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Optics: design, procurement, assembly

and testing plans

Dr Peter Doel, University College London

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Contents

WBS 1.4

• Optical design 1.41- 1.4.2

• Optics procurement and manufacture 1.4.3 -1.4.5, 1.4.9

• Lens cell design and lens mounting 1.46 -1.47

• Lens alignment in camera 1.48

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Optics Roles

• University College London– Optics procurement and testing– Lens cell design/construction and mounting– Optical alignment

• University of Michigan– Optical Design/Stray light analysis– Filter procurement– Filter mechanism design/build– Shutter design /build

• Fermilab– Barrel design/build

• Chicago– Active alignment sensing

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• Field of view– 2.2 degree diameter

• Pixel scale– 57 µm/pixel (f/2.9)

• Image quality:– Resolution Element: < 2.25 pix (0.59”, 34µm)– Goal (as-built) fwhm: ~ 0.33” (18 µm)– Goal (design) fwhm: ~ 0.27” (15 µm)

RMS spot size Rrms= 8.7µm (area weighted)• Wavelengths:

– g, r, i, z (0.4 – 1.0 µm) – with a secondary goal of good performance down to 0.32 µm

• System throughput– Greater than 60% over the focal plane

• Pupil ghost:– intensity gradient < 3% over 61mm

Optical Specification

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Status of Optical Design

• Preliminary design development (Nov 2005-Feb 2006)– Number of elements– Glass choice– Overall size and volume (diameter of first element)– Number of aspheric lens surfaces

• Preliminary Design Review (Feb 2006)

• Final design development (Feb-Oct 2006)– Feedback from PDR included and optimisation of design– Preliminary sensitivity analysis completed

• Critical Design Review (Feb 2007)– UK provisional location– Final review before placing orders

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Optical Design

• 5 lens design

• All fused silica

• Two aspheric surfaces

• C1 lens diameter 0.98m

• Minimum thickness ratio 1:10

• Image scale 1" = 57μm

• 0.26"/pixel

• Sol-Gel/MgF2 coatings

• Rrms= 8.7 umDesign due to Rebecca Bernstein

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Lens Parameters

Surface 1Radius(mm)

Surface 2Radius(mm)

CentreThickness

(mm)

Edge Thickness

(mm)

DiameterSurface 1

(mm)

DiameterSurface 2

(mm)

Lens 1 689.3 719.7 110 72.71 978 920

Lens 2 3634.5 528.2* 52 143.65 688 640

Lens 3 2293.6 4827.9 78.9 45.43 644 644

Lens 4 680.4* 1400.5 99.0 58.88 602 578

Lens 5 960.6 648.7 71.8 - 512 512

* Aspheric surface

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Blank Procurement WBS 1.4.3 :Status

• Preliminary blank specification (Nov 2005-Feb 2006)– Choice of blank material (fused silica, BSL7-Y,etc)– Discussion with manufacturers (Corning, Ohara, Schott, Heraeus) – Availability– Manufacturing issues (slumping, homogeneity) – Schedule– Cost

• Fused Silica chosen (Corning, Heraeus)– Good performance (especially in blue)– Available in sizes and homogeneity required– Production schedule ok

• Tender will be issued in December 2006

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Corning Fused Silica HPFS

Grade C is quoted as have a homogeneity of better than 2ppm. B is better that1.5ppm and A better than 1ppm. The numeric refers to the inclusions: 1 has a total inclusion cross section per 100cm3 of glass of less than or equal to 0.1mm2 and 0 less or equal to 0.03mm2

Delivery

Weeks

Grade

Optic C1 16-22 1C

Optic C2 8-11 1C

Optic C3 8-11 1B

Optic C4 8-11 0B

Optic C5 8-11 0A

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Optics Polishing WBS 1.4.5 :Status

• Input to preliminary optical design (Nov 2005-Feb 2006)– Discussion with manufacturers (SAGEM, SESO, Tinsley) – Manufacturing issues

• Lens size• Asphere on convex or concave surface • Size/gradient of asphere

– Slope 1mm departure over 50mm was acceptable– All companies happy to quote on the proposed (or similar) design

