Osservatoriodi Arcetri

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Optical Test Tower for the LBT Adaptive Optics

System

A. Riccardi1, P. Salinari1, S. Esposito1, D. Gallieni2

1Osservatorio Astrofisico di Arcetri, Italy2ADS International, Italy

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi 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 1st light

Adaptive Secondary Tests:•Optical Flattening and calibration•Optical behavior at “mountain” ambient temperature•Dynamical Behavior at “mountain” atmospheric pressureWFS Optical Test:•Optical interaction with LBT672•Optical Closed loop operation

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Optical Layout Concept

Elliptical secondary

F2

F1

F/15.0

F/1.22

137

13

mm

106

4.7

mm911mm

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. RiccardiInterferometer light injection

Fisba interferomet

er

Movable beam-splitter

Beam to/from AdSec

Beam to WFS

110mm 45mm

190

mm

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Reference OpticsWFS 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

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Reference Optics

Reference optics

Commercial Thorlab C240-TMBF/0.8 diam:8mmbetter then /20 PtV on-axisMolded – highly aspherical

Design: 3 lenses, 4sph surf, 2flat surfF/1.1, /20 PtV on-axis(microscope obj:Trapped back-focus)

Parabola F/1.1 Diam:10-20mmBetter then /20 PtV on-axisBetter behavior off-axis>0.06 to allow +/-200vw of tilt

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. RiccardiOptical Test Tower in Arcetri

15m optical bench to simulate the telescope

Arcetri Solar Tower

Reference optics

Tube supported byIsolators (pendolum) Optical Bench (WFS unit)

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Optical Test Tower

Lab

WinchMass:5200kg (tube+Adsec+OptBench+Complete WFS unit)

Tube height: 13.5mIn/Out diameter: 1.1/1.2m

Assembly:6 sections with flanges

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. RiccardiVibration 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 dampingDiam: 355mm H: 317mm

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi 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

6mIron/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 SpringPreload 1000kg/actFreq 2.5-3.5Hz

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Dynamics (FEA)

18Hz(Hexapod

mode)

27Hz(Bending)

Tip-Tilt and Piston(Rigid modes):1.4Hz, 1.9Hz, 0.98Hz(isolators)

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi 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)

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Alignment procedure

Interferom.: F/10Mirror: F/15

1. Hex to move the spot on F12. Hex to move the spot on F2 keeping the spot on F13. Interf. Stage to set the focus4. 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

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. RiccardiOptomechanical tolerances

Source of error Defocus PtV

Tilt PtV

Shell-RefOpt distance 0.28 wv/m

Interfer.-Shell distance 1.1wv/mm

Shell+RefOpt decentering

0.21wv/m

Shell+RefOpt tilt 14wv/arcsec

Shell or RefOpt decentering

2.9wv/m

Shell tilt 20wv/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?)

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. RiccardiTower tilt and Hexapod disp/tt

G

Wind

RefOpt

Hexapod flexion:3.3 nm/arcsec5.1 arcsec/arcsec

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi Arcetri

A. Riccardi

Wind and test towerf*

PSD

[ra

d2]

Vwind=10m/sTop 8m subject to wind

Wind Static Force: 120NGust Wind Force: 86N rmsTower tilt: 7.5 arcsec rms

0.15 vw PtV of tilt (rms)(resonance at 1Hz)

Critical measurements withV<3m/s or active tiltcompensation with AdSec

It is not a problem at the telescope (the dome is closed)

Potsdam 16-17 May 2002 - 1st light LBT AO: PDR

Osservatoriodi 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)