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Development of the first light AO system for Large Binocular Telescope. S.Esposito, A.Tozzi, A.Puglisi, L.Fini, P.Stefanini, D.Gallieni, J.Storm,. Presented by Andrea Tozzi. SPIE Meeting, San Diego, August 04 th , 2003. Introduction.

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Development of the first light AO system for Large Binocular Telescope

S.Esposito, A.Tozzi, A.Puglisi,

L.Fini, P.Stefanini, D.Gallieni,


Presented by Andrea Tozzi

SPIE Meeting, San Diego, August 04th, 2003

Introduction Telescope

  • The first light Adaptive Optic system for LBT is supposed to be ready in late summer 2004

  • Location: front bent gregorian focus, into the Acquisition Guiding and Wavefront sensing unit (AGW)

  • Detailed design has been completed by the end of 2002

  • Important modifications with respect SPIE 2002

  • Laboratory tests and assembly in March 2003

The wfs into agw
The WFS into AGW Telescope


Auxiliary units

WFS board

Support structure

Wfs arrangment stages

front view Telescope

AGW flange plane

Input LBT beam

Z stage

Lucifer window

Y stage

X stage

WFS arrangment stages

  • Movable vs Fixed

  • Advantages:

  • Reduced size

  • Number and cost of

    • optical elements

  • High optical throughput

  • Minimiza non common path

    • aberrations

  • Reduce system

    • differential flexure

  • Reduce turbolence

  • Easy testing

    • Drawbacks:

  • System misalignement

    • and tilt due the

    • translation stages

    • Well centered structure

    • Reduced size

    • For central position FOV no exursion stage

    Front surface of Lucifer window center is at 27 mm from AGW flange

    Working wfs fov

    Telecentic Telescope


    116 mm

    116 mm



    86 mm

    86 mm








    X stage

    Y stage



    Working WFS FOV

    Exploring area:

    FOV in arcmin from the

    centre of the telecentric lens

    Scale f/15 = 36 mm/arcmin

    The “new” AO WFS board Telescope


    We have changed the optical

    arrangemnt of the T.V. and H.O.


    W shape!!

    • Linear stages position for

    • center FOV is centered

    • under the board

    • Better weight distribution on

    • the board

    • The board is well centered

    • around the AGW axis

    Optical beams w shape
    Optical beams: W shape Telescope

    320 mm







    Lucifer Window



    triplet lens

    400 mm


    Tip Tilt


    LBT f15 focus




    Ads finite element analysis
    ADS finite element analysis Telescope

    The model takes into account of:

    AGW, Lucifer, Bayside Stages, WFS, Off axis unit, Auxiliary units,...

    Load case definition:

    Structure stiffness

    Flexure &


    0.86 µm (1h obs.)

    0.50 µm (1h obs.)

    ADS FE analysis

    1.0 µm (1h obs.)

    Maximum displacements for the mid point of the NGS board (Load case at EL= Zenith, ROT=0° is taken as reference) :

    ~107 asec  2.8 µm

    ~ 35 asec  0.9 µm

    Structure Stiffness

    Old configuration

    New configuration

    CCD image shifting in the worst load case


    Flexure &


    • elevation angle changes =

    • rotation angle changes =

    3.60 µm (1h obs.)

    2.00 µm (1h obs.)

    ADS FE analysis

    4.1 µm (1h obs.)


    CCD39 pixel = 24 micron

    with NGS support structure fixed:

    ~ 34 asec  0.88 µm

    Wfs board
    WFS board Telescope

    Aerial view

    • Filter Wheel #1 (8 pos avaible):

    • 20/80

    • 50/50

    • 100/0

    • LW/SW @ LW<600nm/SW<600nm

    • ..........

      (Trasmission H.O./T.V. Beam)

    Filter wheel #1

    Top view

    Filter Wheel Tech. Viewer (8 pos avaible)

    Technical Viewer FOV:

    10’’ X 10’’ (Zemax optical project)

    7.4’’ X 7.4’’ (with Marconi CCD47 BI)

    Scale = 1.8 mm/”

    Filter wheel TV

    Wfs board tests
    WFS board tests Telescope

    Inventor Project

    • Standard Optical parts

    • (lens, mirrors…): ready!

