Abstract

External occulters for NASA exoplanet missions have been proposed as the means to suppressing the Poisson spot intensity by at least 10 orders of magnitude. The leading proposed external occulter shapes adhere to the binary petaled occulters with sharp petal tips. In a recent paper, Wasylkiwskyj and Shiri [J. Opt. Soc. Am. A 28, 1668 (2011) [CrossRef]  ] (WS2011) investigated two forms of occulters: a binary petaled occulter and a circular partially transparent occulter. They showed that the achievable intensity reduction for a petal-style occulter is limited by the radii of curvature at the petal tips. For a partially transparent occulter they derived the optimum transparency function that minimizes the intensity on the optic axis within a prescribed wavelength range and provides the required intensity suppression. Since the publication of WS2011, a paper by Cash describes the analytical model of the occulter [Astrophys. J. 738, 76 (2011) [CrossRef]  ] and recent commentary by Cash and Lo [J. Opt. Soc. Am. A 29, 913 (2012)] (CL2011) compares the intensity reduction of petal shape functions and concludes prematurely against the petal shapes in WS2011. In this correspondence, we analyze the performance of a petal shaped occulter with petals tips of 0.1 mm width (following the prescription of CL2011) and show that its suppression performance is compatible with the calculations reported in WS2011 and measured intensity reduction reported in [Proc. SPIE 6687, 66871B (2007) [CrossRef]  ] and [Proc. SPIE 6693, 669305 (2007) [CrossRef]  ].

© 2012 Optical Society of America

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