Christian Guillaume

L3CCD results in pure photon-counting mode

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.

CCCP: a CCD controller for counting photons

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.

Custom CCD for adaptive optics applications

ESO and JRA2 OPTICON have funded e2v technologies to develop a compact packaged Peltier cooled 24 μm square 240x240 pixels split frame transfer 8-output back-illuminated L3Vision CCD3, L3Vision CCD for Adaptive Optic Wave Front Sensor (AO WFS) applications. The device is designed to achieve sub-electron read noise at frame rates from 25 Hz to 1,500 Hz and dark current lower than 0.01 e-/pixel/frame. The development has many unique features. To obtain high frame rates, multi-output EMCCD gain registers and metal buttressing of row clock lines are used. The baseline device is built in standard silicon. In addition, a split wafer run has enabled two speculative variants to be built; deep depletion silicon devices to improve red response and devices with an electronic shutter to extend use to Rayleigh and Pulsed Laser Guide Star applications. These are all firsts for L3Vision CCDs. The designs of the CCD and Peltier package have passed their reviews and fabrication has begun. This paper will describe the progress to date, the requirements and the design of the CCD and compact Peltier package, technology trade-offs, schedule and proposed test plan. High readout speed, low noise and compactness (requirement to fit in confined spaces) provide special challenges to ESOs AO variant of its NGC, New General detector Controller to drive this CCD. This paper will describe progress made on the design of the controller to meet these special needs.

Zero Noise Wavefront Sensor Development within the Opticon European Network

This activity, funded by ESO and the European Commission through the Opticon Network will attempt to define, fabricate and fully characterize the best possible detector working at visible wavelengths suitable for wavefront sensors in Adaptive Optics (AO) systems. The detector will be a split frame transfer array built by e2v technologies and called CCD220. The frame rate will be very fast (up to 1.2 kHz) while the readout noise will be kept extremely low (typically below 1 e - ). The goal of this paper is to justify the choice of detector: an EMCCD with 240×240 pixels and 8 outputs that will provide sub- electron readout noise at 1-1.2 kHz frame rate. This paper shows that, despite the fact that EMCDDs have an excess noise factor of 1.4 due to the charge multiplication process; their virtually zero read noise should allow them to outperform the classical CCD. Such detectors do not yet exist and must be developed. Moreover, this paper explains how the OPTICON European network is organized.

A Dedicated L3Vision CCD for Adaptive Optics Applications

ESO and JRA2 OPTICON have funded the development of a compact packaged Peltier cooled 24 µm square 240×240 pixel split frame transfer 8-output back illuminated L3Vision CCD, L3CCD, by e2v technologies. The device will achieve sub-electron (goal 0.1e - ) read noise at frame rates from 25 Hz to 1.5 kHz and low dark current of 0.01 e - /pixel/frame. The development has many unique features. To obtain high frame rates, multi-output EMCCD gain registers and metal buttressing of parallel clocks will be used. To minimize risk, the baseline device will be built in standard silicon. In addition, a split wafer run will enable two speculative variants to be built; deep depletion silicon devices to improve red response and devices with an electronic shutter to extend use to Rayleigh Laser Guide Star (RLGS) applications. These are all unprecedented advancements for L3CCDs. This paper will describe requirements and outline the design established after careful consideration of the application, detector architecture, compact Peltier package, technology trade-offs, schedule and proposed test plan.

Advances in detector technologies for visible and infrared wavefront sensing

The purpose of this paper is to give an overview of the state of the art wavefront sensor detectors developments held in Europe for the last decade. The success of the next generation of instruments for 8 to 40-m class telescopes will depend on the ability of Adaptive Optics (AO) systems to provide excellent image quality and stability. This will be achieved by increasing the sampling, wavelength range and correction quality of the wave front error in both spatial and time domains. The modern generation of AO wavefront sensor detectors development started in the late nineties with the CCD50 detector fabricated by e2v technologies under ESO contract for the ESO NACO AO system. With a 128x128 pixels format, this 8 outputs CCD offered a 500 Hz frame rate with a readout noise of 7e-. A major breakthrough has been achieved with the recent development by e2v technologies of the CCD220. This 240x240 pixels 8 outputs EMCCD (CCD with internal multiplication) has been jointly funded by ESO and Europe under the FP6 programme. The CCD220 and the OCAM2 camera that operates the detector are now the most sensitive system in the world for advanced adaptive optics systems, offering less than 0.2 e readout noise at a frame rate of 1500 Hz with negligible dark current. Extremely easy to operate, OCAM2 only needs a 24 V power supply and a modest water cooling circuit. This system, commercialized by First Light Imaging, is extensively described in this paper. An upgrade of OCAM2 is foreseen to boost its frame rate to 2 kHz, opening the window of XAO wavefront sensing for the ELT using 4 synchronized cameras and pyramid wavefront sensing. Since this major success, new developments started in Europe. One is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with ESO involvement. The spot elongation from a LGS Shack Hartman wavefront sensor necessitates an increase of the pixel format. Two detectors are currently developed by e2v. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate. The LGSD is a scaling of the NGSD with 1760x1680 pixels and 3 e readout noise (goal 1e) at 700 Hz (goal 1000 Hz) frame rate. New technologies will be developed for that purpose: advanced CMOS pixel architecture, CMOS back thinned and back illuminated device for very high QE, full digital outputs with signal digital conversion on chip. In addition, the CMOS technology is extremely robust in a telescope environment. Both detectors will be used on the European ELT but also interest potentially all giant telescopes under development. Additional developments also started for wavefront sensing in the infrared based on a new technological breakthrough using ultra low noise Avalanche Photodiode (APD) arrays within the RAPID project. Developed by the SOFRADIR and CEA/LETI manufacturers, the latter will offer a 320x240 8 outputs 30 microns IR array, sensitive from 0.4 to 3.2 microns, with 2 e readout noise at 1500 Hz frame rate. The high QE response is almost flat over this wavelength range. Advanced packaging with miniature cryostat using liquid nitrogen free pulse tube cryocoolers is currently developed for this programme in order to allow use on this detector in any type of environment. First results of this project are detailed here. These programs are held with several partners, among them are the French astronomical laboratories (LAM, OHP, IPAG), the detector manufacturers (e2v technologies, Sofradir, CEA/LETI) and other partners (ESO, ONERA, IAC, GTC). Funding is: Opticon FP6 and FP7 from European Commission, ESO, CNRS and Université de Provence, Sofradir, ONERA, CEA/LETI and the French FUI (DGCIS).

