Adaptive Optics for the Thirty Meter Telescope
Brent Ellerbroek
Thirty Meter Telescope Observatory Corporation
AO4ELT3
Florence, Italy
May 27, 2013
TMT.AOS.PRE.13.081.DRF01
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Contributors
Brent Ellerbroeka, Sean Adkinsb, David Andersenc, Jenny Atwoodc, Arnaud
Bastardd, Yong Boe, Marc-André Boucherc, Corinne Boyera, Dmitri Budkerf,
Peter W. G. Byrnesc, Kris Caputac, Jeffrey Cavacog, Shanqiu Chenh, Carlos
Correiac, Raphael Coustyd, Joeleff Fitzsimmonsc ,Luc Gillesa, James
Gregoryi, Glen Herriotc, Paul Hicksonj, Alexis Hillc, Zuo Junweie, Zoran
Ljusicc, N. Marchetd, Angel Otarolaa, Dan O’Marai, Leo Myerk, Benoit
Neichell, John Pazderc, Hubert Pagesd, Spano Paoloc, Robert Priorc,
Vladimir Reshetovc, Simon Rochesterf, Jean-Christophe Sinquing, Matthias
Schoeckc, Malcolm Smithc, Kei Szetoc, Jinlong Tangh, Jean-Pierre Veranc,
Lianqi Wanga, Kai Weih, Ivan Weversc, and Sylvana Yeldak
aTMT
Observatory Corporation, bW. M. Keck Observatory, cNRC Herzberg, dCILAS,
eTechnical Institute of Physics and Chemistry, fRochester Scientific, gAOA Xinetics,
hInstitute of Optics and Electronics, iMIT Lincoln Laboratory, jUniversity of British
Columbia, kUniversity of California at Los Angeles, lGemini Observatory
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Presentation Outline
TMT Project highlights
First light AO requirements review
Derived architecture and technology choices
Subsystem status report
– NFIRAOS; LGSF
Component development
– Deformable mirrors; wavefront sensing detectors; guidestar
lasers; real time controller
Modeling and algorithm development
Related papers at AO4ELT3
Acknowledgements
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TMT Project Highlights
Site permit approved by the Hawaiian BLNR
– Geotechnical studies and ground preparation to begin this year
– Construction start date slated for April 2014
Construction Phase funding proposals under review in
Canada, India, and Japan, and China
Yale University has committed to joining the Project
NSF Cooperative Agreement signed
Instrument design work progressing well
– IRIS Preliminary Design Phase initiated May 2013
– IRMS delta Design Review (from MOSFIRE) held April 2013
– MOBIE Conceptual Design Review in September 2013
First light scheduled for 2022
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First Light AO Requirements Review
3 science ports at f/15 with 2 arc min unvignetted field
High throughput (85% in J, H, K, and I bands)
Low thermal emission (15% of sky + telescope)
Diffraction-limited IR image quality on a moderate FoV
– [187, 191, 208] nm wavefront error over a [0,17,30] arc sec field
High sky coverage (50% at galactic pole)
High photometric accuracy
– 2% over 30 arc sec at l=1 mm for a 10 minute observation
High astrometric accuracy
– 50 mas over 30 arc sec in H band for a 100 second observation
High observing efficiency
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How First Light Performance Requirements
Drive AO Architecture Decisions
High throughput
Minimize surface count
Low thermal emission
-30C operating temperature
Diffraction limited performance in
J, H, K bands
Order 60x60 wavefront sensing and
correction
30”corrected science field
Atmospheric tomography + MCAO
High Sky coverage
Laser guide star (LGS) wavefront sensing
NGS tip/tilt/focus sensing in the near IR
MCAO to “sharpen” NGS images
High precision astrometry and
photometry on 30” fields
Distortion-free optical design form
MCAO for uniform, stable PSF
AO telemetry for PSF reconstruction
High-order LGS MCAO with
Available at TMT first light with
Utilize existing and near term components
low risk and
acceptable
cost
and
system concepts
possible
NGS
tip/tilt/focus
sensing
in thewhenever
Near IR
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First Light AO System Architecture
and Technology Choices
Laser
Launch
Telescope
Beam
Transfer
Optics
