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

2. 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

3. 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

4. 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?

5. 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

6. 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)

7. 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

8. Generic ‘Go-to’ & Closed Loop System

9. 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

10. 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.

11. 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

12. 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 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

13. Conclusions
Other Questions?

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

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

16. 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

17. Cartoon PD calibrations
From Sauvage et al,
see references

18. 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