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W. Yang, C. Ftaclas (Physics Department, Michigan Tech)
The obstacles to the detection of extrasolar planets by imaging vary with the wavelength at which the detection is made, but in all cases there is general agreement that the first step in detection is suppression of the diffraction pattern of the parent star. The stellar coronagraph has proven to be an attractive way of doing this but it suffers from the need to have some minimal star-planet angular separation measured in diffraction radii. This limits applicability of the instrument particularly at long wavelengths or for small orbital radii. We present a new coronagraph design using a phase rather than an amplitude mask that creates two, almost identical, out of phase pupil images. The cancellation varies with Lyot stop radius but it is as much as a part in 10,000. There is excellent performance even without under-sizing the Lyot stop and there is no need for any amplitude matching. This allows planet detection at radii very close to the image core. We discuss the design, its performance, how it could be made, and limitations of the approach.
W. Yang wishes to thank NASA for supporting this research and CF wishes to acknowledge both NASA and NSF for their support