High speed optical inspection apparatus for a transparent disk using gaussian distribution analysis and method therefor

• US 6,294,793 B1
• Filed: 12/03/1992
• Issued: 09/25/2001
• Est. Priority Date: 12/03/1992
• Status: Expired due to Fees

• Current Assignee: Orbotech Limited (KLA Corporation)
• Original Assignee: Brown & Sharpe Surface Inspection Systems, Inc. (KLA Corporation)
• Inventors: Brunfeld, Andrei, Laver, Ilan, Pekel, Ely, Toker, Gregory, Shamir, Joseph, Singher, Liviu
• Primary Examiner(s): Allen, Stephone B.
• Application Number:
  US07/985,631
• Time in Patent Office: 3,218 Days
• Field of Search: 250/234-236, 250/562, 250/563, 250/571, 250/572, 250/559.45, 250/559.48, 250/559.49, 356/238, 356/239, 356/429-431, 356/237.2, 356/239.1, 356/237.1, 364/507, 209/588
• US Class Current: 250/559.45
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/9506 Optical discs

Abstract

An optical inspection apparatus operates at high speed at very high resolution for detecting defects in transparent disks in a production environment. These transparent disks are of the type commonly used as disk platters in hard disk drives. This apparatus uses a laser beam directed to a polygon scanner, which provides a linear scan of the beam along a radius of the disk. The disk to be inspected is rotated such that its entire surface passes the scan path of the laser beam. The laser beam, after passing through the unit to be inspected, is directed to a parallel detector array, which detects changes in the nominal Gaussian distribution of the laser beam that correspond to defects in the surface of the transparent disk above a programmable threshold level. This parallel detection method allows the inspection apparatus to identify defects much smaller than the diffraction limits of the optics used, and will accurately identify changes of the laser beam caused by defects in the disk. An automatic disk handler loads untested disks into the apparatus and unloads and sorts tested disks according to the results of the inspection.

Claims

1. An optical inspection apparatus for inspecting flat, transparent circular disk comprising, in combination:

computer means for controlling said apparatus;

operator interface means coupled to said computer means for providing input data from an operator to said computer means and for providing output data from said computer means to said operator;

an optical inspection assembly, coupled to said computer means having output means for reporting to said computer means results of an inspection performed by said optical inspection assembly, comprising inspection means consisting of detector means for detecting changes of a normal Gaussian distribution of a light beam passing through a transparent disk; and

said transparent disk which is placed in said optical inspection assembly to inspect said transparent disk for defects.

2. The apparatus of claim 1 further comprising automatic disk handler means coupled to said computer means for loading under control of said computer means said transparent disk into said optical inspection assembly and for unloading under control of said computer means said transparent disk out of said optical inspection assembly.

3. The apparatus of claim 1 wherein said computer means comprising, in combination:

an IBM compatible personal computer; and

control software means loaded into memory of said IBM compatible personal computer for determining function and sequence of operations of said apparatus.

4. The apparatus of claim 3 wherein said control software means comprising:

a main control program; and

a plurality of device drivers which provide subroutines for said main control program and which control individual components of said apparatus.

5. The apparatus of claim 1 wherein said computer means periodically polls said output means of said optical inspection assembly to determine whether a defect has been detected by said optical inspection assembly.

6. The apparatus of claim 1 wherein said output means of said optical inspection means is coupled to said computer means such that said output means interrupts said computer means when a defect is detected by said optical inspection assembly.

7. The apparatus of claim 1 wherein said operator interface means comprising, in combination:

keyboard means coupled to said computer means for providing said input data from said operator to said computer means; and

display means coupled to said computer means for displaying said output data from said computer means to said operator.

8. The apparatus of claim 7 wherein said operator interface means further comprising printer means for printing said output data from said computer means.

9. The apparatus of claim 7 wherein said operator interface means further comprising operator panel means having knobs and switches for selecting one of a plurality of detection thresholds for said optical inspection assembly.

10. The apparatus of claim 7 including means for permitting said operator to select one of a plurality of detection thresholds for said optical inspection assembly via said keyboard means.

