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The on-sky NGS/LGS MOAO demonstrator for EAGLE

The on-sky NGS/LGS MOAO demonstrator for EAGLE. Tim Morris Durham University. Talk overview. MOAO with EAGLE CANARY concept Optomechanical design Subsystem performance System performance System calibration tasks. MOAO with EAGLE. With the current baseline design, EAGLE will:

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The on-sky NGS/LGS MOAO demonstrator for EAGLE

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  1. The on-sky NGS/LGS MOAO demonstrator for EAGLE Tim Morris Durham University

  2. Talk overview • MOAO with EAGLE • CANARY concept • Optomechanical design • Subsystem performance • System performance • System calibration tasks CANARY: NGS/LGS MOAO demonstrator

  3. MOAO with EAGLE • With the current baseline design, EAGLE will: • use 6 LGS and up to 5 NGS to map the turbulence above the E-ELT • correct up to 20 x ~2” diameter science fields anywhere within the central 5’ diameter field using open-loop AO • 250Hz frame rate • E-ELT has a deformable ‘secondary’ that will be used as a closed-loop woofer (GLAO-like DM) • EAGLE is both a closed and open-loop system • 30% ensquared energy with 75mas (H-band) required performance CANARY: NGS/LGS MOAO demonstrator

  4. MOAO with EAGLE: big questions • Can we achieve tomographic reconstruction to the required accuracy over such wide fields? • Can we reliably control a DM in open-loop? • How do we calibrate the system? • How accurately do we need to measure the Cn2 profile to optimise performance? • What is the impact of running the system with both open and closed loop DMs? • How do we compensate for LGS specific effects that can impact MOAO performance? • What are the principle performance drivers required when designing an MOAO system? • What is the best way to combine both NGS and LGS WFS signals to measure tomography? • Answer as many of these questions as possible as soon as possible to feed into the EAGLE design • Some can be (and have been) answered in simulation or using a lab system such as SESAME CANARY: NGS/LGS MOAO demonstrator

  5. CANARY concept CANARY: NGS/LGS MOAO demonstrator

  6. CANARY Aims • Perform NGS then LGS based tomographic WFSing • Perform open-loop AO correction on-sky • Develop calibration and alignment techniques • Fully characterise system and subsystem performance • Create a single MOAO channel EAGLE as closely as possibly using the 4.2m William Herschel Telescope • Effectively a 1/10th scale model of E-ELT using a 10km Rayleigh LGS CANARY: NGS/LGS MOAO demonstrator

  7. CANARY phased development • Based around a set of reconfigurable optical modules to allow ‘easy’ changes between three CANARY phases • Phase A: Low-order NGS-only MOAO (2010) • Phase B: Low-order LGS MOAO (2011) • Phase C: High-order LGS + NGS MOAO (2012) • All phases will include an extensive calibration and diagnostics package CANARY: NGS/LGS MOAO demonstrator

  8. Diagnostics and Performance monitoring • On-axis NGS WFS behind AO corrected focal plane (Truth Sensor) • On-axis NIR imaging camera (Science Verification Camera) • High-order high-bandwidth DM figure sensor • SLODAR analysis performed using open-loop WFSs • External turbulence profilers • SLODAR • MASS-DIMM • Telescope simulator • Turbulent phase screens • NGS and LGS alignment and calibration sources CANARY: NGS/LGS MOAO demonstrator

  9. Phase A: NGS MOAO Science Verification NGS FSM Low-order DM NGS Pickoffs WHT Nasmyth GHRIL Derotator Truth Sensor Figure Sensor Calibration Unit 3 x NGS WFS Phase A : NGS MOAO • Components: • Low-order 8x8 DM • 3 x L3CCD open-loop NGS WFSs • Open-loop optimised Fast Steering Mirror • Hardware accelerated Real Time control system • NGS MOAO Calibration Unit 10" Truth sensor & IR camera FOV NGS WFS NGS WFS NGS WFS 2.5’ Derotated WHT field CANARY: NGS/LGS MOAO demonstrator

