18 July 2014 Restraint deformation and corrosion protection of gold deposited aluminum mirrors for cold optics of mid-infrared instruments
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Abstract
We report the restraint deformation and the corrosion protection of gold deposited aluminum mirrors for mid-infrared instruments. To evaluate the deformation of the aluminum mirrors by thermal shrinkage, monitoring measurement of the surface of a mirror has been carried out in the cooling cycles from the room temperature to 100 K. The result showed that the effect of the deformation was reduced to one fourth if the mirror was screwed with spring washers. We have explored an effective way to prevent the mirror from being galvanically corroded. A number of samples have been prepared by changing the coating conditions, such as inserting an insulation layer, making a multi-layer and overcoating water blocking layer, or carrying out precision cleaning before coating. Precision cleaning before the deposition and protecting coat with SiO over the gold layer seemed to be effective in blocking corrosion of the aluminum. The SiO over-coated mirror has survived the cooling test for the mid-infrared use and approximately 1 percent decrease in the reflectance has been detected at 6-25 microns compared to gold deposited mirror without coating.
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Mizuho Uchiyama, Mizuho Uchiyama, Takashi Miyata, Takashi Miyata, Shigeyuki Sako, Shigeyuki Sako, Takafumi Kamizuka, Takafumi Kamizuka, Tomohiko Nakamura, Tomohiko Nakamura, Kentaro Asano, Kentaro Asano, Kazushi Okada, Kazushi Okada, Takashi Onaka, Takashi Onaka, Itsuki Sakon, Itsuki Sakon, Hirokazu Kataza, Hirokazu Kataza, Yuki Sarugaku, Yuki Sarugaku, Okiharu Kirino, Okiharu Kirino, Hiroyuki Nakagawa, Hiroyuki Nakagawa, Norio Okada, Norio Okada, Kenji Mitsui, Kenji Mitsui, "Restraint deformation and corrosion protection of gold deposited aluminum mirrors for cold optics of mid-infrared instruments", Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 915143 (18 July 2014); doi: 10.1117/12.2054917; https://doi.org/10.1117/12.2054917
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