Apparatus and method for beam drift compensation

• US 20060202115A1
• Filed: 03/10/2005
• Published: 09/14/2006
• Est. Priority Date: 03/10/2005
• Status: Active Grant

• Current Assignee: Via Mechanics, Ltd.
• Original Assignee: Hitachi VIA Mechanics Limited (Hitachi, Ltd.)
• Inventors: Lizotte, Todd E., Ohar, Orest P.
• Granted Patent: US 7,321,114 B2
• Time in Patent Office: Days
• US Class Current: 250/234
• CPC Class Codes: B23K 26/04 Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• CPC Class Codes: B23K 26/043 along the beam path, i.e. alignment of laser beam axis relative to laser beam apparatus
• CPC Class Codes: B23K 26/702 Auxiliary equipment
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: H04N 1/047 Detection, control or error compensation of scanning velocity or position H04N1/0402 and H04N1/17 take precedence

Abstract

An apparatus and method for maintaining a desired position of a collimated light beam are provided. An optical system includes one or more passive optical elements movably positioned in the beam path. Beam position is responsive to movement of at least one of the passive optical elements. The actual position of the beam is detected and compared with the desired beam position. An error signal is generated and the beam path is altered responsive to movement of one or more of the passive optical elements. In further aspects, beam shaping optics, such diffractive optics, are provided to shape the sensed beam portion. In still other aspects, thermal conditions of the laser may be monitored and a thermal map is provided to automatically compensate for estimated beam drift due to thermal conditions.

Claims

1. An apparatus for maintaining a desired position of a laser beam comprising:

an optical system including one or more passive optical elements movably positioned in a path of said beam, the position of said beam being responsive to movement of at least one of said passive optical elements;

detector means for detecting an actual position of the beam;

comparison means for comparing the actual position of the beam with the desired position of the beam and generating an error signal representative of the difference between the detected actual position of the beam and the desired position of the beam;

means for moving at least one of said one or more movable passive optical elements, whereby the optical path of the beam is altered responsive to said moving; and

a position controller responsive to the error signal received from the comparison means and for generating an output signal to said means for moving at least one of said one or more movable passive optical elements so that the beam is shifted to the desired beam position.

2. The apparatus of claim 1, wherein said one or more passive optical elements includes one or more refractive optical elements.

3. The apparatus o claim 1, wherein said one or more passive optical elements includes one or more reflective optical elements.

4. The apparatus of claim 1, wherein said optical system comprises a prismatic wedge movably positioned in the beam path.

5. The apparatus of claim 1, wherein said optical system comprises first, second, and third prismatic wedges positioned in the beam path in spaced-apart relation:

said first prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said first face disposed transverse to the beam path and the first prismatic wedge being tapered in a first direction perpendicular to the beam path;

said second prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said second wedge second face disposed transverse to the beam path and the second prismatic wedge being tapered in a second direction perpendicular to the beam path and said first direction; and

said third prismatic wedge disposed between the first and second wedges and having a first, light receiving face and a second face opposite the first face, wherein the third wedge first face is facing and aligned with the first wedge second face and wherein the third wedge second face is facing and aligned with the second wedge first face.

6. The apparatus of claim 1, wherein said optical system comprises first and second prismatic wedges positioned in the beam path in spaced-apart relation, the first and second wedges rotatable together about the beam path:

said first prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said first face disposed transverse to the beam path and the first prismatic wedge being tapered in a direction perpendicular to the beam path; and

said second prismatic wedge having a first, light receiving face and a second face opposite the first face, said second wedge first face facing and aligned with said second wedge first face and said second wedge second face disposed transverse to the beam path.

7. The apparatus of claim 1, wherein said optical system comprises a piano lens positioned in the beam path and having a first, light receiving face and a second face opposite the first face, said piano lens independently rotatable about a first axis of rotation and a second axis of rotation, wherein the first axis, second axis, and the beam path are mutually orthogonal.

8. The apparatus of claim 7, wherein said means for moving comprises an optical element support selected from a gimbal support and a kinematic plate.

9. The apparatus of claim 1, wherein said optical system comprises:

a first wedge rotatable about a first axis and positioned in the beam path, said first wedge having a first reflective light-receiving face, wherein said first reflective light-receiving face is canted with respect to said first axis of rotation;

a second wedge rotatable about a second axis and having a second reflective light-receiving face in optical communication with said first wedge light-receiving face, wherein said second reflective light-receiving face is canted with respect to said second axis of rotation;

10. The apparatus of claim 1, wherein said detector means includes a detector selected from the group consisting of a photosensor array, a quadrant photodetector, a pyramid having mirrored faces and a photodetector in optical alignment with each of said mirrored faces, a duolateral position sensing photodetector, a CCD camera, a CMOS camera, an array of one-dimensional position sensitive detectors, an array of linear photo detectors, and a thermopile array.

11. The apparatus of claim 1, further comprising a beam splitter for directing a portion of said beam to said detector means.

12. The apparatus of claim 11, further comprising a diffractive optical element for shaping the portion of the beam directed to said detector means.

13. The apparatus of claim 1, further comprising a beam shaper shaping a portion of said beam directed to said detector means.

14. The apparatus of claim 13, wherein said beam shaper is a diffractive optical element.

15. The apparatus of claim 14, wherein said diffractive optical element comprises a reflective portion for reflecting and shaping said beam portion directed to said detector means.

16. The apparatus of claim 15, wherein the reflected, shaped beam portion is selected from a continuous ring and a segmented ring.

17. The apparatus of claim 16, wherein said continuous ring is selected from a continuous circle and continuous rectangle and said segmented ring is selected from a segmented circle and a segmented rectangle.

