HgCdTe detector arrays with a cutoff wavelength of ∼10 μm intended for the Near-Earth Object Camera (NEOCam) space mission were subjected to proton-beam irradiation at the University of California Davis Crocker Nuclear Laboratory. Three arrays were tested—one with 800-μm substrate intact, one with 30-μm substrate, and one completely substrate-removed. The CdZnTe substrate, on which the HgCdTe detector is grown, has been shown to produce luminescence in shorter wave HgCdTe arrays that causes an elevated signal in nonhit pixels when subjected to proton irradiation. This testing was conducted to ascertain whether or not full substrate removal is necessary. At the dark level of the dewar, we detect no luminescence in nonhit pixels during proton testing for both the substrate-removed detector array and the array with 30-μm substrate. The detector array with full 800-μm substrate exhibited substantial photocurrent for a flux of 103 protons/cm2 s at a beam energy of 18.1 MeV (∼750 e−/s) and 34.4 MeV (∼65 e−/s). For the integrated space-like ambient proton flux level measured by the Spitzer Space Telescope, the luminescence would be well below the NEOCam dark current requirement of <200 e−/s, but the pattern of luminescence could be problematic, possibly complicating calibration.
The Echelon-Cross-Echelle Spectrograph (EXES) is one of the first generation instruments for the Stratospheric Observatory for Infrared Astronomy (SOFIA). The primary goal of EXES is to provide high-resolution, cross-dispersed spectroscopy, with resolutions of 50,000-100,000 and wavelength coverage of 0.5-1.5% between 4.5 μm and 28.3 μm. EXES will also have medium (R=5000-25000) and low (R=1500-4000) modes available, as well as a target acquisition imaging mode and a pupil-imaging mode for alignment testing. EXES is scheduled for commissioning flights in February 2014. It will be available to the public for shared-risk observations in SOFIA’s Cycle 2. Here we give an overview of the design and capabilities of EXES as well as its laboratory performance to date.
The Echelon-cross-Echelle Spectrograph (EXES) is one of the first generation instruments for the Stratospheric
Observatory for Infrared Astronomy (SOFIA). It operates at high, medium, and low spectral resolution in the
wavelength region 4.5 to 28.3 microns using a 1024x1024 Si:As detector array. From SOFIA, the high spectral
resolution mode (R ≈ 100,000) will provide truly unique data given the improved atmospheric transmission. We
are currently involved with system testing in preparation for our first ground-based telescope run to occur in
Jan 2011 at the NASA IRTF 3m. We present the current status of EXES including lab results in our high and
medium resolution modes, our plans for ground-based observing, and our expectations for operations on SOFIA.
Direct imaging of extrasolar planets, and Earth-like planets in particular, is an exciting but difficult problem requiring a
telescope imaging system with 1010 contrast at separations of 100mas and less. Furthermore, the current NASA science
budget may only allow for a small 1-2m space telescope for this task, which puts strong demands on the performance of
the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA)
coronagraph has been maturing and may enable Earth-like planet imaging for such small telescopes. In this paper, we
report on the latest results from a new testbed at NASA Ames focused on testing the PIAA coronagraph. This laboratory
facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to
complement existing efforts at NASA JPL. For our wavefront control we are focusing on using small Micro-Electro-
Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall
instrument, a consideration that becomes very important for small telescopes. At time of this writing, we are operating a
refractive PIAA system and have achieved contrasts of about 1.2x10-7 in a dark zone from 2.0 to 4.8 λ/D (with 6.6x10-8
in selected regions). In this paper, we present these results, describe our methods, present an analysis of current limiting
factors, and solutions to overcome them.
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.
The Wide-field Infrared Survey Explorer (WISE) is a NASA MidEx mission which will survey the entire sky at 3.3, 4.7,
12 and 23 microns. As with most all-sky surveys, WISE results will address many fundamental topics, but the
passbands and sensitivity are particularly well suited to study the distribution and evolutionary history of brown dwarfs
and ultra-luminous IR galaxies. The two long wavelength bands will use 1024x1024 Si:As BIB detectors manufactured
by DRS Sensors & Targeting Systems. NASA ARC has optimized the operating parameters as well as conducted
detailed cryogenic performance and radiation testing of a prototype array. Dark current, noise performance, and radiation
test results will be reported.
The Infrared Array Camera (IRAC) on Spitzer Space Telescope includes four Raytheon Vision Systems focal plane arrays, two with InSb detectors, and two with Si:As detectors. A brief comparison of pre- flight laboratory results vs. in-flight performance is given, including quantum efficiency and noise, as well as a discussion of irregular effects, such as residual image performance, "first frame effect", "banding", "column pull-down" and multiplexer bleed. Anomalies not encountered in pre-flight testing, as well as post-flight laboratory tests on these anomalies at the University of Rochester and at NASA Ames using sister parts to the flight arrays, are emphasized.
