The Nancy Grace Roman Space Telescope (Roman) formerly known as the Wide-Field Infrared Survey Telescope will answer fundamental questions about the evolution of dark energy over time and expand the catalog of known exoplanets into new regions of parameter space. Using a Hubble-sized mirror and 18 newly developed HgCdTe 4K × 4K photodiode arrays (H4RG-10), the Roman Space Telescope will measure the positions and shapes of hundreds of millions of galaxies, the light curves of thousands of supernovae, and the microlensing signals of over a thousand exoplanets toward the bulge of the Galaxy. These measurements require unprecedented sensitivity and characterization of the Wide Field Instrument, particularly its detectors. The Roman project undertook an extensive detector development program to create focal plane arrays that meet these science requirements. We present the performance characteristics of these TRL-6 demonstration devices.
The Nancy Grace Roman Space Telescope (Roman) formerly known as the Wide-Field Infrared Survey Telescope will answer fundamental questions about the evolution of dark energy over time and expand the catalog of known exoplanets into new regions of parameter space. Using a Hubble-sized mirror and 18 newly developed HgCdTe 4K × 4K photodiode arrays (H4RG-10), the Roman Space Telescope will measure the positions and shapes of hundreds of millions of galaxies, the light curves of thousands of supernovae, and the microlensing signals of over a thousand exoplanets toward the bulge of the Galaxy. These measurements require unprecedented sensitivity and characterization of the Wide Field Instrument, particularly its detectors. The Roman project undertook an extensive detector development program to create focal plane arrays that meet these science requirements. These prototype detectors have been characterized and their performance demonstrated in a relevant space-like environment (thermal vacuum, vibration, acoustic, and radiation testing), advancing the H4RG-10’s technology readiness level (TRL) to TRL-6. We present the performance characteristics of these TRL-6 demonstration devices.
Although there are a large number of known exoplanets, there is little data on their global atmospheric properties. Phase-resolved spectroscopy of transiting planets – continuous spectroscopic observation of planets during their full orbits – probes varied depths and longitudes in the atmospheres thus measuring their three-dimensional thermal and chemical structure and contributing to our understanding of their global circulation. Planets with characteristics suitable for atmospheric characterization have orbits of several days, so phase curve observations are highly resource intensive, especially for shared use facilities. The Exoplanet Climate Infrared TElescope (EXCITE) is a balloon-borne near-infrared spectrometer designed to observe from 1 to 5 μm to perform phaseresolved spectroscopy of hot Jupiters. Flying from a long duration balloon (LDB) platform, EXCITE will have the stability to continuously stare at targets for days at a time and the sensitivity to produce data of the quality and quantity needed to significantly advance our understanding of exoplanet atmospheres. We describe the EXCITE design and show results of analytic and numerical calculations of the instrument sensitivity. We show that an instrument like EXCITE will produce a wealth of quality data, both complementing and serving as a critical bridge between current and future space-based near infrared spectroscopic instruments.
KEYWORDS: Sensors, Electrons, James Webb Space Telescope, Spectroscopy, Mercury cadmium telluride, Detection and tracking algorithms, Photometry, Space telescopes
Snowballs are transient events observed in HgCdTe detectors with a sudden increase of charge in a few pixels. They appear between consecutive reads of the detector, after which the affected pixels return to their normal behavior. The origin of the snowballs is unknown, but it was speculated that they could be the result of alpha decay of naturally radioactive contaminants in the detectors, but a cosmic ray origin cannot be ruled out. Even though previous studies predicted a low rate of occurrence of these events, and consequently, a minimal impact on science, it is interesting to investigate the cause or causes that may generate snowballs and their impact in detectors designed for future missions. We searched for the presence of snowballs in the dark current data in Euclid and Wide Field Infrared Survey Telescope (WFIRST) detectors tested in the Detector Characterization Laboratory at Goddard Space Flight Center. Our investigation shows that for Euclid and WFIRST detectors, there are snowballs that appear only one time, and others than repeat in the same spatial localization. For Euclid detectors, there is a correlation between the snowballs that repeat and bad pixels in the operational masks (pixels that do not fulfill the requirements to pass spectroscopy, photometry noise, quantum efficiency, and/or linearity). The rate of occurrence for a snowball event is about 0.9 snowballs/hr. in Euclid detectors (for the ones that do not have associated bad pixels in the mask), and about 0.7 snowballs/hr. in PV3 Full Array Lot WFIRST detectors.