A New Digital CCD Readout Technique for Ultra–Low‐Noise CCDs

We present a completely new technique to read out the CCD matrix that can achieve much lower noise than classical techniques used since the 1970s. This technique is based on digital analysis of the CCDs output signal instead of analog filtering coupled to an original filtering method. Despite several attempts carried out in the past to implement digital correlated double sampling, this is the first time that a radical improvement in readout noise performance is shown. This is highly interesting for low light level conditions, where the detector works in the readout‐noise regime and not in the photon‐noise regime. This is particularly the case when carrying out medium‐ to high‐resolution spectroscopy or multiplex (scanning) observations.

Backside-illuminated, high-QE, 3e- RoN, fast 700fps, 1760x1680 pixels CMOS imager for AO with highly parallel readout

The success of the next generation of instruments for 8 to 40-m class telescopes will depend upon improving the image quality (correcting the distortion caused by atmospheric turbulence) by exploiting sophisticated Adaptive Optics (AO) systems. One of the critical components of the AO systems for the E-ELT has been identified as the Laser/Natural Guide Star (LGS/NGS) WaveFront Sensing (WFS) detector. The combination of large format, 1760x1680 pixels to finely sample (84x84 sub-apertures) the wavefront and the spot elongation of laser guide stars, fast frame rate of 700 (up to 1000) frames per second, low read noise (< 3e-), and high QE (> 90%) makes the development of such a device extremely challenging. Design studies by industry concluded that a thinned and backside-illuminated CMOS Imager as the most promising technology. This paper describes the multi-phased development plan that will ensure devices are available on-time for E-ELT first-light AO systems; the different CMOS pixel architectures studied; measured results of technology demonstrators that have validated the CMOS Imager approach; the design explaining the approach of massive parallelism (70,000 ADCs) needed to achieve low noise at high pixel rates of ~3 Gpixel/s ; the 88 channel LVDS data interface; the restriction that stitching (required due to the 5x6cm size) posed on the design and the solutions found to overcome these limitations. Two generations of the CMOS Imager will be built: a pioneering quarter sized device of 880x840 pixels capable of meeting first light needs of the E-ELT called NGSD (Natural Guide Star Detector); followed by the full size device, the LGSD (Laser Guide Star Detector). Funding sources: OPTICON FP6 and FP7 from European Commission and ESO.

Characterization of OCam and CCD220, the fastest and most sensitive camera to date for AO wavefront sensing

For the first time, sub-electron read noise has been achieved with a camera suitable for astronomical wavefront-sensing (WFS) applications. The OCam system has demonstrated this performance at 1300 Hz frame rate and with 240×240-pixel frame rate. ESO and JRA2 OPTICON2 have jointly funded e2v technologies to develop a custom CCD for Adaptive Optics (AO) wavefront sensing applications. The device, called CCD220, is a compact Peltier-cooled 240×240 pixel frame-transfer 8-output back-illuminated sensor using the EMCCD technology. This paper demonstrates sub-electron read noise at frame rates from 25 Hz to 1300 Hz and dark current lower than 0.01 e-/pixel/frame. It reports on the comprehensive, quantitative performance characterization of OCam and the CCD220 such as readout noise, dark current, multiplication gain, quantum efficiency, charge transfer efficiency... OCam includes a low noise preamplifier stage, a digital board to generate the clocks and a microcontroller. The data acquisition system includes a user friendly timer file editor to generate any type of clocking scheme. A second version of OCam, called OCam2, was designed offering enhanced performances, a completely sealed camera package and an additional Peltier stage to facilitate operation on a telescope or environmentally rugged applications. OCam2 offers two types of built-in data link to the Real Time Computer: the CameraLink industry standard interface and various fiber link options like the sFPDP interface. OCam2 includes also a modified mechanical design to ease the integration of microlens arrays for use of this camera in all types of wavefront sensing AO system. The front cover of OCam2 can be customized to include a microlens exchange mechanism.

OCAM2S: an integral shutter ultrafast and low noise wavefront sensor camera for laser guide stars adaptive optics systems

To date, the OCAM2 system has demonstrated to be the fastest and lowest noise production ready wavefront sensor, achieving 2067 full frames per second with subelectron readout noise. This makes OCAM2 the ideal system for natural as well as continuous wave laser guide star wavefront sensing. In this paper we present the new gated version of OCAM2 named OCAM2-S, using E2V’s CCD219 sensor with integral shutter. This new camera offers the same superb characteristics than OCAM2 both in terms of speed and readout noise but also offers a shutter function that makes the sensor only sensitive to light for very short periods, at will. We will report on gating time and extinction ratio performances of this new camera. This device opens new possibilities for Rayleigh pulsed lasers adaptive optics systems. With a shutter time constant well below 1 microsecond, this camera opens new solutions for pulsed sodium lasers with backscatter suppression or even spot elongation minimization for ELT LGS.