The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14,000 sq. deg. will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the ProtoDESI experiment, planned for installation and commissioning at the Mayall telescope in the fall of 2016, which will test the fiber positioning system for DESI. The ProtoDESI focal plate, consisting of 10 fiber positioners, illuminated fiducials, and a guide, focus and alignment (GFA) sensor module, will be installed behind the existing Mosaic prime focus corrector. A Fiber View Camera (FVC) will be mounted to the lower surface of the primary mirror cell and a subset of the Instrument Control System (ICS) will control the ProtoDESI subsystems, communicate with the Telescope Control System (TCS), and collect instrument monitoring data. Short optical fibers from the positioners will be routed to the back of the focal plane where they will be imaged by the Fiber Photometry Camera (FPC) or back-illuminated by a LED system. Target objects will be identified relative to guide stars, and using the GFA in a control loop with the ICS/TCS system, the guide stars will remain stable on pre-identified GFA pixels. The fiber positioners will then be commanded to the target locations and placed on the targets iteratively, using the FVC to centroid on back-illuminated fibers and fiducials to make corrective delta motions. When the positioners are aligned with the targets on-sky, the FPC will measure the intensities from the positioners’ fibers which can then be dithered to look for intensity changes, indicating how well the fibers were initially positioned on target centers. The final goal is to operate ProtoDESI on the Mayall telescope for a 6-hour period during one night, successfully placing targets on the intended fibers for the duration of a typical DESI science exposure.
The Dark Energy Spectroscopic Instrument (DESI) is under construction and will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation (BAO) technique and the growth of structure using redshift-space distortions (RSD). The spectra of 30 million galaxies over 14000 sq deg will be measured over the course of the experiment. In order to provide spectroscopic targets for the DESI survey, we are carrying out a three-band (g,r,z ) imaging survey of the sky using the NOAO 4-m telescopes at Kitt Peak National Observatory (KPNO) and the Cerro Tololo Interamerican Observatory (CTIO). At KPNO, we will use an upgraded version of the Mayall 4m telescope prime focus camera, Mosaic3, to carry out a z-band survey of the Northern Galactic Cap at declinations δ≥+30 degrees. By equipping an existing Dewar with four 4kx4k fully depleted CCDs manufactured by the Lawrence Berkeley National Laboratory (LBNL), we increased the z-band throughput of the system by a factor of 1.6. These devices have the thickest active area fielded at a telescope. The Mosaic3 z-band survey will be complemented by g-band and r-band observations using the Bok telescope and 90 Prime imager on Kitt Peak. We describe the upgrade and performance of the Mosaic3 instrument and the scope of the northern survey.
In this work we describe efforts to reduce the read noise in fully depleted, scientific charge-coupled devices (CCDs). The read noise is proportional to the total capacitance at the floating-diffusion node. Reductions in the capacitance at the floating diffusion are accomplished by implementing a direct contact between the output transistor, polysilicon-gate electrode and the floating diffusion. We have previously reported promising results for this technology that were measured on small-format CCDs with 4-channel readout where each channel had a different output transistor geometry. In this work we present the results of the use of this technology on 12 and 16-channel, large-format CCDs in order to determine the reproducibility of the process. The contact size for this work is two microns by two microns, and projection lithography was used to print the contacts. We have also utilized selective wafer-stepper lithography to generate contacts that are one micron on a side. We also describe efforts in the device design of the output transistor to further reduce the noise.
The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w0) and its evolution with redshift (wa) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS1) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.
The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar spectroscopic redshift survey. The DESI instrument consists of a new wide-field (3.2 deg. linear field of view) corrector plus a multi-object spectrometer with up to 5000 robotically positioned optical fibers and will be installed at prime focus on the Mayall 4m telescope at Kitt Peak, Arizona. The fibers feed 10 three-arm spectrographs producing spectra that cover a wavelength range from 360-980 nm and have resolution of 2000-5500 depending on the wavelength. The DESI instrument is designed for a 14,000 sq. deg. multi-year survey of targets that trace the evolution of dark energy out to redshift 3.5 using the redshifts of luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars. DESI is the successor to the successful Stage-III BOSS spectroscopic redshift survey and complements imaging surveys such as the Stage-III Dark Energy Survey (DES, currently operating) and the Stage-IV Large Synoptic Survey Telescope (LSST, planned start early in the next decade).
