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Ambiguity Elimination in Confocal Microscopy

IP.com Disclosure Number: IPCOM000040745D
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR

Abstract

Incorrect surface height measurements on tortuous or textured surfaces under confocal microscope inspection can be eliminated by comparing a measurement where the illumination and detection points are coincident with a measurement where the illumination and detection points are separated. A problem in confocal inspection of metal and ceramic parts is that there is a family of equivalent surfaces of an object under inspection which produces identical confocal signals. This is unacceptable where the measurement is being used to indicate the height of the surface. For example, a surface with a radius of curvature matching that of the incoming spherical wave will create a return signal corresponding to a planar surface located at the center of the radius of curvature.

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Ambiguity Elimination in Confocal Microscopy

Incorrect surface height measurements on tortuous or textured surfaces under confocal microscope inspection can be eliminated by comparing a measurement where the illumination and detection points are coincident with a measurement where the illumination and detection points are separated. A problem in confocal inspection of metal and ceramic parts is that there is a family of equivalent surfaces of an object under inspection which produces identical confocal signals. This is unacceptable where the measurement is being used to indicate the height of the surface. For example, a surface with a radius of curvature matching that of the incoming spherical wave will create a return signal corresponding to a planar surface located at the center of the radius of curvature. In order to remove the ambiguity as to whether a return signal is coming from a planar surface or one of its equivalent curved surface, at least two measurements should be made. The first is a standard measurement with the source and detector images superimposed on the object plane. If there is substantial return signal, this indicates that the surface must be either locally planar or spherical with a center of curvature on the object plane. The second measurement is made with the source and detector images separated by equal distances on either side of the object plane. In this case, a substantial return signal indicates that the surface of the sample must e...