Raytheon Vision Systems (RVS) has been developing high performance low background VisSWIR focal plane arrays suitable for the NASA WFIRST mission. These near infrared sensor chip assemblies (SCAs) are manufactured using HgCdTe on CdZnTe substrates with a 10 micron pixel pitch. WFIRST requirements are for a 4k x 4K format 4-side buttable package to populate a large scale 6 x 3 mosaic focal plane array of 18 SCAs. RVS devices will be compatible with the NASA developed FPA 4-side buttable package, and flight interface electronics. Initial development efforts at RVS have focused on a 2k x 2k format 10 micron pixel design based on an existing readout integrated circuit (ROIC) to demonstrate desired detector material performance at a relevant scale. This paper will provide performance results on the RVS efforts. RVS has successfully developed multiple 4k x 4k 10 micron pixel ROICs and we plan to demonstrate readiness to scale our design efforts to the desired 4k x 4k format for WFIRST in 2016.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant to many astrophysical problems. ACCESS, Absolute Color Calibration Experiment for Standard Stars", is a series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving power of 500 across the 0.35 - 1.7μm bandpass. This paper describes the payload status, sub-system testing, and data transfer for the ACCESS instrument.
KEYWORDS: Principal component analysis, Modulation, Sensors, James Webb Space Telescope, Temperature metrology, Staring arrays, Detector arrays, Control systems, Space telescopes, Near infrared
We present principal component analysis (PCA) of a flight-representative James Webb Space Telescope Near Infrared Spectrograph (NIRSpec) Detector Subsystem. Although our results are specific to NIRSpec and its T ~ 40 K SIDECAR ASICs and 5 μm cutoff H2RG detector arrays, the underlying technical approach is more general. We describe how we measured the system’s response to small environmental perturbations by modulating a set of bias voltages and temperature. We used this information to compute the system’s principal noise components. Together with information from the astronomical scene, we show how the zeroth principal component can be used to calibrate out the effects of small thermal and electrical instabilities to produce cosmetically cleaner images with significantly less correlated noise. Alternatively, if one were designing a new instrument, one could use PCA to determine a set of environmental requirements (temperature stability, electrical stability, etc.) that enabled the planned instrument to meet performance requirements.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. ACCESS, “Absolute Color Calibration Experiment for Standard Stars”, is a
series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in
the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from
the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration
accuracy of 1% and a spectral resolving power of 500 across the 0.35−1.7μm bandpass. Achieving a calibration
accuracy of 1% not only requires an accurate calibration transfer from the detector standards to the instrument,
but it also requires characterization and stability of the detector as well as a thermal background that contributes
less than 1% to the flux per resolution element in the near-infrared (1.7μm) spectral region of the ACCESS
bandpass. This paper describes the thermal mechanical design for achieving a low thermal background across
the ACCESS spectral bandpass.
KEYWORDS: Sensors, Electronics, Cameras, Connectors, Control systems, Data storage, Interfaces, Data acquisition, Field programmable gate arrays, Staring arrays
Several of the next generation instruments require high-resolution visible or infrared focal plane arrays that can only be
achieved by building large mosaics of individual detector arrays. A significant step towards enabling these mosaics has
been the introduction of the SIDECAR ASIC by Teledyne Imaging Sensors, a single chip for generating biases and
clocks to the image sensor, and for digitizing up to 36 sensor outputs. To support large detector mosaics, we have
developed a new control electronics approach that operates up to 32 SIDECAR ASIC / HxRG detectors in parallel.
