Characterization of Subsurface Damage in Glass and Metal Optics

    Published: Jan 1991

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    Even unusual care in polishing, leads to optics with somewhat damaged working faces. The question is, to what degree? the physical nature of this damage depends on the ductility or plasticity of the construction material. Glassy materials (glass, brittle metals and semiconductors) fracture, while ductile materials work harden. Beryllium suffers from both modes. To physically model damage, we oversimplify and picture a surface layer with two features, a depth and an intensity of the bulk property changes. A statistical alternative to intensity is the visible flaw density. We use a variety of analytical methods, but mainly x-ray diffraction, metallography and instrumented microindentation, and frequently use them in combination. Our problem is to develop a general basis and means of characterizing subsurface damage. To illustrate the diversity, difficulty and our progress with the problem, we will report experiences with a variety of examples. The talk will consider damage in “ductile regime” ground, classically polished fused silica BK-7, pyrex optics, “super” polished BK-7, precision ground silicon nitride and alumina ceramics, and precision CBN turned beryllium.7

    Author Information:

    Polvani, RS
    National Institute for Standards and Technology, Gaithersburg, MD

    Evans, CJ
    National Institute for Standards and Technology, Gaithersburg, MD

    Committee/Subcommittee: F01.03

    DOI: 10.1520/STP23624S

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