The Gemini Adaptive Optics Program MCAO for Gemini-South

1
The Gemini Adaptive Optics ProgramMCAO for
Gemini-South

• Gemini Adaptive Optics Team
• B. Ellerbroek and F.Rigaut

2
Top Level Perf. 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
• 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.

3
AO and Science

• AO is a rather new domain...
• First AO instrument for astro. -gt Come-on, ESO
  1990
• UH curvature system, Mauna Kea 1992
• 1994-1998 Exponential progression of of
  systems
• but science is already flowing
• Number of Astro paper is growing exponentially
• Total of 70 refereed papers (lost count).
  Highlights Discovery of an asteroid satellite,
  wrap of ? Pic disk, Surface and orbital
  parameters of solar system bodies, YSO disks and
  outflows (e.g. HL and GG Tau), Stellar motions in
  GC, Stellar multiplicity surveys, Structure in
  AGNs, Galaxy dynamic (e.g. CFHT AOSIS), etc...

4
A short history of astronomical AO

• 1989 First AO images w/ Come-On (OHP ESO)
  110mas

• 1992 First Curvature system (UH) 70mas
• 1996 First Facility system (CFHT AOB)

5
CFHT Pueo 1996 Galactic Center 2.2 ?m
FWHM 130 mas
6
A short history of astronomical AO

• 1989 First AO images w/ Come-On (OHP ESO)
  110mas
• 1992 First Curvature system (UH) 70mas
• 1996 First Facility system (CFHT AOB)

• 1996 First compensation in the visible (Mt
  Wilson) 58mas
• 1996 First LGS systems
• 1998 LGS systems getting closing expectations
• 1999 First h.order system on a large telescope
  (Keck) 40mas

7
Keck AO System 1999 Vesta 1.5 ?m
FWHM lt40 mas
1
8
Geminis Dedication
Courtesy C.Roddier, UH-IfA
9
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

10
Where is AO standing ?

• AO technology for astronomy is maturing rapidly
• Well designed and calibrated NGS AO systems (CFHT
  Pueo, Hokupaa, MIT/Lincoln Laboratory, SOR) now
  closely approach their performance predictions.
• Rayleigh beacon LGS AO programs (MIT/LL, SOR)
  have been technically successful
• Astronomical sodium beacon LGS AO systems have
  progressed from Strehls of 0.03 to 0.30 in two
  years
• Sodium layer variability has been well
  characterized by numerous LIDAR campaigns

11
Proposed Baseline AO Program
NORTH
SOUTH
12
Baseline Program Altair
1999
2000
2001
2002
2003
2004
NORTH
10W LGS

• Progresses well (CDR 02/99)
• Statement of work for Altair LGS upgrade nearly
  ready

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
13
Baseline Program 10W LGS
1999
2000
2001
2002
2003
2004
NORTH
10W LGS

• 10 W Laser RFP to go out early October
• Power requirements vary from 7 to 23W depending
  on laser pulse format
• Design of the LLT and BTO underway

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
14
Baseline Program MK-Hokupaa
1999
2000
2001
2002
2003
2004
NORTH
10W LGS

• Hokupaa-36 installed on the telescope early June
  this year
• Images fully compatible with expectations (seeing
  ok but not exceptional), near diffraction limit
  in K band w/ Strehl 15-30. Great tool for
  telescope engineering
• 85 Actuators upgrade to be done next year by UH
  team on UH/NSF internal funds. Small transferred
  field (30)
• Performance w/ NGS (AO only) (2 fold vs 36
  actuators)
• Seeing Strehl(J) Strehl(K)
• 0.45 50 80
• 0.65 25 62

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
15
Cerro Pachon-AOS/LGS ForumApril 1999, Review
Panel Recommendations

• The IGPO should develop a strategy for its
  overall adaptive optics program which satisfies
  the Gemini community. Timing of the program,
  staff resources, and cost must be addressed. The
  RP also notes that the experience gained with the
  Altair AO and Hokupa'a teams are valuable to the
  overall program and should be folded into the
  planning.
• The Project should conduct a significant but
  time-limited study of a multiconjugate adaptive
  optics system for Cerro Pachon. This would
  provide an exciting advancement in capabilities
  but implementing the system should be conditional
  on "filling" the AO gap on Gemini-South and
  addressing the requirements of the coronagraphic
  imager. The study should address the theoretical
  analysis, science drivers, technical challenges,
  systems engineering, and programmatics of such an
  AO system. With the development of a plan, the
  RP recommends that Gemini adopt as aggressive a
  schedule as possible to bring this capability to
  the community.
• The IGPO should lead the conceptual design
  program of the Gemini-South AO system, including
  defining the allocation of subsystems across the
  Gemini Community
• In light of the proposals presented for turn-key
  laser systems, the RP recommends that the IGPO
  explore with LiteCycles the manufacture of a Sum
  Frequency laser. To reduce cost and risk for the
  laser, procurement through a consortium should be
  explored, including Keck, and possibly other
  groups if they can participate on timescales
  which are consistent with Gemini's schedule for
  laser deployment.
• The project should avoid relying on major
  technological developments such as MEMs, liquid
  crystals, and other 'advanced' DMs for the CP AOS

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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
17
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
18
Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH
10W LGS

• Context
• Simplest case duplicate Altair -gt No AO
  facility until late 2002.
• Other observatories have very capable AOSs in
  the north (Keck 1999) and in the south (VLT-NAOS
  2001) -gt Competitiveness issue
• Rationale (Why?)
• 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

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
19
Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH
10W LGS

• Proposal (What?)
• 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)

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
20
What is Tomography ?1. Cone effect
21
What is tomography ?2. Multiple guide star and
tomography
22
What is multiconjugate?
23
What is multiconjugate?
24
What is multiconjugate?
Telescope
Turb. Layers
WFS
1
2
DM2
DM1
Atmosphere
UP
25
Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH
10W LGS

• What does MCAO do that another system wouldnt ?
• 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 taken care
  of
• Increased field of view (well matched to IRMOS)
• Uniform PSF across the FoV -gt Easier and more
  accurate Data Reduc.

