The AO system for the GTC an update

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The AO system for the GTC-an update

• Nicholas Devaney, Dolores Bello, Bruno Femenía,
  Alejandro Villegas, Javier Castro
• Grantecan, Instituto de Astrofísica de Canarias
• Marcos Reyes, Jesús Jimenez
• Instituto de Astrofísica de Canarias

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Summary

• Specifications
• Status of Design
• Interface with AO Instrument
• The PDR
• Planning

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Preaching to the converted....(I hope!)
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GTC AO specifications

• Correction in the near IR 1.0-2.5 ?m (goal 0.8-5
  ?m)
• On-axis Strehl ratio gt 0.75 at 2.2 ?m when
  r020cm at 0.5 ?m (bright guide star)
• SR gt 0.1 a 2.2 ?m for guide star mRgt14.5
• Corrected field 1 arcminute (goal 2 arcmin)
• Range of zenith angles 0-60?
• Transmission to science focus gt 70 (1.0 lt ? lt
  2.5 ?m)
• Emissivity lt 20 a ?3.8 ?m

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Seeing stats at GTC site
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Bright star Strehl ratio
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AO system outline

• Whole system mounted on a fixed bench at Nasmyth.
  Optical derotation of image.
• Deformable mirror has 21 actuators across the
  pupil (11.309mpupil3 radius)
• 250-300 actuators in use
• Tip-tilt correction carried out by GTC M2
• residual corrected by deformable mirror
• Shack-Hartmann wavefront sensor
• tip-tilt derived from Shack-Hartmann measure
• Designed to upgrade for use with Sodium Laser
  Guide Star

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AO system outline
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GTCAO optical design

• Corrector
• optical de-rotator
• 2 off-axis parabolas
• 2 DMs conjugate to atmospheric layers at 0 and 8
  km altitude
• Beamsplitter
• ADC in the science path
• Wavefront Sensor
• field lens (maintains pupil distance)
• collimator
• camera
• ADC included

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Optics design - Correction system
ADC
OAP1
dichroic
OAP2
deformable mirror (pupil)
fold mirror (8km)
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Optical design of WFS
Lenslet array
collimator
camera
ADC
Field lens
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Mechanical design
AO system
Scientific Instrument
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Wavefront sensor
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Faint guide star performance
k
CCD60
CCD50
H
Proabability of finding star in ?1.5 arcmin at
NGP is 13 for mR15.0, 29 for mR16.5
J
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Interface with AO Instrument

• Output beam focal ratio same as GTC
• Dichroic cut-off at 0.9 ?m
• Distance of exit pupil from focus 6680mm (goal
  was to leave at position GTC exit pupil)
• Need to fix tolerance on output beam position and
  direction
• affects tolerances of AO alignment
• current values ?6, ?3mm
• Non-common path errors will be measured using
  Phase Diversity may affect focus range of AO
  Instrument (or detector). Will probably be
  measured by moving the wavefront sensor

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Interface with AO Instrument
600mm
2400mm
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Mechanical design
AO system
Image rotator
Optics bench
Scientific Instrument
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Comments on comments....

• Keep loop closed while nodding
• main problem is repeatability
• Jitter of 0.004 arcsec corresponds to SR0.96 at
  2.2 ?m. In the image plane, this is 3.3 microns
  !!!!
• IR WFS
• good in regions of high obscuration
• otherwise less sensitive (higher read noise and
  background)
• best to have both IR and vis.

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Upgrade path...

• The first upgrade should be install a sodium
  laser guide star for single-conjugate operation
• This will provide good sky-coverage and allow
  more science
• Development of suitable sold state lasers is
  on-going (LLNL, CTI, Lightwaves, ESO...).
  Considering to contribute to development costs
  now.
• There should be a parallel development of MCAO
  wavefront sensing.

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The PDR

• Dates fixed July 26-28
• Three external reviewers confirmed
• Mechanical design not as advanced as would be
  expected for PDR. Control system not designed.
• List of documents for PDR

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PDR Documents
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AO Common user Science Instrument

• FRIDA collaboration just started
• Main contributors
• Optics Mexico and U. of Florida
• Mechanics Mexico and IAC
• Software and detector control IAC
• Preparing a conceptual design. Should be ready by
  October 2004
• Initial discussions are focussing on an imager
  and IFU spectrograph
• Resolutions foreseen range from 500 to about
  30000
• People willing to contribute should contact Beto
  López (jal_at_astrosen.unam.mx)hb

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Planning
?