Electron-multiplying charge-coupled devices (EMCCDs) allow for subelectron effective read noise and thus for imaging at extremely low flux levels. In the ultraviolet, quantum yield creates an additional source of stochastic gain variation, which can be difficult to quantify using existing techniques. We propose a method for measuring the quantum yield gain of these devices, independent of existing methods, using images that are part of the existing test regimen for new EMCCDs. With this method, we were able to recover the quantum yield used to create simulated images within an accuracy of ∼5 % and the method provided consistent results with test images after only minor modifications. However, the measured quantum yield remains anomalously low, consistent with other measurements on Teledyne-e2v devices. We hypothesize that this discrepancy is due to lateral transfer of secondary electrons between pixels at the surface explained by the band structure and crystal geometry of typical silicon wafers used in array detector manufacture.
We present the status of on-going detector development efforts for our joint NASA/Centre National d’Études Spatiales balloon-borne UV multiobject spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2; FB-2). FB-2 demonstrates a UV detector technology, the delta-doped electron-multiplying CCD (EMCCD), in a low-risk suborbital environment, to prove the performance of EMCCDs for future space missions and technology readiness level advancement. EMCCDs can be used in photon-counting mode to achieve extremely low readout noise (<1 electron). Our testing has focused on reducing clock-induced-charge (CIC) through wave shaping and well-depth optimization with a Nüvü V2 CCCP controller, measuring CIC at 0.001 e − / pixel / frame. This optimization also includes methods for reducing dark current, via cooling, and substrate voltage levels. We discuss the challenges of removing cosmic rays, which are also amplified by these detectors, as well as a data reduction pipeline designed for our noise measurement objectives. FB-2 flew in 2018, providing the first time an EMCCD, was used for UV observations in the stratosphere. FB-2 is currently being built up to fly again in 2020, and improvements are being made to the EMCCD to continue optimizing its performance for better noise control.
Electron multiplying charged coupled devices (EMCCD’s) can provide significantly greater signal to noise ratios in low light conditions and/or for higher speed readout than traditional CCDs. Due to the electron multiplication before readout, the effective readout noise can be at the sub-electron level, enabling single photon counting. Traditional far UV (150 – 200 nm) imaging detectors have utilized micro-channel plates to detect usually scarce UV photons at low efficiency, amplify them into electron showers which strike a phosphor, allowing a silicon detector array to perform the final detection of the resulting visible light pulse. The typical efficiencies of UV photo detection with MCP systems ranges from a low of a few percent to as high as 25%. Given that the theoretical probability of absorption of UV photons in silicon is at least 30% in this wavelength range, then it should be possible to make use of a photon counting EMCCD to directly detect UV photons that is competitive with MCP performance. We approached Teledyne-e2v and they confirmed that a backside thinned EMCCD with their ‘astro no-coat’ process should provide reasonable quantum efficiency (ie. > 30%) in this range. The primary application in which we are interested is UV imaging of the aurora from space-based platforms. In this application there are system level advantages to replacing an MCP based detector with an EMCCD which is directly sensitive to UV illumination, namely the elimination of a high voltage power supply and higher spatial resolution. An MCP produces an electron shower which degrades image quality and also requires a relatively thick detector window which has to be accommodated in the imager optical design. We acquired five CCD201 engineering model EMCCDs with e2v’s ‘astro no-coat’ process, and incorporated one of these into a standard flexible liquid nitrogen cooled EMCCD camera produced by Nüvü Camēras. Once installed the EMCCD operation was confirmed with standard Nüvü Camēras test procedures. The camera was then mounted in a test vacuum chamber along with a McPherson UV monochromator so that the UV performance could be assessed. A NIST traceable photodiode was used for the absolute calibration. The resulting intrinsic QE was found to be 34% at 180 nm rising to 44% at 150 nm. The quantum yield was found to be quite low, only a few percent at 180 nm rising to only 1.13-1.18 at 150 nm. This is considerably lower than comparable results from CCDs where delta-doping has been used to improve the responsive quantum efficiency and also lower than a Teledyne-e2v CMOS sensor with the same surface treatment.
