The Next Generation Transit Survey (NGTS) has now been operating for six years, discovering and characterizing transiting exoplanets around bright stars. We outline the NGTS project, including the Andor CCD cameras used to perform high-precision time-series photometry. We quantify the photometric precision for a sample of over 20,000 bright star observations. We find for single NGTS telescope observations we achieve a 30-minute photometric precision of 400 ppm at low airmass. This is in good agreement with the photometric noise predicted using a four-component noise model. We find that the photometric noise for bright stars (G < 12) is dominated by atmospheric scintillation. We also present details of the NGTS multi-telescope observing mode, whereby 12 telescopes can be used simultaneously on a single target star to achieve a 30-minute photometric precision of 100 ppm. Finally, we describe a new generation scientific CMOS camera that we will be testing on-sky at the NGTS facility to determine if it can compete with state-of-the-art CCD cameras used for high precision bright star photometry.
Super-resolution radial fluctuations (SRRF) is a combination of temporal fluctuation analysis and localization microscopy. One of the key differences between SRRF and other super-resolution methods is its applicability to live-cell dynamics because it functions across a very wide range of fluorophore densities and excitation powers. SRRF is applied to data from imaging modes which include widefield, TIRF and confocal, where short frame bursts (e.g. 50 frames) can be processed to deliver spatial resolution enhancements similar to or better than structured illumination microscopy (SIM). On the other hand, with sparse data e.g. stochastic optical reconstruction microscopy (STORM), SRRF can deliver resolution similar to Gaussian fitting localization methods. Thus, SRRF could provide a route to super-resolution without the need for specialized optical hardware, exotic probes or very high-power densities. We present a fast GPUbased SRRF algorithm termed “SRRF-Stream” and apply it to imagery from an iXon EMCCD coupled to a multi-modal imaging platform, Dragonfly. The new implementation is <300 times faster than the standard CPU version running on an Intel Xeon 3.5GHz 4 core processor, and < 20 times faster than the NanoJ GPU implementation, while also being integrated with acquisition for real time use. In this paper we explore the image resolution and quality with EMCCD and sCMOS cameras and various fluorophores including fluorescent proteins and organic dyes.
The back-illuminated electron multiplying charge-coupled device (EMCCD) camera is having a profound influence on the field of low-light dynamic cellular microscopy, combining highest possible photon collection efficiency with the ability to virtually eliminate the readout noise detection limit. We report here the use of this camera, in 512×512 frame-transfer chip format at 10-MHz pixel readout speed, in optimizing a demanding ultra-low-light intracellular calcium flux microscopy setup. The arrangement employed includes a spinning confocal Nipkow disk, which, while facilitating the need to both generate images at very rapid frame rates and minimize background photons, yields very weak signals. The challenge for the camera lies not just in detecting as many of these scarce photons as possible, but also in operating at a frame rate that meets the temporal resolution requirements of many low-light microscopy approaches, a particular demand of smooth muscle calcium flux microscopy. Results presented illustrate both the significant sensitivity improvement offered by this technology over the previous standard in ultra-low-light CCD detection, the GenIII+intensified charge-coupled device (ICCD), and also portray the advanced temporal and spatial resolution capabilities of the EMCCD.
KEYWORDS: Electron multiplying charge coupled devices, Stars, Charge-coupled devices, Photometry, Cameras, Quantum efficiency, Interference (communication), Sensors, Back illuminated sensors, Signal to noise ratio
Electron Multiplying Charge Coupled Devices (EMCCDs) are CCD cameras with potentially single-photon detection ability. Signal amplification is achieved by way of a unique electron-multiplying structure built into the silicon, and the gain can be varied in order to overcome the read-noise floor, which is the usual limiting factor in reading out a conventional CCD at high frame rates. In combination with its high quantum efficiencies, the EMCCD holds great promise for time-resolved photometry. We report here results from two observing campaigns aimed at assessing the suitability of EMCCD technology for detecting short-timescale, low-amplitude variability in blazars. Data were taken on the 2.2m telescope at Calar Alto using both front-illuminated and back-illuminated EMCCD cameras from Andor Technology’s iXon range. Approximately 410,000 science frames were recorded over 10 nights. The results presented here illustrate the photometric stability achieved with the cameras, under typical observing conditions. In general, photometric precision down to the level of a few millimagnitudes is found to be possible. We argue that reliable photometry is best achieved with high data collection rates (typically 4 frames per second) coupled to ultra-low-noise detectors such as the EMCCD.