11. The apparatus of claim 2 wherein said automatic disk handler means comprising, in combination:

at least one input tray wherein said transparent disk is placed prior to inspection by said apparatus;

at least one movable gripper hand located in proximity to said input tray for gripping and transporting said transparent disk from said input tray to said optical inspection assembly;

a first output tray located in proximity to said movable gripper hand such that said transparent disk is moved from said optical inspection assembly to said first output tray by said movable gripper hand if said output of said optical inspection assembly signals to said computer means that said transparent disk has no defects; and

a second output tray located in proximity to said movable gripper hand such that said transparent disk is moved from said optical inspection assembly to said second output tray by said movable gripper hand if said output of said optical inspection assembly signals to said computer means that said transparent disk has defects.

12. The apparatus of claim 1 wherein said optical inspection assembly comprising, in combination:

disk movement actuator means in physical proximity to said inspection means for moving said transparent disk to allow said inspection means to fully inspect said transparent disk for defects; and

disk movement driver means electrically coupled to said disk movement actuator means and to said computer means for allowing said computer means to control said disk movement actuator means by providing appropriate commands to said disk movement driver means.

13. The apparatus of claim 12 wherein said inspection means comprises surface inspection assembly means for inspecting at least one flat surface of said transparent disk for defects while said disk movement actuator means moves said unit under test.

14. The apparatus of claim 13 wherein said inspection means further comprises edge inspection assembly means in physical proximity to said surface inspection assembly means for inspecting at least one edge of said transparent disk for defects while said disk movement actuator means moves said transparent disk.

15. The apparatus of claim 14 wherein said edge inspection assembly means comprising, in combination:

an outer radius inspection assembly for inspecting at least one outer edge of said transparent disk; and

an inner radius inspection assembly for inspecting at least one inner edge of said transparent disk.

16. The apparatus of claim 15 wherein said outer radius inspection assembly and said inner radius inspection assembly perform their respective inspections simultaneously.

17. The apparatus of claim 15 wherein said outer radius inspection assembly comprising, in combination:

a light source;

power supply means electrically coupled to said light source for providing power to said light source;

projection means optically coupled to said light source for projecting said light source onto at least one outer edge of said transparent disk, thereby creating an illuminated portion; and

at least one detection means for monitoring said illuminated portion, having output means for reporting the existence of defects in said illuminated portion.

18. The apparatus of claim 17 wherein said detection means further comprising:

a linear array of optical detectors; and

detection optics means for directing and projecting an image of said illuminated portion to said linear array.

19. The apparatus of claim 18 wherein said optical detectors comprising Charge-Coupled Devices (CCDs).

20. The apparatus of claim 17 wherein said projection means providing illumination to at least one inner edge of said transparent disk due to light from said light source passing from said outer edge through the transparent media of said transparent disk to said inner edge, thereby illuminating said inner edge.

21. The apparatus of claim 15 wherein said inner radius inspection assembly comprising at least one detection means for monitoring at least one inner edge of said transparent disk, having output means for reporting the existence of defects on said inner edge of said transparent disk.

22. The apparatus of claim 21 wherein said detection means further comprising:

a linear array of optical detectors; and

detection optics means for directing and projecting an image of a portion of said inner edge to said linear array.

23. The apparatus of claim 22 wherein said optical detectors comprising Charge-Coupled Devices (CCDs).

24. The apparatus of claim 12 wherein said transparent disk comprising a round disk having an outer edge and a hole in a center portion and wherein said disk movement actuator means comprising at least one actuated roller and motor means for driving said actuated roller for turning said round disk.

25. The apparatus of claim 24 wherein said disk movement actuator means further comprising at least one idler roller, said idler roller and said actuated roller contact said outer edge of said round disk, said actuated roller rotating in response to said motor means driving said actuated roller causing rotation of said round disk, said rotation of said disk causing said idler roller to rotate.

26. The apparatus of claim 25 wherein said actuated roller and said idler roller both having notch means in their circumferential faces in which said outer edge of said round disk is placed for preventing said round disk from slipping off said actuated roller and said idler roller during rotation.

