TMT Early Light Adaptive Optics
Brent Ellerbroek
TMT Instrumentation @ SPIE 2010
San Diego, June 26, 2010.
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Presentation Outline
Adaptive optics (AO) requirements summary
Derived AO architecture
Principal AO subsystems
– Narrow Field IR AO System (NFIRAOS)
– Laser Guide Star Facility (LGSF)
Key components
Estimated system performance
Schedule and procurement plans
Summary
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AO Requirements at Early Light (1/2)
High throughput in J, H, K, and I bands, with low emission
– Minimize optical surface count
– Cooled (-30C) optical system
Diffraction-limited near IR image quality over a “narrow”
field-of-view of 10-30 arc seconds
– Order 60x60 wavefront compensation
– Multi-conjugate AO (MCAO) with 6 guide stars and 2 deformable
mirrors (DMs)
50% sky coverage at the galactic pole
– Laser guide star (LGS) wavefront sensing
– Low order (tip/tilt/focus) natural guide star (NGS) wavefront
sensing in the near IR with a 2 arc min patrol field
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AO Requirements at Early Light (2/2)
Excellent photometric and astrometric accuracy
– Well characterized and stable point spread function
 Telemetry for PSF reconstruction
 Three low-order NGS WFS for tilt anisoplanatism compensation
High observing efficiency
– Automated, reliable system
– Low downtime and nightime calibration
Available at first light with low risk and acceptable cost
– Utilizing existing/near-term AO technologies
– Design AO into TMT from the start
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Derived AO System Architecture
Narrow Field IR AO System
(NFIRAOS)
– Mounted on Nasmyth Platform
– Interfaces for 3 instruments
– 4-OAP, distortion free design
Laser Guide Star Facility
(LGSF)
– Laser launch telescope
mounted behind M2
– Lasers mounted on TMT
elevation journal
– All-sky and bore-sighted
cameras for aircraft safety (not
shown)
AO Executive Software
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“Split Tomography” Wavefront Control
Architecture
LGSF
T/T
Laser
Pointing
NFIRAOS
6 LGS
WFS
NFIRAOS RTC
Gradient
Estimation
LGS Wavefront Recon.
Reference
processing
Science
Instrument
3 NGS
OIWFS
Focus
Gradient
Estimation
NGS Modal
Recon.
Higher-order
wavefront
modes
DM and TT
Control
S
NFIRAOS
2 DMs
TTP
Tip/Tilt and Plate
Scale (Tilt Anisoplanatism) Modes
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AO Component Technology Choices
Laser Guide Star Facility (LGSF)
– Continuous wave (CW) sum frequency or Raman fiber laser
– Conventional optics (not fiber-based) beam transport
Narrow Field IR AO System (NFIRAOS)
–
–
–
–
Piezostack actuator deformable mirrors and tip/tilt stage
“Polar coordinate” CCD array for the LGS WFS
HgCdTe CMOS array for the IR low order NGS WFS
Computationally efficient real-time control algorithms
implemented on DSP and FPGA hardware
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NFIRAOS Dimensions (10.35x7.93x4.41m)
and Plan View of Nasmyth Platform
•Instruments
•NFIRAOS
Electronics
•M1
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•Science
Calibrator
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Cooled Enclosure with Calibration Unit, 3
Instruments, and Support Structure
•Thermal enclosure
•- 30° C
•NSCU
•NFIRAOS Science
Calibration Unit
•Telescope Beam
•Light Gray Trusses
supplied by Instruments
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•Instrument
Rotator
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NFIRAOS Science Optical Path
4-OAP design provides
excellent image quality and
nulls distortion
•Output
Focus
•OAP 4
•Light From TMT
•OAP 3
•Telescope Focus
•DM11
•Instrument
Selection
Fold Mirror
•Output
Focus
•Entrance
Windows
•Off-axis
Paraboloid
(OAP) 1
•Beam
splitter
•DM0 on
Tip/Tilt
Stage
Dimensions driven by f/15
optical design and 0.30m pupil
size at deformable mirrorTMT.AOS.PRE.10.054.REL01
•OAP 2
All science optics lie in a
horizontal plane
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New Top-Level LGSF Architecture
•Laser launch location (0.4m
launch telescope, asterism
generator, and diagnostics bench)
•Beam transfer
optics path
•Laser location (behind
elevation journal)
•Laser Location on Inside face of
elevation journal
• Feasible with new, smaller, gravityinvariant, low-maintenance lasers
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Key AO Components
Component
Key Requirements
Deformable mirrors
63x63 and 76x76 actuators at 5 mm spacing
10 mm stroke and 5% hysteresis at -30C
Tip/tilt stage
500 mrad stroke with 0.05 mrad noise
20 Hz bandwidth
NGS WFS detector
240x240 pixels
~0.8 quantum efficiency,~1 electron at 10-800 Hz
LGS WFS detectors
60x60 subapertures with 6x6 to 6x15 pixels each
~0.9 quantum efficiency, 3 electrons at 800 Hz
Low-order IR NGS
WFS detectors
1024x1024 pixels (subarray readout on ~8x8 windows)
Real time controller
Solve 35k x 7k reconstruction problem at 800 Hz
Sodium guidestar lasers
25W, near diffraction-limited beam quality
~0.6 quantum efficiency, 3 electrons at 10-200 Hz
Coupling efficiency of 130 photons-m2/s/W/atom
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Performance Estimate Summary
Error term
Delivered wavefront error
On-axis RMS WFE, nm
187
LGS mode error
154
First-order turbulence compensation
122
Implementation errors
95
Opto-mechanical
74
AO component and higher-order effects
59
NGS mode error
62
Contingency
86
Median Seeing with 50% sky coverage at the Galactic Pole
187 nm RMS  Strehl ratios of [0.41 0.60 0.75] in [J H K] bands
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Sky Coverage vs. Galactic Latitude
and Zenith Angle
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AO Schedule Overview
Unit 2
Unit 1
RTC
DM12
DM0+TTS
DMs/TTS
11/19/14
WFS Cams
3/19/15
2/12/16
5/31/16
1/9/15
FAT
Complete
7/18/17
NFIRAOS
FDR
12/9/13
Integration
Review
3/24/15
Ready for onSky Tests
3/9/18 8/24/18
TMT SITE
Unit 1
Lasers
12/23/13
1/26/16
4/27/18
Units 2-7
1st Light
Complete
12/22/18
LGSF
FDR
12/9/13
FAT Complete
5/22/17
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Procurement Plans
AO Systems
NFIRAOS
NRC Canada
LGSF
TBD (partner or vendor)
AO Executive Software
TBD (partner, vendor, or PO)
Subsystems and Components
Wavefront Correctors
CILAS
Visible WFS CCDs
MIT Lincoln Laboratory
Visible WFS cameras and readout electronics
TBD (partner or vendor)
IR WFS detectors
Teledyne (TBC)
IR WFS cameras and readout electronics
TBD (partner or vendor)
Real Time Controller
TBD (partner or vendor)
Guidestar laser systems
TBD (partner or vendor)
Contracts begin at or near the beginning of the TMT construction phase in October, 2011
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Summary
TMT has been designed from the start to exploit AO
– Facility AO is a major science requirement for the observatory
The overall AO architecture and subsystem requirements
have been derived from the AO science requirements
– Builds on demonstrated concepts and technologies, with low risk
and acceptable cost
AO subsystem designs have been developed
Analysis/simulation confirm the designs meet requirements
Component prototyping and lab/field tests are underway
Construction phase schedule leads to AO first light in 2018
– Most subsystem and component procurement contracts schedule
to begin in late 2011
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