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The AO system for the GTC -an update

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. Log scaling to show PSF structure due to

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The AO system for the GTC -an update

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  1. 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

  2. Log scaling to show PSF structure due to segmentation. Integration will smooth this structure to ~Airy rings as pupil rotates Preaching to the converted....(I hope!)

  3. GTC AO specifications • Correction in the near IR 1.0-2.5 m (goal: 0.8-5 m) • On-axis Strehl ratio > 0.75 at 2.2 m when r0=20cm at 0.5 m (bright guide star) • SR > 0.1 a 2.2 m for guide star mR>14.5 • Corrected field = 1 arcminute (goal 2 arcmin) • Range of zenith angles 0-60 • Transmission to science focus > 70% (1.0 <  < 2.5 m) • Emissivity < 20% a =3.8 m

  4. Seeing stats at GTC site

  5. Bright star Strehl ratio

  6. AO system outline • Whole system mounted on a fixed bench at Nasmyth. Optical derotation of image. • Deformable mirror has 21 actuators across the pupil (11.309m=pupil+3% 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

  7. AO system outline

  8. 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

  9. Optics design - Correction system ADC OAP1 dichroic OAP2 deformable mirror (pupil) fold mirror (8km)

  10. Optical design of WFS Lenslet array collimator camera ADC Field lens

  11. Mechanical design AO system Scientific Instrument

  12. Wavefront sensor

  13. 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

  14. Mechanical design AO system Image rotator Optics bench Scientific Instrument

  15. Comments on comments.... • Keep loop closed while nodding • main problem is repeatability: • Jitter of 0.004 arcsec corresponds to SR=0.96 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.

  16. 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.

  17. 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:

  18. PDR Documents

  19. 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@astrosen.unam.mx)hb

  20. Planning ?

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