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Performance of wave-front measurement Performance of wave-front measurement concepts for GLAO concepts for GLAO
M. NICOLLE1, T. FUSCO1, V. MICHAU1, G. ROUSSET1, J.-L. BEUZIT2
1ONERA - DOTA, Châtillon, France 2LAOG, Grenoble, France Mail: magali.nicolle@onera.fr
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OutlineOutline
• Problem statement,
• An analytical criterion for GLAO performance estimation,
• SO and LO performance analysis,
• Optimization of SO and LO measurement,
• Conclusions and future works.
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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Ground Layer turbulence measurement : Ground Layer turbulence measurement :
Altitude
PUP = 1 + 2 + 3 = 3 sol + 1
alt + 2alt +3
alt
0
D
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
GLAO: wide FOV seeing reducer;
Needs a uniform correction in FOV:
That ’s why we want to measure only the boundary layer,
A solution for that is to estimate:
We only can measure :
BUT available phases are:
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5 Wave-front sensing devices
Shack-Hartmann ?
Other ?
Pyramid ?
A triple problem :A triple problem :
Number ? Magnitude ?
Natural ? Artificial ?
Star Oriented ? Layer Oriented ? Other ?
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Guides Stars(available phases)
Wave-front measurement concept (measured phases)
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Tools for GLAO performance analysis :Tools for GLAO performance analysis :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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; 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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Wave-front measurement error:
Wave-front measurement Error :Wave-front measurement Error :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Phase to be estimated:
Measured phase:
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QC VS usual quality criterions for GLAO :QC VS usual quality criterions for GLAO :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Wave-front measurement error:
Conditions of the numerical simulation : Technical FoV : 8 arcmin; Seeing : 0.9 arcsec @ 0.5 µm; Turbulence profile : 60% in pupil plane, 40% in altitude; WFS : 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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Secondary Quality criterions on phase :Secondary Quality criterions on phase :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Phase to be estimated
Measured phase
Independent from WFMC
Phase to be measured
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QCQCquantize quantize characteristics:characteristics:
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
1./K
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Secondary Quality criterions on phase :Secondary Quality criterions on phase :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Phase to be estimated
Measured phase
Independent from WFMC
Phase to be measured
Star Oriented Layer Oriented
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QCQCWFMCWFMC for Star Oriented: for Star Oriented:
Introduction – Analytical criterion – SO & LO Optimization - ConclusionAnalytical criterion :
Criterion derivation for SO :
Photon Noise termDepends on: Flux per GS • Flux per GS (= flux per WFS)
• CCD Read-out noise
Detector Noise term:Depends on:
COMMANDPupil
1 WFS / GS
DM We measure:
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QCQCWFMCWFMC for Layer Oriented: for Layer Oriented:
DM
COMMANDPupil
1 WFS
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Phases weighted by GS flux 1 WFS only
Photon Noise termDepends on:
Total flux in FOV. •Total flux in FOV,• CCD Read-out noise.
Detector Noise termDepends on:
Turbulence related termDepends on:
• Total flux in FOV, • GS flux dispersion ,• Covariance of phase perturbations From one direction to another.
Analytical criterion :
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Performance analysis for SO / LO :Performance analysis for SO / LO :Conditions of the numerical simulation : Technical FoV : 8 arcmin; Seeing : 0.9 arcsec @ 0.5 µm; Turbulence profile : 60% in pupil plane, 40% in altitude; lWFS : 0.7 µm; s2
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.
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
4 GS ~30 GS
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Star Oriented Optimization:Star Oriented Optimization:We measure: That we can employ as we want.
We can consider :
Criterion derivation for OSO :
i optimal only if :
Linear Matricial equation to invert. Solution exists.
numerical coefficients to be optimized
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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Performance analysis for SO / LO :Performance analysis for SO / LO :Conditions of the numerical simulation : Technical FoV : 8 arcmin; Seeing : 0.9 arcsec @ 0.5 µm; Turbulence profile : 60% in pupil plane, 40% in altitude; lWFS : 0.7 µm; s2
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.
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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Layer Oriented Optimization:Layer Oriented Optimization:We measure only one integrated phase !
We can consider :
We can optimize it by attenuating optically some GS; We can account for the WFS SNR in the use of this phase measurement;
numerical coefficient to be optimized Optical attenuations to be optimized
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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Layer Oriented Optimization:Layer Oriented Optimization: Criterion derivation for OLO :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
analytical solution exists. optimization:
NON linear equation to invert. Multi-variable optimization.
i optimization:
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Analyse performance SO / LO :Analyse performance SO / LO :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
4 GS 30 GS
Galactic coordinates : (30, 0)8x8 arcmin FoV
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Conclusions …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:
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.
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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… … And future works :And future works :
GLAO:
Global optimization of
Complete Sky coverage study,
Scaling to ELT,
MCAO: Generalization to Multiple FOV concept,
Real data process (MAD results ?)
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
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Wave-front measurement Error :Wave-front measurement Error :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Wave-front measurement error:
Conditions of the numerical simulation : Technical FoV : 8 arcmin; Seeing : 0.9 arcsec @ 0.5 µm; Turbulence profile : 60% in pupil plane, 40% in altitude; WFS : 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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Splitting of QC:Splitting of QC:
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
QCQC
QCQCquantizequantize
QCQCWFMCWFMC
Saturation due to pupil footprints superimposition
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Secondary Quality criterions on phase :Secondary Quality criterions on phase :
Introduction – Analytical criterion – SO & LO Optimization - Conclusion
Phase to be estimated
Measured phase
Independent from WFMC
Phase to be measured
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