Christelle Rossin

Euclid near-infrared spectrophotometer instrument concept at the end of the phase A study

The Euclid mission objective is to map the geometry of the dark Universe by investigating the distance-redshift relationship and the evolution of cosmic structures. The NISP (Near Infrared Spectro-Photometer) is one of the two Euclid instruments operating in the near-IR spectral region (0.9-2μm). The instrument is composed of: - a cold (140K) optomechanical subsystem constituted by a SiC structure, an optical assembly, a filter wheel mechanism, a grism wheel mechanism, a calibration unit and a thermal control - a detection subsystem based on a mosaic of 16 Teledyne HAWAII2RG 2.4μm. 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. This presentation will describe the architecture of the instrument, the expected performance and the technological key challenges. This paper is presented on behalf of the Euclid Consortium.

The microchannel x-ray telescope for the gamma-ray burst mission SVOM

We present the Microchannel X-ray Telescope, a new light and compact focussing telescope that will be ying on the Sino-French SVOM mission dedicated to Gamma-Ray Burst science. The MXT design is based on the coupling of square pore micro-channel plates with a low noise pnCCD. MXT will provide an effective area of about 50 cm2, and its point spread function is expected to be better than 3.7 arc min (FWHM) on axis. The estimated sensitivity is adequate to detect all the afterglows of the SVOM GRBs, and to localize them to better then 60 arc sec after five minutes of observation.

An integral field spectrograph for SNAP

A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Iz supernovae and to standardize the magnitude of each candidate by determining explosion parameters. The spectrograph is also a key element for the calibration of the science mission. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.

Final design of the grism cryogenic mount for the Euclid-NISP mission

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.

Design, development, and test of a grism prototype for Euclid-NISP mission

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.

Semi-kinematic mount of the FIREBALL large optics

In the context of the NASA CNES FIREBALL balloon borne experiment, we present the design of a semi-kinematic mount to hold the 1 meter class mirrors of this mission. To maintain these large optics in a reasonable mass and price budgets we choose thin ULE mirrors with a thickness over diameter ratio of 1/16. Such thin mirrors require a multi support mount to reduce self weight deflection. Classical multi support mount used for ground based telescope would not survive the level of shock observed in a balloon experiment either at parachute opening or landing. To firmly maintain these mirrors in several points without noticeably deforming them we investigated the design of a two stages semi-kinematic mount composed of 24 monopods. We present the detailed design of this innovative mirror mount, the finite element modeling with the deduced optical wavefront deformation. During the FIREBALL integration and flight campaign in July 2007 at CSBF, we confirmed the validity of the mechanical concept by obtaining an image quality well within the required specifications. Variants of this approach are potentially applicable to large thin mirrors on ground-based observatories.

GALEX UV grism for slitless spectroscopy survey

The NASA Space Mission Galex is designed to map the history of star formation by performing imaging and spectroscopic surveys in vacuum ultraviolet. The dispersive component for the spectroscopic mode is a CaF2 Grism which can be inserted with loose tolerances in the convergent beam to produce slitless spectra. Grisms are widely used in ground based astronomy in the visible or near infrared bands but the UV cutoff of the resin involved in their manufacturing process prevents their use in the UV range. LAS and Jobin-Yvon developed a proprietary process to imprint the blazed profile into the CaF2 crystal. We will present the measured optical performance of prototypes and flight models delivered this summer to NASA/JPL. We will also present a three bipod flexures mount we designed to minimize the mechanical stress on the optical component. The flight Grism bonded to such a mount has successfully passed the Galex environmental qualification.

The EUCLID NISP grisms flight models performance

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.

Optical verification tests of the NISP/Euclid grism qualification model

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.

Final design and choices for EUCLID NISP grism

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.