Prefocal wave front correction and field stabilization for the EELT

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Pre-focal wave front correction and field
stabilization for the E-ELT

• L. Jochum, N. Hubin, E. Vernet, P.-Y. Madec, M.
  Dimmler, M. Mueller, B.Sedghi

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Outline

• E-ELT optics layout
• E-ELT AO components
• Main axes control
• Field Stabilization Unit
• Adaptive Unit
• Conclusions

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E-ELT Optics Layout
5 mirror adaptive telescope
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E-ELT AO components

• Disturbers
• Atmospheric turbulence
• Windload
• Gravity and thermal effects
• Task for E-ELT pre-focal AO
• real time wave front correction for theE-ELT
  focal plane, reaching diffractionlimit of the
  telescope in the NIR
• Correction devices
• Telescope main axes control
• Field stabilization mirror
• Adaptive mirror
• Wave front sensing systems
• NGS, LGS, laser sources, beam transport and
  launch, WFS, RTC

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Main axes control
Residual of main axes control ? input disturbance
for image stabilization
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M5 Field Stabilization Unit

• Task Tip tilt correction forimage stabilization
• Components
• Mirror
• Field stabilization system
• Mounting structure
• Control system
• Auxiliary Equipment
• Incoming disturbance
• 1 rms residual tip tilt
• Dominated by wind shaking

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M5 correction

• Required output
• Residual on sky tip-tilt
• lt 0.07 rms (goal 0.06) over the entire
  frequency range
• lt 0.004 rms for 9Hz to ? all peaks lt 2s
• Conditions
• WFS sampling 100Hz
• RON no noise
• WFS delay 10 ms
• RTC delay 1 ms
• Phase margin gt45 deg
• Modulus margin gt0.6
• Communication with RTC25 - 1200Hz

Remaining wave front correction ? adaptive mirror
with positioning system
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M4 Adaptive Unit

• Components
• Adaptive mirror, Positioning system,Mounting
  structure, Control system, Auxiliary Equipment
• Tasks correction of
• small amplitude residual tip-tilt
• high order wavefront (real-time)
• Atmosphere
• wind shake
• low spatial frequency telescope errors
• large amplitude low frequency tip-tilt
• lateral pupil position
• Telescope gravity
• Thermal load
• adapter tracking wobble run-out errors
• Nasmyth foci selection

Adaptive mirror
Positioning system (4 DoF)
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M4 positioning system requirements
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Adaptive mirror main requirements

• Fitting error 145 nm rms (goal 110)
• Temporal error 60 nm rms (goal 43)
• Tip-tilt after M4 1.3 mas _at_ 1 kHz WFS sampling
• Total stroke defined for worst seeing conditions
  (2.5arcsec seeing, 100 m outer scale)
• Optical quality, mass, power consumption, dynamic
  behavior, passive stability (lookup tables),
  environment, .
• High reliability (key element for E ELT)

under median seeing conditions
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Required tip-tilt correction after M4

• Incomming disturbance0.119 residual on sky
  rmsafter telescope M5 correction

• Conservative assumptions
• 10m/s wind speed _at_ 10 m
• Exponential wind profile
• No dome
• 30 safety margin in original data

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3 step disturbance correction
Telescope main axes control
Remaining tip tilt lt 1 rms
M5
Low frequency, high stroke
M4
High frequency, low stroke
1.3 mas residual rms error compatible with
diffraction limit in NIR
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Conclusions

• E-ELT will be an adaptive telescope, NIR
  diffraction limited
• In-built Field stabilization mirror
• In-built adaptive mirror
• Demanding requirements pushing state of the art
  technology
• Feasibility studies, conceptual and preliminary
  design, breadboarding and prototyping of critical
  components carried out by industry under ESO
  contracts

• 16h00 Armando Riccardi, 16h40 Daniele Gallieni
  E-ELT M4AU development at Microgate
• 16h20 Bruno Crépy, 17h20 Jean-Christophe Sinquin
  E-ELT M4AU development at CILAS
• 17h40 Javier Barriga E-ELT M5FU development
  at NTE

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c'est tout