California Association for Research in Astronomy W. M. Keck Observatory KPAO Keck Precision Adaptive Optics 1 Keck Precision AO (KPAO) Notes for AOWG telecom July 22, 2005 Ralf Flicker, Olivier Lai & Christopher Neyman for the KPAO team

2 Presentation Outline KPAO animationKPAO animation AOWG historyAOWG history Science CaseScience Case KPAO simulation statusKPAO simulation status Review of current AO architecturesReview of current AO architectures

3 KPAO was identified by the AOWG as their highest long-term priority in support of the Observatory’s Strategic PlanKPAO was identified by the AOWG as their highest long-term priority in support of the Observatory’s Strategic Plan A very high Strehl system with stable image quality & good sky coverage (LGS AO)A very high Strehl system with stable image quality & good sky coverage (LGS AO) Current effort: Produce a conceptual design by early 2006Current effort: Produce a conceptual design by early 2006 Performance simulations, detailed science case development & draft designs in processPerformance simulations, detailed science case development & draft designs in process Will then seek external fundingWill then seek external funding The following galactic center images (from the current Keck AO system at 3.5 microns wavelength) illustrate KPAO’s intended capability at shorter wavelengths. In reality the resolution would also improve (linearly with wavelength).The following galactic center images (from the current Keck AO system at 3.5 microns wavelength) illustrate KPAO’s intended capability at shorter wavelengths. In reality the resolution would also improve (linearly with wavelength). KPAO Baseline 120 nm KPAO: Keck Precision AO Strehl ~0.6 Compare to current AO at K, ~2x resolution (J vs. K) Strehl ~0.2 Resolution 4x HST and collection gain 16x HST with 10 meter Keck Strehl ~0.85 High contrast astronomy Best separation of detail in crowded fields

4 14 more years to go to reach “all AO all the time” NSF-funded laser K1 AOWG Strategic Planning Proposed timeline defined at 11/02 Strategic Planning (SP) meeting.Proposed timeline defined at 11/02 Strategic Planning (SP) meeting. K1 laser added in early 03K1 laser added in early 03 Priorities confirmed at 9/04 SP meeting.Priorities confirmed at 9/04 SP meeting. Mike Brown: “AOWG vision is that high Strehl, single-object, AO will be the most important competitive point for Keck AO in the next decade.”Mike Brown: “AOWG vision is that high Strehl, single-object, AO will be the most important competitive point for Keck AO in the next decade.” Based on science cases presented/discussed by AOWG membersBased on science cases presented/discussed by AOWG members Top-level requirements defined by a subgroup & approved by AOWGTop-level requirements defined by a subgroup & approved by AOWG Proposed Time line 11/02

5 KPAO Technical Requirements (KAON 237) High IR Strehls -> evaluate 120 & 180 nm rmsHigh IR Strehls -> evaluate 120 & 180 nm rms On-axis LGS & NGS, median seeing, El > 45 , NGS m v 45 , NGS m v < 17 High Strehl stability -> ± 15 nmHigh Strehl stability -> ± 15 nm Moderate field of view -> 30” radiusModerate field of view -> 30” radius Near complete sky coverageNear complete sky coverage Good knowledge of the delivered PSFGood knowledge of the delivered PSF Wavelength coverage -> 0.45 to 14  mWavelength coverage -> 0.45 to 14  m Facility-class systemFacility-class system Sensitivity & angular resolution not yet addressedSensitivity & angular resolution not yet addressed

6 Science case Science case draft has been completed by the Olivier Lai with input from the AOWG (See KAON 331).Science case draft has been completed by the Olivier Lai with input from the AOWG (See KAON 331). Olivier presented science case to Keck SSC 6/29/05Olivier presented science case to Keck SSC 6/29/05 Work needs to continue in the area of “flowing down” these scientific goals into system and subsystem requirements.Work needs to continue in the area of “flowing down” these scientific goals into system and subsystem requirements. This work will go forward with the input of the new AOWG and KPAO science team.This work will go forward with the input of the new AOWG and KPAO science team.

7 KPAO performance predictions Flicker and Neyman has been working on analysis and computer simulations that can predict the performance of the KPAO systemFlicker and Neyman has been working on analysis and computer simulations that can predict the performance of the KPAO system Evaluated wavefront error budgets that total 120 nm and 180 nm respectivelyEvaluated wavefront error budgets that total 120 nm and 180 nm respectively The 120 nm is a combination of analytical and Monte Carlo models.The 120 nm is a combination of analytical and Monte Carlo models. 180 nm is from Monte Carlo simulation only180 nm is from Monte Carlo simulation only Basic AO system parameters for a narrow field AO (NFAO) version of KPAO have been determinedBasic AO system parameters for a narrow field AO (NFAO) version of KPAO have been determined

