Optiques Prototype pour les ELT

Sagem - REOSC

R&D INSU – Grenoble – 12/05/2011

Roland GEYL

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Outline

The E-ELT Project

The Primary Mirror Segments challenges

ESO Contract for 7 prototypes

The GTC reference

Segment Manufacturing Steps

Other studies performed

Focus on AO thin shells

Conclusion

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REOSC - A Prestigious Scientific FoundationThe REOSC company has been set up in 1937 by a grou p of scientists from Paris Institute of Optics including :

Charles FABRY : the Fabry - Perot interferometer

Henry CHRETIEN : the Ritchey-Chretien Telescope the HYPERGONAR for the CINEMASCOPECatadiopter, Machine gun collimator, Slit periscope for tanks,

…

Henri Chretien1879 - 1956

REOSC = Recherche et Etude en Optique et Sciences Connexes

During more than 40 years REOSC designs and manufac ture instruments for demanding applications like astronomy, science and defense.

1978 REOSC joins SFIM Group

1998 All SFIM joins SAGEM 2005 SAGEM and SNECMA merge and form the SAFRAN Gr oup

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Relations SAFRAN / Sagem / REOSC avec la Recherche

SAFRAN entretien une longue relation avec de nombre ux laboratoires de recherche. Convention CNRS renouvelée en 2009. � 150 thésards

� Plusieurs dizaines de labo concernés

Sagem est dans une dynamique similaire avec 16 thés ards

REOSC � Finance aujourd’hui 2 thèses

� Relations avec de nombreux laboratoires

� Echanges bi-directionnels

� Astro / Spatial / Energie / Semi-conducteurs

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The E-ELT ProjectThe E-ELT is the planned successor of the VLT A giant 42-m primary mirror made of 984 segmentsAO and Image stabilization integrated in a novel 5 mirror designSmall mirrors of 6,5-m, 5-m, 2.5 and 2.4-m Dome : 100-m diameter, 5500 tonsAlt-Az Mount 3350 tonsTwo Nasmyth & 1 Coudé foci

Detailed Design Phase conductedSite selected : Chili – Armazones (close to VLT Paran al)Go ahead for construction in 2011 ?

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E-ELT: A giant telescope with a novel 5 mirror desi gn

Focal Surface M1 segmented

M2

M3

M4

M5

M1 : 984 actively controlled segments

M2 : 6.5-m active meniscus

M3 : 4-m active meniscus

M4 : 2.5-m plano adaptive mirror based on a 2-mm glass thin shell

M5 : 2.4-m plano stiff Tip-Tilt mirror

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The E-ELT Segmented Primary Mirror Challenge984 segments for 42-m total diameter

Each segment has 1.5-m large size

F/1 fast aperture

Hyperbolic aspheric shape

Segments with no axial symetry

Precise radius or curvatureR = 84 000 +/- 200 mmMatch between segment < 0.01 mm

Ultra smooth surface residualsHigh Frequ. < 15 nm RMS

No edge effect : up to the last mm !

Schedule : 1 segment / day

A performance breakthrough combined to an industrial c hallenge.

E-ELT

GTC

���� 2 X better than GTC !

E-ELT Primary mirror segments have a total area larger than the combined area

of all telescopes built so far !���� 10 X faster than GTC !

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From Science Case to Optics Specification

There are many exciting science cases for the ELT’s : � Exoplanets, Black holes, Stars and galaxies formati on,

� Cosmology closer to Big Bang, etc.

Exoplanets direct imaging is the most exciting.

Requires 10 -9 contrast within less than 0.1 arcsec from star. � Use of Xtreme Adaptive optics (XAO) with 200x200 actu ators� Smooth optical surfaces with low mid frequency residuals

� Lowest possible segment interstice and optics edge rol l-off.

XAO, S~90% Diffraction + staticaberration correction

Speckle Calibration,

Differential Methods

Contrast ~ 10 -3-10-4 Contrast ~ 10 -6 Contrast ~ 10 -9E-ELT PSF with XAO & coronograph

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ELT M1 Segments WFE Requirements

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Contract for Seven Proto E-ELT Segments

Contract for polishing 7 E-ELT Proto segments: � Demonstrate the performance for 7 most difficult segme nts

� Evaluate several glass materials (Zerodur, ULE, ClearC eram)

� Progress on testing issues

� Contract upgraded fro : �Validate integration on support (3 segments)

�Add edge sensors I/F bonding task

High speed GTC technology

� Evaluation of alternatives like Stress Mirror Polish ing Technology (SMP)

In paralell Sagem-REOSC conducted intense work to demo nstrate its:� Capability to improve production rate by 5 to 10 wrt G TC

� Capability to reduce production costs by similar factor

� Our baseline :

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GTC Optics delivered in 2005

World most accurate segmented telescope36 1.8-m segments10.5-m total aperture1 segment / 2 weeks

� 7 segments on the optical metrology bench

� Reconstructed fringes over the 10.5-m total

aperture

12 nm average figure errorUltra low edge effect

2X JWST aperture area ! � M2 in Be - 7 nm RMS

� 36 segments - 6 types

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GTC Primary Mirror Segments - Main Fabrication Steps

Aspheric generationAspheric profile millingRapid & accurateLow subsurface damages

Robotic polishing Surface polishing Set of special toolsFigure errors reduction

Ion Beam FiguringSurface final figuringNanometer accuracyNo edge effect

250 µm 10 µm 1 µm < 0.1 µm

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GTC Primary Mirror Segments - Main Metrology Steps

3D CMMGlobal profile Radius of curvature

SpherometerAspheric ProfileDuring lapping

CGH benchIndividual

test

Matching benchGlobal Test Radius match

Metrology shall be 1 order of magnitudebetter than spec

250 µm 10 µm 1 µm < 0.1 µm

6+1 GTC segments on the test table

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VLT M1 # 4 : The best oneWFE = 17.6 nm RMS

Diam 8-m Produced in 1998

GTC M1 : Batches 2 to 7WFE = 24.4 nm RMS

Diam 11-m produced in 2005

Despite being segmented, GTC M1 shows extremely smo oth surface structure and very accurate figure control.