The operability requirements of NASA's James Webb Space Telescope (JWST) impose specific challenges on radiation effects mitigation and analysis. For example, the NIRSpec Instrument has the following requirements: •The percentage of pixels defined as operable for target acquisition shall not be less than 97% (TBR) (goal 99%) of the total number of pixels... An inoperable pixel is: ο A dead pixel: a pixel with no radiometric response o A noisy pixel: a pixel with a total noise greater than 21 e-, per Fowler 8 exposure •The percentage of pixels defined as operable for science observations shall not be less than 92% (TBR) (goal 98%) of the total number of pixels... An inoperable pixel is: ο A dead/low-DQE pixel: a pixel deviating by >30% from the DQE mean value ο A noisy pixel: a pixel with a total noise greater than 12 e- (goal 9e-). With these performance requirements and operation in space, the radiation environment from galactic cosmic rays (GCR), energetic solar particles, and activation of spacecraft materials can contribute significantly to the number of inoperable pixels. The two most important issues to date are radiation-induced transient effects and hot pixels. This paper focuses on the methods used to assess the impact of ionizing radiation induced transients on the HgCdTe SCA selected by JWST. Hot pixel effects in these detectors has been previously presented. Both effects are currently under investigation.
The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.
As the logical extension of the 20-year mission of the Hubble Space Telescope, NASA plans to launch the James Webb Space Telescope (JWST, formerly NGST) near the end of this decade. As Hubble's scientific and technological successor, equipped with a 6-meter-class deployable mirror, JWST will allow observations of the very early universe
and initial formation of galaxies at levels not achievable today. JWST's unprecedented sensitivity cannot be utilized without a new class of IR focal plane arrays whose performance matches that of the telescope. In particular, JWST focal planes must be able to withstand the ionizing-particle radiation environment expected for its Lagrange-point (L2) orbit and ten-year mission lifetime goal. To help determine their suitability for JWST, NASA is evaluating prototype
megapixel-class readouts and hybrid detector arrays under proton bombardment to simulate the anticipated JWST lifetime radiation dose. This report describes the results of early tests on devices from two manufacturers using photovoltaic (HgCdTe or InSb) candidate near-infrared detector structures. Results to date have shown encouraging
performance, along with some areas of continuing concern.
Si:As Impurity Band Conduction (IBC) detectors offer many significant advantages over other conventional photon detectors utilized for the infrared. SiAs offer excellent spectral response out to 28 μm with dark current in the 0.01e/second range at 7K over a wide bias range with no tunneling limitations. In addition, because of the perfect thermal match between the Si:As IBC detector and the readout IC (ROIC), hybrids formed by mating Si:As IBCs and ROICs are mechanically stable and have no hybrid reliability problems. Since Si:As IBC detectore are fabricated on readily available Si substrates, large formats are realizable. Si:As IBC detectors have been under development since the mid 80's at Raytheon Vision Systems (RVS). Under the NSAS SIRTF program, a 256 x 256 Si:As array was developed and successfully integrated into the SIRTF IRAC instrument. This same array is also utilized in the ASTRO-F IRC instrument. Both missions will be launched shortly and provide a significant improvement in our ability to measure the spectral signatures of solar type stars and galaxies at high redshifts under very low background conditions in space. Under the NASA Origins program, in collaboration with NASA Ames Research Center (ARC), RVS developed a high performance 1024 x 1024 Si:As IBC array. This array was tested at Ames Research Center. This paper will review the progress of Si:As IBC development at RVS, present test data from ARC, and discuss the more recent developments in Si:As IBC detectors for the JWST MIRI instrument and future missions such as SPICA, TPF, FIRST and DARWIN.
A mid-infrared(5-30 micron) instrument aboard a cryogenic space telescope can have an enormous impact in resolving key questions in astronomy and cosmology. A space platform's greatly reduced thermal backgrounds (compared to airborne or ground-based platforms), allow for more sensitive observations of dusty young galaxies at high redshifts, star formation of solar-type stars in the local universe, and formation and evolution of planetary disks and systems. The previous generation's largest, most sensitive infrared detectors at these wavelengths are 256 x 256 pixel Si:As impurity band conduction devices built by Raytheon Infrared Operations for the SIRTF/IRAC instrument. Raytheon has successfully enhanced these devices, increasing the pixel count by a factor of 16 while matching or exceeding SIRTF/IRAC device performance. NASA-Ames Research Center in collaboration with Raytheon has tested the first high performance large format (1024 x 1024) Si:As IBC arrays for low background applications, such as for the mid-IR instrument on NGST and future IR Explorer missions. These hybrid devices consist of radiation-hard SIRTF/IRAC-type Si:As IBC material mated to a readout multiplexer that has been specially processed for operation at low cryogenic temperatures (below 10 K), yielding high device sensitivity over a wavelength range of 5-28 microns. In this paper, we present laboratory test results from these benchmark devices. Continued development in this technology is essential for conducting large-area surveys of the local and early universe through observation and for complementing future missions such as NGST, TPF, and FIRST.
