Ground-based Sensor to Detect GEOs Without the Use of a Laser Guide- star.

摘要

We are developing a highly sensitive non-linear Curvature Wavefront Sensor (nlCWFS) which will make it possible to detect objects as dim as m(sub v) = 11-14. Current Space Situational Awareness (SSA) programs rely on laser guide stars (LGSs) to detect dim objects near GEOs, however LGSs are expensive to use and require permission to lase. The nlCWFS will be able to detect objects near GEOs without the use of a LGS and will be able to obtain higher contrast then possible with the SHWFS. The nlCWFS senses at the diffraction limit whereas currently used WFSs such as the SHWFS sense at the seeing limit. This difference awards the nlCWFS a gain in photon flux of (D/r(sub 0))2 at low spatial modes such as tip-tilt. The SHWFS allows interference of points separated only by a subaperture making it insensitive to low order modes. The nlCWFS, on the other hand, uses the full spatial coherence of the pupil making it sensitive to low order modes which dominate the atmosphere and scatter light within a close angular separation of a GEO where a dim object might be hiding. In order to find dim objects near a bright target it is important to obtain a high contrast ratio within a small angular resolution of the central PSF core. The PSF contrast obtained with the nlCWFS is two orders of magnitude better than the SHWFS. In this paper we present results from building the nlCWFS for the 6.5 m MMT Smithsonian Observatory. We outline our progress towards building a nlCWFS for a 1.5 m telescope.