Apparatus and method for providing high intensity non-coherent light and for speckle reduction

• US 20050207160A1
• Filed: 08/24/2004
• Published: 09/22/2005
• Est. Priority Date: 08/25/2003
• Status: Active Grant

• Current Assignee: Align Technology Incorporated
• Original Assignee: Cadent Ltd (Align Technology Incorporated)
• Inventors: Babayoff, Noam, Atiya, Yossef, Philipp, Tzvi
• Granted Patent: US 7,202,466 B2
• Time in Patent Office: Days
• US Class Current: 362/259
• CPC Class Codes: G02B 21/0032 Optical details of illumination, e.g. light-sources, pinholes, beam splitters, slits, fibers G02B21/0036 - G02B21/008; means for illumination of specimens in general G02B21/06
• CPC Class Codes: G02B 21/004 fixed arrays, e.g. switchable aperture arrays
• CPC Class Codes: G02B 27/0933 Systems for active beam shaping by rapid movement of an element
• CPC Class Codes: G02B 27/0938 Using specific optical elements
• CPC Class Codes: G02B 27/1086 operating by diffraction only
• CPC Class Codes: G02B 27/123 The splitting element being a lens or a system of lenses, including arrays and surfaces with refractive power
• CPC Class Codes: G02B 27/14 operating by reflection only
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G02B 3/0006 Arrays G02B3/02, G02B5/188 take precedence
• CPC Class Codes: G02B 5/02 Diffusing elements; Afocal elements

Abstract

An apparatus adapted for confocal imaging of a non-flat specimen comprising a light source for producing a light beam, imaging optics adapted to focus the light beam into at least one spot on a surface of a specimen, and a detector adapted to receive and detect light reflected from the specimen surface. The light source comprises an optical system for converting a coherent beam into a plurality of beams, each of which is modified by a moving diffuser within a range of movement that is correlated to the detector'"'"'s integration time.

Claims

1. Optical system for converting a substantially coherent parent light source into a plurality of light sources having at least reduced spatial coherence of illumination compared to said coherent parent light source, comprising:

—

a beam splitter for splitting a parent beam from a said coherent parent light source into an array of incident beams, each beam being focused at a spot; and

a moving diffuser arrangement located at or near said spots, and adapted for presenting a different diffuser part to each focused spot as the diffuser arrangement is moved in a path between at least two positions.

2. System according to claim 1, further comprising a collimator arrangement for collimating the light from a said coherent light source.

3. System according to claim 2, wherein said beam splitter comprises a fixed grating or fixed micro-lens array comprising a plurality of micro-lens elements adapted for focusing collimated light from said collimator arrangement to a plurality of said spots.

4. System according to claim 3, wherein said micro-lens elements are plano-convex lens elements, including any one of spherical or aspherical plano-convex lends elements.

5. System according to claim 3, further comprising a relay lens for refocusing the said spots to refocused spots, wherein said moving diffuser arrangement is located at or near the said refocused spots.

6. System according to claim 5, wherein a length of said path of said diffuser arrangement and at least one diffuser characteristic thereof presented to each said spot are such as to provide a plurality of differently modified wavefronts from each spot, which provide a corresponding plurality of different speckle configurations at an object illuminated via said system.

7. System according to claim 6, wherein said diffuser arrangement comprises any one of:

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated via said system;

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, said diffuser element comprising a plurality of equal-angled segments about the rotational axis each having identical diffuser features one to the other, such that the complete path experienced by each said spot during any integral number of complete segments of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated via said system;

a rotating diffuser element adapted for eccentrically rotating within an orbit element, the center of the orbit being aligned with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement in the orbit is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated via said system;

an oscillating diffuser element, such that the complete path experienced by each said spot during any integral number of full-amplitude translations of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated via said system.

8. System according to claim 6, wherein said diffuser arrangement movement has a predetermined speed such that said plurality of different speckle configurations may be obtained within a predetermined time period.

9. System according to claim 8, wherein said time period may be correlated to an integration time period of a detector that may be used in conjunction with said system for detecting light reflected from an object illuminated via said system.

10. A multiple light source for providing a plurality of light beams, comprising:

a parent coherent light source for providing a parent beam of coherent light;

a beam splitter for splitting said parent beam into an array of incident beams, each beam being focused at a spot; and

a moving diffuser arrangement located at or near said spots, and adapted for presenting a different diffuser part to each focused spot as the diffuser arrangement is moved in a path between at least two positions.

11. Source according to claim 10, further comprising a collimator arrangement for collimating the light from said coherent light source.