Laser
Systems
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Laser Guide Star
Facility (LGSF)
– Nd:YAG or Raman
fiber laser technology
– Lasers mounted on
telescope elevation
journal
– Conventional beam
transport (mirrors)
– Center-launch laser
projection
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First Light AO System Architecture
and Technology Choices
Narrow Field IR AO
System (NFIRAOS)
NFIRAOS
facility AO
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– Piezostack
deformable mirrors
and tip/tilt stage
– “Polar coordinate”
CCD array for the
LGS WFS
– HgCdTe CMOS
arrays for low order,
infra-red NGS
WFSs (in client
instruments)
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UBC, Vancouver
(Sodium LIDAR)
Project Participants
TOPTICA, Munich
(Laser Systems)
TIPC, Beijing
(Laser Systems)
HIA, Victoria
(NFIRAOS)
DRAO, Penticton
(RTC)
MIT/LL, Lexington
(WFS CCDs)
AOA/Xinetics, Devens
(Wavefront Correctors)
CILAS, Orleans
(Wavefront Correctors)
IOE, Chengdu (Laser
Guide Star Facility)
Keck Observatory, Waimea
(WFS readout electronics)
Also Rochester Scientific (Berkeley, Sodium Atomic Physics)
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TMT, Pasadena
(Management and SE)
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NFIRAOS Status Update
“Pre-Final” Design Phase is now underway Opto-mechanical layout
Prototyping/test activities include:
– DM drive electronics development
– DM breadboard testing
– WFS lenslet testing
– Instrument rotator interface
NFIRAOS on Nasmyth
– Component testing at -30C
– MCAO lab bench development
Design work will include:
– NGS WFS optics bench
– LGS WFS zoom optics
– NFIRAOS instrument support tower
– FEA for vibration/thermal/seismic effects
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NFIRAOS Prototypes and Testbeds
96-channel DM drive
electronics board
MCAO test bench
Phase
Screen
Location
DM’s
LGS
WFS
Path
Source
simulators
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“Science”
Path
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Recent LGSF Design Activities
Design updated for new MELCO telescope structure:
– (Yet another) optical path trade study
– 2-axis launch telescope flexure compensation system
– Laser system and laser bench layout on telescope elevation
journal
– Details of beam tube diameter, relay lens design, and top end
layout
Beam tube turbulence modeling underway
LGSF Preliminary Design phase scheduled to begin
November 2013
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LGSF Optical Path Trade Study
•Baseline OP
•New OP
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Work in Progress on Beam Duct
Turbulence Modeling
CAD model of Fold mirror array
and relay lenses
Difference from mean
interior air temperature
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AO Component Requirement Summary
Deformable
mirrors
63x63 and 76x76 actuators at 5 mm spacing
Tip/tilt stage
500 mrad stroke with 0.05 mrad noise
10 mm stroke and 5-10 % hysteresis at -30C
80 Hz bandwidth
NGS WFS
detector
240x240 pixels, 4x4 pixels per subaperture
LGS WFS
detectors
60x60 subapertures with 6x6 to 6x15 pixels each
Low-order IR
NGS WFS
detectors
1024x1024 pixels (subarray readout on ~8x8 windows)
Sodium guidestar
lasers
25W (20W with backpumping), M2 < 1.17
Real time
controller
Solve 35k x 7k reconstruction problem at 800 Hz
~0.8 quantum efficiency,~1 electron at 10-800 Hz
~0.9 quantum efficiency, 3 electrons at 800 Hz
~0.6 quantum efficiency, 3 electrons at 10-200 Hz
Coupling efficiency of 130 photons-m2/s/W/atom
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DM Development
Initial testing of the CILAS 6x60 actuator breadboard has
been completed in early 2013
– Good actuator-level performance at ambient and low
temperature (-30C)
– Not all requirements met at the full breadboard level
– New round of development underway
New study initiated at AOA Xinetics
