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R. Schlitz, M. Aziz (Harvard University), V. Tolls (CfA)
Direct imaging of extra-solar planets is important for determining the properties of individual planets and to study multi-planet systems. Obtaining spectra of extra-solar planets enables us to constrain the composition of planetary atmospheres and surfaces, their climates, and their rotation periods. The techniques required to isolate and detect an extra-solar planet next to its host star are quite challenging and require significant improvement. SAO has set up a testbed to study coronagraphic techniques, starting with Labeyrie's multi-step speckle reduction technique. An essential element of this testbed are the soft-edge occulter masks to achieve the required high suppression of the light from the host star. Currently, there is only one method to manufacture gray-scale occulter masks for Lyot coronagraphs achieving high light suppression. High Energy Beam Sensitive (HEBS) glass photomask occulters reach an optical density of up to 9 - 10 in the visible. However, this optical density decreases significantly at infra-red wavelength. In order to support our testbed, we are investigating the manufacturing of occulter masks using a focused ion beam (FIB) which allows the controlled fabrication of arbitrary profiles. Current results show this method is capable of fabricating small optically smooth structures with fine control over height at a given radius; structures have been fabricated with diameters ~5 \mum with control over the radial depth profile. Through the proper choice of materials, this method will enable us to manufacture occulter masks with high optical density from the visible to infra-red wavelength.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.