Robert Stobie Prime Focus Imaging Spectrograph Status

1
Robert StobiePrime Focus Imaging
SpectrographStatus

• Optics repair
• Schedule
• Status of other fix and improvement projects
• Budget

2
Optics Reprise Throughput/ Ghosts

• Instrument removed (Nov 2006), optics shipped
  to Pilot Group in Calif (Dec)
• Disassembled into multiplets, throughput
  measured by monochromator (Feb - Apr 2007)

• 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

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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
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

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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 CaF2 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

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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

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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
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/ MgF2)

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Comparison with on-sky

• Projected improvement
• UV 10x (5x so far)
• Visible 10 - 30

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Repair 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

Schedule
11
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

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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