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

2. Summary of GLAO simulations @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’ -> 10’’)
EE x 2 in 0.2’’ pixel or Diffraction limited (NFM)
Visible (450 to 930 nm)
OWL – GLAO/MOAO
3-6 NGSs
Up to 6’ FOV or IFU
GLAO as such (WF imaging ?) or first stage of MOAO

3. Atmosphere - HawkI GL r0=0.11 m at 0.5μm 0: 3.25 ms θ0=1.7’’ L0= 25m
Turbulence Height (m)
Fraction of Cn2
0.0000
300.00
900.00
1800.0
4500.0
7100.0
11000.
12800.
14500.
16500. GL
r0=0.11 m at 0.5μm
0: 3.25 ms
θ0=1.7’’
L0= 25m

4. PSF estimation stars 8’

5. AO parameters Muse NFM Hawaii 2 RG (?) Parameter Value
Number of sub-apertures (linear) / LGS
32x32
Number of active sub-apertures / LGS
768
Active actuators
881
Number of LGS 4
Position of LGS
5.65’ off-axis (i.e. x=4’, y=4’)
Flux from LGS
84 photons / sub-aperture / frame
High order WFS frame rate
500 Hz
Temporal delay
2 frames pure delay
WFS CCD read-out noise
3 e- rms
Loop gain
0.4
Position of NGS
2.8’ off-axis (x=2’,y=2’)
Tip-tilt guide star flux
~ photons / sub-aperture / frame (K~10)
Tip-tilt frame-rate
100 Hz
Tip-tilt centroiding pixels
16x16
TT detector read-out noise
17 e- rms
Wavelength
2.2 μm
Seeing at 0.5 μm
0.94’’
Correlation time at 0.5 μm
3.25 ms
Hawaii 2 RG (?)

6. EE in 0.1’’ pixel
K Band
Y Band

7. 50% EE diameter
K Band
Y Band

8. FWHM (Gaussian fit)
K Band
Y Band

9. Different LGS config as previous slides
Number of TT stars
LGS locations
1 TT star
TT stars
4 TT star
Different LGS config as previous slides

10. Sub-aperture number (K band)

11. Single Rayleigh LGS
On Axis
R=1.4’
R=4’

12. Diamonds: seeing, stars: multi RLGS, crosses: Multi-Na LGS
4 Rayleigh LGS
Diamonds: seeing, stars: multi RLGS, crosses: Multi-Na LGS

13. 4 R LGS R-LGSs for GLAO as good as Na (or ~better) Cheap
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 ESO
New designs required (launch telescopes ? Beam transfer ?)…

14. 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” !

15. Muse wide field performance
Pixel size (arcseconds)
Muse WFM
On-axis and
0.5’ Off-axis
1.1’’ seeing

16. MUSE Narrow Field Mode on-axis : ~15% Median (0.65'') seeing
Strehl 650nm
on-axis : ~15%
Median (0.65'') seeing
Conditions
Without error budget!

17. Muse Narrow field mode No Error budget 100 nm WFE 150 nm WFE
See Hubin & al.
For more on MUSE

18. 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…

19. 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

20. OWL-GLAO Goal: Keep the same DM as in SCAO, (90x90 / 83x83)
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

21. OWL-GL: Radial averaged profiles
10m
30m
60m
100m
L0 effect like for seeing (R. Conan 03)

22. OWL GLAO (90x90), 0.5’’ seeing
6 NGS
3 NGS
10 ph /s /integ time

23. OWL GLAO (90x90), 50 mas, 0.8’’ Constellation edge
10 ph /s /integ time

24. 1.9' (radius), mag 16, transmission 20%,
GLAO vs seeing (100m) – 3 NGS K H J
1.9' (radius), mag 16, transmission 20%,
200 Hz, r0=0.15, 1m sub-apertures.
Cibola

25. MOAO – (Falcon like) 3 NGSH J
1.9' (radius), mag 16, transmission 20%,
200 Hz, r0=0.15, 1m sub-apertures.
Cibola

26. 1.9' (radius), mag 16, transmission 20%,
GLAO vs. MOAO
1.9' (radius), mag 16, transmission 20%,
200 Hz, r0=0.15, 1m sub-apertures.

27. 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

28. 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 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

30. Muse : Requirements Muse: Multi-Unit Spectroscopic Explorer 2 Modes:
24 4kx4k integral field spectrographs
Very deep field spectroscopy
2 Modes:
Wide Field Mode (WFM)
1’x1’ 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)
~10’’x10’’ 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)

31. Muse: The AO 4 x High order (32x32) SH WFSs 4 Sodium LGSs
high sky coverage (~60% at galactic poles, WFM)
2.5 – 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).

32. TT correction only ? – K-band