Adaptive optics systems for the thirty meter telescope
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Adaptive Optics Systems for the Thirty Meter Telescope. Brent Ellerbroek Thirty Meter Telescope Observatory Corporation Adaptive Optics for Extremely Large Telescopes Paris, June 23, 2009. Presentation Outline. AO requirements flowdown Top-level science-based requirements for AO at TMT

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Adaptive Optics Systems for the Thirty Meter Telescope

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Adaptive optics systems for the thirty meter telescope

Adaptive Optics Systems for the Thirty Meter Telescope

Brent Ellerbroek

Thirty Meter Telescope Observatory Corporation

Adaptive Optics for Extremely Large Telescopes

Paris, June 23, 2009

TMT.AOS.PRE.09.027.REL01

Ellerbroek, AO4ELT, Paris, June 23 2009


Presentation outline

Presentation Outline

  • AO requirements flowdown

    • Top-level science-based requirements for AO at TMT

    • Derived requirements and design choices

    • First light AO architecture summary

  • Subsystem designs

    • Narrow Field Infra-Red AO System (NFIRAOS)

    • Laser Guide Star Facility (LGSF)

  • System performance analysis

  • Component requirements and prototype results

  • Lab and field tests

  • Upgrade paths

  • Summary

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Ellerbroek, AO4ELT, Paris, June 23 2009


Top level requirements at first light

Top-Level Requirements at First Light

Derived to enable diffraction-limited imaging and spectroscopy at near IR wavelengths:

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Ellerbroek, AO4ELT, Paris, June 23 2009


Implied ao architectural decisions

Implied AO Architectural Decisions

Very High Order AO (60x60)

Diffraction-Limited Image Quality

10-30” Corrected FoV

Tomography (6 GS) + MCAO (2 DMs)

(Sodium) Laser Guide Stars

High Sky Coverage

Near IR (J+H) Tip/Tilt NGS

Large Guide Field (2’)

MCAO to “Sharpen” NGS

Multiple (3) NGS to Correct Tilt Aniso.

High Throughput

Minimal Surface Count; AR coatings

Cooled Optical Path (-30° C)

Low Emission

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Ellerbroek, AO4ELT, Paris, June 23 2009


Technology and design choices i

Technology and Design Choices (I)

Utilize existing or near-term approaches whenever possible

  • Solid state, CW, sum-frequency (or frequency doubled) lasers for bright sodium laser guidestars

    • Located in telescope azimuth structure with a fixed gravity vector

  • Impact of guidestar elongation is managed by:

    • Laser launch from behind secondary mirror

    • “Polar coordinate CCD” with pixel layout matched to elongation

    • Noise-optimal pixel processing, updated in real time

  • Mirror-based beam transport from lasers to launch telescope is current baseline

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Ellerbroek, AO4ELT, Paris, June 23 2009


Technology and design choices ii

Technology and Design Choices (II)

  • Piezostack DMs for high-order wavefront correction

    • “Hard” piezo for large stroke, low hysteresis at low temperature

    • 5 mm inter-actuator pitch implies a large AO system

  • Surface count minimized to improve throughput and emissivity

    • Tip/tilt correction using a tip/tilt stage, not separate mirror

    • Field de-rotation at instrument-AO interface (no K-mirror)

  • Tomographic wavefront reconstruction implemented using efficient algorithms and FPGA/DSP processors

  • Tip/tilt/focus NGS WFSs located in science instruments

    • Baseline detector is the H2RG array

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Ellerbroek, AO4ELT, Paris, June 23 2009


Ao architecture realization

Lasers

AO Architecture Realization

  • Narrow Field IR AO System (NFIRAOS)

    • Mounted on Nasmyth Platform

    • Ports for 3 instruments

  • Laser Guide Star Facility (LGSF)

    • Lasers located within TMT azimuth structure

    • Laser launch telescope mounted behind M2

    • All-sky and bore-sighted cameras for aircraft safety (not shown)

  • AO Executive Software (not shown)

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Ellerbroek, AO4ELT, Paris, June 23 2009


