The Skipper is a special type of charge-coupled device (CCD) that allows pixel measurements with sub-electron noise levels due to its non-destructive readout operation. Over the last decade, these sensors have been used as particle detectors on a variety of experiments, such as the direct detection of galactic dark matter and neutrino experiments. Skipper CCD achieves low-noise by reading multiple times, and sequentially, the pixel charge packet, which translates to longer readout times. This becomes a limiting factor for those applications that require sub-electron detection and faster readout speeds. A novel analysis method for reducing the total pixel readout time is presented in this work. The method relies on analyzing the time-domain properties of the video signal including the clock feedthroughs and their shapes to optimize the clock transitions that define the pixel. The analysis technique is experimentally demonstrated using a standard scientific detector and also with a Skipper CCD with single photon sensitivity. In both cases the sensors are operated and readout using the Low Threshold Acquisition (LTA) controller with an updated firmware for faster clock sequencing. A good compromise between noise performance and total readout time was achieved. This will allows the use of the Skipper CCD and/or the LTA for astronomy, quantum imaging, and other applications that require faster readout times than previous uses of the sensor and the controller.
We present the development of a Skipper Charge-Coupled Device (CCD) focal plane prototype for the SOAR Telescope Integral Field Spectrograph (SIFS). This mosaic focal plane consists of four 6k × 1k, 15 μm pixel Skipper CCDs mounted inside a vacuum dewar. We describe the process of packaging the CCDs so that they can be easily tested, transported, and installed in a mosaic focal plane. We characterize the performance of ∼ 650μm thick, fully-depleted engineering-grade Skipper CCDs in preparation for performing similar characterization tests on science-grade Skipper CCDs which will be thinned to 250μm and backside processed with an antireflective coating. We achieve a single-sample readout noise of 4.5 e− rms/pix for the best performing amplifiers and subelectron resolution (photon counting capabilities) with readout noise σ ∼ 0.16 e− rms/pix from 800 measurements of the charge in each pixel. We describe the design and construction of the Skipper CCD focal plane and provide details about the synchronized readout electronics system that will be implemented to simultaneously read 16 amplifiers from the four Skipper CCDs (4-amplifiers per detector). Finally, we outline future plans for laboratory testing, installation, commissioning, and science verification of our Skipper CCD focal plane.
The development of the Skipper-charge-coupled devices (Skipper-CCDs) has been a major technological breakthrough for sensing very weak ionizing particles. The sensor allows to reach the ultimate sensitivity of silicon material as a charge signal sensor by unambiguous determination of the charge signal collected by each cell or pixel, even for single electron–hole pair ionization. Extensive use of the technology was limited by the lack of specific equipment to operate the sensor at the ultimate performance. A simple, single-board Skipper-CCD controller designed by the authors is presented and aimed for the operation of the detector in high sensitivity scientific applications. Our article describes the main components and functionality of the so-called low threshold acquisition controller together with experimental results when connected to a Skipper-CCD sensor. Measurements show unprecedented deep subelectron noise of 0.039 erms−/pix by nondestructively measuring the charge 5000 times in each pixel.
We present a fully-automated CCD testbench. The system performs all the tests in about 12 hours, and when done reduces the data, grading the device and presenting the results in the form of both a pdf report and web-based tables . All the data goes automatically to a database where both the raw and processed data can be visualized and compared with other devices, allowing for detector statistical graphs (number of devices over certain threshold in any given parameter, etc). The testbench was developed in the context of a FermiLab and CTIO collaboration for the packaging and characterization of the red and NIR science ccds for the Dark Energy Spectroscopic Instrument (DESI), where over 40 devices were tested. The system was further expanded at CTIO to be used with any ccd or detector controller. The characterization includes non-linearity (high and low), full well, flats and darks cosmetics (hot and dark pixels, bad columns,etc), dark current, noise, CTE, absolute QE and lateral diffusion.
