Photon counting pioneers
As pioneers, astronomers always aim at the foremost innovation in imaging technologies. Over the past centuries, they ensured the field’s constant progress in their never-ending discovery of the cosmos. Within only five years, Nüvü Camēras’ EMCCD and photon counting technologies have successfully paired up with leading international research groups.
The NASA Goddard Space Flight Center and the University of Maryland conclude that Nüvü Camēras is conservative when reporting its product specifications.
What’s more, the colossal potential of this technology is starting to emerge, and yet needs to be fully grasped. The following EMCCD applications are only the tip of the iceberg.
Nüvü Camēras’ EM N2 camera at Mont Mégantic Observatory (Canada).
Higher SNR for overcoming research frontiers
New instruments designed and optimized for Nüvü Camēras’ cutting edge technology are generating certain interest for the conception of versatile space astronomy instruments.
To learn more about spaceborne applications considered for Nüvü™’ EMCCD technology, read the article linked below, courtesy of Canadian Space Agency’s Dr. Oleg Djazovski.
ABB Inc. presented the proposed Canadian Technologies for the Coronograph of the WFIRST space mission.
ABB Inc., presented the Canadian contributions study for the coronagraph instrument of the WFIRST mission.
COM DEV, presented the effect of radiation on the EMCCD detector for future space mission.
Leon K. Harding, from the Jet Propulsion Laboratory, presented the characterization results of Nüvü’s EMCCD camera by considering the unique challenges of the WFIRST space environment.
Technology advancement of the CCD201-20 EMCCD for the WFIRST coronograph instrument Click on the + signs for more details.
EMCCD ADVANTAGES FOR FUTURE SPACE APPLICATIONS
Direct exoplanet observation
Nearly 2000 extrasolar planets have been identified, most being Jupiter- and Neptune-class. Yet astronomers believe it is just the tip of the iceberg: recent studies predict an average of one planet per star in the Milky Way. Nevertheless, most exoplanet detections are indirect and based on star monitoring for minute luminosity changes induced by its planetary companion (see the Transient Photometry section). In the quest to uncover more Earth twins, astronomers now turn themselves to direct observation, studying their host’s light reflected onto their surface by masking the star’s brightness with a coronagraph.
10 billion star to planet light contrast
Such emission is extremely weak. A Jupiter-like planet’s is about 100,000 times dimmer than its host. For Earth analogs, their brightness drops even more, being 10 billion times lesser than the nearby star. Direct exoplanet imaging or spectroscopy thus calls for a device capable of detecting the few photons emitted from the planet’ surface that reach us, and they are scarce.
Higher sensitivities to discover new Earths
Direct extrasolar planet observation requires the most sensitive sensor there is, and Nüvü Camēras’ technology is perfectly suited for such demanding application. Nüvü™’s revolutionary CCCP technology ensures the lowest clock-induced charge levels while its innovative packaging guarantees minimal dark current. The result is a camera that can detect every photon of an Earth-like planet that may support life.
Demonstration: WFIRST project
Results from the Jet Propulsion Laboratory’s characterization of the EMCCD for the space mission WFIRST were obtained thanks to Nüvü™’s EM N2 camera. WFIRST is a NASA observatory designed to settle essential questions as in the area of exoplanets amongst others.
Demonstration: MAPLE project
Christian Marois from the National Research Council of Canada presented a stratospheric balloon project, known under the name Mission to Find a Planet Like Earth (MAPLE), to acquire images of exoplanets using the HNü 512 and 1024 by Nüvü Caméras.
Characterisation of the HNü 512 camera by Nüvü
Ashlee Wilkins, from the University of Maryland, shared the results of the characterisation of the HNü 512 from Nüvü Caméras, obtained in collaboration with the Goddard Space Flight Center by NASA.
Characterisation of the ATLAST detector needs
Bernard J. Rauscher, of the NASA Goddard Space Flight Center, presented the results of the characterisation of the needs of the ATLAST detector for a spatial mission.
Asteroid and Spatial Debris Monitoring
With the increase of spatial missions, a strong density of spatial debris has accumulated in the terrestrial atmosphere. In order to protect infrastructures that are in orbit, such as telecommunications satellites, there exists a growing demand for the monitoring of such debris.
Further, at times at the borders of our solar system, the orbits of certain asteroids and comets can cross that of Earth. These objects, also known as Near Earth-Objects (NEO), will threaten life as we know it if they ever come in collision with our planet. The identification of such objects, with a diameter greater than 100 meters and with the potential to hit Earth, is therefore vitally important.
