Optics:%20design,%20procurement,%20assembly%20and%20testing%20plans

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Optics design, procurement, assembly and testing
plans
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 of Michigan
• Optical Design/Stray light analysis
• Filter procurement
• Filter mechanism design/build
• University College London
• Optics procurement and testing
• Lens cell design/construction and mounting
• Optical alignment
• Fermilab
• Barrel design/build
• Active alignment sensing

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Optical Specification

• Field of view
• 2.2 degree diameter
• Pixel scale
• 57 µm/pixel (f/2.9)
• Image quality
• Resolution Element lt 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 9.3µm (area weighted)
• Wavelengths
• g, r, i, z (0.4 1.0 µm)
• with a secondary goal of good performance down to
  0.32 µm
• Pupil ghost
• intensity gradient lt 2.5 over 61mm

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Status of Optical Design

• Developing of preliminary design WBS1.4.11 (Nov
  2005-Feb 2006)
• Number of elements
• Glass choice
• Size of front element
• Number of aspheres
• Preliminary Design Review (Feb 2006)
• Final design development (Feb-Oct 2006)
• Feedback from PDR included and optimisation of
  design
• Sensitivity analysis completed
• Critical Design Review (Feb 2007)

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Optical Design

• 5 lens design
• All fused silica
• Two aspheric surfaces
• C1 lens diameter 0.98m
• Minimum thickness ratio 110
• Image scale 1" 57µm
• 0.26"/pixel
• Sol-Gel/MgF2 coatings
• Rrms 8.7 um

Design due to Rebecca Bernstein
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Lens Parameters
Surface 1 Radius (mm) Surface 2 Radius (mm) Centre Thickness (mm) Edge Thickness (mm) Diameter Surface 1 (mm) Diameter Surface 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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Optics Procurement

• Blank Procurement (WBS1.4.3)
• Manufacturing issues (homogeneity, size)
• Schedule
• Cost
• Optics Polishing (WBS 1.4.5)
• Manufacturing issues (testing, risk)
• Schedule
• Cost
• Filter Procurement (1.4.9)
• Specification
• Schedule
• Cost

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Blank Status

• Developing of preliminary optical design (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
• 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
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

• Grade C is quoted as have a homogeneity of better
  than 2ppm. B is better that
• 1.5ppm 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

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Optics Polishing

• Developing of preliminary optical design (Nov
  2005-Feb 2006)
• Discussion with manufacturers (SAGEM, SESO,
  Tinsley)
• Manufacturing issues (size, asphercity, testing,
  coatings)
• 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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Production Feedback

• Contacted SAGEM(MEGACAM, LBT), SESO, and Tinsley
• Asphere on convex or concave surface
• SAGEM had no particular preference
• SESO preferred concave surface, but could produce
  convex
• Tinsley preferred convex surface
• Size/gradient of asphere
• Slope 1mm departure over 50mm was acceptable
• All companies happy to quote on the proposed (or
  similar) design
• Testing
• SAGEM recommended all optics tested in
  transmission to allow compensation for
  inhomogeneity

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DES Filters

• 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

Filter changer will be a cartridge system similar
to PanStarrs design
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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
ZCR 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)
• Design of lens cell and bonding technique (FEA,
  testing)
• Handling of lenses
• Alignment procedure definition
• Lens mounting C5 (WBS 1.4.7)
• Design of lens cell and bonding technique (FEA,
  testing)
• Alignment procedure definition
• Alignment of lenses in barrel (WBS 1.4.8)
• Handling of lens and cells
• Alignment procedure definition

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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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Alignment

• Alignment will be undertaken at UCL
• Lens to cell
• Baseline elastomeric bonding technique
• Lens to cell alignment performed using rotary
  table and digital dial gauges.
• Lens-cell alignment in barrel
• Mechanical alignment
• Passive using on machined fiducials
• Active using rotary table and digital dial
  gauges
• Optical Alignment
• Using rotary table and laser beam

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Optics Cost/Time Allocated
Cost Time allocated
Blanks (inc grinding) 900,000 8 months
Polishing 656,000-918,400 18 months
Coating 123,000-150,000 3 months
Filters 105,857-378,000 6 months
Total 1.8-2.4million
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Optics Timetable 1

• December 2006
• Issue blank tender
• February 2007
• Critical Design Review
• Issue tenders to polishers
• March 2007
• Order blanks
• March 2007 to August 2008
• Blank Manufacture (22wks quoted,allowing 28
  weeks)
• May 2007
• Issue polishing contract to manufacturer
• July 2007
• First lens blank delivered to polishers
• C2-C5 lens polishing start (13 months quoted,
  allowing 15-19months)

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Optics Timetable 2

• October 2007
• Last lens blank (C1) delivered to polishers
• C1 lens polishing start (13 months quoted,
  allowing 18months)
• August 2008
• First lenses polishing complete, sent for coating
  (3 months)
• October 2008
• Cells and first coated lens delivered to UCL
• Alignment of lenses in cells start (7 months),
  UCL Mich _at_ UCL
• Feb 2009
• Last lens polishing complete, sent for coating (3
  months)

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Optics Timetable 3

• April 2009
• Last lens coated and delivered to UCL
• May 2009
• Alignment of lenses in cells complete
• October 2009
• Integration at UCL complete, ship to Chile
• November 2009
• Assembly and test at CTIO start
• March 2010
• Testing complete