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6 July 2006 Ultra low thermal expansion material for telescope mirror substrate
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The material property of CLEARCERAM®-Z series, which is the low thermal expansion glass-ceramics products by Ohara Inc., with an integrated product size of Dia.1.4meter was investigated along with confirmation of the surface finish performances. The material property investigation for the Dia.1.4meter CLEARCERAM®-Z HS indicated the mean CTE of 0.01×10-7/degree C, the CTE uniformity (CTEmax.-CTEmin.) of 0.10×10-7/degree C based on developed precision CTE measurement system with 2ppb/degree C repeatability and the maximum stress birefringence of 4.4nm/cm within the disk, which are meeting the mirror substrate material specification for near future large telescope project (Thirty Meter Telescope project). From the experiments to determine surface finish performance, no practical change was observed for the surface profile in millimeter scan filed per Ion Beam Figuring processing. Also the surface robustness against acid solutions, which are used at mirror cleaning, was proved from dipping tests using Hydrochloric acid and Nitric acid. With the material property based on the precision metrology and the surface finish performances, the suitability of CLEARCERAM®-Z for telescope mirror substrate application was presented.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Kousuke Nakajima, Nobuo Kawasaki, Toshihide Nakajima, Yoshiyuki Owari, and Hiroyuki Minamikawa "Ultra low thermal expansion material for telescope mirror substrate", Proc. SPIE 6273, Optomechanical Technologies for Astronomy, 62732M (6 July 2006);


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