1 iris oiwfs concept study d. loop 1, m. fletcher 1, v. reshetov 1, r. wooff 1, j. dunn 1, g....

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IRIS OIWFS Concept Study

D. Loop1, M. Fletcher1, V. Reshetov1, R. Wooff1, J. Dunn1, G. Herriot1 A. Moore2, R. Dekany2, A. Delacroix2, R. Smith2, D. Hale2,

J. Larkin3, L. Simard4, D. Crampton4, B. Ellerbroek4, C. Boyer4, L. Wang4

1NRC-Herzberg Institute of Astrophysics

2California Institute of Technology3University of California Los Angeles

4TMT Observatory Corporation

AO4ELT 2009 ConferenceJune 25, 2009

TMT.IAO.PRE.09.036.DRF01

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Outline

We report on the concept study of the On-Instrument low order natural guide star WaveFront Sensors (OIWFS) for the TMT IRIS science instrument, a collaborative effort by NRC-HIA, Caltech, UCLA, TMT AO team, and TMT Instrument team. This includes work on sky coverage modeling, patrol geometry, detector alternatives, acquisition, guiding, and dithering scenarios, probe optics & mechanics, control architecture, and interfaces with NFIRAOS, IRIS, and TMT observatory.


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IRIS on TMT

IRIS

NFIRAOS


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Key OIWFS Requirements

Instrument rotator & services wrap - alignment between NFIRAOS delivered beam and IRIS science instrument– Critical to IRIS image quality

2 tip/tilt and 1 tip/tilt/focus wavefront sensors– Fast guiding, focus and tilt anisoplanatism

2 mas positioning accuracy > 4.4 µm at focal plane– OIWFS are the positional reference for astrometric performance

High sky coverage - < 2 mas tip/tilt jitter at galactic pole– Near infrared, 1.0 to 1.7 µm, sensing on ‘sharpened’ guide stars

High acquisition probability = low acquisition time


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Work Breakdown Structure

MGT OIWFS Management D Loop, HIA, A Moore, CIT

SYS OIWFS Systems Engineering R Dekany, CIT, D Loop, HIA

ENC OIWFS Enclosure V Reshetov, HIA

ENC.ROT Instrument Rotator, Cable Wrap V Reshetov, HIA

ARM OIWFS Probe Arms D Loop, HIA

ARM.MEC Probe Arm Mechanics V Reshetov, HIA

ARM.OPT Probe Arm Optics M Fletcher, HIA

CC OIWFS Component Controller B Wooff, J Dunn, HIA

CAM OIWFS Cameras R Smith, CIT

CAM.DET Camera Detectors R Smith, CIT

CAM.MEC Camera Mechanics A Delacroix, CIT

CAM.AC Detector Controllers D Hale, CIT

INT OIWFS Integration & Test Equip. D Loop, HIA, A Moore, CIT


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Sky Coverage(Lianqi Wang, Brent Ellerbroek, 2008)

1 TTF + 2TT probes


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Object Selection Mechanism

Object Select Mechanisms considered

– Robot placed pickoff & pathlength mirrors (EAGLE concept)

– Tip/tilt mirror tiling of focal plane (Caltech TIPI concept)

– Theta-Phi, 2 rotation stages (Flamingos-2 OIWFS, etc)

– Theta-R, 1 rotation + 1 linear stages (IRMOS, KMOS, etc)

Requirements for positioning accuracy, dithering, non-sidereal tracking

Theta-R concept chosen for initial sky coverage analysis

TT and TTF function change – versus - 2 probe planes


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Patrol Geometry(Lianqi Wang, Brent Ellerbroek, 2008)

3 identical ‘theta-R’ probes at 120 degree spacing

Each probe capable of TT or TTF (key for sky coverage)

Only need to reach 50% across 2’ field


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Theta-R Patrol Geometry

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


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Theta-R Probe Optics

•Detector

•Converter lens•and fold mirror

•Field stop

•Collimator

•‘Trombone’ mirrors

•Fold mirrors

•Fold mirrors

•ADC•ADC

•Lenslet array•Imager

•Detector Dewar ‘face’

TTF TT


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Theta-R Probe Mechanics


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Macro Mechanics



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Exploded View



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OIWFS Probe Platform


G10 or titanium flexures

Dewar interface frame

(aluminum)

Thermal insulation

(bottom part)

OIWFS platform assembly (with pickoff

arms integrated)


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OIWFS Cameras

TT pixel scale = H/2D = 5.67 mas/pixel

TTF pixel scale = H/D = 11.34 mas/pixel

– Same detectors can be used for TT and TTF functions

Analysis of tip/tilt jitter & image wander during acquisition shows worst case of ~250 mas

at 4 sigma and 5.67 mas/pixel > minimum of ~180x180 pixels

Acquisition probability > larger probe FoV > more pixels

Hawaii HxRG 1024x1024 HgCdTe detector w/new MBE material testing underway – read noise, dynamics

Speedster 128x128 HgCdTe detector testing soon

HgCdTe e-APDs and InGaAs emerging technologies


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Acquisition Probability(Corinne Boyer, Luc Simard, 2008)

1024x1024 pixels

5.8’ probe FoV

1’ Telescope pointing σθ (worse at 1st light)

provide on-chip small dithering capability (2-3’)


Sky Coverage Update(Lianqi Wang, Brent Ellerbroek, Jean-Pierre Veran, 2009)

NGS mode errors combined with LGS mode errors of 178 nm RMSOverall on-axis budget of 187 nm RMS met at 45% sky coverageShortfall (in quadrature) of ~28 nm RMS at 50%System optimization still underway– Detector performance– “Fitting field” for LGS modes– Optimal choice of NGS modes

and reconstructor 17


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Control Architecture

•IRIS IS•IRIS IS

•AO Sequencer•AO Sequencer

•Time Service•Time Service

•NFIRAOS RTC•NFIRAOS RTC•Engineering GUI•Engineering GUI

•Engineering Data

•System

•Engineering Data

•System

•TCS•TCS•Position

•Service

•Position

•Service

•Logging &

•Status

•Service

•Logging &

•Status

•Service

•Command

•Service

•Command

•Service

•Environ-

•mental

•Service

•Environ-

•mental

•Service •House-

•keeping

•Service

•House-

•keeping

•Service

•Motion

•Control

•Service

•Motion

•Control

•Service

•Shared Memory


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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.


1 iris oiwfs concept study d. loop 1, m. fletcher 1, v. reshetov 1, r. wooff 1, j. dunn 1, g....

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