Small objects and cosmic rays
All spatial debris that are more than one centimetre constitute a threat to devices in orbit around our planet and require a great sensitivity in order to be detected. In addition, an imaging device must distinguish these objects from other sources of noise like cosmic rays that can affect areas of development. In the same manner, NEOs are objects with very little luminosity that require an excellent level of sensitivity from detectors to determine trajectories.
Accrued sensitivity and elimination of cosmic rays
With the CCCP, a patented technology that reduces clock induced charges, Nüvü Caméras are conceived for the precise imaging in low light environments. To this day, the sensitivity of these cameras cannot be matched. Furthermore, Nüvü Caméras’ products have greater quantum efficiency and faster acquisition speeds that lead to short integration times, thus limiting the impacts of cosmic rays on the quality of captured images.
Demonstration: Surveillance of maintenance satellites
R.L Scott (Research and Development for Research Canada) and A. Ellery (Carlton University) have studied ground-based surveillance of geostationary on-orbit servicing operations – therefore capable of reducing spatial debris- with an EMCCD EM N2 1024 camera from Nüvü, mounted to the 1.6m telescope at Mont-Megantic Observatory. They have demonstrated the potential satellite surveillance from the ground for future servicing missions.
Difficult to detect on ground due to the absorption of sound in Earth’s atmosphere, ultraviolet (UV) rays reveal to be an incredible source of information: this portion of the spectre unveils notably the chemical composition of the warmest stars, as well as the characteristics of the interstellar medium of our galaxy or beyond. To maximise its use however, an efficient detection of these energetic rays is needed.
Limitations of current UV detectors
Although CCD technology has greatly contributed to detect new sources of UV, it offers a limited performance with weak quantum efficiency and significant readout noise. These factors negatively affect the signal to noise ratio (SNR) and leads to incorrect results due to weak luminosity and acquisition speeds.
EMCCDs to detect near-by UV
the HNü camera from Nüvü™, made with superior quality components, reaches maximum quantum efficiency with the help of current technologies. In addition, due to the electron multiplying (EM) process, the EMCCDs reduce the inherent readout noise and consequently increase the resolution of the acquisitions. The CCP controller from Nüvü Camēras offers performances where the SNR can be multiplied an order of magnitude. For this reason, we even envision integrating this technology in the new generation of spatial telescopes dedicated to the wide field imaging of UV and the visible spectrum.
Demonstration: CCCP for ultra low flux imaging
The below article confirms the performance of the CCCP to control an EMCCD in extreme low light conditions, such is the case for near UV imaging.
Erika T. Hamden, from the California Institute of Technology (Department of Astronomy), shared the results of an experiment conceived to observe ultra low light emissions with the help of an EMCCD camera from Nüvü.
Asteroseismology is a promising method, in constant evolution, which consists of probing the interior of a star using these modes of oscillation. Such techniques provides important information about the mass, rays, chemical composition as well as the age of the star, information that otherwise would be difficult, or near impossible, to attain through traditional astronomic means.
Low luminosity and fast observations
To study stellar vibrations, we examine their effects on the light emitted by a star: the oscillations modulate a light curve or an emission ray in minutes. However, high-resolution spectroscopy and photometry, particularly for weak objects, requires long uninterrupted acquisitions, incompatible with the analysis of fast light variations or the sufficient collection of photons, and can only be realized by large telescopes.
Notable reduction in noise for stars of low magnitudes
The low readout noise of EMCCDs, equipped with the CCCP controller from Nüvü Camēras, a technology that reduces the clock induced charges of these detectors, makes higher frequency and low light imaging possible in photometry and spectroscopy. This technology allows for higher flexibility in asteroseismology studies without relying on large telescopes to obtain high resolution data.
Demonstration: Fast acquisitions and reduction of noise
Researchers have demonstrated that the CCCP controller from Nüvü™ significantly reduces the sources of noise from an EMCCD all the while achieving fast image acquisitions in the article EMCCDs: 10 MHz and Beyond.
Ocean and Coastal Monitoring
The surveillance of coastal phenomenon is essentially for a number of government agencies: for example, it provides important information on fish populations, maritime transit routes, and even allows for the prediction of climate behaviours in the region. Such data, acquired through the surveillance of oceanic water columns, can reduce the risks of maritime navigation, explorations of the sea and coastal settlements.
