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Negating effects from sodium profile variations for TMT: the MOR truth wavefront sensor of NFIRAOS

Andersen, David R. and Conan, Rodolphe and Ellerbroek, Brent and Herriot, Glen and Véran, Jean-Pierre (2008) Negating effects from sodium profile variations for TMT: the MOR truth wavefront sensor of NFIRAOS. In: Adaptive Optics Systems. Proceedings of SPIE. No.7015. Society of Photo-Optical Instrumentation Engineers , Bellingham, WA, Art. No. 70155V. ISBN 9780819472250.

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The Moderate Order Radial (MOR) Truth Wavefront Sensor (TWFS) of NFIRAOS, the facility AO system for TMT, is a visible light order 12x12 subaperture Shack-Hartmann WFS. Its role is to sense radial wavefront errors arising from variations in the Sodium layer profile that are not sensed by the on-instrument near infrared tip-tilt focus wavefront sensor at a sampling frequency on the order of one Herz. It works in concert with the High Order Low bandwidth (HOL) TWFS, which will use a 120x120 subaperture Shack-Hartmann WFS that senses slow variations in telescope flexure and the rotation of the pupil. Top-level requirements for NFIRAOS leave little margin for degradation in sky coverage or additional implementation wavefront errors introduced by the operation of the MOR TWFS. In this paper, we explore MOR TWFS design trade studies on the number of subapertures, sampling rate, the width of the MOR TWFS visible bandpass, and the split in light between the MOR and HOL TWFS, and present a design for a system which meets the top level requirements by not degrading the high sky coverage of NFIRAOS (50% sky coverage at the Galactic poles) and rejecting the radial modes with a residual wavefront error of 10nm.

Item Type:Book Section
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Additional Information:© 2008 Society of Photo-Optical Instrumentation Engineers.
Group:Thirty Meter Telescope
Subject Keywords:Adapive Optics, Extremely Large Telescopes
Series Name:Proceedings of SPIE
Issue or Number:7015
Record Number:CaltechAUTHORS:20181217-145307297
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Official Citation:David R. Andersen, Rodolphe Conan, Brent Ellerbroek, Glen Herriot, Jean-Pierre Véran, "Negating effects from sodium profile variations for TMT: the MOR truth wavefront sensor of NFIRAOS," Proc. SPIE 7015, Adaptive Optics Systems, 70155V (15 July 2008); doi: 10.1117/12.789841
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91871
Deposited By: Tony Diaz
Deposited On:18 Dec 2018 18:25
Last Modified:03 Oct 2019 20:39

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