  10. Phase B: Low-order LGS MOAO Figure Sensor 3 x NGS WFS GLAS BLT Diffractive Optic LGS Rotator GLAS Laser • New modules include: • Electronically shuttered LGS WFS CCD • Modified GLAS launch system • LGS dichroic and relay system • LGS MOAO Calibration Unit NGS Pickoffs NGS FSM Low-order DM LGS Dichroic WHT Nasmyth GHRIL Derotator LGS Pickoffs Truth Sensor Science Verification Calibration Unit 1.5’ Diameter LGS asterism LGS FSM Phase B: Low-order LGS MOAO 4 x LGS WFS CANARY: NGS/LGS MOAO demonstrator LGS WFS

  11. Figure Sensor GLAS BLT Diffractive Optic LGS Rotator GLAS Laser MEMS DM LGS Dichroic NGS FSM Low-order DM NGS Pickoffs WHT Nasmyth GHRIL Derotator Calibration Unit LGS Pickoffs 3 x NGS WFS • Phase C: High-order woofer-tweeter LGS MOAO (woofer closed loop) Science Verification Truth Sensor LGS FSM 4 x LGS WFS Phase C: High-order LGS MOAO • Closest resemblance to proposed EAGLE MOAO implementation • Largest upgrade here is to the RTCS. From Phase B we have: • ~ 2 times increase in pixel bandwidth • ~ 5 times increase in slope bandwidth • ~ 17 times increase in actuator bandwidth CANARY: NGS/LGS MOAO demonstrator

  12. Optomechanical design CANARY: NGS/LGS MOAO demonstrator

  13. Phase A optical design Output focal plane Truth Sensor focal plane Input Focal Plane Science Verification Camera focal plane CANARY: NGS/LGS MOAO demonstrator

  14. Phase B optical design LGS TT mirror NGS WFS placed at corrected focal plane Acquisition camera moved to input focal plane CANARY: NGS/LGS MOAO demonstrator

  15. Phase C optical design concept LGS WFS(s) moved behind closed-loop DM Possible locations of MEMS MOAO DM CANARY: NGS/LGS MOAO demonstrator

  16. NGS WFS Assembly CANARY: NGS/LGS MOAO demonstrator

  17. Telescope Simulator CANARY: NGS/LGS MOAO demonstrator

  18. Subsystem performance CANARY: NGS/LGS MOAO demonstrator

  19. Open-loop DM Control • 4% open-loop error with hard PZT DM demonstrated in laboratory with SESAME • 40nm RMS error if a 1000nm RMS DM surface is requested • Figure sensor could be used to control any long term drifts in DM surface shape • Will introduce some additional latency • Has been used with a Xinetics DM and produces a similar surface error to the hard PZT DM • Open loop control of a DM doesn’t seem to be a problem for CANARY low-order DM • High-order MEMS DM open-loop control has already been demonstrated CANARY: NGS/LGS MOAO demonstrator

  20. Subsystem performance: LGS Launch • Test system installed on WHT and tested in May • Uses DOE in GLAS launch system to create a 4 star asterism (MMT approach) • Several possible asterisms available by changing DOE • 10 to 90” diameter asterisms (takes about 15 minutes) • 80% of light into 4 diffracted LGS beams but altitude is lowered c.f. GLAS • Still want an upgraded laser to increase WFS SNR • Software problem with LGS detector meant range gated images couldn’t be obtained Non-gated image of ~40” LGS radius asterism at 6.7km DOE mounted in rotation stage at GLAS BLT entrance CANARY: NGS/LGS MOAO demonstrator

  21. RTCS • Hybrid FPGA-CPU Realtime Control System • FPGA pixel processing developed for HOT and SPARTA • Reconstructor in CPU • DM control in CPU • Currently runs at Phase A/B at 300-400Hz using a single threaded reconstructor pipeline • Latency and jitter to be measured • Upgrade required to cope with high-order LGS WFSs and DM in Phase C • Parallelise reconstructor • GPU acceleration CANARY: NGS/LGS MOAO demonstrator