HiCIBaS-LOWFS is a spatially modulated pyramid wavefront sensor to be used on the HiCIBaS project, a high-contrast imaging balloon borne telescope, as a fine pointing and atmospheric turbulence sensor. Since the project will be using a relatively small telescope on a limited budget, creative solutions must be developed to respond to the requirements for such systems. For example, we need a linear response to large error in order to be able to correct for pointing error in a photon-limited regime caused by the telescope small size. Most solutions aren't well suited for the optical design in HiCIBaS since the high-contrast coronagraph and the Low-Order Wavefront Sensor (LOWFS) both run as separate instruments. The design is centered around the modification of existing pyramid wavefront sensor by adding static, spatial modulation to an otherwise unmodulated system. The spatial modulation is achieved by adding an axicon (a conical optical element) at an imaged telescope pupil plane. This has for effect to add a very large non- common path aberration between the imaging plane and the wavefront sensor. This has for effect to shape the point-spread function incident on the pyramid to a ring shape, which minimize diffraction effect on the apex of imperfect pyramids. We present the first lab results involving the wavefront sensor and its performances for wavefront reconstruction and pointing accuracy. We also discuss the first on-sky results that were recorded with the 1.6-m telescope at the Observatoire du Mont-Megantic in Qubec, Canada using Universite Lavals optical AO test-bench. These results pave the way to the design and integration of the wavefront sensor in the context of the HiCIBaS project.
The HiCIBaS (High-Contrast Imaging Balloon System) project aims at launching a balloon borne telescope up to 36km to test high contrast imaging equipment and algorithms. The payload consists of a off the shelf 14-inch telescope with a custom-built Alt-Az mount. This telescope provides lights to two sensors, a pyramidal low order wave front sensor, and a coronagraphic wavefront sensor. Since the payload will reach its cruise altitude at about midnight mission, two target stars have been designated for observations, Capella as the night target, and Polaris as the early morning target. Data will be collected mainly on the magnitude of atmospheric and gondola’s turbulences, the luminosity of the background. The whole system is already built and ready to ship to Timmins for the launch in mid-August 2018.
We present the progress in characterization of a Nuv¨ u Cam ¨ eras CCD Controller for Counting Photons ¯ (CCCP) designed for extreme low light imaging in space environment with the 1024×1024 Teledyne-e2V EMCCD detector (the CCD201-20). The EMCCD controller was designed using space qualified parts before being extensively tested in thermal vacuum. The performance test results include the readout noise, clock-induced charges, dark current, dynamic range and EM gain. We also discuss the CCCP’s integration in the coronagraph of the High-Contrast Imaging Balloon System project: a fine-pointing and optical payload for a future Canadian stratospheric balloon mission. This first space qualified EMCCD controller, named CCCPs, will enhance sensitivity of the future low-light imaging instruments for space applications such as the detection, characterization and imaging of exoplanets, search and monitoring of asteroids and space debris, UV imaging, and satellite tracking.
Scientific EMCCD cameras have demonstrated excellent imaging performance under extreme low light conditions. Photon counting capability combined with a very low dark current offered by the CCD technology have made EMCCDs the detector of choice for high-performance applications such as time resolved spectroscopy and low light imaging. However, future astronomical instrumentation requires high spatial resolution while commercially available EMCCD devices are limited by a relatively modest area format of (1kx1k). To address this requirement, the Universitė de Montrėal and Teledyne-e2v have jointly developed a 4kx4k EMCCD, the CCD282. This paper presents the results of cryogenic characterization of the CCD282 operated with Nüvü Camēras’ CCD Controller for Counting Photons version 3. The advantages of a novel large format EMCCD over existing technology for high resolution spectroscopy are discussed.
We report on the proton radiation effects on a 1k x 1k e2v EMCCD utilized in the Nüvü EM N2 1024 camera. Radiation testing was performed at the TRIUMF Proton Irradiation Facility in Canada, where the e2v CCD201-20 EMCCD received a 105 MeV proton fluence up to 5.2x109 protons/cm2, emulating a 1 year’s radiation dose of solar protons in low earth orbit with nominal shielding that would be expected from a small or microsatellite. The primary space-based application is for Space Situational Awareness (SSA), where a small telescope images faint orbiting Resident Space Objects (RSOs) on the EMCCD, resulting in faint streaks at the photon level of signal in the images. Of particular concern is the effect of proton radiation on low level CTE, where very low level signals could be severely impaired if not lost. Although other groups have reported on the characteristics of irradiated EMCCDs, their CTE results are not portable to this application. To understand the real impact of proton irradiation the device must be tested under realistic operating conditions with representative backgrounds, clock periods, and signal levels. Testing was performed both in the laboratory and under a night sky on the ground in order to emulate a complex star background environment containing RSOs. The degradation is presented and mitigation techniques are proposed. As compared to conventional CCDs, the EMCCD with high gain allows faint and moving RSOs to be detected with a relatively small telescope aperture, at improved signal to noise ratio at high frame rates. This allows the satellite platform to take sharp images immediately upon slewing to the target without the need for complex and relatively slow attitude stabilization systems.