27. The apparatus of claim 13 wherein said surface inspection assembly means comprising, in combination:

a light source providing said a light beam;

optical scanner means having an aperture in physical proximity to said light source for permitting said light beam to contact said aperture on said optical scanner means and for reflecting said light beam thereby providing a linear sweep of said light beam;

scanning optics means having a front face portion and a rear face portion for permitting said linear sweep of said light beam to contact said front face portion of said scanning optics means for causing said light beam that contacts said front face portion to exit said rear face portion and to contact said flat surface of said transparent disk;

trigger detector means coupled to said computer means and placed within said linear sweep of said light beam for providing a synchronizing electrical signal to said computer means for indicating a position of said light beam along said linear sweep;

detection optics means having a front face portion and a rear face portion for permitting said light beam after contacting and passing through, said transparent disk to contact said rear face portion and exit said front face portion; and

said detector means for permitting said light beam exiting said front face portion of said detection optics means to be received by said detector means for detecting changes of a nominal Gaussian distribution of said light beam, said changes corresponding to and identifying defects in said flat surface of said transparent disk.

28. The apparatus of claim 27 wherein said light source comprising a laser diode and said light beam comprising a laser beam from said laser diode.

29. The apparatus of claim 27 wherein said light source comprising a helium-neon laser, and said light beam comprising a laser beam from said helium-neon laser.

30. The apparatus of claim 27 wherein said optical scanner means having a motor-driven polygonal head coupled to said computer means and having reflective faces such that said light beam contacts said reflective faces of said polygonal head through said aperture, and having means for rotating said polygonal head for causing said light beam reflected off said reflective faces to create said linear sweep of said light beam across said scanning optics means.

31. The apparatus of claim 30 wherein said motor-driven polygonal head is turned on and off by said computer means.

32. The apparatus of claim 27 wherein said aperture of said optical scanner means being located at a distance from said scanning optics means equal to the focal length of said scanning optics means.

33. The apparatus of claim 32 wherein said scanning optics means direct said light beam entering said front face portion such that said light beam exits said rear face portion in a direction normal to the focal plane of said scanning optics means.

34. The apparatus of claim 27 wherein said scanning optics means focus said light beam on said flat surface of said transparent disk.

35. The apparatus of claim 27 wherein said trigger detector means comprising an optical sensor having an electrical output corresponding to the presence of said light beam on said optical sensor which is coupled to said computer means.

36. The apparatus of claim 35 wherein said optical sensor comprising a photodiode.

37. The apparatus of claim 35 wherein said optical sensor comprising a charge-coupled device (CCD).

38. The apparatus of claim 27 wherein said detector means comprising, in combination:

at least two optical detectors having electrical outputs, said optical detectors functioning in parallel; and

electronic circuitry means for processing said electrical outputs of said optical detectors and generating an electrical signal to said computer means comprising, in combination;

first input means coupled to said electrical outputs of said optical detectors for monitoring said electrical outputs;

second input means coupled to said computer means for receiving a threshold value from said computer means;

processing means coupled to said first input means and to said second input means for measuring said electrical outputs of said optical detectors and for determining the existence of changes of said nominal Gaussian distribution of said light beam above said threshold value on said second input means; and

output means coupled to said computer means for signaling an occurrence of a change above said threshold value to said computer means.

39. The apparatus of claim 38 wherein said optical detectors comprise photodiodes.

40. The apparatus of claim 38 wherein said optical detectors comprise charge-coupled devices (CCDs).

41. The apparatus of claim 38 wherein said optical detectors are arranged in rows and columns to form a substantially square matrix.

42. The apparatus of claim 38 wherein said optical detectors are arranged in a series of concentric circular rings.

43. The apparatus of claim 27 further comprising filter optics means for increasing spatial coherence of said light beam.