Important properties of the electronics include separately programmable voltage supplies for each ASIC with
programmable over-current and over-voltage protection, synchronized operation of all ASICs, and support for post-processing
of science data like co-adding of frames, sample-up-the-ramp processing, or centroiding. All ASIC and
detector modes are supported, including window/guide mode operation. The electronics uses a full mode CameraLink
interface to provide 680 MBytes/s of sustained bandwidth.
In this paper, we present an overview of the electronics architecture, including the general computer infrastructure for
data acquisition, storage and sharing. We will discuss benefits and features of the chosen approach, and present data
captured using a SIDECAR ASIC and H2RG detector. The effort was funded by NASA's WFIRST project as part of an
initial technology demonstration for large space-based detector mosaics.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. ACCESS, “Absolute Color Calibration Experiment for Standard Stars”, is a
series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in
the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from
the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration
accuracy of 1% and a spectral resolving power of 500 across the 0.35-1.7µm bandpass.
ACCESS, Absolute Color Calibration Experiment for Standard Stars, is a series of rocket-borne sub-orbital
missions and ground-based experiments designed to enable improvements in the precision of the astrophysical
flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards
and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving
power of 500 across the 0.35.1.7μm bandpass.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. Systematic errors associated with problems such as dark energy now compete
with the statistical errors and thus limit our ability to answer fundamental questions in astrophysics.
The ACCESS design, calibration strategy, and an updated preliminary performance estimate are discussed.
The Detector Characterization Laboratory at NASA/GSFC has investigated the reciprocity failure characteristics of
1.7μm cut-off HgCdTe devices provided by Teledyne Imaging Sensors to the Hubble Space Telescope (HST) Wide
Field Camera 3 (WFC3) project. The reciprocity failure follows a power law behavior over the range of fluxes tested
(0.1-104 photons/second). The slope of the power law varies among detectors, ranging from ~0.3-1%/dex at 1.0μm,
which is much smaller than the ~6%/dex effect observed with the HST NICMOS 2.5μm cut-off detectors. In addition,
the reciprocity failure exhibits no wavelength dependence, although only a restricted range of wavelengths (0.85-1.0μm)
has been explored to date. Despite its relatively small magnitude, reciprocity failure is nevertheless an important effect in
the calibration of WFC3 data, as well as in other applications in which there is a large difference in flux between the
photometric standards and the scientific sources of interest.
In ground testing of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3), the CCDs of its UV/visible channel exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. The QEH first manifested itself as an occasionally observed contrast in response across the format of the CCDs, with an amplitude of typically 0.1-0.2% or less at the nominal -83°C operating temperature, but with contrasts of up to 3-5% observed at warmer temperatures. The behavior has been replicated in the laboratory using flight spare detectors and has been found to be related to an initial response deficiency of ~5% amplitude when the CCDs
are cooled with no illumination. A visible light flat-field (540nm) with a several times full-well signal level is found to pin the detector response at both optical (600nm) and near-UV (230nm) wavelengths, suppressing the QEH behavior. We have characterized the timescale for the detectors to become unpinned (days for significant
response loss at -83°C and have developed a protocol to stabilize the response in flight by flashing the WFC3 CCDs with the instrument's internal calibration system.
KEYWORDS: Sensors, James Webb Space Telescope, Electronics, Near infrared, Calibration, Infrared sensors, Space telescopes, Infrared telescopes, Infrared radiation, Astronomy
The James Webb Space Telescope, an infrared-optimized space telescope being developed by NASA for launch in 2014,
will utilize cutting-edge detector technology in its investigation of fundamental questions in astrophysics. JWST's near
infrared spectrograph, NIRSpec utilizes two 2048 × 2048 HdCdTe arrays with Sidecar ASIC readout electronics
developed by Teledyne to provide spectral coverage from 0.6 microns to 5 microns. We present recent test and
calibration results for the "pathfinder NIRSpec detector subsystem" as well as data processing routines for noise
reduction and cosmic ray rejection.
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.
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.
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.
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.
We present early results from the performance 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 summarize the initial test results obtained with engineering grade components.
