Other
Scientific paper
Aug 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008spie.7012e.121d&link_type=abstract
Ground-based and Airborne Telescopes II. Edited by Stepp, Larry M.; Gilmozzi, Roberto. Proceedings of the SPIE, Volume 7012, p
Other
Scientific paper
We discuss a transmission primary objective grating (POG) telescope that is nearly flat to the ground with its secondary components buried below ground in a protected environment that enjoys a controlled atmosphere. Temperature gradients can be held steady by sealing this enclosure. End-to-end ray paths need not be interrupted by spiders or other structural support elements. Unlike mirror and lens telescopes, this layout is intrinsically off-axis. Light diffracted from a POG at a grazing angle can be collected a few meters below the POG, and the substructures do not require a deep excavation, as would be required for buried on-axis mirrors such as a zenith tube. The POG principle can take advantage of the rotation of the earth to acquire spectra sequentially, so active tilt and rotate axes are not necessary during observations. The POG aperture is extensible as a ribbon optic to kilometer scale at a linear increase in cost, as compared to other choices where infrastructure grows as the cube of the telescope size. The principle of operation was proven in miniature during bench tests that show high resolution spectra can be obtained at angular resolutions equal to seeing. Mathematical models of the underlying relationships show that flux collection increases with increased angles of grazing exodus even as efficiency decreases. Zemax models show a 30° field-of-view and the capacity to take spectra of all sources within that very wide field-of-view. The method lends itself to large apertures, because it is tolerant of POG surface unevenness.
Ditto Thomas D.
Ritter Joseph M.
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