44. A method for inspecting a flat, transparent disk using an optical inspection apparatus including the steps of:

providing computer means for controlling said apparatus;

providing operator interface means coupled to said computer means for providing input data from an operator to said computer means and for providing output data from said computer means to said operator;

providing an optical inspection assembly, coupled to said computer means having output means for reporting to said computer means results of an inspection performed by said optical inspection assembly, comprising inspection means consisting of detector means for detecting changes of a nominal Gaussian distribution of a light beam passing through a transparent disk; and

providing said transparent disk which is placed in said optical inspection assembly to inspect said transparent disk for defects.

45. The method of claim 44 further comprising the step of providing automatic disk handler means coupled to said computer means for loading under control of said computer means said transparent disk into said optical inspection assembly and for unloading under control of said computer means said transparent disk out of said optical inspection assembly.

46. The method of claim 44 wherein said computer means comprising, in combination:

an IBM compatible personal computer; and

control software means loaded into memory of said IBM compatible personal computer for determining function and sequence of operations of said apparatus.

47. The method of claim 44 wherein said computer means periodically polls said output means of said optical inspection assembly to determine whether a defect has been detected by said optical inspection assembly.

48. The method of claim 44 wherein said output means of said optical inspection means is coupled to said computer means such that said output means interrupts said computer means when a defect is detected by said optical inspection assembly.

49. The method of claim 44 wherein said operator interface means comprising, in combination:

keyboard means coupled to said computer means for providing said input data from said operator to said computer means; and

display means coupled to said computer means for displaying said output data from said computer means to said operator.

50. The method of claim 49 wherein said operator interface means further comprising operator panel means having knobs and switches for selecting one of a plurality of detection thresholds for said optical inspection assembly.

51. The method of claim 49 including means for permitting said operator to select one of a plurality of detection thresholds for said optical inspection assembly via said keyboard means.

52. The method of claim 45 wherein said automatic disk handler means comprising, in combination:

at least one input tray wherein said transparent disk is placed prior to inspection by said apparatus;

at least one movable gripper hand located in proximity to said input tray for gripping and transporting said transparent disk from said input tray to said optical inspection assembly;

a first output tray located in proximity to said movable gripper hand such that said transparent disk is moved from said optical inspection assembly to said first output tray by said movable gripper hand if said output of said optical inspection assembly signals to said computer means that said transparent disk has no defects; and

a second output tray located in proximity to said movable gripper hand such that said transparent disk is moved from said optical inspection assembly to said second output tray by said movable gripper hand if said output of said optical inspection assembly signals to said computer means that said transparent disk has defects.

53. The method of claim 44 wherein said optical inspection assembly comprising, in combination:

disk movement actuator means in physical proximity to said inspection means for moving said transparent disk to allow said inspection means to fully inspect said transparent disk for defects; and

disk movement driver means electrically coupled to said disk movement actuator means and to said computer means for allowing said computer means to control said disk movement actuator means by providing appropriate commands to said disk movement driver means.

54. The method of claim 53 wherein said inspection means comprises surface inspection assembly means for inspecting at least one flat surface of said transparent disk for defects while said disk movement actuator means moves said transparent disk.

55. The method of claim 54 wherein said inspection means further comprises edge inspection assembly means in physical proximity to said surface inspection assembly means for inspecting at least one edge of said transparent disk for defects while said disk movement actuator means moves said transparent disk.

56. The method of claim 52 wherein said transparent disk comprising a round disk having an outer edge and a hole in a center portion and wherein said disk movement actuator means comprising at least one actuated roller and motor means for driving said actuated roller for turning said round disk.

57. The method of claim 56 wherein said disk movement actuator means further comprising at least one idler roller, said idler roller and said actuated roller contact said outer edge of said round disk, said actuated roller rotating in response, to said motor means driving said actuated roller causing rotation of said round disk, said rotation of said disk causing said idler roller to rotate.

58. The method of claim 57 wherein said actuated roller and said idler roller both having notch means in their circumferential faces in which said outer edge of said round disk is placed for preventing said round disk from slipping off said actuated roller and said idler roller during rotation.

