Post on 27-Mar-2015
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 1
Laurent Koechlin 1, Jean-Pierre Rivet 2, Truswin Raksasataya 1, Paul Deba 1,Denis Serre 3.
1 Université de Toulouse CNRS2 Observatoire de la côte d'Azur CNRS3 Leiden University, the Netherlands
The Fresnel Imager for exoplanet study
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 2
I. Concept
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 3
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
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 4
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?
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 5
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
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 6 Position in the field (resels)
1/4 field represented
Log dynamic
Basic concepts: Dynamic range & resolution PSF for 300 zones (720 000 apertures)
apodized prolate, order 0 masked
Numerical Fresnel propagation
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"Against" Fresnel Arrays:
Chromaticity... But can be canceledby 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 = D2/8zλ
D
f = D2/8zλ
f
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 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
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: 108 on compact objects, more with coronagraphy & postprocessing.
High angular resolution: as a solid aperture the size of the array.
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 9
II. TestsDoes it work ?
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 10
2x2 cm array
I have it here,It's working.
live demoafter this session.
For those whoHaven't alreadySeen it…
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 11
8x8 cm array: tests on lab sources (2005-2008)
116 zones, 8 x 8 cm26680 apertures"orthocircular" design.
F= 23 m at = 600 nm
Precision: 5m on holes positioning=> /70 on wavefront.
Achievements:
Diffraction limitedBroad band imaging (450-850nm)10-6 dynamic range
Photo T.Raksasataya
metal foil 100 m thick
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 12
20x20 cm array: test on sky sources (2009-2011)
Photo D.Serre
0.8" resolution 1000x1000 field λ0 = 800 nm Δλ = 100 nm
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 13
Metal foil9.7 105 apertures,Slightly apodized,696 Fresnel zones.
20 cm
Photo P.Deba
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 14
20x20 cm array: first light on stars
52 Cygni a-bVa= 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-bVa=4.36 ; Vb=10.0 Sep= 15"
more results at our workshop in Nice next week
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 15
20 cm array goals
Assess performances on real sky objects:do better than other 20 cm aperture instruments.
Targets:High contrast objectsextended sources dense fieldsdeep sky
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 16
ESA study
ESA call for Feasibility study of a membrane telescope 350 k€
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 17
III. Space MissionScience ?
Credibility ?
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 18
The Fresnel Imager Space Mission
Field optics telescope1/10th to 1/20th the diameterof Primary Array.
Dispersion correction: order -1 diffractionBlazed lens or concave grating,10 to 30 cm diameter
focal Instrumentation:Spectro-imagers
Thin membrane "Primary Array" module:
3m to 100m diameter, or more.
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 19
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 conceptsλ/50 wavefront, at any λ => High Dynamic range from IR to UVmas angular resolution1000x1000 resel. fieldsSpectral resolution
Suitable for Exoplanetsand other fieds too…
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 20
Strategy, sky targets
- Start with UV domain?
- spectral lines in UV for: Photosynthesis break, O3, CH4, CO2 , auroras …
- polarimetry
- limited budget => limited aperture, but high resolution
- High quality wavefront at any wavelength
- angular resolution : 7 mas with a 4m Fresnel array
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 21
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 1dispersed
Diffraction order 1: focused, but with chromatic aberration.
Diffraction order 0: unfocussedwill 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.
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 22
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 < 3Signal / 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 uv
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 23
Conclusion
Science cases: Exoplanets, and also
stellar physicscompact objectsreflection nebulaeextragalacticsolar system objectsobservation of the earth
21/2 days workshop in Nice, Sept. 23-25 (next week)Free registration
Build up a proposal for a 2020 / 2025 launch
Web site: search with key words "fresnel imager Nice"http://www.ast.obs-mip.fr/users/lkoechli/w3/space_borne_page/page_congres.html
We are starting a "Fresnel Imager Astro Applications" group.
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Thank you for your attention!
You are welcome to join us.Workshop: sept 23-25 (next week)
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 25
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 26
Bonus slides
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 27
Circular Fresnel Zone Plate => PSF with isotropic rings
Image
Optical concept : Image formation
non linear luminosity scaleto show the rings.
Aperture
Isotropic rings
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 28
Géométrie "orthogonale pure" (2005)
4 % de la lumière focalisée
expansion 2D Cartésienne
Réseau de Fresnel ou
Interféromètre à forte densité d’ouvertures ?
1740 motifs individuels
Géométrie "ortho-circulaire" (2008)
6 % de la lumière focalisée
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 29
The field vs spectral bandpas tradeoff
Chromatically aberrated beam at prime focus
Field delimited by field mirror
The chromatic correctordoes a good job,but it corrects only what it collects.
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 30
Fresnel Imager specifications
UV spectro-Imaging at High Dynamic Range4m aperture3 spectral bands Δλ/λ=20%: 2 in the UV, 1 in the visible λ/50 wavefrontspectral resolution λ/δλ=50angular resolution 7 to 25 mas depending on λfield 1000x1000 => 7 to 25 arc secondsraw dynamic range >108
- with 10 hours integrations time:jovian exoplanets with apertures of 1 m or moretelluric Exoplanets: only with 10 meters apertures or larger
- Other fields of astrophysics
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 31
Gen III prototype: Primary array
Size : 8 cm, square
240 Fresnel zones (110 000 apertures)
metal sheet 100 m thick, laser carved
Operates in the UV (250-350 nm)
Focal length: 26.6 m for = 250 nm
Precision on array : 5mi.e. /30 on wavefront
R&T financed by CNES & STAE
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Gen III prototype Critical point: concave blazed mirror in focal module
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 33
eclipticque
sun
petite Lissajou
periode : 6 mois
1 eclipse en 6 ans, évitable
sun
éclipticqueTerre
Lune
L2
20
0 0
00
km
8°14°
Fresnelbaffle
Lingne de visée
Antenne RA fixe et GS fixe possible à partir de 100 000km 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
Moon
40°
SUN
Trajectoire typique montrant qu'au -delà de 100 000 km de la Terre,la MGA pointée comme le GS voit la Terre avec ses 40° d'ouvertur e
Moon
40°
SUN
Trajectoire typique montrant qu'au -delà de 100 000 km de la Terre,la MGA pointée comme le GS voit la Terre avec ses 40° d'ouvertur e
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 34
Résultats qualitatifs : dynamique mesure optique et simulation numérique
8 cm 116 zones
image Optique
8 cm 116 zonespropagation 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
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 35
Géométrie "orthogonale pure" (2005)
4 % de la lumière focalisée
expansion 2D Cartésienne
Réseau de Fresnel ou
Interféromètre à forte densité d’ouvertures ?
1740 motifs individuels
Géométrie "ortho-circulaire" (2008)
6 % de la lumière focalisée
The Fresnel Imager for Exoplanet Study, Pathways to Habitable Planets Barcelona September 17, 2009 36
Fields obtained with 2 exposures rotated 45°
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scenarios