GLAO simulations at ESO

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• GLAO simulations at ESO
• M. Le Louarn, Ch. Verinaud,
• V. Korkiakoski, N. Hubin
• European Southern Observatory

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Summary of GLAO simulations _at_ESO

• Hawk-I (GRAAL)
• Large field (8)
• Near IR (1-2.5 µm)
• Improved seeing, improved energy in pixel
• 4 Na-LGS
• MUSE (GALACSI)
• Moderate field (1 -gt 10)
• EE x 2 in 0.2 pixel or Diffraction limited
  (NFM)
• Visible (450 to 930 nm)
• 4 Na-LGS
• OWL GLAO/MOAO
• 3-6 NGSs
• Up to 6 FOV or IFU
• GLAO as such (WF imaging ?) or first stage of MOAO

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Atmosphere - HawkI
GL
r00.11 m at 0.5µm ?0 3.25 ms ?01.7 L0 25m
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PSF estimation stars
8
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AO parameters
Muse NFM
Hawaii 2 RG (?)
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EE in 0.1 pixel
K Band
Y Band
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50 EE diameter
K Band
Y Band
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FWHM (Gaussian fit)
K Band
Y Band
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Number of TT stars
Peaks _at_ LGS locations
1 TT star
4 TT star
Peaks _at_ TT stars
Different LGS config as previous slides
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Sub-aperture number (K band)
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Single Rayleigh LGS
On Axis
R1.4
R4
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4 Rayleigh LGS
Diamonds seeing, stars multi RLGS, crosses
Multi-Na LGS
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4 R LGS

• R-LGSs for GLAO as good as Na (or better)
• Decrease height to increase homogeneity
• Focusing problems ? (H a few km) ?
• Spot elongation reduced (enough ?) by narrow
  gating
• Power req should be investigated
• Synchronization with WFSs must be dealt with
• Cheap
• No synergy with other LGS efforts _at_ ESO
• New designs required (launch telescopes ? Beam
  transfer ?)

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Hawk-I GLAO conclusions

• Conventional GLAO
• Gain in FWHM, telescope time (EE)
• Cn2 is a big unknown
• TT sensing scheme is still under study
• Hawaii 2 RG on-chip TT sensing seems promising.
• Use of narrow band filters might make things
  complicated
• Pick-off arms for TT are ugly !

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Muse wide field performance
Muse WFM On-axis and 0.5 Off-axis
1.1 seeing
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MUSE Narrow Field Mode
?Strehl Ratio _at_ 650nm on-axis 15
Median (0.65'') seeing Conditions Without error
budget!
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Muse Narrow field mode
No Error budget
100 nm WFE
150 nm WFE
See Hubin al. For more on MUSE
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Muse GLAO conclusions

• Muse explores a slightly different parameter
  space than conventional GLAO
• Visible light, high Strehl mode is challenging
• First attempt at Cone effect correction
• Drives ASM requirements laser power req
• Calibration issues on ASM

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Simulations for ELTs

• Averaging control algorithm
• Average WFS measurements from N (3-6) stars
• Use much smaller control matrix
• Faster, less memory (good for simulations !)
• But not especially clever algorithm
• GLAO highly parallelizable for simulations
• Atmospheric propagations independent
• Each WFS runs separately
• On small (single star) matrix-vector
  multiplication
• Drawback usually want stability in the field ?
  many PSFs to compute ? many (large) FFTs (but
  can be //-ized)
• Also used Cibola (Analytic, B. Ellerbroek) for
  rapid perf. estimation

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OWL-GLAO

• Goal
• Improved seeing over 6 FOV
• K-Band
• Ground layer correction scheme
• Keep the same DM as in SCAO, (90x90 / 83x83)
• Use 3-6 Shack-Hartmann WFSs
• SH for GLAO Linearity, no RON
• NGSs only for this study
• Located at the edges of 6 FOV
• Performance estimation at FOV center

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OWL-GL Radial averaged profiles
10m
30m
60m
100m
L0 effect like for seeing (R. Conan 03)
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OWL GLAO (90x90), 0.5 seeing
6 NGS
3 NGS
10 ph /s /integ time
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OWL GLAO (90x90), 50 mas, 0.8
Constellation edge
10 ph /s /integ time
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GLAO vs seeing (100m) 3 NGS
K
H
J
1.9' (radius), mag 16, transmission 20, 200 Hz,
r00.15, 1m sub-apertures.
Cibola
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MOAO (Falcon like) 3 NGS
K
H
J
1.9' (radius), mag 16, transmission 20, 200 Hz,
r00.15, 1m sub-apertures.
Cibola
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GLAO vs. MOAO
1.9' (radius), mag 16, transmission 20, 200 Hz,
r00.15, 1m sub-apertures.
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OWL GLAO conclusions

• Woofer for MOAO seems mandatory (stroke issues of
  MEMs)
• MOAO provides better performance in small FOV
• Homogeneity of MOAO (in different IFUs must be
  studied)
• In GLAO, better PSF uniformity than on 8m
• Beam overlap gets better
• Performance not necessarily much better
• GLAO might constraints site for ELT

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Conclusions

• Cn2 properties largely unknown (!)
• Statistics
• Beginning vs. middle of night vs. end of night
• Variations within one night
• Seasonal variations
• Correlations
• Good seeing vs. bad seeing
• With wind direction (especially in Paranal)
• With other meteo Parameters
• SLODAR MASS DIMM running _at_ Paranal
• Balloon data unreliable for Paranal (site has
  changed significantly since campaign)
• NGS case effect of in-equal NGS brightness
• ? Optim modal gains being implemented for GLAO

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Muse Requirements

• Muse Multi-Unit Spectroscopic Explorer
• 24 4kx4k integral field spectrographs
• Very deep field spectroscopy
• 2 Modes
• Wide Field Mode (WFM)
• 1x1 FOV
• from 450 nm to 930 nm
• 2 x EE of seeing in 0.2 pixel
• 1.1 seeing (80h integration times)
• Narrow Field Mode (NFM)
• 10x10 FOV
• Diffraction limited (Sr(650nm)10)
• 25 mas pixels (?).
• 0.65 seeing
• Absolutely no scattered light in science field
  (WFM)
• High sky coverage (towards poles)

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Muse The AO

• 4 x High order (32x32) SH WFSs
• 4 Sodium LGSs
• high sky coverage (60 at galactic poles, WFM)
• 2.5 5.0 106 ph/s/m2
• Single high order DM conjugated to ground
• Ground-Layer AO (Rigaut 2002)
• 2 designs with or without Adaptive secondary
• Visible (WFM) or IR (NFM) TT sensor
• Search field 3 (diam, WFM), 10 (diam, NFM)
• Repositionning of the LGSs to switch from WFM to
  NFM (cone effect correction).

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TT correction only ? K-band