WFIRST-AFTA is the NASA’s highest ranked astrophysics mission for the next decade that was identified in the New
World, New Horizon survey. The mission scientific drivers correspond to some of the deep questions identified in the
Canadian LRP2010, and are also of great interest for the Canadian scientists. Given that there is also a great interest in
having an international collaboration in this mission, the Canadian Space Agency awarded two contracts to study a
Canadian participation in the mission, one related to each instrument. This paper presents a summary of the technical
contributions that were considered for a Canadian contribution to the coronagraph and wide field instruments.
EMCCDs are capable of MHz pixel rate whilst maintaining sub-electron readout noise. Tens of frames per second are common place for large and medium EMCCD formats (1k×1k, 512×512), while smaller formats can reach hundreds and even thousand of frames per second. For applications where speed is a key factor, overclocked EMCCD were used at or beyond the manufacturer’s specifications. Very few data were published on the impacts of high speed clocking of EMCCDs, either vertically or horizontally. This paper presents characterization results of EMCCDs clocked at high speed.
Several post-processing methods were proposed to overcome the excess noise factor induced by EMCCD multiplication register. Each method has a unique effect on SNR. However, since SNR does not account for photometric accuracy, it cannot be reliably used to directly compare the performance of these algorithms. A normalized quadratic error that accounts for both SNR and accuracy is proposed as an alternative figure of merit. This approach provides a quantitative and rigorous comparison. Using both experimental and simulated frames in the faint-flux range, it is used to compare the existing EMCCD post-processing methods.
Astronomical imaging is always limited by the detection system signal-to-noise ratio (SNR). EMCCD cameras offer many advantages for low light applications, such as sub-electron read-out noise, and low dark current with appropriate cooling. High frame rate achieved with these devices is often employed for the enhancement of SNR by acquiring and stacking multiple short exposures instead of one long exposure. EMCCDs are also suitable for applications requiring very long exposures, even when only a few photons are detected per hour. During long exposure acquisitions with a conventional CCD, slower pixel rates are usually employed to reduce the read-out noise, which dominates the CCD noise budget. For EMCCD cameras, this approach may not result in the lowest possible total noise and the effect of increasing the total exposure time may not yield the highest possible SNR for a given total integration time. In this paper, we present and discuss the experimental results obtained with an EMCCD camera that has been optimized for taking long exposures (from several seconds to several hours) of low light-level targets. These results helped to ascertain an EMCCD camera best operating parameters for long exposure astronomical imaging.
The Cosmological Advanced Survey Telescope for Optical and UV Research (CASTOR) is a proposed Canadian Space Agency (CSA) mission that would provide panoramic, high-resolution imaging of 1/8th of the sky in the UV/optical (150-550 nm) spectral region. This small-satellite class mission would provide high angular resolution ultra-deep imaging in three broad filters to supplement data from planned international dark energy missions (Euclid, WFIRST) as well as from the Large Synoptic Survey Telescope (LSST). One of the leading technical risks on this mission is the UV sensitivity required to approach 26th magnitude in the near UV band. We are planning to characterize a selected candidate technology down to 150 nm. We will review the main scientific and technical drivers for the mission and show how they constrain the available detector options. We will compare the sensitivity and general applicability of CCD, EMCCD, hybridized and monolithic CMOS FPA options.
The rapid proliferation of Electron Multiplying Charge Coupled Devices (EMCCDs) in recent years has revolutionized
low light imaging applications. EMCCDs in particular show promise to enable the construction of versatile space
astronomy instruments while space-based observations enable unique capabilities such as high-speed accurate
photometry due to reduced sky background and the absence of atmospheric scintillation. The Canadian Space Agency is
supporting innovation in EMCCD technology by increasing its Technology Readiness Level (TRL) aimed at reducing
risk, cost, size and development time of instruments for future space missions. This paper will describe the advantages of
EMCCDs compared to alternative low light imaging technologies. We will discuss the specific issues associated with
using EMCCDs for high-speed photon counting applications in astronomy. We will show that a careful design provided
by the CCD Controller for Counting Photons (CCCP) makes it possible to operate the EMCCD devices at rates in excess
of 10 MHz, and that levels of clock induced charge and dark current are dramatically lower than those experienced with
commercial cameras. The results of laboratory characterization and examples of astronomical images obtained with
EMCCD cameras will be presented. Issues of radiation tolerance, charge transfer efficiency at low signal levels and life
time effects on the electron-multiplication gain will be discussed in the context of potential space applications.
