TMT SEEINGLIMITED Instruments

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TMT SEEING-LIMITED Instruments

• David Crampton
• AOIWG meeting, Nov 17 2004

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WFOS Requirements Goals

• Wavelength range
• 0.31-1.0?m (requirement) 0.3-1.3?m (goal)
• Simultaneous is a goal, but not currently a
  requirement
• Resolution
• This is serious not achieving it will compromise
  much of R
• the science currently envisioned.
• FoV
• 75 arcmin2 (requirement) 300 arcmin2 (goal)
• Not necessarily contiguous
• Throughput
• 30 (0.31-1.0?m)
• Image quality
• Spatial sampling (per pixel)

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WFOS studies

• 3 independent studies
• HIA (Bev Oke, Denis Laurin, Ian Powell)
• Caltech (Keith Taylor, Damien Jones)
• UCSC (Harlan Epps, Joe Miller)
• 3 completely different solutions
• UCSC uses raw Nasmyth focus to deliver a
  single, contiguous field, spectrograph
• Caltech II (MILES) and HIA designs use 2-by-2
  mosaics of off-axis focal reducers feeding 4
  independent spectrographs
• MILES designed for Gregorian, HIA I for RC, HIA
  II for Gregorian
• All come close to, or exceed, the FoV
  requirements
• UCSCs ELVIS falls short in FoV but is very
  attractive in other ways
• HIAs and MILES designs meets the FoV requirement
• Spectral resolution problematic
• ELVIS requires 0.25slits and large CaF2
• MILES requires even larger CaF2
• HIA designs meet requirement (but HIA I suffers
  from larger central obstruction)
• Pixel scale problematic
• ELVIS 17 15micron pix per arcsec
• HIA I 15
• HIA II

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ELVIS layout (Epps)
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ELVIS (in person)
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ELVIS (detector layout)
234mm
150 Mega-pixel array
142mm
0.04/pixel (17 pixels/slit)
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WFOS _at_ UCSC summary

• Accepts raw f/15 Nasmyth focus
• Requires Gregorian configuration
• Trombone ADC ahead of image surface
• Fully refractive collimator/cameras
• Collimator forms 250mm beam
• R5000 spectral resolution met with 0.25 slit
• Image quality probably OK?
• 3 selectable wavelength ranges
• 2 simultaneous with suitable dichroic
• FoV 8 arcmin. dia (50 arcmin2)
• Imaging and spectroscopy
• Single contiguous field
• Uses VPH transmission gratings
• Articulated cameras
• Could be built now lowest risk
• Uses large (but not too large) CaF2

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HIA I Variations on B. Okes WFOS Concept

• A Thirty metre telescope imager and low
  resolution spectrograph

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HIA I Relay optics with 3-mirror design

• Relay optics - 3 mirror anastigmat

Square Telescope image surface
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Multi-instrument Options

• 4-instrument layout possibility (fore optics
  only)

Square Telescope image surface
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2
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Square field limits (1.5,1.5) to (6,6) each.
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f/2.2 camera (0.75 15 pixels, assuming 15?m
pixels)
HIA detector layout
60 Mega-pixel array (4)
0.05/pixel (15 pixels/slit)
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WFOS _at_ HIA I summary

• 4-shooter design
• Relays raw f/15 Nasmyth to an intermediate f/5
  focus
• Prefers R-C configuration
• Masks at intermediate focus ADC (tbd) but
  practical
• Catadioptric collimators cameras
• Collimator forms 1m beam
• R0.75 more than adequate
• Why not smaller beam ? (internal vignetting)
• All wavelengths ranges (0.31?m 1.0?m) supported
• Dual beam option
• FoV 4.5 -by- 4.5 arcmin. square field
• (4-shooter gives 81 arcmin2)
• non-contiguous
• Access to center of field for other capabilities
• Requires mosaic gratings
• VPH/Articulated cameras may not be practical
• Simple optics, large beamsplitter but no large
  CaF2
• No obvious show stoppers (except overall size)

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WFOS _at_ HIA Many options investigated

• All 4-shooter designs

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AWESOME Concept
AWESOME

• AWESOME
• A Wide-field Efficient Spectrograph / Optical /
  Multi-object for ELT

• Simplified WFOS, no relay, 2-mirror (aspheric)
  collimator, reflective camera with corrective
  lenses, no CaF2.