  22. RTCS overview CANARY: NGS/LGS MOAO demonstrator

  23. System performance CANARY: NGS/LGS MOAO demonstrator

  24. Phase A Performance • Monte-Carlo simulations performed using independent codes in Durham and Paris • Single open-loop DM • 8x8 actuators • DM (and science path) on-axis • 3 x NGS WFSs • Off-axis (30” to 90”) • 7 x 7 subapertures • 0.1e- read noise • Mv = 8 to 14 • 250Hz frame rate • Representative summer La Palma turbulence profile used1 • r0 = 12cm • 45% @ 0km • 15% @ 2.5km • 30% @ 4km • 10% @ 13.5km 1 Fuensalida et al, RevMexAA, 31, 84-90 (2007) CANARY: NGS/LGS MOAO demonstrator

  25. Simulated Performance CANARY: NGS/LGS MOAO demonstrator

  26. Error terms • Principle term is tomographic reconstruction error • 30” radius means metapupils at highest turbulent layer are almost completely separated • 30” is still pretty small to find a 4-star mv = 12 asterism • Have identified several suitable targets within a 2.5’ diameter FOV observable between June-October • Will be even worse with the 10km Rayleigh LGS at Phases B and C • Requires the external turbulence profiling to determine how much of the turbulence is above the LGS • The Truth Sensor will be used as the principle system diagnostic • Science camera can be used when the turbulence cooperates • >60% turbulence in the ground layer is often observed at the WHT CANARY: NGS/LGS MOAO demonstrator

  27. System Calibration CANARY: NGS/LGS MOAO demonstrator

  28. Phase A calibration • Interaction matrix measurement using a reverse path calibration source • On-axis point source pointing backwards at output focal plane can be observed by each NGS WFS in turn • Requires stable pupil image at lenslet array across full FOV • Or use TS to measure DM influence functions • Observe ground-layer only turbulent sources within the telescope simulator with NGS WFSs and TS • Translate TS measure influence functions to each DM • Or measure matrices on-sky • Learn and Apply method from Fabrice Vidal first thing this morning NGS WFS pickoff prism From reverse path calibration source To WFS From telescope CANARY: NGS/LGS MOAO demonstrator

  29. Other calibration tasks • Field dependent aberrations • Pupil image stability is <1/100th pupil diameter • Monitoring and compensation changing field aberrations • Non-common path error compensation • Deployable point sources in most focal planes • Some pointing backwards for reverse path calibration • WFS linearity/gain optimisation (for WCOG etc.) • Use sources in NGS focal plane • NGS pickoff positioning accuracy • Confirm with full field acquisition camera • Detector calibration • At Phase B/C: • LGS WFS offsets/centroid gain • Range gate setting and optimisation • LGS WFS interaction matrix • To be developed further during the Integration and Testing phase • Runs from October 09 – April 10 CANARY: NGS/LGS MOAO demonstrator

  30. Conclusions • Already answered some of the big questions that MOAO with EAGLE raises • Open-loop DM control • Several calibration schemes proposed • CANARY will have the capability to answer the remaining ones by demonstrating and testing wide-field LGS tomographic AO • Critical subsystems are being testing and the initial integration phase is about to begin • We’re on track to go on-sky mid 2010 with the Phase A NGS tomography experiment • Phase B design to be reviewed at the end of this year CANARY: NGS/LGS MOAO demonstrator

  31. The CANARY team CANARY: NGS/LGS MOAO demonstrator

  32. CANARY capabilities • CANARY can: • Perform, calibrate and characterise accuracy of open-loop LGS tomography on-sky • Measure/monitor everything to make sure we understand performance of each component as well as the system as a whole • Develop alignment and calibration techniques • Combine several off-axis NGS and LGS WFSs to map the turbulence • Eventually use a closed-loop woofer and open-loop tweeter • Emulate arbitrary LGS intensity profiles and elongation • CANARY cannot: • Reach EAGLE performance goal • Match the total number of subapertures/actuators within EAGLE • Match the exactly LGS/NGS FOV afforded by the E-ELT • Take advantage of the multiplex normally afforded by MOAO – only a single channel CANARY: NGS/LGS MOAO demonstrator

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