Multimodal imaging is quickly becoming a standard in pre-clinical studies, and new developments have already confirmed the strength of acquiring and analyzing parallel information obtained in a single imaging session. One such application is the introduction of an internal reference moiety (e.g. radioisotope) to an activatable fluorescent probe. One of the limitations of this approach consists of working at concentrations which are within the overlapping range of sensitivities of each modality. In the case of PET/Fluorescence imaging, this range is in the order of 10-9 nM. Working in epi-illumination fluorescence imaging at such concentrations remains challenging. Here, we present in vitro and in vivo detection limits of a new fluorescent compound.
EMCCDs are capable of extreme low light imaging thanks to sub-electron read-out noise, enabling single-photon counting.
The characterization of e2v's CCD60 (128 x 128), CCD97 (512 x 512) and CCD201-20 (1024 x 1024) using a controller
optimized for the driving of EMCCDs at a high (≥10 MHz) pixel rate per output with < 0.002 e- total background signal.
Using the CCD Controller for Counting Photons (CCCP), the horizontal and vertical CIC, dark current and EM gain
stability are characterized.
We present in this paper a performance characterization of an Electron Multiplication CCD (EMCCD) camera which has
been deployed on the Brazilian Tunable Filter Imager (BTFI) instrument for the SOAR telescope in Chile. The BTFI
instrument has two e2v CCD207 EMCCDs with a format of 1600-by-1600 pixels. The CCD207s are full-frame devices
and are read out at a pixel rate of 10MHz with very low noise using an EMCCD controller (the CCD Controller for
Counting Photons or CCCP for short) which was custom-built by a group based in the University of Montreal and is now
commercialized by Nüvü Camēras. The first laboratory characterizations were done in Montreal in October, 2011 and the
"first-light" results with the camera operating at the telescope are presented.
In this paper we present the cryogenic design of the EMCCD (Electron Multiplication Charged Couple Device) cameras
for the Brazilian Tunable Filter Imager instrument for the 4 meters SOAR telescope in Chile. The camera uses a E2V
1600 × 1600 pixels full-frame device, which is controlled by the new CCCP (CCD Controller for Counting Photons), an
EMCCD controller developed by the University of Montreal. We present the design of the camera, its thermal analysis
and cryogenic performance.
EMCCDs are devices capable of sub-electron read-out noise at high pixel rate, together with a high quantum efficiency
(QE). However, they are plagued by an excess noise factor (ENF) which has the same effect on photometric measurement
as if the QE would be halved. In order to get rid of the ENF, the photon counting (PC) operation is mandatory, with the
drawback of counting only one photon per pixel per frame. The high frame rate capability of the EMCCDs comes to the
rescue, at the price of increased clock induced charges (CIC), which dominates the noise budget of the EMCCD. The CIC
can be greatly reduced with an appropriate clocking, which renders the PC operation of the EMCCD very efficient for faint
flux photometry or spectroscopy, adaptive optics, ultrafast imaging and Lucky Imaging. This clocking is achievable with
a new EMCCD controller: CCCP, the CCD Controller for Counting Photons. This new controller, which is now commercialized
by Nüvü cameras inc., was integrated into an EMCCD camera and tested at the observatoire du mont-M'egantic.
The results are presented in this paper.
Proc. SPIE. 7536, Sensors, Cameras, and Systems for Industrial/Scientific Applications XI
KEYWORDS: Signal to noise ratio, Human-machine interfaces, Photon counting, Clocks, Cameras, Video, Data acquisition, Electron multiplying charge coupled devices, Charge-coupled devices, Data communications
In order to make faint flux imaging efficient with an EMCCD, the Clock Induced Charges (CIC) must be reduced to a minimum.
Some techniques were proposed to reduce the CIC but until now, neither commercially available CCD controller
nor commercial cameras were able to implement them and get satisfying results. CCCP, the CCD Controller for Counting
Photons, has been designed with the aim of reducing the CIC generated when an EMCCD is read out. It is optimized for
driving EMCCDs at high speed (≥ 10MHz), but may be used also for driving conventional CCDs (or the conventional
output of an EMCCD) at high, moderate, or low speed. This new controller provides an arbitrary clock generator, yielding
a timing resolution of ~20 ps and a voltage resolution of ~2mV of the overlap of the clocks used to drive the EMCCD.
