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Proceedings Paper

Longitudinal dispersion control for the Keck interferometer nuller
Author(s): Christopher D. Koresko; Bertrand P. Mennesson; Eugene Serabyn; Mark Colavita; Rachel L. Akeson; Mark R. Swain
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Paper Abstract

The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase).

Paper Details

Date Published: 21 February 2003
PDF: 11 pages
Proc. SPIE 4838, Interferometry for Optical Astronomy II, (21 February 2003); doi: 10.1117/12.458032
Show Author Affiliations
Christopher D. Koresko, California Institute of Technology (United States)
Bertrand P. Mennesson, Jet Propulsion Lab. (United States)
Eugene Serabyn, Jet Propulsion Lab. (United States)
Mark Colavita, Jet Propulsion Lab. (United States)
Rachel L. Akeson, California Institute of Technology (United States)
Mark R. Swain, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 4838:
Interferometry for Optical Astronomy II
Wesley A. Traub, Editor(s)

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