The achievement : Segmented is as good as monolithic !

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Step 1: Aspherical Generation

Start from a spherical lapped surface and generate up to 200µm non axis-symetrical aspherical profile:� Accurately

� With a fine ground texture

� With low level of SSD

� Rapidly, thank to process boost

Mesure rapidly and accurately� 3D CMM

� Profilometry

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The proto segments are measured at the center of curvature using dedicated CGH per segment.� Use of VLT high tower

� Double folding the beam (R = 84m)

Step 2: Prepolishing

Step 2 goals : � Bring the surface to be shiny � Reduce the micro-roughness level� Maintain or improve figure errors� Conduct first optical tests

High process automation and speed boosting

First optical test : 1050 nm RMS

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Step 3: Fine Polishing and Smoothing

Step 3 goals:�Bring the polished surface within the final

micro-roughness level.� Improve the figure errors down to ≈≈≈≈ 200nm

RMS (before any active correction applied).�Goal of two runs only thanks to process

automation and boost. � In the same time, obtain the final high

spatial frequency residuals level.

HF residuals : 10 nm RMS

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Step 4 : Hexagonal cutting

Hex contour is an issue for the optician.

Most of the work is done « circular ».

First Proto segment cut in March 2010.

Most of the segments have moderate figure change due to cutting : � Moderate amount of nm RMS with a central

bump (linked to the IF central hole)

� Smooth – No HF content – No edge effect

� Easy to remove by IBF.

� Some segments : quite no figure change.

� One segment : high warp of a few µm PTV

Before IBF : 85 nm RMS

March 2010 : First ELT segment hex cut

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Step 5 : Ion Beam Figuring

In 2001, Sagem invested in a large Ion BeamFiguring machine for the GTC segment finishing phase.

Accurate / Deterministic / No edge effect

Segment final edge effect residuals is limitedto 30-80 nm PTV.

Loading ELT segment in IBF chamber

IBF run 1 : 25 nm RMS

Goal is to limit to 2-3 IBF runs in serial production.

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Step 6 : Integration on its support

Three segments have been integrated on their active support provided by ESO. �2 supports made by TNO

�1 support by CESA

Objectives of this integration work:�Verify that integration does not distort the

optical surface by more than 100 nm RMS.

�Contribute to support system debug

�Correct the optical surface by IBF after integration. (no dismounting during IBF)

�Verify the efficiency of the active correction.

Photo TNO

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First E-ELT Segment Integrated & Delivered to ESO

10.2 nm WFE RMS residualsafter active correction

First ELT segment integrated on its support, fully tested

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Other contribution to ELT Optics Development (1)

M2 Mirror (6-m diameter)� Design study of the 6-m Active Mirror� Similar to VLT M1 but upside down

Refined study with MT Mechatronic� Reversed Support System � Safety study� Optical manufacturing� Optical testing� Integration� Transportation

M3 Mirror (4-m diameter)� Very similar to M2.

Study of the 39-m M1 option consequenceson a new M2 design of only 4-m.

M3-4-5 AO Relay

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Other contribution to ELT Optics Development (2)M4 : A 2.5-m Adaptive Mirror� Correct atmospheric turbulences

� A 2-mm precision thin glass sheet restingon 5000 actuators moving at 100Hz.

Demonstration of the capability to manufacture the large glass thin shell� 2 mm thickness only� Handling � Transportation

Sub-cell AO demonstration2-mm 2.5-m

thin shelldemonstrated

M5 : 3 x 2.5-m Tip-Tilt Mirror � Evaluation of SiC, lightweight glass or hybrid struc tures

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Latest news of the VLT M2 AO Thin Shell

Heritage in large glass thin shells The VLT M2 AO thin shell�1.1-m / 2-mm

�50 µm asphericity

�2 µm th uniformity

Development of �Refined manufacturing and testing

process for the asphere meniscus

�Automated th measurement

1985 : ESO VLT proto1-m / 10 mm

1988 : ESA AO demo80-cm / 5 mm

1995 : NASA NMSD160-cm / 3 mm 2011 : ESO ELT M4 shell demo

250-cm / 2 mm �Today : th = 1,961 mm / 23 µm irreg

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Conclusion Sagem-REOSC a produit avec succès et intégré sur le urs supports plusieurs segments prototypes de l’E-ELT.

Trois matières ont été évaluées

Une gamme de fabrication a été définie pour un nive au de qualitéfinale inégalé à ce jour en astronomie

Les bases d’une productions industrielle sont établ ies: � Faster - Better - Cheaper� Off axis aspheric, non circular contour, low edge effe ct, smooth residuals,

1 segment per day, integration on support

Des études et démonstrations sont menées pour les M 2, M4, M5

La VLT M2 AO thin shell est en phase finale d’égalisa tion d’épaisseur

Sagem-REOSC sera fière d’apporter sa technologie et sa force industrielle au service de la prochaine génération de télescope.

Merci à l’ESO pour sa confiance

Merci de votre attention !