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Optical Test Tower for the LBT Adaptive Optics System

Optical Test Tower for the LBT Adaptive Optics System. A. Riccardi 1 , P. Salinari 1 , S. Esposito 1 , D. Gallieni 2. 1 Osservatorio Astrofisico di Arcetri, Italy 2 ADS International, Italy. Purpose of the test tower. Adaptive Secondary Tests: Optical Flattening and calibration

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Optical Test Tower for the LBT Adaptive Optics System

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  1. Optical Test Tower for the LBT Adaptive Optics System A. Riccardi1, P. Salinari1, S. Esposito1, D. Gallieni2 1Osservatorio Astrofisico di Arcetri, Italy 2ADS International, Italy

  2. Purpose of the test tower • Adaptive Secondary Tests: • Optical Flattening and calibration • Optical behavior at “mountain” ambient temperature • Dynamical Behavior at “mountain” atmospheric pressure • WFS Optical Test: • Optical interaction with LBT672 • Optical Closed loop operation Main target: Test and characterization of the Optical Closed Loop for the Complete and Final AO System before 1st light

  3. Optical Layout Concept 911mm Elliptical secondary 1064.7mm F1 F/1.22 13713mm F2 F/15.0

  4. 110mm 45mm 190mm Interferometer light injection Beam to/from AdSec Beam to WFS Movable beam-splitter Fisba interferometer

  5. Reference Optics WFS needs exit pupil on the AdSec mirror! No simple reference sphere: Collimating optics+flat on the pupil image Single Aspheric lens+flat Spheric obj+flat Parabola+flat

  6. Reference optics Reference Optics Design: 3 lenses, 4sph surf, 2flat surf F/1.1, l/20 PtV on-axis(microscope obj:Trapped back-focus) Commercial Thorlab C240-TMBF/0.8 diam:8mmbetter then l/20 PtV on-axis Molded – highly aspherical Parabola F/1.1 Diam:10-20mm Better then l/20 PtV on-axis Better behavior off-axise>0.06 to allow +/-200vw of tilt

  7. Reference optics Tube supported by Isolators (pendolum) Optical Bench (WFS unit) Optical Test Tower in Arcetri 15m optical bench to simulate the telescope Arcetri Solar Tower

  8. Optical Test Tower Winch Mass: 5200kg (tube+Adsec+Opt Bench+Complete WFS unit) Tube height: 13.5m In/Out diameter: 1.1/1.2m Assembly: 6 sections with flanges Lab

  9. Vibration isolators and supports 3 Newport I-4000 Pneumatic Isolators (max load: 6300kg) resonance frequency: 1.0Hz (vert) 1.3Hz (hor.) Damping: 15% of the critical damping Diam: 355mm H: 317mm

  10. Isolators (horizontal springs and leveling system) Iron/steel Ring rigidly connected to the structure (section) 6m 14m CM Heavy-load isolators (horizontal and vertical springs and vertical leveling system) 5m Top isolators Iron/steel ring rigidly connected to the top tower structure Isolators between the tube top and the ring Enidine or Fabreeka Air Spring Preload 1000kg/act Freq 2.5-3.5Hz

  11. Dynamics (FEA) Tip-Tilt and Piston (Rigid modes): 1.4Hz, 1.9Hz, 0.98Hz (isolators) 18Hz (Hexapod mode) 27Hz (Bending)

  12. Thermal stabilization Thermal control: Goal: 0.2K stability, max. DT=30K wrt ambient Double cylinder structure 20mbar pressure in the gap (Acetone: liquid-vapour eq.) 3cm hd polyurethane outer skin (3kW@DT=30K)

  13. Alignment procedure 1. Hex to move the spot on F1 2. Hex to move the spot on F2 keeping the spot on F1 3. Interf. Stage to set the focus 4. Hex+Interf. Stage to compensate spherical ab. Reference Optics mechanical pre-alignment: +/-3mm x-y (WFS +/-0.1 pix) +/-5mm z (WFS z+ stage clearance) +/-2deg (F/1.1 instead of F/1.2) Interferom.: F/10 Mirror: F/15 BS WFS

  14. 0.8 K/min (invar) 1.5 K/min (steel) Target: l/10 in 1.5sec (single meas. Time) 23nm/s Optomechanical tolerances Target: l/10 focus stability in 7.5sec (differential meas. time) Active control of the Tip-Tilt (AdSec?)

  15. Tower tilt and Hexapod disp/tt Wind Hexapod flexion: 3.3 nm/arcsec5.1 arcsec/arcsec G RefOpt

  16. f*PSD [rad2] Wind and test tower Vwind=10m/s Top 8m subject to wind Wind Static Force: 120N Gust Wind Force: 86N rms Tower tilt: 7.5 arcsec rms 0.15 vw PtV of tilt (rms) (resonance at 1Hz) Critical measurements withV<3m/s or active tilt compensation with AdSec It is not a problem at the telescope (the dome is closed)

  17. Conclusions • Test tower facility not charged to the project • Optical test tower design is on progress • Civil works (started) • Mechanical design (ready for manufact. design) • Opical design • Thermal control • Tilt stabilization • Must be operative for the end of electronic tests of LBT672 (2nd-half 2003)

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