Adaptive Optics at the Max Planck Institute for Astronomy

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Adaptive Optics at theMax Planck Institute for
Astronomy
Stefan HipplerMarkus Feldt Robert Weiß Elena
Puga Antolin David Butler Max-Planck- Institut
für Astronomie (MPIA) Heidelberg Germany
September 1993 Trapezium with MAGIC and CHARM. M.
McCaughrean and J.R. Stauffer, AJ 108 (1994).
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Outline of this talk

• The principle of Adaptive Optics.
• The Earths atmosphere.
• Current restrictions of Adaptive Optics systems.
• New techniques, new ideas.
• MPIAs future contributions.
• Whats next.

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The Principle of Adaptive Optics - Basics
Plane wavefront Turbulent atmosphere Distorted
image
Plane wavefront Turbulent atmosphere Deformable
mirror compensates the atmosphere Perfect image
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The Principle of Adaptive Optics - Example

• Closed Loop
  Open Loop

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The Principle of Adaptive Optics - Sketch
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The Principle of Adaptive Optics - ALFA Bench
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The Principle of Adaptive Optics -ALFA/OMEGA
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The Principle of Adaptive Optics - Summary
Turbulence Phase Distortions. Phase
Distortions Blurring Blurring Telescope
Resolution Order Of Magnitude Worse ... The
goal of Adaptive Optics is to overcome these
limitations!
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The Earths Atmosphere - Structure
Kolmogorov law of turbulence
Dn Index Structure Function
Cn2 Index Structure Coefficient
n refractive indexr 3D position? 3D
separationlt...gt ensemble average
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The Earths Atmosphere - Parameters / 1
Fried parameter
r0 characterizes the Seeing at a particular
wavelength Seeing FWHM ?/ r0 Seeing in
V-band (550 nm) 1 -gt r0 8.8 cm r0 scales
with the 6/5 power of wavelength -gt r0 at 2.2?m
46 cm -gt Seeing in K-band 0.76 (Seeing scales
with the 1/5 power of wavelength) r0 scales with
the -3/5 power of airmass (D/ r0)2 defines the
number of sub-apertures for wavefront sensors
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The Earths Atmosphere - Parameters / 2
Isoplanatic angle (or patch) ?0 0.3 r0 / heff
?0 characterizes the field of view that a
classical AO system can compensate.
Greenwood time delay (Taylor approximation)t0
0.3 r0 / veff
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The Earths Atmosphere - Parameters / 2
Calar Alto SCIDAR campaign September 2000
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Measuring Cn2(h) with SCIDAR
?
Rocca et al. 1974, Tallon 1989, Avila et al. 1997
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h
hgs
d1? ( h hgs )
Scintillation
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The MPIA-LBTSCIDAR Project

• AO Science Data
• Processing
• Seeing Measurements
• Atmosphere Diagnostics
• Flexible Scheduling
• In-kind contribution, 100 TDM.

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Current restrictions of AO systems Sky coverage

• Requirement bright guide star within isoplanatic
  angle.
• Example ALFAs current limit mV14.5 (20) gt
  Sky coverage 0.01
• Solutions
• Infrared Wavefront Sensor (Infrared AO!)
• Sky coverage 0.2-0.6 for embedded galactic
  sources, Star Formation Research!
• Artificial guide star
• Sky coverage 1.0 (without tip-tilt and focus
  compensation!)
• Multi-conjugate (multi layer) AO Sky coverage
  depends on telescope size, isoplanatic angle up
  to 3

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Pyramid Wavefront Sensor - Sketch
Foucault-like Wavefront Sensor Ragazzoni et al.
1995
MPIA replace CCD by near-infrared detector
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Pyramid Wavefront Sensor - Demo
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Good IR-WFS target S106
ALFA in active optics mode! Resolution 0.35
mV21 mK5.5
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Current restrictions of AO systems Sky coverage

• Requirement bright guide star within isoplanatic
  angle.
• Example ALFAs current limit mV14.5 (20) gt
  Sky coverage 0.01
• Solutions
• Infrared Wavefront Sensor (Infrared AO!)
• Sky coverage 0.2-0.6 for embedded galactic
  sources, Star Formation Research!
• Artificial guide star
• Sky coverage 1.0 (without tip-tilt and focus
  compensation!)
• Multi-conjugate (multi layer) AO Sky coverage
  depends on telescope size, isoplanatic angle up
  to 3

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VLT LGSF Overview
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VLT Laser Guide Star FacilityESO, MPE, MPIA