The recently commissioned Dark Energy Spectroscopic Instrument (DESI) will measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sqdeg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope delivers light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. A consortium of Aix-Marseille University (AMU) and CNRS laboratories (LAM, OHP and CPPM) together with LPNHE (CNRS, IN2P3, Sorbonne Université and Université de Paris) and the WINLIGHT Systems company based in Pertuis (France), were in charge of integrating and validating the performance requirements of the ten full spectrographs, equipped with their cryostats, shutters and other mechanisms. We present a summary of our activity which allowed an efficient validation of the systems in a short-time schedule. We detail the main results. We emphasize the benefits of our approach and also its limitations.
We characterize the response of a novel 250 µm thick, fully-depleted Skipper Charged-Coupled Device (CCD) to visible/near-infrared light with a focus on potential applications for astronomical observations. We achieve stable, single-electron resolution with readout noise σ 0.18 e− rms/pix from 400 non-destructive measurements of the charge in each pixel. We verify that the gain derived from photon transfer curve measurements agrees with the gain calculated from the quantized charge of individual electrons to within < 1%. We also perform relative quantum efficiency measurements and demonstrate high relative quantum efficiency at optical/near- infrared wavelengths, as is expected for a thick, fully depleted detector. Finally, we demonstrate the ability to perform multiple non-destructive measurements and achieve sub-electron readout noise over configurable sub- regions of the detector. This work is the first step toward demonstrating the utility of Skipper CCDs for future astronomical and cosmological applications.
The Skipper-CCDs, a special type of charge-coupled device (CCD) sensor that features sub-electron readout noise levels, was proposed decades ago. However, only in recent years it has been possible to develop large size Skipper-CCDs ensuring stable operation. Their extreme low noise operation makes them suitable for experiments that require low thresholds and high energy resolution, such as dark matter and neutrino interactions detection, and more recently quantum-imaging and astronomy. New experiments are planning to use kilograms of active silicon from Skipper-CCDs as sensitive mass. In this way, they can achieve extremely low detection thresholds and a high probability of particle interaction. However, this approach needs arrays of thousands of Skipper- CCDs operating at the same time imposing challenging requirements. Also, introduction of this technology in astronomy and quantum-imaging applications requires a large number of channels per sensor to speed up the readout. The front-end needs to be redesigned from scratch: it must achieve low noise performance, be simple for easy integration and allow the routing of thousands of channels out of the sensors with minimal connections. This paper presents a detailed analysis of options for the front-end electronics and their noise performance. It describes a novel way of using a dual-slope integrator with minimal components to pile up the charge of consecutive readouts of the same pixel in a concept that we call a multi-slope integrator. This reduces drastically the output bandwidth, simplifying the wiring and the warm electronics. These proposals will allow the generation of new scientific instruments based on Skippers-CCD arrays.
H. Diehl, T. M. Abbott, J. Annis, R. Armstrong, L. Baruah, A. Bermeo, G. Bernstein, E. Beynon, C. Bruderer, E. Buckley-Geer, H. Campbell, D. Capozzi, M. Carter, R. Casas, L. Clerkin, R. Covarrubias, C. Cuhna, C. D'Andrea, L. da Costa, R. Das, D. DePoy, J. Dietrich, A. Drlica-Wagner, A. Elliott, T. Eifler, J. Estrada, J. Etherington, B. Flaugher, J. Frieman, A. Fausti Neto, M. Gelman, D. Gerdes, D. Gruen, R. Gruendl, J. Hao, H. Head, J. Helsby, K. Hoffman, K. Honscheid, D. James, M. Johnson, T. Kacprzac, J. Katsaros, R. Kennedy, S. Kent, R. Kessler, A. Kim, E. Krause, R. Kron, S. Kuhlmann, A. Kunder, T. Li, H. Lin, N. Maccrann, M. March, J. Marshall, E. Neilsen, P. Nugent, P. Martini, P. Melchior, F. Menanteau, R. Nichol, B. Nord, R. Ogando, L. Old, A. Papadopoulos, K. Patton, D. Petravick, A. Plazas, R. Poulton, A. Pujol, K. Reil, T. Rigby, A. Romer, A. Roodman, P. Rooney, E. Sanchez Alvaro, S. Serrano, E. Sheldon, A. Smith, R. Smith, M. Soares-Santos, M. Soumagnac, H. Spinka, E. Suchyta, D. Tucker, A. Walker, W. Wester, M. Wiesner, H. Wilcox, R. Williams, B. Yanny, Y. Zhang
The Dark Energy Survey (DES) is a next generation optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES started its first observing season on August 31, 2013 and observed for 105 nights through mid-February 2014. This paper describes DES “Year 1” (Y1), the strategy and goals for the first year's data, provides an outline of the operations procedures, lists the efficiency of survey operations and the causes of lost observing time, provides details about the quality of the first year's data, and hints at the “Year 2” plan and outlook.
