The Gemini Adaptive Optics Program MCAO for Gemini-South

1
The Gemini Adaptive Optics ProgramMCAO for
Gemini-South

• F.Rigaut and B.Ellerbroek

• Presentation Overview
• Dedication success
• The Gemini Adaptive Optics Program Revisited
• Multi-Conjugate Adaptive Optics
• A Science Opportunity Context and rationale
• Principles and performance
• Feasibility
• Cost and Schedule

2
Geminis Dedication
3
Gemini Top Level Performance Requirement 2

• Image quality of better than 0.1 arcsec with
  AO
• Achievement of outstanding image quality will
  have the highest scientific priority for the
  project
• 85 of the science topics in the Abingdon report
  need AO to be effectively addressed
• The proposed evolution of the program at CP will
  enable unique NGST-class science 4 years ahead of
  NGST launch. It will keep Gemini competitive
  during the NGST era

4
Proposed Baseline AO Program
NORTH
SOUTH
5
Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH

• Context
• The Gemini science mission relies heavily on
  high angular resolution
• Other observatories have high performance AOSs
  in the north (Keck 1999) and in the south (VLT
  2001) -gt Competitiveness issue
• Rationale
• Provide the Gemini community with NGST-like
  capabilities (spatial res. and field), matching
  the Gemini science goals and instrumentation
• Sets up Gemini to be a lead ground-based
  facility in the NGST era with matching resolution
  and similar field of view
• Future ELTs require wide field of view AO

6
Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH

• Proposal
• Build a high performance, 2 arcminutes field of
  view AOS with homogeneous PSF quality over the
  entire field of view, with very high sky coverage
• How ?
• Using Multi-Conjugate AO, i.e. 4-5 LGSs and
  wavefront sensors to measure the turbulence in 3D
  and 2-3 deformable mirrors to correct it
• This uses currently available technology. NO
  hardware development required other than lasers
  (same as MK-LGS)

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What is Tomography ?1. Cone effect
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What is Tomography ?2. Multiple guide star and
tomography
90 km
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What is multiconjugate?
Deformable mirror
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What is multiconjugate?
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Effectiveness of MCAO

• Numerical simulations
• 5 Natural guide stars
• 5 Wavefront sensors
• 2 mirrors
• 8 turbulence layers
• MK turbulence profile
• Field of view 1.2
• H band

12
MCAO Performance SummaryEarly NGS results, MK
Profile
2 DMs / 5 NGS
1 DM / 1 NGS
165
320 stars / K band / 0.7 seeing
Stars magnified for clarity
13
Sample Numerical Results

• 0 degree zenith
• 50 seeing
• CP turbulence profile
• K band
• 12x12 subapertures
• NGS-AO (triangles)
• MCAO with 5 LGSs and 3 Tip-tilt NGS (crosses)

K
H
J
I
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Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH

• Advantages of MCAO versus Classical AO
• Sky coverage (50) increased (50-500x) w/
  respect to a NGS system
• Increased performance on axis w/ respect to a
  LGS system because the cone effect is compensated
• Increased field of view (well matched to IRMOS)
• Uniform PSF across the FoV -gt Easier and more
  accurate Data Reduction

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MCAO Implementation-Feasibility study
conclusions

• Optics and optics bench
• Mass, volume similar to Altair
• Wave front sensor camera
• Goal of a single camera for all laser guide stars
• 80 by 80 to 128 by 128 pixels, 5 to 10 read noise
  electrons
• Deformable mirrors and tip/tilt mirror
• Number of actuators, other parameters
  demonstrated
• Wave front reconstruction electronics
• Frame rate, number of inputs/outputs demonstrated
• Flexible algorithms and architectures necessary
  for NGS tip/tilt measurements
• Tip/tilt sensors, laser transfer optics and
  launch telescope
• Appear straightforward, feasibility designs in
  progress
• 2-3 T/T sensors 1 more provided by OIWFS
• Laser(s) Technology and engineering development
  required

16
MCAO Science Optical Path

• 3 DMs at R0, 4, and 8 km
• 13 actuators across beamprint
• 4 folds, 2 off-axis parabolas,
• 1 dichroic beamsplitter (not shown)
• - Near-minimum number of surfaces for
• facility MCAO
• f/30 output focus

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Laser Issues

• Power requirement
• Equivalent to conventional LGS AO on a per beacon
  basis
• 20-40 Watts per LGS, 80-200 Watts total for short
  pulse, flashlampNdYAG-pumped dye lasers (LLNL)
• 20 Watts demonstrated
• Scaling a cost/engineering issue (electrical
  power, heat dissipation, flammable dye)
• 7-12 Watts per LGS, 28-60 Watts total for
  diode-pumped, NdYAG sum frequency lasers (MIT/LL
  and others)
• 5 Watts demonstrated
• Scaling a technical issue (NdYAG beam quality
  and sum frequency feasibility at higher powers)

