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

2. 4 Advanced Tomography with Laser for AO systems 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 ATLAS LTAO

3. 4 Advanced Tomography with Laser for AO systems General Requirements for ATLAS 4m 1m 250mm InstrumentM6 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. 4 Advanced Tomography with Laser for AO systems ATLAS performance requirements

5. 4 Advanced Tomography with Laser for AO systems 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 »)

6. 4 Advanced Tomography with Laser for AO systems 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

7. 4 Advanced Tomography with Laser for AO systems LGS configurations (number & positions) Optimum Baseline 6 LGS Baseline ~ 4.3’  No LGS beam overlap  NGS patrol FoV Ø = 2’  3D parameter space (number position flux)  Performance with 4 LGS << 5 LGS << 6 LGS  Small evolution with LGS FoV diameter Patrol Fov Ø = 2 arcmin

8. 4 Advanced Tomography with Laser for AO systems 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) 8 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)

9. 4 Advanced Tomography with Laser for AO systems 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

10. 4 Advanced Tomography with Laser for AO systems LGS WFS concept 3 concepts are studying SH WFS (various config) YAW Pyramid choice of a baseline SH 12x12 YAWPyr 4Q Noise performance GoodPoorGood Gain variations GoodBad Detector availability Not yetCOST Sensitivity to RON HighLow Baseline for phase A : SH 12x12 Options (still under study) : 4Q & YAW

11. 4 Advanced Tomography with Laser for AO systems 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

12. 4 Advanced Tomography with Laser for AO systems 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

13. 4 Advanced Tomography with Laser for AO systems Tomographic reconstruction Altitude evolution per layer Strength evolution per layer Initial Cn² profile  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 !

14. 4 Advanced Tomography with Laser for AO systems Laser Guide Stars error budget

15. 4 Advanced Tomography with Laser for AO systems Requirements and Strategy PERTURBATION REQUIREMENTS  Strong WindShake (WS): 280 mas rms  Turbulence : below WS/10 (in rms) On Tip/Tilt/Focus Int KALMAN Low magnitude GS Low signal rejection 500Hz STRATEGY  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)

16. 4 Advanced Tomography with Laser for AO systems Sky Coverage results Nominal (Lo = 25m) Pessimistic (Lo = 50m) Close to 100 % SC @ 60° Around 50 % SC @ Galactic pole

17. 4 Advanced Tomography with Laser for AO systems Trade-off / possible simplifications Main constraint : deal with the telescope 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 !!!!!!!!!!!

18. 4 Advanced Tomography with Laser for AO systems Expected Performance Optimization 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

19. 4 Advanced Tomography with Laser for AO systems Expected Performance Comparison with other AO systems AO systemsSR on axisSky Coverage @ Galactic pole SCAO Mag < 11 Mag < 12 Mag < 13.5 70 % 55 % 35 % << 1 % (15” FoV) < 1 % (20” FoV) 1 % (30” FoV) GLAO< 1 %100 % MCAO46 % (average perf. over 53”x53”) ~ 50 % LTAO55 %~ 50 %

20. 4 Advanced Tomography with Laser for AO systems 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 %

21. 4 Advanced Tomography with Laser for AO systems ATLAS design : summary 6 LGS in 4.2 arcmin Ø (launch from M1 side) SH WFS 84x84 sub-aperture 12x12 pixels per sub-aperture Sampling freq: 500 Hz LGS / NGS separation with mirrors only Pupil stabilisation by ATLAS rotation LGS fix w.r.t telescope referential 2 arcmin natural guide star FoV Patrol foV : 30”  2’ Ø Scientific FoV : 30”  1’ Ø 2 low order NGS WFS 2x2 SH-WFS Pixel size : 15 mas 500 Hz (windshake correction) IR band (H-Ks) with ADC Internal DM for “MOAO-like” correction (using LGS tomographic data) 1 high order NGS WFS 84x84 sub-apertures From 500 Hz (SCAO case)  0.1 Hz (truth sensor) VIS band (with ADC) One LGS arm With VCM PERF (K band on axis) : 55 % SC (in H-Ks) : 50 % @ galactic pole Potential issue : Size of M6 !!!

22. 4 Advanced Tomography with Laser for AO systems Atmospheric dispersion 1600 – 1800 nm  30 mas (60°) / 10 mas (30°) 1500 – 1800 nm  60 mas (60°) / 20 mas (30°)