Large-format infrared detectors are at the heart of major ground and space-based astronomical instruments, and the HgCdTe HxRG is the most widely used. The Near Infrared Spectrometer and Photometer (NISP) of the ESA’s Euclid mission launched in July 2023 hosts 16 H2RG detectors in the focal plane. Their performance relies heavily on the effect of image persistence, which results in residual images that can remain in the detector for a long time contaminating any subsequent observations. Deriving a precise model of image persistence is challenging due to the sensitivity of this effect to observation history going back hours or even days. Nevertheless, persistence removal is a critical part of image processing because it limits the accuracy of the derived cosmological parameters. We will present the empirical model of image persistence derived from ground characterization data, adapted to the Euclid observation sequence and compared with the data obtained during the in-orbit calibrations of the satellite.
Euclid, the M2 mission of the ESA’s Cosmic Vision 2015-2025 program, aims to explore the Dark Universe by conducting a survey of approximately 14 000 deg2 and creating a 3D map of the observable Universe of around 1.5 billion galaxies up to redshift z ∼ 2. This mission uses two main cosmological probes: weak gravitational lensing and galaxy clustering, leveraging the high-resolution imaging capabilities of the Visual Imaging (VIS) instrument and the photometric and spectroscopic measurements of the Near Infrared Spectrometer and Photometer (NISP) instrument. This paper details some of the activities performed during the commissioning phase of the NISP instrument, following the launch of Euclid on July 1, 2023. In particular, we focus on the calibration of the NISP detectors’ baseline and on the performance of a parameter provided by the onboard data processing (called NISP Quality Factor, QF) in detecting the variability of the flux of cosmic rays hitting the NISP detectors. The NISP focal plane hosts sixteen Teledyne HAWAII-2RG (H2RG) detectors. The calibration of these detectors includes the baseline optimization, which optimizes the dynamic range and stability of the signal acquisition. Additionally, this paper investigates the impact of Solar proton flux on the NISP QF, particularly during periods of high Solar activity. Applying a selection criterion on the QF (called NISP QF Proxy), the excess counts are used to monitor the amount of charged particles hitting the NISP detectors. A good correlation was found between the Solar proton flux component above 30 MeV and the NISP QF Proxy, revealing that NISP detectors are not subject to the lower energy components, which are absorbed by the shielding provided by the spacecraft.
The NISP (Near Infrared Spectrometer and Photometer) is one of the two Euclid instruments (see ref [1]). It operates in the near-IR spectral region (950-2020nm) as a photometer and spectrometer. The instrument is composed of: - a cold (135K) optomechanical subsystem consisting of a Silicon carbide structure, an optical assembly, a filter wheel mechanism, a grism wheel mechanism, a calibration unit and a thermal control system - a detection system based on a mosaic of 16 H2RG with their front-end readout electronic. - a warm electronic system (290K) composed of a data processing / detector control unit and of an instrument control unit that interfaces with the spacecraft via a 1553 bus for command and control and via Spacewire links for science data This paper presents: - the final architecture of the flight model instrument and subsystems - the performances and the ground calibration measurement done at NISP level and at Euclid Payload Module level at operational cold temperature.
The Coronagraphic Instrument (CGI) of the Roman Space Telescope NASA space mission is a demonstrator of critical technologies for future space coronagraphs aiming at imaging and spectroscopy of exoplanets and debris disks. Extremely high optical performances are required in term of optical quality of the components inside this instrument. The Stress Mirror Polishing (SMP) technique have been developed for several decades at Laboratoire d’Astrophysique de Marseille (LAM). SMP allows reaching exquisite optical quality on the optics demonstrated through very low Surface Figure Errors (SFE): <5nm RMS on low frequencies, <2nm RMS on middle frequencies (from 3 to 10 cycles per pupil), an extremely low level of high frequencies (no ripples) and micro-roughness < 5Å RMS. In the frame of a scientific international collaboration between NASA and CNES, the French space agency, LAM is selected for the manufacturing of all Off-Axis Parabolas (OAP) for the WFIRST-CGI. LAM has delivered 17 models including one prototype, 8 flight models in July 2021 and 8 flight spares delivered in May 2022. In this paper, we give an overview of the SMP process, from design to manufacturing and verification tests validating the performance. We will present the performance obtained on the first models that have been manufactured compared to theoretical calculations based on requirements for these OAPs.