– Evaluate actuator performance at -30C
– Develop DM conceptual designs meeting TMT performance and
interface requirements
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One-Quadrant Prototype
LGS WFS CCDs
Front- and back-illuminated
devices now tested
– Meet specs for QE and CTE
– Read noise of 2.7 to 3.7 eat 3.5 MHz (3 erequirement)
– Dark current sufficiently low
for 800 Hz frame rate
BI devices have good yield
– 3 of 8 probed CCDs show
very good performance
– 99% of outputs functional,
99% low noise
Black: QE spec and allowed nonuniformity
Red: Measuremented QE
(Courtesy Keck Observatory)
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NGS WFS CCDs for NFIRAOS
MIT/LL CCID-74
Engineering Grade Device in Test Station
– 256x256 pixels
– 64 planar JFET amplifiers
Testing of back-illuminated
engineering devices now in
progress at Keck
– High QE as above (for Polar CCD) Measured read noise at -15C with 32 Amplifiers
– Dark current of 26
electrons/pixel/second
– Read noise approaches 1 electron
at 100 FPS
– Candidate science grade CCDs
will be packaged for testing and
potential use as the deliverable
NGS WFS CCD for NFIRAOS
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Guidestar Laser Systems
TMT continues to follow two laser development efforts:
Toptica/MPB frequency-doubled Raman fiber laser meets all
TMT requirements for output power, line width, beam quality,
volume, and power dissipation
– some TMT interfaces will require development
Work on TIPC prototype SFG Nd:YAG laser is continuing:
– Currently 18W@800Hz power for 100μs pulse
– M2 ~ 1.5
– Line width of 0.6 GHz, with 0.2 GHz wavelength stability
On-sky tests in early 2013 confirm high sodium coupling
efficiency for a large spot size without repumping
Further on-sky tests (with repumping) planned later this year
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TIPC Nd:YAG SFG Guidestar
Laser System
Laser System and Optical Schematic
Lijiang Observatory, February 2013
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Laser Coupling Efficiency (Sce) vs. Irradiance
Results from Lijiang, China, February-March 2013
Results were obtained
for:
–
–
–
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Various Power Levels
800 Hz or 600 Hz Pulse
Repetition Rate
Pulse lengths 95 to 100
micro-secs
Results, as expected,
show the effect of
optical saturation
TMT Specification: 120
Photos/W/s/(atoms/m2)
Sce at higher Irradiance
levels can be improved
with D2b repumping
and may reach the
TMT Specification
More tests with
repumping and smaller
spot sizes planned
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Real Time Controller (RTC)
Architectures
RTC architecture study now
underway at NRC Herzberg
and TMT to update RTC
conceptual designs from
2008-09
Benchmarking and design of
a GPU-based architecture is
currently most advanced
– 2 GPUs per WFS implement
gradient computation and
matrix-vector-multiply (MVM)
wavefront reconstruction
– Matrix updated at 0.1 Hz
Benchmark results: 0.95ms
mean latency, 1.05 ms peak
Timing includes gradient
computation, MVM computation,
data transfer over 10 Gig ethernet
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Recent Work in AO Modeling and
Control Algorithm Development
AO Error budget maintenance and sky coverage analysis
– Incorporates improved modes for optical surface errors and sodium range
tracking
Performance trade studies for OIWFS passband and detector choices
High precision astrometry
High contrast imaging
PSF reconstruction lab tests with GeMS
Analysis of LGS Fratricide amplitude for GeMS
On-instrument WFS guidestar acquisition
Distributed (computationally efficient) Kalman Filter tomography
LGS SLODAR for Cn2 _and wind velocity_ profile estimation
MCAO Lab Bench development at NRC-Herzberg also continuing
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Term
WFE, nm RMS
Delivered Performance
191
Higher-order error (LGS modes)