Nfiraos on nasmyth platform with client instruments

NFIRAOS on Nasmyth Platform with Client Instruments

Future (third) Instrument

NFIRAOS Optics Enclosure

Instrument Support Structure

LGS WFS Optics

Nasmyth Platform Interface

Nasmyth Platform

Electronics Enclosure

Laser Path

IRIS (and on-instrument WFS)

IRMS

(and on-instrument WFS)

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Ellerbroek, AO4ELT, Paris, June 23 2009


Nfiraos science optical path

NFIRAOS Science Optical Path

1-1 OAP optical relay

DMs located in collimated path

Light From

TMT

WFS Beam-splitter

DM0/TTS

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Ellerbroek, AO4ELT, Paris, June 23 2009


Nfiraos opto mechanical layout

NFIRAOS Opto-mechanical Layout

2 Truth NGS WFSs

1 60x60 NGS WFS

IR Acquisition camera

Input from

telescope

OAP1

OAP2

76x76 DM at h=11.2km

63x63 DM at h=0km

On tip/tilt platform

(0.3m clear apeture)

Output to science instruments and IR T/T/F WFSs

6 60x60 LGS WFSs

AO and science calibration units not illustrated

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Ellerbroek, AO4ELT, Paris, June 23 2009


Laser guide star facility conservative design approach

Laser Guide Star FacilityConservative Design Approach

  • Approach based upon existing LGS facilities (i.e. Gemini North and South)

  • Laser system

    • Initially 6 25W solid state, CW laser devices with one spare

    • Space for future upgrades to additional or more advanced lasers

  • Beam transfer optics

    • Azimuth structure path

    • “Deployable” path to transfer beams to elevation structure along telescope elevation axis

    • Elevation structure path, including pupil relay optics and pointing/centering mirrors for misalignment compensation

    • Top-end beam quality, power, and alignment sensors

    • Optics for asterism generation, de-rotation, and fast tip/tilt correction

  • Laser launch telescope

    • 0.5m unobscured aperture and environmental window

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Ellerbroek, AO4ELT, Paris, June 23 2009


Approach to performance analysis

Approach to Performance Analysis

  • Key requirement is 187 nm RMS wavefront error on-axis

    • 50% sky coverage at Galactic pole

    • At zenith with median observing conditions

    • Delivered wavefront with all error sources included

  • Performance estimates are based upon detailed time-domain AO simulations

    • Physical optics WFS modeling with LGS elongation

    • Telescope aberrations and AO component effects included

    • Actual RTC algorithms for pixel processing and tomography

    • “Split” tomography enables simulation of 100’s of NGS asterisms

  • Simulated disturbances are based upon TMT site measurements, sodium LIDAR data, telescope modeling

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Ellerbroek, AO4ELT, Paris, June 23 2009


Examples of ao simulation data and intermediate results

Examples of AO Simulation Data and Intermediate Results

Input Disturbance:

Atmospheric phase screen

TMT aperture function

M1 phase map

M1+M2+M3 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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Ellerbroek, AO4ELT, Paris, June 23 2009


Example ngs guide field from monte carlo sky coverage simulation

Example NGS Guide Field from Monte Carlo Sky Coverage Simulation

Tip/Tilt NGS

Tip/Tilt/Focus NGS

Tip/Tilt NGS

Sample Asterism near 50% Sky Coverage (Besançon Model, Galactic Pole)

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Ellerbroek, AO4ELT, Paris, June 23 2009


Performance estimate summary

Performance Estimate Summary

  • 178 nm RMS error in LGS modes

    • 127 nm first order, 97 nm AO components, 79 nm opto-mechanical

  • 47.4 nm tip/tilt at 50% sky coverage

  • 63.4 nm overall error in NGS modes

  • 187 nm RMS total at 45% sky coverage

  • NGS Algorithm optimization and detector characterization still underway

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Sky coverage results for enclosed energy on a 4 mas detector

Sky Coverage Results for Enclosed Energy on a 4 mas Detector

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Ellerbroek, AO4ELT, Paris, June 23 2009


Key ao component technologies

Key AO Component Technologies

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Ellerbroek, AO4ELT, Paris, June 23 2009


Laser systems

Laser Systems

  • 50W+ power successfully demonstrated by a prototype Nd:YAG, sum frequency, CW laser

