Design and development of a freeform active mirror for an astronomy application

The advent of extremely large telescopes will bring unprecedented light-collecting power and spatial resolution, but it will also lead to a significant increase in the size and complexity of focal-plane instruments. The use of freeform mirrors could drastically reduce the number of components in optical systems. Currently, manufacturing issues limit the common use of freeform mirrors at short wavelengths. This article outlines the use of freeform mirrors in astronomical instruments with a description of two efficient freeform optical systems. A new manufacturing method is presented which seeks to overcome the manufacturing issues through hydroforming of thin polished substrates. A specific design of an active array is detailed, which will compensate for residual manufacturing errors, thermoelastic deformation, and gravity-induced errors during observations. The combined hydroformed mirror and the active array comprise the Freeform Active Mirror Experiment, which will produce an accurate, compact, and stable freeform optics dedicated to visible and near-infrared observations.Comment: 11 pages, 12 figure

Astronomical optics and plasticity : developments in optical fabrication dedicated to freeform active mirrors.

La prochaine décennie instrumentale en astronomie se veut extrême. Elle s’ouvre avec l'arrivée des ELTs (Extremely Large Telescopes). Leur miroir primaire géant permettra d'augmenter considérablement la quantité de flux collectée et d'améliorer la résolution angulaire, paramètres clés pour l'observation et l'imagerie de sources astrophysiques. Des conséquences directes sont l'augmentation de la complexité, de l'envergure et de la masse des instruments placés aux foyers de ces télescopes. Une solution passe par l'utilisation de miroirs de formes libres. Or aujourd’hui, obtenir ces formes exotiques via les méthodes traditionnelles de fabrication optique n’est pas possible et un appel à de nouvelles ruptures technologiques s'avère nécessaire. Cette thèse présente un travail de recherche et développement amont portant sur un procédé de fabrication innovant permettant de fournir des miroirs de formes libres, avec les performances optiques requises en observations visibles et infrarouges. Ce procédé est une évolution des techniques d'Optique Active et exploite la déformation plastique des matériaux métalliques. Cependant, le domaine plastique reste un domaine de comportements non-linéaires analytiquement complexes. Il est alors d'intérêt de comparer des modèles par éléments finis avec des essais réels. Ces derniers ont nécessité la mise en place de la gamme complète de fabrication des substrats et des moyens d’essais. Les premiers miroirs obtenus pourront mettre en évidence les paramètres principaux à prendre en compte ainsi que leur niveau de sensibilité, pour ensuite converger vers des modèles éléments finis fiables et une solution de fabrication optique maîtrisée.The next instrumental decade in astronomy aims to be extreme. It opens with the arrival of ELTs (Extremely Large Telescopes). Their giant primary mirrors will increase the light collecting power and the angular resolution, key parameters for observing and imaging of celestial bodies. However, this also leads to an increase in the complexity, size and weight of their focal-plane instruments, to minimize flux lost and to correct for the aberrations introduced. A solution would be to implement freeform mirrors inside the optical systems of these instruments. Today, it is not possible to obtain these exotic mirror shapes using the current optical fabrication techniques and new technological breakthroughs in this domain are essential. This PhD thesis present research and development work, in upstream phase, of an innovative manufacturing process to supply freeform mirrors, which should meet required optical performances in Visible and Infrared wavelength astronomical observations. This method is an evolution of Active Optics techniques and based on the ability of metallic materials to plasticize. However, the plasticity of metallic materials remains a field of non-linear behaviours and analytically complex. It is important to compare modeling from finite element analysis and real tests. For these tests, the complete manufacturing steps of the metallic substrates were put in place. The first mirrors obtained will highlight the main working parameters and their sensibility levels, and then converge toward reliable finite elements models and a mastered solution of optical freeform mirrors fabrication