The Zwicky Transient Facility (ZTF) is a synoptic optical survey for high-cadence time-domain astronomy. Building
upon the experience and infrastructure of the highly successful Palomar Transient Factory (PTF) team, ZTF will survey
more than an order of magnitude faster than PTF in sky area and volume in order to identify rare, rapidly varying optical
sources. These sources will include a trove of supernovae, exotic explosive transients, unusual stellar variables,
compact binaries, active galactic nuclei, and asteroids. The single-visit depth of 20.4 mag is well matched to
spectroscopic follow-up observations, while the co-added images will provide wide sky coverage 1.5 – 2 mag deeper
than SDSS. The ZTF survey will cover the entire Northern Sky and revisit fields on timescales of a few hours, providing
hundreds of visits per field each year, an unprecedented cadence, as required to detect fast transients and
variability. This high-cadence survey is enabled by an observing system based on a new camera having 47 deg2 field of
view – a factor of 6.5 greater than the existing PTF camera - equipped with fast readout electronics, a large, fast
exposure shutter, faster telescope and dome drives, and various measures to optimize delivered image quality. Our
project has already received an initial procurement of e2v wafer-scale CCDs and we are currently fabricating the camera
cryostat. International partners and the NSF committed funds in June 2014 so construction can proceed as planned to
commence engineering commissioning in 2016 and begin operations in 2017. Public release will allow broad utilization
of these data by the US astronomical community. ZTF will also promote the development of transient and variable
science methods in preparation for the seminal first light of LSST.
[The BigBOSS experiment is a redshift survey designed to map the large scale structure of the universe and probe the nature of dark energy. Using massively-multiplexed _ber spectroscopy over 14,000 deg2 of sky, the survey will deliver more than 20 million galaxy and quasar redshifts. The resulting three dimensional sky map will contain signatures from primordial baryon acoustic oscillations (BAO) that set a "standard ruler" distance scale. Using the BAO signature, BigBOSS will measure the cosmological distance scale to < 1% accuracy from 0.5<z<3.0, shedding new light on the expansion history and growth of large scale structure in the Universe at a time when dark energy began to dominate. In this work, we give an overview of the BigBOSS survey goals and methodology, focusing on measuring the [O II] λ3727 emission line doublet from star-forming galaxies. We detail a new spectral simulation tool used in generating BigBOSS observations for emission-line galaxy targets. We perform a trade study of the detected galaxy redshift distribution under two observational cases relative to the baseline survey and discuss the impact on the BigBOSS science goal.
We describe work at Lawrence Berkeley National Laboratory (LBNL) to develop enhanced performance, fully
depleted, back-illuminated charge-coupled devices for astronomy and astrophysics. The CCDs are fabricated on
high-resistivity substrates and are typically 200–300 μm thick for improved near-infrared response. The primary
research and development areas include methods to reduce read noise, increase quantum efficiency and readout
speed, and the development of fabrication methods for the efficient production of CCDs for large focal planes.
In terms of noise reduction, we will describe technology developments with our industrial partner Teledyne
DALSA Semiconductor to develop a buried-contact technology for reduced floating-diffusion capacitance, as well
as efforts to develop ”skipper” CCDs with sub-electron noise utilizing non-destructive readout amplifiers allowing
for multiple sampling of the charge packets. Improvements in quantum efficiency in the near-infrared utilizing
ultra-high resistivity substrates that allow full depletion of 500 μm and thicker substrates will be described, as
well as studies to improve the blue and UV sensitivity by investigating the limits on the thickness of the back-side
ohmic contact layer used in the LBNL technology. Improvements in readout speed by increasing the number of
readout ports will be described, including work on high frame-rate CCDs for x-ray synchrotrons with as many as
192 amplifiers per CCD. Finally, we will describe improvements in fabrication methods, developed in the course
of producing over 100 science-grade 2k × 4k CCDs for the Dark Energy Survey Camera.
