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DevCon: 11 May

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Kyle Westfall edited this page May 22, 2018 · 7 revisions

Microlens Development (Tim, KG)

UCLA Workshop Debrief Discussion

Agenda:

  • Microlens development (Tim, KG)

    • using model of Keck focal plane: 20 arcmin field
    • examining full DESI wavelength passband
    • 0.46 arcsec pitch: made smaller to handle chromatic aberration and fit pupil on DESI's 107 um fiber
      • still not telecentric: need to quantify error contribution and compare to stack up from other terms
      • optimize for throughput; telecentricity errors leads to greater FRD; if few % then need to quantify and address.
    • effects from changing field position
      • impact of de-focus seems manageable - needs further work to include PSF
      • foreoptics are not obviously needed - lenslet size is manufacturable
        • be careful: laser drilled fiber bundles may have too thin a wall thickness to match the pitch without foreoptics
          • how well has the Keck focal plane image quality been characterized as function of radius?
            • mainly just modeled, e.g., based on ADC work by Drew — no quantitative measurements
            • guiders may be more helpful than say, LRIS, where de-coupling the instrument effects would be hard

  • FOBOS UCLA workshop debrief

    • Some notes from Kyle:

      • Talks can be found here: https://www.dropbox.com/sh/91tpbuf4vdcdote/AABGMoabrMuIgolGom6CCcxHa?dl=0

      • Little discussion-only time due to significant discussion during talks

      • Discussion of placement of the instrument at Keck:

        • Below Nasmyth deck? Constraints of fiber run length?

      • Nick showed design using fiber-WFOS spectrograph

        • 1 arcsec apertures with single fibers with multiplex ~650
        • Higher resolution than DESI baseline
        • Extends blue spectral range to ~0.31 micron

      • Uniqueness of blue response

        • Bluer than basically any upcoming instrument; closest are PFS at 0.38 (0.41?) and MSE at (nominally?) 0.36
        • Relevant to conversation regarding comparison with PFS

      • Many noted desire to push toward approx. 1.3 micron

        • How much of this is only driven be "doing the science we know" instead of the unique science that could be done with the blue wavelength coverage?
        • Will 4 arms be enough if we go to lower resolution?
        • Invite someone with first-hand knowledge of GeCCD development to join FOBOS team?

      • Resolution:

        • Want to resolve between sky lines in the red arm (R~3500)
        • May not be necessary to have R>2000 in the blue
        • Some stellar cases want R>15k (over smaller spectral range)
          • high-resolution extension?
          • Flexible focal plane

      • Calibration? We need it but how?

      • More care needed in comparison to other instruments and development terminology

        • PFS comparison:
          • Need to check that we have an accurate curve from PFS team
          • Need to be careful with comparison and how it is shown
          • Other Keck instruments
        • PDF vs CDR

    • Some discussion points:

      What kind of spectrographs

      • WFOS-like spectrographs with larger fibers?
      • Could DESI specs be used at bluer wavelengths?
        • Bluer sensitivity would make FOBOS more unique
      • Use of DESI design saves some cost (in design) and some risk (at least you know what you get)
      • 4th arm to go into the near-IR? Slit head is currently in position of where the third dichroic ought to go
        • make a third "red" camera

      What spectral resolution?

      • R ~ 3500
      • R ~ 15,000

      GLAO

      • existing slit mask drilling is not precise enough
      • LRIS pixel sapmle and internal optics are sufficient
      • DEIMOS FoV may be too large for correction: LRIS and MOSFIRE has been the focus; MOSFIRE slits are on-axis; MOSFIRE pixels are not currently over-sampled

  • White paper planning, due June 8

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