using this statistical avalanche model of TES operating on Si substrate and suspended SiN membrane.
Micro-fabricated magnetic microcalorimeter development for x-ray astronomy
X-ray microcalorimeters using magnetic sensors show great promise for use in astronomical x-ray spectroscopy. We have begun to develop technology for fabricating arrays of magnetic calorimeters for X-ray astronomy. The magnetization change in each pixel of the paramagnetic sensor material due to the heat input of an absorbed x-ray is sensed by a meander shaped coil. With this geometry it is possible to obtain excellent energy sensitivity, low magnetic cross-talk and large format arrays fabricated on wafers that are separate from the SQUID read-out. We report on the results from our prototype arrays, which are coupled to low noise 2-stage SQUIDs developed at the PTB Berlin. The first testing results are presented and the sensitivity compared with calculations.
Poster Session
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Test of x-ray microcalorimeters with bilayer absorbers
E. Perinati, M. Barbera, J. Beeman, et al.
Superconducting absorbers for thermal X-ray microcalorimeters should convert into thermalized phonons and transfer to the thermal sensor most of the energy deposited by single photons, on a time scale as short as a few tens of microseconds. Since deposition of X-ray energy in a superconductor produces quasiparticles by breaking up of Cooper pairs, the thermalization efficiency depends on the time scale on which they survive within the absorber volume, trapping part of the absorbed energy. According to the predicted values of their microscopic parameters, in many standard type-I superconducting metals the quasiparticle life time at very low temperatures results too long to allow for recombination on the relatively short time scale of the thermal sensors. In type-II superconductors the existence of a mixed state with Abrikosov vortices could speed up the recombination process and increase the efficiency of thermalization. We discuss this topic by presenting experimental results of laboratory tests conducted on tantalum and lead-bismuth absorbers in a comparison with an absorber made of gold, where no trapping is expected.
The x-ray performance of high resistivity (high-rho) scientific CCDs
Neil Murray, Andrew D. Holland, David Burt, et al.
e2v technologies have recently been developing large area (2k*4k), high resistivity (>8 kΩcm) silicon CCDs intended for infrared astronomy. The use of high resistivity silicon allows for a greater device thickness, allowing deeper, or full, depletion across the CCD that significantly improves the red wavelength sensitivity. The increased depletion in these CCDs also improves the quantum efficiency for incident X-ray photons of energies above 5 keV, whilst maintaining spectral resolution. The use of high resistivity silicon would therefore be advantageous for use in future X-ray astronomy missions and other applications. This paper presents the measured X-ray performance of the high resistivity CCD247 for X-ray photons of energies between 5.4 keV to 17.4 keV. Here we describe the laboratory experiment and results obtained to determine the responsivity, noise, effective depletion depth and quantum efficiency of the CCD247.
The design of EUV CCD camera
Yuanyuan Shang, Yong Guan, Yingfei Liu, et al.
This paper describes the design of CCD camera that is part of the EUV detector to be used in Space Solar Telescope. It will run at the solar synchronous circular orbit with 735 km height. In this paper, a CCD camera is designed composed of the CCD sensor module, the analog system and the embedded controller with an NIOSII soft-core processor based on FPGA. The analog system is first introduced in detail including power and bias voltage supply circuit, 16 bit A/D converter, power protecting circuit, amplifier circuit, and CCD driving clocks generation circuit. NIOS II embedded system is then presented including system hardware and NIOS II processor. Finally, evaluation results of this camera are also presented including readout noise, gain, linearity, dynamic range and full well capacity.
Modelling radiation damage to ESA's Gaia satellite CCDs
The Gaia satellite is a high-precision astrometry, photometry and spectroscopic ESA cornerstone mission, currently scheduled for launch in late 2011. Its primary science drivers are the composition, formation and evolution of the Galaxy. Gaia will not achieve its scientific requirements without detailed calibration and correction for radiation damage. Microscopic models of Gaia's CCDs are being developed to simulate the effect of radiation damage, charge trapping, which causes charge transfer inefficiency. The key to calculating the probability of a photoelectron being captured by a trap is the 3D electron density within each CCD pixel. However, this has not been physically modelled for Gaia CCD pixels. In this paper, the first of a series, we motivate the need for such specialised 3D device modelling and outline how its future results will fit into Gaia's overall radiation calibration strategy.