BigBOSS is a proposed ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the
growth of structure with a 14,000 square degree galaxy and quasi-stellar object redshift survey. It consists of a 5,000-
fiber-positioner focal plane feeding the spectrographs. The optical fibers are separated into ten 500 fiber slit heads at the
entrance of ten identical spectrographs in a thermally insulated room. Each of the ten spectrographs has a spectral
resolution (λ/Δλ) between 1500 and 4000 over a wavelength range from 360 - 980 nm. Each spectrograph uses two
dichroic beam splitters to separate the spectrograph into three arms. It uses volume phase holographic (VPH) gratings for
high efficiency and compactness. Each arm uses a 4096x4096 15 μm pixel charge coupled device (CCD) for the
detector. We describe the requirements and current design of the BigBOSS spectrograph. Design trades (e.g. refractive
versus reflective) and manufacturability are also discussed.
Throughput of a fiber-robot-based multi-object spectrograph depends on the accuracy and precision of the fiber position
system. An efficient and accurate method of quantifying the performance of an actuator is necessary during the design
iteration process, final design, and for post-production characterization. A CCD camera-based optical setup was
developed at the Lawrence Berkeley National Laboratory to test these parameters of fiber robot positioners. The setup is
described, as well as tests used to quantify distortion and cross-check measurement by smart scope.
BigBOSS is a proposed ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the
growth of large scale structure. It consists of a fiber-fed multi-object spectrograph designed to be installed on the Mayall
4-meter telescope at Kitt Peak, Arizona. BigBOSS includes an optical corrector assembly and 5000-fiber-positioner
focal plane assembly that replace the existing Mayall prime focus hardware. 40-meter long optical fiber bundles are
routed from the focal plane, through the telescope declination and right ascension pivots, to spectrographs in the
thermally insulated FTS Laboratory, immediately adjacent to the telescope. Each of the ten spectrographs includes three
separate spectral bands. The FTS Laboratory also houses support electronics, cooling, and vacuum equipment. The
prime focus assembly includes mounts for the existing Mayall f/8 secondary mirror to allow observations with
Cassegrain instruments. We describe the major elements of the BigBOSS instrument, plans for integrating with the
Telescope, and proposed modifications and additions to existing Mayall facilities.
BigBOSS is a Stage IV dark energy experiment based on proven techniques to study baryon acoustic oscillations and the growth of large scale structure. The 2010 Astronomy and Astrophysics Decadal Survey labeled dark energy as a key area of exploration. BigBOSS is designed to perform a 14,000 square degree survey of 20 million galaxies and quasi-stellar objects. The project involves installation of a new instrument on the Mayall 4m telescope, operated by the National Optical
Astronomy Observatory. The instrument includes a new optical widefield corrector, a 5,000 fiber actuator system, and a multi-object spectrometer. Systems engineering flowdown from data set requirements to instrument requirements are discussed, along with the trade considerations and a pre-conceptual baseline design of the widefield optical corrector, spectrometer and fiber positioner systems.
The BigBOSS experiment is a proposed DOE-NSF Stage IV dark energy survey. The all sky survey will be used
to study the baryon acoustic oscillation (BAO) and growth of large scale structure from 0.2 < z < 3.5. Key to
the timely success of BigBOSS is the total optical throughput of the system. The guide, focus/alignment system
will provide essential pointing information,
eld acquisition, atmospheric monitoring and alignment corrections
all used to maximize light throughput.
