Two-wavelength confocal interferometer for measuring multiple surfaces
First Claim
1. A scanning interferometer for measuring first and second surfaces of a test piece in sequence comprising:
- a test arm and a reference arm that convey test and reference beams of light;
a beamsplitter within the test arm that separates the test beam into first and second sub-test beams;
a focusing optic within the test arm that focuses the first and second sub-test beams to different points of focus;
a compound probe within the test arm that conveys the first and second sub-test beams to the different points of focus;
an actuator that relatively moves the probe with respect to the test piece between a first position at which;
(a) the point of focus of the first sub-test beam is positioned on the first surface of the test piece and (b) the point of focus of the second sub-test beam is positioned off both the first and second surfaces of the test piece, and a second position at which;
(a) the point of focus of the second sub-test beam is positioned on the second surface of the test piece and (b) the point of focus of the first sub-test beam is positioned off both the first and second surfaces of the test piece; and
a detection system that detects interference signals between the reference beam and the first sub-test beam when the probe is located at the first position and detects interference signals between the reference beam and the second sub-test beam when the probe is located at the second position.
1 Assignment
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Accused Products
Abstract
A scanning interferometer employs dual interferometer modules at different wavelengths to expand a dynamic range of measurement, a compound probe for measuring multiple surfaces, and a confocal optical system for distinguishing between the surfaces measured by the compound probe. Within the compound probe, miniature optics divide a test beam into two sub-test beams that are focused normal to different test surfaces. Both sub-test beams contain the different wavelengths. A separate interferometer monitors movements of the compound probe for producing absolute measures of the test surfaces.
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Citations
56 Claims
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1. A scanning interferometer for measuring first and second surfaces of a test piece in sequence comprising:
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a test arm and a reference arm that convey test and reference beams of light;
a beamsplitter within the test arm that separates the test beam into first and second sub-test beams;
a focusing optic within the test arm that focuses the first and second sub-test beams to different points of focus;
a compound probe within the test arm that conveys the first and second sub-test beams to the different points of focus;
an actuator that relatively moves the probe with respect to the test piece between a first position at which;
(a) the point of focus of the first sub-test beam is positioned on the first surface of the test piece and (b) the point of focus of the second sub-test beam is positioned off both the first and second surfaces of the test piece, and a second position at which;
(a) the point of focus of the second sub-test beam is positioned on the second surface of the test piece and (b) the point of focus of the first sub-test beam is positioned off both the first and second surfaces of the test piece; and
a detection system that detects interference signals between the reference beam and the first sub-test beam when the probe is located at the first position and detects interference signals between the reference beam and the second sub-test beam when the probe is located at the second position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method of measuring multiple surfaces of a test piece with a scanning interferometer comprising the steps of:
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dividing a beam of light into test and reference beams;
further dividing the test beam into first and second sub-test beams;
focusing the first and second sub-test beams to different points of focus for separately measuring first and second surfaces of the test piece;
positioning the point of focus of the first sub-test beam on the first surface of the test piece while positioning the point of focus of the second sub-test beam off of both the first and second surfaces of the test piece;
relatively moving the point of focus of the first sub-test beam across the first surface of the test piece;
positioning the point of focus of the second sub-test beam on the second surface of the test piece while positioning the point of focus of the first sub-test beam off of both the first and second surfaces of the test piece;
relatively moving the point of focus of the second sub-test beam across the second surface of the test piece;
retroreflecting the first and second sub-test beams from their respective points of focus on the surfaces of the test piece;
directing the retroreflected first and second sub-test beams together with the reference beam proximate to a detector; and
separately detecting interference signals between the reference beam and the first and second sub-test beams according to which of the sub-test beams is positioned in focus on one of the first and second surfaces of the test piece. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44)
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45. A method of making absolute measurements with a confocal scanning interferometer comprising the steps of:
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dividing a beam of light into test and reference beams;
focusing the test beam to a point of focus;
adjusting the point of focus with respect to a surface of a test piece;
retroreflecting the test beam from the surface of the test piece;
refocusing the retroreflected test beam through a limiting aperture near a conjugate point of focus;
combining the retroreflected test beam with the reference beam for producing an interference signal;
monitoring variations of the test beam component of the interference signal;
determining a position at which the point of focus lies on the surface of the test piece based on the monitored variations of the interference signal;
separately measuring relative movements of the point of focus with respect to a known point of reference to the position at which the point of focus lies on the surface of the test piece; and
resolving phase ambiguities of the interference signal based on the measured relative movements of the point of focus with respect to the known point of reference for making absolute measurements of the test surface. - View Dependent Claims (46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56)
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Specification