Thierry Beaufort

ESA's CCD test bench for the Euclid visible channel

The visual imaging instrument VIS on board Euclid baselines 36 newly designed CCD273-84 devices from e2v. While these new devices have a 4kx4k format with four readout nodes, the Euclid Imaging Consortium (EIC) has performed extensive test campaigns on both irradiated and un-irradiated devices of the 4kx1k Euclid precursor variant CCD204-22. In support of the CCD development and characterization, and to enable an independent assessment of the Euclid CCDs (the procurement of which is ESA’s responsibility), ESA/ESTEC has built a test bench. This test bench allows for a flexible operation and readout of the CCDs, originally for CCD204 and shortly also for CCD273-84. It provides the basic tools for noise and gain calibration, and CTI, QE, MTF and PRNU measurements. In addition, the bench provides scanning spot illumination with a spot size well below the pixel size, for measurement of the intra-pixel response of the CCDs before and after radiation damage. Such measurements are of great importance for the characterization and modeling of the VIS instrument’s PSF, in particular to enable the prediction of the evolution of the PSF shape under the influence of the L2 radiation environment during the mission. This set-up will also allow for simulation of typical Euclid sky images in the lab. The capabilities and validation of this bench at ESA are described in this paper.

Characterization of HAWAII-2RG detector and SIDECAR ASIC for the Euclid mission at ESA

In the frame work of the European Space Agencys Cosmic Vision program, the Euclid mission has the objective to map the geometry of the Dark Universe. Galaxies and clusters of galaxies will be observed in the visible and near-infrared wavelengths by an imaging and spectroscopic channel. For the Near Infrared Spectrometer instrument (NISP), the state-of-the-art HAWAII-2RG detectors will be used, associated with the SIDECAR ASIC readout electronic which will perform the image frame acquisitions. To characterize and validate the performance of these detectors, a test bench has been designed, tested and validated. This publication will present preliminary measurements on dark current, read noise, conversion gain and power consumption, In summary, the following results have been obtained in our system: dark current of 0.014 e-/s/pixel at 82K; readout noise of 23 e- for a single CDS pair and 5.4e- for a Fowler(32); a total electric power consumption of 203 mW in LVDS (excluding I/O power) mode. The SIDECAR ASIC has also been characterized separately at room temperature. Two references voltages, VPreAmpRef1 and VrefMain, used to adjust the offset of the pre-amp DAC has been studied. The reset voltage, Vreset, was measured to have a root mean square stability of 22μV over 15 minutes and a root mean square stability value of 24μV over a 15 hours measurement period. An offset between set value and measured value of around 60mV for low set voltages has been noticed. The behavior of VPreAmpRef1 and VrefMain with a adjustable external input voltage has been conducted in order to tune these two biases to cover the desired input range with the best linearity.

Quantum efficiency performances of the NIR European Large Format Array detectors tested at ESTEC

Publishers Note: This paper, originally published on 10/12/2015, was replaced with a corrected/revised version on 10/23/2015. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. The Payload Technology Validation Section (SRE-FV) at ESTEC has the goal to validate new technology for future or on-going mission. In this framework, a test set up to characterize the quantum efficiency of near-infrared (NIR) detectors has been created. In the context of the NIR European Large Format Array (“LFA”), 3 deliverables detectors coming from SELEX-UK/ATC (UK) on one side, and CEA/LETI- CEA/IRFU-SOFRADIR (FR) on the other side were characterized. The quantum efficiency of an HAWAII-2RG detector from Teledyne was as well measured. The capability to compare on the same setup detectors from different manufacturers is a unique asset for the future mission preparation office. This publication will present the quantum efficiency results of a HAWAII-2RG detector from Teledyne with a 2.5um cut off compared to the LFA European detectors prototypes developed independently by SELEX-UK/ATC (UK) on one side, and CEA/LETI- CEA/IRFU-SOFRADIR (FR) on the other side.

