Mirror Substrate Fabrication Techniques Of Low Expansion Glasses

J. Spangenberg-Jolley; T. Hobbs

doi:10.1117/12.949379

13 April 1989 Mirror Substrate Fabrication Techniques Of Low Expansion Glasses

J. Spangenberg-Jolley, T. Hobbs

Proceedings Volume 1013, Optical Design Methods, Applications and Large Optics; (1989) https://doi.org/10.1117/12.949379
Event: 1988 International Congress on Optical Science and Engineering, 1988, Hamburg, Germany

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 pie 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.

Citation Download Citation

J. Spangenberg-Jolley and T. Hobbs "Mirror Substrate Fabrication Techniques Of Low Expansion Glasses", Proc. SPIE 1013, Optical Design Methods, Applications and Large Optics, (13 April 1989); https://doi.org/10.1117/12.949379

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