AO for ELT – Paris, 22-26 June 2009

MAORYMulti conjugate Adaptive Optics RelaY for the E-ELT

Emiliano Diolaiti (INAF–Osservatorio Astronomico di Bologna)

On behalf of the MAORY Consortium

http://www.bo.astro.it/~maory

INAF + University of Bologna

ONERA

ESO

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Concept Corrected field of view

– Central 53"x53" unvignetted for MICADO– Outer field Ø=160" for Natural Guide Star search and other

instruments Wavefront sensing

– 6 Sodium Laser Guide Stars for high-order wavefront measurement

– 3 Natural Guide Stars for low-order and windshake measurement

– 1 Natural Guide Star used as high-order reference WFS Wavefront correction

– Telescope M4 + M5– 2 post-focal deformable mirrors– Simplified option with 1 post-focal DM and reduced outer field

under study

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Two ports1) gravity invariant w/ field derotation2) vertical w/o field derotation

Preliminary bench size:6335 mm 6755 mm

Preliminary mass estimate:13 t

See poster by Italo Foppiani

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Optical design

M7R = 10 mK = -0.87D = 1 m

M9R = 9.8 mK = -0.91D = 1.1 m

M11R = 9,.8 mK = -0.91D = 0.9 m

M13R = 10 mK = -0.87D = 0.9 m

M13R = 10 mK = -0.87D = 0.9 m

M8 DM @4kmD = 370~45 act/D

M10FlatD = 0.9 m

M12DM @12.7kmD = 414 mm~52 act./D

Field Ø160"WFE 25 nmDistortion < 0.1%Field curvature R = 1.3m

To LGS channel

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LGS optics and aberrations

Dichroic

L1 D = 800 mm

L2D = 700 mm

L3D = 580 mm

L4D = 460 mm

200 km 80 km

350 mm

Design features– All lenses made of BK7, spherical surfaces (with wedge)– Output focus F/5, telecentric

Image quality– LGS spot FWHM 0.17 arcsec (LGS image through atmosphere 1.5 arcsec) – RMS WFE 2.6 (average for 6 LGS) SH WFS slope offset 0.5 arcsec

Solutions to LGS aberrations– Correcting optics (likely not static) in each LGS probe– Handled as slope offset

Pupil stabilization and jitter control to be implemented in each LGS probe

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Thermal emission

Telescope emissivity = 10%Sky brightness K = 13 mag/arcsec2

Emissivity of MAORY optics = 1% per surface (left) or 2% per surface (right)

No cooling for T < 30C No cooling for T < 16C

Requirement on thermal emission < 50% (telescope + sky) @ K

Requirement seems to be fulfilled at ambient temperatureParanal average temperature year 2003 (highest average 1985-2006): T = (13.12.6) C (from http://www.eso.org/gen-fac/pubs/astclim/paranal/temperature/)

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Pupil rotations Baseline

– LGS fixed wrt telescope

– Post-focal DMs derotated by 60° (30°)

– LGS WFS probes derotated by 60° (30°)

How do things move in this scheme?– All DMs (M4 and post-focal) appear fixed wrt LGS WFS

– Pupil rotates wrt post-focal NGS WFS at maximum speed ~15/s for a Zenith angle of 1°. Reconstruction matrix of low order modal loop to be updated every 10s

– High order loop reconstruction matrix (25GB of data) must be updated every 140s (LGS footprint variation)

Alternatives– Post-focal DMs cannot be derotated

reconstruction matrix to be updated every 35s

– LGS fixed wrt sky reconstruction matrix to be updated every 0.5s

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LGS Wavefront Sensor

0.75 "/pixel

1.0 "/pixel

1.5 "/pixel

Weighted Center of GravityPhotons / subap = 500, RON = 3Subaperture FoV = 15"15"

0.75 "/pixel

1.0 "/pixel

1.5 "/pixel

Non linearity

WCoG vs. Quad-cell

Evaluation of algorithms performance for SH WFS

– WFS noise

– Impact of Sodium profile

– LGS aberrations

Alternative WFS– Pyramid (smaller detectors)

– Dynamic refocus (by segmented mirrors on sub-pupils?)