59. The method of claim 54 wherein said surface inspection assembly means comprising, in combination:

a light source providing said light beam;

optical scanner means having an aperture in physical proximity to said light source for permitting said light beam to contact said aperture on said optical scanner means and for reflecting said light beam thereby providing a linear sweep of said light beam;

scanning optics means having a front face portion and a rear face portion for permitting said linear sweep of said light beam to contact said front face portion of said scanning optics means for causing said light beam that contacts said front face portion to exit said rear face portion and to contact said flat surface of said transparent disk;

trigger detector means coupled to said computer means and placed within said linear sweep of said light beam for providing a synchronizing electrical signal to said computer means for indicating a position of said light beam along said linear sweep;

detection optics means having a front face portion and a rear face portion for permitting said light beam after contacting and passing through, said transparent disk to contact said rear face portion and exit said front face portion; and

said detector means for permitting said light beam exiting said front face portion of said detection optics means to be received by said detector means for detecting changes of a nominal Gaussian distribution of said light beam, said changes corresponding to and identifying defects in said flat surface of said transparent disk.

60. The method of claim 59 wherein said optical scanner means having a motor-driven polygonal head coupled to said computer means and having reflective faces such that said light beam contacts said reflective faces of said polygonal head through said aperture, and having means for rotating said polygonal head for causing said light beam reflected off said reflective faces to create said linear sweep of said light beam across said scanning optics means.

61. The method of claim 60 wherein said motor-driven polygonal head is turned on and off by said computer means.

62. The method of claim 59 wherein said optical scanner means being located at a distance from said scanning optics means equal to the focal length of said scanning optics means.

63. The method of claim 62 wherein said scanning optics means direct said light beam entering said front face portion such that said light beam exits said rear face portion in a direction normal to the focal plane of said scanning optics means.

64. The method of claim 59 wherein said scanning optics means focus said light beam on said flat surface of said transparent disk.

65. The method of claim 59 wherein said trigger detector means comprising an optical sensor having an electrical output corresponding to the presence of said light beam on said optical sensor which is coupled to said computer means.

66. The method of claim 59 wherein said detector means comprising, in combination:

at least two optical detectors having electrical outputs, said optical detectors functioning in parallel; and

electronic circuitry means for processing said electrical outputs of said optical detectors and generating an electrical signal to said computer means comprising, in combination;

first input means coupled to said electrical outputs of said optical detectors for monitoring said electrical outputs;

second input means coupled to said computer means for receiving a threshold value from said computer means;

processing means coupled to said first input means and to said second input means for measuring said electrical outputs of said optical detectors and for determining the existence of changes of said nominal Gaussian distribution of said light beam above said threshold value on said second input means; and

output means coupled to said computer means for signaling an occurrence of a change above said threshold value to said computer means.

67. The method of claim 66 wherein said optical detectors are arranged in rows and columns to form a substantially square matrix.

68. The method of claim 66 wherein said optical detectors are arranged in a series of concentric circular rings.

69. The method of claim 53 further comprising the steps of:

loading said transparent disk into said disk movement actuator means in said optical inspection assembly;

activating said surface inspection assembly means with said computer means;

said computer means providing commands to said disk movement driver means, thereby causing said disk movement actuator means to rotate said transparent disk such that the entirety of said flat surface is inspected;

checking with said computer means said output of said optical inspection assembly to determine whether a defect was detected by said optical inspection assembly; and

unloading said transparent disk from said optical inspection assembly into a first destination if said output on said optical inspection assembly did not indicate the presence of a defect on said transparent disk, and unloading said transparent disk from said optical inspection assembly into a second destination if said output of said optical inspection assembly did indicate the presence of a defect on said transparent disk.

70. An apparatus for optically scanning the flat portions of a transparent disk comprising, in combination:

a light source providing a light beam;

light beam reflecting means for reflecting said light beam for providing a linear sweep of said light beam;

a transparent disk having a flat surface to be inspected positioned in said linear sweep of said light beam;

detector means for receiving said light beam after it has passed through said transparent disk and for detecting changes of a nominal Gaussian distribution of said light beam corresponding to defects in said flat surface of said transparent disk; and

means for moving said transparent disk within said linear sweep of said light beam and for permitting a linear scan of said flat surface for complete scanning of all of said flat surface to be inspected.

