Presentation is loading. Please wait.

Presentation is loading. Please wait.

The Fresnel Imager for exoplanet study

Similar presentations

Presentation on theme: "The Fresnel Imager for exoplanet study"— Presentation transcript:

1 The Fresnel Imager for exoplanet study
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 I will present here an optical concept to enable very large apertures in space. This cobncept yields high resolution and high dynamic range images With very simple optics (no optics at all?) I will try to summarize four years of work in 10 minutes.

2 I. Concept Three parts : concepts, tests, space mission

3 Optical concept: Light focalization
Lens Plane wavefront focus Spherical wavefront Lens (or miror): focusing by refraction (or reflexion) Fresnel array: focusing by diffraction … Binary transmission function g(x) focus Order 0 : plane wave Order 1 : convergent The wavefront is clipped by the mask segments as beams from individual apertures. wavefronts segments interfere constructively together. With a zero phase shift, => order zero: a plane wave in, a plane wave out. 2pi phase shift => also interfere constructively, =>. Focalization Alll shifts at same time, beam is split. part is focused : maxi 10% of light.

4 Optical concept : Image formation
Can light travel free in vacuum all the way from source to focus? Image Aperture Quasi no stray light except in four spikes. remove glass support, light travel in vacuum all the way to focus => no aberrations, no spectral limitations need 2D development, need hold structure. circular, => FZP, I came up with this "XOR" solution, mechanically connex, Apod Square Aper EITHER interferometer no beam combiner millions of subapertures : dense array ortho => HDR, interf and FZP too. Transmission: g(x) "xor" g(y) Transmission: g(x) non linear luminosity scale, to show the spikes.

5 Basic concepts: Fresnel arrays versus solid aperture
Images of a point source by: 300 Fresnel zones 3000 Fresnel zones Solid square aperture At large Fresnel zone numbers, the PSF is the same as with a solid aperture the same size. luminosity scale: Power 1/4 to show spikes

6 Basic concepts: Dynamic range & resolution PSF for 300 zones (720 000 apertures)
Numerical Fresnel propagation apodized prolate, order 0 masked Log dynamic Numerical sumulation by Fresnel propagation prolate Apodisation is achieved by apertures size modulation. It could also be done by "PIAA Guyon" in focal optics Show central peak, spikes, fHD field. Detection can go beyond raw dynamic range : only the variance of the noise counts. 1/4 field represented Position in the field (resels)

7 "Against" Fresnel Arrays:
Chromaticity... But can be canceled by order -1 chromaticity after focus, Channel bandpass limitations: Δλ/λ= 15% f = D2/8zλ D transmission efficiency to focus: 6% to 10% Shupmann design : cancel by order -1 at pupil plane Removes the 2pi phase shifts => COPHASED ! Beam combiner Cost per photon rather than cost per aperture diameter 1km to 100km focal lengths => Formation flying in space f = D2/8zλ

8 "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 High angular resolution: as a solid aperture the size of the array. High dynamic range: 108 on compact objects, more with coronagraphy & postprocessing. 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. A factor of compared to classical optical constraints Light weight deployable membrane Requires field telescope 1/6th to 1/10th of the diameter

9 II. Tests Does it work ?

10 2x2 cm array I have it here, It's working. live demo
after this session. For those who Haven't already Seen it… La montrer

11 8x8 cm array: tests on lab sources (2005-2008)
116 zones, x 8 cm 26680 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) 10-6 dynamic range Achievements. improved light efficiency : bars contribute to focalization. metal foil 100 m thick Photo T.Raksasataya

12 20x20 cm array: test on sky sources (2009-2011)
0.8" resolution 1000x1000 field λ0 = 800 nm Δλ = 100 nm Simulate formation flying in space: Primary array module; refractor, 19 meter long tube, Focalization (click) Focal instrumentation module Photo D.Serre

13 20 cm Metal foil 9.7 105 apertures, Slightly apodized,
696 Fresnel zones. Close up on primary array module Close to a million aperture in this APODIZED array Photo P.Deba

14 20x20 cm array: first light on stars
ALINEMENT PHASE images: temporary 116 zones secondary (instead of 702 zones) Tip-Tilt not yet implemented fresh results Made this summer. First time show to public First alignment tests, on binary stars. NOT representative of the real resol nor Dyn. Much better expected expected soon 52 Cygni a-b Va= 4.2 vb= 8.7 sep= 6.4" STT 433 a-b Va=4.36 ; Vb=10.0 Sep= 15" more results at our workshop in Nice next week

15 20 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 do better than other 20 cm aperture instruments. Check the behaviour

16 ESA study ESA call for Feasibility study of a membrane telescope 350 k€ ESA is interested in the concept

17 III. Space Mission Science ? Credibility ?

18 The Fresnel Imager Space Mission
3m to 100m diameter, or more. Thin membrane "Primary Array" module: Field optics telescope 1/10th to 1/20th the diameter of Primary Array. Dispersion correction: order -1 diffraction Blazed lens or concave grating, 10 to 30 cm diameter Opens the way to very large apertures in space focal Instrumentation: Spectro-imagers

