One-sided Achromatic Phase Apodization for Imaging of Extrasolar Planets

We propose a new approach to direct imaging of extrasolar planets: one-sided phase apodization. It is based on a discovery that an antisymmetric spatial phase modulation pattern imposed over a pupil or a relay plane causes diffracted starlight suppression sufficient for imaging of extrasolar planets. Calculations with specific square-pupil (side D) phase functions, such as x; y ð Þ 1⁄4 a ln 1þ ð Þ þ 2x=D 1þ ð Þ 2x=D 1þ ð Þ þ 2y=D 1þ ð Þ 2y=D ; demonstrate annulling in at least one quadrant of the diffraction plane to the contrast level of better than 10 , with an inner working angle down to 3:5k=D (with a 1⁄4 3 and 1⁄4 10 ). Furthermore, our computer experiments show that phase apodization remains effective throughout a broad spectrum (60% of the central wavelength) covering the entire visible-light range. Phase-only modulation has the additional appeal of potential implementation via active segmented or deformable mirrors, thereby combining compensation of random phase aberrations and diffraction halo removal in a single optical element. Subject headings: instrumentation: adaptive optics — planetary systems — techniques: interferometric