Sensitive, photon counting array detectors have the potential to dramatically improve the sensitivity of space-based
astronomical spectrographs. We present first results from a program evaluating e2v L3 electron-multiplying CCDs as
photon counting arrays. We find that L3 CCDs function well as photon counters, and see no show stoppers for our target
applications. These include both ground and space-based instruments. Although we do detect spurious charge exceeding
the dark current floor of the CCD, we find that physical dark current in the multiplication register is a significant
component. This finding is significant because dark current, unlike clock induced charge (another potential culprit), is a
problem that CCD designers have solved before.
KEYWORDS: James Webb Space Telescope, Sensors, Spectrographs, Staring arrays, Near infrared, Space telescopes, Silicon, Infrared sensors, Infrared telescopes, Cameras
The Near Infrared Spectrograph (NIRSpec) will be the James Webb Space Telescope's (JWST's) primary near-infrared spectrograph. NIRSpec is a multi-object spectrograph with fixed-slit and integral field modes. EADS/Astrium is building NIRSpec for the European Space Agency (ESA), with NASA is providing the detector subsystem and programmable multi-aperture mask. In this paper, we summarize recent progress on the detector subsystem including tests demonstrating that JWST's Rockwell HAWAII-2RG sensor chip assemblies have achieved Technology Readiness Level 6 (TRL-6). Achieving TRL-6 is an important milestone because TRL-6 is required for flight.
A Hubble Space Telescope Wide Field Camera 3 (WFC3) CCD detector was tested for radiation effects while operating at -83C. The goal of the experiment was to evaluate the introduction and annealing rates of hot pixels and to assess the dynamics of that process. The device was irradiated while cold and warmed to +30°C for a 4 hour soak, then cooled back down to -83°C. Hot pixel populations were tracked during warm up and cool down. The results showed that the hot pixels begin to anneal around -40°C and the anneal process was largely completed before the detector reached +30°C. It was also found that, although a large fraction of the hot pixels dropped below the threshold, they remained warmer than the remaining population.
The Near-Infrared Spectrograph (NIRSpec) is the James Webb Space Telescope’s primary near-infrared spectrograph. NASA is providing the NIRSpec detector subsystem, which consists of the focal plane array, focal plane electronics, cable harnesses, and software. The focal plane array comprises two closely-butted λco ~ 5 μm Rockwell HAWAII-2RG sensor chip assemblies. After briefly describing the NIRSpec instrument, we summarize some of the driving requirements for the detector subsystem, discuss the baseline architecture (and alternatives), and presents some recent detector test results including a description of a newly identified noise component that we have found in some archival JWST test data. We dub this new noise component, which appears to be similar to classical two-state popcorn noise in many aspects, “popcorn mesa noise.” We close with the current status of the detector subsystem development effort.
We present the performance of the IR detectors developed for the WFC3 project. These are HgCdTe 1Kx1K devices with cutoff wavelength at 1.7 μm and 150K operating temperature. The two selected flight parts, FPA#64 (prime) and FPA#59 (spare) show quantum efficiency higher than 80% at λ=1.6 μm and greater than 40% at λ>1.1μm, readout noise of ~25 e- rms with double correlated sampling, and mean dark current of ~0.04 e/s/pix at 150K. We also report the results obtained at NASA GSFC/DCL on these and other similar devices in what concerns the QE long-term stability, intra-pixel response, and dark current variation following illumination or reset.
Wide Field Camera 3 is a fourth generation instrument for the
Hubble Space Telescope (HST), to be installed during the next HST Servicing Mission 4. For its infrared channel Rockwell Scientific Company has developed a new type of HgCdTe 1Kx1K detector, called WFC3-1R, with cutoff wavelength at 1.7μm and 150K operating temperature. The WFC3-IR detectors are based on HgCdTe MBE grown on a CdZnTe substrate and use a new type of multiplexer, the Hawaii-1R
MUX. Two flight detectors, a prime and a spare, have been recently selected on the basis of the measures performed at NASA Goddard Research Center - Detector Characterization Laboratory. These parts show quantum efficiency higher than 80% at λ=1.6μm and greater than 40% at λ>1.1μm, readout noise of ~25 e- rms with double correlated sampling, and mean dark current of ~0.04 e/s/pix at 150K. We show that the IR channel of WFC3, equipped with one of these flight detectors, beats the instrument requirements in all configurations and promises to have a discovery efficiency
significantly higher than NICMOS. In particular, a two-band
wide-area, deep survey made with WFC3 exceeds the discovery
efficiency of NICMOS before and after the installation of NCS
by a factor of 15 and 10, respectively.