The Wide-Field Camera 3 detectors
The Wide-field Camera 3 (WFC3) is a fourth-generation instrument planned for installation in Hubble Space Telescope (HST). Designed as a panchromatic camera, WFC3's UVIS and IR channels will complement the other instruments onboard HST and enhance the observatory's scientific performance. UVIS images are obtained via two 4096×2051 pixel e2v CCDs while the IR images are taken with a 1024×1024 pixel HgCdTe focal plane array from Teledyne Imaging Sensors. Based upon characterization tests performed at NASA/GSFC, the final flight detectors have been chosen and installed in the instrument. This paper summarizes the performance characteristics of the WFC3 flight detectors based upon component and instrument-level testing in ambient and thermal vacuum environments.
Characterization of E2V CCD 203_82 with low noise AACAS controller
Yuanyuan Shang, Qian Song, Yong Guan, et al.
National Astronomical Observatories of Chinese Academy of Sciences have successfully developed a universal astronomical CCD controller, which is called Astronomical Array Control & Acquisition System (AACAS). It behaves excellent performance and ultra low system noise. In this paper, results of E2V 4K×4K CCD203_82 characterization using AACAS controller are presented and also the comparison with the specifications E2V supplied is given. It concludes some important merits, such as dark current, readout noise, CTE and etc. The readout noise is smaller than 3e- (50KHz) at -100°C working temperature. The system linearity is better than 99.99% and the full well is about 110027e-. The horizontal and vertical CTE are 0.999993 and 0.999997, measured by Fe55 X-ray source and extended pixel edge response (EPER) separately.
Evaluation of the fully-depleted back-illuminated CCD for Subaru Suprime-Cam
In order to improve the quantum efficiency (QE) at longer wavelength, we have developed fully-depleted backilluminated CCDs in collaboration with Hamamatsu Photonics K.K (HPK). Recently, HPK delivered 10 CCDs for Subaru Prime Focus Camera (Suprime-Cam). These CCDs are made on N-type, high resistivity silicon wafers. Each CCD has a 200 μm thick depletion layer. The CCD format is four-side buttable, 2k × 4k, 15 μm square pixels with 4 low noise output amplifiers. The characteristics of the CCDs have been tested in the laboratory before they are installed into Suprime-Cam dewar. These CCDs have excellent performance; readout noise < 5 e-, dark current < 2 e-/hour/pixel, parallel and serial charge transfer efficiency (CTE) > 0.999995, and full-well ~ 180,000 e-. The QE of λ = 1 μm was 40 % at -100°C. All CCDs have good cosmetics. Surface flatness is ~ 25 μm peak to value (P-V). The specification was acceptable. We are also developing CCDs for Hype Suprime-Cam (HSC), the next generation instrument for Subaru Telescope. HPK optimized back side process and has developed blue enhanced CCDs for HSC.
Image mosaics technology of the 2D coordinates measurement
Xianwei Zhang, Weimin Li, Xiaofeng Li, et al.
This paper discusses an extension of image mosaics technology of the 2D coordinates measurement technique. Fourier-Mellin Transform (FMT) is widely used as an image mosaics method. Based on analyses of frequency spectrum, FMT automatically stitches images with relationships of translation, rotation, scaling. The course of FMT is simulated and optimized, and the character of FMT for shifted images is educed. Furthermore, the particular rules for polar coordinate transform of rotated and zoomed images are advanced, making noise depressed and the feasibility of the algorithm greatly increased. Moreover, The proposed method that adopt filter technique aiming at finite discrete images can eliminate efficiently the artifact in the Fourier-Mellin space, and obtain significant correlated peak values and resist the influence of noise interference. Finally, making use of the separation pattern technology based on difference calibrations to evaluate the precision of registration image. Experimental results demonstrate this method is effective.
