TMT.AOS.PRE.09.024.REL01

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TMT Adaptive Optics Program

• Brent Ellerbroek
• NIAOT visit to TMT
• June 4, 2009

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Presentation Outline

• Context
• AO state-of-the-art at 8-10m class telescopes
• Requirements flowdown for first light AO at TMT
• System-level requirements and development
  strategy
• Flowdown to AO architecture choices and overall
  design approach
• Flowdown to AO component choices and design
  parameters
• AO subsystems (NFIRAOS and LGSF)
• Key AO components
• Error budget and performance analysis
• Development plan and Construction schedule
• Conclusion

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Astronomical AdaptiveOptics State-of-the Art
Gemini

• Natural guide star (NGS) AO
• High contrast, coronagraphic imaging of
  extra-solar planets at Keck and Gemini (Kalas et
  al, Science 28 November 2008)
• Laser guide star (LGS) AO
• Diffraction-limited imaging and astrometry of the
  galactic center at Keck (Ghez et al, AAS Bulletin
  36, p.1384 )
• Multi-conjugate AO (MCAO)
• High resolution imaging of globular clusters at
  VLT (Petr-Gotzens et al 2008 J. Phys. Conf. Ser.
  131 012026)
• Highly useful and well understood levels of
  performance
• Well-subscribed systems with high scientific
  productivity

Keck
VLT
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Sample Results
Imaging of Extra-Solar Planets (Gemini)
Galactic Center Astrometry (Keck)
MCAO Strehl Uniformity over 2 FoV (VLT)
LGS AO Science Papers vs. Year (All)
M Liu, 2008
Classical AO
MCAO
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AO Requirements Flowdownfor TMT
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AO Development Philosophy for TMT

• Address science-based requirements via a low-risk
  approach to maximize system productivity
  immediately following TMT first light
• Build on proven system architectures and
  component technologies
• Strive to match performance (Strehls) of best
  existing 8-10M class system
• D4 scaling will yield factors of 80-200 gains
  in sensitivity
• Utilize and coordinate all available expertise
  within and beyond TMT
• TMT AO group develops AO requirements, leads
  performance analysis, and coordinates/manages all
  subsystem and component development
• TMT partners lead subsystem development
• Component development opportunities open to all
  qualified suppliers
• Pursue early risk reduction via high fidelity
  analysis/simulation, component prototyping, and
  breadboard demonstrations
• Pursue advanced technologies and system
  architectures for further capabilities with 2nd
  generation AO systems

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Science-Based Requirements for Adaptive Optics at
TMT

• Requirements derived to enable diffraction-limited
  imaging and spectroscopy at near IR wavelengths
  with IRIS

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Implied AO Architectural Decisions
Very High Order AO
Diffraction-Limited Image Quality
Multiple Guidestars MCAO
10-30 Corrected FoV
Laser Guide Stars
Near IR Tip/Tilt NGS
High Sky Coverage
MCAO to Sharpen NGS
Large Guide Field
Multiple NGS to Correct Anisoplanatism
High Throughput
Minimal Surface Count AR coatings
Low Emission
Cooled Optical Path
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Derived AO Component Technologies and Design
Choices (I)
Large AO system due to actuator pitch
Very High-order wavefront correction
Piezostack DMs
Cooled system
Large actuator stroke, low hysteresis at low T
Minimum surface count
Tip/tilt stage
DSP/FPGA processors
High-order tomo- graphy and MCAO
Efficient Algorithms
Low-order, near IR NGS WFS
H2RG detectors
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Derived AO Component Technologies and Design
Choices (II)
Polar coordi- nate CCD
Solid state, CW, Sum Freq. Gen. lasers
Noise-optimal LGS WFS pixel processing
Guidestar elongation
Bright lasers for high-order LGS AO
Fixed gravity laser environment in TMT
azimuth structure
Laser launch behind M2
Free-space beam xport
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AO Architecture Realization

• Narrow Field IR AO System (NFIRAOS)
• Mounted on Nasmyth Platform
• Ports for 3 instruments
• Instruments responsible for field derotation and
  low-order NGS wavefront sensing
• Laser Guide Star Facility (LGSF)
• Lasers located within TMT azimuth structure
• Laser launch telescope mounted behind M2