A Hubble Space Telescope Wide Field Camera 3 (WFC3) CCD detector was tested for radiation effects while operating at -83°C. The detector has a format of 2048 x 2048 pixels with a 15 μm square pixel size, a supplemental buried channel, an MPP implant, and is back side illuminated. Detector response was tested for total radiation fluences ranging from 1x103 to 2.5x109 of 63.3 MeV protons/cm2 and for a
range of beam intensities. Radiation damage was investigated and the annealing of damage was tested by warming up to +30°C. The introduction rate of hot pixels and their statistics, hot pixel annealing as a function of temperature and time, and radiation changes to the mean value of dark current were investigated. Results are compared with the experiences of other HST instruments.
A Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) flight-like IR detector was tested for radiation hardness by exposing it to high energy protons while operating at the nominal flight temperature of 150 K. The detector is a 1.7 μm cutoff HgCdTe detector with a CdZnTe substrate. The device is hybridized to a silicon multiplexer. The detector response was tested for gradually increasing fluence from less than 1x103 to a total of 5x109 63 MeV protons/cm2. Dark current changes were evaluated after each step. An increase in dark current and new hot pixels were observed after large steps of irradiation. The increased dark current was observed to partially anneal at 190K and fully anneal at room temperature. Radiation effects, hot pixel distribution, and results of annealing at different temperatures are presented here.
Rockwell Scientific Company is developing a new type of HgCdTe 1K 1K detector, called WFC3-1R, with cutoff
wavelength at 1.7 m and 150K operating temperature. The detector will be installed on the Wide Field Camera 3, the
fourth generation panchromatic instrument for the Hubble Space Telescope (HST) to be installed during HST Servicing
Mission 4, currently scheduled for 2004. The detector uses HgCdTe MBE grown on a CdZnTe substrate and a new type
of multiplexer, the Hawaii-1R MUX. Six lots of detectors have been produced so far, and have demonstrated the
capability to meet or exceed the project requirements. In particular, detectors show quantum efficiency as high as ~90%
at =1.4-1.6 m and greater than 50% at >1.0 m, readout noise of 30 e- rms with double correlated sampling, and dark
current <0.2 e/s/pix at 150K. We illustrate the behavior of the reference pixels, showing that they allow the
compensation of drifts in the dc output level. A number of detectors show a peculiar instability related to the variations
of diode polarization, still under investigation. We also report on the environmental testing needed to qualify the WFC3-
1R detectors as suitable for flight on the HST. We finally provide an update of the project status.
The Wide Field Camera 3 (WFC3) is an instrument which is being developed for the Hubble Space Telescope. It will have a UV/VIS channel which will include two 2051 X 4096 pixel, thin, backside illuminated CCDs. These CCDs produce interference fringes in narrow band or monochromatic light images taken in the 700 nm to 1000 nm wavelength range. We have obtained 146 monochromatic images for each of the four flight candidate CCDs. These images can be used to model the physical structure of the CCD, which are described by a set of parameters deduced by solving the Fresnel equations for the absorption within the CCD as a function of wavelength. We have used the formalism developed to model the Space Telescope Imaging Spectrograph's CCD by Malumuth et. al. to determine the free parameters for a large portion of one of the WFC3 flight candidate CCDs. From these fits we are able to evaluate the ability to fit the fringing of real data by comparing a model fringe flat to an observed fringe flat. We find that we should be able to reduce the observed fringe amplitude by a factor of five or better. Finally we show that for a certain class of object (extended emission line object with a variety of radial velocities) this model is an excellent method for removing the effect of fringing.
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