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Workshop Leiden 2005
Performance of wave-front measurement
concepts for GLAO
M. NICOLLE1, T. FUSCO1, V. MICHAU1, G. ROUSSET1, J.-L. BEUZIT2
- DOTA, Châtillon, France
2LAOG, Grenoble, France
1ONERA
Mail: [email protected]
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Outline
• Problem statement,
• An analytical criterion for GLAO performance estimation,
• SO and LO performance analysis,
Workshop Leiden 2005
• Optimization of SO and LO measurement,
• Conclusions and future works.
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Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Ground Layer turbulence measurement :
GLAO: wide FOV seeing reducer;
D
Altitude
Needs a uniform correction in FOV:
 That ’s why we want to measure only the boundary layer,
Workshop Leiden 2005
 A solution for that is to estimate:
fPUP = f1 + f2 + f3 = 3 jsol
+ j1alt + j2alt +j3alt
0
 We only can measure :
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 BUT available phases are:
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
A triple problem :
Star Oriented ?
Layer Oriented ?
Other ?
Wave-front measurement concept
(measured phases)
Shack-Hartmann ?
Workshop Leiden 2005
Number ? Magnitude ?
Guides Stars
(available phases)
Natural ? Artificial ?
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Wave-front sensing
devices
Pyramid ?
Other ?
Introduction
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Analytical criterion – SO & LO Optimization - Conclusion
Tools for GLAO performance analysis :
Two models have been used:
 Numerical model, for both study of Guides Stars impact and WFMC performance:
 Simulates uniform, random or Galactic-model based Guide Stars fields;
Workshop Leiden 2005
 Simulates Star Oriented and Layer Oriented WFMC;
 Complex turbulence profile;
 Decomposition of phases onto Zernike polynomials;
 Simulates photon and detector noises;
 Modal optimization;
 Computes long exposure PSF, encircled energy, residual phase variances.
Analytical model, for WFMC performance analysis:
 Based on an analytical criterion
 Considered variable: phase slopes as measured by Shack-Hartmann WFS
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Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
Wave-front measurement Error :
Phase to be estimated:
Workshop Leiden 2005
 Wave-front measurement error:
Measured phase:
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Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
QC VS usual quality criterions for GLAO :
 Wave-front measurement error:
Conditions of the numerical simulation :
Workshop Leiden 2005
 Technical FoV
: 8 arcmin;
 Seeing
: 0.9 arcsec @ 0.5 µm;
 Turbulence profile : 60% in pupil plane, 40% in altitude;
 lWFS
: 0.7 µm;
 Photon noise only
 GS integrated magnitude in R : 12.
 GS uniformly spread in FOV;
Phases measurement  Shack-Hartmann slopes.
FOV 8 arcmin wide,
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Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
Secondary Quality criterions on phase :
Phase to be estimated
Independent from WFMC
Workshop Leiden 2005
Phase to be measured
Measured phase
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Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
QCquantize characteristics:
Workshop Leiden 2005
 1./K
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Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
Secondary Quality criterions on phase :
Phase to be estimated
Independent from WFMC
Workshop Leiden 2005
Phase to be measured
Measured phase
Star Oriented
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Layer Oriented
Introduction
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Analytical criterion – SO & LO Optimization - Conclusion
Analytical criterion :
QCWFMC for Star Oriented:
DM
Pupil
Workshop Leiden 2005
1 WFS /
GS
We measure:
COMMAND
 Criterion derivation for SO :
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Photon Noise term
Depends on:
Flux per GS
Detector Noise term:
Depends on:
• Flux per GS (= flux per WFS)
• CCD Read-out noise
Introduction
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Analytical criterion – SO & LO Optimization - Conclusion
Analytical criterion :
QCWFMC for Layer Oriented:
DM
Pupil
COMMAND
Workshop Leiden 2005
1 WFS
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Phases weighted by GS flux
Turbulence related term
Depends on:
Photon Noise term
Depends on:
• Total flux in FOV,
• GS flux dispersion ,
• Covariance of phase perturbations
From one direction to another.
Total flux in FOV.
1 WFS only
Detector Noise term
Depends on:
•Total flux in FOV,
• CCD Read-out noise.
Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
Performance analysis for SO / LO :
Conditions of the numerical simulation :
Workshop Leiden 2005
 Technical FoV
: 8 arcmin;
 Seeing
: 0.9 arcsec @ 0.5 µm;
 Turbulence profile : 60% in pupil plane, 40% in altitude;
 lWFS
: 0.7 µm;
2
 s det
: 3 e- (when simulated);
 Galactic coordinates : lat = 30°, lon = 0°;
 Repartition of GS mag. simulated from Besançon Model;
 At least 4 GS in Technical FoV;
 Phases measurement  Shack-Hartmann slopes.
4 GS
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~30 GS
Introduction
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Analytical criterion – SO & LO Optimization -
Conclusion
Star Oriented Optimization:
We measure:
That we can employ as we want.
 We can consider :
numerical coefficients to be optimized
Workshop Leiden 2005
 Criterion derivation for OSO :
 hi optimal only if :
 Linear Matricial equation to invert.
 Solution exists.
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Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
Performance analysis for SO / LO :
Conditions of the numerical simulation :
Workshop Leiden 2005
 Technical FoV
: 8 arcmin;
 Seeing
: 0.9 arcsec @ 0.5 µm;
 Turbulence profile : 60% in pupil plane, 40% in altitude;
 lWFS
: 0.7 µm;
2
 s det
: 1 e- (when simulated);
 Galactic coordinates : lat = 30°, lon = 0°;
 Repartition of GS mag. simulated from Besançon Model;
 At least 4 GS in Technical FoV;
 Phases measurement  Shack-Hartmann slopes.
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Introduction
–
Analytical criterion – SO & LO Optimization -
Conclusion
Layer Oriented Optimization:
We measure only one integrated phase !
 We can optimize it by attenuating optically some GS;
 We can account for the WFS SNR in the use of this phase measurement;
Workshop Leiden 2005
 We can consider :
numerical coefficient to be optimized
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Optical attenuations to be optimized
Introduction
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Analytical criterion – SO & LO Optimization -
Conclusion
Layer Oriented Optimization:
 Criterion derivation for OLO :
h optimization:
Workshop Leiden 2005
li optimization:
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 analytical solution exists.
 NON linear equation to invert.
 Multi-variable optimization.
Introduction
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Analytical criterion – SO & LO Optimization -
Analyse performance SO / LO :
Workshop Leiden 2005
Galactic coordinates : (30, 0)
8x8 arcmin FoV
4 GS
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30 GS
Conclusion
Introduction
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Analytical criterion – SO & LO Optimization -
Conclusion
Conclusions …
Study of the influence of GS number and repartition on GLAO performance uniformity
Performance analysis for both SO and LO WFMC:
 Analytical modelization and definition of a quality criterion based on phase measurement
error for SO and LO WFMC,
 SO performance is mainly limited by Detector noise,
 LO performance is mainly limited by GS flux dispersion;
Optimisation of both SO and LO measurements:
Workshop Leiden 2005
 SO: numerical optimization
 LO: both numerical and optical optimizations;
 Identical performance of SO and LO in photon noise,
 Slight gain for LO in detector noise,
 Very small dependency of the errors with respect to GS number.
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Introduction
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Analytical criterion – SO & LO Optimization -
… And future works :
 GLAO:
Global optimization of
Complete Sky coverage study,
Scaling to ELT,
Workshop Leiden 2005
 MCAO: Generalization to Multiple FOV concept,
 Real data process (MAD results ?)
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Conclusion
Introduction
–
Analytical criterion – SO & LO Optimization - Conclusion
Wave-front measurement Error :
 Wave-front measurement error:
Conditions of the numerical simulation :
Workshop Leiden 2005
 Technical FoV
: 8 arcmin;
 Seeing
: 0.9 arcsec @ 0.5 µm;
 Turbulence profile : 60% in pupil plane, 40% in altitude;
 lWFS
: 0.7 µm;
 Photon noise only
 GS integrated magnitude in R : 12.
 GS uniformly spread in FOV;
Phases measurement  Shack-Hartmann slopes.
FOV 8 arcmin wide,
37 guide stars
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Introduction
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Analytical criterion – SO & LO Optimization - Conclusion
Splitting of QC:
QC
QCWFMC
QCquantize
Workshop Leiden 2005
Saturation due to
pupil footprints
superimposition
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Introduction
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Analytical criterion – SO & LO Optimization - Conclusion
Secondary Quality criterions on phase :
Phase to be estimated
Independent from WFMC
Workshop Leiden 2005
Phase to be measured
Measured phase
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