Scientific CCD detectors are typically readout using the Correlated Double Sampling (CDS) technique. At low
pixel rates, noise of ~2e- RMS is typically achieved. The limitation for reaching lower noise comes from the 1/f
component on the output of the CCD, and this noise cannot be eliminated using CDS. A new readout technique
based on a digital filter is presented here for suppressing the 1/f. Using this new technique a noise of 0.4e- is
achieved.
The Dark Energy Survey CCD imager was constructed at the Fermi National Accelerator Laboratory and delivered to
the Cerro Tololo Inter-American Observatory in Chile for installation onto the Blanco 4m telescope. Several efforts are
described relating to preparation of the instrument for transport, development and testing of a shipping crate designed to
minimize transportation loads transmitted to the camera, and inspection of the imager upon arrival at the observatory.
Transportation loads were monitored and are described. For installation of the imager at the telescope prime focus,
where it mates with its previously-installed optical corrector, specialized tooling was developed to safely lift, support,
and position the vessel. The installation and removal processes were tested on the Telescope Simulator mockup at
FNAL, thus minimizing technical and schedule risk for the work performed at CTIO. Final installation of the imager is
scheduled for August 2012.
The Dark Energy Camera and its cooling system has been shipped to Cerro Tololo Inter-American Observatory in Chile
for installation onto the Blanco 4m telescope. Along with the camera, the cooling system has been installed in the Coudé
room at the Blanco Telescope. Final installation of the cooling system and operations on the telescope is planned for the
middle of 2012. Initial commissioning experiences and cooling system performance is described.
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.
The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO.
This instrument is a 2.2 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k
CCDs and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. DECam includes the
vessel shell, the optical window cell, the CCDs with their readout electronics and vacuum interface, the focal plane
support plate and its mounts, and the cooling system and thermal controls. Assembly of the imager, alignment of the
focal plane and installation of the CCDs are described. During DECam development a full scale prototype was used for
multi-CCD readout tests. This test vessel went through several stages as the CCDs and related hardware progressed
from early prototypes to final production designs.
The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO. This
instrument is a 3 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k CCDs
and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. The DECam CCD array is
inside the imager vessel. The focal plate is cooled using a closed loop liquid nitrogen system. As part of the development
of the mechanical and cooling design, a full scale prototype imager vessel has been constructed and is now being used
for Multi-CCD readout tests. The cryogenic cooling system and thermal controls are described along with cooling
results from the prototype camera. The cooling system layout on the Blanco telescope in Chile is described.
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.
Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely
red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty
two 4k2k and twelve 2k2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and
a eld of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will
cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from
2011.
To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down
for the design of DECam. Among them, the
atness of the focal plane needs to be controlled within a 60-micron
envelope in order to achieve the specied PSF variation limit. It is very challenging to measure the
atness of
the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image
based techniques to measure the
atness of the focal plane. By imaging a regular grid of dots on the focal plane,
the CCD oset along the optical axis is converted to the variation the grid spacings at dierent positions on the
focal plane. After extracting the patterns and comparing the change in spacings, we can measure the
atness
to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal
plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the
pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by dierent
CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are
in good agreement with the direct optical measurements.
The Dark Energy Camera is a new prime-focus instrument to be delivered to the Blanco 4-meter telescope at the Cerro
Tololo Inter-American Observatory (CTIO) in 2011. Construction is in-progress at this time at Fermilab. In order to
verify that the camera meets technical specifications for the Dark Energy Survey and to reduce the time required to
commission the instrument while it is on the telescope, we are constructing a "Telescope Simulator" and performing full
system testing prior to shipping to CTIO. This presentation will describe the Telescope Simulator and how we use it to
verify some of the technical specifications.
