1. Osservatorio di Arcetri Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR 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

2. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Purpose of the test tower Main target: Test and characterization of the Optical Closed Loop for the Complete and Final AO System before 1 st light 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

3. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Optical Layout Concept Elliptical secondary F2 F1 F/15.0 F/1.22 13713mm 1064.7mm 911mm

4. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Interferometer light injection Fisba interferometer Movable beam-splitter Beam to/from AdSec Beam to WFS 110mm 45mm 190mm

5. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Reference Optics WFS needs exit pupil on the AdSec mirror! No simple reference sphere: Collimating optics+flat on the pupil image Parabola+flat Single Aspheric lens+flat Spheric obj+flat

6. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Reference Optics Reference optics Commercial Thorlab C240-TMB F/0.8 diam:8mm better then /20 PtV on-axis Molded – highly aspherical Design: 3 lenses, 4sph surf, 2flat surf F/1.1, /20 PtV on-axis (microscope obj:Trapped back-focus) Parabola F/1.1 Diam:10-20mm Better then /20 PtV on-axis Better behavior off-axis  >0.06 to allow +/-200vw of tilt

7. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Optical Test Tower in Arcetri 15m optical bench to simulate the telescope Arcetri Solar Tower Reference optics Tube supported by Isolators (pendolum) Optical Bench (WFS unit)

8. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Optical Test Tower Lab 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

9. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi 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. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Top isolators Heavy-load isolators (horizontal and vertical springs and vertical leveling system) Isolators (horizontal springs and leveling system) 5m 14m CM 6m Iron/steel Ring rigidly connected to the structure (section) Isolators between the tube top and the ring Iron/steel ring rigidly connected to the top tower structure Enidine or Fabreeka Air Spring Preload 1000kg/act Freq 2.5-3.5Hz

11. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Dynamics (FEA) 18Hz (Hexapod mode) 27Hz (Bending) Tip-Tilt and Piston (Rigid modes): 1.4Hz, 1.9Hz, 0.98Hz (isolators)

12. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi 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@  T=30K)

13. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Alignment procedure Interferom.: F/10 Mirror: F/15 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) WFS BS

14. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Optomechanical tolerances Source of errorDefocus PtVTilt PtV Shell-RefOpt distance 0.28 wv/  m Interfer.-Shell distance1.1wv/mm Shell+RefOpt decentering 0.21wv/  m Shell+RefOpt tilt14wv/arcsec Shell or RefOpt decentering 2.9wv/  m Shell tilt20wv/arcsec Target: /10 focus stability in 7.5sec (differential meas. time) 0.8 K/min (invar) 1.5 K/min (steel) Target: /10 in 1.5sec (single meas. Time) 23nm/s Active control of the Tip-Tilt (AdSec?)

15. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Tower tilt and Hexapod disp/tt G Wind RefOpt Hexapod flexion: 3.3 nm/arcsec 5.1 arcsec/arcsec

16. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi Wind and test tower f*PSD [rad 2 ] V wind =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 with V<3m/s or active tilt compensation with AdSec It is not a problem at the telescope (the dome is closed)

17. Potsdam 16-17 May 2002 - 1 st light LBT AO: PDR Osservatorio di Arcetri A. Riccardi 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)