Radiation effects on the Gaia CCDs after 30 months at L2

Since the launch of ESAs Gaia satellite in December 2013, the 106 large-format scientific CCDs onboard have been operating at L2. Due to a combination of the high-precision measurement requirements of the mission and the predicted proton environment at L2, the effect of non-ionizing radiation damage on the detectors was early identified pre-launch as potentially imposing a major limitation on the scientific value of the data. In this paper we compare pre-flight radiation-induced Charge Transfer Inefficiency (CTI) predictions against in-flight measurements, focusing especially on charge injection diagnostics, as well as correlating these CTI diagnostic results with solar proton event data. We show that L2-directed solar activity has been relatively low since launch, and radiation damage (so far) is less than originally expected. Despite this, there are clear cases of correlation between earth-directed solar coronal mass ejection events and abrupt changes in CTI diagnostics over time. These sudden jumps are lying on top of a rather constant increase in CTI which we show is primarily due to the continuous bombardment of the devices by high-energy Galactic Cosmic Rays. We examine the possible reasons for the lower than expected levels of CTI as well as examining the effect of controlled payload heating events on the CTI diagnostics. Radiation-induced CTI in the CCD serial registers and effects of ionizing radiation are also correspondingly lower than expected, however these topics are not examined here in detail.

Optical and dark characterization of the PLATO CCD at ESA

PLATO – PLAnetary Transits and Oscillations of stars – is the third medium-class mission (M3) to be selected in the European Space Agency (ESA) Science and Robotic Exploration Cosmic Vision programme. It is due for launch in 2025 with the main objective to find and study terrestrial planets in the habitable zone around solar-like stars. The payload consists of >20 cameras; with each camera comprising 4 Charge-Coupled Devices (CCDs), a large number of flight model devices procured by ESA shall ultimately be integrated on the spacecraft. The CCD270 – specially designed and manufactured by e2v for the PLATO mission – is a large format (8 cm x 8 cm) back-illuminated device operating at 4 MHz pixel rate and coming in two variants: full frame and frame transfer. In order to de-risk the PLATO CCD procurement and aid the mission definition process, ESA’s Payload Technology Validation section is currently validating the PLATO CCD270. This validation consists in demonstrating that the device achieves its specified electrooptical performance in the relevant environment: operated at 4 MHz, at cold and before and after proton irradiation. As part of this validation, CCD270 devices have been characterized in the dark as well as optically with respect to performance parameters directly relevant for the photometric application of the CCDs. Dark tests comprise the measurement of gain sensitivity to bias voltages, charge injection tests, and measurement of hot and variable pixels after irradiation. In addition, the results of measurements of Quantum Efficiency for a range of angles of incidence, intra– pixel response (non-)uniformity, and response to spot illumination, before and after proton irradiation. In particular, the effect of radiation induced degradation of the charge transfer efficiency on the measured charge in a star-like spot has been studied as a function of signal level and of position on the pixel grid, Also, the effect of various levels of background light on the amount of charge lost from a star image are described. These results can serve as a direct input to the PLATO consortium to study the mission performance and as a basis for further optimization of the CCD operation.

Comparison of persistence in spot versus flat field illumination and single pixel response on a Euclid HAWAII-2RG at ESTEC

Euclid is an ESA mission to map the geometry of the dark Universe with a planned launch date in 2020. Euclid is optimised for two primary cosmological probes, weak gravitational lensing and galaxy clustering. They are implemented through two science instruments on-board Euclid, a visible imager (VIS) and a near-infrared spectro-photometer (NISP), which are being developed and built by the Euclid Consortium instrument development teams. The NISP instrument contains a large focal plane assembly of 16 Teledyne HgCdTe HAWAII-2RG detectors with 2.3μm cut-off wavelength and SIDECAR readout electronics. While most Euclid NISP detector system on-ground tests involve flat-field illumination, some performance tests require point-like sources to be projected onto the detector. For this purpose a dedicated test bench has been developed by ESA at ESTEC including a spot projector capable of generating a Euclid-like PSF. This paper describes the test setup and results from two characterisation tests involving the spot projector. One performance parameter to be addressed by Euclid is image (charge) persistence resulting from previous exposures in the science acquisition sequence. To correlate results from standard on-ground persistence tests from flat-field illumination to realistic scenes, the persistence effect from spot illumination has been evaluated and compared to the flat-field. Another important aspect is the photometric impact of intra-pixel response variations. Preliminary results of this measurement on a single pixel are presented.

