ATLAS The LTAO module for the E-ELT Thierry Fusco ONERA / DOTA On behalf of the ATLAS consortium

1. Advanced Tomography with Laser for AO systems ATLAS The LTAO module for the E-ELT Thierry Fusco ONERA / DOTA On behalf of the ATLAS consortium

2. LTAO ATLAS The ATLAS project • “Advanced Tomography with Laser for Ao Systems” • Institute : ONERA, GEPI, LESIA • Duration : 16 months in 2 phases • Phase 1 : 7 months (already done) • Phase 2 : 9 months • Associated scientific instruments • HARMONI, • METIS, • SIMPLE, Other potential users • MICADO, OPTIMOS

3. 1m M6 Instrument 4m 250mm General Requirements for ATLAS • Geometry • ATLAS is a 4m diameter, 1m thick module. • Nasmyth focal plane is located inside ATLAS • Mass • ATLAS maximum mass is 2.5 tons (1.5 tons for the rotating structure plus 1 Ton for the supporting structure) focal plane Field derotation provided by ATLAS rotation

4. ATLAS Error budget • Specification : 50 (70%) @ K => 290 (210) nm rms • LGS : 260 nm rms (goal = 170 nm rms) • high order correction through tomographic process • NGS : 125 nm rms (2 mas rms for TT) • Fast tip-tilt correction (telescope windshake + turbulence) • Slow measurement of high order modes (« truth sensor »)

5. Laser Guide Stars error budget • Deformable optics:M4 and M5 already “defined” – no possible optimization • LGS number and positions • LGS WFS design • Control: • Tomographic reconstruction • Temporal effects • RTC design

6. LGS configurations (number & positions) • 6 LGS • Baseline ~ 4.3’ •  No LGS beam overlap •  NGS patrol FoV Ø = 2’ Patrol Fov Ø = 2 arcmin Optimum Baseline • 3D parameter space (number position flux) • Performance with 4 LGS << 5 LGS << 6 LGS • Small evolution with LGS FoV diameter

7. LGS : choice of a launching scheme Fratricide effects Launch behind M2 • Huge impact for some subapertures • Rayleigh signal >> sodium one • Useless sub-apertures • Evolve with time (pupil rotation) • Impact in nm rm ~ a few tens of nm rms to be consolidated • Contamination of scientific instruments (HARMONI) Launch from M1 side • No fratricide effects But : • Laser reconfiguration every TBC min/hours to avoid beam crosses • loop has to be open at these moments for TBC min(to be consolidated) 8

8. LGS : choice of a launching scheme Spot elongation and noise propagation • Spot elongation and noise propagation E2E simulation . Telescope = 21m . Scaling factors 6 LGS position : 1 min ring Representative of 42 m Tomographic performance M1 ≡ M2 Even a small gain from a pure performance point of view ! More uniform propagation onto modes ! 9

9. LGS WFS concept • 3 concepts are studying • SH WFS (various config) • YAW • Pyramid • choice of a baseline Baseline for phase A : SH 12x12 Options (still under study) : 4Q & YAW

10. Number of photons per sub-ap • Assumption : SH-WFS 12x12 pixels Noise propagation elongated < 2 x symmetric Loop filtering => attenuation factor of 1.5 Sampling frequency : 500 Hz

11. Tomographic reconstruction • P = Turbulent layer altitudes • & GS positions • M = WFS/DM model (IM) • direct model • Critical parameters ! • Turbulent layer strength • Regularisation term • Less critical • WFS noise model • Regularisation term • Less critical

12. Tomographic reconstruction Altitude evolution per layer Initial Cn² profile Strength evolution per layer • Accurate knowledge on layer position is required • especially for highest layer ( > 5 km) • knowledge @ ± 250 m or less • Cn² strength is less an issue Need of :  Good Cn² profiler & identification procedure  More data & more analysis !

13. Laser Guide Stars error budget

14. Requirements and Strategy STRATEGY REQUIREMENTS On Tip/Tilt/Focus Int PERTURBATION KALMAN • Strong WindShake (WS): 280 mas rms • Turbulence : below WS/10 (in rms) 500Hz Low magnitude GS Low signal rejection • Control optimization : Kalman Filter @ 500Hz • Use of 2 NGS to perform tomography when there is no bright & close NGS • Increase sky coverage • Optimization of the WFS spot size and energy • ADC (H & Ks bands) • Dedicated local DM • use of LGS data • open loop correction (a la MOAO)

15. Sky Coverage results Pessimistic (Lo = 50m) Nominal (Lo = 25m) Close to 100 % SC @ 60° Around 50 % SC @ Galactic pole

16. Trade-off / possible simplifications • Main constraint : deal with thetelescope windshake • at least 500 Hz of sampling frequency • Turbulence only required 100 to 200 Hz • If the telescope windshake is reduced at the level of the turbulence • no more need of μDM • probably no more need of ADC • EXTREME SIMPLIFICATION OF THE NGS DESIGN • HIGHLY DEPENDS ON THE OUTER SCALE !!!!!!!!!!!

17. Expected PerformanceOptimization area Possibility to “play” with the performance optimisation area -> best performance on axis -> optimisation in a given FoV It just requires a matrix modification in the RTC

18. Expected Performance Comparison with other AO systems

19. ATLAS performance : 100% SC • Use of the “telescope” NGS for windshake estimation • between 200 and 350 nm rms (assuming a 25 m outer scale and a 0.71 arcsec seeing). • This roughly leads to a final ATLAS performance in K band (depending on the GS position from 5 -> 10 arcmin): SR = 0.6->0.5 %, FWHM = 15.5->16.9 mas, Jitter = 3.9->5.6 mas • This value drops to SR = 0.4->0.2 %, FWHM = 20.9->33.1 mas, Jitter = 8.4->12.7 mas • Use of 1 NGS magnitude 19 (in the patrol FoV [2’ Ø]) • 87 % SC @ galactic pole • 98.3 % SC for the whole sky • Can be used for WS correction Between 4 mas and 12 mas rms for TT Between 95 and 200 nm rms of defocus SR : a few  few tens of %