1. Oct 22, 2007SSWG #18 UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Status Optics repair Schedule Status of other fix and improvement projects Budget

2. Oct 22, 2007SSWG #18 UKZN2 Optics Reprise: Throughput/ Ghosts Three problems –Yellow ghost due to coating problem on dewar window –Grey loss in camera triplet –UV loss in contaminated lens fluid of four multiplets Instrument removed (Nov 2006), optics shipped to Pilot Group in Calif (Dec) Disassembled into multiplets, throughput measured by monochromator (Feb - Apr 2007):

3. Oct 22, 2007SSWG #18 UKZN3 #1,2: fixed Field flattener (ghost). Bad coating polished off by Janos, new coating applied by Spectrum Thin Films (with new moisture repellant overcoat). Satisfactory. Camera triplet contact. Backed off pressure, contact and grey loss vanished, has not reappeared.

4. Oct 22, 2007SSWG #18 UKZN4 #3: Repair (still) "in work" Found absorption in lens fluid (Cargille LL5610) due to polyurethane expansion bladders, and (lesser extent) viton O-Rings Original plan (May - July): flush/ replace fluid with LL3421 (viton compatible), replace bladder with polyethylene –Can be done without disassembling multiplets, although index slightly low Plan A: Did not work –fluid gaps too small, some could not be flushed –ethanol flushing agent sometimes fogged test NaCl pieces

5. Oct 22, 2007SSWG #18 UKZN5 Plans B, C (and D) Plan B: Disassemble multiplets, clean, replace expansion polyurethane bladders and viton O-rings –Back to LL5610 fluid (better index match) except for Collimator Field Lens and Triplet: LL3421 a better choice for common NIR beam (Aug - Sept) Four of five multiplets repaired. During reassembly of the last, two surfaces of first CaF 2 element in collimator triplet ("OL5") damaged by technician error! Plan C: Recovery –use existing spare blank (thanks to CDR panel!) –Pilot to cover blank, figuring, coating costs –figuring underway by TORC –considering Lick Obs hardened solgel coating –3 - 6 month delay –Plan D (in case this one breaks!): regrind damaged element

6. Oct 22, 2007SSWG #18 UKZN6 Throughput – Collimator Field Lens repair: UV loss was very small - repaired as precaution Triplet repair: interrupted by accident: projection shown Doublet repair –UV loss gone except slight dip at 350 nm –~10% grey loss still seen

7. Oct 22, 2007SSWG #18 UKZN7 Throughput - Camera/ Spec Quartet Repair. Looks good. Triplet Repair –surface contact fix remedies grey loss –fluid repair improves UV, leaves ~15% loss at 320 nm Project visible ~5% below FPRD spec, 30% low at 320 nm

8. Oct 22, 2007SSWG #18 UKZN8 Remaining UV loss - multilayer coatings? Notice that all elements having Spectrum Thin Film multilayer coatings (including singlet field flattener after recoat) have "ripples", one in the UV. Suspect absorption effect, not caught with reflectivity witness Small effect not worth risk and cost of disassembly, polish off coat, recoat, etc Effect may also be in SALTICAM If true, should not be seen in repaired collimator triplet (solgel/ MgF 2 )

9. Oct 22, 2007SSWG #18 UKZN9 Comparison with on-sky Projected improvement –UV 10x (5x so far) –Visible 10 - 30%

10. Oct 22, 2007SSWG #18 UKZN10 Repair Schedule Schedule With departure of Eric Burgh, new UW optics reintegration support team: Alan Shier (Pilot Group), Marsha Wolf (NIR project) Reintegration schedule –No earlier than: 7 Feb - 31 Mar –With 3 month contingency: 1 May - 23 June

11. Oct 22, 2007SSWG #18 UKZN11 RSS Fixes/ Improvements Slitmask mechanism –severe reliability problems due to difficulty of aligning magazine, carrier, and focal plane chute –redesigned, rebuilt; sensor electronics board iteration Grating stage flexure –out-of spec flexure perpendicular to dispersion –repaired current grating stage; purchased new, improved one Etalon flexure –ring centers do not flex the same: dual etalon difficulty –improve etalon "seat". Done Fix guider interference (limits field): Done Improve baffling –moving baffle damage, maintainability. Material received –payload/ instrument interface. Material received; design complete High level software. Design Complete; coding in progress Detector fast readout modification (last SSWG). Done

12. Oct 22, 2007SSWG #18 UKZN12 Cost to Completion Does not include ~$40K repair overrun due to additional work disassembling multiplets ("Plan B") Replacement of damaged element OL5 borne by Pilot Group Still predicting CTC ~20% over CDR budget