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LGS-AO Performance Characterization Plan

LGS-AO Performance Characterization Plan. AOWG meeting Dec. 5, 2003 A. Bouchez, D. Le Mignant, M. van Dam for the Keck AO team. LGS-AO performance characterization effort. Purpose (from CfAO proposal):

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LGS-AO Performance Characterization Plan

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  1. LGS-AO Performance Characterization Plan AOWG meetingDec. 5, 2003A. Bouchez, D. Le Mignant, M. van Damfor the Keck AO team

  2. LGS-AO performance characterization effort • Purpose (from CfAO proposal): • Demonstrate and characterize the Keck II LGS AO system for science via collaboration with the LGS and science AO community. • Using the output from goal 1, optimize the Keck LGS AO system and feed back the lessons learned to future LGS AO systems. • Products: • Full LGS-AO error budget. • Accurate planning information for users. • New data on sodium layer structure and density variations.

  3. LGS-AO Characterization Plan • LGS-AO characterization effort is closely related to • LGS-AO development priorities • demonstration of LGS-AO observing modes. • Goals • On-axis performance (Strehl & FWHM vs. magnitude) fully characterized by Feb. 2004. • Off-axis performance (anisoplanatism, dither accuracy, etc.) documented by Aug. 2004.

  4. Error budgets • Not one single error budget! • Performance • Subsystems • LGS performance • Integrated system performance • Throughput • Field of view • off-axis FOV • dithering precision • Operational aspects • Overheads • Stability

  5. Performance error budget (on-axis)

  6. Sodium layer characterization • Continuously monitor mean altitude through WFS focus. • Continuously monitor sodium density through return power / projected power. • Nightly map of density structure with unstacked images

  7. NGS Strehl vs. magnitude

  8. Subsystem performance • Tip-tilt sensor stage - STRAP Residual tip-tilt as function of: • Star magnitude. • TT reference motion (asteroid, etc.) • Sky background (moonlight, raleigh). • Resolved sources (AGN, close binaries). • Low-bandwidth wavefront sensor - Precision of wavefront measurement as function of: • Star magnitude & integration time. • Limit due to aberrations in LBWFS. • Off-axis location of tip-tilt stage. • Pupil rotation rate • Tip-tilt sensor positioning accuracy • Repeatability • Accuracy • Effect of LGS spot elongation on WFS measurement

  9. LGS performance • Laser spot size / elongation / power • Temporal stability • How it is affected by seeing • Correlation against laser table diagnostic measurements • LGS tip-tilt and jitter • Flexure compensation performance • Magnitude of atmosphere-induced jitter • Residual tip-tilt after up-tip-tilt implementation • Sodium layer • Track mean altitude • Power returned vs. power out (sodium density) • Layer structure from unstacked images.

  10. Integrated system performance • Strehl on target versus • Tip-tilt star magnitude. • Tip-tilt star separation. • Spot elongation / sodium altitude / elevation • Laser power / sodium density • Integration time • Anisoplanatism • Different from NGS? • Focal anisoplanatism • Predict from Cn2 profiles • Measure from total error budget • Operational aspects • Acquisition overhead • Dithering overhead • Mean time between failures

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