The BigBOSS instrument is a proposed multi-object spectrograph for the Mayall 4m telescope at Kitt Peak, which will
measure the redshift of 20 million galaxies and map the expansion history of the universe over the past 8 billion years,
surveying 10-20 times the volume of existing studies. For each 20 minute observation, 5000 optical fibers are
individually positioned by a close-packed array of 5000 robotic positioner mechanisms. Key mechanical constraints on
the positioners are: ø12mm hardware envelope, ø14mm overlapping patrol zones, open-loop targeting accuracy ≤ 40μm,
and step resolution ≤ 5μm, among other requirements on envelope, power, stability, and speed. This paper describes the
design and performance of a newly-developed fiber positioner with R-θ polar kinematics, in which a flexure-based linear
R-axis is stacked on a rotational θ-axis. Benefits over the usual eccentric parallel axis θ-φ kinematic approach include
faster repositioning, simplified anti-collision schemes, and inherent anti-backlash preload. Performance results are given
for complete positioner assemblies as well as sub-component hardware characterization.
BigBOSS is a proposed DOE-NSF Stage IV ground-based dark energy experiment designed to study
baryon acoustic oscillations (BAO) and the growth of large scale structure with a 14,000 square
degree survey of the redshifts of galaxies and quasi-stellar objects. The project involves
modification of existing facilities operated by the National Optical Astronomy Observatory
(NOAO). Design and systems engineering of a preliminary 3 degree field of view refractive
corrector, atmospheric dispersion corrector (ADC), and 5000 actuator fiber positioning system are
We describe a non-contact optical measurement method used to determine the surface flatness of a cryogenic sensor
array developed for the JDEM mission. Large focal planes envisioned for future visible to near infra-red astronomical
large area point-source surveys such as JDEM, WFIRST, or EUCLID must operate at cryogenic temperatures while
maintaining focal plane flatness within a few 10's of μm over half-meter scales. These constraints are imposed by
sensitivity conditions that demand low noise observations from the sensors and the large-field, fast optical telescopes
necessary to obtain the science yield. Verifying cryogenic focal plane flatness is challenging because μm level
excursions need to be measured within and across many multi-cm sized sensors using no physical contact and while
situated within a high-vacuum chamber. We have used an optical metrology Shack-Hartmann scheme to measure the
36x18 cm focal plane developed for the JDEM mission at the Lawrence Berkeley National Laboratory. The focal plane
holds a 4x8 array of CCDs and HgCdTe detectors. The flatness measurement scheme uses a telescope-fed micro-lens
array that samples the focal plane to determine slope changes of individual sensor zones.
Mission concepts for NASA's Wide Field Infrared Survey Telescope (WFIRST)1,2, ESA's Euclid3,4 mission, as well as
next-generation ground-based surveys require large mosaic focal planes sensitive in both visible and near infrared (NIR)
wavelengths. We have developed space-qualified detectors, readout electronics and focal plane design techniques that
can be used to intermingle CCDs and NIR detectors on a single, silicon carbide (SiC) cold plate. This enables optimized,
wideband observing strategies. The CCDs, developed at Lawrence Berkeley National Laboratory, are fully-depleted, pchannel
devices that are backside illuminated and capable of operating at temperatures down to 120K. The NIR
detectors are 1.7 μm and 2.0 μm wavelength cutoff H2RG® HgCdTe, manufactured by Teledyne Imaging Sensors under
contract to LBNL. Both the CCDs and NIR detectors are packaged on 4-side abuttable SiC pedestals with a common
mounting footprint supporting a 44 mm mosaic pitch. Both types of detectors have direct-attached readout electronics
that convert the detector signal directly to serial, digital data streams and allow a flexible, low cost data acquisition
strategy to enable large data rates. A mosaic of these detectors can be operated at a common temperature that achieves
the required dark current and read noise performance necessary for dark energy observations. We report here the
qualification testing and performance verification for a focal plane that accommodates a 4x8 array of CCDs and HgCdTe
We have developed a design for packaging Charged Coupled Devices (CCDs) for use as optical imaging devices for
space applications, although the design is also useful for any large ground-based mosaic. We have constructed and
assembled prototype packages using this design. Testing of these prototypes has demonstrated that these packaged
CCDs are flight worthy. The design, construction, and testing of these prototypes are described in this article.
Charge trapping in bulk silicon lattice structures is a source of charge transfer inefficiency (CTI) in CCDs. These
traps can be introduced into the lattice by low-energy proton radiation in the space environment, decreasing the
performance of the CCD detectors over time. Detailed knowledge of the inherent trap properties, including energy
level and cross section, is important for understanding the impact of the defects on charge transfer as a function
of operating parameters such as temperature and clocking speeds. This understanding is also important for
mitigation of charge transfer inefficiency through annealing, software correction, or improved device fabrication
techniques. In this paper, we measure the bulk trap properties created by 12.5 MeV proton irradiation on
p+ channel, full-depletion CCDs developed at LBNL. Using the pocket pumping technique, we identify the
majority trap populations responsible for CTI in both the parallel and serial transfer processes. We find the
dominant parallel transfer trap properties are well described by the silicon lattice divacancy trap, in agreement
with other studies. While the properties of the defects responsible for CTI in the serial transfer are more difficult
to measure, we conclude that divacancy-oxygen defect centers would be efficient at our serial clocking rate and
exhibit properties consistent with our serial pocket pumping data.
We compare a more complete characterization of the low temperature performance of a nominal 1.7um cut-off
wavelength 1kx1k InGaAs (lattice-matched to an InP substrate) photodiode array against similar, 2kx2k HgCdTe
imagers to assess the suitability of InGaAs FPA technology for scientific imaging applications. The data we present
indicate that the low temperature performance of existing InGaAs detector technology is well behaved and comparable
to those obtained for state-of-the-art HgCdTe imagers for many space astronomical applications. We also discuss key
differences observed between imagers in the two material systems.
Precision near infrared (NIR) measurements are essential for the next generation of ground and space based instruments. The SuperNova Acceleration Probe (SNAP) will measure thousands of type Ia supernovae up to a redshift of 1.7. The highest redshift supernovae provide the most leverage for determining cosmological parameters, in particular the dark energy equation of state and its possible time evolution. Accurate NIR observations are needed to utilize the full potential of the highest redshift supernovae. Technological improvements in NIR detector fabrication have lead to high quantum efficiency, low noise detectors using a HgCdTe diode with a band-gap that is tuned to cutoff at 1.7 μm. The effects of detector quantum efficiency, read noise, and dark current on lightcurve signal to noise, lightcurve parameter errors, and distance modulus fits are simulated in the SNAPsim framework. Results show that improving quantum efficiency leads to the largest gains in photometric accuracy for type Ia supernovae. High quantum efficiency in the NIR reduces statistical errors and helps control systematic uncertainties at the levels necessary to achieve the primary SNAP science goals.
We present the results of a detailed study of the noise performance of candidate NIR detectors for the proposed Super-Nova Acceleration Probe. Effects of Fowler sampling depth and frequency, temperature, exposure time, detector material, detector reverse-bias and multiplexer type are quantified. We discuss several tools for determining which sources of low frequency noise are primarily responsible for the sub-optimal noise improvement when multiple sampling, and the selection of optimum fowler sampling depth. The effectiveness of reference pixel subtraction to mitigate zero point drifts is demonstrated, and the circumstances under which reference pixel subtraction should or should not be applied are examined. Spatial and temporal noise measurements are compared, and a simple method for quantifying the effect of hot pixels and RTS noise on spatial noise is described.
We present the results of a study of the performance of InGaAs detectors conducted for the SuperNova Acceleration
Probe (SNAP) dark energy mission concept. Low temperature data from a nominal 1.7um cut-off wavelength 1kx1k
InGaAs photodiode array, hybridized to a Rockwell H1RG multiplexer suggest that InGaAs detector performance is
comparable to those of existing 1.7um cut-off HgCdTe arrays. Advances in 1.7um HgCdTe dark current and noise
initiated by the SNAP detector research and development program makes it the baseline detector technology for SNAP.
However, the results presented herein suggest that existing InGaAs technology is a suitable alternative for other future
Large format (1k × 1k and 2k × 2k) near infrared detectors manufactured by Rockwell Scientific Center and Raytheon Vision Systems are characterized as part of the near infrared R&D effort for SNAP (the Super-Nova/Acceleration Probe). These are hybridized HgCdTe focal plane arrays with a sharp high wavelength cut-off at 1.7 μm. This cut-off provides a sufficiently deep reach in redshift while it allows at the same time low dark current operation of the passively cooled detectors at 140 K. Here the baseline SNAP near infrared system is briefly described and the science driven requirements for the near infrared detectors are summarized. A few results obtained during the testing of engineering grade near infrared devices procured for the SNAP project are highlighted. In particular some recent measurements that target correlated noise between adjacent detector pixels due to capacitive coupling and the response uniformity within individual detector pixels are discussed.
We describe charge-coupled device (CCD) development activities at the Lawrence Berkeley National Laboratory (LBNL). Back-illuminated CCDs fabricated on 200-300 μm thick, fully depleted, high-resistivity silicon substrates are produced in partnership with a commercial CCD foundry. The CCDs are fully depleted by the application of a substrate bias voltage. Spatial resolution considerations require operation of thick, fully depleted CCDs at high substrate bias voltages. We have developed CCDs that are compatible with substrate bias voltages of at least 200V. This improves spatial resolution for a given thickness, and allows for full depletion of thicker CCDs than previously considered. We have demonstrated full depletion of 650-675 μm thick CCDs, with potential applications in direct x-ray detection. In this work we discuss the issues related to high-voltage operation of fully depleted CCDs, as well as experimental results on high-voltage-compatible CCDs.
The usual QE measurement heavily relies on a calibrated photodiode (PD) and the knowledge of the CCD's gain. Either can introduce significant systematic errors. But 1-R ≥QE, where R is the reflectivity. Over a significant wavelength range, 1-R = QE. An unconventional reflectometer has been developed to make this measurement. R is measured in two steps, using light from the lateral monochromator port via an optical fiber. The beam intensity is measured directly with a PD, then both the PD and CCD are moved so that the optical path length is unchanged and the light reflects once from the CCD; the PD current ratio is R. Unlike the traditional VW scheme this approach makes only one reflection from the CCD surface. Since the reflectivity of the LBNL CCDs might be as low as 2% this increases the signal to noise ratio dramatically. The goal is a 1% accuracy. We obtain good agreement between 1 - R and the direct QE results.
Instrumentation was developed in 2004 and 2005 to measure the quantum efficiency of the Lawrence Berkeley National Lab (LBNL) total-depletion CCD's, intended for astronomy and space applications. This paper describes the basic instrument. Although it is conventional even to the parts list, there are important innovations. A xenon arc light source was chosen for its high blue/UV and low red/IR output as compared with a tungsten light. Intensity stabilization has been difficult, but since only flux ratios matter this is not critical. Between the light source and an Oriel MS257 monochromator are a shutter and two filter wheels. High-bandpass and low-bandpass filter pairs isolate the 150-nm wide bands appropriate to the wavelength, thus minimizing scattered light and providing order blocking. Light from the auxiliary port enters a 20-inch optical sphere, and the 4-inch output port is at right angles to the input port. An 80 cm drift space produces near-uniform illumination on the CCD. Next to the cold CCD inside the horizontal dewar is a calibrated reference photodiode which is regulated to the PD calibration temperature, 25° C. The ratio of the CCD and in-dewar reference PD signals provides the QE measurement. Additional cross-calibration to a PD on the integrating sphere permits lower-intensity exposures.
We present new characterization results for a large format, 15 um pixel pitch, 2kx4k format, p-channel CCD fabricated on high resistivity silicon at Lawrence Berkeley National Laboratory. The fully-depleted device is 300 um thick and backside illuminated utilizing 4-side buttable packaging. We report on measurements of standard operating characteristics including charge transfer efficiency, readout noise, cosmetics performance, dark current, and well depth. We have also made preliminary measurements of the device's X-Ray energy resolution and tests of device linearity.
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Iz supernovae and to standardize the magnitude of each candidate by determining explosion parameters. The spectrograph is also a key element for the calibration of the science mission. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.
Mission requirements, the baseline design, and optical systems budgets for the SuperNova/Acceleration Probe (SNAP) telescope are presented. SNAP is a proposed space-based experiment designed to study dark energy and alternate explanations of the acceleration of the universe’s expansion by performing a series of complementary systematics-controlled astrophysical measurements. The goals of the mission are a Type Ia supernova Hubble diagram and a wide-field weak gravitational lensing survey. A 2m widefield three-mirror telescope feeds a focal plane consisting of 36 CCDs and 36 HgCdTe detectors and a high-efficiency, low resolution integral field spectrograph. Details of the maturing optical system, with emphasis on structural stability during terrestrial testing as well as expected environments during operations at L2 are discussed. The overall stray light mitigation system, including illuminated surfaces and visible objects are also presented.
The status of CCD development efforts at Lawrence Berkeley National
Laboratory is reviewed. Fabrication technologies for the production
of back-illuminated, fully depleted CCD's on 150 mm diameter wafers
are described. In addition, preliminary performance results for
high-voltage compatible CCD's, including a 3512 x 3512, 10.5 μm
pixel CCD for the proposed SuperNova Acceleration Probe project, are presented.
We have developed a precision, 4-side buttable CCD package for 2kx2k and 2kx4k format devices with minimal mechanical stress on the CCD, excellent thermal properties, reliable electrical connectivity, and shim-free mounting. We report on the package design, assembly and quality assurance procedures, measurements of packaged device flatness and flatness excursions when cooled from room temperature to 140 K, package performance and plans for future development.
We present the baseline telescope design for the telescope for the SuperNova/Acceleration Probe (SNAP) space mission. SNAP’s purpose is to determine expansion history of the Universe by measuring the redshifts, magnitudes, and spectral classifications of thousands of supernovae with unprecedented accuracy. Discovering and measuring these supernovae demand both a wide optical field and a high sensitivity throughout the visible and near IR wavebands. We have adopted the annular-field three-mirror anastigmat (TMA) telescope configuration, whose classical aberrations (including chromatic) are zero. We show a preliminary optmechanical design that includes important features for stray light control and on-orbit adjustment and alignment of the optics. We briefly discuss stray light and tolerance issues, and present a preliminary wavefront error budget for the SNAP Telescope. We conclude by describing some of the design tasks being carried out during the current SNAP research and development phase.
An overview of CCD development efforts at Lawrence Berkeley National
Laboratory is presented. Operation of fully-depleted, back-illuminated CCD's fabricated on high resistivity silicon is described, along with results on the use of such CCD's at ground-based observatories. Radiation damage and point-spread function measurements are described, as well as discussion of CCD fabrication technologies.
The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square degree field in the visible and near-infrared wavelength regime. The requirements for the instrument suite and the present configuration of the focal plane concept are presented. A two year R&D phase, largely supported by the Department of Energy, is just beginning. We describe the development activities that are taking place to advance our preparedness for mission proposal in the areas of detectors and electronics.
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Ia supernovae and to standardize the magnitude of each candidate by determining explosion parameters. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have very high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.