Airborne and space telescope astronomical observations in the 5-25 micron wavelength region are critical for understanding the physical conditions, composition, chemistry, and excitation of many environments in the interstellar medium, external galaxies, solar system objects, extra-solar systems, and stars. The scientific impact is particularly unique in the 5-8 micron and 14-25 micron regions which are inaccessible or poorly observed from ground-based observatories. Large format mid-infrared detectors sensitive over these wavelengths and operable under moderate backgrounds (~106 photons/s/pixel at R=2000, at 10 microns) are essential for efficient large-area survey imaging and for taking moderate resolution spectra over a large spectral range. Both SOFIA and passively cooled Explorer observatories could benefit from this technology. Current first-light SOFIA instruments use small-format mid-infrared focal plane arrays of sizes 256 × 256 pixels. With the collaboration of Raytheon Infrared Operations, NASA-Ames Research Center has developed and tested the first 1024 × 1024 mid-infrared device suitable for operating under moderate backgrounds: a combination of the ALADDIN III readout multiplexer, cryo-processed for 6 K operation, with Si:As IBC detector material designed for high QE. This device has exhibited low dark current, moderate noise levels, and > 200,000 electron linear well size at 6 K operation. We conclude with suggestions for future device development for optimal performance under moderate background, SOFIA- and low Earth orbit observing conditions.
The goal of achieving background-limited performance in SIRTF's cryogenic telescope environment places stringent demands on focal plane sensitivity. SIRTF's prime imaging instrument, the InfraRed Array Camera (IRAC), employs 256 X 256 Si:As Impurity-Band Conduction (IBC) arrays for its two longest wavelength channels at 5.8 micrometers and 8.0 micrometers . Background-limited performance is achieved at very low levels of zodiacal background radiation with cryo-optimized readout and detector technology from Raytheon. Presented here are performance measurements of IRAC flight candidate IBC arrays. Operating at a temperature of 6 K, these devices meet all IRAC sensitivity requirements, with dark currents well below the 10 e-/s specification, Fowler-sampled noise levels of 16 e-, and excellent photometric stability.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
Raytheon/SBRC has demonstrated high quality Si:As IBC IR FPAs for both ground-based and space-based Mid-IR astronomy applications. These arrays offer in-band quantum efficiencies of approximately 50 percent over a wavelength range from 6 micrometers to 26 micrometers and usable responses from 2 micrometers to 28 micrometers . For high background, ground-based applications the readout input circuit is a direct injection (DI) FET, while for low background, space-based applications a source follower per detector (SFD) is used. The SFD offers extremely low noise and power dissipation, and is implemented in a very small unit cell. The DI input circuit offers much larger bucket capacity and better linearity compared with the SFD, and is implemented in a 50 micrometers unit cell. SBRC's Si:As IBC detector process results in very low dark current sand our Raytheon/MED readout process is optimized for very low redout noise at low temperature operation. SBRC is committed to achieving still better performance to serve the future needs of the IR astronomy community.
Cryogenic space telescopes such as the Space Infrared Telescope Facility (SIRTF) require large-area focal plane arrays (FPAs) with high sensitivity. Such applications set requirements for the readout arrays to simultaneously provide low noise and low power dissipation at very low temperatures. The Hughes Technology Center (HTC) has developed a low-noise 256 X 256-pixel hybrid FPA composed of a PMOS readout array hybridized to an arsenic- doped silicon (Si:As) impurity-band conduction (IBC) detector which is designed to operate below 10 K. The readout unit cell employs a switched source-follower-per-detector (SFD) design where in signals are multiplexed onto four outputs. The detector was processed using high-purity, multilayered epitaxial processing. The readout was processed using the p-channel subset of HTC's CryoCMOS process.
Four 58 X 62-element Si:As impurity-band-conduction (IBC) detector arrays produced by the Hughes Technology Center were tested to evaluate their usefulness for space- and ground- based astronomical observations. PMOS circuitry was used in the multiplexers to improve low-temperature noise performance. Laboratory tests at background levels simulating those expected on space-based observing platforms were combined with ground-based telescope IR observations. The devices have shown read noise levels below 120 rms e-, dark currents below 10 e-/s, and detective quantum efficiencies of 20%.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.