GLAO simulations at ESOGLAO simulations at ESO

M. Le Louarn, Ch. Verinaud,

V. Korkiakoski, N. Hubin

European Southern Observatory

Summary of GLAO simulations @ESOSummary 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) 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

Atmosphere - HawkIAtmosphere - HawkITurbulence Height (m) Fraction of Cn2

0.0000 0.334611

300.00 0.223074

900.00 0.111537

1800.0 0.09040635

4500.0 0.079603013

7100.0 0.05155671

11000. 0.04498746

12800. 0.0339061

14500. 0.0191147

16500. 0.0112030

r0=0.11 m at 0.5μm0: 3.25 msθ0=1.7’’L0= 25m

GL

PSF estimation starsPSF estimation stars

8’

AO parametersAO parameters

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 ~115000 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

Muse NFM

Hawaii 2 RG (?)

EE in 0.1’’ pixelEE in 0.1’’ pixel

Y Band

K Band

50% EE diameter50% EE diameter

Y Band

K Band

FWHM (Gaussian fit)FWHM (Gaussian fit)

Y Band

K Band

Number of TT stars Number of TT stars

1 TT star 4 TT star

Peaks @ LGS locations

Peaks @ TT stars

Different LGS config as previous slidesDifferent LGS config as previous slides

Sub-aperture number (K band)Sub-aperture number (K band)

Single Rayleigh LGSSingle Rayleigh LGS

On Axis

R=1.4’

R=4’

4 Rayleigh LGS4 Rayleigh LGS

Diamonds: seeing, stars: multi RLGS, crosses: Multi-Na LGS

4 R LGS4 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 @ ESO

New designs required (launch telescopes ? Beam transfer ?)…

Hawk-I GLAO conclusionsHawk-I GLAO conclusions

“Conventional GLAO” Gain in FWHM, telescope time (EE) Cn

2 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” !

Muse wide field performanceMuse wide field performance

Muse WFMOn-axis and 0.5’ Off-axis

1.1’’ seeing

Pixel size (arcseconds)

MUSE Narrow Field ModeMUSE Narrow Field Mode

Median (0.65'') seeing ConditionsWithout error budget!

Strehl Ratio @ 650nm

on-axis : ~15%

Muse Narrow field modeMuse Narrow field mode

No Error budget

100 nm WFE

150 nm WFE

See Hubin & al.For more on MUSE

Muse GLAO conclusionsMuse 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…

Simulations for ELTsSimulations 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

OWL-GLAOOWL-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

OWL-GL: Radial averaged profilesOWL-GL: Radial averaged profiles

L0 effect like for seeing (R. Conan 03)

10m

60m

30m

100m

OWL GLAO (90x90), 0.5’’ seeingOWL GLAO (90x90), 0.5’’ seeing

10 ph /s /integ time

6 NGS

3 NGS

OWL GLAO (90x90), 50 mas, 0.8’’OWL GLAO (90x90), 50 mas, 0.8’’

10 ph /s /integ time

Constellation edge

GLAO vs seeing (100m) – 3 NGSGLAO vs seeing (100m) – 3 NGS

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

K

H

J

MOAO – (Falcon like) 3 NGSMOAO – (Falcon like) 3 NGS

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

K

H

J

GLAO vs. MOAOGLAO vs. MOAO

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

OWL GLAO conclusionsOWL 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

ConclusionsConclusions

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 @ 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

Muse : RequirementsMuse : Requirements Muse: Multi-Unit Spectroscopic Explorer

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)

Muse: The AOMuse: 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).

TT correction only ? – K-bandTT correction only ? – K-band