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AWESOME Imaging

• Imaging performance
• Circle 1 arcsec dia.
• RMS approx. 35 um radius (0.14 arcsec).
• 50 EE approx. 30 um radius (0.10 arcsec).
• SRD requires 0.2, so almost meets requirements,
  and no error budget left!

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4-Instrument Layout

• AWESOME on TMT
• Nasmyth platform
• Vertical
• Image de-rotation
• Envelope
• 6.2 m high, 6 m dia. cylinder.
• Total mass approx.
• Optical 5 tonnes
• Structure 4optical
• Total 25 tonnes

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WFOS _at_ HIA II AWESOME

• 4-shooter design
• No focal reducer stage
• Designed for Gregorian
• Two mirror lens collimator
• Difficult mirrors!!
• Catadioptric cameras
• All wavelengths ranges (0.31?m 1.0?m) supported
• Dual beam option
• FoV 4.5 -by- 4.5 arcmin. square field
• (4-shooter gives 81 arcmin2)
• non-contiguous
• Access to center of field for other capabilities
• High throughput
• VPH gratings
• Mirrors are biggest risk item
• But simpler mirror lens solutions may exist
  (Morbey)

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WFOS Caltech II (MILES)

• 4-shooter arrangement
• Each field 4.3 square

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WFOS Caltech II (MILES)
M2 constrained to be at pupil Facilitates image
compensation

• 4-shooter arrangement
• Each field 4.3 square

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WFOS Caltech (MILES) summary

• 4-shooter arrangement
• Each field 4.3 square
• Separate ADC for each (ADC design verified)
• TM focal reducer for each subfield
• Relays raw f/15 Gregorian to an intermediate
  f/7.5 focus
• M2 is at a pupil - could be a DM possibility
  for AO compensation
• Masks at intermediate focus
• Refractive collimator, 400mm beam
• Feeds VPH gratings, delivers R 5000 with 0.75
  slit
• Catadioptric f/1.2 camera
• Detector internal, 4 obstruction
• Needs mosaic of 3K6K curved CCDs
• 86 mas per 15micron pixel
• CaF2? Needs 525mm diam
• Wavefront sensing??

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WFOS comparison
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WFOS comparison, cont.
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Common threads

• Many similar problems
• Size of CaF2 refractive elements?
• need large beam to get required resolution
• Size of beamsplitters filters
• Efficiency of AR and reflective coatings?
• 0.31-1.1?m
• Efficiency and size of VPH gratings?
• may need VPH gratings to get spectral resolution
• May need to mosaic gratings and filters
• MILES and AWESOME would like curved detectors
• DIFFERENCES
• HIA design is dual beam, simultaneous blue and
  red spectra
• UCSC offers selection of UV, broad-band or NIR
  spectra
• Caltech design offers interchangeable optics for
  blue red
• MILES offers possibility of AO image compensation

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Some WFOS requirements

• Require large mask maker, mask handling system
  storage
• ALL will need HRWFS to improve IQ
• Either bright NGS off-axis
• Or LGS (on-axis?) for GLAO
• All must incorporate ability to nod shuffle
• to reach Poisson-limited sky subtraction
• Nods 30sec
• ideally with
• Must synchronize nods, WFS, CCD controller
• Is simultaneous operation with HROS a goal?
• AG and cal solutions??

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HROS (MTHR)

• MTHR design well studied by Steve Vogt
• Meets SRD requirements
• Gregorian telescope design OK
• not sensitive to f/ratio (f/15 nominal)
• ADC and image rotation internal to instrument
• Huge, requires tennis court sized Nasmyth
• 12m 16m area with fixed gravity
• separate level of Nasmyth platform attractive
• Volume could be reduced could be interupted by
  e.g., supports
• Mass
• Fibre mode desirable?
• If yes, then fibre positioner should be located
  close to minimize losses
• No new technologies
• Good candidate for first light instrument
  (natural seeing, any conditions)
• Could build minimalist version first
• Descope options exist

For details see Vogt slides from Mar
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HROS (MTHR Concept)
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HROS (Options)

• Could build minimalist version for first light
• Descope options exist

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HROS (MTHR)

• Could be used simultaneously with (some) WFOS
  concepts
• End