First-order turbulence compensation
Generalized fitting error
AO
Performance
Estimate
(Zenith,
median seeing,
50% sky
coverage)
163
132
106
Noise-free estimation error
59
Servo lag
17
WFS noise and nonlinearity
52
Opto-mechanical implementation errors
71
TMT pupil misregistration
12
Telescope/enclosure wavefront
37
NFIRAOS wavefront
53
Science instrument wavefront
30
AO components and higher-order effects
66
Deformable mirrors
49
LGS WFS and sodium layer
39
Control algorithm implementation
21
Tip/tilt and plate scale (NGS controlled modes)
58
Telescope windshake
17
Telescope vibration and tracking error
20
Turbulence
and measurement noise
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Contingency
52
80
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AO Sky Coverage vs. OIWFS Detector
Option and Spectral Passband
Median seeing
Galactic pole guidestar
densities
Zenith angles from 0 to
50 degrees
Widening the spectral
passband from JH to
JHKs improves sky
coverage by ~10%
Switching from the
H2RG detector to
SELEX APDs would
yield another ~5%
improvement
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Median AO Performance vs. Galactic
Latitude and Longitude (at Transit)
• Median seeing
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Median AO Performance vs. Galactic
Latitude and Longitude (at Transit)
• Good (25%) seeing
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High Precision Astrometry for
Observations of the Galactic Center
Many sources of error have
been investigated:
– Photon, detector, thermal noise
– Differential tip/tilt jitter
– Distortions:
Probe arm positioning error
Geometric (static)
– PSF estimation
– Confusion
Single-epoch error budget:
– Bright stars (K < 15): distortion
dominates (~8 μas)
– Faint stars (K > 15): confusion
dominates (> 8 μas)
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High Contrast Imaging
IRIS imager optics now
included in modeling
NFIRAOS+IRIS equivalent to
~1h of Gemini/Keck in 30 s
Approaches GPI
performance in 1-2 h,
assuming 50x of SSDI
speckle suppression (hard)
– Better astrometry and higher
SNR for high res. spectroscopy
– Fainter and more distant
targets?
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Progress in PSF Reconstruction
• GEMs (Canopus) references sources and ground-conjugate DM used to
generate long-exposure PSFs and simultaneous WFS telemetry
• PSFs with Strehls of ~40% estimated to within 1-2% relative error
• Next step: Wide-field PSF reconstruction for MCAO using both DMs
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Related Papers at AO4ELT3
Schoeck
1010 Monday
High precision astrometry
Hickson
0830 Tuesday
Mesospheric sodium layer
Marois
1120 Tuesday
High contrast Imaging
Ellerbroek
1140 Tuesday
High precision astrometry
Gilles
1200 Tuesday
LGS Fourier Tomography
Veran
1810 Tuesday
RTC architecture study
Veran
1130 Wednesday
Improved tilt sensing
Yelda
1700 Wednesday
Galactic center astrometry
Thompson
1720 Thursday
Vibration requirements
Simard
0830 Friday
TMT Science
Lu
0950 Friday
Astrometry with MCAO
Wang
1120 Friday
GPU-based RTC
Wang
Poster
NFIRAOS sky coverage
Herriot
Poster
T/T/F NGS Acquisition
Herriot
Poster
RTC timing jitter specifications
Otarola
Poster
GeMS fratricide analysis
Gilles
Poster
PSF reconstruction
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Acknowledgements
The TMT Project gratefully acknowledges the support of the TMT partner institutions.
They are
–
–
–
–
–
–
the Association of Canadian Universities for Research in Astronomy (ACURA),
the California Institute of Technology
the University of California
the National Astronomical Observatory of Japan
the National Astronomical Observatories and their consortium partners
And the Department of Science and Technology of India and their supported institutes.
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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