The frequency components of the clocks can be precisely controlled, and the inter-clock capacitance effect of the CCD can
be nulled to avoid overshoots and undershoots. Using this controller, CIC levels as low as 0.001 - 0.002 ¯e per pixel per
frame were measured on a 512×512 CCD97 operating in inverted mode, at an EM gain of ~2000. This is 5 to 10 times
less than what is usually seen in commercial EMCCD cameras using the same EMCCD chip.
The 3D-NTT is a visible integral field spectro-imager offering two modes. A low resolution mode (R ~ 300 to 6 000)
with a large field of view Tunable Filter (17'x17') and a high resolution mode (R ~ 10 000 to 40 000)
with a scanning Fabry-Perot (7'x7'). It will be operated as a visitor instrument on the NTT from 2009.
Two large programmes will be led: "Characterizing the interstellar medium of nearby galaxies with 2D maps of
extinction and abundances" (PI M. Marcelin) and "Gas accretion and radiative feedback in the early universe" (PI J.
Bland Hawthorn). Both will be mainly based on the Tunable Filter mode. This instrument is being built as a
collaborative effort between LAM (Marseille), GEPI (Paris) and LAE (Montreal). The website adress of the instrument
is : http://www.astro.umontreal.ca/3DNTT
Proc. SPIE. 7014, Ground-based and Airborne Instrumentation for Astronomy II
KEYWORDS: Signal to noise ratio, Photon counting, Clocks, Photons, Quantum efficiency, Interference (communication), Signal processing, Electron multiplying charge coupled devices, Charge-coupled devices, Temperature metrology
CCCP, a CCD Controller for Counting Photons, is presented. This new controller uses a totally new clocking architecture
and allows to drive the CCD in a novel way. Its design is optimized for the driving of EMCCDs at up to 20MHz of pixel
rate and fast vertical transfer. Using this controller, the dominant source of noise of EMCCDs at low flux level and high
frame rate, the Clock Induced Charges, were reduced to 0.001 - 0.0018 electron/pixel/frame (depending of the electron
multiplying gain), making efficient photon counting possible. CCCP will be deployed in 2009 on the ESO NTT through
the 3D-NTT1 project and on the SOAR through the BTFI project.
An entirely new type of imaging tunable filter has been developed by Photon etc. and the California Institute of Technology. The Volume Bragg Grating based device is able to select a single wavelength for each pixel in a full camera field. The demonstration tabletop prototype was able to select images with a 2 nm bandwidth from 400 to 750 nm. Data cubes were produced through a wavelength scan from which a spectrum per pixel can be extracted. The prototype showed no image distortion, a very stable instrument profile, and high efficiency. The compact and robust tunable filter can operate from 350 nm to 2.5 mm with bandwidths from 3 Å to 200 nm, showing a great potential for both ground based and space astronomy.
Proc. SPIE. 6276, High Energy, Optical, and Infrared Detectors for Astronomy II
KEYWORDS: Signal to noise ratio, Photon counting, Digital signal processing, Quantum efficiency, Interference (communication), Numerical simulations, Amplifiers, Signal processing, Electron multiplying charge coupled devices, Charge-coupled devices
Thorough numerical simulations were run to test the performance of three processing methods of the data coming out from an electron multiplying charge coupled device (EMCCD), or low light level charge coupled device (L3CCD), operated at high gain, under real operating conditions. The effect of read-out noise and spurious charges is tested under various low flux conditions (0.001 event/pixel/frame< f < 20 events/pixel/frame). Moreover, a method for finding the value of the gain applied by the EMCCD amplification register is also developed. It allows one to determine the gain value to an accuracy of a fraction of a percent from dark frames alone.
Theoretically, L3CCDs are perfect photon counting devices promising high quantum efficiency (~90%) and sub-electron readout noise (σ<0.1 e-). We discuss how a back-thinned 512x512 frame-transfer L3CCD (CCD97) camera operating in pure photon counting mode would behave based on experimental data. The chip is operated at high electromultiplication gain, high analogic gain and high frame rate. Its performance is compared with a modern photon counting camera (GaAs photocathode, QE ~28%) to see if L3CCD technology, in its current state, could supersede photocathode-based devices.