Comparison of laser and CO2 snow cleaning of astronomical mirror samples

Wayne D. Kimura; Gerald H. Kim; Bruce Balick

doi:10.1117/12.176177

1 June 1994 Comparison of laser and CO₂ snow cleaning of astronomical mirror samples

Wayne D. Kimura, Gerald H. Kim, Bruce Balick

Proceedings Volume 2199, Advanced Technology Optical Telescopes V; (1994) https://doi.org/10.1117/12.176177
Event: 1994 Symposium on Astronomical Telescopes and Instrumentation for the 21st Century, 1994, Kailua, Kona, HI, United States

Abstract

The cleaning of mirrors in large, remote telescopes is essential if these telescopes are to meet their performance goals, including low (2%) thermal emissivity in the infrared. Aluminum- coated mirror samples which were naturally or artificially contaminated with materials representative of those at observatories, were cleaned with a UV laser beam or CO₂ snow. Cleaning effectiveness was determined from studies of residual particle densities and size distributions (measured from low-magnification optical imaging). For exposures under two weeks both laser and CO₂ cleaning yield comparable results; however, for longer exposures (up to three months) UV laser cleaning is about twice as effective in our tests. At the laser energy densities required for effective cleaning, no surface changes or damage was observed even after cleaning the same spot 200 times. For 8-m class telescopes, the annual consumption cost of sufficiently pure CO₂ is comparable to the capital cost of a UV laser. Both methods clean such surfaces in less than one day. Two attractive features of laser cleaning are that the method can be fully automated and run frequently without significant cost of manpower or expendables, and that by focusing the laser beam tighter it can be used to strip old surface coatings prior to recoating.

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Wayne D. Kimura, Gerald H. Kim, and Bruce Balick "Comparison of laser and CO₂ snow cleaning of astronomical mirror samples", Proc. SPIE 2199, Advanced Technology Optical Telescopes V, (1 June 1994); https://doi.org/10.1117/12.176177

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