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Proceedings Paper

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

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.

Paper Details

Date Published: 15 July 2008
PDF: 11 pages
Proc. SPIE 7015, Adaptive Optics Systems, 70155V (15 July 2008); doi: 10.1117/12.789841
Show Author Affiliations
David R. Andersen, National Research Council Canada, Herzberg Institute of Astrophysics (Canada)
Rodolphe Conan, Univ. of Victoria (Canada)
Brent Ellerbroek, TMT Observatory Corp. (United States)
Glen Herriot, National Research Council Canada, Herzberg Institute of Astrophysics (Canada)
Jean-Pierre Véran, National Research Council Canada, Herzberg Institute of Astrophysics (Canada)


Published in SPIE Proceedings Vol. 7015:
Adaptive Optics Systems
Norbert Hubin; Claire E. Max; Peter L. Wizinowich, Editor(s)

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