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Proceedings Paper

Focal ratio degradation performance of fiber positioning technology used in the Dark Energy Spectroscopic Instrument (DESI)
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Paper Abstract

The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment and will be used to conduct a five year survey covering 14,000 deg2 to z=3.5. This survey is accomplished using five thousand robotically positioned optical fibers that can be quickly reconfigured with a 5 μm positioning accuracy. The fiber performance in the near and far field of two types of robotic positioners are currently being investigated: tilting spine mechanical simulators and eccentric axis (or θ-φ) positioners. The far field performance of the fiber is important since the instrument efficiency is adversely affected if light from the fibers enters the spectrograph at a faster focal ratio than the spectrograph can accept (f/3.57 in the DESI design). This degradation of the focal ratio of light is caused by light entering the fiber off axis (tiliting positioner) or bending, twisting, and stress of the fiber (eccentric axis) positioner. The stability of the near field intensity distribution of the fiber is important since this determines the spectrograph point spread function (PSF). If the PSF changes from the calibration to the science exposures, this will result in an extraction bias. For DESI, a particular concern is the distortions in the PSF due to movement of the fibers during re-pointing.

Paper Details

Date Published: 28 July 2014
PDF: 10 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 914763 (28 July 2014); doi: 10.1117/12.2054454
Show Author Affiliations
Claire L. Poppett, Lawrence Berkeley National Lab. (United States)
Jerry Edelstein, Space Sciences Lab. (United States)
Robert Besuner, Space Sciences Lab. (United States)
Joseph H. Silber, Lawrence Berkeley National Lab. (United States)

Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)

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