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AO Subsystems
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NFIRAOS on TMT
Future Client Instrument
Cooled (-30 C) Optics Enclosure
TMT M1
Light from TMT
LGS WFS Optics Electronics Enclosure
IRMS
IRIS
Nasmyth Platform
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NFIRAOS Science Optical Path

• Classical AO optical design form
• 1-1 OAP optical relay
• DMs located in collimated path

Light From TMT
WFS Beam-splitter
DM0/TTS
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NFIRAOS Functional Block Diagram

• Additional subsystems implemented for
• LGS wavefront sensing
• NGS wavefront sensing (for classical NGS AO and
  on-sky LGS WFS calibration)
• AO calibration sources
• Science calibration sources

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NFIRAOS Opto-mechanical Layout
2 Truth NGS WFSs 1 60x60 NGS WFS
IR Acquisition camera
Input from telescope
OAP1
OAP2
76x76 DM at h11.2km
63x63 DM at h0km On tip/tilt platform (0.3m
clear apeture)
Output to science instruments and IR T/T/F WFSs
6 60x60 LGS WFSs
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NFIRAOS Operation at -30 C

• Performance and reliability considerations
• Optical alignment
• Mechanism reliability
• Component performance (DMs, tip/tilt stage,
  coatings)
• Thermal plumes
• Air leakage, humidity and frost
• Design and component validation
• Subscale DMs and prototype tip/tilt stage already
  tested cold
• Now building sub-scale prototype cold chamber
  with evacuated window, super-insulation and
  buried cold plates in walls
• Components (e.g. motorized stages) will be
  qualified in cold
• CFD of local seeing effects

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Conservative LGSF Design Approach

• Design consists of 3 systems
• Laser System within telescope azimuth structure
• BTO/LLT System, to transport beams to the
  telescope top end and project them from the LLT.
• Laser Safety System for protection of people,
  observatory hardware, aircraft and neighboring
  telescopes.
• Design based upon existing LGSF systems (i.e.
  Gemini North and Gemini South).

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LGSF Optical Schematic
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LGSF Top End Conceptual Design

• Diagnostic optical bench monitors beam alignment,
  power, and quality
• Asterism generator maps 3x3 pattern of beams into
  desired asterism
• Rotating K mirror maintains fixed asterism at the
  LGS wavefront sensor focal plane
• Laser launch telescope projects beams onto sky
• 0.5m aperture
• Off axis reflective design
• Pivot mount for telescope top end flexure
  compensation
• Convex secondary could be upgraded to DM for Up
  link AO
• 11 mirrors per beam (4 actuated)

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AO Components
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Component Requirements Summary and Technology
Readiness Levels
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Guide Star Lasers Requirements vs. Current
Performance
Flowed down from higher-level requirements for
LGS signal level, LGSF reliability
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Guide Star Lasers Risks and Risk Mitigation
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Wavefront Correctors Requirements vs. Current
Performance
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Wavefront Correctors Prototyping Results
Prototype Tip/Tilt Stage
Simulated DM Wiring included in bandwidth
demonstration
Subscale DM with 9x9 actuators and 5 mm spacing
20 Hz Reqt
-3dB TTS bandwidth of 107 Hz at -35C
Low hysteresis of only 5-6 from -40 to 20 C
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Polar Coordinate CCD Array Concept for
Wavefront Sensing with Elongated Laser Guidestars
Fewer illuminated pixels reduces pixel read rates
and readout noise
sodium layer ?H 10km
D 30m ? Elongation ? 3-4
H100km
LLT
TMT
AODP Design
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Laser Guide Star (LGS) WFS Detector Requirements
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Polar Coordinate CCD Development Status

• Design and prototyping has been supported under
  an Adaptive Optics Development Program (AODP)
  grant, in two phases
• Phase I designed, fabricated, and tested the
  160x160 CCID-56 detector array
• Noise performance of planar JFET amplifier
  demonstrated
• To date, Phase II has developed the design for a
  polar coordinate CCD array prototype
• 724 active subapertures in a 30x30 quadrant.
• 6 x 6 pixels in inner subapertures, growing to 6
  x 15 in the outermost
• 51198 total imager pixels, 32 video outputs.
• 3.5 MHz clock, 250 ns row transfer time, 2018 Hz
  effective frame rate
• Now waiting to fabricate and test the prototype
  design

