US 6,206,531 B1Granted

Lightweight precision optical mirror substrate and method of making

AssigneesUltramet, Ono Labratiories

InventorsBrian E. Williams, Russell M. Ono

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Abstract

A high precision composite optical mirror substrate comprising a lightweight reticulated foam core which is less than about 25 percent dense, an initially separate dense or small pore size faceplate mounted to the core, and a continuous formed in situ encapsulating coating. The coating fully encapsulates the ligaments throughout the reticulated foam core, the juncture between the core and the faceplate, and the faceplate, including the exposed face of the faceplate (the mirror surface). The exposed face of the dense faceplate is shaped to about the desired mirror surface shape. The deposit of coating material on the exposed face of the faceplate is near net shape to the desired mirror surface. The physical characteristics of the composite substrate are dominated by the properties of the coating material. When the coating material is a chemical vapor deposit of silicon carbide, the interlayer is preferably graphite with a thermal expansion coefficient that closely matches that of the silicon carbide. The silicon carbide encapsulated substrate is very strong, rigid, and thermally and structurally stable.

Claims13

Dependent claims

A method of making a composite optical mirror substrate including a mirror surface having a shape comprising the steps of:

selecting a reticulated foam skeleton which is less than approximately 10 percent dense and comprises ligaments, and forming said reticulated foam skeleton into a core for said mirror, a first face of said reticulated foam skeleton being formed into approximately the shape of said mirror surface;
selecting a prefabricated dense material having a first surface and a second surface generally opposed to said first surface, said dense material having a first thermal expansion coefficient, and forming said first surface to approximately the shape of said mirror surface, and said second surface to approximately conform to the shape of said first face;
rigidly mounting said second surface to said first face through a bonding material to form a workpiece;
selecting a structural and optical coating material having a second thermal expansion coefficient, said first and second thermal expansion coefficients being within about 10 percent of each;
and
fully encapsulating said workpiece in a formed in situ layer of said coating material, said layer comprising an optical grade deposit on said mirror surface and encapsulating said bonding material and said ligaments throughout said reticulated foam skeleton, said mirror surface being on said first surface, whereby the thermal expansion coefficient, thermal conductivity, elastic modulus, specific stiffness, inertia loading parameter, thermal distortion parameter, and thermal stress parameter properties of said composite optical mirror substrate are substantially those of said coating material.

3 more elements

Dependencies are inferred from the claim text.