The fresnel imager for exoplanet study
Sponsored Links
This presentation is the property of its rightful owner.
1 / 37

The Fresnel Imager for exoplanet study PowerPoint PPT Presentation


  • 80 Views
  • Uploaded on
  • Presentation posted in: General

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 c ôte d'Azur CNRS 3 Leiden University, the Netherlands. I. Concept.

Download Presentation

The Fresnel Imager for exoplanet study

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


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. Concept


Lens (or miror): focusing by refraction (or reflexion)

focus

Plane wavefront

Fresnel array: focusing by diffraction …

focus

Optical concept: Light focalization

Lens

Spherical wavefront

Binary transmission function g(x)

Order 0 : plane wave

Order 1 : convergent


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.

Transmission:

g(x)

Transmission:

g(x)"xor" g(y)

non linear luminosity scale,

to show the spikes.


Basic concepts: Fresnel arrays versus solid aperture

Images of a point source by:

300 Fresnel zones

3000 Fresnel zones

Solid square aperture

luminosity scale:Power 1/4 to show spikes


Basic concepts: Dynamic range & resolution PSF for 300 zones (720 000 apertures)

Numerical

Fresnel propagation

apodized prolate,

order 0 masked

Log dynamic

1/4 field represented

Position in the field (resels)


"Against" Fresnel Arrays:

f

Chromaticity... But can be canceled

by order -1 chromaticityafter focus,

Channel bandpass limitations: Δλ/λ= 15%

f = D2/8zλ

D

transmission efficiency to focus:

6% to 10%

1km to 100km focal lengths => Formation flying in space

f = D2/8zλ


"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.


II. Tests

Does it work ?


2x2 cm array

I have it here,

It's working.

live demo

after this session.

For those who

Haven't already

Seen it…


8x8 cm array: tests on lab sources (2005-2008)

116 zones, 8 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 (450-850nm)

10-6dynamic range

metal foil 100 m thick

Photo T.Raksasataya


20x20 cm array: test on sky sources (2009-2011)

0.8" resolution1000x1000 fieldλ0 = 800 nm Δλ = 100 nm

Photo D.Serre


Metal foil

9.7 105 apertures,

Slightly apodized,

696 Fresnel zones.

20 cm

Photo P.Deba


20x20 cm array: first light on stars

ALINEMENT PHASE images:

temporary 116 zones secondary

(instead of 702 zones)

Tip-Tilt not yet implemented

52 Cygni a-b

Va= 4.2 vb= 8.7 sep= 6.4"

STT 433 a-b

Va=4.36 ; Vb=10.0Sep= 15"

more results at our workshop in Nice next week


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


ESA study

ESA call for Feasibility study of a membrane telescope350 k€


III. Space Mission

Science ?

Credibility ?


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

focal Instrumentation:

Spectro-imagers


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 ofcompeting 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…


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

- spectral lines in UV for:

Photosynthesis break, O3, CH4, CO2 , auroras …

- polarimetry


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

Chromatic correction:

Blazed

Fresnel grating

5 km (for a 4m aperture)

to 100 km (for a 30m aperture)

image plane 1dispersed

image plane 2 achromatic


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

Images & spectra of exoplanets:

1 UA from solar type star, 10Pc away

4m aperture, 10h integration

spectral res.  /= 50

dynamic range of raw image: 2 10^-8


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. 23-25 (next week)

Free registration

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.


Thank you for your attention!

You are welcome to join us.

Workshop: sept 23-25 (next week)


Bonus slides


Optical concept : Image formation

Circular Fresnel Zone Plate => PSF with isotropic rings

Image

Aperture

Isotropic rings

non linear luminosity scale

to show the rings.


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

Géométrie "ortho-circulaire" (2008)

6 % de la lumière focalisée


Chromatically aberrated beam at prime focus

The field vs spectral bandpas tradeoff

Field delimited by field mirror

The chromatic corrector

does a good job,

but it corrects only what it collects.


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


Gen III prototype: Primary array

R&T financed by CNES & STAE

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 : 5m

i.e./30 on wavefront


Gen III prototype Critical point: concave blazed mirror infocal module


Orbites et pointages

petite Lissajou

periode : 6 mois1 eclipse en 6 ans, évitable

Lingne de visée

eclipticque

Fresnel

baffle

sun

sun

200 000 km

Terre

éclipticque

L2

14°

Lune

  • 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

Antenne RA fixe et GS fixe possible à partir de

100 000km de la Terre


Résultats qualitatifs : dynamiquemesure optiqueet simulation numérique

Dans ces images d'un point, saturées, le fond moyen est à 2 *10 -6

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


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

Géométrie "ortho-circulaire" (2008)

6 % de la lumière focalisée


Fields obtained with 2 exposures rotated 45°


scenarios


  • Login