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

Participation (tentative)

Dial-in

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

Agenda

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

Minutes

• 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).