Scanning interferometry technique for through-thickness evaluation in multi-layered transparent structures
First Claim
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1. A method of scanning a multi-layered specimen, the method comprising:
- receiving a coherent radiation beam and separating the coherent radiation beam into an object beam and a reference beam, the object beam and the reference beam being coherent with one another;
directing the object beam at the specimen and collecting a resulting sampled beam from the specimen, wherein the sampled beam comprises reflected radiation from the specimen and/or backscattered radiation from the specimen;
maintaining the reference beam along a reference beam path and free from incidence on the specimen, and scanning the reference beam along different optical path lengths of the reference beam path, wherein the scanning of the reference beam is along a reference axis coinciding with an axis into the specimen and over a depth region into the specimen;
combining the sampled beam with the reference beam to produce an interferometric intensity signal or pattern, where, as a result of the scanning of the reference beam, the interferometric pattern contains amplitude peaks that are caused by reflection or scattering from discontinuities at different depths within the depth region of the specimen;
identifying, in a signal processing machine, the depth positions, within the specimen, of each of the discontinuities from the positions of the amplitude peaks in the interferometric pattern, wherein the discontinuities represent fiducial markers within the specimen;
determining, in the signal processing machine, a distance between at least two of the fiducial markers;
deforming the specimen in at least one direction;
identifying, in the signal processing machine, updated depth positions, within the specimen, of the at least two fiducial markers; and
determining, in the signal processing machine, an updated distance between the at least two fiducial markers.
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Abstract
A multi-layer transparent composite detection technique includes producing two beams from a single, low-coherence source, a test beam and a reference beam, and scanning the reference beam to determine, with high precision, the depths of flaws (e.g., delaminations, bubbles, inclusions or other reflective or scattering objects) within a specimen or test object. The techniques combine light back-reflected or back-scattered from an internal flaw or interface with light in a reference path to identify such features and locations.
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Citations
19 Claims
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1. A method of scanning a multi-layered specimen, the method comprising:
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receiving a coherent radiation beam and separating the coherent radiation beam into an object beam and a reference beam, the object beam and the reference beam being coherent with one another; directing the object beam at the specimen and collecting a resulting sampled beam from the specimen, wherein the sampled beam comprises reflected radiation from the specimen and/or backscattered radiation from the specimen; maintaining the reference beam along a reference beam path and free from incidence on the specimen, and scanning the reference beam along different optical path lengths of the reference beam path, wherein the scanning of the reference beam is along a reference axis coinciding with an axis into the specimen and over a depth region into the specimen; combining the sampled beam with the reference beam to produce an interferometric intensity signal or pattern, where, as a result of the scanning of the reference beam, the interferometric pattern contains amplitude peaks that are caused by reflection or scattering from discontinuities at different depths within the depth region of the specimen; identifying, in a signal processing machine, the depth positions, within the specimen, of each of the discontinuities from the positions of the amplitude peaks in the interferometric pattern, wherein the discontinuities represent fiducial markers within the specimen; determining, in the signal processing machine, a distance between at least two of the fiducial markers; deforming the specimen in at least one direction; identifying, in the signal processing machine, updated depth positions, within the specimen, of the at least two fiducial markers; and determining, in the signal processing machine, an updated distance between the at least two fiducial markers. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for scanning a multi-layered specimen, the apparatus comprising:
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a beam splitter positioned to receive a coherent radiation beam and configured to separate the coherent radiation beam into an object beam and a reference beam, the object beam and the reference beam being coherent with one another; a specimen scanning stage configured to direct the object beam at the specimen and collect a resulting sampled beam from the specimen, wherein the sampled beam comprises reflected radiation from the specimen and/or backscattered radiation from the specimen; a reference beam stage having a scanning mirror and configured (i) to maintain the reference beam along a reference beam path and free from incidence on the specimen and (ii) to scan the reference beam along different optical path lengths of the reference beam path, wherein the scanning of the reference beam is along a reference axis coinciding with an axis into the specimen and over a depth region into the specimen; and a signal processing machine configured to, in response to combining the sampled beam with the reference beam and producing an interferometric pattern, where, as a result of the scanning of the reference beam, the interferometric pattern contains amplitude peaks corresponding to discontinuities at different depths within the depth region of the specimen, and (ii) to (i) analyze the interferometric pattern to identify discontinuities in the specimen from the peaks in the interferometric pattern, (ii) identify the depth positions, within the specimen, of each of the discontinuities from the positions of the amplitude peaks in the interferometric pattern, wherein the discontinuities represent fiducial markers within the specimen, (iii) determine a distance between at least two of the fiducial markers; (iv) in response to deforming the specimen in at least one direction, identify updated depth positions, within the specimen, of the at least two fiducial markers; and (v) determine an updated distance between the at least two fiducial markers. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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Specification