Scanning interferometer for aspheric surfaces and wavefronts
First Claim
1. A scanning method for measuring rotationally and non-rotationally symmetric test optics having aspherical surfaces, said method comprising the steps of:
- generating at least a partial spherical wavefront from a known origin along a scanning axis through the use of a spherical reference surface along said scanning axis upstream of said known origin;
aligning a test optic with respect to said scanning axis and selectively moving said test optic along said scanning axis relative to said known origin so that said spherical wavefront intersects the test optic at the apex of the aspherical surface and at one or more radial positions where the spherical wavefront and the aspheric surface intersect at points of common tangency to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions;
imaging said interferogram onto a detector to provide an electronic signal carrying said phase information;
interferometrically measuring the axial distance, v, by which said test optic is moved with respect to said origin and calculating the optical path length differences, p, between the center of test optic and the one or more radial positions based on said phase differences contained in said electronic signal;
calculating the coordinates, z and h, of the aspherical surface wherever said circles of curvature have intersected the aspherical surface at common points of tangency and in correspondence with the interferometrically measured distance, v and calculated optical path lengths, p; and
determining the shape of said aspheric surface based on said coordinate values and said optical path length differences.
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Abstract
Interferometric scanning method(s) and apparatus for measuring rotationally and non-rotationally symmetric test optics having spherical, mildly aspherical and multiple, mildly aspherical surfaces. At least a partial spherical wavefront is generated from a known origin along a scanning axis through the use of a spherical reference surface positioned along the scanning axis upstream of the known origin. A test optic is aligned with respect to the scanning axis and selectively moved along said scanning axis relative to the known origin so that the spherical wavefront intersects the test optic at the apex of the aspherical surface and at one or more radial positions where the spherical wavefront and the aspheric surface intersect at points of common tangency to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions. The interferogram is imaged onto a detector to provide an electronic signal carrying the phase information. The axial distance, v, by which said test optic is moved with respect to said origin is interferometrically measured and the optical path length differences, p, between the center of test optic and the one or more radial positions is calculated based on the phase differences contained in the electronic signal. The coordinates, z and h, of the aspherical surface are calculated wherever the circles of curvature have intersected the aspherical surface at common points of tangency and in correspondence with the interferometrically measured distance, v and calculated optical path lengths, p. The shape of the aspheric surface is then determined based on the coordinate values and the optical path length differences.
35 Citations
24 Claims
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1. A scanning method for measuring rotationally and non-rotationally symmetric test optics having aspherical surfaces, said method comprising the steps of:
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generating at least a partial spherical wavefront from a known origin along a scanning axis through the use of a spherical reference surface along said scanning axis upstream of said known origin;
aligning a test optic with respect to said scanning axis and selectively moving said test optic along said scanning axis relative to said known origin so that said spherical wavefront intersects the test optic at the apex of the aspherical surface and at one or more radial positions where the spherical wavefront and the aspheric surface intersect at points of common tangency to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions;
imaging said interferogram onto a detector to provide an electronic signal carrying said phase information;
interferometrically measuring the axial distance, v, by which said test optic is moved with respect to said origin and calculating the optical path length differences, p, between the center of test optic and the one or more radial positions based on said phase differences contained in said electronic signal;
calculating the coordinates, z and h, of the aspherical surface wherever said circles of curvature have intersected the aspherical surface at common points of tangency and in correspondence with the interferometrically measured distance, v and calculated optical path lengths, p; and
determining the shape of said aspheric surface based on said coordinate values and said optical path length differences. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. Scanning apparatus for measuring rotationally and non-rotationally symmetric test optics having aspherical surfaces, said apparatus comprising:
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means for generating at least a partial spherical wavefront from a known origin along a scanning axis, said generating means including a spherical reference surface positioned along said scanning axis upstream of said known origin;
means for aligning a test optic with respect to said scanning axis and selectively moving said test optic along said scanning axis relative to said known origin so that said spherical wavefront intersects the test optic at the apex of the aspherical surface and at one or more radial positions where the spherical wavefront and the aspheric surface intersect at points of common tangency to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions;
a areal detector;
means for imaging said interferogram onto said areal detector to provide an electronic signal carrying said phase information;
means for interferometrically measuring the axial distance, v, by which said test optic is moved with respect to said origin and calculating the optical path length differences, p, between the center of test optic and the one or more radial positions based on said phase differences contained in said electronic signal; and
means for calculating the coordinates, z and h, of the aspherical surface wherever said circles of curvature have intersected the aspherical surface at common points of tangency and in correspondence with the interferometrically measured distance, v and calculated optical path lengths, p; and
determining the shape of said aspheric surface based on said coordinate values and said optical path length differences. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification