[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 deg<sup>2</sup> 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 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 Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square
degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be
used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. All components of
DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A
summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and
commissioning will be presented.
We describe the design and optimization of low-noise, single-stage output amplifiers for p-channel charge-coupled
devices (CCDs) used for scientific applications in astronomy and other fields. The CCDs are fabricated on highresistivity,
4000-5000 Ω-cm, n-type silicon substrates. Single-stage amplifiers with different output structure
designs and technologies have been characterized. The standard output amplifier is designed with an n<sup>+</sup> polysilicon
gate that has a metal connection to the sense node. In an effort to lower the output amplifier readout
noise by minimizing the capacitance seen at the sense node, buried-contact technology has been investigated. In
this case, the output transistor has a p<sup>+</sup> polysilicon gate that connects directly to the p<sup>+</sup> sense node. Output
structures with buried-contact areas as small as 2 μm × 2 μm are characterized. In addition, the geometry of the
source-follower transistor was varied, and we report test results on the conversion gain and noise of the various
amplifier structures. By use of buried-contact technology, better amplifier geometry, optimization of the amplifier
biases and improvements in the test electronics design, we obtain a 45% reduction in noise, corresponding to
1.7 e- rms at 70 kpixels/sec.
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
Mission concepts for NASA's Wide Field Infrared Survey Telescope (WFIRST)<sup>1,2</sup>, ESA's Euclid<sup>3,4</sup> 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
The Dark Energy Survey Camera (DECam) will be comprised of a mosaic of 74 charge-coupled devices (CCDs). The
Dark Energy Survey (DES) science goals set stringent technical requirements for the CCDs. The CCDs are provided by
LBNL with valuable cold probe data at 233 K, providing an indication of which CCDs are more likely to pass. After
comprehensive testing at 173 K, about half of these qualify as science grade. Testing this large number of CCDs to
determine which best meet the DES requirements is a very time-consuming task. We have developed a multistage
testing program to automatically collect and analyze CCD test data. The test results are reviewed to select those CCDs
that best meet the technical specifications for charge transfer efficiency, linearity, full well capacity, quantum efficiency,
noise, dark current, cross talk, diffusion, and cosmetics.
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.
The Dark Energy Camera is an wide field imager currently
under construction for the Dark Energy Survey.
This instrument will use fully depleted 250 μm thick
CCD detectors selected for their higher quantum efficiency
in the near infrared with respect to thinner devices.
The detectors were developed by LBNL using
high resistivity Si substrate. The full set of scientific
detectors needed for DECam has now been fabricated,
packaged and tested. We present here the results of
the testing and characterization for these devices and
compare these results with the technical requirements
for the Dark Energy Survey.
The Dark Energy Survey Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 520
Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to
perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. Construction of
DECam is well underway. Integration and testing of the major system components has already begun at Fermilab and
the collaborating institutions.
Fully depleted, back-illuminated, p-channel CCDs developed at Lawrence Berkeley National Laboratory exhibit high
quantum efficiency in the near-infrared (700-1050nm), low fringing effects, low lateral charge diffusion (and hence
small, well-controlled point spread function), and high radiation tolerance. Building on previous efforts, we have
developed techniques and hardware that have produced space-qualified 4-side abuttable, high-precision detector
packages for 10.5μm pixel, 3.5k x 3.5k p-channel LBNL CCDs. These packages are built around a silicon carbide
mounting pedestal, providing excellent rigidity, thermal stability, and heat transfer. Precision fixturing produces
packages with detector surface flatness better than 10μm P-V. These packages with active areas of 36.8mm square may
be packed on a detector pitch as small as 44mm. LBNL-developed Front End Electronics (FEE) packages can mount
directly to the detector packages within the same footprint and detector pitch. This combination, along with identically
interfaced NIR detector/FEE packages offers excellent opportunities for high density, high pixel count focal planes for
space-based, ground-based, and airborne astronomy.
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.
We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey.
DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo
International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector,
five filters (g,r,i,z,Y), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of
62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of
view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley
National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms,
and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.
A description of the plans and infrastructure developed for CCD testing and characterization for the DES focal plane detectors is presented. Examples of the results obtained are shown and discussed in the context of the device requirements for the survey instrument.
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-<i>R</i> ≥QE, where R is the reflectivity. Over a significant wavelength range, 1-<i>R</i> = QE. An unconventional reflectometer has been developed to make this measurement. <i>R</i> 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 <i>R</i>. 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 - <i>R</i> 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.
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.
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.
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.
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.
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.
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 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 <i>AB</i>=27.7 in each of the SNAP filters, spanning 3500-17000Å. Co-adding images over all epochs will give <i>AB</i>=30.3 per filter. In addition, a 300 square-degree field will be surveyed to <i>AB</i>=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 <i>n</i>-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.