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The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, 20091 Laurent Koechlin 1, Jean-Pierre Rivet 2, Truswin Raksasataya.

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Presentation on theme: "The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, 20091 Laurent Koechlin 1, Jean-Pierre Rivet 2, Truswin Raksasataya."— Presentation transcript:

1 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Laurent Koechlin 1, Jean-Pierre Rivet 2, Truswin Raksasataya 1, Paul Deba 1, Denis Serre 3. 1 Université de Toulouse CNRS 2 Observatoire de la côte d'Azur CNRS 3 Leiden University, the Netherlands The Fresnel Imager for exoplanet study

2 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, I. Concept

3 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Plane wavefront focus Order 0 : plane wave Lens (or miror): focusing by refraction (or reflexion) Fresnel array: focusing by diffraction … Optical concept: Light focalization Order 1 : convergent focus Lens Binary transmission function g(x) Spherical wavefront

4 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Optical concept : Image formation non linear luminosity scale, to show the spikes. Image Aperture Quasi no stray light except in four spikes. Transmission: g(x) Transmission: g(x) "xor" g(y) Can light travel free in vacuum all the way from source to focus?

5 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Basic concepts: Fresnel arrays versus solid aperture 3000 Fresnel zones Images of a point source by: 300 Fresnel zones Solid square aperture luminosity scale: Power 1/4 to show spikes

6 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Position in the field (resels) 1/4 field represented Log dynamic Basic concepts: Dynamic range & resolution PSF for 300 zones ( apertures) apodized prolate, order 0 masked Numerical Fresnel propagation

7 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, "Against" Fresnel Arrays: Chromaticity... But can be canceled by order -1 chromaticity after focus, Channel bandpass limitations: Δλ/λ= 15% transmission efficiency to focus: 6% to 10% 1km to 100km focal lengths => Formation flying in space f = D 2 /8zλ D f

8 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, "pro" Fresnel Arrays: No mirror, no lens : just vacuum and opaque material (except near focal plane). broad spectral domain: λ = 90nm (UV) to (IR) 25μm Large tolerance in positioning of subapertures: for λ/50 wavefront quality in the UV on a 30 meters membrane array: 50 μm in the plane of the membrane, 10 mm perp. to membrane, The tolerance is wavelength independent. Opens the way to large (up to 100m?) aberration-free apertures. High dynamic range: 10 8 on compact objects, more with coronagraphy & postprocessing. High angular resolution: as a solid aperture the size of the array.

9 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, II. Tests Does it work ?

10 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, x2 cm array I have it here, It's working. live demo after this session. For those who Haven't already Seen it…

11 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, x8 cm array: tests on lab sources ( ) 116 zones, 8 x 8 cm apertures "orthocircular" design. F= 23 m at = 600 nm Precision: 5 m on holes positioning => /70 on wavefront. Achievements: Diffraction limited Broad band imaging ( nm) dynamic range Photo T.Raksasataya metal foil 100 m thick

12 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, x20 cm array: test on sky sources ( ) Photo D.Serre 0.8" resolution1000x1000 fieldλ 0 = 800 nm Δλ = 100 nm

13 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Metal foil apertures, Slightly apodized, 696 Fresnel zones. 20 cm Photo P.Deba

14 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, x20 cm array: first light on stars 52 Cygni a-b Va= 4.2 vb= 8.7 sep= 6.4" ALINEMENT PHASE images: temporary 116 zones secondary (instead of 702 zones) Tip-Tilt not yet implemented STT 433 a-b Va=4.36 ; Vb=10.0Sep= 15" more results at our workshop in Nice next week

15 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, cm array goals Assess performances on real sky objects: do better than other 20 cm aperture instruments. Targets: High contrast objects extended sources dense fields deep sky

16 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, ESA study ESA call for Feasibility study of a membrane telescope350 k

17 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, III. Space Mission Science ? Credibility ?

18 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, The Fresnel Imager Space Mission Field optics telescope 1/10 th to 1/20 th the diameter of Primary Array. Dispersion correction: order -1 diffraction Blazed lens or concave grating, 10 to 30 cm diameter focal Instrumentation: Spectro-imagers Thin membrane "Primary Array" module: 3m to 100m diameter, or more.

