Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20091

Laurent Koechlin

Laboratoire d'astrophysique de Toulouse Tarbes,Université de Toulouse CNRS

A quick review of tesbed imagers

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20092

Tesbed imagersResearch on these testbeds is financed by

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20093

2x2 cm array

I have it here,It's working.

live demoFor those whoHaven't alreadySeen it…

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20094

Testbed Gen I (2005-2009): 8x8 cm array

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

Will be presented by Denis Serre

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20095

Testbed Gen II: 20x20 cm, on sky sources (2009-2011)

Photo D.Serre

0.8" resolution 1000x1000 field λ0 = 800 nm Δλ = 100 nm

Implementation of testbed Gen II at Nice observatory will be presented by Jean-Pierre Rivet

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20096

Metal foil9.7 105 apertures,Slightly apodized,696 Fresnel zones.

20 cm

Photo P.Deba

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20097

Testbed Gen II

First light on a star

done July 17thNot yet the nominal optics

Results & targets will be presented by Truswin Raksasataya

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20098

Goals and first results of testbed Gen II

Assess performances on real sky objects:do better than other 20 cm aperture instruments.

Targets:Dynamic range on real starsLimiting magnitude

Will be presented by Truswin Raksasataya

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 20099

Assessment of a membrane telescopeis currently envisioned by ESA

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200910

Space mission proposal

Science cases?

Credibility?

We have a concept that opens the way to very large apertures in space.

It can be validated on ground based facilities only for small apertures.

Large apertures need to be tested in space, but it's hard to get a large mission approved if it's based on a new technology.

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200911

Rationale

Meet acceptability threshold for a new technology mission

Make it simple, try to keep the 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 several astrophysical fields...

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200912

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.

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200913

Strategy, sky targets

- Start with UV domain?

- The UV universe is almost unknown at these resolution and dynamic range

- limited budget => limited aperture, but high resolution

- High quality wavefront at any wavelength

- angular resolution : 7 mas with a 4m Fresnel array

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200914

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.

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200915

Goals and conception of testbed Gen III: UV domain

Will be presented by Paul Deba

Before proposing a UV space mission, we need to validate the technology in the UV.

Build a testbed to validate :

- the dynamic range, - wavefront quality, - angular resolution, - spectral bandwidth, - light transmission efficiency.

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200916

Testbed Gen III: UV domain

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

Will be presented by Paul Deba

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200917

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

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200918

Conclusion: Future space mission.

Science cases:Exoplanetsstellar physicscompact objectsreflection nebulaeextragalacticsolar system objectsobservation of the

earth

Build up a proposal for a 2020 / 2025 launch

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200919

Thank you for your attention!

Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers Nice September 23-25, 200920