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.
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.
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.
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 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.
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<sup>-</sup> total background signal.
Using the CCD Controller for Counting Photons (CCCP), the horizontal and vertical CIC, dark current and EM gain
stability are characterized.
Frequency multiplexed readout systems for large TES bolometer arrays are in use for ground and balloonbased
mm-wavelength telescopes. New digital backend electronics for these systems implement advanced signal
processing algorithms on FPGAs. Future satellite instruments will likely use similar technology. We address
the challenges of operating FPGAs in an orbital radiation environment using neighbour-neighbour monitoring,
where each FPGA monitors its neighbour and can correct errors due to radiation events. This approach reduces
the FPGA's susceptibility to crippling events without relying on triple redundancy or radiation-hardened parts,
which raise the system cost, power budget, and complexity. This approach also permits earlier adoption of the
latest FPGAs, since radiation-hardened variants typically lag the state of the art.
We present the prototyping results and laboratory characterization of a narrow band Fabry-Perot etalon flight model
which is one of the wavelength selecting elements of the Tunable Filter Imager. The latter is a part of the Fine Guidance
Sensor which represents the Canadian contribution to NASA's James Webb Space Telescope. The unique design of this
etalon provides the JWST observatory with the ability to image at 30 Kelvin, a 2.2'x2.2' portion of its field of view in a
narrow spectral bandwidth of R~100 at any wavelength ranging between 1.6 and 4.9 μm (with a gap in coverage
between 2.5 and 3.2 μm). Extensive testing has resulted in better understanding of the thermal properties of the
piezoelectric transducers used as an actuation system for the etalon gap tuning. Good throughput, spectral resolution and
contrast have been demonstrated for the full wavelength range.
Rapid advances in photonic and electro-optic technologies have given rise to sophisticated spaceborne optical instruments with important applications ranging from remote sensing to high-resolution hyperspectral imaging systems. This paper reviews past, present and future space missions employing Canadian optical instruments, discusses required detector technologies and their key performance parameters.