AO4ELT5 Proceedings

Pyramid WFS Tolerance Study for NFIRAOS NGS AO

Wang, Lianqi (TMT, USA), Veran, Jean-Pierre (NRC, Canada), Ellerbroek, Brent (Retired)

The pyramid wavefront sensor (WFS) is becoming a popular choice for natural guide star (NGS) based adaptive optics (AO) systems on account of its improved sensitivity and reduced spatial aliasing effect compared to the Shack-Hartmann WFS. However, AO system performance degradations due to implementation errors regarding the Pyramid WFS are still not very well understood. These include the quality of the pyramid (sharpness of the edges and vertex, orthogonality of the faces), image quality of the relay optics, pyramid-to-detector misregistration, etc.. Understanding these effects is crucial to setting proper tolerances, deciding which degree of freedom should be adjustable and optimizing the performance to cost ratio. In this paper, we present our simulations methods and results on the pyramid WFS and these implementation errors for the NGS AO mode of the Thirty Meter Telescope (TMT) facility Narrow Field Infrared AO System (NFIRAOS). We have found that the AO system performance is mildly sensitive to certain effects, such as pupil image distortion or drift, but more sensitive to other effects, such as pyramid imperfections, etc.. For the TMT pupil geometry, we find that it is also important to update the control matrix as the telescope pupil rotates on account of the pupil segmentation due to the M2 support struts.

DOI: 10.26698/AO4ELT5.0054- Proceeding PDF

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