The Provence Adaptive optics Pyramid Run System (PAPYRUS) is a pyramid-based Adaptive Optics (AO) system that will be installed at the Coude focus of the 1.52m telescope (T152) at the Observatoire de Haute Provence (OHP). The project is being developed by PhD students and Postdocs across France with support from staff members consolidating the existing expertise and hardware into an RD testbed. This testbed allows us to run various pyramid wavefront sensing (WFS) control algorithms on-sky and experiment on new concepts for wavefront control with additional benefit from the high number of available nights at this telescope. It will also function as a teaching tool for students during the planned AO summer school at OHP. To our knowledge, this is one of the first pedagogic pyramid-based AO systems on-sky. The key components of PAPYRUS are a 17x17 actuators Alpao deformable mirror with a Alpao RTC, a very low noise camera OCAM2k, and a 4-faces glass pyramid. PAPYRUS is designed in order to be a simple and modular system to explore wavefront control with a pyramid WFS on sky. We present an overview of PAPYRUS, a description of the opto-mechanical design and the current status of the project.
The segmented pupil experiment for exoplanet detection (SPEED) facility aims to improve knowledge and insight into various areas required for gearing up high-contrast imaging instruments adapted to the unprecedented high angular resolution and complexity of the forthcoming extremely large telescopes (ELTs). SPEED combines an ELT simulator, cophasing optics, wavefront control and shaping with a multi-deformable mirror (DM) system, and optimized small inner-working angle (IWA) coronagraphy. The fundamental objective of the SPEED setup is to demonstrate deep contrast into a dark hole optimized for small field of view and very small IWA, adapted to the hunt of exoplanets in the habitable zone around late-type stars. SPEED is designed to implement an optimized small IWA coronagraph: the phase-induced amplitude apodization complex mask coronagraph (PIAACMC). The PIAACMC consists in a multi-zone phase-shifting focal plane mask (FPM) and two apodization mirrors (PIAA-M1 and PIAA-M2), with strong manufacturing specifications. Recently, a first-generation prototype of a PIAACMC optimized for the SPEED facility has been designed and manufactured. The manufacturing components exhibit high optical quality that meets specifications. In this paper, we present how these components have been characterized by a metrological instrument, an interferential microscope, and then we show what is yielded from this characterization for the FPM and the mirrors. Eventually, we discuss the results and the perspectives of the implementation of the PIAACMC components on the SPEED setup.
Historically, ultraviolet (UV) gratings used in astronomical spectrographs have been made using two different techniques.
Mechanically-ruled gratings have been produced for more than an hundred years. A diamond tool is used to create parallel grooves onto a fine metallic coating layer that has been previously deposited on a polished substrate. The edge-on profile of these grooves is a sawtooth tilted at a specific angle called the "blaze" angle. The blaze angle is the deciding factor that will allow for maximum efficiency at a specific wavelength called the "blaze" wavelength.
Holographic gratings are produced using interference lithography. A layer of photoresist deposited on a substrate is exposed to fringes usually formed by exposure to two coherent laser beams. After development, the resulting pattern is sinusoidal by nature. Blazing one side of the sinusoidal profile of holographic gratings is possible through ion etching, but is only commonly used for a limited subset of grating parameters.
Both types of gratings have different advantages:
- Ruled gratings have a sharp, blazed profile that ensures good efficiency. However, they suffer from groove spacing inconsistencies that lead to stray light and ghosting.
- Holographic gratings do not suffer from groove spacing errors which minimizes stray light. However, their sinusoidal profile (if not ion etched) leads to efficiency losses.
At Penn State University, we are studying new processes that allow to fabricate blazed, high efficiency and high spectral resolution UV gratings for astronomical purposes. These processes are derived from the ones we used in creating X-ray gratings and consist of:
- writing an electron-beam pattern consisting of parallel grooves on a layer of positive resist that has been deposited on a Si substrate.
- dry etching this profile into a hard mask made of silicon nitride.
- wet etching with KOH that will create the sawtooth profile at a specific blaze angle thanks to the properties of the different crystallographic planes of silicon.