12. Source according to claim 11, wherein said beam splitter comprises a fixed grating or fixed micro-lens array comprising a plurality of micro-lens elements adapted for focusing collimated light from said collimator arrangement to a plurality of said spots.

13. Source according to claim 12, wherein said micro-lens elements are plano-convex lens elements, including any one of spherical or aspherical plano-convex lends elements.

14. Source according to claim 12, further comprising a relay lens for refocusing the said spots to refocused spots, wherein said moving diffuser arrangement is located at or near the said refocused spots.

15. Source according to claim 14, wherein a length of said path of said diffuser arrangement and at least one diffuser characteristic thereof presented to each said spot are such as to provide a plurality of differently modified wavefronts from each spot, which provide a corresponding plurality of different speckle configurations at an object illuminated by said source.

16. Source according to claim 15, wherein said diffuser arrangement comprises any one of:

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said source;

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, said diffuser element comprising a plurality of equal-angled segments about the rotational axis each having identical diffuser features one to the other, such that the complete path experienced by each said spot during any integral number of complete segments of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said source;

a rotating diffuser element adapted for eccentrically rotating within an orbit element, the center of the orbit being aligned with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement in the orbit is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said source;

an oscillating diffuser element, such that the complete path experienced by each said spot during any integral number of full-amplitude translations of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said source.

17. Source according to claim 15, wherein said diffuser arrangement movement has a predetermined speed such that said plurality of different speckle configurations may be obtained within a predetermined time period.

18. Source according to claim 17, wherein said time period may be correlated to an integration time period of a detector that may be used in conjunction with said system for detecting light reflected from an object illuminated by said source.

19. An apparatus adapted for confocal imaging of a non-flat specimen, said apparatus having an optical axis and a predetermined lateral resolution and comprising a light source for producing a light beam, imaging optics adapted to focus the light beam into at least one spot on a surface of a specimen, and a detector having an integration time and adapted to receive and detect light reflected from said surface;

said light source comprising;

a parent coherent light source for providing a parent beam of coherent light;

a beam splitter for splitting said parent beam into an array of incident beams, each beam being focused at a spot; and

a moving diffuser arrangement located at or near said spots, and adapted for presenting a different diffuser part to each focused spot as the diffuser arrangement is moved in a path between at least two positions.

20. Apparatus according to claim 19, further comprising a collimator arrangement for collimating the light from said coherent light source.

21. Apparatus according to claim 20, wherein said beam splitter comprises a fixed grating or fixed micro-lens array comprising a plurality of micro-lens elements adapted for focusing collimated light from said collimator arrangement to a plurality of said spots.

22. Apparatus according to claim 21, wherein said micro-lens elements are plano-convex lens elements, including any one of spherical or aspherical piano-convex lends elements.

23. Apparatus according to claim 21, further comprising a relay lens for refocusing the said spots to refocused spots, wherein said moving diffuser arrangement is located at or near the said refocused spots.

24. Apparatus according to claim 23, wherein a length of said path of said diffuser arrangement and at least one diffuser characteristic thereof presented to each said spot is such as to provide a plurality of differently modified wavefronts from each spot, which provide a corresponding plurality of different speckle configurations at an object illuminated by said source.

25. Apparatus according to claim 24, wherein said diffuser arrangement movement has a predetermined speed such that said plurality of different speckle configurations may be obtained within a predetermined time period.

26. Apparatus according to claim 25, wherein said time period may be correlated to an integration time period of said detector.

27. Apparatus according to claim 26, wherein a movement of said diffuser arrangement is synchronized to said integration time of said detector such that the averaging of independent said speckle configurations may be performed over one full period of diffuser movement, or a portion of it.

28. Apparatus according to claim 26, wherein said diffuser arrangement comprises any one of:

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations to said detector;

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, said diffuser element comprising a plurality of equal-angled segments about the rotational axis each having identical diffuser features one to the other, such that the complete path experienced by each said spot during any integral number of complete segments of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations to said detector;

a rotating diffuser element adapted for eccentrically rotating within an orbit element, the center of the orbit being aligned with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement in the orbit is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations to said detector;

an oscillating diffuser element, such that the complete path experienced by each said spot during any integral number of full-amplitude translations of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations to said detector.

29. The apparatus according to claim 19, wherein the apparatus further comprises a second beam-splitter for directing reflected light from an object to said detector.