Signal mitigation and limitations associated to a spectral range
Costal surveillance requires imaging systems that operate in the visible and near infra-red wave lengths, but such devices have a limited quantum efficiency in this spectre. Additionally, only 20% of the light emitted by the oceans can be detected due to the atmospheric diffusion as well as the light reflection on the surface of the water. Consequently, this signal is quite weak.
Meeting the requirements of coastal monitoring in space
Recent studies have obtained interesting results by using EMCCD detectors such as the HNü. With its remarkable sensitivity in visible and near infra-red wave lengths, as well as its performance in photon counting, Nüvü Camēras’ technology will improve the precision and the diversity of phenomenon data affecting coastal regions and the seabed.
Demonstration: Increase in the efficiency of telescopes
The article The Darkest EMCCD Ever demonstrates that low EMCCD noise levels attained thanks to the patented CCCP camera controller from Nüvü™ allows for the increase in telescope efficiency and the widening of their observation scopes.
Climate and Environmental Behaviour
The observation of Earth from space brings a different, but fundamental, perspective towards the protection and durability of the environment. The imaging of the dark side of Earth during night time provides a more complete outlook on climate and environmental changes affecting human life.
Limited accuracy in the dark
Developed for imaging in low light, the EMCCD technology meets its limits in environments with near total darkness. Indeed in such cases, the readout noise is too large to collect accurate data. This problem is by-passed by the photon counting method, in addition to the clock induced charges, which then become the dominant source of noise.
The Darkest EMCCD ever conceived
The effects of clock induced charges on readout noise can be minimized, even eliminated, by regulating in the appropriate manner the clock induced charge of the camera controller. This is what Nüvü Camēras offers with its CCCP controller that reduces an EMCCD readout noise to less than one electron per pixel. This patented innovation allows for photon counting with the best quantum efficiency and an excellent charge transfer for accurate results even in conditions with near total darkness.
APPLICATIONS IN LOW LIGHT IMAGING
An exoplanet modifies the luminous flow emitted by a star when it passes by it. Numerous characteristics of this star can then be deducted from the variation in luminosity during this time: atmospheric composition, size, mass and rays.
Schematic representation of a planet’s light curve transiting in front of its star.
Crucial information lost during the integration time
During the exoplanet’s transit in front of its host star, the first and last moments are of paramount importance: they unveil many of the planet’s features and occur on very short time scales. Such meaningful information can be lost in the integration time necessary for a less sensitive camera to capture images of moving objects at low light levels. Likewise, for planets with short revolution periods, the light curve shape may be hard to recover and is sometimes unreliable.
High speed, high SNR cameras
CCCP, Nüvü Camēras’ EMCCD innovative controller, achieves very high speeds while multiplying the signal to obtain a much superior SNR. The inherently lower readout noise offers a tenfold increase of an optical system’s efficiency, leading to a tremendous improvement in precision, richness and reliability of transient events’ light curves.
Demonstration: Fast Imaging with Low Noise
Researchers have concluded that the CCCP is capable of performing high-speed acquisitions while maintaining a low noise floor and preserving charge transfer efficiency.
The atmosphere is in constant motion due to wind and temperature variations. This phenomenon, atmospheric turbulence, randomly deflects light as it passes through air, hence limiting the precision and accuracy of optical systems. These fluctuations have a characteristic time scale of roughly 30 ms. In the event that a picture is taken under that time span, the turbulence appears static on the frame, leading to a technique known as lucky imaging. It combines multiple fast frames to create a single near-perfect frame without turbulence-generated artefacts.
Need for high signal to noise ratios and large field of views
Combining multiple images require a high signal to noise ratio for each frames; otherwise, the resulting image may be compromised. Furthermore, in order to track atmospheric fluctuations, lucky imaging uses comparison stars for superposition: the instrument must offer good sky coverage, thus calling for large detectors capable of acquiring images at high frame rates.
Fast acquisition speeds with large detectors
Nüvü™’ HNü is the first EMCCD camera to offer readout speeds of up to 20 MHz with the largest detector size available for this type of camera (1024 × 1024 pixels) while maintaining highly satisfactory SNRs. With binning and region of interest (ROI) options, the HNü achieves the necessary speed for lucky imaging while offering a large field of view to keep all reference stars in sight.
Air in the atmosphere drifts in foot-long pockets that get carried by wind and convective currents. Having different temperature and density, each pocket possesses its own refractive index. While moving and merging randomly, they bend light, thus affecting the original light path and degrading the incoming signal. Such turbulent motions hinder observations at a telescope theoretical resolution.
