29 January 1989 Mirror Substrate Fabrication Techniques Of Low Expansion Glasses
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Abstract
Low expansion glasses offer many advantages as mirror blank materials due to their thermal and mechanical properties as well as the flexility they offer in design and fabrication. Fused Silica, Corning Code 7940 and ULE titanium silicate, Code 7971, produced by the flame hydrolysis process, are high purity and homogeneous glasses. Determination of the average and the variation pattern of ghe Coefficient of thermal expansion (CTE) within ULE mirror blanks (nominally 0 x 10 /°C over the 5°C to 35°C temperature interval) is readily accomplished to an accuracy of + 2 parts per billion per degree centigrade (ppb/°C) by ultrasonic measurements. The ability to fusion seal each of the glasses offers mirror manufacturing design freedom of shape, size and weight. Solid monolithic mirror blanks have been successfully manufactured by the hex-seal method up to 4 meters diameter and 10 meter blanks are an extension of the proven fusion techniques. Lightweight fusion bonded ULE mirrors, such as the primary used in the Hubble Space Telescope, are fabricated by first "welding" selected glass pieces together to form a structurally rigid core and then fusing it between two plates. Ultralightweight (10% solid weight) low expansion mirrors produced by "frit bonding" a fusion core between two precision machined plates, maintain an optical figure when exposed to thermal cycling and mechanical abuse environments.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
J. Spangenberg-Jolley, J. Spangenberg-Jolley, T. Hobbs, T. Hobbs, } "Mirror Substrate Fabrication Techniques Of Low Expansion Glasses", Proc. SPIE 0966, Advances in Fabrication and Metrology for Optics and Large Optics, (29 January 1989); doi: 10.1117/12.948074; https://doi.org/10.1117/12.948074
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