  • Development of a facility class 25W design now underway at ESO, with AURA/Keck/GMT/TMT support for prototyping

  • Sodium layer coupling of ~260 photons–m2/s/W/atom demonstrated, but issues remain

    • Magnetic field orientation, photon recoil, inaccessible ground states

    • coupling of ~ 70 photons-m2/s/W/atom predicted at ELT sites

  • Possible solutions include combined D2a/D2b pumping and multiple (3-5) laser lines

    • Performance penalty is ~40 nm RMS without laser improvements

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Wavefront correctors prototyping results

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

Req’t

-3dB TTS bandwidth of 107 Hz at -35C

Low hysteresis of only 5-6% from -40° to 20° C

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Ellerbroek, AO4ELT, Paris, June 23 2009


Polar coordinate ccd array concept for wavefront sensing with elongated laser guidestars

“Polar Coordinate” CCD Array Concept for Wavefront Sensing with Elongated Laser Guidestars

Fewer illuminated pixels reduces pixel read rates and readout noise

sodium layer

ΔH =10km

D = 30m

 Elongation 3-4”

H=100km

LLT

TMT

AODP Design

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Ellerbroek, AO4ELT, Paris, June 23 2009


Laser guide star lgs wfs detector requirements

Laser Guide Star (LGS) WFS Detector Requirements

Now waiting to fabricate and test the 1-quadrant prototype design developed under AO Development Program (AODP) funding

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Real time controller rtc requirements and design approach

Real Time Controller (RTC): Requirements and Design Approach

  • Perform pixel processing for LGS and NGS WFS at 800 Hz

  • Solve a 35k x 7k wavefront control problem at 800Hz

    • End-to-end latency of 1000s (strong goal of 400 ms)

  • Update algorithms in real time as conditions change

  • Store data needed for PSF reconstruction in post-processing

  • Using conventional approaches, memory and processing requirements would be >100 times greater than for an 8m class MCAO system

  • Two conceptual design studies by tOSC and DRAO provide effective solutions through computationally efficient algorithms and innovative hardware implementations

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Ellerbroek, AO4ELT, Paris, June 23 2009


Lab tests and field measurements

Lab Tests and Field Measurements

  • University of Victoria Wavefront Sensor Test Bench

    • Tests of matched filter wavefront sensing with real time updates as sodium layer evolves

  • University of British Columbia sodium layer LIDAR system

    • 5W laser, 6m receiver

    • 5m spatial resolution at 50 Hz

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Ellerbroek, AO4ELT, Paris, June 23 2009


Options for first decade ao upgrades and systems

Options for First Decade AO Upgrades and Systems

  • MEMS-based MOAO in future NFIRAOS instruments

    • Increased sky coverage via improved NGS sharpening

    • Multiple MOAO-fed IFUs on a 2 arc minute FoV

    • Order 120x120 wavefront correctors for ~130 nm RMS WFE (with upgraded lasers, wavefront sensors, and RTC)

    • MEMS correct NFIRAOS residuals; simplified stroke/linearity requirements

  • Additional AO systems for “first decade” instrumentation:

    • Mid-IR AO (Order 30x30 DM, 3 LGS)

    • MOAO (Order 64x64 MEMS, 5’ field, ~8 LGS)

    • ExAO (Order 128x128 MEMS, amplitude/phase correction for M1 segments, advanced IR WFS, post-coronagraph calibration WFS)

    • GLAO (Adaptive secondary to control ~500 wavefront modes, 4-5 LGS)

  • Adaptive secondary mirror could be useful for all systems

    • Only corrector needed for GLAO and Mid-IR AO

    • Large-stroke “woofer” for MOAO, ExAO, and NFIRAOS+

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Summary

Summary

  • TMT will be designed from the start to exploit AO

    • Facility AO is a major science requirement for the observatory

  • An 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

  • Designs and performance estimates are anchored by detailed analysis and simulation

  • Component prototyping and lab/field tests are underway

  • Construction phase schedule leads to AO first light in 2018

  • Upgrade paths are defined for improved performance and new AO capabilities during the first decade of TMT

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Additional posters and talks

Additional Posters and Talks

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Acknowledgements

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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Ellerbroek, AO4ELT, Paris, June 23 2009


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