8 KPAO Monte Carlo simulation The next slide is a sample screen shot of the KPAO Monte Carlo simulationThe next slide is a sample screen shot of the KPAO Monte Carlo simulation Based on F. Rigaut’s AO simulation (YAO), Modified by Flicker for KPAOBased on F. Rigaut’s AO simulation (YAO), Modified by Flicker for KPAO Basic KPAO simulation includes:Basic KPAO simulation includes: atmospheric phase screensatmospheric phase screens geometric optics model for wavefront propagationgeometric optics model for wavefront propagation Physical optics propagation model for Shack Hartmann wavefront sensorPhysical optics propagation model for Shack Hartmann wavefront sensor Closed loop operation, photon and read noise.Closed loop operation, photon and read noise. LGS spot elongation, Rayleigh backscatter, LGS centroid gain optimizationLGS spot elongation, Rayleigh backscatter, LGS centroid gain optimization Evaluate the PSF at user selectable locations over field of viewEvaluate the PSF at user selectable locations over field of view

9 Long exposure PSFLong exposure PSF WFS display (5 LGS)WFS display (5 LGS) DM shapeDM shape Residual WavefrontResidual Wavefront Strehl HistoryStrehl History Instantaneous PSFInstantaneous PSF

10 Keck specific simulation inputs Segment phase errorsVibration spectrum Simulation infrastructure exists to handle telescope optical aberration and vibration effectsSimulation infrastructure exists to handle telescope optical aberration and vibration effects Input as temporal and spatially varying phase screen for now. Integrated Modeling in the future (??)Input as temporal and spatially varying phase screen for now. Integrated Modeling in the future (??) Need to verifyNeed to verify the inputs to the simulation the inputs to the simulation Some test inputs to simulation shown belowSome test inputs to simulation shown below

11 Large part of KPAO cost will be lasers Need to understand Watts/$ tradeoffsNeed to understand Watts/$ tradeoffs Obtained several year data set of Na Column densities for Maui ( )Obtained several year data set of Na Column densities for Maui ( ) Model for photon return from Na laser guide stars, included laser saturation effects (Both Pulsed and CW formats)Model for photon return from Na laser guide stars, included laser saturation effects (Both Pulsed and CW formats) Models compared to Keck/Gemini simultaneous LGS propagation on May Models compared to Keck/Gemini simultaneous LGS propagation on May Comparison between models and theory good to about 0.4 magnitudes:Comparison between models and theory good to about 0.4 magnitudes: actual Na density is large uncertainty in verifying modelsactual Na density is large uncertainty in verifying models

12 Sky Coverage Important to finalize requirement as it drives AO architecture (NFAO vs. MOAO/MCAO)Important to finalize requirement as it drives AO architecture (NFAO vs. MOAO/MCAO) Large sky coverage will requireLarge sky coverage will require IR tracking detectorsIR tracking detectors Some sharpening of NGSSome sharpening of NGS Need to measure 3-4 NGS (tip/tilt only) or 1 NGS (tip/tilt focus/astigmatism)Need to measure 3-4 NGS (tip/tilt only) or 1 NGS (tip/tilt focus/astigmatism) Using tools developed by Richard Clare for TMT to evaluate KPAO sky coverageUsing tools developed by Richard Clare for TMT to evaluate KPAO sky coverage

13 Explanation of KPAO error budget Atmospheric parameters from KAON 303Atmospheric parameters from KAON 303 rescaled to r 0 of 16 cm at 0.5  m.rescaled to r 0 of 16 cm at 0.5  m. Error allocation for Telescope, Instrument and Tracking using best estimates.Error allocation for Telescope, Instrument and Tracking using best estimates. 180 nm: 5 LGS simple SVD reconstructor with close loop constraints180 nm: 5 LGS simple SVD reconstructor with close loop constraints 120 nm: estimate the focus anisoplanatism and wavefront reconstruction error are estimated from an analytical AO model120 nm: estimate the focus anisoplanatism and wavefront reconstruction error are estimated from an analytical AO model Working on implementing better tomography algorithmsWorking on implementing better tomography algorithms

14 Sample KPAO Wavefront Error Budget Error TypeSimulation parameters Fitting Error act (32x32)1300 act (40x40) Servo Error Hz1500 Hz Measurement Error (noise) W (CW) laser, 6e- CCD20 W (CW), 1e- CCD Focus Anisoplanatism58455 LGS (corners + center)7 LGS (hex. + center) Alias, reconstruction4835SVDEstimate from Linear AO model Total for Higher Order AO Telescope7050Allocation Instrument5035Allocation Tracking (noise, servo & iso.) 9740Allocation Total180120

15 Summary Important to develop science requirements as part of the conceptual design process.Important to develop science requirements as part of the conceptual design process. Therefore desire more community involvement.Therefore desire more community involvement. Performance analysis tools in place to do science/technical trade studies.Performance analysis tools in place to do science/technical trade studies. Emphasis soon to switch to system design issues.Emphasis soon to switch to system design issues.

