Calibration Plan Chris Neyman W. M. Keck Observatory April 20, 2010

Outline Background and related work by team Brief review of calibration procedure Unusual parts of the procedure More details see KAON 739 “NGAO Calibration Methods and Procedures” revised version based on review inputs Response to reviewers questions Conclusion

Background NGAO calibration plan based team’s experience with ExAO and ‘go-to’ AO Image sharpening & NCPA compensation with Palomar system Modified Gerchberg-Saxton Phase Retrieval Palomar 98% Strehl (higher at JPL with controlled environment) “Go-to” adaptive optics at CfAO and Lick MOAO test bench: Calibration of LGS WFS for larger dynamic range MEMs operation and repeatability VILLAGES Lick 1m telescope – integration experience Verify error rejection benefits of ‘go-to’ control

Calibration Plan (just the weird stuff) Calibrate HODM and LOWFS MEMS response (once per year) Open system and add high resolution Shack-Hartmann Sensors Small self contained units (Imagine Optic or Other) More of a maintenance procedure The AO relay optomechanical design needs to be revisited to make sure we can supply the kinematic fixtures. Phase diversity on DAVINCI and LOWFS sensor (once per observing run) Use high resolution algorithms Move calibration source for defocus (LODM also possible) Interleave or “Drizzle” for sub Nyquist sampled detectors (LOWFS) Use IFS data-cube to synthesis image Marcos on retainer to do this for OSIRIS Possible risk reduction for NGAO?

Calibration Plan (just the weird stuff) Measure LGS WFS response for ‘go-to’ operation (once per observing run) Use LODM tip tilt stage to scan sources across subapertures Record LGS WFS centroids process to determine non linearity correction Suggested to use aberration plate at pupil to check calibrations All LGS WFS should see same phase (at pupil) Alternative is to command LODM measure with NGS WFS 5

Calibration Plan (just the weird stuff) Register LODM actuators to subapertures use waffle pattern (once per observing run, as frequent as once each afternoon) Calculate translation, rotation, magnification from measurement LGS WFS and LOWFS sensor (needs defocus)

Calibration Plan (just the weird stuff) Register LGS WFS on axis sensors to HODM actuators (once per observing run, as frequent as once each afternoon) Apply static shape to LODM Measure the error on a fixed LGS WFS Use RTC to calculate needed correction to apply to HODM Measure the PSF on the science camera, for effect of translations, rotation, and magnification errors Register LGS WGS patrolling sensors to LOWFS DM actuators (once per observing run, as frequent as once each afternoon) Measure the error on a patrolling LGS WFS Use RTC to calculate needed correction to apply to LOWGS DM Measure the PSF on the LOWFS camera, for effect of translations, rotation, and magnification errors

Generic ‘Go-to’ & Closed Loop System

Calibration-Solutions summary What we concluded we needed Increased specification on wavefront error of calibration source Calibration source wavefront is common mode (rms error ~30 nm) Error in measurement is determining factor Flat field source (no integrating sphere!) Astrometric grid Multiple point sources (NGS/LGS) Phase diversity algorithms High Resolution mode (~128x128) for NGS wavefront as additional calibration measurement What might be removed (but we kept some capabilities see calibration source presentation) Turbulence simulator with phase plates

Response to Reviews Questions 4.5 Comments on LGS WFS calibration: 1. I suggest putting the LGS sources on z-translation to simulate “elongation” This is a quasi static test as low bandwidth? The calibration source can move the LGS is z but only at slow speeds 2. Calibrating the open-loop WFS for open loop measurement has been demonstrated in the lab, but not on the sky yet. [CN] I used this reference: Ammons, et al, “Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10-Meter Telescope at Visible Wavelengths” 3. It would be nice to have a set of aberrator plates that have known low-order aberrations for testing calibration. This would be in addition to atmospheric aberrator plates. LAO may be able to make these. [CN] We proposed using the LODM as a way to be able to run the same test, it’s at a pupil so all the LGS WFS should “see” the same aberrations. I believe we will have the ability to put some aberration plates in the calibration source.

Response to Reviews Questions Sec 3. Calibration Tasks 3.11 Acquisition Camera Pointing Origin “Minor point but rotation center is defined as the optical axis and is one of many "pointing origins" for the AO system. It is also the origin of the focal plane coordinate system.” I'll fix this oversight in the final KAON, and just call it optical axis. 11

Response to Reviews Questions 4.1 Radiometric calibration of instrument and AO detectors: “Just a word of caution that in astronomy, "radiometric" calibration is the treated as the exact response of a system to a given input of photons. The calibration unit as describe provides a flat field and arc lamps and not a radiometric calibration.” Oversight, I'll change this to flat field in revised KAON 4.2 Astrometric calibration of AO system and instrument distortion: “NIRC2 grid is inside the dewar, this will be outside the dewar. May need adjustments to verify the grid is perpendicular to the optical axis.” I think this would be a issue in either case. Overall alignment plan between cal source and instrument will be finalized during DD phase 4.5 Calibrate LGS WFS response for 'go-to' operation: ”LGS on sky is about 1.5-3.0 arc seconds depending on seeing. Will LGS calibration source also subtend a range of angular sizes?” I believe that the calibration source could hold larger LGS sources if needed, also NGAO will use a center launch so the LGS should be smaller than we currently have on Keck II. Bias from Na layer and size changes are compensated with TWFS during operations

Conclusions Other Questions?

Extra Slides I don’t plan to talk to the following slides, but I’ve included them for questions

Key points for NGAO Open loop control requires: Predictable response of the DM Absolute measurement of the wavefront with high dynamic range 15 15

Key points for NGAO With go-to or “open loop” control the low frequency behavior is dominate by calibration errors Plot from Villages experiment Closed Loop Open Loop 16 16

Cartoon PD calibrations From Sauvage et al, see references

References Sauvage et al, “Calibration and precompensation of noncommon path aberrations for extreme adaptive optics”, J. Opt. Soc. Am. A, Vol. 24, August 2007 S. Bikkannavara et al, “Autonomous Phase Retrieval Control for Calibration of the Palomar Adaptive Optics System”, Proc. of SPIE Vol. 7015, 2008. Green, J., et al, “Extreme Wave Front Sensing Accuracy for the Eclipse Coronagraphic Space Telescope”, Proc. SPIE 4860, 2003. M. Oliker, “Alignment Techniques for DM, Lenslet, and WFS Camera at the SOR”, SPIE 3126 Gavel et al, “Visible light laser guidestar experimental system (Villages): on-sky tests of new technologies for visible wavelength all-sky coverage adaptive optics systems”, SPIE 7015 2008.