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High-order coronagraphic phase diversity:

demonstration of COFFEE on SPHERE.

B.Paul1,2, J-F Sauvage1, L. Mugnier1,

K. Dohlen2, D. Mouillet3, T. Fusco1,2 , J.-L. Beuzit3, M. Ferrari2, M. N’Diaye4

1 Onera, DOTA/HRA2 Laboratoire d’Astrophysique de Marseille

3 Institut de Planétologie et d'Astrophysique de Grenoble4 Space Telescope Science Institute

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Outline

Context: high-contrast imaging

Principle of COFFEE

COFFEE's optimization & performance evaluation

Application to the SPHERE instrument

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Context: XAO for high-contrast imaging

High contrast needs for exoplanet imaging Today:

Angular separations from 0.1 to arcsec(a few /D to 100 /D)

Contrast up to 106 - 107

Observation made from the ground (turbulence)

Tomorrow: Angular separations below 0.1 arcsec Contrast up to 109 - 1010 (Earth like planets) Ground / space observations

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Limitation:Light residuals in final focal plane created by quasi-static

aberrations (Non Common Path Aberrations)

Solution : focal plane wavefront sensing with the scientific detector

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Upstream aberrations (ϕu)

i(ϕu, ϕd) i(ϕu+ϕdiv, ϕd)Diversity

phase (ϕdiv)

COFFEE : phase diversity using coronagraphic images (1/2)

Coronagraphic imaging system

Coronagraphic focal plane maskDownstream aberrations (ϕd)

+ One image: not enough data

Two images: OK

Image formation model

Coronagraphic phase diversity: Uses only two images to estimate the aberrations upstream of the coronagraph Rely on a coronagraphic image formation model:

ic (ϕu, ϕd) = Model(ϕu, ϕd)

Pupil plane Detector

COFFEE : phase diversity using coronagraphic images (2/2)

),(),(

),(,

2

dudivfoc noise

dudu regul

ModelimageJ

COFFEE: COronagraphic Focal-plane wave-Front Estimator for Exoplanet detection

Estimation of aberrations upstream (ϕu) and downstream (ϕd) of the coronagraph by criterion J minimization

« Maximum Likelihood »:

Distance experimental images / computed images

Regularization metrics:

A priori information on the parameters

J.-F. Sauvage, L. Mugnier, B. Paul et R. Villecroze, Coronagraphic phase diversity: a simple focal plane sensor for high-contrast imaging, Optics Letter, Dec. 2012

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Definition of a maximum a posteriori criterion:

Aberration estimation: pixel map

Estimation of high-order aberration Reduction of the aliasing error

Aberration estimation: Zernike modes

Estimation of low-order aberrations only Strong aliasing error

Model : electric field propagation

No model mismatch Can be adapted to any coronagraphic focal plane mask M (ALC, FQPM, VPM…)

COFFEE's optimization (1/3)

Adaptation to any coronagraphic device

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Estimation of high-order aberrations

Model : perfect coronagraph model

Model mismatch Application to the apodized Roddier & Roddier coronagraph only

100 parameters

> 3.103 parameters

SPIE 2012 AO4ELT3 2013

B. Paul, J.-F. Sauvage et L. M. Mugnier, Coronagraphic phase diversity: performance study and laboratory demonstration, A&A, April 2013

COFFEE's optimization (2/3) : performance evaluation

Aberration estimation: simulation Coronagraph: ALC (4,52 λ/D); Lyot Stop = 100% WFEup = 50 nm ; WFEdown = 20 nm (λ = 1589 nm, monochromatic images)

Incoming flux: 1e9 photons ; detector noise: σe-= 1 e-; photon noise

No residual turbulence

up

ifoc idiv

εrec =

1.71 nm RMS

Simulation

Estimation

Image computation

up

COFFEE: aberration estimation

Image computation

Pseudo-closed loop: simulation Coronagraph: ALC; Lyot Stop = 96% WFEup = 50 nm ; WFEdown = 20 nm (λ = 1589 nm, monochromatic images)

DM: 41x41 actuators Incoming flux: 1e9 photons ; detector noise: σe-= 1 e-; photon noise

No residual turbulence

No compensation

After NCPA compensation

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COFFEE’s optimization(3/3) : NCPA compensation

No compensation

After NCPA compensation

10-0

10-3

10-4

10-1

10-2

10-5

10-6

10-7

Contrast

COFFEE : validation on SPHERE (1/5)

Coronagraph : ALC (dM = 4.5 λ/D)

Coronagraphic images : IRDIS Diversity phase : AO loop

COFFEE :

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Dead actuator

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COFFEE

Rec. images

Calibration Point-Source,

H band

XAO system,

41 act, 1200Hz

IRDIS imager,

H2 band, ALC Stop

Coronagraph

ALC (incl. Apodizer)

Exp. images

Defocus

Astigmatism

IRDISCoronagraphic image computed by COFFEE Estimated

aberration

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COFFEE : validation on SPHERE (2/5)

Low order aberration estimation : Zernike modes

Wavelength : 1589 nm Coronagraph : APO1 / ALC2 Lyot Stop : Stop ALC (96% entrance pupil + 15% central obstruction)

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High order aberration estimation : poke

Wavelength : 1589 nm Coronagraph : APO1 / ALC2 Lyot Stop : Stop ALC (96% entrance pupil + 15% central obstruction)

COFFEE : validation on SPHERE (3/5)

Introduced poke

Estimated poke

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COFFEE : validation on SPHERE (4/5)

Pseudo – closed loop process

Closed loop on initial reference

slopes

Acquisition of two images

ifoc, idiv

Measurment of u and d

COFFEECOFFEE From u, computation off correction

slopes

Modification of reference

slopes

Wavelength : 1589 nm Coronagraph : apodized Lyot coronagraph (dM = 4.5 λ/D)

Lyot Stop : Stop ALC (96% entrance pupil + 15% central obstruction) Gain = 0.5

COFFEE : validation on SPHERE (5/5)

First validation of the compensation process:

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No compensation

After NCPA compensation (5 iterations)

Energy decrease

Contrast : gain x2 – x5Energy increase

10-4

10-5

10-6

Contrast

COFFEE’s optimization: Estimation of a pixel-wise map New imaging model: Adaptation to any coronagraphic

mask M

Application to SPHERE : Estimation of introduced aberration First experimental validation of the compensation process

Conclusion & Perspectives

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COFFEE : application of the phase diversity to coronagraphic images

Perspectives COFFEE: full validation of iterative process on SPHERE Combination with ZELDA for a SPHERE upgrade (K.

Dohlen talk, Thu. 14h) Ultimate extinction

Creation of a dark hole on the detector Impact of a segmented mirror => refined cophasing

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…. Thanks for your attention !