18. The apparatus of claim 13, wherein said detector means comprises a photodetector array selected from and array of one-dimensional position sensitive detectors and an array of linear photodetector arrays.

19. The apparatus of claim 18, wherein the linear position sensitive detectors are spaced and extend radially about an axis of said shaped beam portion.

20. The apparatus of claim 19, wherein the shaped beam portion and the incident beam are coaxial.

21. The apparatus of claim 13, wherein the beam shaper is a complex diffractive optical system comprising an input diffractive optical element for directing a portion of said beam to a position sensor and an output diffractive optical element for outputting a beam having one or both of a preselected shape and a preselected intensity profile.

22. The apparatus of claim 1, wherein the comparison means includes comparison circuitry selected from the group consisting of a comparator circuit and image processing circuitry for calculating the difference between a digital image representation of detected beam position and the desired beam position.

23. The apparatus of claim 1, further comprising a laser light source for generating said beam.

24. The apparatus of claim 23, further comprising:

one or more thermal sensors for sensing one or more thermal conditions of said laser source;

a thermal map which correlates said sensed thermal conditions with an estimated beam drift;

a control circuit for generating a thermal drift compensation signal representative of said estimated beam drift based on said sensed thermal conditions and said thermal map;

said position controller outputting a signal to said means for moving at least one of said one or more movable passive optical elements so that the beam is shifted by an amount which compensates for said estimated beam drift, said position controller output signal responsive to said thermal drift compensation signal.

25. A method for compensating for laser beam drift, comprising:

directing a laser beam to a beam shifter comprising one or more passive optical elements, wherein at least one of said one or more passive optical elements are movably positioned in a path of said beam such that the position of said beam is responsive to movement of at least one of said passive optical elements;

detecting an actual position of said beam;

comparing the actual position of said beam with said desired beam position;

if the detected actual position is not the desired position, moving at least one of the one or more passive optical elements until the beam attains the desired position.

26. The method of claim 25, wherein the beam shifter includes one or more refractive optical elements.

27. The method of claim 25, wherein the beam shifter includes one or more reflective optical elements.

28. The method of claim 25, wherein the beam shifter includes a prismatic wedge.

29. The method of claim 25, wherein said beam shifter comprises:

first, second, and third prismatic wedges positioned in the beam path in spaced-apart relation;

said first prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said first face disposed transverse to the beam path and the first prismatic wedge being tapered in a first direction perpendicular to the beam path;

said second prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said second wedge second face disposed transverse to the beam path and the second prismatic wedge being tapered in a second direction perpendicular to the beam path and said first direction; and

said third prismatic wedge disposed between the first and second wedges and having a first, light receiving face and a second face opposite the first face, wherein the third wedge first face is facing and aligned with the first wedge second face and wherein the third wedge second face is facing and aligned with the second wedge first face.

30. The method of claim 29, further including:

determining a deviation between the actual beam position and the desired beam position, said deviation including a first error component representative of an extent of said deviation in said first direction and a second error component representative of an extent of said deviation in said second direction;

compensating for the first error component by moving the first prismatic wedge along the beam path; and

compensating for the second error component by moving said second prismatic wedge along the beam path.

31. The method of claim 25, wherein said beam shifter comprises:

first and second prismatic wedges positioned in the beam path in spaced-apart relation, the first and second wedges rotatable together about the beam path;

said first prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said first face disposed transverse to the beam path and the first prismatic wedge being tapered in a direction perpendicular to the beam path; and

said second prismatic wedge having a first, light receiving face and a second face opposite the first face, said second wedge first face facing and aligned with said second wedge first face and said second wedge second face disposed transverse to the beam path.

32. The method of claim 31, further including:

determining a deviation between the actual beam position and the desired beam position;

resolving said deviation into a magnitude component and an angular component;

compensating for the magnitude component by moving the first prismatic wedge along the beam path;

compensating for the angular component by rotating the first and second prismatic wedges about the beam path.

33. The method of claim 25, wherein said beam shifter comprises:

a piano lens positioned in the beam path and having a first, light receiving face and a second face opposite and aligned with the first face, said piano lens independently rotatable about a first axis of rotation and a second axis of rotation, wherein the first axis, second axis, and the beam path are mutually orthogonal.

34. The method of claim 33, further comprising:

determining a deviation between the actual beam position and the desired beam position, said deviation including a first error component representative of an extent of said deviation along said first axis and a second error component representative of an extent of said deviation in said second axis;

compensating for the first error component by rotating said lens about said second axis; and

compensating for the second error component by rotating said lens about said first axis.

35. The method of claim 25, wherein said detecting step includes:

positioning a beam splitter along the beam path to direct a portion of said beam to a position-sensitive device.

36. The method of claim 35, wherein said position sensitive device is selected from the group consisting of a photosensor array, a quadrant photodetector, a pyramid having mirrored faces and a photodetector in optical alignment with each of said mirrored faces, a duolateral position sensing photodetector, a CCD camera, a CMOS camera, an array of one-dimensional position sensitive detectors, an array of linear photo detectors, and a thermopile array.

37. The method of claim 25, wherein said detecting step includes:

positioning an apertured beam shaper along the beam path, said apertured beam shaper configured to pass a first portion of the beam through said aperture and to direct a second portion of the beam to a position-sensitive device.

38. The method of claim 37, wherein said second beam portion is shaped ring which is coaxial with the first beam portion.

39. The method of claim 38, wherein said shaped ring is reflected to travel in a direction opposite the direction of travel of the incident beam.