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Real Time Controller (RTC) Requirements vs.
Current Performance

• Real-time atmospheric compensation functions for
  the RTC
• Pixel processing for LGS and NGS wavefront
  sensors at 800 Hz
• Solve a 35k x 7k wavefront control problem at
  800Hz
• End-to-end latency of 1000?s, with strong goal of
  400 ms
• Memory and processing requirements would be at
  least 2 orders of magnitude greater than an 8m
  class MCAO system (Gemini-South) using
  conventional approaches
• Computationally efficient algorithms and
  innovative hardware implementations provide
  effective solution
• Update algorithms in real time as conditions
  change
• Store data needed for PSF reconstruction in
  post-processing
• Essential tool for data reduction of science
  observations
• Two Conceptual Design Studies by DRAO and tOSC
  have demonstrated the feasibility of the NFIRAOS
  RTC using todays technology, within our
  schedule, and at an affordable cost

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Error Budgeting and AO Performance Analysis
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Top-Level Wavefront Error Budget Summary (RMS nm)
ORD Reqt 187

• Performance for 50 sky coverage at the Galactic
  pole
• On-axis performance
• 0 degree zenith angle
• Strehls of 0.41, 0.60, and 0.75 in J, H, and K
• Computed for nominal atmospheric turbulence,
  sodium layer, and telescope windshake parameters
• OIWFS errors include tip/tilt, tilt
  aniso-planatism, and LGS focus uncertainty

Contingency 30
LGS-Corrected Errors 178
OIWFS-Corrected Errors 48
1st-Order Turbulence Compensation 127
AO components 2nd order effects 97
Opto- mechanical 79
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AO Performance Estimates Are Based upon Detailed
Simulation and Modeling

• Principal LGS-controlled errors evaluated via
  detailed time-domain simulation
• Principal OIWFS-controlled errors (tip/tilt and
  tilt anisoplanatism) evaluated via Monte Carlo
  simulation of randomly generated guide star
  fields
• Term-by-term analysis of remaining component
  errors and higher-order effects, e.g
• Allocated non-common-path wavefront aberrations
• Time delays in optimizing control algorithms for
  changing atmospheric conditions
• Atmospheric dispersion, DM hysteresis, RTC
  numerical precision, etc., etc.,,,

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Example AO Simulation Data and Intermediate
Results
Input Disturbance
Atmospheric phase screen
TMT aperture function
M1 phase map
M1M2M3 on-axis phase map
Sodium layer profile
AO System Responses
LGS sub-aperture image
Polar coordinate CCD pixel intensities
Residual error phase map
DM phase maps
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NFIRAOS Performance Variations with Respect to
Site, Seeing, and Zenith Angle

• Excellent and very similar AO performance at both
  sites
• Further results available as function of seeing,
  sodium column density
• Results will be used to develop estimates of
  overall AO observing efficiency over a standard
  year

Armazones
Mauna Kea
75 seeing 50 seeing 25 seeing


187 nm RMS requirement at zenith with 50
seeing
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Sky Coverage Simulation Results Show that 50 Sky
Coverage Requirement Is Met
Cumulative Probability of Tip/Tilt Jitter
Tip/Tilt NGS
Tip/Tilt/Focus NGS
50 tip/tilt jitter of 28 nm RMS for these system
parameters and guide star field
Tip/Tilt NGS
Sample Asterism near 50 Sky Coverage (Besançon
Model, Galactic Pole)
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Anchoring Simulation Models and Input Parameters

• Completed and planned validation activities for
  three key issues include
• Wavefront sensing with highly elongated and
  varying laser guide stars
• Polar coordinate CCD prototyping
• Lab tests of noise optimal, adaptive LGS WFS
  processing algorithms
• High resolution LIDAR measurements of the sodium
  layer
• Low order (tip/tilt/focus) wavefront sensing with
  faint NGS
• Lab tests of baseline H2RG OIWFS detector array
• Prototype Tip/Tilt Stage fabrication and testing
• AO simulations use actual reconstruction and
  pixel processing algorithms
• Wavefront tomography and MCAO
• AO simulations use our actual reconstruction
  algorithms
• RTC Conceptual Design Studies of hardware to
  implement algorithms
• Ongoing offer of modeling/algorithm support for
  GEMS at Gemini South
• Results to date confirm designs and performance
  estimates

