The Fresnel Diffractive Imager project --- Principles, Instrumentation and Mission scenarios Laurent Koechlin, Denis Serre, Paul Deba, Truswin Raksasataya, Christelle Peillon, Emmanuel Hinglais, Paul Duchon, Pierre Etcheto, Christian Dupuy, Benoît Meyssignac, Laurent Doumic. Université de Toulouse, CNRS France

The Fresnel Diffractive Imager project I. Optical Principles Focalization by diffraction Chromatic correction High dynamic range III. Space mission scenarios Primary array vessel design Focal instrumentation design Orbits and Formation flying configuration IV. Astrophysical targets Some of the possible scenarios II. Lab prototype, optical and numerical tests Optical setup Tests results on artificial sources Tests planned on sky sources Numerical simulations for large arrays

I. Optical Principles

focus Order 0 : plane wave Lens (or miror): focusing by refraction (or reflexion) Fresnel array: focusing by diffraction … Focalization : different ways Plane wavefront Order 1 : convergent focus Lens

Concentric geometry (Soret 1875) Efficiency at order 1: 10% Exemple for 15 Fresnel zones 2D radial expansion

Orthogonal geometry (2005) Efficiency at order 1: 4 to 8 % 2D Cartesian expansion g(x)= 1 si (x 2 +f 2 ) 1/2  [ (f/m  + (k-off)  +1  ) m ; (f/m  + (k-off)  +1) m [ sinon g(x) = 0 Transmission (x, y) = g (x) xor g (y) Fresnel Zone plate or Aperture synthesis array ? (here: 1740 ouvertures) Exemple for 30 Fresnel zones

circular geometry => isotropic PSF Image Image formation non linear luminosity scale In order to show the faint isotropic rings. Aperture

Orthogonal geometry => orthogonal PSF Transmission: g(x)  g(y) Image formation non linear luminosity scale In order to show the faint spikes. Image Aperture Quasi no stray light except in the spikes.

Case of a second source in the field: Image formation

Case of a second source in the field:

Image formation Case of a second source in the field:

Comparison: Fresnel arrays versus a solid aperture 1500 Fresnel zones Images of a point source by: 150 Fresnel zones Solid square aperture luminosity scale: Power 1/4 to show spikes

"for" Fresnel Arrays: No mirror, no lens to focalize : just vacuum and opaque material. => a potentially very broad operational domain: 90nm - 25  m Large tolerance in positioning of subapertures for /20 wavefront quality: 100  m in the plane of the array 10 cm in the wave propagation direction (perp. to array) The tolerance is wavelength independent => Opens a way to build very large aberration-free apertures for astrophysics. High dynamic range: 10 8 on compact objects for a 300 zones array Angular resolution: as high as with a mirror the size of the whole array.

"against" Fresnel Arrays: Chromaticity... corrected by small diffractive lens after focus, (order 1 chromaticity cancelled by order -1 chromaticity), but bandpass limitations remain:  = √2 S/C Low transmission compared to a mirror : t = 5 to 10% kilometric focal lengths => requires formation flying in space F = C 2 /8N C

10 to 100 km Optical scheme of the Fresnel Diffractive Imager 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

The field - bandpas compromise 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.

II. Lab prototype, optical and numerical test results Prototype built at Observatoire Midi Pyrénées in Toulouse

Lab Prototype: light source module Étoiles doubles photo Galaxies en spirales photo Gravure : Micro Usinage Laser. mire 72 " d'arc Exemples de sources test Disque Ø 32 " d'arc Binaire Disque Ø 0,8" d'arc source test

Lab prototype: Fresnel array module C = 8 cm 116 zones ( apertures) Opaque foil: inox 80 µ m thick Tested in the visible ( nm) F= 23 m for = 600 nm

Lab prototype, Focal module Field "lens"Order 0 MaskChromatic correction + doublet focalization Final image 23 m

Lab prototype, focal module, zoom on the corrector lens 116 zones, 16 mm diameter, Blazed for 600 nm Fused silica Résolution selon le plan de la lentille de 1nm, hauteur des marches PTV 1.37 µm Ion beam etched (SILIOS), 128 levels, 1  m "location" precision, 10 nm "depth" precision Diverging Fresnel lens mounted in the optical train

Qualitative results: images of artificial sources uniform Disk 32 arc sec uniform Disk 0.8 arc sec Galaxy-shaped target 72 arc sec broad spectral illumination: nm uniform Disk 0.8 arc sec with turbulence double source high dynamic range

Quantitative results: measured angular resolution Diffraction limited theoretical profile Sampled optical point spread function The prototype is quasi diffraction limited

