(r1) Homework < Keck/NGAO

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*Brian Bauman*
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Request: 

1) Please be prepared to consider the optical aberrations and tolerancing of several 1:1 AO relays that pass unvignetted field of view in the 3-5 arcmin range, including:

	* OAP
	* Offner
	* Ellipsoidal

We will wish to consider single and dual DM configurations with notional conjugate heights of 0km and 8km above the Keck telescope.  We are interested in feeding both contiguously sampled narrow fields, and sparsely sampled deployable IFU fields of view that may enjoy an independent 1-4 micron stroke MEMS-DM for aberration correction, per IFU channel.

2) Please be prepared to provide advice on the control of non-common-path LGS aberrations for NGAO wavefront sensors, understanding the approach taken in the current Keck AO system and that adopted by Gemini MCAO.  Although we expect WFS design to not occur until the NGAO design phase, a good understanding of the requirements, scope, and system trades necessary to reduce complexity and cost would be helpful.

3) Please be prepared to specifically comment on the aberrations induced in the Keck telescope beam (incl. field aberrations) if we were to push the Nasmyth focus down (that is, away from M3) to create greater back focal distance from the elevation ring.

Resources:

An initial .zmx file of the Keck Telescope is attached, along with earlier models created by C. Neyman (OAP) and Eric Prieto (Offner).  Please be prepared to iteratively exercise these models to provide feedback to the point design effort.

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*Antonin Bouchez*
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Request:

1) Please be prepared to discuss tip/tilt limitations to sky coverage fraction (in terms of XX% sky coverage available with YY milliarcseconds of tip/tilt anisoplantism error.  Please be prepared to comment on the merits of the following concepts:

        * Visible light Shack-Hartmann and pyramid WFS (2x2 and 3x3 subaperture)
	* Infrared light Shack-Hartmann and pyramid WFS (2x2 and 3x3 subaperture)
        * Combinations of 2 visible, 2 IR, or 1 visible + 1 IR WFS
        * Fundamental limits of using all available stars' light (at visible and IR wavelengths)

2) Please be prepared to comment on the effect of centroid anisoplantism due to aliasing of coma aberrations into low-order (e.g. tip/tilt measurements).

Resources:

Attached is a new report from Richard Clare (future CARA postdoc) on the comparison of J, H, and K-band for WFS'ing with TMT's NFIRAOS system.  Please understand the assumptions, calculations, and differences between that case and Keck NGAO.

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*Don Gavel*
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Request: 

1) Please be prepared to iteratively consider residual wavefront error due to imperfect tomographic wavefront sensing (possibly combined with fitting error) for NGAO asterisms supporting

	* Minimum on-axis WFE, with a req'ment of 70nm rms and goal of 45nm rms
	* Areally averaged WFE spanning FoV in the range of 3' - 5'

Make no a priori assumptions regarding physical WFS packaging constraints, but be prepared to comment on the degradation of WFS'ing performance for perturbations to notional asterism geometries.

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*Viswa Velur*
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Request: 

1) Please be prepared to comment on the focus-tracking requirements for a low-order tip/tilt/focus WFS.  Using current knowledge of the variability in sodium layer height, consider the focus update rate that the LOWFS must provide.

Resources:

Attached is a technical report generated by the TMT NFIRAOS team.  Please understand the assumptions, calculations, and differences between that case and Keck NGAO.

-- Main.RichardDekany - 07 Apr 2006

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
pdf	JHK_for_NGS_WFS_for_NFIRAOS.pdf	r1	manage	161.1 K	2006-04-07 - 17:13	RichardDekany	TMT NFIRAOS study
ZMX	KeckTelescope.ZMX	r1	manage	18.5 K	2006-04-07 - 16:33	RichardDekany	Keck Telescope .zmx file
pdf	Sensitivity_to_focus_from_sodium_laser_guide_star.pdf	r1	manage	135.8 K	2006-04-07 - 17:12	RichardDekany	TMT NFIRAOS study

Topic revision: r1 - 2006-04-07 - RichardDekany

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