Measurement of complex surface shapes using a spherical wavefront
First Claim
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1. An interferometry method, comprising:
- directing a measurement wavefront to reflect from a measurement surface and a reference wavefront to reflect from a reference surface, the measurement and reference wavefronts being derived from a common light source;
directing the reflected measurement and reference wavefronts to overlap with one another and form an interference pattern, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a constant optical path length difference between the measurement and reference wavefronts; and
varying the radius of curvature of a locally spherical portion of the optical measurement surface to contact a conical portion of the measurement surface, and detecting the interference pattern as a function of the radius of curvature.
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Abstract
Conical surfaces (and other complex surface shapes) can be interferometrically characterized using a locally spherical measurement wavefront (e.g., spherical and aspherical wavefronts). In particular, complex surface shapes are measured relative to a measurement point datum. This is achieved by varying the radius of curvature of a virtual surface corresponding to a theoretical test surface that would reflect a measurement wavefront to produce a constant optical path length difference (e.g., zero OPD) between the measurement and reference wavefronts.
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Citations
93 Claims
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1. An interferometry method, comprising:
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directing a measurement wavefront to reflect from a measurement surface and a reference wavefront to reflect from a reference surface, the measurement and reference wavefronts being derived from a common light source;
directing the reflected measurement and reference wavefronts to overlap with one another and form an interference pattern, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a constant optical path length difference between the measurement and reference wavefronts; and
varying the radius of curvature of a locally spherical portion of the optical measurement surface to contact a conical portion of the measurement surface, and detecting the interference pattern as a function of the radius of curvature. - View Dependent Claims (2, 3, 4, 5)
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6. An interferometry method, comprising:
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directing a measurement wavefront to reflect from a measurement surface and a reference wavefront to reflect from a reference surface, the measurement and reference wavefronts being derived from a common light source having a coherence length;
directing the reflected measurement and reference wavefronts to overlap with one another and form an interference pattern, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a constant optical path length difference between the measurement and reference wavefronts; and
varying the radius of curvature of a locally spherical portion of the optical measurement surface to contact the measurement surface, and detecting the interference pattern as a function of the radius of curvature, wherein the radius of curvature is varied over a distance greater than the coherence length of the light source. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
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43. An interferometry method, comprising:
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directing a measurement wavefront to reflect from a measurement surface and a reference wavefront to reflect from a reference surface, the measurement and reference wavefronts being derived from a common light source;
directing the reflected measurement and reference wavefronts to overlap with one another and form an interference pattern, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a constant optical path length difference between the measurement and reference wavefronts;
varying the radius of curvature of a locally spherical portion of the optical measurement surface to contact the measurement surface, and detecting the interference pattern as a function of the radius of curvature, and generating a radial height profile, the radial height profile corresponding to the distance between the measurement surface and the optical measurement surface at a particular radius of curvature along a normal to the optical measurement surface at the particular radius of curvature. - View Dependent Claims (44, 45, 46, 47, 48, 49, 50)
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51. A method for calibrating an interferometric system using a calibration artifact having a known shape, comprising:
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directing a measurement wavefront to reflect from the calibration artifact and a reference wavefront to reflect from a reference surface, the measurement and reference wavefronts being derived from a common light source;
directing the reflected measurement and reference wavefronts to overlap with one another and form an interference pattern, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a constant optical path length difference between the measurement and reference wavefronts;
varying the radius of curvature of a locally spherical portion of the optical measurement surface to contact the calibration artifact, and detecting the interference pattern as a function of the radius of curvature;
generating a radial height profile, the radial height profile corresponding to the distance between the calibration artifact and the optical measurement surface at a particular radius of curvature along a normal to the optical measurement surface at the particular radius of curvature; and
calibrating the interferometry system based on the radial height profile. - View Dependent Claims (52, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93)
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57. An interferometry system, comprising
a light source having a coherence length; -
an interferometer positioned to derive measurement and reference wavefronts from the light source, wherein during operation the interferometer directs the measurement wavefront to reflect from a measurement surface and the reference wavefront to reflect from a reference surface, and further directs reflected measurement and reflected reference wavefronts to overlap with one another and to form an interference pattern, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a constant optical path length difference between the measurement and reference wavefronts;
a translation stage coupled to the interferometer to vary the radius of curvature of a locally spherical portion of the optical measurement surface to contact the measurement surface, wherein the translation stage varies the radius of curvature over a distance greater than the coherence length of the light source; and
a detector positioned to detect the interference pattern as a function of the radius of curvature.
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Specification