16 Thoughts on various AO architectures Conventional LGS/NGS AO What we have todayWhat we have today Current NGS systems have ~200 nm rms wavefront error, but only around bright guide stars (V~13)Current NGS systems have ~200 nm rms wavefront error, but only around bright guide stars (V~13) Current LGS system have ~300 nm rms wavefront errorCurrent LGS system have ~300 nm rms wavefront error At a good site the cone effect error is ~150 nmAt a good site the cone effect error is ~150 nm This imposes a fundamental lower limit to single LGS AO correction between nmThis imposes a fundamental lower limit to single LGS AO correction between nm 250 = ( ) 1/2250 = ( ) 1/2

17 Thoughts on various AO architectures Extreme AO One solution it to decide that NGS are the only viable reference sourceOne solution it to decide that NGS are the only viable reference source A high Strehl system is still possible (i.e. XAOPI)A high Strehl system is still possible (i.e. XAOPI) But now the number of targets is reduced to the brightest stars (V~9 or brighter)But now the number of targets is reduced to the brightest stars (V~9 or brighter) This is perfectly acceptable for certain types of very compelling observationsThis is perfectly acceptable for certain types of very compelling observations Extra-solar planetsExtra-solar planets

18 Thoughts on various AO architectures Tomography Using multiple LGS to reduce cone effect was proposed in the original LGS paper (~1985)Using multiple LGS to reduce cone effect was proposed in the original LGS paper (~1985) Several variations have been proposed in recent yearsSeveral variations have been proposed in recent years Multi conjugate AO (MCAO)Multi conjugate AO (MCAO) Multi object AO (MOAO)Multi object AO (MOAO) Narrow Field AO (NFAO)Narrow Field AO (NFAO) Ground Layer AO (GLAO)Ground Layer AO (GLAO) These concepts all rely on measuring the volume turbulence above the telescope with several LGSThese concepts all rely on measuring the volume turbulence above the telescope with several LGS The multi LGS measurement process has been named tomography in analogy with medical imagingThe multi LGS measurement process has been named tomography in analogy with medical imaging

19 Thoughts on various AO architectures GLAO Measure volume turbulenceMeasure volume turbulence select out only the turbulence at the ground and boundary layer (~ first km)select out only the turbulence at the ground and boundary layer (~ first km) Apply this correction with a single corrector at the telescope pupilApply this correction with a single corrector at the telescope pupil Field of view is large because turbulence correction at pupil is approximately the same for all field anglesField of view is large because turbulence correction at pupil is approximately the same for all field angles wavefront error ~ 500 nm rms wavefront error ~ 500 nm rms

20 Thoughts on various AO architectures MCAO Measure volume turbulence with several LGSMeasure volume turbulence with several LGS Approximate turbulence as occurring at several discrete altitudesApproximate turbulence as occurring at several discrete altitudes Apply this correction with correcting elements that are conjugate to each altitude (from step above)Apply this correction with correcting elements that are conjugate to each altitude (from step above) Field of view is large because turbulence correction is “applied” at altitudeField of view is large because turbulence correction is “applied” at altitude Cone effect reduced as wellCone effect reduced as well wavefront error ~ nm rms (field average) wavefront error ~ nm rms (field average) Fundamental limits set by tomography, number of correctors and need for NGS tip/tilt starsFundamental limits set by tomography, number of correctors and need for NGS tip/tilt stars

21 Thoughts on various AO architectures MOAO Measure volume turbulence with several LGSMeasure volume turbulence with several LGS Select preferred directions for correction, i.e. science objects and possibly tip/tilt NGSSelect preferred directions for correction, i.e. science objects and possibly tip/tilt NGS Apply each direction optimized correction with a optic that is unique to that direction (field separated)Apply each direction optimized correction with a optic that is unique to that direction (field separated) Correction is only applied at interesting locations in a large field of view: don’t correct blank sky!Correction is only applied at interesting locations in a large field of view: don’t correct blank sky! As currently conceived LGS AO light is open loopAs currently conceived LGS AO light is open loop This requires linear AO correctors and wavefront sensing over a large dynamic rangeThis requires linear AO correctors and wavefront sensing over a large dynamic range Required technology has yet to be demonstrated/testedRequired technology has yet to be demonstrated/tested UCSC is doing conceptual design of MOAO for TMTUCSC is doing conceptual design of MOAO for TMT Fundamental limits set by tomography, non linearity of AO system elements and need for NGS tip/tilt starsFundamental limits set by tomography, non linearity of AO system elements and need for NGS tip/tilt stars

22 Thoughts on various AO architectures NFAO Measure volume turbulence with several LGSMeasure volume turbulence with several LGS Select correction needed for on axis objectsSelect correction needed for on axis objects Corrected field of view smallCorrected field of view small System can run closed loop around LGS with proper reconstruction matrixSystem can run closed loop around LGS with proper reconstruction matrix System upgrade to full MCAO straightforwardSystem upgrade to full MCAO straightforward Wavefront error nm rmsWavefront error nm rms Fundamental limits set by tomography and need for NGS tip/tilt starsFundamental limits set by tomography and need for NGS tip/tilt stars