Characterization of wafer-scale and many-output CCD detectors
Michael Lesser, Roy Tucker
The latest CCD detectors destined for advanced astronomical instruments are larger and have more output amplifiers than previous devices. Examples are the Semiconductor Technology Associates, Inc. 16-output STA1600 and STA1900 devices and the 8-output STA2200 Orthogonal Transfer Array CCDs. Back illuminated versions of these devices have been processed and evaluated at the University of Arizona Imaging Technology Laboratory and are the subject of this paper. Characterizing these devices has required new optical testing equipment and optimized techniques to efficiently evaluate device performance. This is especially true when even limited volume production is required. In this paper we discuss the hardware related to characterization of the large format (135 mm diagonal) and 8- and 16- output CCDs at cold temperatures, including quantum efficiency, charge transfer efficiency, noise, full well, cross-talk, and operating parameters. We also discuss related developments in dewar construction and operation, including a hybrid closed cycle and liquid nitrogen cooling system used for long-term testing, the characterization optical system, and related device packaging. We also describe the equipment for wafer level probe testing of the same devices.
Simulations of sample-up-the-ramp for space-based observations of faint sources
We have conducted simulations of a memory-efficient up-the-ramp sampling algorithm for infrared detector arrays. Our simulations use realistic sky models of galaxy brightness, shapes, and distributions, and include the contributions of zodiacal light and cosmic rays. A simulated readout is based on the HAWAII-2RG arrays, and includes read noise, dark current, KTC noise, reset anomaly, persistence, and random telegraph noise. The up-the-ramp algorithm rejects cosmic rays, RTN, and KTC noise. The reset anomaly and persistence are also correctable. It produces a best estimate of the source flux under the assumption of very low signal-to-noise, while the overall dynamic range is increased. We present an analysis of the fidelity of image brightness recovery with this algorithm. This work is motivated by the need for sensitive, precise, accurate photometry for Destiny, a mission concept under study for the Joint Dark Energy Mission (JDEM).
Fabrication and photon detection experiments of Nb/Al and Ta/Al superconducting tunnel junctions
We report on fabrication and photon detection experiments of Nb/Al and Ta/Al superconducting tunnel junctions (STJs). 5-layer STJ thin-films were fabricated using UV photolithography, DC magnetron sputtering, reactive ion etching, and chemical vapor deposition techniques. STJs with 4 different sizes (20, 40, 60 and 80 μm) were deposited on sapphire substrates and tested in a two stage adiabatic demagnetization refrigerator with an operating temperature ~ 50 mK. Photons from different light sources are injected into the junctions via an optical fiber in combination with a monochromator which can produce photons from 30 nm to 550 nm with 0.1 nm resolution. The junction is read out through a charge-sensitive preamplifier followed by a shaping stage. We have measured some performance indicators and quality factors of the junctions from resultant I-V curves.
Design and fabrication of TES microcalorimeters for x-ray astrophysics in Japan
Yuichiro Ezoe, Tomotaka Yoshino, Kazuma Mukai, et al.
Our recent development of transition-edge sensor (TES) microcalorimeters for future X-ray astronomical missions such as DIOS is reported. In-house micromaching processes has been established aiming at prompt fabrication of TES devices. With a single-pixel TES microcalorimeter and an Au absorber, the energy resolution of 4.8 eV at 5.9 keV is achieved. 16×16 pixel arrays of TES microcalorimeters are successfully fabricated by using deep dry etching technique. The energy resolution is 11 eV and 26 eV with and without an Au absorber, respectively. The worse energy resolution than a single-pixel TES is due to large decrease of TES sensitivity and increase of transition temperature after etching. The reason for these phenomena is under investigation. In parallel, mushroom-type Au absorber structures are being tested. Furthermore, to precisely measure TES sensitivities and heat capacity, an experimental setup for impedance measurements is established.
