Resolved imaging of extra-solar photosynthesis patches with a "Laser Driven Hypertelescope Flotilla" Antoine Labeyrie

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Resolved imaging of extra-solar photosynthesis
patches with a "Laser Driven Hypertelescope
Flotilla"Antoine Labeyrie Julien Dejonghe
(College de France ) Stéfania Residori
Umberto Bortolozzo ( Institut Non Linéaire de
Nice)Hervé Le Coroller ( Observatoire
Astronomique Marseille Provence)
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Exo-Earth Imager

• Simulations of hypertelescope imaging with
  coronagraph ( Labeyrie, 1999)

Earth at 3 parsecs

simulated direct image with a 100km flotilla of
150 mirrors, 3m in size 30mn exposure 30x30
resels, 50nm spectral resolution
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Signatures of exo-life

• Seasonal photosyntetic patterns are robust
  signatures of life
• Example plankton blooms on Earth

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Principle of the hypertelescopeor
 multi-aperture imaging interferometer with
densified pupil   makes Fizeau interferometry
efficient by shrinking the side-lobes
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Off-axis star

• Its image is shifted more than the envelope
• and eventually moves out of it gt
  limitation of "Direct Imaging Field"

Fizeau focus
camera
densifier
Stepped wave
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Fizeau imaging Comparison of few large
many small apertures, at same collecting
area and array size
6 apertures, rotating
6 apertures, fixed

• with the small apertures - more stars
  seen
• - lower gain with rotation

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Fizeau imaging ( numerical simulated)
comparison of 605 small apertures with 6 large
ones, imaging 1000 stars at same collecting
area and array size
605 small apertures
Aperture patterns
star cluster

• Better image with small apertures
• Also when densifying

6 large apertures
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Interferometer flotilla The science
gain with more apertures (Labeyrie et al.,
Experimental Astronomy, 2008)

• Max. number of "active" resels grows as N2
• Size of "Direct Imaging Field" is
• Infinite for a Fizeau
• - limited to l/s with fully
  densified pupil ( s is the aperture spacing)
• Science vs. mirror size d , at given cost Cpa
  N dg , where g 2 to 3
• Sc Cpa2 d-2g (7/4) log2 Cpa (1-7g/4) log2
  d
• Strong science gain with decreasing d
• 1000 times more science with 10cm than 1m
• But how small ? Minimum size is about 30mm for
  tolerable beam spread
• 40,000 mirrors of 30mm for same area as JWST .
  Laser-trapped flotilla

science
Science mirror count vs. mirror size at given
array cost
1010
g 3
108
106
g 1
104
g 2
102
N
g 3
104
g 1
102
d
g 2
g 3
1
2
3
4
5
g 3
10
10
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Flying mirrors small is beautyful !

• Why ?
• More science with small mirrors, at given
  collecting area
• - Lower mass because thinner mirrors

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The Luciola concept, proposed to ESA Cosmic
Vision ( not selected )

• flotilla of nanosats, 1km size
• driven by solar radiation pressure
• typical nanosat size 30cm, mass lt 0.2 kg

model used for testing radiation pressure drive
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Now studied "Laser Trapped Hypertelescope
Flotilla"laser-trapped mirrors as passive
"space chips"
Framed diamond membrane Size 4cm
Pair of laser beams
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"Laser-Trapped Hypertelescope
Flotilla"(Labeyrie et al., Experimental
Astronomy, 2009 )
Expandable toward a 100km "Laser Trapped
Exo-Earth Imager (LT-EEI)
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Principle of laser-trapped mirror
Dichroic coating Semi-reflective at laser
wavelengths Reflective at star wavelength
Laser fringes Monochromatic white

• interference of beams modulates the output
  intensities
• radiation pressure P/c reverses vs.
  position
• at l/4 intervals
• laser is repeatedly blue-shifted for
  "pumping" toward central fringe

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Pellicle beam-splitters for "Laser Trapped
Hypertelescope"
F
Self-centering
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Transverse trapping Self-centering in laser
beam through "laser tweezer" effect

• attitude also self-adjusting

torquing force
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Laser trapped hypertelescope flotilla at least
2 satellites needed, with virtual delay line
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Laser Trapped Exo-Earth Imager Apodization and
coronagraphy

• Needed to null the parent star
• mirrors smaller than 12cm do not separate a
  habitable planet from its star at gt 1pc
• But flotilla can be apodized to be explored
• With sparser mirrors near the flotilla's edge
• With clusters
• Coronagraphic techniques also applicable in
  sub-array images to be explored