Gratings fabricated using these techniques show an excellent behavior all around, combining the best qualities from both ruled and holographic gratings. Indeed, they display a sharp sawtooth profile, they do not suffer from periodicity errors, and grating facets show low roughness. Recent testing show efficiencies that are close to the maximum, theoretical limit. Combined with the possibility to create custom blaze angles through the use of custom cut Si wafers, this opens the way to new applications in the field of astronomical UV spectroscopy.
Historically, ultraviolet (UV) gratings used in astronomical spectrographs have been made using two different techniques.
Mechanically-ruled gratings have been produced for more than a hundred years. A diamond tool is used to create parallel grooves onto a fine metallic coating layer that has been previously deposited on a polished substrate. The edge-on profile of these grooves is a sawtooth tilted at a specific angle called the "blaze" angle. The blaze angle is the deciding factor that will allow for maximum efficiency at a specific wavelength called the "blaze" wavelength.
Holographic gratings are produced using interference lithography. A layer of photoresist deposited on a substrate is exposed to fringes usually formed by exposure to two coherent laser beams. After development, the resulting pattern is sinusoidal by nature. Blazing one side of the sinusoidal profile of holographic gratings is possible through ion etching, but is only commonly used for a limited subset of grating parameters.
Both types of gratings have different advantages:
- Ruled gratings have a sharp, blazed profile that ensures good efficiency. However, they suffer from groove spacing inconsistencies that lead to stray light and ghosting.
- Holographic gratings do not suffer from groove spacing errors which minimizes stray light. However, their sinusoidal profile (if not ion etched) leads to efficiency losses.
At Penn State University, we are studying new processes that allow to fabricate blazed, high efficiency and high spectral resolution UV gratings for astronomical purposes. These processes are derived from the ones we used in creating X-ray gratings and consist of:
1) writing an electron-beam pattern consisting of parallel grooves on a layer of positive resist that has been deposited on a Si substrate.
2) dry etching this profile into a hard mask made of silicon nitride.
3) wet etching with KOH that will create the sawtooth profile at a specific blaze angle thanks to the properties of the different crystallographic planes of silicon.
Gratings fabricated using these techniques show an excellent behavior all around, combining the best qualities from both ruled and holographic gratings. Indeed, they display a sharp sawtooth profile, they do not suffer from periodicity errors, and grating facets show low roughness. Recent testing done at UC Boulder shows efficiencies that are close to the maximum, theoretical limit. Combined with the possibility to create custom blaze angles through the use of custom cut Si wafers, this opens the way to new applications in the field of astronomical UV spectroscopy.
The launch of ESA EUCLID mission is foreseen in 36020. The goal of the mission is to understand the nature of the dark energy and to map the geometry of the dark matter. The EUCLID telescope will be equipped with two instruments working in the visible range (VIS) and in the IR range (NISP) to investigate the distance-redshift relationship and the evolution of cosmic structures. The NISP (Near Infrared Spectro-Photometer) will operate in the near-IR spectral range (0.9-2μm) with two observing modes: the photometric mode for the acquisition of images with broadband filters, and the spectroscopic mode for the acquisition of slitless dispersed images on the detectors. NISP is then using four low resolution grisms to acquire spectroscopic image in different orientations to better distinguish the spectra observed and to cover two spectral ranges: 1250-1850nm range, and 920-1300nm range. Since 2010, Laboratoire d’Astrophysique de Marseille is working on the development and the test of the NISP grisms, that are complex optical components. The grism combines four main optical functions: a grism function done by the grating on the prism hypotenuse, a spectral filter done by a multilayer filter deposited on the first face of the prism, a focus function done by the curved filter face of the prism and a spectral wavefront correction done by the grating which grooves paths are nor parallel, neither straight. The NISP instrument is now entering in the integration phase of the proto flight model of the instrument. Therefore, the NISP grism flight models have been manufactured and delivered to the grism wheel assembly for integration by end of 2017. In this paper, we present the optical performance and characteristics of the four EUCLID NISP grisms flight models that have been developed and manufactured by four different industrial partners then integrated and tested by LAM. We focus on the performance obtained on the optical performance of the component; wavefront error of the components, the spectral transmission and groove profiles. The test results analysis show that the grisms flight models for NISP are well within specifications with an efficiency better than 70% on the spectral bandpass and a wavefront error on surfaces better than 30nm RMS. The results on the component show a good control of the manufacturing and integration process despite the difficulties at the beginning of the project to manufacture these components.