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AO Development Plan
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Approach to Construction Phase

• Procurement of key AO components to be managed by
  TMT Project Office
• Guidestar lasers Competitively awarded risk
  reduction design and prototyping contract(s),
  followed by construction contract
• Wavefront correctors Construction contract with
  CILAS
• LGS and NGS WFS cameras/electronics
  Construction contract with WMKO and MIT/LL (Polar
  coordinate CCD developers)
• RTC Competitively awarded construction
  contract, with Project Office involvement in
  related software development
• PSF reconstruction
• Reconstructor parameter generation
• AO subsystems to be developed by TMT partners
• NFIRAOS Construction contract with HIA
• LGSF Separate Preliminary Design and
  Construction contracts

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Summary AO Schedule

• The Information Herein is Subject to the
  Restrictions Contained on the Cover Page of this
  Document

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Conclusion

• Our development program demonstrates that the TMT
  first-light AO architecture will meet the
  requirements for AO-assisted science observations
• Essential for achieving overall goals of the
  observatory
• Our development philosophy focuses on maximizing
  scientific utility at or shortly following
  telescope first light
• Our approach builds upon existing concepts that
  have been demonstrated to work
• Component development, subsystem designs, and
  risk mitigation activities are progressing well
• Construction phase plans and schedules are
  formulated
• We will pursue advanced technologies and system
  concepts for further capabilities with 2nd
  generation systems

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Acknowledgements

• The authors gratefully acknowledge the support of
  the TMT partner institutions. They are the
  Association of Canadian Universities for Research
  in Astronomy (ACURA), the California Institute of
  Technology and the University of California. This
  work was supported as well by the Gordon and
  Betty Moore Foundation, the Canada Foundation for
  Innovation, the Ontario Ministry of Research and
  Innovation, the National Research Council of
  Canada, the Natural Sciences and Engineering
  Research Council of Canada, the British Columbia
  Knowledge Development Fund, the Association of
  Universities for Research in Astronomy (AURA) and
  the U.S. National Science Foundation.

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Backup Slides
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LGSF Beam Transfer Optics Performance Validation

• Highly important for LGS AO performance and
  observing efficiency
• Specifications are achievable based on Gemini
  experience, given high quality laser optics and
  an enclosed optical path
• Further FEA, beam quality, and control system
  modeling will be performed during the Preliminary
  Design phase
• End-to-end, full power testing will be performed
  at the LGSF supplier during system integration
  and test
• Finally, laser power requirements have been
  defined for year-round AO operation
• This provides approximately 50 margin during
  seasons of median (or higher) sodium density

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Sample Simulation Result (IRIS PSF Uniformity
over a 15 Arc Sec FoV)
Time-Averaged PSFs at Center, Edge, and Corner of
IRIS Imager FoV
J-Band
K-Band
LGS-controlled error terms only
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Options for Follow-on AO Systems and Upgrades

• NFIRAOS upgrade to 130 nm RMS wavefront error
• Greatest technical challenges are (i) 120x120
  wavefront correctors, (ii) doubling laser power,
  and (iii) upgrading from CW to pulsed lasers
• Additional AO systems for first decade
  instrumentation
• MIRES and NIRES-b Mid IR AO (Order 30x30 DM, 3
  LGS)
• IRMOS MOAO (Order 64x64 MEMS, 8 LGS)
• WFOS GLAO (Adaptive secondary mirror to control
  500 wavefront modes, 4-5 LGS)
• PFI ExAO (Order 128x128 MEMS, amplitudephase
  correction for M1 segments, advanced IR WFS,
  post-coronagraph calibration WFS)
• Adaptive secondary mirror is a useful option for
  all systems
• Control of 500 wavefront modes
• Only corrector needed for GLAO and MIRAO
• Large-stroke woofer for MOAO, ExAO, and
  NFIRAOS
• E-ELT technology development projects will reduce
  cost and risk
• Funding is allocated in Early Operations budget
  for timely AO upgrades