71. The apparatus of claim 70 wherein said light source comprising a laser diode and said light beam comprising a laser beam from said laser diode.

72. The apparatus of claim 70 wherein said light source comprising a helium-neon laser, and said light beam comprising a laser beam from said helium-neon laser.

73. The apparatus of claim 70 wherein said light beam reflecting means comprising an optical scanner.

74. The apparatus of claim 73 wherein said optical scanner having a motor-driven polygonal head having reflective faces positioned to permit said light beam to contact said reflective faces of said polygonal head, and having means for rotating said polygonal head for causing said light beam reflected off said reflective faces to create said linear sweep of said light beam.

75. The apparatus of claim 70 wherein said transparent disk comprising a round disk having an outer edge and a hole in a center portion and wherein said means for moving said transparent disk comprising at least one actuated roller and motor means for driving said actuated roller for turning said round disk.

76. The apparatus of claim 75 wherein said means for moving said transparent disk further comprising at least one idler roller, said idler roller and said actuated roller contact said outer edge of said round disk, said actuated roller rotating in response to said motor means driving said actuated roller causing rotation of said round disk, said rotation of said disk causing said idler roller to rotate.

77. The apparatus of claim 76 wherein said actuated roller and said idler roller both having notch means in their circumferential faces in which said outer edge of said round disk is placed for preventing said round disk from slipping off said actuated roller and said idler roller during rotation.

78. A method for optically scanning the flat surface of a transparent disk comprising, in combination:

providing a light source having a light beam;

providing light beam reflecting means for reflecting said light beam for providing a linear sweep of said light beam;

providing a transparent disk having a flat surface to be inspected positioned in said linear sweep of said light beam;

providing detector means for receiving said light beam after it has passed through said transparent disk and for detecting changes of a nominal Gaussian distribution of said light beam corresponding to defects in said flat surface of said transparent disk; and

providing means for moving said transparent disk within said linear sweep of said light beam and for permitting a linear scan of said flat surface for complete scanning of all of said flat surface to be inspected.

79. The method of claim 78 wherein said light beam reflecting means comprising an optical scanner.

80. The method of claim 79 wherein said optical scanner having a motor-driven polygonal head having reflective faces positioned to permit said light beam to contact said reflective faces of said polygonal head, and having means for rotating said polygonal head for causing said light beam reflected off said reflective faces to create said linear sweep of said light beam.

81. The method of claim 78 wherein said means for moving said transparent disk comprising at least one actuated roller and motor means for driving said actuated roller for turning said transparent disk.

82. The method of claim 81 wherein said means for moving said transparent disk further comprising at least one idler roller, said idler roller and said actuated roller contact said outer edge of said round disk, said actuated roller rotating in response to said motor means driving said actuated roller causing rotation of said round disk, said rotation of said disk causing said idler roller to rotate.

83. The method of claim 82 wherein said actuated roller and said idler roller both having notch means in their circumferential faces in which said outer edge of said round disk is placed for preventing said round disk from slipping off said actuated roller and said idler roller during rotation.

84. The method of claim 78 further comprising the steps of:

placing said transparent disk into said means for moving said transparent disk; and

activating said means for moving said transparent disk causing all of said flat surface to pass through said linear sweep of said light beam.

85. An apparatus for detecting surface defects in the flat surface of a transparent disk comprising, in combination:

a light source providing a light beam;

light beam reflecting means for reflecting said light beam for providing a linear sweep of said light beam;

a transparent disk having a flat surface to be inspected positioned in said linear sweep of said light beam;

means for moving said transparent disk within said linear sweep of said light beam and for permitting a linear scan of said flat surface for complete scanning of all of said flat surface to be inspected; and

detector means for measuring changes in said light beam corresponding to defects on said flat surface of said transparent disk, wherein said detector means receives said light beam after it has passed through said transparent disk and detects changes of a nominal Gaussian distribution of said light beam, said changes corresponding to defects in said flat surface of said transparent disk.

