Ms. Shilpa N. Raja Profile

Shilpa N. Raja

at Harvard Univ

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Proceedings Article | 20 August 2009 Paper

FIB machining of occulting masks for imaging of extrasolar planets

Shilpa Raja, Michael Aziz, James Foley, Volker Tolls

Proceedings Volume 7440, 744018 (2009) https://doi.org/10.1117/12.828515

KEYWORDS: Photomasks, Polymethylmethacrylate, Absorbance, Exoplanets, Refractive index, Ion beams, Coronagraphy, Polymers, Lithography, Mask making

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We are developing the ability for Focused Ion Beam (FIB) machining of occulting masks for use in coronagraphs. These masks will be used as soft-edged Lyot stops to suppress light from stars and allow direct imaging of extrasolar planets. The FIB approach is attractive because it has the potential for higher precision than mechanical machining and for larger volumes than electron-beam lithography. The mask fabrication process is trifold: 1) a transparent material-currently, poly(methyl methacrylate) (PMMA)-is doped with dyes; 2) the mask shape is FIB milled into the material; and 3) the mask is coated with another layer of index-matching transparent absorber. Using a Zeiss NVision 40 FIB system, we have fabricated conical-shaped masks of various slopes in dye-doped PMMA. Inherent in this process is the advantage of control of the features through programming the ion beam track. We have also optically characterized these masks as well as the dye-doped absorbing material. We have found that the dye-doped PMMA has a very high absorbance, >1 OD.

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