ESA EUCLID mission will be launched in 2020 to understand the nature of the dark energy responsible of the accelerated expansion of the Universe and to map the geometry of the dark matter. The map will investigate the distanceredshift relationship and the evolution of cosmic structures thanks to two instruments: the NISP and the VIS. The NISP (Near Infrared Spectro-Photometer) is operating in the near-IR spectral range (0.9-2μm) with two observing modes: the photometric mode for the acquisition of images with broad band filters, and the spectroscopic mode for the acquisition of slitless dispersed images on the detectors. The spectroscopic mode uses four low resolution grisms to cover two spectral ranges: three "red" grisms for 1250-1850nm range, with three different orientations, and one "blue" grism for 920- 1300nm range. The NISP grisms are complex optical components combining four main optical functions: a grism function (dispersion without beam deviation of the first diffracted order) done by the grating on the prism hypotenuse, a spectral filter done by a multilayer filter deposited on the first face of the prism to select the spectral bandpass, a focus function done by the curved filter face of the prism (curvature radius of 10m) and a spectral wavefront correction done by the grating which grooves paths are nor parallel, neither straight. The development of these components have been started since 10 years at the Laboratoire d’Astrophysique de Marseille (LAM) and was linked to the project phases: prototypes have been developed to demonstrate the feasibility, then engineering and qualification models to validate the optical and mechanical performance of the component, finally the flight models have been manufactured and tested and will be installed on NISP instrument. In this paper, we present the optical performance of the four EUCLID NISP grisms flight models characterized at LAM: wavefront error, spectral transmission and grating groove profiles. The test devices and the methods developed for the characterization of these specific optical components are described. The analysis of the test results have shown that the grisms flight models for NISP are within specifications with an efficiency better than 70% on the spectral bandpass and a wavefront error on surfaces better than 30nm RMS. The components have withstood vibration qualification level up to 11.6g RMS in random test and vacuum cryogenics test down to 130K with measurement of optical quality in transmission. The EUCLID grisms flight models have been delivered to NISP project in November 2017 after the test campaign done at LAM that has demonstrated the compliance to the specifications.
The ESA Euclid mission is intended to explore the dark side of the Universe, particularly to understand the nature of the dark energy responsible of the accelerating expansion of the Universe. One of the two probes carried by this mission is the Baryonic Acoustic Oscillation (BAO) that requires the redshift measurements of millions of galaxies. In the Euclid design, these massive NIR spectroscopic measurements are based on slitless low resolution grisms. These grisms with low groove density and small blaze angle are difficult to manufacture by conventional replica process. Two years ago we started a CNES R&D program to develop grism manufacturing by the photolithographic process which is well adapted to coarse gratings. In addition, this original method allows introducing optical aberration correction by ruling curved and non-parallel grooves in order to simplify the instrument optical design. During the Euclid Phase A, we developed several prototypes of gratings made by photolithography. In this paper, we present the optical performance test results, including tests in the specific environment of the Euclid mission.
In order to study the dark universe (energy and matter), EUCLID space mission will collect near infrared spectra and images of millions of galaxies. This massive measurement survey requires a slitless spectroscopic channel including GRISMs (for “Grating pRISMs”) in NISP (Near Infrared SpectroPhotometer). Very special technical specifications are required for the grating manufacturing: large aperture, low groove frequency and blaze angle, line curvature. In addition, it has to withstand space environment. Therefore, in the frame of a R&D project funded by the CNES, we developed bulk silica gratings in close collaboration with the French company SILIOS Technologies. SILIOS delivered two resin-free blazed gratings with curved lines engraved directly into the fused silica substrate of 80mm and 108mm useful aperture. At LAM, we measured very high optical performances of these prototypes: <80% transmitted efficiency, <30nm RMS wavefront error, groove shape and roughness very close to theory and uniform over the useful aperture. In this paper, we give specifications of these gratings, we describe the manufacturing process developed by SILIOS Technologies, we present briefly optical setups and models allowing optical performances verifications at LAM and we show very encouraging results obtained on the two gratings.