19 Rationale Make it simple, try to keep cost below 300 M€
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… Wavefront is lambda intependant

20 Strategy, sky targets - Start with UV domain?
- limited budget => limited aperture, but high resolution - High quality wavefront at any wavelength - angular resolution : 7 mas with a 4m Fresnel array One visible channel too - spectral lines in UV for: Photosynthesis break, O3, CH4, CO2 , auroras … - polarimetry

21 Space Mission: optical scheme
Spacecraft 1 Solar Baffle, to protect from sunlight Large "Primary Fresnel Array: Thin foil, 4 to 30 m diameter, or more. Field optics telescope Order zero blocked Focal instrum. Diffraction order 1: focused, but with chromatic aberration. Spacecraft 2 pupil plane Diffraction order 0: unfocussed will be focused by field optics, then blocked. Focal instruments From phase Zero study I'll not go into it Chromatic correction: Blazed Fresnel grating 5 km (for a 4m aperture) to 100 km (for a 30m aperture) image plane 1 dispersed image plane 2 achromatic

22 Targets: S/N on exoplanets in UV
Signal / noise as a function of  uv uv Signal / noise > 30 0.5 Jupiter diameter 1 Jupiter diameter planet Signal / noise > 3 Signal / noise < 3 Signal / noise > 3 Signal / noise < 3 Exposure time calculators on the web soon by Denis Serre and Truswin Raksasataya. You enter your object and spectral res, it replies with the S/N vs integration time chart Check them, stay tuned Images & spectra of exoplanets: 1 UA from solar type star, 10 Pc away 4m aperture, 10h integration spectral res.  / = 50 dynamic range of raw image: 2 10^-8

23 Conclusion Build up a proposal for a 2020 / 2025 launch
Science cases: Exoplanets, and also stellar physics compact objects reflection nebulae extragalactic solar system objects observation of the earth 21/2 days workshop in Nice, Sept (next week) Free registration This concept allows for exoplanet study But can also be competitive in many other fields of astrophysics We have some funding and We are looking foe collaborations with specialists of different domains: Stellar, galactic, solar system, To find the mission proposal that would serve the best. Web site: search with key words "fresnel imager Nice" We are starting a "Fresnel Imager Astro Applications" group.

24 Thank you for your attention!
You are welcome to join us. Have plans for next week? Don't forget the demo after the session Workshop: sept (next week)


26 Bonus slides

27 Optical concept : Image formation
Circular Fresnel Zone Plate => PSF with isotropic rings Image Aperture Isotropic rings Iregular FZP. deas for using it in space have been proposed by Chesnokov 1993, Hyde 1999, Massonnet 2003 This has also been proposed for EUV and X by Baez 1960 with radial beams to support the rings. In the case of an FZP, the stray light is not confined into spikes, but spread isotropically into rings => lower dynamic range. non linear luminosity scale to show the rings.

28 expansion 2D Cartésienne
 Réseau de Fresnel ou Interféromètre à forte densité d’ouvertures ? Géométrie "orthogonale pure" (2005) 4 % de la lumière focalisée 1740 motifs individuels As the light is focused by diffraction, each hole in this grid behaves like an individual aperture in an interferometric array Géométrie "ortho-circulaire" (2008) 6 % de la lumière focalisée 28

29 The field vs spectral bandpas tradeoff
Field delimited by field mirror Chromatically aberrated beam at prime focus The chromatic corrector does a good job, but it corrects only what it collects.

30 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 >108 - 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 Gen III prototype: Primary array
R&T financed by CNES & STAE 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

32 Gen III prototype Critical point: concave blazed mirror in focal module

33 Orbites et pointages 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 eclipticque sun petite Lissajou periode : 6 mois 1 eclipse en 6 ans, évitable éclipticque Terre Lune L2 km 14° Fresnel baffle Lingne de visée Antenne RA fixe et GS fixe possible à partir de km de la Terre

34 Résultats qualitatifs : dynamique mesure optique et simulation numérique
Dans ces images d'un point, saturées, le fond moyen est à 2 *10 -6 Dynamique: DEFINIR : valeur moyenne dans le champ propre) / (maximum du pic central Simulation numérique par Denis Serre. Luminosité amplifiée x1000 Luminosité amplifiée x1000 8 cm 116 zones image Optique 8 cm 116 zones propagation de Fresnel numerique par tous les éléments optiques propagation numerique de Fresnel développée pour tester de grands réseaux 34

35 expansion 2D Cartésienne
 Réseau de Fresnel ou Interféromètre à forte densité d’ouvertures ? Géométrie "orthogonale pure" (2005) 4 % de la lumière focalisée 1740 motifs individuels As the light is focused by diffraction, each hole in this grid behaves like an individual aperture in an interferometric array Géométrie "ortho-circulaire" (2008) 6 % de la lumière focalisée 35

36 Fields obtained with 2 exposures rotated 45°
Fields form A&A paper Koechlin Serre Duchon 2005

37 scenarios

Download ppt "The Fresnel Imager for exoplanet study"

Similar presentations

Ads by Google