Electron multiplying charge-coupled devices (EMCCDs) enable imaging with subelectron noise up to video frame rates and beyond, providing the multiplication gain is sufficiently high. The ultra-low noise, high resolution, high-quantum efficiency, and robustness to over exposure make these sensors ideally suited to applications traditionally served by image intensifiers. One important performance parameter of such low-light imaging systems is the noise introduced by the gain process. This work investigates the noise introduced by the electron multiplication within the EMCCD. The theory and measurements of the excess noise factor are presented. The measurement technique for determining the excess noise factor is described in detail. The results show that the noise performance matches that of the ideal staircase avalanche photodiode. A Monte Carlo method for simulating the low-light level images is demonstrated and the results compared with practical experience.

The noise performance of electron multiplying charge-coupled devices

ULTRACAM is a portable, high-speed imaging photometer designed to study faint astronomical objects at high temporal resolutions. ULTRACAM employs two dichroic beamsplitters and three frame-transfer CCD cameras to provide three-colour optical imaging at frame rates of up to 500 Hz. The instrument has been mounted on both the 4.2-m William Herschel Telescope on La Palma and the 8.2-m Very Large Telescope in Chile, and has been used to study white dwarfs, brown dwarfs, pulsars, black hole/neutron star X-ray binaries, gamma-ray bursts, cataclysmic variables, eclipsing binary stars, extrasolar planets, flare stars, ultracompact binaries, active galactic nuclei, asteroseismology and occultations by Solar System objects (Titan, Pluto and Kuiper Belt objects). In this paper we describe the scientific motivation behind ULTRACAM, present an outline of its design and report on its measured performance.

/pdf/ultracam-an-ultrafast-triple-beam-ccd-camera-for-high-speed-38slclewto.pdf

ULTRACAM: an ultrafast, triple - beam CCD camera for high-speed astrophysics

Here I review the current state of the field of optical stellar interferometry, concentrating on ground-based work although a brief report of space interferometry missions is included. We pause both to reflect on decades of immense progress in the field as well as to prepare for a new generation of large interferometers just now being commissioned (most notably, the CHARA, Keck and VLT Interferometers). First, this review summarizes the basic principles behind stellar interferometry needed by the lay-physicist and general astronomer to understand the scientific potential as well as technical challenges of interferometry. Next, the basic design principles of practical interferometers are discussed, using the experience of past and existing facilities to illustrate important points. Here there is significant discussion of current trends in the field, including the new facilities under construction and advanced technologies being debuted. This decade has seen the influence of stellar interferometry extend beyond classical regimes of stellar diameters and binary orbits to new areas such as mapping the accretion discs around young stars, novel calibration of the cepheid period-luminosity relation, and imaging of stellar surfaces. The third section is devoted to the major scientific results from interferometry, grouped into natural categories reflecting these current developments. Lastly, I consider the future of interferometry, highlighting the kinds of new science promised by the interferometers coming on-line in the next few years. I also discuss the longer-term future of optical interferometry, including the prospects for space interferometry and the possibilities of large-scale ground-based projects. Critical technological developments are still needed to make these projects attractive and affordable.

/pdf/optical-interferometry-in-astronomy-290ps14qag.pdf

Optical interferometry in astronomy

We demonstrate the realization of a quantum register using a string of single neutral atoms which are trapped in an optical dipole trap. The atoms are selectively and coherently manipulated in a magnetic field gradient using microwave radiation. Our addressing scheme operates with a high spatial resolution, and qubit rotations on individual atoms are performed with 99% contrast. In a final readout operation we analyze each individual atomic state. Finally, we have measured the coherence time and identified the predominant dephasing mechanism for our register.