Performance Degradation after Proton Irradiation in Charge-Coupled Devices: A Cross-Device Comparison

In the context of the technology validation of Charge-Coupled Devices for Euclid and PLATO, two European Space Agency missions dedicated to Astronomy, we present a comparison between the performance degradation (dark current and charge transfer inefficiency) after proton irradiation of two types of device manufactured by e2v.

Test set up description and performances for HAWAII-2RG detector characterization at ESTEC

In the frame work of the European Space Agencys Cosmic Vision program, the Euclid mission has the objective to map the geometry of the Dark Universe. Galaxies and clusters of galaxies will be observed in the visible and near-infrared wavelengths by an imaging and spectroscopic channel. For the Near Infrared Spectrometer instrument (NISP), the state-of-the-art HAWAII-2RG detectors will be used, associated with the SIDECAR ASIC readout electronic which will perform the image frame acquisitions. To characterize and validate the performance of these detectors, a test bench has been designed, tested and validated. This publication describes the pre-tests performed to build the set up dedicated to dark current measurements and tests requiring reasonably uniform light levels (such as for conversion gain measurements). Successful cryogenic and vacuum tests on commercial LEDs and photodiodes are shown. An optimized feed through in stainless steel with a V-groove to pot the flex cable connecting the SIDECAR ASIC to the room temperature board (JADE2) has been designed and tested. The test set up for quantum efficiency measurements consisting of a lamp, a monochromator, an integrating sphere and set of cold filters, and which is currently under construction will ensure a uniform illumination across the detector with variations lower than 2%. A dedicated spot projector for intra-pixel measurements has been designed and built to reach a spot diameter of 5 μm at 920nm with 2nm of bandwidth [1].

Euclid H2RG detectors: Impact of crosshatch patterns on photometric and centroid errors

In the framework of the ESA’s Science programme, the Euclid mission has the objective to map the geometry of the Dark Universe. For the Near Infrared Spectrometer and Photometer instrument (NISP), the state-of-the-art HAWAII-2RG detectors will be used, in association with the SIDECAR ASIC readout electronics. A dedicated test bench has been designed, developed and validated at ESTEC to perform tests on these detectors. This test bench is equipped with a spot projector system as well as a set of LEDs allowing to project the Euclid like beam and perform persistence measurements. The detector under test shows crosshatch patterns that may correspond to sub-pixel variations in Quantum Efficiency or charge redistribution. The goal of the tests was to evaluate the impact of crosshatches patterns on the Euclid photometric performance and centroid calculation after flat fielding correction. The second part of the publication discusses different persistence mitigation tests using the LEDs test set up.

Investigating end-of-life performance of the PLATO CCD: cryogenic versus room temperature proton irradiation comparison

In the context of PLATO | ESAs exo-Earth hunting mission due for launch in 2026 | the Science Payload Validation team at ESA/ESTEC have performed a cryogenic proton irradiation and testing campaign of the PLATO CCD radiation test vehicle the Teledyne-e2v CCD280. Following the irradiation in standard conditions (room temperature, unbiased) of one device, and the irradiation of another in close to flight conditions (at T=203K and operated), the devices performance (CTI, dark current, hot pixels, trap population) were concurrently monitored over a two month period, first at a constant temperature and then following several temperature cycles. The results of these investigations will be presented.