The Euclid mission selected by ESA in the Cosmic Vision program is dedicated to understand dark energy and dark matter. One of the probes based on detection of Baryonic Acoustic Oscillations required the redshift of millions of galaxies. This massive spectroscopic survey relies on the Near Infrared SpectroPhotometer (NISP) using grism in slitless mode. In this Euclid NISP context, we designed a cryogenic mount for the four grisms of the spectroscopic channel. This mount has to maintain optical performances and alignment at the cryogenic temperature of 120K and to survive launch vibrations. Due to a very small mass and volume budget allowed in the Grism Wheel Assembly our design relies on a weight relief Invar ring glued to the grism by tangential flexures. Tangential flexures have the advantage of small height but the drawback of less decoupling capabilities than bipods. We will present the design of the mount and the integration and functional tests to stay within the 60 nm RMS transmitted wavefront error budget allowed to the grism.
Dark matter and dark energy mysteries will be explored by the Euclid ESA M-class space mission which will be launched in 2020. Millions of galaxies will be surveyed through visible imagery and NIR imagery and spectroscopy in order to map in three dimensions the Universe at different evolution stages over the past 10 billion years. The massive NIR spectroscopic survey will be done efficiently by the NISP instrument thanks to the use of grisms (for “Grating pRISMs”) developed under the responsibility of the LAM. In this paper, we present the verification philosophy applied to test and validate each grism before the delivery to the project. The test sequence covers a large set of verifications: optical tests to validate efficiency and WFE of the component, mechanical tests to validate the robustness to vibration, thermal tests to validate its behavior in cryogenic environment and a complete metrology of the assembled component. We show the test results obtained on the first grism Engineering and Qualification Model (EQM) which will be delivered to the NISP project in fall 2016.
In the framework of the European FP7-FISICA (Far Infrared Space Interferometer Critical Assessment) program, we developed a miniaturized version of the hyper-telescope to demonstrate multi-aperture interferometry on ground. This setup would be ultimately integrated into a CubeSat platform, therefore providing the first real demonstrator of a multi aperture Fizeau interferometer in space. In this paper, we describe the optical design of the ground testbed and the data processing pipeline implemented to reconstruct the object image from interferometric data. As a scientific application, we measured the Sun diameter by fitting a limb-darkening model to our data. Finally, we present the design of a CubeSat platform carrying this miniature Fizeau interferometer, which could be used to monitor the Sun diameter over a long in-orbit period.
The Euclid mission objective is to understand why the expansion of the Universe is accelerating through by mapping the geometry of the dark Universe
by investigating the distance-redshift relationship and tracing the evolution of cosmic structures. The Euclid project is part of ESA's Cosmic Vision
program with its launch planned for 2020 (ref [1]).
The NISP (Near Infrared Spectrometer and Photometer) is one of the two Euclid instruments and is operating in the near-IR spectral region (900-
2000nm) as a photometer and spectrometer. The instrument is composed of:
- a cold (135K) optomechanical subsystem consisting of a Silicon carbide structure, an optical assembly (corrector and camera lens), a filter wheel
mechanism, a grism wheel mechanism, a calibration unit and a thermal control system
- a detection subsystem based on a mosaic of 16 HAWAII2RG cooled to 95K with their front-end readout electronic cooled to 140K, integrated on a
mechanical focal plane structure made with molybdenum and aluminum. The detection subsystem is mounted on the optomechanical subsystem
structure
- a warm electronic subsystem (280K) composed of a data processing / detector control unit and of an instrument control unit that interfaces with the
spacecraft via a 1553 bus for command and control and via Spacewire links for science data
This presentation describes the architecture of the instrument at the end of the phase C (Detailed Design Review), the expected performance, the
technological key challenges and preliminary test results obtained for different NISP subsystem breadboards and for the NISP Structural and Thermal
model (STM).
The Euclid space mission aims at elucidating dark matter and dark energy mysteries thanks to two scientific instruments:
VIS, the visible camera and NISP, the Near Infrared Spectro-Photometer. Millions of galaxies spectra will be recorded
thanks to its spectroscopic mode using four grisms developed under LAM (Laboratoire d’Astrophysique de Marseille)
responsibility. These dispersive optical components are made of a grating on a prism and include also, specifically for
NISP, three other optical functions: spectral filtering, focus adjustment and spectral wavefront correction. Therefore,
these optical elements are very challenging to manufacture (four industrial partners work on a single optical component)
and to test before integration into NISP. In this paper, first we describe the optical specifications and the manufacturing
process. Second, we explain the optical validation tests campaign: optical setups, measurements and data processing
procedures used to validate these complex optical components, particularly for transmitted efficiency and wavefront
error for which specifications are very stringent. Finally, we present the first results obtained on the grism EQM which
manufacturing is on-going and almost finished.