SPIRou @CFHT: full in-lab and on-sky performances

International audienceSPIRou is the new high resolution echelle spectropolarimeter and high-precision velocimeter, in the near infra- red, for the 3.6m Canada-France-Hawaii Telescope (CFHT Mauna Kea). This next generation instrument aims at detecting and characterizing Earth-like planets in the habitable zone of low-mass dwarfs and at investigating how magnetic fields impact star and planet formation. SPIRou consists of an achromatic polarimetric module coupled with a fluoride fiber link to a thermally-controlled cryogenic echelle spectrograph, and a Calibration Unit which can fed the light of hollow-cathod lamps, a radial velocity reference (Fabry-Pérot), or a cold source to the polarimeter and/or the spectrograph. Here we present a summary of the full performances obtained in laboratory tests carried in Toulouse (France), and the first results of the on-going commissioning at the CFHT. SPIRou covers a spectral range from 0.96 to 2.48 μm (YJHK domain) in one single exposure at a resolving power of 70 K, providing unpolarized and polarized spectra (with sensitivity 10 ppm) of stars, with a 10 15% peak throughput. Lab tests demonstrate that SPIRou is capable of achieving a relative radial velocity precision better than 0.2 m/s rms on timescales of 24 hr. Science operations of SPIRou are expected to start in 2018 S2, enabling significant synergies with major space and ground instruments such as the JWST, TESS, ALMA and later-on PLATO and the ELT

LUCAS Experiment : searching for vegetation and other biosignatures on planet Earth

International audienc

LUCAS Experiment : searching for vegetation and other biosignatures on planet Earth

International audienc

LUCAS Experiment : searching for vegetation and other biosignatures on planet Earth

International audienc

The LUCAS program: detecting vegetation and traces of life in the Earthshine

International audienceThe aim of the LUCAS program is to observe chlorophyll and atmospheric molecules in the Earthshine spectrum in order to prepare the detection of life in terrestrial extrasolar planets to be discovered. Actually, observations from Antarctica offer a unique possibility to study the variations of Earthshine spectrum during Earth rotation while various parts of Earth are facing the Moon. Special instrumentation for the LUCAS program was designed and put in the Concordia station in the Dome C. Observations are in progress

MOSAIC on the ELT : optomechanical design of the NIR spectrograph

International audienceContext. The circumgalactic medium (CGM) is the location where the interplay between large-scale outflows and accretion onto galaxies occurs. Metals in different ionization states flowing between the circumgalactic and intergalactic mediums are affected by large galactic outflows and low-ionization state inflowing gas. Observational studies on their spatial distribution and their relation with galaxy properties may provide important constraints on models of galaxy formation and evolution. Aims. The main goal of this paper is to provide new insights into the spatial distribution of the circumgalactic of star-forming galaxies at 1.5  1.5) and stellar mass (log[ M ⋆ / M ⊙ ] > 10.2) show stronger C IV absorptions compared with those low SFR (log[SFR/( M ⊙ yr −1 )] < 0.9) and low stellar mass (log[ M ⋆ / M ⊙ ] < 9.26). The latter population instead shows stronger C II absorption than their more massive or more star-forming counterparts. We compute the C II /C IV W 0 line ratio that confirms the C II and C IV correlations with impact parameter, stellar mass, and star formation rate. We do not find any correlation with ϕ in agreement with other high-redshift studies and in contradiction to what is observed at low redshift where large-scale outflows along the minor axis forming bipolar outflows are detected. Conclusions. We find that the stronger C IV line absorptions in the outer regions of these star-forming galaxies could be explained by stronger outflows in galaxies with higher star formation rates and stellar masses that are capable of projecting the ionized gas up to large distances and/or by stronger UV ionizing radiation in these galaxies that is able to ionize the gas even at large distances. On the other hand, low-mass galaxies show stronger C II absorptions, suggesting larger reservoirs of cold gas that could be explained by a softer radiation field unable to ionize high-ionization state lines or by the galactic fountain scenario where metal-rich gas ejected from previous star formation episodes falls back to the galaxy. These large reservoirs of cold neutral gas around low-mass galaxies could be funnelled into the galaxies and eventually provide the necessary fuel to sustain star formation activity

SPIRou at CFHT: fiber links and pupil slicer

International audienceSPIRou is a near-IR (0.98-2.35μm) echelle spectropolarimeter / high precision velocimeter installed at the beginning of the year 2018 on the 3.6m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea, Hawaii, with the main goal of detecting Earth-like planets around low mass stars and magnetic fields of forming stars. In this paper, the fiber links which connects the polarimeter unit to the cryogenic spectrograph unit (35 meter apart) are described. The pupil slicer which forms a slit compatible with the spectrograph entrance specifications is also discussed in this paper. Some challenging aspects are presented. In particular this paper will focus on the manufacturing of 35 meter fibers with a very low loss attenuation (< 13dB/km) in the non-usual fiber spectral domain from 0.98 μm to 2.35 μm. Other aspects as the scrambling performance of the fiber links to reach high accuracy radial velocity measurements (<1m/s) and the performances of the pupil slicer exposed at a cryogenic and vacuum environment will be discussed