Quantitative results: dynamic range optically measured versus numerically simulated 8 cm 116 zones Optical image 8 cm 116 zones Numerical Fresnel wave propagation Through all the optical elements In these saturated images of a point source, the average background is at 2 *10 -6 Luminosity scale amplified x1000 The numerical Fresnel propagation tool has been developed for testing large arrays

Quantitative results: PSF of a 300 zones Fresnel Imager ( apertures) Not apodized, no order 0 mask numerically simulated Log dynamc range

Quantitative results: PSF of a 300 zones Fresnel Imager ( apertures) Apodized, order 0 masked numerically simulated Log dynamc range

Position in the field (resels) 1/4 of the field represented Log dynamc range Quantitative results: PSF of a 300 zones Fresnel Imager ( apertures) Prolate apodized, order 0 masked

Beyond Orthogonality : improving transmission efficiency and dynamic range directionnal " Spergle" type

Quantitative results: PSFs of non-orthogonal, square aperture imagers luminosity scale: Power 1/4 to show background 300 zones, Square aperture cosine apodized, order 0 masked

Quantitative results: Convolution simulations 300 zones, Square aperture cosine apodized, order 0 masked HH_30BW, raw image (from HST) HH_30BW, convoluted The spikes do not degrade extended images PSF

III. Space missions scenarios To be proposed for the period

Not quite yet XIXth century, 19 meter long, 76 cm Nice Obs refractor Generation II prototype: tests on high dynamic range sky sources

Generation II prototype: tests on the sky 350 zones, 20 cm aperture 20 meter focal, 700 mas resolution 10 6 or more dynamic range To be built and operated , financed by CNES, subject of a present Ph.D. thesis

III. Space missions scenarios

Space Missions scenarios: Formation flying configuration "lens" and "receptor" vessels for a 10m circular array configuration

Space Missions scenarios: Formation flying configuration

Principe des mesures (2x2 d.d.l. + F) : 1) Le « dépointage » du grand axe optique (Zopt) par rapport à la cible Z G est représenté par  L. Il permet d’estimer le déport latéral  x L = F.  L. Sa figuration sur le plan focal du SSSL (ci-contre) est représenté par l’écart entre le motif des diodes laser implanté sur la grande lentille et la cible stellaire, caractérisée, en fait, par un « motif stellaire » avec ou sans la cible (cachée par la lentille en « contrôle fin »). 2) Le dépointage de l’axe optique du Récepteur par rapport au grand axe optique (  R ) est représenté par l’écart angulaire [ Z OR, Z OPT ]. 3) Mesure de la distance F ocale: En fin de phase d’acquisition, on estimera F à partir de la taille du motif de diodes laser. Par contre, la mesure fine de la focale sera effectuée par télémétrie Laser en phase de contrôle fin. Space Missions scenarios: Navigation Control Scheme Plan focal du SSSL dans l’Optique Réceptrice Z G (la cible) Axe Optique du Récepteur : Z OR Z OPT (grand axe optique)  R  L (=  x L /F) Lentille de Fresnel Satellite Récepteur Grand Axe « optique » O lp  L P O or Zopt Z OR  R Z G (étoile) xLxL Satellite Lentille de Fresnel ZLPZLP F  L Schéma de principe de l’instrument distribué Diode Laser

Space Missions scenarios: key parameters for spacecraft architecture Orbit and mission - environment - Communications to ground - Vessel to vessel communications - technology - fabrication - Lissajou orbits  TM/TC 2 par satellite terre/anti- terre  Liaison RF sensing (type SimbolX) inter-satellite pour la formation ecliptic plane sun small Lissajou typically:period: 6 months 1 avoidable eclipse every 6 years acceptable depointing angle of the line of sight = total shield angle protection – Earth, Sun and Moon covering (fonction of the L2 orbit) sun ecliptic plane Earth Moon worst case every 28 days L km 8° 14° Fresnel lens light shield line of sight  TMI Reflector Array (0 à 40°) 1 on receptor spacecraft facing earth fixed RA Antenna & GS Possible a partir de km from Earth

Space Missions scenarios: focal instrumentation Intégration of science and navigation channels: privileged Scenarios

Space Missions scenarios: focal instrumentation chromatic correction optics By réfractionBy reflection R&T CNES NUV+VIS+NIR : lentille de Fresnel blazée à l’ordre –1 qui fonctionne en transmission, suivie d’un doublet convergent et achromatique  technologie validée TRL04 : R&T CNES UV : miroir de Fresnel blazée à l’ordre –1 ayant double fonction : 1- Réseau correcteur en réflexion et hors axe. 2- Focalisation du faisceau par une concavité globale additionnelle R&T CNES à venir  R&T CNES à venir. LFCMFCF