• Mission give the ESO AO systems (NAOSCONICA,
  SINFONI) on UT4 an artificial laser guide star
  (LGS), to boost their sky coverage and science
  throughput.
• Present LGS-AO is being implemented on all large
  (?8m) telescopes. Keck II is likely to be the
  first one this year. Gemini, LBT, Subaru to
  follow. 40 K-Strehl demonstrated at Lick Obs.,
  20 K-Strehl demonstrated with ALFA.
• Future Multiple LGS promise full sky coverage
  through Turbulence Tomography

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LGSF on the VLT Quick Look

• 4 subsystems
• Laser and Laser Room
• Beam relay (fiber modules)
• Launch Telescope diagnostics
• LIDAR Facility (ALFA/LIDAR)

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Laser Beam Relay using a single mode fiber module

• Allows diffraction limited beam relay
• Flexible, compact, better than mirrors
• Non linear effects due to high power
  densities (up to 25 MW/cm2)
• Input beam matching and alignment critical,
  servoed

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PARSEC Laser Choice

• Paranal Artificial Reference Source for Extended
  Coverage
• Original ESO proposal was to combine two 6.5W CW
  laser modules. ESO Messenger No. 99,
  December 1999
• This concept (backup solution) is an ALFA
  modification tested at Calar Alto. ESO
  Messenger No. 100, July 2000
• ESO concept moved to backup solution.
• MPE/MPIA propose new MOPA (Master Oscillator
  Power Amplifier) laser concept, better
  performing, more stable CW dye laser (October
  2000).
• MPE/MPIA PARSEC HAS BEEN ADOPTED AS BASELINE
  CHOICE gt10W CW output power (goal 15
  W), solid state pump lasers.
• MPIA contribution 600 TDM, 2 man-years return
  8 nights with LGS-AO instruments!

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PARSEC - Sketch
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Current restrictions of AO systems Sky coverage

• Requirement bright guide star within isoplanatic
  angle.
• Example ALFAs current limit mV14.5 (20) gt
  Sky coverage 0.01
• Solutions
• Infrared Wavefront Sensor (Infrared AO!)
• Sky coverage 0.2-0.6 for embedded galactic
  sources, Star Formation Research!
• Artificial guide star
• Sky coverage 1.0 (without tip-tilt and focus
  compensation!)
• Multi-conjugate (multi layer) AO Sky coverage
  depends on telescope size, isoplanatic angle up
  to 3

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Current restrictions of AO systems Compensated
Field of View
Wish Make Compensated Field of View infinite
(get rid of the atmosphere!) Solution Increas
ing of the isoplanatic angle with Multi-conjugate
adaptive optics Atmospheric Tomography.
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Atmospheric Tomography
Ragazzoni et al., Nature 403, 2000
Configuration
Pupil images
Calculated wavefront map of central star and
difference of ref. stars to central star
The intensity distribution on each individual
defocused pupil is given by a linear combination
of the wavefront perturbation contributions of
each single turbulent layer.
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AO for ELTs Research and Training Network

• Extremely Large Telescope (ELT) Projects
• 30 m CELT (California ELT)
• the 30-50 m MAXAT (MAXimum Aperture Telescope)
• the 30-m ELT (McDonald Observatory)
• Swedish 50-m Telescope (Lund Observatory)
• 100 m OWL (ESO Overwhelmingly Large Telescope)

• High angular resolution (V-band 1.4 mas).
• Huge photon gathering capability (V38).

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Resolution Comparison
0.6 arcsec
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MPIAs role in the AO-ELT network
Primary goal investigate Natural Guide Star
(NGS) and Laser Guide Star (LGS) tomography
methods coupled with multi-conjugate AO.
Technology deformable mirrors (DM) with about
500000 actuators, e.g. MEMS micro
mirrors. cophasing of 1000-2000 mirrors with
accuracy compatible with AO in the visible. Study
of novel techniques of on-sky segment phasing
using AO wavefront sensors to minimize the loss
of telescope time. MPIA contribution and funding
from EU commission Man-power and infrastructure
from MPIA, 340 TDM from EU (2 postdocs).Turbulenc
e simulator with ferroelectric LCD spatial light
modulator. Simulations to find best MCAO
configuration for ELTs. Side project MCAO-demons
trator for the VLT.
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Members of the AO-ELT network

• European Southern Observatory (ESO), Germany (N.
  Hubin)
• Osservatorio Astrofisico di Arcetri (OAA), Italy
  (S. Esposito)
• Osservatorio Astronomico di Padova (OADP), Italy
  (R. Ragazzoni)
• Office National dEtudes et de Recherches
  Aerospatiales (ONERA), France (G. Rousset)
• MPIA (S. Hippler)
• Observatoire de Marseille (OM), France (M.
  Ferrari)
• Gran Telescopio Canarias (GRANTECAN), Spain (N.
  Devaney)
• Associated partner Lund Observatoy Sweden
• Total Network Budget from EU commission 1.4 M.

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Whats next?