19 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Rationale Meet acceptability threshold for a new technology mission Make it simple, try to keep cost below 300 M Scientific return over cost : must be higher than that of competing concepts λ/50 wavefront, at any λ => High Dynamic range from IR to UV mas angular resolution 1000x1000 resel. fields Spectral resolution Suitable for Exoplanets and other fieds too…

20 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Strategy, sky targets - Start with UV domain? - spectral lines in UV for: Photosynthesis break, O 3, CH 4, CO 2, auroras … - polarimetry - limited budget => limited aperture, but high resolution - High quality wavefront at any wavelength - angular resolution : 7 mas with a 4m Fresnel array

21 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Space Mission: optical scheme Focal instruments 5 km (for a 4m aperture) to 100 km (for a 30m aperture) image plane 2 achromatic pupil plane Spacecraft 1 Spacecraft 2 image plane 1 dispersed Diffraction order 1: focused, but with chromatic aberration. Diffraction order 0: unfocussed will be focused by field optics, then blocked. Field optics telescope Chromatic correction: Blazed Fresnel grating Large "Primary Fresnel Array: Thin foil, 4 to 30 m diameter, or more. Order zero blocked Solar Baffle, to protect from sunlight Focal instrum.

22 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Targets: S/N on exoplanets in UV Signal / noise as a function of 1 Jupiter diameter planet 0.5 Jupiter diameter Images & spectra of exoplanets: 1 UA from solar type star, 10 Pc away Signal / noise < 3 Signal / noise > 3 Signal / noise > 30 Signal / noise < 3 Signal / noise > 3 4m aperture, 10h integration spectral res. = 50 dynamic range of raw image: 2 10^-8 uv

23 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Conclusion Science cases: Exoplanets, and also stellar physics compact objects reflection nebulae extragalactic solar system objects observation of the earth 2 1/2 days workshop in Nice, Sept (next week) Free registration Build up a proposal for a 2020 / 2025 launch Web site: search with key words "fresnel imager Nice" We are starting a "Fresnel Imager Astro Applications" group.

24 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Thank you for your attention! You are welcome to join us. Workshop: sept (next week)

25 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17,

26 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Bonus slides

27 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Circular Fresnel Zone Plate => PSF with isotropic rings Image Optical concept : Image formation non linear luminosity scale to show the rings. Aperture Isotropic rings

28 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Géométrie "orthogonale pure" (2005) 4 % de la lumière focalisée expansion 2D Cartésienne Réseau de Fresnel ou Interféromètre à forte densité douvertures ? 1740 motifs individuels Géométrie "ortho-circulaire" (2008) 6 % de la lumière focalisée

29 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, The field vs spectral bandpas tradeoff Chromatically aberrated beam at prime focus Field delimited by field mirror The chromatic corrector does a good job, but it corrects only what it collects.

30 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Fresnel Imager specifications UV spectro-Imaging at High Dynamic Range 4m aperture 3 spectral bands Δλ/λ=20%: 2 in the UV, 1 in the visible λ/50 wavefront spectral resolution λ/δλ=50 angular resolution 7 to 25 mas depending on λ field 1000x1000 => 7 to 25 arc seconds raw dynamic range > with 10 hours integrations time: jovian exoplanets with apertures of 1 m or more telluric Exoplanets: only with 10 meters apertures or larger - Other fields of astrophysics

31 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Gen III prototype: Primary array Size : 8 cm, square 240 Fresnel zones ( apertures) metal sheet 100 m thick, laser carved Operates in the UV ( nm) Focal length: 26.6 m for = 250 nm Precision on array : 5 m i.e. /30 on wavefront R&T financed by CNES & STAE

32 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Gen III prototype Critical point: concave blazed mirror in focal module

33 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, eclipticque sun petite Lissajou periode : 6 mois 1 eclipse en 6 ans, évitable sun éclipticque Terre Lune L km 8° 14° Fresnel baffle Lingne de visée Antenne RA fixe et GS fixe possible à partir de km de la Terre Seul, Lagrange L2 répond à tous les besoins: –pas de gradient de gravité sur une grande base –masquage du soleil et de la Terre dans un angle réduit –bonne liberté de pointage Pour la très haute dynamique: nécessité de masquer toute lumière parasite avec taille pare soleil réduit et possibilité de dépointage acceptable: 35% de la voûte à tout instant, 100% en 4 mois. implique petite ou moyenne orbite de Lissajou Orbites et pointages

34 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Résultats qualitatifs : dynamique mesure optique et simulation numérique 8 cm 116 zones image Optique 8 cm 116 zones propagation de Fresnel numerique par tous les éléments optiques Dans ces images d'un point, saturées, le fond moyen est à 2 *10 -6 Luminosité amplifiée x1000 propagation numerique de Fresnel développée pour tester de grands réseaux Luminosité amplifiée x1000

35 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Géométrie "orthogonale pure" (2005) 4 % de la lumière focalisée expansion 2D Cartésienne Réseau de Fresnel ou Interféromètre à forte densité douvertures ? 1740 motifs individuels Géométrie "ortho-circulaire" (2008) 6 % de la lumière focalisée

36 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, Fields obtained with 2 exposures rotated 45°

37 The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets BarcelonaSeptember 17, scenarios


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