1 Optics: design, procurement, assembly and testing plans Dr Peter Doel, University College London

2 Contents WBS 1.4 Optical design Optics procurement and manufacture , Lens cell design and lens mounting Lens alignment in camera 1.48

3 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

4 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 R rms = 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

5 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

6 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/MgF 2 coatings R rms = 8.7 um Design due to Rebecca Bernstein

7 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 Lens * Lens Lens * Lens * Aspheric surface

8 Blank Procurement WBS :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

9 Corning Fused Silica HPFS 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 100cm 3 of glass of less than or equal to 0.1mm 2 and 0 less or equal to 0.03mm 2 Delivery Weeks Grade Optic C C Optic C28-111C Optic C38-111B Optic C48-110B Optic C58-110A

10 Optics Polishing WBS :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

11 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 :Status

12 Filters bids as of June 2006 VendorBidDeliveryTotal CostData SAGEMNo--- Asahi-SpectraNo--- EMF Corp.No--- Barr Assoc.Yes26 wks ARO$213,000Yes Infinite OpticsYes?? wks ARO$300,000Yes JDS UniphaseYes20 wks ARO$378,000Yes Reynard Corp.Yes12 wks ARO$105,587Yes ZC&R Inc.Yes16-20 wks ARO$149,000Yes (Bruce Bigelow)

13 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

14 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

15 Alignment Tolerances Lens Decentre Tolerance (μm) Tilt Tolerance (arcsec) Separation Tolerance to next lens (μm) C C C C C519020

16 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

17 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

18 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

19 Optics Cost/Time Allocated CostTime Quoted Time allocated Blanks (inc grinding)$900,0005 months8 months Polishing$656, ,40013 months18 months Coating$123, ,000-3 months Filters$105, , months6 months Total$ million

20 Milestones MilestoneDate CDRFebruary 2007 Blanks Contract placedMarch 2007 Polishing Contract placedMay 2005 First lens to polishersJuly 2007 Last lens to polishers (C1)October 2007 First lens to UCLOctober 2008 Last lens to UCLApril 2009 Alignment of lens in cells completeMay 2009 Integration at UCL complete, ship to ChileOctober 2009 Assembly and test at CTIO completeMarch 2010