Future high-contrast imagers on ground-based extremely large telescopes will have to deal with the segmentation of the primary mirrors. Residual phase errors coming from the phase steps at the edges of the segments will have to be minimized in order to reach the highest possible wavefront correction and thus the best contrast performance. To study these effects, we have developed the MITHIC high-contrast testbed, which is designed to test various strategies for wavefront sensing, including the Zernike sensor for Extremely accurate measurements of Low-level Differential Aberrations (ZELDA) and COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection (COFFEE). We recently equipped the bench with a new atmospheric turbulence simulation module that offers both static phase patterns representing segmented primary mirrors and continuous phase strips representing atmospheric turbulence filtered by an AO or an XAO system. We present a characterisation of the module using different instruments and wavefront sensors, and the first coronagraphic measurements obtained on MITHIC.
The high-contrast imaging instruments VLT/SPHERE and GPI have been routinely observing gas giant planets, brown dwarfs, and debris disks around nearby stars since 2013-2014. In these facilities, low-wind effects or differential aberrations between the extreme Adaptive Optics sensing path and the science path represent critical limitations for the observation of exoplanets orbiting their host star with a contrast ratio larger than 106 at small separations. To circumvent this problem, we proposed ZELDA, a Zernike wavefront sensor to measure these quasistatic aberrations at a nanometric level. A prototype was installed on VLT/SPHERE during its integration in Chile. We recently performed measurements on an internal source with ZELDA in the presence of Zernike or Fourier modes introduced with the deformable mirror of the instrument. In this communication, we present the results of our experiment and report on the contrast gain obtained with a first ZELDA-based wavefront correction. We finally discuss the suitability of such a solution for a possible upgrade of VLT/SPHERE and for its use with future E-ELT instruments or space missions with high-contrast capabilities (e.g. WFIRST-AFTA, HDST).
The grism mount design for the Euclid-NISP mission was studied to maintain optical performances and alignment at cryogenic temperature, and to survive to launch vibrations. An Invar mount with strong weight-relief bonded to the Silica grism through tangential blades has been designed. In spring 2015 we proceeded to thermal cycling and vibration tests to successfully qualify the Grism Engineering Model in the Euclid space environment. Thanks to detailed Finite Element analyses, we correlated simulations and tests. Now that phase C began, we are manufacturing the Engineering and Qualification Model and the four Flight Models. Thus, random coupled analyses of the grisms on the complete wheel assembly and impact of interface preloads on the grism behavior have also been studied.
ESA Euclid mission is designed to map the geometry of the dark Universe. The NISP (Near Infrared Spectro- Photometer) is one of its two instruments dedicated to NIR with two main observing modes: the photometric mode and the spectroscopic mode, for the acquisition of slitless dispersed images using four low resolution grisms: three "red" grisms for 1250-1850nm, and one "blue" grism for 920-1300nm. The NISP grisms are complex optical components that combine four main functions: a grism done by the grating on the prism hypotenuse, a spectral filter done by a multilayer filter deposited on the first surface of the prism, a focus function done by a curved surface and a spectral wavefront correction done by the grating with curved grooves. This specific grating is made thanks to a new technic developed with SILIOS Technologies to manufacture a resin-free grating. The optical component is glued onto a mechanical ring, designed to survive to 60g DLL and to keep optical performance at 130K. The design and manufacturing of these components represent an important challenge to obtain the best performances with very constraining requirements. We will present the performance obtained on scale-1 prototypes of the filter, the grating and the mount manufactured to validate the final design choices and used to make the necessary trade-off during the development phase. All the prototypes have shown very good optical performances and have withstood vibrations and vacuum cryogenic tests that confirm the feasibility of NISP grisms and prepare the next phase for the procurement and tests of NISP grism flight models.