• Testing issues – All optics tested in transmission to allow compensation for

inhomogeneity • Schedule• Cost

• Tender for polishing will be issued in February 2007– This will state optical specification and requirements on testing results during

manufacture

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U. Michigan will– handle procurement and testing of the

filters– match SDSS – g,r,i,z and introduce a

well defined cut-off at high wavelength– design and fabricate or procure a

combined filter changer and shutter

DES Filters WBS 1.4.9 :Status

Dark Energy Camera Filters

0.0000

10.0000

20.0000

30.0000

40.0000

50.0000

60.0000

70.0000

80.0000

90.0000

100.0000

300 400 500 600 700 800 900 1000 1100 1200

Wavelength

%Tra

nsm

itta

nce

925nm 775nm 635nm 475nm

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Filters bids as of June 2006

Vendor Bid Delivery Total Cost Data

SAGEM No --- --- ---

Asahi-Spectra No --- --- ---

EMF Corp. No --- --- ---

Barr Assoc. Yes 26 wks ARO $213,000 Yes

Infinite Optics Yes ?? wks ARO $300,000 Yes

JDS Uniphase Yes 20 wks ARO $378,000 Yes

Reynard Corp. Yes 12 wks ARO $105,587 Yes

ZC&R Inc. Yes 16-20 wks ARO $149,000 Yes

(Bruce Bigelow)

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Optics Assembly and Test

• Lens mounting C1-C4 (WBS1.4.6) UCL– Design of lens cell and bonding technique (FEA, testing)– Handling of lenses– Alignment procedure definition

• Lens mounting C5 (WBS 1.4.7) FermiLab– Bonded straight to detector vessel– Design of lens cell and bonding technique (FEA, testing)– Alignment procedure definition

• Alignment of lenses in barrel (WBS 1.4.8) UCL– Handling of lens and cells– Alignment procedure definition

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Production Procedure

• Blanks produced and ground to shape (US?) • Blanks shipped to optical polishers (France?US?)

• Polished lenses shipped for coating (C1 and C5 could be coated by polishing firms) (US)

• Coated lenses shipped to UCL

• Lenses mounted in lens cells at UCL

• Lens and cells mounted in camera barrel at UCL

• Shipped to CTIO

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Alignment Tolerances

Lens

Decentre

Tolerance

(μm)

Tilt Tolerance

(arcsec)

Separation

Tolerance

to next lens

(μm)

C1 130 10 50

C2 70 17 50

C3 110 20 50

C4 100 20 50

C5 190 20

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Lens Mounting

LBT lens mounting (from Diolaiti et al. SPIE 4841)

Baseline athermal elastomeric (RTV rubber) bonding technique

Looking at two cell options

• Invar lens cell + flexures + thin RTV layer (see figure)

• Steel cell + thick RTV layer

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Lens to Cell Alignment

• Lens to cell– Lens to cell alignment performed using rotary table and digital

dial gauges.

Translation Stage

Rotary Table

D.G.I.

Cell

Cell Adjustment Screws

Lens

RTV inserted into gap

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Lens/cell to Barrel

Lens-cell alignment in barrel

• Mechanical alignment

– Passive: using machined fiducials

– Active: using rotary table and digital dial gauges

• Optical Alignment (see figures)

– Using rotary table and laser beam

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Optics Cost/Time Allocated

Cost Time

Quoted

Time allocated

Blanks (inc grinding) $900,000 5 months 8 months

Polishing $656,000-918,400 13 months 18 months

Coating $123,000-150,000 - 3 months

Filters $105,857-378,000 3-6 months 6 months

Total $1.8-2.4million

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Milestones

Milestone DateCDR February 2007

Blanks Contract placed March 2007

Polishing Contract placed May 2005

First lens to polishers July 2007

Last lens to polishers (C1) October 2007

First lens to UCL October 2008

Last lens to UCL April 2009

Alignment of lens in cells complete May 2009

Integration at UCL complete, ship to Chile October 2009

Assembly and test at CTIO complete March 2010