16 September 2004 Will ELT segmentation effects conceal exo-Earths? A physical optics simulation as a test of Fourier methods
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Abstract
All current proposals for the construction of Extremely Large (30- to 100-m) ground-based Telescopes (ELTs) assume segmentation of (at least) the primary mirror. This has implications for the low-level structure of their PSFs which are likely to be significant for a number of important scientific applications, including the potential detection and characterization of terrestrial planets orbiting nearby solar-type stars. Several studies of these effects have been carried out; all rely on Fourier methods applied to an approximate model of the telescope entrance pupil. Concerned that these methods may be prone to quite significant errors we have undertaken a physical optics analysis. This numerical simulation uses methods well-established in long-wave optics, with well-defined convergence criteria, to model the PSF of a 50-m segmented-primary telescope. Our results are in very close agreement with those from Fourier methods when an F/16 system is modelled, but significant differences are seen when a more realistic F/1 system is modelled. We also present preliminary results of simulations of an "imperfect telescope". The regular diffraction pattern seen from the perfect mirror is almost completely destroyed even when the form errors and alignment errors of the segments are sufficiently small to maintain a Strehl ratio of 90%.
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Tully Peacocke, Tully Peacocke, Stephen P. Todd, Stephen P. Todd, Eli Atad, Eli Atad, Timothy G. Hawarden, Timothy G. Hawarden, } "Will ELT segmentation effects conceal exo-Earths? A physical optics simulation as a test of Fourier methods", Proc. SPIE 5497, Modeling and Systems Engineering for Astronomy, (16 September 2004); doi: 10.1117/12.551540; https://doi.org/10.1117/12.551540
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