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
26
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
27
MCAO Performance SummaryEarly NGS results, MK
Profile
MCAO
Classical AO
Guide star location
28
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 34 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
29
Baseline Program Facility CP AOS
1999
2000
2001
2002
2003
2004
SOUTH
10W LGS

• Where are we?
• Feasibility study progressing, including
• First pass on the science drivers
• Theoretical analysis of MCAO control/numerical
  simulations/Performance assessment
• A proof-of-concept optical and mechanical layout
• Assessment of the need in computing issues
• Management plan including schedule and resource
  needs

Hokupaa
36
85
Subaru
Keck
SOUTH
VLT
VLT-LGS
CP AOS/LGS
CP Hokupaa
85
2W LGS
30
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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NGS, LGS, and Multi-conjugate AOSystem
Characteristics
32
NGS, LGS, and Multi-conjugate AOPerformance
Characteristics

• Sky coverage and field-of-view are for J, H, K
  bands with 0.5 arc second seeing

33
Analysis and Simulation Models

• Two approaches available for more detailed
  modeling of MCAO
• Upgraded simulation
• Statistical analysis based opon turbulence
  statistics, MCAO system parameters
• Both approaches treat laser- and natural guide
  stars, WFS/DM geometries, CP turbulence profiles
• Analysis derives optimal wave front
  reconstructors
• Simulation more efficient for standard
  least-squares approach
• Both approaches extendable to model WFS noise,
  servo lag, telescope/instrument aberrations
• Simulation can potentially model wave optics
  effects in wave front sensors and the atmosphere

34
MCAO Parameters for Gemini-CP

• 4 or 5 laser guide stars
• 30 to 60 (48) offset from optical axis
• 10 to 20 Watts CW equivalent power, 1.5 XDL
• 4 or 5 LGS wave front sensors
• 12 by 12 or 16 by 16 subapertures
• 80 by 80 to 128 by 128 pixels
• 5 to 10 read noise electrons, 500 to 1000 Hz
  sampling
• 2 or 3 deformable mirrors
• 13 or 17 actuators across beamprint
• Conjugate ranges of 0, 4-4.5, 8-9 km
• 3-4 T/T or T/T/F natural guide stars, 1 T/T mirror

(Parameters Used for Following Sample Results)
(Parameters not Yet Modeled)
35
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
36
Sample Numerical ResultsVariation with Seeing
and Zenith Angle
0 Degree Zenith
45 Degree Zenith

• 12 by 12 NGS (black), 12 by 12 MCAO (red), and
  16 by 16 MCAO (blue)
• I, J, H, and K spectral bands

37
Sample ResultsSlit Coupling Efficiency at 0
Degrees Zenith

• 16 by 16 MCAO, I, J, H, and K spectral bands
• Horizontal and vertical 0.1 arc second slits

38
Why Multiple Tip/Tilt NGSs?

• Consider a turbulence profile with a focus
  aberrations at two ranges (blue)
• LGS measurements (yellow) cannot determine range
  of the aberration
• Tip/tilt information lost
• Equal focus measurement from each LGS, regardless
  of aberration range
• Tip/tilt NGS measurements can determine range
  from the differential tilt between stars
• Three tip/tilt NGSs needed for all three
  quadratic modes
• Alternate approaches Rayleigh LGSs, or a
  solution to the LGS tilt indeterminacy problem

f(r)a(crd)2 ac2r22acdrad2
ac2r2 After tilt removal
f(r)ar2
39
MCAO Sky Coverage with Multiple Tip/Tilt NGS

• Quantitative sky coverage calculations more
  complex than for conventional AO, but some
  initial estimates are possible
• Only one NGS need be sufficiently bright for
  correction of high-bandwidth, wind-shake induced
  tip/tilt jitter
• The atmospheric modes corrected by remaining
  reference stars are lower frequency, allowing
  lower control bandwidths and dimmer stars (e.g.
  30Hz sampling rate)
• Preliminary calculation for the galactic pole
• LGS AO sky coverage for 60 Strehl in H 17
• MCAO coverage with 1 m18 star and 2 m20 stars
  within 1 radius 34

40
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
• 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

41
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

42
MCAO LGS Optical Path

• Outgoing Single launch telescope for all guide
  stars
• Return One WFS camera for all guide stars

4 LGSs sensed with 1 WFS CCD
ZEMAX optical schematic
43
WFS Camera Options

• MIT/LL read noise level is new information since
  feasibility study

44
Approach to Multiple Tip/Tilt NGS WFSs
200mm

• Fiber-fed APD quadrant detectors
• 2 or 3 T/T WFSs in AO instrument package
• One additional T/T/F WFS in each facility
  instrument, for a total of 3-4 sensors

To APDs
Focal plane
X stage
X stage
Y stage
45
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)

46
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

47
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. Outsourcing
  of work expected after CoDR.