/pdf/neutral-atom-quantum-register-1ztwdn47li.pdf

Neutral atom quantum register

■ Abstract Recent years have witnessed a renaissance of fluorescence microscopy techniques and applications, from live-animal multiphoton confocal microscopy to single-molecule fluorescence spectroscopy and imaging in living cells. These achievements have been made possible not so much because of improvements in microscope design, but rather because of development of new detectors, accessible continuous wave and pulsed laser sources, sophisticated multiparameter analysis on one hand, and the development of new probes and labeling chemistries on the other. This review tracks the lineage of ideas and the evolution of thinking that have led to the actual developments, and presents a comprehensive overview of the field, with emphasis put on our laboratory’s interest in single-molecule microscopy and spectroscopy.

https://groups.physics.ox.ac.uk/genemachines/group/Michalet20AnnRev2003.pdf

The Power and Prospects of Fluorescence Microscopies and Spectroscopies

A new CCD sensor technology has been developed by Marconi Applied Technologies which effectively reduces read-out noise to less than one electron rms. A single low light level CCD can operate over a wide range of read-out rates from TV to slow-scan and give superior performance to that available from either intensified or slow-scan CCD sensors.

The LLCCD: low-light imaging without the need for an intensifier

A radically new CCD development by Marconi Applied Technology has enabled substantial internal gain within the CCD before the signal reaches the output amplifier. With reasonably high gain, sub-electron readout noise levels are achieved even at MHz pixel rates. This paper reports a detailed assessment of these devices, including novel methods of measuring their properties when operated at peak mean signal levels well below one electron per pixel. The devices are shown to be photon shot noise limited at essentially all light levels below saturation. Even at the lowest signal levels the charge transfer efficiency is good. The conclusion is that these new deices have radically changed the balance in the perpetual trade-off between read out noise and the speed of readout. They will force a re- evaluation of camera technologies and imaging strategies to enable the maximum benefit to be gained form these high- speed, essentially noiseless readout devices. This new LLLCCD technology, in conjunction with thinning should provide detectors which will be very close indeed to being theoretically perfect.

/pdf/subelectron-read-noise-at-mhz-pixel-rates-2fkp00wjbi.pdf

Subelectron read noise at MHz pixel rates

Back-thinning of a CCD image sensor is a very well established process for achieving high quantum efficiency and the
majority of high-specification space and science applications have used such back-thinned devices for many years.
CMOS sensors offer advantages over CCDs for a number of these applications and, in principle, it should be possible to
back-thin CMOS devices and obtain the same performance as the CCD. This has now been demonstrated by e2v and
results from two recent programmes to back-thin CMOS sensors show excellent quantum efficiency values.

/pdf/back-thinned-cmos-sensor-optimization-3jnsqjmw21.pdf

Back-thinned CMOS sensor optimization

We present recent development in the technology of silicon sensors for astronomical applications. Novel CCD and CMOS sensors have been designed for low noise and high sensitivity astronomical use. High resistivity sensors allow thicker silicon for higher red sensitivity in several types of new CCD. The capability to manufacture large sets of CCDs to form large focal planes has allowed several very large mosaics to be built for astronomy with increasing formats on the ground and in space. In addition to supplying sensors we discuss increasing capacity and interest in the commercial supply of integrated “camera” systems.

/pdf/e2v-new-ccd-and-cmos-technology-developments-for-4q9nakwpxy.pdf

e2v new CCD and CMOS technology developments for astronomical sensors

e2v have been developing new approaches to mitigate against the effects of radiation damage in CCD sensors. The first of these is our "rad-hard" device technology, primarily developed to reduce the flat-band voltage shift following ionising radiation. With this a very significant improvement has been demonstrated, the flat-band shift reducing from typically 100-200 mV/kRad(Si) with standard devices to only 6 mV/kRad(Si), plus an associated reduction in the increase in surface dark signal. The rad-hard process thereby allows
devices to be operated in environments with up to at least 500kRad total dose and/or with reduced shielding. 
Developments aimed at reducing the impact of proton radiation have included the manufacture of p-channel devices. Our initial data indicates that at -50°C the increase in charge transfer inefficiency is reduced by a factor of two times for parallel transfer and five times for serial transfer.

/pdf/improving-radiation-tolerance-in-e2v-ccd-sensors-3sqjqrtf1b.pdf

Paul Jerram

Papers

The LLCCD: low-light imaging without the need for an intensifier

Subelectron read noise at MHz pixel rates

Back-thinned CMOS sensor optimization

e2v new CCD and CMOS technology developments for astronomical sensors

Improving radiation tolerance in e2v CCD sensors