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Proceedings Paper

Methods for evaluating the performance of volume phase holographic gratings for the VIRUS spectrograph array
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Paper Abstract

The Visible Integral field Replicable Unit Spectrograph (VIRUS) is an array of at least 150 copies of a simple, fiber-fed integral field spectrograph that will be deployed on the Hobby-Eberly Telescope (HET) to carry out the HET Dark Energy Experiment (HETDEX). Each spectrograph contains a volume phase holographic grating as its dispersing element that is used in first order for 350 < λ(nm) < 550. We discuss the test methods used to evaluate the performance of the prototype gratings, which have aided in modifying the fabrication prescription for achieving the specified batch diffraction efficiency required for HETDEX. In particular, we discuss tests in which we measure the diffraction efficiency at the nominal grating angle of incidence in VIRUS for all orders accessible to our test bench that are allowed by the grating equation. For select gratings, these tests have allowed us to account for < 90% of the incident light for wavelengths within the spectral coverage of VIRUS. The remaining light that is unaccounted for is likely being diffracted into reflective orders or being absorbed or scattered within the grating layer (for bluer wavelengths especially, the latter term may dominate the others). Finally, we discuss an apparatus that will be used to quickly verify the first order diffraction efficiency specification for the batch of at least 150 VIRUS production gratings.

Paper Details

Date Published: 24 September 2012
PDF: 18 pages
Proc. SPIE 8446, Ground-based and Airborne Instrumentation for Astronomy IV, 84465H (24 September 2012); doi: 10.1117/12.926189
Show Author Affiliations
Taylor S. Chonis, The Univ. of Texas at Austin (United States)
Gary J. Hill, The Univ. of Texas at Austin (United States)
J. Christopher Clemens, Univ. of North Carolina (United States)
Bart Dunlap, Univ. of North Carolina (United States)
Hanshin Lee, The Univ. of Texas at Austin (United States)

Published in SPIE Proceedings Vol. 8446:
Ground-based and Airborne Instrumentation for Astronomy IV
Ian S. McLean; Suzanne K. Ramsay; Hideki Takami, Editor(s)

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