The VLT/SPHERE instrument includes a unique long-slit spectroscopy (LSS) mode coupled with Lyot coronagraphy dedicated to the spectral characterization of directly imaged giant exoplanets. The performance of this mode is limited by its non-optimal coronagraph, but in a previous work we demonstrated that it could be significantly improved at small inner-working angles using the stop-less Lyot coronagraph (SLLC). A prototype of the SLLC was installed in VLT/SPHERE in 2014 during the reintegration of the instrument in Paranal, and it was extensively tested in 2015 to characterize its performance. The performance is tested in both imaging and spectroscopy using data acquired on the internal source of SPHERE. In imaging, we obtain a raw contrast gain of a factor 10 at 0.3" with the SLLC. We also demonstrate that no Lyot stop is required to reach the full performance, which validates the SLLC concept. Comparison with a realistic simulation model shows that we are currently limited by the internal phase aberrations of SPHERE. In spectroscopy, we obtain a gain of 1 mag in a limited range of angular separations. Simulations show that although the main limitation comes from phase errors, the performance in the non-SLLC case is very close to the ultimate limit of the LSS mode. We present the very first on-sky data with the SLLC, which appear extremely promising for the future scientific exploitation of an apodized LSS mode in SPHERE. Finally, we explore a new possibility for the speckle subtraction in the LSS mode that could significantly improve the data analysis with respect to methods based on spectral differences.
PILOT is a stratospheric experiment designed to measure the polarization of dust FIR emission, towards the diffuse interstellar medium. The first PILOT flight was carried out from Timmins in Ontario-Canada on September 20th 2015. The flight has been part of a launch campaign operated by the CNES, which has allowed to launch 4 experiments, including PILOT. The purpose of this paper is to describe the performance of the instrument in flight and to perform a first comparison with those achieved during ground tests. The analysis of the flight data is on-going, in particular the identification of instrumental systematic effects, the minimization of their impact and the quantification of their remaining effect on the polarization data. At the end of this paper, we shortly illustrate the quality of the scientific observations obtained during this first flight, at the current stage of systematic effect removal.
Direct imaging of exoplanets is very attractive but challenging and specific instruments like Sphere (VLT) or GPI (Gemini) are required to provide contrasts up to 16-17 magnitudes at a fraction of arcsec. To reach higher contrasts and detect fainter exoplanets, more-achromatic coronagraphs and a more-accurate wavefront control are needed. We already demontrated contrasts of ~10-8 at ~4 λ/D at 635nm using a four quadrant phase mask and a self-coherent camera on our THD bench in laboratory. In this paper, we list the different techniques that were tested on the THD bench in monochromatic and polychromatic lights. Then, we present the upgraded version of the THD bench that includes several deformable mirrors for correcting phase and amplitude simultaneously and obtain a field-of-view covering the complete 360 degrees arouns the star with contrasts down to ~10-8 -10-9.
The exoplanet direct imagers Gemini/GPI and VLT/SPHERE are built around extreme adaptive optics (ExAO)
to correct the atmospheric turbulence and the aberrations associated with the optical surfaces. However, additional
strategies are necessary to correct the non-common path aberrations (NCPA) between the ExAO and
science paths that can limit the instrument contrast performance. To perform an adequate calibration, we have
developed ZELDA, a Zernike sensor to achieve NCPA measurements with nanometric accuracy. We report the
results of a new design analysis that maximizes the dynamic range, and from laboratory demonstrations on the
LAM high-contrast testbed and on VLT/SPHERE during its integration.
The ESA mission Euclid is designed to map the geometry of the dark Universe by investigating the distance-redshift
relationship and the evolution of cosmic structures. In the Euclid design of the NISP instrument, the spectroscopic
channel uses four slitless low resolution grisms in NIR wavelength with four different orientations. Euclid grisms
combine two optical functions: a grism function (ie dispersion without deviation at a specific wavelength) done by the
grating associated with the prism and a spectral filter function done by a multilayer filter deposited on the entrance
surface of the prism. After a successful development of a prototype of a grating realized by a photolithography process,
we have begun a new phase of the prototype to manufacture a complete component, with a grism and a filter, and to
validate its performance. Its development is very challenging as it requires manufacturing of the component in several
steps which involve three different companies. We will present first the main optical requirements for the grism defined
for the phase B and how the efficiency and wavefront specifications are split into the different components of the grism
(mechanical mount, grating and filter). Then, we will describe the manufacturing process chosen for the NISP grism.
Finally, we will present the first results of the optical characterisation of the prototype of the grism: global efficiency
measurement, shape of the groove, wavefront contribution, and the trade-off made to achieve the final performance.