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Baseline Schedule

• Conceptual design review 3/00
• Preliminary design reviews 12/00
• Critical design reviews 12/01
• Subsystems complete 6/03
• System integration and test 10/03
• Science handover 3/04

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MCAO Budget Estimate (Part I)
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MCAO Budget Estimate (Part II)
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Labor Requirements by Year
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Gemini AO Program Division of Work within
Partnership

• Gemini AO program ambitious, but IGPO is not
  proceeding alone
• Partnership Workload (including vendors)
• Hokupaa-85 for Gemini-North UH
• Hokupaa-85 for Gemini-South
• WFS and DM UH
• Commercially supplied dye laser
• Altair HIA
• Altair LGS
• WFS upgrades HIA
• Laser source Contract
• Coronograph AO Instrument supplier
• Common infrastructure (IGPO) LGS transfer
  optics, launch telescope, and safety system
• MCAO is the focus of IGPO efforts. Significant
  outsourcing of work expected after CoDR.

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Recent Progress

• Overall roadmap to CoDR drafted
• Science requirements, system requirements, system
  design, cost, labor, and schedule
• System analysis street map drafted
• LGS power requirements, NGS magnitude limits and
  sky coverage, instrument performance, comparison
  with LGS
• Coordination with Gemini partners and community
  underway
• HIA (10/23), CfAO (11/2), NOAO (11/4)
• LGS development meeting planned with CfAO for
  12/7
• Meeting at Durham (and possibly ATC) planned for
  12/9-10
• Launch telescope and transfer optics design in
  progress
• Conversations with component vendors continue
• System modeling, algorithm development continues

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MCAOA Step Beyond
Classical AO
MCAO

• Using the same components as other planned LGS AO
  systems, MCAO on Gemini-South will go a step
  beyond
• Enabling NGST-class observations for the Gemini
  Community

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MCAO for Gemini-SouthPerformance, Feasibility,
and Schedule

• A multi-conjugate AO system for Gemini-south can
  theoretically provide highly uniform turbulence
  compensation over a 1-2 diameter field-of-view
• System can be implemented with largely existing
  hardware and technology
• Fully acceptable deformable mirrors, tip/tilt
  mirrors, and wave front reconstructs have been
  demonstrated
• Most recent high-speed 1282 CD's meet wave front
  sensor requirements with margin
• Significant improvements still required in sodium
  laser power and reliability
• Comparable with conventional LGS AO on a per
  beacon basis
• Estimated schedule for science handover is spring
  2004

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Baseline Program CP-Hokupaa
1999
2000
2001
2002
2003
2004
SOUTH
Hokupaa
36
85

• AO Duplicate of the MK upgrade of Hokupaa to
  85 actuators. UH AO Team. Proposal submitted to
  NSF 08/99. Optomechanical upgrades (FoV 60)
  LGS compatible
• Performance w/ NGS (AO only)
• Seeing Strehl(J) Strehl(K)
• 0.45 50 80
• 0.65 25 62
• LGS Off-the-shelf 2W CW laser. Coherent/Spectra
  physics CW 10W pump laser ring dye laser
  (demonstrated in lab)
• IR Imager ABU

Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
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Baseline Program CP-Hokupaa
1999
2000
2001
2002
2003
2004
SOUTH
Hokupaa
36
85

• Rationale
• Gives us a 2 year window of unchallenged AOLGS
  capability in the southern hemisphere (comp.
  NAOS) w/ Adequate JHK performance.
• Build expertise on LGS by stepping up gradually
  (Laser Launch Telescope Beam Transfer Optics)
• Getting AO on CP as soon as possible relieves
  pressure, allowing us to avoid the rush and do a
  better job on the final CP system

Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
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MCAO Performance SummaryEarly NGS results, MK
Profile
MCAO
Classical AO
Guide star location
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Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH
10W LGS
Performance
Hokupaa
36
85
Mode Sky3 SRJ(0) SRJ(48) FOV Hardware
NGS 1 0.55 0.04 30
1 1DM LGS 17 0.47 0.04 32
1 1DM/1LGS MCAO 30 0.54 0.35
2 2 3DM/5LGS 1 50 Strehl ratio attenuation 2
limited by the AO-Fold aperture 3 Sky coverage at
galactic pole
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
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ALFA AO Results(18 Modes, 0.9-1.0 seeing, K
band)
Open loop
Loop closed with LGS AO

• 4 W dye laser
• 0.23 Strehl
• FWHM dif-fraction limited.

NGS AO

• 0.42 Strehl
• 0.53 predicted

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What is multiconjugate?
Telescope
Turb. Layers
WFS
1
2
DM2
DM1
Atmosphere
UP
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Sample Numerical Results

• 0 degree zenith
• 50 seeing
• 12 by 12 NGS (black)
• 12 by 12 MCAO (red)
• 16 by 16 MCAO (blue)
• I, J, H, and K bands

K
H
J
I