Subwavelength gratings for phase mask coronagraphy: the 4QZOG and AGPM coronagraphs

We present two new phase mask coronagraphs implemented with subwavelength diffractive optical elements. The first one is an evolution of the four quadrant phase mask coronagraph (FQPM), which resolves the π phase shift chromaticity issue: the four quadrant zeroth order grating (4QZOG). The second one is a totally new design consisting of an optical vortex induced by a space-variant grating: the annular groove phase mask (AGPM) coronagraph is fully symmetric and free from any "shaded zones". The potential performances of the 4QZOG and AGPM coronagraph are very good, ensuring, for instance, a theoretical contrast of 1.4 x 10^(-7) at 3λ/D over the whole K band. These coronagraphs could be used alone on single-pupil telescopes either in space or on the ground (with an adaptive optics system) to detect exoplanets

Manufacturing of four-quadrant phase mask for nulling interferometry in the thermal infrared

The Four Quadrant Phase Mask is a key component for the design of advanced coronagraphs that may be used to search exo-planets. The validity of this concept has been demonstrated in the visible and need now to be demonstrated in the mid infrared. For this purpose, two components are manufactured for wavelengths 4.75 and 16.25 μm. This manufacturing requires the deposition of ZnSe layers using Ion Assisted Deposition, followed by a lift off process

A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique

AIMS: We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg^2 of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources. METHODS: The KX method identifies quasars on the basis of their optical (R and z') to near-infrared (Ks) photometry and point-like morphology. We combine these data with optical (u*,g'r',i',z') and mid-infrared (3.6-24 micron) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars. RESULTS: Of 93 sources selected as candidate quasars by the KX method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 < z < 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies.Comment: 13 pages, 9 figures, A&A 494, p. 579-589. Replaced with published version. Fig. 9 in first astro-ph submission has been update

Manufacturing of four-quadrant phase mask for nulling interferometry in the thermal infrared

The Four Quadrant Phase Mask is a key component for the design of advanced coronagraphs that may be used to search exo-planets. The validity of this concept has been demonstrated in the visible and need now to be demonstrated in the mid infrared. For this purpose, two components are manufactured for wavelengths 4.75 and 16.25 μm. This manufacturing requires the deposition of ZnSe layers using Ion Assisted Deposition, followed by a lift off process

Coronographie à masque de phase: applications aux télescopes et interféromètres au sol et dans l'espace

Pr. Pierre Encrenaz , Pr. Jean Gay , Pr. Laurent Koechlin , Pr. Alain Léger , Pr. Salvador Cuevas , Pr. Antoine Labeyrie , Pr. Daniel RouanIn this thesis work a complete study of the four quadrants coronagraph is presented. This new coronagraph offers performances of extremely large theorical rejection factor (>10^6). These performances open possibilities of exo-planets detection around nearby stars. The first laboratory results gave an attenuation rate higher than 90000 on the central peak. Thus, I naturally studied all the possible uses of this coronagraph on ground-based as well as on the space telescopes. On the former, this device can be used, coupled with high order adaptive optics for detection of brown dwarves and hot giant planets around the closest stars. On the latter, I focalized my interest on the MIRI instrument (Mid InfraRed Imager) for the NGST telescope, and on a space interferometer (for ``Terrestrial Planet Finder'') of NASA. Numerical simulations are presented within the framework of the ``Planet Finder'' ESO project. Nevertheless, an important problem must be solved: the chromatism of \pi phase-shift. Thus, I will present three solutions leading to the achromatisation of the coronagraph.Je présente dans mon travail de thèse une étude complète du coronographe à quatre quadrants proposé par D. Rouan (2000). Ce nouveau coronographe offre des performances de réjection théoriques extrêmement importantes (>10^6). Ces performances ouvrent des possibilités de détection d'exo-planètes autour des étoiles proches. Les premiers résultats en laboratoire, ont donné des taux d'atténuation de l'étoile centrale supérieurs à 90000\footnote(: le résumée de la thèse indique 44000, mais une calibration fine de la densité employée nous donne 90000. ) sur le pic central. J'ai donc naturellement étudié toutes les utilisations possibles de ce coronographe au sol comme dans l'espace. En premier lieu, il peut être utilisé sur les télescopes au sol avec une optique adaptative à haut Strehl. Des simulations numériques seront présentées dans le cadre du projet ``Planet Finder'' de l'ESO pour la détection des naines brunes et des planètes géantes chaudes autour des étoiles les plus proches. Ensuite, je me suis intéressé à l'utilisation du 4Q sur l'instrument MIRI (Mid InfraRed Imager) du JWST, puis sur un interféromètre spatial (pour ``Terrestrial Planet Finder'') de la NASA. Néanmoins, un des problèmes majeurs du masque à 4 quadrants reste le chromatisme du déphasage de pi pour une utilisation en large bande dans le cadre de TPF. Je présenterai donc des solutions permettant d'achromatiser le coronographe

Limitation of the Pupil Replication Technique in the Presence of Instrumental Defects

Pupil replication has been proposed by Greenaway et al. as a new optical technique to improve the suppression of starlight in high dynamic imaging. This Letter extends numerical simulations in the two-dimensional case with various realistic imperfections (surface error, chromatic smearing, and pupil shift). These results demonstrate some strong limitations compared to single-pupil apodization techniques for exoplanet detection

Coronographie à masque de phase (applications aux télescopes et interféromètres au sol et dans l'espace)

PARIS-BIUSJ-Thèses (751052125) / SudocMEUDON-Observatoire (920482302) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF