4 February 2003 Evaluation of the thin film for mirror coating at Subaru Telescope
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We conducted the aluminization campaign of the primary mirror of the Subaru Telescope in September 2001. This was the third time with the Subaru's coating facility. The witness samples coated at the same time show reflectance above 91% at 500 nm, the highest of the three coating campaigns. We continue to pursue the film which has high reflectance, high adhesion nature to the glass substratum, and durability with little degradation in time. As part of the effort, we started to compare various evaluation methods of the coating films. The emphasis is on the physical property side, using XPS (X-ray Photoelectron Spectroscopy), SIMS (Secondary Ion Mass Spectrometry), and SEM (Scanning Electron Microscope). We hope to use the findings to improve our coating processes for the Subaru's mirrors and other mirrors. First thing we confirmed is that three oxidization layers exist in the aluminum coatings itself and between the aluminum and the glass substratum. This is caused by the three stage firing in the Subaru's 9 m chamber. The extent of such layers seems to contribute to the adhesion of the film to the glass. Next, we compared the film produced by the conventional evaporation (using 1.6 m chamber at Mitaka, Tokyo) and by the sputtering (using the Tohoku University equipment). The contamination and defects in the film seem to be responsible for the exfoliation, and the reflectance. We will use these physical property evaluations also to optimize the coating process of other coating materials that is suited for the infrared observations.
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Yukiko Kamata, Yukiko Kamata, Toshio Sato, Toshio Sato, Tomio Kanzawa, Tomio Kanzawa, "Evaluation of the thin film for mirror coating at Subaru Telescope", Proc. SPIE 4837, Large Ground-based Telescopes, (4 February 2003); doi: 10.1117/12.457960; https://doi.org/10.1117/12.457960

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