Tracking air fluctuation in real time
While lucky imaging overcomes atmospheric turbulences by virtually freezing random air fluctuations, adaptive optics reconstruct the light’s path through the atmosphere, and adjust the telescope’s mirror shape to flatten the wavefront. The incoming light thusly reconstructed improves a telescope’s performance to its theoretical limit, but doing so calls for both camera speed and accuracy.
Meeting all requirements for adaptive optics
With up to 20 MHz readout rates, low noise and superior sensitivity, Nüvü Camēras’ technology is suited for adaptive optics systems. Its exceptional quantum efficiency across the visible and near-infrared spectra also allows good sampling of the wavefront distortion due to air pockets. Nüvü cameras indeed fulfill the stringent requirements set by adaptive optics to achieve the lowest wavefront error.
Demonstration: Pyramidal Wavefront Sensor
The National Optics Institute has developed a pyramidal wavefront sensor prototype integrating a Nüvü™ 512 HNü camera.
Adaptive Optics for the 4.2m WHT telescope
Daniel Hölck-Santibanez, from Durham University, presented their adaptive optics system for the 4.2m WHT telescope. CHOUGH: spatially filtered Shack-Hartmann wave-front sensor for HOAO
Performance of the mROI feature
François Rigaut, from the Australian National University, presented the performance of the multiple regions of interest (mROI) feature provided by Nüvü Caméras. NGS2: a focal plane array upgrade for the GeMS multiple tip-tilt wavefront sensor
Astronomers resort to high-resolution spectroscopy for a broad range of applications, from redshifted galaxies to nano-flares studies. It provides very precise information on an incident photon’s energy, or unfolds events happening on very short time scales.
Resolution limited by noise sources
Both spectral and temporal resolutions depend on the photon count per pixel being as low as possible. For the former, reaching high resolution means that every pixel ideally measures a unique wavelength. For the latter, high resolution implies richer sampling and lesser chance of aliasing with short integration time. In both cases, the signal coming to the camera is very faint. Single photons need to be processed, requiring excellent SNR so they remain above the noise threshold. Time dependent noises (like dark noise) limit high spectral resolution spectroscopy; fixed noises (like readout and CIC) hinder high temporal spectroscopy.
Drastic noise reduction and post-processing for desired SNRs
Nüvü Camēras’ controller produces the lowest clock-induced charges of any EMCCD on the market, thanks to its re-invented electronics. Its electron-multiplying ability and photon counting mode decreases read noise to a minimum, allowing for very high temporal resolutions. Moreover, with their resolutely low dark current, Nüvü™ thermoelectrically cooled cameras support integration times of several seconds in a high spectral resolution scheme. In fact, with Nüvü™ advanced cameras, there are virtually no disadvantages to gather high-resolution spectrums.
Demonstration: Low Background Noise at All Time
The Characterization results of EMCCDs for extreme low-light imaging article describes how Nüvü™ cameras obtain low background signal, even at high pixel rates.
Fabry-Pérot Imaging Spectroscopy
Usual diffraction grating spectrometers are not efficient when imaging large astronomical objects like the interstellar medium. The resolution of these optical systems is limited by the light cone size that enters the spectrometer. On the other hand, a Fabry-Pérot spectrometer uses a large field imager and accepts large light cones without compromising its spectral resolution. Imaging the desired area for a selected wavelength range consists in collecting a series of frames, which are transposed, into a data volume or cube.
Imaging faint objects multiple times
The recorded objects are often faint, dispersed and do not emit considerable light fluxes. Fabry-Pérot imaging spectroscopy thus requires long exposure times to accumulate enough photons and provide a rich image at a given wavelength. This is a problem especially when considering that this process must be repeated for a number of wavelengths in order to have an accurate representation of an object. Eventually, this time inefficiency limits the scope of the work that can be done.
Superior detection and fast frame acquisitions
Nüvü Camēras EMCCD technology benefits from state-of-the-art quantum efficiency and a >91 % single photon detection probability, thus harnessing more photons in less time. Indeed, with its high gains and sub-electron readout noise, faster frame acquisition can be recorded for each wavelength range, making this spectroscopy technique much more time-affordable.
Integral Field Spectroscopy
Studying either the radial velocities of galaxy clusters or the properties of a newly born planetary system requires both spectral and location information, which integral field spectroscopy (IFS) provides. Unlike Fabry-Pérot imaging spectroscopy, an integral field unit splits the incoming light beam in multiple sections, and then directs them into a spectrometer. The following datacube is a series of spectrums, which, once combined, recreate a target’s image for a vast wavelength range.