Simulating and reproducing instrument background for x-ray CCD spectrometers in space
In anticipation of the European Space Agency (ESA) X-ray Evolving Universe Spectroscopy (XEUS) mission, designed as a follow-on to the ESA X-ray Multi Mirror (XMM-Newton) mission, the instrument background for the XMM-Newton mission, the Japanese Space Agency Suzaku mission and the NASA Swift mission has been studied. The instrument background has been modelled using the Geant4 toolkit to establish the constituent components for the differing orbits and detector designs across the energy range from 1 keV to 12 keV. The results, consistent with the spectra obtained in-orbit, are then discussed. With knowledge of the dominant components of the instrument background, methods targeted at reduction in future missions are considered, with experimental results designed to determine their effects.
Imaging and spectroscopy using a scintillator-coupled EMCCD
The CCD97 is a low light level (L3) device from e2v technologies range of electron multiplying CCDs (EMCCDs). The device uses e2v's patented extended gain register and through the use of appropriately designed electrodes can be used to maximise the signal whilst keeping the impact of the noise to a minimum. The nature of this device makes it ideal for use with a scintillator in order to see individual flashes of light from single X-ray photons. Through the examination of individual X-ray events, it is possible to analyse each interaction in the scintillator to determine the sub-pixel position of the interaction. Using the modelling capabilities of the Geant4 toolkit it is possible to simulate X-ray events and thus examine interactions with known energy and point of interaction. Through bringing together the experimental and simulated results, the spectral capabilities of such a device are discussed.
Panoramic detector with high time resolution on base of GaAs photocathode
Grigory Beskin, Vjacheslav de-Bur, Sergey Karpov, et al.
The Position-Sensitive Detector (PSD) on base of GaAs photocathode and microchannel plate set has been developed. PSD consists of thick semiconductor photocathode with quantum efficiency about 48% in the range of 4000-8000AA, two microchannel plates, and 16-electrode collector. The detector has spatial resolution of 20-30 microns for about 5 • 105 pixels, time resolution of 1 us and effective sensitivity up to 40%.
Characterization of persistence in WIRCam's Hawaii 2-RG arrays
Persistence or image memory is a common problem in infrared array detectors. In WIRCam, the wide-field infrared camera at the Canada France Hawaii Telescope, two of the four Hawaii-2RG (H2RG) HgCdTe imaging arrays in its mosaic exhibit strong persistence while the other two do not. The dependence of the persistence on illumination flux and fluence has been investigated and the persistence measured on the timescale of hundreds of milliseconds to several hours. The goal of this work is to eventually provide an empirical model to correct for the persistence in image post-processing.
High sensitivity infrared extended wavelength response InGaAs detectors
Matthew J. Nelson, Michael F. Skrutskie, Srikrishna Kanneganti, et al.
Recent development of low dark current 2.34 μm-cutoff InGaAs material has resulted in the successful construction of a hybrid focal plane array built on the SB-206 512×512 format astronomical quality Read Out Integrated Circuit(ROIC). This contribution reports on the verification of the quality of the InGaAs material as well as the essential characteristics and performance of the hybrid focal plane array. The results of the investigation indicate that the dark current levels surpass the requirements for ground-based broadband and narrowband imaging as well as for low resolution spectroscopy in the astronomical H and Ks bands.
The (55)Fe x-ray energy response of mercury cadmium telluride near-infrared detector arrays
The accurate determination of a detector's fundamental parameters, including read noise, dark current, and QE, relies on a proper measurement of a detector's conversion gain (e- ADU-1). Charge coupling effects, such as interpixel capacitance, attenuate photon shot noise and result in an overestimation of conversion gain when implementing the photon transfer technique. An approach involving 55Fe X-rays provides a potentially straightforward measurement of conversion gain by comparing the observed instrumental counts (ADU) to the known charge (e-) liberated by the X-ray. This technique is already preferred within the CCD community, as the pair production energy for silicon is well established. In contrast, to date the pair production energy is unknown for HgCdTe, a material commonly used for near-infrared detectors. In this paper, we derive a preliminary calibration of the 55Fe X-ray energy response of HgCdTe using 8 HST WFC3 1.7 μm flight grade detectors. Our conversion of the X-ray intensities from counts into electrons implements a technique that restores the "true" gain via classical propagation of errors. For these detectors, our analysis yields preliminary results of good statistical precision: each Kα event generates 1849 ± 46 electrons, which corresponds to a pair production energy of 3.21 ± 0.08 eV. We are continuing to assess potential systematic effects to further refine the accuracy of this result.
