tmt.aos.pre.10.054.rel01 1 brent ellerbroek tmt instrumentation @ spie 2010 san diego, june 26,...
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TMT.AOS.PRE.10.054.REL011
Brent Ellerbroek
TMT Instrumentation @ SPIE 2010San Diego, June 26, 2010.
TMT Early Light Adaptive Optics
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
TMT.AOS.PRE.10.054.REL012
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
TMT.AOS.PRE.10.052.REL01 3
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 Software5
TMT.AOS.PRE.10.054.REL01
“Split Tomography” Wavefront Control Architecture
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3 NGS OIWFS
6 LGS WFS
Gradient Estimation
Gradient Estimation
LGS Wave-front Recon.
NGS Modal Recon.
Reference processing
DM and TT Control
TTP
2 DMs
Laser Pointing
Focus
T/T
TMT.AOS.PRE.10.052.REL01
Tip/Tilt and Plate Scale (Tilt Aniso-planatism) Modes
Higher-order wavefront
modes
NFIRAOS RTC
NFIRAOS
LGSF
Science Instrument
NFIRAOS
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
•NFIRAOS Electronics
•Instruments
•M1
•Science Calibrator
TMT.AOS.PRE.10.054.REL019
Cooled Enclosure with Calibration Unit, 3 Instruments, and Support Structure
•NSCU
•NFIRAOS Science Calibration Unit
•Thermal enclosure
•- 30° C
•Telescope Beam
•Light Gray Trusses supplied by Instruments
•Instrument Rotator
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NFIRAOS Science Optical Path
•Light From TMT •Entrance Windows
•Telescope Focus
•Off-axis Paraboloid (OAP) 1
•OAP 4
•OAP 2•Output
Focus
•Output Focus
•Beam splitter
•Instrument Selection
Fold Mirror
•DM0 on Tip/Tilt Stage
•DM11
•OAP 3
All science optics lie in a horizontal plane
4-OAP design provides excellent image quality and
nulls distortion
Dimensions driven by f/15 optical design and 0.30m pupil
size at deformable mirror
New Top-Level LGSF Architecture
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•Laser Location on Inside face of elevation journal
• Feasible with new, smaller, gravity-invariant, low-maintenance lasers•Beam transfer
optics path
•Laser launch location (0.4m launch telescope, asterism generator, and diagnostics bench)
•Laser location (behind elevation journal)
TMT.AOS.PRE.10.054.REL01
Key AO Components
Component Key RequirementsDeformable mirrors 63x63 and 76x76 actuators at 5 mm spacing
10 mm stroke and 5% hysteresis at -30C
Tip/tilt stage 500 rad stroke with 0.05 rad 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)
~0.6 quantum efficiency, 3 electrons at 10-200 Hz
Real time controller Solve 35k x 7k reconstruction problem at 800 Hz
Sodium guidestar lasers 25W, near diffraction-limited beam quality
Coupling efficiency of 130 photons-m2/s/W/atom
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Performance Estimate Summary
Error term On-axis RMS WFE, nm
Delivered wavefront error 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
TMT.AOS.PRE.10.054.REL01
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Sky Coverage vs. Galactic Latitude and Zenith Angle
AO Schedule Overview
15TMT.AOS.PRE.10.054.REL01
1st Light Complete 12/22/18
Ready for on-Sky Tests 8/24/18
4/27/18
FAT Complete 5/22/17
LGSF
TMT SITE
NFIRAOS
3/9/18
LasersUnits 2-7
1/26/16Unit 1
12/23/13
FDR 12/9/13
FAT Complete
7/18/17
FDR 12/9/13
WFS Cams
DMs/TTS
RTC
Integration Review 3/24/15
1/9/15
Unit 1 Unit 2
DM0+TTS DM12
11/19/14 3/19/15 2/12/16
5/31/16
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)
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Contracts begin at or near the beginning of the TMT construction phase in October, 2011
17
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
TMT.AOS.PRE.10.054.REL01
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