Sensitivity and wavelength range
By splitting the incoming light into multiple spectra, IFS calls for sensitive sensors with excellent wavelength coverage as the signal strength decreases greatly. Additionally, high signal-to-noise ratios are required to achieve outstanding quality data. A larger detector also allows a greater amount of spectra to be analyzed in finer details in order to successfully reconstruct a frame.
Finely detailed spectra
Offering the most sensitive to date in the visible and near-infrared spectra, Nüvü™ camera easily support the IFS wavelength coverage. They achieves high SNR even with low light flux with its patented and proven CCD Controller for Counting Photons (CCCP) by decreasing clock-induced charges and read noise to their minimum. With its 1024 × 1024 sensor, Nüvü Camēras’ HNü also offers great options for IFS by increasing split spectra surface coverage while still producing exquisite data.
Demonstration: Adapted for IFS
The following article concludes that “the EMCCD is well suited for very low flux applications” such as integral field spectroscopy at high resolution, thanks to the CCCP.
Studying dynamic celestial objects like cataclysmic variables requires efficient techniques to gather more data and better understand them. To this end, real-time photometry acquires variable phenomena images at a frame rate of a few Hz to survey rapid brightness changes of a multitude of celestial objects.
Limiting noise sources
Monitoring events that take place on small time scales calls for fast readout time. However, past CCD controller technologies were not developed for rapid acquisitions. An increase in the pixel rate without a change in the technology only leads to more noise sources such as clock-induced charges (CIC), which ultimately pollute the signal and contaminate frames. Following this requirement, exposure times are shortened, decreasing the total photon count and increasing the need for lower noise levels.
A technology manufactured for fast acquisitions
The expertise developed at Nüvü Camēras lies in its re-invented controller electronics, built from the ground up for faint flux imaging. Through significant CIC level reduction, Nüvü™ cameras gather light with shorter exposure times. Even for large fields of view (1024 × 1024 pixel CCD detector size), frame rates higher than 6 fps with an electron-multiplying gain of 5,000 can be obtained and still yield exquisite image quality.
Demonstration: Pulsating White Dwarf
In The Darkest EMCCD Ever, the authors demonstrate the EMCCD potential to perform high-speed photometry. The figures below are taken from the proceedings linked hereafter.
Light curve of G226-29, a ZZ Ceti pulsating white dwarf, taken in V band on at the 1.6-m Mont Mégantic telescope on a full moon night. Data were acquired at 30 frames per second and binned to 5 seconds.
When every photon counts
NGC7331 radial velocity field extracted from Fabry-Pérot spectroscopy data. The data, gathered at the 1.6-m Mont Mégantic telescope at a spectral resolution of 15000, are among the very first demonstration of the potential of photon-counting imaging.
Imaging devices with the lowest possible readout noise are paramount for high quality observation not limited by background or shot noise. In that regard, the EMCCD’s sub-electron readout noise makes it the ideal candidate for low light imaging applications. However, due to the stochastic nature of the electron-multiplying gain that counters readout noise, EMCCDs are flawed with an Excess Noise Factor (ENF) that has the same effect on the signal-to-noise ratio as halving the camera Quantum Efficiency (QE).
To recover the acquisition system’s full capabilities, it is possible to operate in Photon Counting mode in which a signal as little as a single photon per pixel per image can be recorded. For greater dynamic range, images can be superimposed and the threshold adjusted accordingly. In this context, EMCCDs are to be used for imaging very faint light sources and/or at considerable high speeds. The latter case however produces spurious charges, also referred to as clock-induced charges (CIC), which becomes the dominant noise source in EMCCDs. With high CIC levels and insufficient electron-multiplying gain, it is futile to operate the camera in Photon Counting mode.
Nüvü Camēras’ CCCP controller (CCD Controller for Counting Photons) arises from an academic research endeavour. It was developed from the ground up with the objective of elegantly mastering the major noise source in Photon Counting applications, the CIC. The CCCP is best suited for the modern astronomer needs as it produces an EM gain 5 times greater than that of other CCD controller while generating at least 10 times less CIC. With that much less noise, there are virtually no disadvantages to take high-resolution images and post-process them in order to select the desired SNR and/or spectral resolution. In fact, this is changing the way astronomers use spectroscopy, as one can choose to bin frames temporally or spectrally to any desired extent while keeping track of the higher dynamics inside the high-resolution original images.
Select EMCCD camera that meets your needs
To better understand the principles behind the EMCCD camera and to choose the device that best suits your application, refer to the EMCCD Tutorial