    • (made by Silo - Italy)

    • Non standard Optical parts

    • (Double Pyramid): quite ready!

    • (made by INAF/INOA - Italy)

    Lbt simulator

    LBT simulated focus Telescope

    LBT simulator

    LBT “simulator”

    100 mm

    WFS input beam:

    F/15 telecentric beam

    LBT simulated pupil

    (8 mm diameter)

    Laboratory optical tests
    Laboratory Optical tests Telescope

    Wavefront sensor board

    LBT beam simulator

    Rotational table

    Photo album
    Photo album! Telescope

    First pupil images

    29.8 Telescope








    First pupil images

    With preliminary single pyramid (BK7, angle 2°) !

    • Pupil diameter: 30.0 – 30.2 – 30.0 – 29.8 pixel (720.0 - 724.8 - 720.0 - 715.2 micron)

    • Pupil center position max error: 0.5 pixel (12 micron)

    • Pupil stability vs gravity position (0 to 90 deg rotation) = 0.08 pixel rms  in quadrature = 0.11 pixel (2.6 micron)

    Pyramid quality

    ideal pyramid Telescope

    scratched edges

    Measure of the energy collected into the four pupils vs modulation

    Dimension of the roof, the edge, energy loss

    ideal edges

    Pyramid quality

    • dimension of pyramid roof = 36 μm

    • dimension of pyramid edge = 15 μm

     energy loss = 20%-7% for modulation range ±4-±16

    to increase goodness of optical polishing we are realizing a double pyramid sensor

    which needs bigger angles (about 30°)

    • Pupil center position error in pixel = (0;0) (-0.2;0.1)(-1.5;0.2)(-1.6;-1.0)

    due to a known mechanical allignment error of 2 arcmin

    Wavefront sensor ccd and electronics
    Wavefront sensor CCD and Electronics Telescope

    • Marconi EEV-39 deep depletion CCD

    • Electronic controller made by SciMeasure Inc. (Atlanta)

    • Real Time Electronics (RTC) by MicroGate (Italy)

    • Basic Computing Unit (BCU) by MicroGate (Italy)

    • readout noise about 9 e-

    • readout speed is 2.5 Mpixel/s for each quadrant 

    • reduced readout speed (control electronics) 

    • reduced readout noise and frame rate

    1X1 binning

    (30X30 subap.)

    2X2 binning

    (15X15 subap.)

    650 fps (subap.=15X15)  RON=3.2e-

    Dark current = 600 e-/s @-30°

    Agreement with EEV specifications !!

    Ao system supervisor
    AO system supervisor Telescope

    • General setup (power-on, resident software downloading, ...)

    • Adjusting the otical devices (linear stages, fiter wheels,...)

    • Commanding the secondary mirror (open-loop operations)

    • Start/stop the cles loop operation

    • Acquisition of run-time diagnostic data and evaluation of loop quality parameters

    • Interaction qith the other components of the TCS

    • MsgD-RTDB: the message routing process and the Real Time Data Base

    • On-Ax.AGW ctrl: a process which control the WFS hardware, gest images, computed slopes from the Sloop Computer

    • AdSec ctrl: process which controls the Adaptive Secondary System hardware

    • UserInterface: used for engineering tasks (calibration, diagnostic,...). GUI interface, IDL procedures

    • TCS Interf: two processes which receive commands from TCS and provide status feedback to TCS (Intel base workstation running Linux OS)

    conclusion Telescope

    • New arrangement of the stages assembly for positioning the wavefront sensor:

      • Reduced system flexure of more than a factor of three 

      • pupil displacement is a small fraction of a subaperture

    • All WFS optical components has been acquired together with the majority of mechanical mounts

    • Initial tests on the wavefront sensor board:

      • pupil dimension is the nominal value (30 pixel)

      • Pupil displacements is negligeable (0.1 pixel)

      • positive initial tests on WFS CCD has been developed: RON

    • Control software architecture has been designed in detail and partly coded

    • Interface with TCS has been projected

    Acknowledgement Telescope

    Roberto Ragazzoni

    Jesper Storm

    John Hill

    Walter Seifert

    Svend Bauer

    Piero Ranfagni

    Armando Ricacrdi

    Daniele Gallieni

    Roberto Biasi


    END!! Telescope

    Wfs board design
    WFS board design Telescope