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Strehl Ratio estimation

Strehl Ratio estimation. SR from H band images High Strehl PSF -> fitting with Zernike modes. We suppose: No relevant loss of energy due to high modes (Z>36) . Check on residuals. Amoeba fit with First 36 Zernikes. Generation of DL PSF and SR meas as :

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Strehl Ratio estimation

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  1. StrehlRatioestimation

  2. SR from H band imagesHigh Strehl PSF ->fittingwithZernikemodes We suppose: No relevant loss ofenergy due to high modes (Z>36) Check on residuals Amoebafitwith First 36 Zernikes Generation ofDL PSF and SR measas: Peakfitted / PeakDL NO DEPENDENCE on FLUX estimation

  3. SR from H band imagesLow Strehl PSF: fittingwithtwogaussianditributions Haloenergy >> ringsenergy Point = meas Line = fit Line = residual Fitwith 2 gaussians Repeatedconsidering Different IRTC crops Total fluxestimation flux_im = (Measimage – fittedbias) Flux_imthresholdedto 0 flux = total(flux_im) Line = DL Line = meas SR DL generation and SR meaurement Relativerror on SR IRTC field in pixels psfDLgeneratedwithnominal FWHM and the energy = flux sr_meas = max(y-R[0])/max(psf_dl)

  4. Estimation from real-time data Marechal approximation: Wavefront error estimation: and: Correction residuals: • The optical gain of the pyramid WFS depends on the size of the PSF. • Since the reconstructor, R, is usually calibrated with a diffraction-limited source, the residual WF will be systematically under-estimated through the vector ! Since the gain (1/R) with high peak PSF is higher, when slopes resulting from low peak PSF are used with this lower value of R, the mirror surface error is under-estimated.

  5. Estimation from real-time data There is another reason that this method underestimates the WF error. The factor sigma(res) only estimates the WF error due to spatial modes whose order is less than or equal to the number of actuators used. The higher order modes in the residual error are not included in the WFS slopes. Marechal approximation: Wavefront error estimation: and: Correction residuals: • The optical gain of the pyramid WFS depends on the size of the PSF. • Since the reconstructor, R, is usually calibrated with a diffraction-limited source, the residual WF will be systematically under-estimated through the vector !

  6. Comparison

  7. 20091005_133216 MAG 8.5 ____ Acquired PSF ____ DLPsfwithsameflux H band StrehlRatios Expectedfromsimulations = 62 – 80 % Estimatedwithmirrorpositions = 81 % Estimated on IRTC image = 84+- 8 % [FWHM on IRTC = 41 mas] ClosedLoopparameters Bin = 1 (30x30) Freq = 1000 Hz Flux = 232 ph/subap/frame TT Modulation = +- 2 l/D N modes = 153Gain = 0.7

  8. 20091005_164935 FP3 MAG 10.7 ____ Acquired PSF ____ DLPsfwithsameflux H band StrehlRatios Expectedfromsimulations = 50 – 62 % Estimatedwithmirrorpositions = 55 % Estimated on IRTC image = 55 +- 7 % [FWHM on IRTC = 41 mas] ClosedLoopparameters Bin = 2 (15x15) Freq = 800 Hz Flux = 140 ph/subap/frame TT Modulation = +- 3 l/D N modes = 153Gain = 0.7

  9. 20091005_173152 FP5 MAG 12.4 ____ Acquired PSF ____ DLPsfwithsameflux H band StrehlRatios Expectedfromsimulations = 42 – 54 % Estimatedwithmirrorpositions = 47 % Estimated on IRTC image = 45 +- 5 % [FWHM on IRTC = 42 mas] ClosedLoopparameters Bin = 2 (15x15) Freq = 625 Hz Flux = 40 ph/subap/frame TT Modulation = +- 3 l/D N modes = 153Gain = 0.6

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