30. A method for converting a coherent light source into a plurality of light sources having reduced spatial coherence of illumination compared to said coherent light source, comprising:

—

splitting a parent beam from a coherent light source into an array of incident beams, each beam being focused at a spot; and

moving a diffuser arrangement that is located at or near said spots, and presenting a different diffuser part to each focused spot as the diffuser arrangement is moved in a path between at least two positions.

31. Method according to claim 30, further comprising the step of collimating the light from a said coherent light source.

32. Method according to claim 31, wherein said parent beam is split by means of a fixed grating or fixed micro-lens array comprising a plurality of micro-lens elements adapted for focusing collimated light to a plurality of said spots.

33. Method according to claim 32, further comprising refocusing the said spots, and moving said diffuser arrangement between at least two positions at or near the said refocused spots.

34. Method according to claim 33, wherein a length of the path of movement of said diffuser arrangement and at least one diffuser characteristic thereof presented to each said spot is such as to provide a plurality of differently modified wavefronts from each spot, which provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams.

35. Method according to claim 34, wherein said diffuser arrangement comprises any one of:

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams;

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, said diffuser element comprising a plurality of equal-angled segments about the rotational axis each having identical diffuser features one to the other, such that the complete path experienced by each said spot during any integral number of complete segments of said diffuser arrangement is such as to present a sufficiently varied difser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams;

a rotating diffuser element adapted for eccentrically rotating within an orbit element, the center of the orbit being aligned with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement in the orbit is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams;

an oscillating diffuser element, such that the complete path experienced by each said spot during any integral number of full-amplitude translations of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams.

36. Method according to claim 34, wherein said diffuser arrangement is moved at a predetermined speed such that said plurality of different speckle configurations may be obtained within a predetermined time period.

37. Method according to claim 36, wherein said time period may be correlated to an integration time period of a detector that may be used in for detecting light reflected from an object illuminated by a plurality of light sources generated according to a method for converting a coherent light source into a plurality of light sources having reduced spatial coherence of illumination compared to said coherent light source, comprising:

—

splitting a parent beam from a coherent light source into an array of incident beams, each beam being focused at a spot; and

moving a diffuser arrangement that is located at or near said spots, and presenting a different diffuser part to each focused spot as the diffuser arrangement is moved in a path between at least two positions.

38. A method for confocal imaging of a non-flat specimen, the method comprising:

providing an apparatus comprising a coherent source of light and a detector;

splitting a parent beam from a coherent light source into an array of incident beams, each beam being focused at a spot;

moving a diffuser arrangement at the origin of said plurality of secondary light beams, and presenting a different diffuser part to each said secondary beam as the diffuser arrangement is moved between at least two positions;

focusing the incident beams into at least one spot on a surface of the specimen by means of imaging optics;

directing light reflected by the surface toward the detector;

detecting the light by the detector;

wherein said diffuser arrangement is moved between said positions within the integration time of the detector.

39. Method according to claim 38, further comprising the step of collimating the light from a said coherent light source.

40. Method according to claim 38, wherein said parent beam is split by means of a fixed grating or fixed micro-lens array comprising a plurality of micro-lens elements adapted for focusing collimated light to a plurality of said spots.

41. Method according to claim 40, further comprising refocusing the said spots, and moving said diffuser arrangement between at least two positions at or near the said refocused spots.

42. Method according to claim 41, wherein a length of the path of movement of said diffuser arrangement and at least one diffuser characteristic thereof presented to each said spot is such as to provide a plurality of differently modified wavefronts from each spot, which provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams.

43. Method according to claim 41, wherein a movement of said diffuser arrangement is synchronized to said integration time of said detector such that the averaging of independent said speckle configurations may be performed over one full period of diffuser movement, or a portion of it.

44. Method according to claim 43, wherein said diffuser arrangement comprises any one of:

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams;

a rotating diffuser element having a rotational axis offset with respect to an optical axis of said system, said diffuser element comprising a plurality of equal-angled segments about the rotational axis each having identical diffuser features one to the other, such that the complete path experienced by each said spot during any integral number of complete segments of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams;

a rotating diffuser element adapted for eccentrically rotating within an orbit element, the center of the orbit being aligned with respect to an optical axis of said system, such that the complete path experienced by each said spot during any integral number of complete revolutions of said diffuser arrangement in the orbit is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams;

an oscillating diffuser element, such that the complete path experienced by each said spot during any integral number of full-amplitude translations of said diffuser arrangement is such as to present a sufficiently varied diffuser pattern so as to provide a corresponding plurality of different speckle configurations at an object illuminated by said incident beams.