Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2005-04-12
2005-04-12
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
Reexamination Certificate
active
06879402
ABSTRACT:
Interferometric scanning method(s) and apparatus for measuring rotationally and non-rotationally symmetric test optics either having aspherical surfaces or that produce aspherical wavefronts. A spherical or partial spherical wavefront is generated from a known origin along an optical axis. The test optic is aligned with respect the optical axis and selectively moved along it relative to the known origin so that the spherical wavefront intersects the test optic at the apex of the aspherical surface and at radial positions where the spherical wavefront and the aspheric surface intersect at points of common tangency. An axial distance, ν, and optical path length, p, are interferometrically measured as the test optic is axially scanned by the spherical wavefront where ν is the distance by which the test optic is moved with respect to the origin and p is the optical path length difference between the apex of an aspherical surface associated with the test optic and the apex of the circles of curvature that intersect the aspherical surface at the common points of tangency. Coordinates of the aspherical surface are calculated wherever the circles of curvature have intersected the aspherical surface and in correspondence with the interferometrically measured distances, ν and p. Afterwards, the shape of the aspheric surface is calculated. Where the test optic comprises a refracting optic a known spherical reflecting surface is provided upstream of the refracting optic for movement along the optical axis and a known wavefront is made to transit the refracting optic, reflects from the known spherical surface, again transits the refracting optic traveling towards the known origin after which the interferogram is formed. In another aspect of the invention, a spherical reference surface is provided to form a Fizeau that is used to generate phase information for measuring spheres, mild aspheres, and multiple mild aspheres.
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Caufield Francis J.
Lyons Michael A.
Turner Samuel A.
Zygo Corporation
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