24 July 1998 Importance of telescope alignment for the performance of a stellar interferometer
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Abstract
The visibility performance of a stellar interferometer can be expressed by means of the instrumental visibility factor, defined as the ratio of measured to intrinsic object visibility, in the absence of atmospheric distortion. The instrumental visibility factor can be approximated by a product of Strehl ratios, each related to one of the main components of the instrument. For IOTA, which uses telescopes to collect starlight, the Strehl factor related to telescope alignment is a potentially significant term. This paper focuses on estimating instrumental visibility due to telescope misalignment. In practice we align each telescope using a collimated optics-filling laser beam projected out from the laboratory to the telescope and siderostat, adjusted so that the beam is returned to the laboratory. The return beam is viewed in either of two ways: (a) intensity mode, where the beam is simply;y displayed on a white card; (b) interference mode, where the beam is interfered at a beamsplitter with either a locally retroreflected plane wave, or a return beam from a second telescope.Both modes were simulated with a computer program that displays the expected fringe pattern. Many misalignment combinations were calculated. In either mode, the collection of resulting beam patterns is useful in guiding an iterative alignment procedure, and also in estimating any remaining residual error.
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Irene L. Porro, Irene L. Porro, Wesley A. Traub, Wesley A. Traub, Nathaniel P. Carleton, Nathaniel P. Carleton, } "Importance of telescope alignment for the performance of a stellar interferometer", Proc. SPIE 3350, Astronomical Interferometry, (24 July 1998); doi: 10.1117/12.317105; https://doi.org/10.1117/12.317105
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