<IRMS mini-Study Team Meeting #5 - Optical Design mini-Review >

Date: Tues, Oct 19, 2011
Time: 1pm - 3pm PDT
Location: Caltech, Cahill room 126

Participation (tentative)

Attending: Matthews, Weber, Dekany, Konidaris
Call-in: Mobasher, Ellerbroek, Pazder
Unavailable: Simard


  • (U.S. & Canada): (866) 217-1869
  • Conference Code: 9147077081
  • From China: 8008708911 (or perhaps 4006700523)


  • 1300 - 1310 Goals of this review - Rich
  • 1310 - 1400 IRMS optical design concept relative to MOSFIRE - Nick
  • 1400 - 1420 Optomechanical impact of optical design changes - Bob


  • Rich described the goal of this meeting as assessing whether the MOSFIRE optical design approach can be made to work as IRMS behind NFIRAOS
    • There are many optical issues that we will need to address in the fullness of the project, but for now, should we continue with the current mini-Study, have we enough confidence?
  • Nick pointed out that MOSFIRE has been in construction phase for 5 years beyond DDR, when the design was 'complete' - MOSFIRE is a very difficult instrument to build
  • Nick elected to optimize for sharp slit images in spectrograph mode, allowing a blurred PSF to fall onto the slit, and with only a 'flip' of the CSU effective curvature (no change to radius)
    • This decision needs to be revisited in terms of slit coupling losses
  • John recommended that the full NFIRAOS model be included in Nick iterations in the future, to confirm results end-to-end
  • Initial ghost analysis shows the situation essentially no worse than for MOSFIRE, but there will in the future be more thought necessary about ghosting, the potential for persistence effects, etc.
  • Bob reported that the optical design changes recommended by Nick require only minor rework of the structure
    • The largest cost impact will be re-drawing the production drawings for the small dimensional changes.
  • Rich wondered if the changes are so small, should we forego the thermal study planned in this phase?
    • Keith pointed out the additional of an external OIWFS probe arm (if adopted as our design baseline) could be a larger impact to the thermal budget than the optics changes in the cryostat.
  • After discussion, all concurred the situation looked good, and the IRMS team should continue with the remainder of the mini-Study

Outstanding Actions

  • Nick will parameterize a set of PSFs to be requested from Brent and the TMT AO team
    • Nick will then evaluate the differential impact on slit coupling losses of several design choices, such as sharp slit edge imaging onto the detector.
    • Also key is the question, is the potential benefit of re-engineering the CSU for a different cylindrical curvature (e.g. 5 slit levels vs. 3) worth even opening a discussion with CSEM?
  • Nick will included the NFIRAOS model in future design iterations, or at least verify the independence of results to NFIRAOS details (except for field curvature, which is essential).
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Topic revision: r7 - 2011-11-01 - RichardDekany
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