James Webb Space Telescope Near-Infrared Spectrograph: dark performance of the first flight candidate detector arrays
Bernard J. Rauscher, David Alexander, Clifford K. Brambora, et al.
The James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 μm cutoff (λco =5 μm) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays, and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space at Τ ~ 37 K. This article focuses on the measured performance of the first flight-candidate, and near-flight candidate, detector arrays. These are the first flight-packaged detector arrays that meet NIRSpec's challenging 6 e- rms total noise requirement. The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.
DPIX: an assembly of 6400 CdTe detectors for gamma-ray bursts detection with ECLAIRs
N. Remoué, D. Barret, P. Mandrou, et al.
The French instrument ECLAIRs, to be part of the French and Chinese SVOM mission for the study of gamma-ray bursts (GRBs), will detect bursts between 4 and 250 keV. Its detector plane is an assembly of 200 elementary detection modules (XRDPIX) equipped with 32 Schottky CdTe detectors, produced by ACRORAD in Japan. The innovative concept of XRDPIX will enable a 4 keV low-energy threshold to be achieved. After introducing the SVOM payload, the ECLAIRs instrument and its detector plane, this paper presents the results of the performance evaluation of a first set of 500 detectors, and briefly describes the tests foreseen for the first XRDPIX prototypes.
Characterization of the detector subsystem for the near-infrared spectrograph (NIRSpec) on the James Webb Space Telescope
We present interim results from the characterization test development for the Detector Subsystem of the Near-Infrared Spectrograph (NIRSpec). NIRSpec will be the primary near-infrared spectrograph on the James Webb Space Telescope (JWST). The Detector Subsystem consists of a Focal Plane Assembly containing two Teledyne HAWAII-2RG arrays, two Teledyne SIDECAR cryogenic application specific integrated circuits, and a warm Focal Plane Electronics box. The Detector Characterization Laboratory at NASA's Goddard Space Flight Center will perform the Detector Subsystem characterization tests. In this paper, we update the initial test results obtained with engineering grade components.
Developing infrared array controller with software real time operating system
Real-time capabilities are required for a controller of a large format array to reduce a dead-time attributed by readout and data transfer. The real-time processing has been achieved by dedicated processors including DSP, CPLD, and FPGA devices. However, the dedicated processors have problems with memory resources, inflexibility, and high cost. Meanwhile, a recent PC has sufficient resources of CPUs and memories to control the infrared array and to process a large amount of frame data in real-time. In this study, we have developed an infrared array controller with a software real-time operating system (RTOS) instead of the dedicated processors. A Linux PC equipped with a RTAI extension and a dual-core CPU is used as a main computer, and one of the CPU cores is allocated to the real-time processing. A digital I/O board with DMA functions is used for an I/O interface. The signal-processing cores are integrated in the OS kernel as a real-time driver module, which is composed of two virtual devices of the clock processor and the frame processor tasks. The array controller with the RTOS realizes complicated operations easily, flexibly, and at a low cost.
SPID: single photon imaging device
L. Neri, S. Tudisco, L. Lanzanò, et al.
Today, single photon imaging represents one of the most challenging goals in the field of photonics. Many areas are involved: nuclear and particle physics, astronomy, and, in the biophysics field, the newest technique to investigate the state of several biological systems by detecting the ultra-weak luminescence emitted from the excited sample under study. Aim of the work is the realization of a single photon imaging device able to identify the position and the arrival time of the impinging photons from ultra low intensity sources. The main features of a 2-D array of Single Photon Avalanche Diodes, manufactured by ST-Microelectronics, are shown.