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.
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.
We describe the results obtained cleaning the surface of DECam CCD detectors with a new electrostatic dissipative
formulation of First ContactTM polymer from Photonic Cleaning Technologies. We demonstrate that
cleaning with this new product is possible without ESD damage to the sensors and without degradation of the
antireflective coating used to optimize the optical performance of the detector. We show that First ContactTM
is more effective for cleaning a CCD than the commonly used acetone swab.
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.
KEYWORDS: Charge-coupled devices, Clocks, Electronics, CCD cameras, Cameras, Stars, Silicon, Field programmable gate arrays, Energy efficiency, Control systems
The Dark Energy Camera will be comprised of 74 CCDs with high efficiency out to a wavelength of 1 micron.
The CCDs will be read out by a Monsoon-based system consisting of three boards: Master Control, CCD
Acquisition, and Clock boards. The charge transfer efficiency (CTE) is closely related to the clock waveforms
provided by the Clock Board (CB). The CB has been redesigned to meet the stringent requirements of the Dark
Energy Survey. The number of signals provided by the clock board has been extended from 32 (the number
required for 2 CCDs) up to 135 signals (the number required for 9 CCDs). This modification is required to fit
the electronics into the limited space available on the imager vessel. In addition, the drivers have been changed
to provide more current. The first test result with the new clock board shows a clear improvement in the CTE
response when reading out at the higher frequencies required for the guide CCDs.
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.
DECam, camera for the Dark Energy Survey (DES), is undergoing general design and component testing.
For an overview see DePoy, et al in these proceedings. For a description of the imager, see Cease, et al in
these proceedings. The CCD instrument will be mounted at the prime focus of the CTIO Blanco 4m
telescope. The instrument temperature will be 173K with a heat load of 113W. In similar applications,
cooling CCD instruments at the prime focus has been accomplished by three general methods. Liquid
nitrogen reservoirs have been constructed to operate in any orientation, pulse tube cryocoolers have been used
when tilt angles are limited and Joule-Thompson or Stirling cryocoolers have been used with smaller heat
loads. Gifford-MacMahon cooling has been used at the Cassegrain but not at the prime focus. For DES, the
combined requirements of high heat load, temperature stability, low vibration, operation in any orientation,
liquid nitrogen cost and limited space available led to the design of a pumped, closed loop, circulating
nitrogen system. At zenith the instrument will be twelve meters above the pump/cryocooler station. This
cooling system expected to have a 10,000 hour maintenance interval. This paper will describe the
engineering basis including the thermal model, unbalanced forces, cooldown time, the single and two-phase
flow model.
The Dark Energy Survey is planning to use a 3 sq. deg. camera that houses a ~ 0.5m diameter focal plane of 62 2k×4k
CCDs. The camera vessel including the optical window cell, focal plate, focal plate mounts, cooling system and thermal
controls is described. As part of the development of the mechanical and cooling design, a full scale prototype camera
vessel has been constructed and is now being used for multi-CCD readout tests. Results from this prototype camera are
described.
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.
The Dark Energy Survey Camera focal plane array will consist of 62 2k x 4k CCDs with a pixel size of 15 microns and
a silicon thickness of 250 microns for use at wavelengths between 400 and 1000 nm. Bare CCD die will be received
from the Lawrence Berkeley National Laboratory (LBNL). At the Fermi National Accelerator Laboratory, the bare die
will be packaged into a custom back-side-illuminated module design. Cold probe data from LBNL will be used to
select the CCDs to be packaged. The module design utilizes an aluminum nitride readout board and spacer and an Invar
foot. A module flatness of 3 microns over small (1 sqcm) areas and less than 10 microns over neighboring areas on a
CCD are required for uniform images over the focal plane. A confocal chromatic inspection system is being developed
to precisely measure flatness over a grid up to 300 x 300 mm. This system will be utilized to inspect not only room-temperature
modules, but also cold individual modules and partial arrays through flat dewar windows.
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