1. IRIS OIWFS Concept Study D. Loop1, M. Fletcher1, V. Reshetov1, R
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. Wang NRC-Herzberg Institute of Astrophysics 2California Institute of Technology 3University of California Los Angeles 4TMT Observatory Corporation AO4ELT 2009 Conference June 25, 2009
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2. 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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3. IRIS on TMT
NFIRAOS 
IRIS
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4. 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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5. 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
ARM
OIWFS Probe Arms
D Loop, HIA
ARM.MEC
Probe Arm Mechanics
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
CAM.MEC
Camera Mechanics
A Delacroix, CIT
CAM.AC
Detector Controllers
D Hale, CIT
INT
OIWFS Integration & Test Equip.
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6. Sky Coverage (Lianqi Wang, Brent Ellerbroek, 2008)
1 TTF + 2TT probes
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7. 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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8. 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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9. Theta-R Patrol Geometry
The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document
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10. Theta-R Probe Optics TTF TT Converter lens and fold mirror Field stop
Collimator
‘Trombone’ mirrors
Fold mirrors
ADC
Lenslet array
Imager
Detector Dewar ‘face’
TTF TT
Converter lens brings NFIRAOS exit pupil closer so that collimator can form image further downstream in a more convenient location
Detector
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11. Theta-R Probe Mechanics
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12. Macro Mechanics TMT.IAO.PRE.09.036.DRF01
The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document
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13. Exploded View TMT.IAO.PRE.09.036.DRF01
The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document
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14. OIWFS Probe Platform TMT.IAO.PRE.09.036.DRF01
OIWFS platform assembly (with pickoff arms integrated)
G10 or titanium flexures
Thermal insulation (bottom part)
Dewar interface frame (aluminum)
The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document
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15. OIWFS Cameras TT pixel scale = lH/2D = 5.67 mas/pixel
TTF pixel scale = lH/D = 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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16. 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’)
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17. Sky Coverage Update (Lianqi Wang, Brent Ellerbroek, Jean-Pierre Veran, 2009)
NGS mode errors combined with LGS mode errors of 178 nm RMS
Overall on-axis budget of 187 nm RMS met at 45% sky coverage
Shortfall (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
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18. Control Architecture NFIRAOS RTC Engineering GUI Time Service Position
Logging &
Status
Service
AO Sequencer
TCS
Command
Service
IRIS IS
Shared Memory
Environ-
mental
Service
House-
keeping
Service
Motion
Control
Service
Engineering Data
System
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19. 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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