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Laser Trapped Exo-Earth Imager nulling of the
parent star

• Possible with
• Bracewell ( or phase mask) nulling among close
  pairs of mirrors
• coronagraphy in sub-array clusters, with
  hierarchical pupil densification

Low resolution image
High resolution image
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Typical sizing of a Laser Trapped Exo-Earth
Imager (LT-EEI)
For a snapshot image like this at 3 pc in 10
hours

• 100km flotilla with 10,000 to 100,000 mirrors,
  10 to 3cm in size ( equivalent to Keck 1 area)
• Spaced 1000 to 300m apart
• Total mass of mirrors 236kg " all mirrors fit
  in a suitcase"

100,000 mirrors of 0.03 m, collecting area
70m2, flotilla size 100km small flat mirror
wavefront error 5.6 nm , min wavelength for
Rayleigh 2.2 nm usable also for far UV ?
star envelope at focus, at wavelength 500 nm is
3.3 at min Rayleigh wavelength 2.2 nm is 0.015
mirror spacing 316 m , Direct Imaging Field 1.6
nanoradian, or 326 micro arc-second angular
resolution at 500 nm is 1.03 microarc-second, at
min Rayleigh wavelength 2.2 nm is 4.6
nanoarc-second min. size of laser beam shapers
front 2.6 rear 13.3 m can be diluted mass of
mirrors single 2.3 gram, all 100,000 236
kg Grun's data speed after collision with
meteorite larger than 1 micron is gt 1.4E-08 m/s
, events per year 2.4
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Lab testing in vacuum , suspended from torsion
wire initiated by S.Residori U.Bortolozzo at
Institut Non Linéaire de Nice
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Proposed testing in the International Space
Station

• résidual gravity
• 0,2 micro-g or 2 micron.s-2
• Acceptable with few watts of laser power
• Geostationary satellite also considered

ESA's Columbus lab racks connected to external
vacuum
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Terrestrial hypertelescopes
Fringes (Le Coroller et al., 2005)
Prototype with balloon-borne camera at Haute
Provence observatory (Dejonghe Le Coroller
2009)

• 200m aperture version under study
• Cable suspension tested in the Spanish Pyreneees

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200m aperture
Hypertelescope at Barrosa
200m
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Testing of cable at Barrosa ( August 2009)
Fringes (Le Coroller et al., 2005)
Prototype with balloon-borne camera at Haute
Provence observatory

• 200m aperture version under study
• Cable suspension tested in the Spanish Pyreneees

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Conclusions and future work

• laser-trapped "space chips" must be further
  validated
• through numerical simulation, together with
  dynamic behaviour of flotilla
• and in the laboratory
• and on ISS
• may provide a fast route toward large
  interferometer flotillas
• with high dynamic range, rich science
• including Exo-Earth Imager potential

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Hypertelescope(Labeyrie, 1996 Lardière et
al., 2006)
aperture
Exit pupil

• imaging interferometer, multi-aperture, with a
  densified pupil
• Forms direct images.
• . in a smaller field the a Fizeau
  interferometer, but intensified

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Typical sizing of 1km laser driven flotilla

• Flotilla span 1 kilometer
• Size of mirror elements 30mm, mass 0.5
  gram
• Laser power 3mW per mirror
• max. acceleration 0.02 micron.s-2
• Escape velocity of mirrors ( axial) 30nm/s
• Collecting area of 6.5m JWST matched with
  40,000 mirrors
• requiring a 120 Watt laser.
• Delivery package for mirrors volume lt 0.2 m3
• Deployment with pair of directed laser beams

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Pellicle beam-splitters for "Laser Trapped
Hypertelescope"
paraffin blocking
polishing fixture for bi-conical frame
holding lens
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Exo-planètes, étoiles et galaxies
progrès de l'observation

• cours sur www.college-de-france.fr , fichiers de
  projections
• Articles sur www.oamp.fr/lise

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Synthèse douverture

• Paires ou triplets
• Déformation de la base ou rotation
• Image par synthèse de Fourier

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Comparaison hypertélescope
synthèse d'ouverture cohérent
incohérent

• Gain pic/halo
• Gain en bruit de photons

B
A
?
image integrée
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Gain en signal/bruit hypertélescope/synthèse
douverture
B
A
?