86. The apparatus of claim 85 wherein said light source comprising a laser diode and said light beam comprising a laser beam from said laser diode.

87. The apparatus of claim 85 wherein said light source comprising a helium-neon laser, and said light beam comprising a laser beam from said helium-neon laser.

88. The apparatus of claim 85 wherein said light beam reflecting means comprising an optical scanner.

89. The apparatus of claim 88 wherein said optical scanner having a motor-driven polygonal head having reflective faces positioned to permit said light beam to contact said reflective faces of said polygonal head, and having means for rotating said polygonal head for causing said light beam reflected off said reflective faces to create said linear sweep of said light beam.

90. The apparatus of claim 85 wherein said transparent disk comprising a round disk having an outer edge and a hole in a center portion and wherein said means for moving said transparent disk comprising at least one actuated roller and motor means for driving said actuated roller for turning said round disk.

91. The apparatus of claim 90 wherein said means for moving said transparent disk further comprising at least one idler roller, said idler roller and said actuated roller contact said outer edge of said round disk, said actuated roller rotating in response to said motor means driving said actuated roller causing rotation of said round disk, said rotation of said disk causing said idler roller to rotate.

92. The apparatus of claim 91 wherein said actuated roller and said idler roller both having notch means in their circumferential faces in which said outer edge of said round disk is placed for preventing said round disk from slipping off said actuated roller and said idler roller during rotation.

93. The apparatus of claim 85 wherein said detector means comprising, in combination:

at least two optical detectors having electrical outputs, said optical detectors functioning in parallel; and

electronic circuitry means for processing said electrical outputs of said optical detectors and generating an electrical signal output in response to changes of a nominal Gaussian distribution of said light beam above a selectable threshold value.

94. A method for detecting surface defects in the flat surface of a transparent disk comprising, in combination:

providing a light source providing a light beam;

providing light beam reflecting means for reflecting said light beam for providing a linear sweep of said light beam;

providing a transparent disk having a flat surface to be inspected positioned in said linear sweep of said light beam;

providing means for moving said transparent disk within said linear sweep of said light beam and for permitting a linear scan of said flat surface for complete scanning of all of said flat surface to be inspected; and

providing detector means for measuring changes in said light beam corresponding to defects on said flat surface of said transparent disk, wherein said detector means receives said light beam after it has passed through said transparent disk and detects changes of a nominal Gaussian distribution of said light beam, said changes corresponding to defects in said flat surface of said unit test.

95. The method of claim 94 wherein said light beam reflecting means comprising an optical scanner.

96. The method of claim 95 wherein said optical scanner having a motor-driven polygonal head having reflective faces positioned to permit said light beam to contact said reflective faces of said polygonal head, and having means for rotating said polygonal head for causing said light beam reflected off said reflective faces to create said linear sweep of said light beam.

97. The method of claim 94 wherein said transparent disk comprising a round disk having an outer edge and a hole in a center portion and wherein said means for moving said transparent disk comprising at least one actuated roller and motor means for driving said actuated roller for turning said round disk.

98. The method of claim 97 wherein said means for moving said transparent disk further comprising at least one idler roller, said idler roller and said actuated roller contact said outer edge of said round disk, said actuated roller rotating in response to said motor means driving said actuated roller causing rotation of said round disk, said rotation of said disk causing said idler roller to rotate.

99. The method of claim 98 wherein said actuated roller and said idler roller both having notch means in their circumferential faces in which said outer edge of said round disk is placed for preventing said round disk from slipping off said actuated roller and said idler roller during rotation.

100. The method of claim 94 wherein said detector means comprising, in combination:

at least two optical detectors having electrical outputs, said optical detectors functioning in parallel; and

electronic circuitry means for processing said electrical outputs of said optical detectors and generating an electrical signal output in response to changes of a nominal Gaussian distribution of said light beam above a selectable threshold value.

101. The method of claim 94 further comprising the steps of:

placing said transparent disk into said means for moving said transparent disk;

activating said means for moving said transparent disk causing all of said flat surface to pass through said linear sweep of said light beam; and

activating said detector means.