Poster by Matteo Lombini

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Focus reconstruction scheme

Sodium focus sequence on 42 m aperture Requires NGS reference

6 LGS measure atmospheric + Sodium focusUsed to “predict” focus in direction of NGSComparison of predicted NGS focus with actual focus gives Sodium term

F(θ1) + Na

F(θ2) + Na F(θ3) + Na

F(θ4) + Na

F(θ5) + NaF(θ6) + Na

F(θ)

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NGS Wavefront Sensor

Target WFE = 100 nm (3 NGS) 4 mas residual jitter per NGS

NGS measured in IR benefit from high-order loop correctionBaseline H band

Windshake is the most challenging issue for tip-tilt. After feedback on telescope main axes a residual jitter ~0.3 RMS is expected.

Making use of a predictive control filter (like Kalman) it may be drastically reduced exploiting its high temporal correlation (low frequency components)

4-5 mas/pixel, 1"1" FoV at least 256256 pixels detector required. This is 2 the foreseen high speed IR sensor by Teledyne (128128, 5e- RON @900Hz, J. Beletic, SPIE 2008 Marseille)

T = 5 ms

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D

HLGS

FoV/2LGS off-axis angle a

Point source at infinity

LGS

MCAO tomography

WFS1 WFS2 WFS3

More details by Jean-Marc Conan and Clélia Robert

Tomography performed by– 6 LGS, launched from M1 edge, kept

fixed with telescope to relax requirements on RTC. LGS FoV = 2'

– 3 NGS for low-orders reconstruction

Star oriented architecture

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Error sources

Item RMS WFEMCAO (High order) 255 nm

Generalized fitting + tomography 232 nm

LGS WFS noise 77 nm

Generalized aliasing 41 nm

Temporal error 60 nm

NGS WFS 100 nmNGS WFS noise and time delay 100 nm

Implementation errors 140 nmOptics (including non-common path errors)

Deformable mirrors

AO control

Sodium layer

Atmosphere

TOTAL 308 nm

Current PSF estimates include MCAO error budgetOther error sources included in Strehl Ratio and Encircled EnergyEnd-to-end simulations ready soon

Estimated by “Fourier” code + cone effect degradation factor

Input to NGS WFS design and sky coverage estimation

Top level allocations

More details on simulations by Cyril Petit

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Strehl Ratio

NGS search field

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Encircled Energy (0.8" seeing)

500 mas

200 mas

75 mas

50 mas

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Performance & Sky coverage

Seeing@0.5 µm

Strehl Ratio %

Ks (2.16 µm) H (1.65 µm) J (1.215 µm) Y (1.021 µm) I (0.9 µm)

0.8" 53.1 33.8 13.6 6.0 2.7

0.6" 60.7 42.5 20.7 10.7 5.7

Nominal average performance over MICADO field of view (53"53")

Seeing@0.5 µm

Minimum field-averaged Strehl Ratio Probability

Ks (2.16 µm) H (1.65 µm) J (1.215 µm) Y (1.021 µm) I (0.9 µm)

0.8" 53.1 33.8 13.6 6.0 2.7 26%

47.8 28.2 9.7 3.7 1.5 38%

41.2 21.9 6.1 1.9 0.6 48%

0.6" 60.7 42.5 20.7 10.7 5.7 33%

54.6 35.4 14.8 6.6 3.1 48%

47.1 27.5 9.3 3.4 1.3 57%

Sky coverage at North Galactic Pole (L0 = 25m, windshake included)3 NGS (2 Tip-Tilt, 1 Tip-Tilt & Focus) measured at H band, NGS search field Ø = 2.5‘Sky cov. estimated by Monte Carlo simulations of asterisms based on TRILEGAL code

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PSF modeling for scientific analysis

Airy Hexagonal Moffat Moffat Moffat

Simulated PSF

DIFFRACTION FITTING ERRORS, UNSEEN MODES SEEING

Model components

PSF model

Strehl Ratio 0.6Image size = 2.7"

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Acknlowledgment

The activities outlined in this talk were partially funded by the European Community under the following grants:– Framework Programme 6, ELT Design Study, contract No

011863 – Framework Programme 7, Preparing for the Construction of

the European Extremely Large Telescope, contract No INFRA-2007-2.2.1.28