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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 Technology
                  3University of California Los Angeles
                    4TMT Observatory Corporation




                AO4ELT 2009 Conference
                    June 25, 2009

                                                                            1

                       TMT.IAO.PRE.09.036.DRF01
                        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.

                                                             2

                   TMT.IAO.PRE.09.036.DRF01
IRIS on TMT




                                  NFIRAOS
           


                           IRIS



                                            3

TMT.IAO.PRE.09.036.DRF01
          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

                                                                     4

                      TMT.IAO.PRE.09.036.DRF01
            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,
                                                                          5
                                                   A Moore, CIT

                        TMT.IAO.PRE.09.036.DRF01
      Sky Coverage
(Lianqi Wang, Brent Ellerbroek, 2008)




                                  1 TTF + 2TT
                                  probes




                                                6

       TMT.IAO.PRE.09.036.DRF01
         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


                                                                 7

                       TMT.IAO.PRE.09.036.DRF01
    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


                                                     8

       TMT.IAO.PRE.09.036.DRF01
Theta-R Patrol Geometry




                                                                                                     9
The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document


                        TMT.IAO.PRE.09.036.DRF01
                       Theta-R Probe Optics
                                                •Converter lens
                                                •and fold mirror

         TTF                                     •Field stop       TT
                                                 •Collimator
                 •Fold mirrors
                                               •Fold mirrors

         •ADC
                                                 •ADC

                                            •Imager
•Lenslet array
                                   •‘Trombone’ mirrors

                                 •Detector Dewar ‘face’
                                        •Detector
                                                                        10

                                   TMT.IAO.PRE.09.036.DRF01
Theta-R Probe Mechanics




                                11

     TMT.IAO.PRE.09.036.DRF01
               Macro Mechanics




                                                                                                     12
The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document


                        TMT.IAO.PRE.09.036.DRF01
Exploded
  View




                                                                                                                13
           The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document


                                   TMT.IAO.PRE.09.036.DRF01
                            OIWFS Probe Platform
                            OIWFS platform
                         assembly (with pickoff
                           arms integrated)




                                                                                                                             G10 or titanium
                                                                                                                                flexures




   Thermal
  insulation
(bottom part)




      Dewar interface
          frame
       (aluminum)
                                                                                                                                               14
                        The Information Herein is Subject to the Restrictions Contained on the Cover Page of this Document


                                                TMT.IAO.PRE.09.036.DRF01
                 OIWFS Cameras
TT pixel scale = lH/2D = 5.67 mas/pixel
TTF pixel scale = lH/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                 15

                     TMT.IAO.PRE.09.036.DRF01
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’)

                                                   16

      TMT.IAO.PRE.09.036.DRF01
                   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                                                   17

                        TMT.IAO.PRE.09.036.DRF01
                 Control Architecture
                 •NFIRAOS RTC
                                         •Engineering GUI

•Time Service
                                  •Logging &             •AO Sequencer
                   •Position
  •TCS              •Service         •Status
                                    •Service

                                                   •Command
•IRIS IS
                           •Shared Memory           •Service
           •Environ-
            •mental
            •Service    •House-         •Motion
                                                         •Engineering Data
                       •keeping         •Control
                                                              •System
                       •Service         •Service                         18

                        TMT.IAO.PRE.09.036.DRF01
                       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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                            TMT.IAO.PRE.09.036.DRF01

				
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