The SuperNova/Acceleration Probe (SNAP) will measure precisely the cosmological expansion history over both the acceleration and deceleration epochs and thereby constrain the nature of the dark energy that dominates our universe today. The SNAP focal plane contains equal areas of optical CCDs and NIR sensors and an integral field spectrograph. Having over 150 million pixels and a field-of-view of 0.34 square degrees, the SNAP NIR system will be the largest yet constructed. With sensitivity in the range 0.9-1.7 μm, it will detect Type Ia supernovae between z = 1 and 1.7 and will provide follow-up precision photometry for all supernovae. HgCdTe technology, with a cut-off tuned to 1.7 μm, will permit passive cooling at 140 K while maintaining noise below zodiacal levels. By dithering to remove the effects of intrapixel variations and by careful attention to other instrumental effects, we expect to control relative photometric accuracy below a few hundredths of a magnitude. Because SNAP continuously revisits the same fields we will be able to achieve outstanding statistical precision on the photometry of reference stars in these fields, allowing precise monitoring of our detectors. The capabilities of the NIR system for broadening the science reach of SNAP are discussed.
The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square-degree field sensitive in the visible and near-infrared wavelength regime. We describe the requirements for the instrument suite and the evolution of the focal plane design to the present concept in which all the instrumentation -- visible and near-infrared imagers, spectrograph, and star guiders -- share one common focal plane.
The Supernova / Acceleration Probe (SNAP) is a proposed space-borne observatory that will survey the sky with a wide-field optical/near-infrared (NIR) imager. The images produced by SNAP will have an unprecedented combination of depth, solid-angle, angular resolution, and temporal sampling. For 16 months each, two 7.5 square-degree fields will be observed every four days to a magnitude depth of AB=27.7 in each of the SNAP filters, spanning 3500-17000Å. Co-adding images over all epochs will give AB=30.3 per filter. In addition, a 300 square-degree field will be surveyed to AB=28 per filter, with no repeated temporal sampling. Although the survey strategy is tailored for supernova and weak gravitational lensing observations, the resulting data will support a broad range of auxiliary science programs.
The SuperNova/Acceleration Probe (SNAP) mission will require a two-meter class telescope delivering diffraction limited images spanning a one degree field in the visible and near infrared wavelength regime. This requirement, equivalent to nearly one billion pixel resolution, places stringent demands on its optical system in terms of field flatness, image quality, and freedom from chromatic aberration. We discuss the advantages of annular-field three-mirror anastigmat (TMA) telescopes for applications such as SNAP, and describe the features of the specific optical configuration that we have baselined for the SNAP mission. We discuss the mechanical design and choice of materials for the telescope. Then we present detailed ray traces and diffraction calculations for our baseline optical design. We briefly discuss stray light and tolerance issues, and present a preliminary wavefront error budget for the SNAP Telescope. We conclude by describing some of tasks to be carried out during the upcoming SNAP research and development phase.
The SuperNova / Acceleration Probe (SNAP) is a space-based experiment to measure the expansion history of the Universe and study both its dark energy and the dark matter. The experiment is motivated by the startling discovery that the expansion of the Universe is accelerating. A 0.7~square-degree imager comprised of 36 large format fully-depleted n-type CCD's sharing a focal plane with 36 HgCdTe detectors forms the heart of SNAP, allowing discovery and lightcurve measurements simultaneously for many supernovae. The imager and a high-efficiency low-resolution integral field spectrograph are coupled to a 2-m three mirror anastigmat wide-field telescope, which will be placed in a high-earth orbit. The SNAP mission can obtain high-signal-to-noise calibrated light-curves and spectra for over 2000 Type Ia supernovae at redshifts between z = 0.1 and 1.7. The resulting data set can not only determine the amount of dark energy with high precision, but test the nature of the dark energy by examining its equation of state. In particular, dark energy due to a cosmological constant can be differentiated from alternatives such as "quintessence", by measuring the dark energy's equation of state to an accuracy of ± 0.05, and by studying its time dependence.
A new type of p-channel CCD constructed on high-resistivity n-type silicon was exposed to 12 MeV protons at doses up to 1 X 1011 protons/cm2. The charge transfer efficiency was measured as a function of radiation dose and temperature. We previously reported that these CCDs are significantly more tolerant to radiation damage than conventional n-channel devices. In the work reported here, we used pocket pumping techniques and charge transfer efficiency measurements to determine the identity and concentrations of radiation induced traps present in the damaged devices.