1. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 1 Fresnel Imagers Observatoire de Nice September 23-25 2009 Preparing the way To space borne

2. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 2 This workshop is organized and financed by:

3. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 3 Plan of the workshop Session A The basics of Fresnel imaging Session B Validation of concepts & performance assessment Session C The baselines of a Fresnel Imager space mission Session D Science cases in general Session E Exoplanets in particular Session F Strategies for a successful space mission proposal

4. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 4 Fresnel Imagers Observatoire de Nice September 23-25 2009 Preparing the way To space borne

5. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 5 Laurent Koechlin Laboratoire d'Astrophysique de Toulouse-Tarbes Université de Toulouse, CNRS Optical principles of diffraction focusing

6. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 6 Plane wavefront focus Order 0 : plane wave Lens (or miror): focusing by refraction (or reflexion) Fresnel array: focusing by diffraction … Optical concepts: Light focalization Order 1 : convergent focus Lens Binary transmission function g(x) Spherical wavefront

7. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 7 Light focalization focus Binary transmission function g(x) f x OPD(x)

8. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 8 Circular Fresnel Zone Plate => PSF with isotropic rings Image Image formation non linear luminosity scale to show the rings. Isotropic rings Binary transmission function g(r) Aperture

9. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 9 Image formation Binary transmission function g(r) Rings radii: For z max Fresnel zones f

10. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 10 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?

11. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 11 Image formation Second source in the field:

12. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 12 Image formation Second source in the field:

13. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 13 Light focalization: transmission function focus Binary transmission function g(x) f x OPD(x)

14. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 14 Light focalization: efficiency Image Aperture Transmission: g(x) Transmission: g(x) "xor" g(y) or "orthocircular" Order 1 4 to 8% Order 0 40% Order -1 4 to 8% Incident light 100%

15. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 15 Pure orthogonale geometry (2005) 4 % of incident light focused Light focalization: optimizing efficiency Fresnel zone plate or High density interferometer ? 1740 motifs individuels ortho-circular Geometry (2008) 6 % of incident light focused

16. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 16 Light focalization: optimizing efficiency 4% 6 to 8% The bars contribute to focalization Phase shift within one aperture: 2π OPD / λ

17. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 17 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

18. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 18 Position in the field (resels) 1/4 field represented Log dynamic Dynamic range & resolution Example for 300 zones (720 000 apertures) apodized prolate, order 0 masked Numerical Fresnel propagation Code & results By Denis Serre Will be presented in more detail by Denis Serre

19. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 19 Examples of fields obtained by combining 2 exposures rotated 45° 4.5 λ/D 8 λ/D <6 10 -6 <2 10 -6

20. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 20 "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 Square aperture: f = C 2 /8 z max λ C f = D 2 /8zλ f

21. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 21 "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.

22. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 22 10 to 100 km Optical scheme of dispersion correction in Fresnel Arrays Diffractive lens at order -1 e.g. 10 cm Field Optics e.g. 2m Img. plane 2: achromatic Primary Fresnel array e.g. 20 m pupil plane Spacecraft 1 holding primary Fresnel array Spacecraft 2 holding focal instrumentation mask image plane 1 dispersed Order 1 rays, focused by primary array Order 0 rays Converging lens e.g. 10 cm Focal Instrumentation

23. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 23 The field vs spectral bandpass 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.

24. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 24 The field vs spectral bandpass tradeoff Illustration and formulas by Paul Deba Will be presented in more detail by Paul Deba

25. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 25 Conclusion Science cases: Exoplanets stellar physics compact objects reflection nebulae extragalactic solar system objects observation of the earth Build up a proposal for a 2020 / 2025 launch 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, ut it's hard to get a large mission approved if ti's based on a new technology

26. Optical principles of diffraction focussing, Preparing the way to space borne Fresnel imagers NiceSeptember 23-25, 2009 26 Fresnel Imagers Observatoire de Nice September 23-25 2009 Preparing the way To space borne