ULETM, a zero expansion glass, offers many advantages as mirror blank material due to its thermal and mechanical
properties as well as the flexibility it offers in design and fabrication. Produced by the flame hydrolysis process, this
titanium silicate has high homogeneity of Coefficient of Thermal Expansion (CTE) that can be determined within any
piece of ULE by nondestructive ultrasonic measurements. The ability to fusion-seal the glass while maintaining strength
offers mirror manufacturing design freedom. Coming has produced a 12 inch square plano blank and a 24 inch diameter
meniscus, both fabricated with cooling channels, using existing fusion techniques. The square blank was manufactured by
actually machining grooves into the plates prior to fusing them together. The meniscus production consisted of fusing bars
of ULE between the two outside plates. The meniscus was subsequently thermally tested by NOAO. A 4 meter solid
monolithic meniscus with cooling channels is an extension of this fusion technology.
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