The advent of Electron Multiplying Charge Coupled Device (EMCCD) technology and it's ability to overcome previous hurdles in low-light fluorescence microscopy, such as phototoxicity to live cells, photobleaching of fluorophores and exposure time restrictions, has resulted in a significant resurgence of interest in use of confocal spinning disk techniques for live cell microscopy. Here provide an understanding of, and technical solutions to, the issues of synchronization that have previously marred the coupling of fast CCD camera technology to confocal spinning disk arrangements. We examine the challenges arising from both old and new models of the Nipkow spinning disk confocal unit and suggest solutions throughout based on a sound comprehension of both (a) relative scan/exposure times; (b) relative orientation of the coupled devices; (c) optimisation of EMCCD clocking parameters.
The back-illuminated Electron Multiplying Charge Coupled Device (EMCCD) camera is having a profound influence on the field of low-light dynamic cellular microscopy, combining highest possible photon collection efficiency with the ability to virtually eliminate the readout noise detection limit. We report here the use of this camera, in 512 x 512 frame-transfer chip format at 10 MHz pixel readout speed, in optimising a demanding ultra low-light intracellular calcium flux microscopy set-up. The arrangement employed includes a spinning confocal Nipkow disk, which whilst facilitating the need to both generate images at very rapid frame rates and minimize background photons, yields very weak signals. The challenge for the camera lies not just in detecting as many of these scarce photons as possible, but also in operating at a frame rate that meets the temporal resolution requirements of many low-light microscopy approaches, a particular demand of smooth muscle calcium flux microscopy. Results presented illustrate both the significant sensitivity improvement offered by this revolutionary technology over the previous standard in ultra low light CCD detection, the GenIII+ ICCD, and also portray the advanced temporal and spatial resolution capabilities of the EMCCD.
Caitriona Creely, John Kelly, M. Feeney, S. Hudson, J. Penedo, Werner Blau, B. Elias, Andree Kirsch-De Mesmaeker, P. Matousek, M. Towrie, A. Parker, J. Dyer, Mikhael George, C. Coates, John McGarvey
We report on ultrafast pump and probe studies of biological systems, in the form of polynucleotide and calf thymus DNA complexes. Molecules for study are bound to the polynucleotides and probed in the visible region to observe changes in the absorption over time. Various dipyridophenazine metal complexes are studied alone and complexed with DNA or synthetic polynucleotides to investigate changes occurring in their excited states upon interacting with nucleobases. Transient absorption measurements are performed pumping at 400nm and probing from 450-700nm with pulse duration of 400fs.
The back-illuminated Electron Multiplying Charge Coupled Device (EMCCD) camera stands to be one of the most revolutionary contributions ever to the burgeoning fields of low-light dynamic cellular microscopy and single molecule detection, combining extremely high photon conversion efficiency with the ability to eliminate the readout noise detection limit. Here, we present some preliminary measurements recorded by a vary rapid frame rate version of this camera technology, incorporated into a spinning disk confocal microscopy set-up that is used for fast intracellular calcium flux measurements. The results presented demonstrate the united effects of (1) EMCCD technology in amplifying the very weak signal from these fluorescently labelled cells above the readout noise detection limit, that they would otherwise be completely lost in; (2) back-thinned CCD technology in maximizing the singal/shot noise ratio from such weak photon fluxes. It has also been shown how this innovative development can offer significant signal improvements over that afforded by ICCD technology. Practially, this marked advancement in detector sensitivity affords benefits such as shorter exposure times (therefore faster frame rates), lower dye concentrations and reduced excitation powers and will remove some of the barriers that have been restricting the development of new innovative low-light microscopy techniques.
A novel Charge Coupled Device (CCD) has been commercially produced by Marconi Applied Technology, UK under the trade name of L3Vision, incorporating a solid-state electron multiplying structure based on the Impact Ionization phenomenon in silicon. Here we review this technology, and evaluate the first electron multiplying CCD camera, in particular using it to image weak emissions form microtitre plates. A theoretical model was constructed to predict S/N and Z-factor performances, which were compared to actual measurements, verifying that a greater than one order of magnitude improvement can be achieved over conventional CCDs. The demonstrations of remarkable sensitivity enhancement presented here are discussed in terms of the EMCCD camera's suitability for use in life sciences applications such as High-Throughput Screening (HTS), and other approaches requiring ultrasensitive detection of biomolecules, including Single Molecule Detection.
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