• gain par intensification du pic en N et
  atténuation des pieds en N-3/2 ( Lardière 2007) ,
  voire plus par coronographie
• Cas limité par le bruit de photons
• gain 0,6 N7/4 à préciser, selon
  lapodisation, coronographie
• Exemple gain 2.105 avec 1000 miroirs de 1m,
  par rapport à deux de 23m

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Laser -trapped mirror

• Requires a delay line, or virtual delay line

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Spaceships and "space chips"
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Hypertelescope in space "Laser-Trapped
Diluted Mirror"(Labeyrie et al., Experimental
Astronomy, 2008 )
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"Laser-Trapped Hypertelescope
Flotilla"(Labeyrie et al., Experimental
Astronomy, 2008 )
A laser-illuminated beam-splitter generates a
pair of counter-propagating waves. Their
interference generates a standing wave which
accurately traps small pellicle beam-splitters.
The giant diluted mirror thus obtained focuses
starlight. The flotilla is located at the
Lagrange L2 point of the Earth and Sun.
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Miroir élémentaire piégé par laseranneau
rainuré de centrage, vu en coupe
Les rayons laser réfléchis et réfractés par les
sillons produisent des composantes de pression de
radiation qui orientent le miroir piégé et le
centrent sur le pinceau de lumière laser
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Comparison of hypertélescope with optical
aperture synthesis Signal and photon
noise (Labeyrie 2007, Labeyrie 2008)

• Hypertelescope signal/noiseh (N Pt /
  kd)1/2
• aperture synthesis signal/noisep 2 (Pt /N)
  1/2
• hypertelescope gain is (1/2) N ( kd) -1/2
• kd is the dark zone attenuation in the "clean
  field"
• example
• SNR gain 15,000 if N1000, kd 10 -3

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Champ de l'hypertélescope combien de
(secondes)2 ?
l/d
caméra

• Grille de densifieurs pour exploiter les "lobes
  de diffraction" adjacents si d 1m et l
  500nm gt dimension l/d 0,1"
• Limitée en dimension par les aberrations de
  champ coma, astigmatisme
• Lesquelles dépendent de la combinaison optique
• Exemple d'un miroir parabolique à F/3,6
• 33m coma diffraction visible pour 1/2
  champ 2"
• 1000 m " " 64 m"

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Grille de densifieurs, pour exploiter les "lobes"
adjacents

• et y corriger séparément la coma et la
  turbulence

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Ouvertures inégales et densification inégale
. homogénéisant la pupille de sortie
Densification de pupille inégale 1 et 40

• ELT de 50m hypertélescope 1km, à
  200 ouvertures de 1m
• pic rétréci et intensifié x 17

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Pellicle beam-splitters for "Laser Trapped
Hypertelescope"
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200m aperture at Barrosa (Spanish Pyrenees)
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Interferometer

• Still works with only two elements image is
  degraded, but resolution is not affected

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Fizeau interference with 2, 3, 5,9 27
aperturespoint source

• The peak/halo ratio improves with more apertures
  .
• and thus the dynamic range on resolved sources

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Hypertelescope(Labeyrie, 1996 Lardière et
al., 2006)
aperture
Exit pupil

• imaging interferometer, multi-aperture, with a
  densified pupil
• Forms direct images.
• . in a smaller field the a Fizeau
  interferometer, but intensified

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Simulated Fizeau imagingcomparison of 205 small
apertures and 2 large ones ( 10x), 288 stars
spread function
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Laser trapping also cools mirrors
Of interest for mid-infrared
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Gain de l'hypertélescope par rapport à la
synthèse d'ouverture incohérente

• Signal/(bruit de photons) d'un hypertélescope
  périodique , complètement densifié (Labeyrie
  2007)
• SNRh sqr (N Pt / kd) 1.29 N5/4 Pt1/2
• Relativement à la synthèse d'ouverture
• gain en signal/bruit Ghyper 0,64 N7/4
• Soit gain 2000 avec 100 ouvertures

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1-

• spherical geometry

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Fizeau imaging
random pinholes
Aluminum foil

Full aperture
50 apertures
235 apertures
600 apertures
15 apertures

• image improves with more apertures
• as it emerges from the halo
• caused by diffraction through the small
  sub-apertures, and which takes energy away from
  the image
• a situation avoided by "hypertelescope"
  imaging

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Fizeau imaging with aperture rotation ( lab
simulation)

fixed rotated 19 apertures
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Simulated Fizeau imaging30 apertures and 1000
stars
spread function
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Operation at L2 in Earth shadow

• Laser located outside of shadow
• Sky coverage in 6 months with continuous scan,
  transverse to Sun direction