26 September 2016 Characterizing the performance of cryogenic lens mounts for the HARMONI spectograph
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Abstract
Two different cryogenic lens mounts have been developed and tested for potential use in the HARMONI spectrograph cameras. Problems were encountered during initial tests whereby the lenses were cracking where they were adhered to the mount. This was found to be caused by the choice of adhesive and solved by changing to a silicone RTV glue. The cryogenic performance of the two lens mount designs was tested, with the baseline design seeing the lens move by 18 μm radially from warm to cold, which is just within the tightest tolerances from the optical design, as long as any misalignments in the mounting procedure can be removed when aligning the lenses in the camera barrel. The alternative design was found have much worse performance with the lens moving by 40 μm due to fragile flexures and so is no longer being considered. A mounting procedure for spherical lenses has also been developed which is capable of peak to valley alignments of 10 μm axially, and 5 μm radially.
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Jamie R. Allen, Kieran O'Brien, James D. Lynn, Niranjan A. Thatte, Ian A. J. Tosh, Mike Tacon, "Characterizing the performance of cryogenic lens mounts for the HARMONI spectograph", Proc. SPIE 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 99124Q (26 September 2016); doi: 10.1117/12.2233613; https://doi.org/10.1117/12.2233613
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