27 July 2016 Ethylene glycol contamination effects on first surface aluminized mirrors
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Abstract
The Dark Energy Spectroscopic Instrument (DESI) is under construction for installation on the Mayall 4 Meter telescope. The use of a liquid cooling system is proposed to maintain the DESI prime focus assembly temperature within ±1°C of ambient. Due to concerns of fluid deposition onto optical surfaces from possible leaks, systematic tests were performed of the effects on first surface aluminized mirrors of ethylene glycol and two other candidate coolants. Objective measurement of scattering and reflectivity was an important supplement to visual inspection. Rapid cleanup of a coolant spill followed by a hand wash of the mirror limited surface degradation to the equivalent of a few months of general environmental exposure. Prolonged exposure to corrosive coolants dissolved the aluminum, necesitating mirror recoating.
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Patrick Dunlop, Ronald G. Probst, Matthew Evatt, Larry Reddell, David Sprayberry, "Ethylene glycol contamination effects on first surface aluminized mirrors", Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 99063F (27 July 2016); doi: 10.1117/12.2233233; https://doi.org/10.1117/12.2233233
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