Compact shearography system with adjustable shear distance

Patent metadata

Field	Value
Publication number	US-12566058-B2
Application number	US-202318183855-A
Country	US
Kind code	B2
Filing date	Mar 14, 2023
Priority date	Mar 16, 2022
Publication date	Mar 3, 2026
Grant date	Mar 3, 2026

Abstract

Shearography systems provide independent setting of fringe frequency and shear magnitude by situating an interferometer with a tiltable reflector proximate a pupil plane of an imaging optical system. Fringe frequency can be selected based on a modified Savart plate. In other examples, a Wollaston prism or a polarization grating is translated with respect to an image sensor to vary shear magnitude while maintaining a substantially fixed fringe frequency.

First claim

We claim:

1 . A shearography system, comprising:
a shearing optic operable to provide a variable shear between a first image and a second image of a test object, wherein the first image and the second image are speckle images; a detector; and an optical system operable to direct the variably sheared first image and second image to the detector at respective angles to establish a substantially fixed fringe frequency associated with interference of the variably sheared first and second images.

2 . The shearography system of claim 1 , wherein the shearing optic is situated at a pupil of the optical system.

3 . The shearography system of claim 1 , wherein the shearing optic is an interferometer.

4 . The shearography system of claim 3 , wherein the interferometer includes a beam splitter situated to produce a first beam and a second beam associated with the first image and the second image and a first reflector and a second reflector situated to direct the first beam and the second beam, respectively, to the detector.

5 . The shearography system of claim 4 , further comprising a rotational actuator coupled to rotate the first reflector or the second reflector, wherein a shear magnitude is adjustable with the rotation.

6 . The shearography system of claim 5 , wherein the beam splitter is a polarizing beam splitter and the first and second reflectors are quarter-wave reflectors and the first beam and second beam are directed towards the detector in a first state of polarization and a second state of polarization, respectively.

7 . The shearography system of claim 6 , further comprising a polarizer situated between the polarizing beam splitter and the detector and operable to transmit at least portions of the first beam and the second beam.

8 . The shearography system of claim 7 , wherein the optical system includes a modified Savart plate situated between the polarizing beam splitter and the detector, wherein the substantially fixed fringe frequency is based at least in part on a displacement of the first beam and the second beam produced with the modified Savart plate.

9 . The shearography system of claim 1 , wherein the optical system includes a modified Savart plate situated between the shearing optic and the detector, wherein the substantially fixed fringe frequency is based at least in part on a displacement of a first beam and a second beam produced with the modified Savart plate.

10 . The shearography system of claim 1 , wherein the optical system includes at least one lens situated to produce the first image and the second image and the substantially fixed fringe frequency is established at least in part based on the at least one lens.

11 . The shearography system of claim 1 , wherein the shearing optic is a Wollaston prism that is translatable to provide a variable shear magnitude between the first image and the second image of the test object, and wherein the variable shear magnitude is based on a separation of the Wollaston prism and the detector.

12 . The shearography system of claim 11 , wherein the Wollaston prism defines a divergence angle between states of polarization associated with the first image and the second image, and the fringe frequency is determined by the divergence angle.

13 . The shearography system of claim 12 , further comprising a translation stage coupled to translate the Wollaston prism to select the variable shear magnitude.

14 . The shearography system of claim 11 , further comprising a translation stage coupled to translate a polarizing grating to select the variable shear magnitude.

15 . The shearography system of claim 1 , wherein the shearing optic is a polarizing grating that is translatable to provide a variable shear magnitude between the first image and the second image of the test object and the variable shear magnitude is based on a separation of the polarizing grating and the detector.

16 . A shearography system, comprising:
a detector; and an optical system operable to vary a shear between a first image and a second image of a test object independently of a fringe frequency produced by interference of beams associated with the first image and the second image at the detector, wherein the first image and the second image are speckle images.

17 . The shearography system of claim 16 , wherein the optical system includes a Wollaston prism that at least partially establishes a substantially fixed fringe frequency and is translatable to vary the shear.

18 . The shearography system of claim 16 , wherein the optical system includes an interferometer that is adjustable to vary the shear and a modified Savart plate that establishes the fringe frequency as a fixed fringe frequency.

19 . The shearography system of claim 18 , wherein the modified Savart plate is a symmetric modified Savart plate.

20 . The shearography system of claim 18 , wherein the optical system includes imaging optics situated to produce the first image and the second image, wherein the interferometer is situated proximate a pupil of the imaging optics.

21 . The shearography system of claim 16 , wherein the optical system includes an interferometer that is adjustable to vary the shear, an imaging optical system situated to produce the first image and the second image, wherein the interferometer is situated proximate a pupil of the optical system, and pair of polarization gratings with a halfwave plate situated between the polarization gratings, wherein the fringe frequency is based in part on separation of a first polarization grating and a second polarization grating of the pair of polarization gratings.

22 . A shearography method, comprising:
situating a shear optic at a pupil of an imaging system to variably establish a shear; and interfering sheared first and second images produced with the imaging system to produce a fringe frequency that is independent of the variably established shear.

23 . The shearography method of claim 22 , wherein variably establishing the shear comprises dividing an optical beam from a test object into first and second optical beams corresponding to the first and second images and adjusting a tilt angle between the first and second optical beams.

24 . A metrology instrument that measures an object based on shearography, comprising:
a polarizing beam splitter situated to divide an optical beam from an object into a first polarized beam and a second polarized beam, wherein a state of polarization of the second polarized beam is different from a state of polarization of the first polarized beam; a shearing optic situated to laterally shift the first polarized beam and the second polarized beam from the polarizing beam splitter with respect to each other; an imaging system situated to produce a first image and a second image corresponding to the first polarized beam and the second polarized beam, respectively; and a detector situated to detect an interference of the first image and the second image, wherein the shearing optic is situated proximate a pupil of the imaging system.

25 . The metrology instrument of claim 24 , wherein the shearing optic is a reflector situated to produce the lateral shift based on a reflector tilt.

26 . The metrology instrument of claim 24 , wherein the shearing optic situated proximate a pupil of the imaging system to produces a fringe frequency that is independent of the variably established

Assignees

• Nikon Corp

Inventors

• Goodwin Eric Peter
• Smith Daniel Gene

Classifications

• G01B11/2441 Primary

  using interferometry · CPC title

• G01B9/02087

  Combining two or more images of the same region · CPC title

• G01B9/02095

  detecting deformation from original shape · CPC title

• G01B9/02089

  Displaying the signal, e.g. for user interaction · CPC title

• G01B2290/70

  Using polarization in the interferometer · CPC title