Removal of central obscuration and spider arm effects with beam-shaping coronagraphy

¹ Optical and Infrared Division and Extrasolar Planet Project Office, National Astronomical Observatory of Japan, Ōsawa 2-21-1, Mitaka-city, 181-8588 Tōkyō, Japan e-mail: abe@optik.mtk.nao.ac.jp
² MIRA project, National Astronomical Observatory of Japan, Ōsawa 2-21-1, Mitaka-city, 181-8588 Tōkyō, Japan

Received: 5 August 2005
Accepted: 16 November 2005

Abstract

This paper describes a method for removing the effect of a centrally obscured aperture with additional spider arms in arbitrary geometrical configurations. The proposed method is based on a two-stage process where the light beam is first shaped to remove the central obscuration and spider arms, in order to feed a second, highly efficient coronagraph. The beam-shaping stage is a combination of a diffraction mask in the first focal plane and a complex amplitude filter located in the conjugate pupil. This paper specifically describes the case of using Lyot occulting masks and circular phase-shifting masks as diffracting components. The basic principle of the method is given along with an analytical description and numerical simulations. Substantial improvement in the performance of high-contrast coronagraphs can be obtained with this method, even if the beam-shaping filter is not perfectly manufactured.