Pixel area variation in CCDs and implications for precision photometry
Images with smooth and moderately flat illumination are commonly used to calibrate pixel to pixel sensitivity variation without consideration that some structure on short spatial scales may be due to reallocation of area between pixels. Errors in the position of pixel boundaries have the effect of repartitioning charge between pixels but do not affect the total charge collected. Since the resulting errors tend to cancel when combining signal from adjacent pixels, this effect has gone largely unnoticed. However proposed wide field astronomical surveys, which strive to achieve high photometric precision with coarse spatial sampling, must take this into account. We present simple analysis techniques to identify how much flat field structure is due to systematic and random variations in pixel area, rather than sensitivity, as a function of row/column direction and spatial frequency. Analysis of data from CCDs made with radically different technologies and pixel sizes by different manufacturers suggests that pixel size variation in the column direction probably dominates QE variations on short spatial scales for all CCDs. Refinements to flat field calibration methods and tests to confirm their efficacy are proposed.
Intra-pixel response of infrared detector arrays for JWST
The near-infrared instruments on the James Webb Space Telescope will use 5 micron cutoff HAWAII-2RG detector arrays. We have investigated the response of this type of detector at sub-pixel resolution to determine whether variations at this scale would affect the performance of the instruments. Using a simple experimental setup we were able to get measurements with a resolution of approximately 4 microns. We have measured an un-hybridized HAWAII-1RG multiplexer, a hybridized HAWAII-1RG device with a 5 micron cutoff HgCdTe detector layer, and a hybridized HAWAII-2RG device with a 5 micron cutoff substrate-removed HgCdTe detector layer. We found that the intra-pixel response functions of the hybrid devices are basically smooth and well behaved, and vary little from pixel to pixel. However, we did find numerous sub-pixel sized defects, notably some long straight thin features like scratches. We were not able to detect any significant variations with wavelength between 0.65 and 2.2 microns, but in the -1RG device there was a variation with temperature. When cooled from 80K to 40K, the pixel response became narrower, and some signal began to be lost at the edges of the pixel. We believe this reflects a reduction in charge diffusion at the lower temperature.
Modeling the suitability of EMCCDs for spectroscopic applications
A model of EMCCDs has been developed to predict the areas of application where they offer superior performance to a conventional CCD. The sub electron read noise of an EMCCD makes it an obvious choice for observations that are normally detector noise limited, for example the detection of faint emission lines. In other regimes where photon noise is dominant, for example the measurement of absorption lines or emission lines superimposed on a bright continuum, EMCCDs offer less advantage. This model is used to generate a large number of synthetic spectral lines both in absorption and emission, including the effects of clock induced charge and multiplication noise. The line parameters are then measured by fitting a Gaussian profile and the 'goodness of fit' of this profile used to calculate the SNR of the measurement. The model allows the performance parameters of the EMCCD to be varied freely to see the effect on SNR. As a confidence check, the model is compared against actual images taken with an EMCCD camera in the laboratory.
Development of a CCD array detector for combined XRD\XRF applications
This project is based on the design and testing of a CCD (charge coupled device) based detector to be used for the simultaneous collection of x-ray diffraction (XRD) and x-ray fluorescence (XRF) data from powdered rock samples. The detector designed for this project uses four e2v technologies CCD 30-11 (FI, AIMO) devices tiled in a curved geometry to allow the centre of each of the four CCDs to be exactly 120 mm from the sample. The CCDs are operated in single photon counting mode which allows the detector to simultaneously determine the spatial position of diffracted x-rays as well as resolve the energy of characteristic x-rays fluoresced from the sample. Energy discrimination is then used to reveal the XRD data and radial integration is performed on the four CCD images to extract the "2θ vs. intensity" spectrum. The project also involves the use of a high brightness x-ray micro-source from Bede Scientific Instruments, used to deliver a focused beam of low divergent x-rays to the sample. Collimation and monochromation are also introduced into the system to produce a 93% monochromatic beam of CuKθ x-rays, delivered to the powder sample through a 50 µm spot. Details into the design of the CCD array are discussed as well as results presented from various samples.