1. 1 MCAO at CfAO meeting M. Le Louarn CfAO - UC Santa Cruz Nov. 22 2000

2. Goal of MCAO modeling Can one use 1 NGS measuring 5 modes instead of 3 NGS measuring TT ? –Limiting magnitude with NGS ? –Sky coverage ? Astrophysical implications of MCAO ELTs: Is it possible to use N LGS and only 1DM (closed loop problem ?) for correction in the visible ? Effect of spot elongation on MCAO […] AO engineering modelling (engineering tolerences) Lasers ? NGS - MCAO ? Probably not because of low SC, but can use a lot of faint stars (?) Effect of the NGS star distribution (no perfect triangles) MCAO: smaller SC than with single NGS AO. –JPV: MCAO SC on HST targets -> MCAO CoDR

3. MCAO Modeling Full numerical Monte Carlo Simulation –3 DMs, 5 LGS, 7 atmospheric layers (~ Gemini) –13x13 SH for each LGS (with SH spot speckles) –3x3 SH for 1 NGS (instead of 3 TT NGS @ Gemini) –Least-squares inversion of IM (SVD) –Closed loop, obtain PSF anywhere in the FOV Analytic covariance code (Tokovinin et al.) –Covariances of Zernikes computed for measurements & reconstructions –Knowledge of C n 2 profile –Optimal estimation of the correction –Open loop –Obtain residual WF error anywhere in the FOV

5. Analytic vs. Numerical Black: Analytic & Numerical isoplanatism, Red: Numerical MCAO, Blue: Analytical MCAO

6. H Band

7. J Band

8. What could go wrong in simulations ? Atmosphere is not as simulated: –There are many turbulent layers, almost continuous profile, outer scale L0 -> effect on high altitude DM density ? –Strong turbulence profile variations in closed loop –Propagation effects –Non-Kolmogorov turbulence, Non-Taylor turbulence Na layer / LGS properties –Height variations: difficult to put in but can get an estimate –Spot elongation (  ELTs): can be simulated for 8m tel. –Lasers for MCAO Hardware issues: AO simulation validity ??? –High order aberrations in mirrors, DM mis-registration... –MCAO waffle modes on real DMs –DM hysteresis effects –edge effects –laser launch telescope jitter -> total least squares

9. C n 2 profiles

11. Lab/sky tests Atmosphere: –Continuous turbulence (not repeatable ?) + thin layers (?) Turbulence generator Phase screens –Propagation effects Phase screens –Non-Kolmogorov screens Na Layer: –Studies on LGS AO systems ? –Site monitoring (Na profile measurements) Lab MCAO system: –control algorithm testing, system tolerances –DM hysteresis AO Systems: DO NGS AO system work as modelled ? (Lick AO, Keck, Pueo…)

12. Why lab / sky tests ? Lab test = acceptance test of the MCAO system: saves money Have you thought of everything ? 1DM LGS AO system: –Na Layer saturation checked –Engineering for Keck, VLT,... Sky testing / site monitoring -> Do we have the right parameters ? Ragazzoni test on the sky did it bring anything good ?