IV. Astrophysical targets

Extra Galactic and Young Universe MissionPhysical Phenomenon Spectral Range (nm) Dynamic Range within. 5 resels Angular Resolutions (mas) Extra Galactic lensing Column density mapping Black Body, Axion Ray Detection" Extra Galactic lensing Column Density mapping, Black Body Extra Galactic to Z, Lyman  Young Universe, Galaxy formation Extra Galactic to Z, Lyman break Re-inonization period of the universe Color Code => Spectral Band : IR NIR Vis NUV FUV Scientific Requirements

Extra Galactic and Young Universe Mission D (m) D, Field of View (m) Channel Capture size and Bands x y Transfer Rate kbps Amount captured Images Integr ated time (h) Mission Duration (years) Extra Galactic lensing 302 Pointing M2 2000* bands ,4 Extra Galactic lensing 101,2 Pointing M2 /Separati on 2000* bands ,3 Extra Galactic at Z, Lyman  302 Pointing M2 2000* *10* ,9 Extra Galactic at z, Lyman break 302 Pointing M2 2000* *10* ,3 Instrumentation specifications t =3 h : for Changing Object t = 6 h :for Changing Spectral Band

Active Regions in Our Galaxy MissionsPhysical Phenomenon Spectral Band (nm) Dynamic range in 5 resels Angular Resoluti on (mas) Central Galactic Region, Dust and Globular Cluster Density mass, Central Black hole, I.R. absorption in interstella Ionized density of Galactic Clouds, Active Core “Astrochemistry” - Extra Galactic core Ionized density of Galactic Clouds, Active Core Astrochemistry, development of interstellar in Heavy element, High Energy Scientific Requirements Color Code => Spectral Band : IR NIR Vis NUV FUV Distance Between Objects : 0,2° - 0,5°No of Objects per spectral Band : 20

Active Regions in Our Galaxy Mission Cgr (m) D, Field of View (m) Channel Capture size and Bands x y Transfe r Rate kbps Amoun t capture d Images Integrat ed time (h) Mission Duration (years) Central Galactic Region, Dust and Globular Cluster 302 Pointing M2 2000* bands ,7 Ionized density of Galactic Clouds, Active Core 101,2 Pointing M2 /Separatio n 2000$ *10* ,0 Ionized density of Galactic Clouds, Active Core 3,50,6 Pointing M2 2000* *10* ,9 Instruments specifications IR NIR Vis NUV FUV

Imagery Stellar and Circumstellar With a 500 m array ?

Imagery Stellar and Circumstellar MissionsPhysical Phenomenon Spectral Band (nm) Dynamic range in 5 resels Angular Resoluti on (mas) Accretion disk, Jets, Photospheres Evolution of stellar, Mass in Extreme conditions Pphotospheres and Circumstellar Physic stellar Photospheres and Circumstellar : Near objects Physic stellar, Circumstellar Clouds Photosphere et Circumstellar : Far objects Physic stellar, Circumstellar Clouds Scientific Requirements IR NIR Vis NUV FUV

Mission Cgr (m) D, Field of View (m) Channel Capture size and Bands x y Transfer Rate kbps Amount captured Images Integra ted time (h) Mission Duration (years) Accretion disk, Jets, Photospheres 302none 4000* *400* ,0 Photospheres, Circumstellar 3,50,6 Pointing M2 /Seperati on 2000* *400* ,8 Photospheres, Circumstellar : Near objects 101,2none 2000* *400* ,6 Photosphere, Circumstellar : Far objects 302none 4000* *400* ,2 Instrument Specifications IR NIR Vis NUV FUV Imagery stellar et circumstellar

Exoplanets 10 pc detection and spectroscopy 40m array, 300 Fresnel zones, PIAA, spectral resolution 50, 2*48h exposure time

"Exoplanets" MissionsPhysical Phenomenon Spectral Band (nm) Dynam ic range in 5 resels Angular Resolution (mas) Exoplanets joviennes Planets Systems, atmospheres Exoplanets telluric in IR Planets Systems, atmospheres Exoplanets joviennes and telluriques Planets Systems, atmospheres Exoplanets tellurics in IR Planets Systems, atmospheres Scientific Requirements IR NIR Vis NUV FUV

Exoplanets Mission Cgr (m) D, Field of View (m) Channel Capture size and Bands x y Transfer Rate kbps Amou nt captur ed Images Integra ted time (h) Mission Duration (years) Exoplanets 101,2 Point at M2 4000* *300* ,6 Exoplanets 101,2 Point at M2 4000* *300* ,4 Exoplanets 303 Point at M2 4000* *300* ,6 Exoplanets 303 Point at M2 4000* *300* ,0 Instruments Specifications IR NIR Vis NUV FUV

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Bonus slides

Achromatisation principle Converging lens Operating at order -1