A GRISM, made of a grating on a prism, allow combining image and spectroscopy of the same field of view with the
same optical system and detector, thus simplify instrument concept. New GRISM designs impose technical
specifications difficult to reach with classical grating manufacturing processes: large useful aperture (>100mm), low
groove frequency (<30g/mm), small blaze angle (<3°) and, last but not least, line curvature allowing wavefront
corrections. In addition, gratings are commonly made of resin which may not be suitable to withstand the extreme space
environment. Therefore, in the frame of a R&D project financed by the CNES, SILIOS Technologies developed a new
resin-free grating manufacturing process and realized a first 80mm diameter prototype optically tested at LAM. We
present detailed specifications of this resin-free grating, the manufacturing process, optical setups and models for optical
performance verification and very encouraging results obtained on the first 80mm diameter grating prototype: >80%
transmitted efficiency, <30nm RMS wavefront error, groove shape and roughness very close to theory and uniform over
the useful aperture.
Direct imaging of exoplanets is very attractive but challenging. It requires high angular resolution and very high-contrast imaging. One solution is the use of coronagraphs behind the adaptive optics of large telescopes. Unfortunately, optics of space telescope and ground telescope introduce quasi-static aberrations which strongly limit the quality of the final image and a dedicated stage of adaptive optics is required. We proposed a self- coherent camera (SCC) in 2006 and we obtained contrast levels of (approximately equal to) 2 10-8 at a few λ0=D at 638 nm in laboratory. In this paper, we explain how to achromatize the SCC. We present laboratory performance in wide spectral band (approximately equal to) 5 - 10 % bandpass.
The FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon-2) is a balloon-borne ultraviolet spectro-imaging mission optimized for the study of faint diffuse emission around galaxies. A key optical component of the new spectrograph design is the high throughput cost-effective holographic 2400 ℓ =mm, 110x130mm aspherized reflective grating used in the range 200 - 208nm, near 28°deviation angle. In order to anticipate the efficiency in flight conditions, we have developed a PCGrate model for the FIREBall grating calibrated on linearly polarized measurements at 12° deviation angle in the range 240-350nm of a 50x50mm replica of the same master selected for the flight grating. This model predicts an efficiency within [64:7; 64:9]±0:7% (S polarization) and [38:3; 45]±2:2% (P-polarization) for the baseline aluminum coated grating with an Al2O3 natural oxidation layer and within [63:5; 65] ±1% (S-polarization) and [51:3; 54:8] ±2:8% (P-polarization) for an aluminum plus a 70nm MgF2 coating, in the range 200 - 208nm and for a 28°deviation angle. The model also shows there is room for significant improvements at shorter wavelengths, of interest for future deep UV spectroscopic missions.
The spectroscopic channel of the Euclid Near Infrared SpectroPhotometer (NISP) relies on four grisms mounted on a
wheel via Invar mounts. The mount design was studied to maintain the optical performances and alignment at cryogenic
operating temperature (120K), and to survive launch vibrations. We designed two stages of radially compliant blades:
one set of 9 blades is bonded to the Silica grism and the second set of 3 blades is located at interface points with the
wheel. Severe packaging and mass constraints yielded us to design a ring mount with strong weight relief. In fall 2013
we proceeded to thermal cycling (323K-105K), vibration tests (10.7 g rms) to successfully qualify the grism mount in the
Euclid environment. Thanks to detailed finite element analyses, we correlated simulations and tests.
The ESA mission Euclid is designed to explore the dark side of the Universe and to understand the nature of the dark energy responsible of the accelerating expansion of the Universe. One of the two probes carried by this mission is based on the Baryonic Acoustic Oscillation (BAO) method that requires the redshift measurements of millions of galaxies. In the Euclid design the spectroscopic channel uses slitless low resolution grisms. Classical grisms, manufactured by replication of a ruled master on the hypotenuse of a prism, are extremely difficult to make for Euclid due to the combination of low groove density and small blaze angle. Two years ago we started an RandD program to develop grisms by the photolithography process that is well adapted to coarse gratings and allows introducing aberration correction by ruling curved and non parallel grooves. During the Euclid Phase A, we developed several prototypes made by photolithography and we present in this paper the test results done in the specific environment of the Euclid mission.
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