Laser ablation system, and method of decontaminating surfaces

• US 5,780,806 A
• Filed: 07/25/1995
• Issued: 07/14/1998
• Est. Priority Date: 07/25/1995
• Status: Expired due to Term

• Current Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute), Iowa State University Research Foundation Incorporated (Iowa State University), United States Department of Energy
• Original Assignee: Lockheed Idaho Technologies Company
• Inventors: Pang, Ho-ming, Edelson, Martin C., Ferguson, Russell L.
• Primary Examiner(s): Evans, Geoffrey S.
• Application Number:
  US08/506,585
• Time in Patent Office: 1,085 Days
• Field of Search: 219/121.84, 219/121.68, 219/121.69, 219/121.83, 219/121.76, 219/121.65, 219/121.66, 219/121.78, 219/121.8, 219/121.72, 134/1
• US Class Current: 219/121.68
• CPC Class Codes: B08B 7/0042 by laser
• CPC Class Codes: B23K 26/0622 by shaping pulses
• CPC Class Codes: B23K 26/142 for the removal of by-products
• CPC Class Codes: B23K 26/16 Removal of by-products, e.g. particles or vapours produced during treatment of a workpiece by a fluid stream B23K26/142

Abstract

A laser ablation system comprising a laser head providing a laser output; a flexible fiber optic cable optically coupled to the laser output and transmitting laser light; an output optics assembly including a nozzle through which laser light passes; an exhaust tube in communication with the nozzle; and a blower generating a vacuum on the exhaust tube. A method of decontaminating a surface comprising the following steps: providing an acousto-optic, Q-switched Nd:YAG laser light ablation system having a fiber optically coupled output optics assembly; and operating the laser light ablation system to produce an irradiance greater than 1×10⁷ W/cm², and a pulse width between 80 and 170 ns.

Claims

1. A laser ablation system for conducting ablation in an ambient atmosphere, comprising:

a Nd;

YAG laser head providing a laser output;

a flexible fiber optic cable optically coupled to the laser output to transmit laser light;

an acousto-optic Q-switch coupled to the laser head upstream of the fiber optic cable to switch the laser output of the laser head to provide a controlled laser output to the fiber optic cable with a repetition rate between 3 and 7 kHz, a pulse width between 100 and 140 ns, and an irradiance greater than 1×

10⁷ w/cm² ;

an output optics assembly including a nozzle through which laser light passes;

an exhaust tube in communication with the nozzle; and

a blower generating a vacuum on the exhaust tube.

2. A laser ablation system in accordance with claim 1 and further comprising a filter in fluid communication with the blower.

3. A laser ablation system in accordance with claim 1 wherein the blower draws air through the exhaust tube, in the direction away from the nozzle, at a rate between 20 and 90 cubic feet per minute.

4. A laser ablation system in accordance with claim 1 wherein the output optics assembly comprises a collimating lens, and a focusing lens downstream of the collimating lens.

5. A laser ablation system in accordance with claim 4 wherein the focusing lens is a 57 mm focal length convex lens.

6. A laser ablation system in accordance with claim 1 wherein the controlled laser output has a repetition rate between 4 and 6 kHz.

7. A laser ablation system in accordance with claim 1 wherein the controlled laser output has a repetition rate of 5 kHz.

8. A laser ablation system in accordance with claim 1 wherein the controlled laser output has a pulse width of 136 ns.

9. A laser ablation system in accordance with claim 1 wherein the controlled laser output has an irradiance between 2.2×

10⁷ and 3.2×

10⁷ W/cm².

10. A laser ablation system in accordance with claim 1 wherein the controlled laser output has an irradiance of 2.7×

10⁷ W/cm².

11. A laser ablation system for conducting ablation in an ambient atmosphere, comprising:

a Nd;

YAG laser head;

an acousto-optic Q-switch coupled to the laser head and providing a controlled laser output, wherein the controlled laser output has a repetition rate between 3 and 7 kHz, has a pulse width between 100 and 140 ns, and has an irradiance greater than 1×

10⁷ W/cm² ;

a flexible fiber optic cable having a first end optically coupled to the laser output and receiving a power input above 110 W and having a second end transmitting laser light without being destroyed by the laser output; and

an output optics assembly including an output coupler having a first end connected to the second end of the fiber optic cable and having a second end, the output coupler supporting a collimating lens and supporting a focusing lens downstream of the collimating lens.

12. A laser ablation system in accordance with claim 11 and further comprising a laser capable of emitting a visible laser beam oriented to transmit a laser beam through the laser head, the fiber optic cable, and the output optics assembly, whereby a visible laser beam is provided to assist in aligning the laser head, fiber optic cable, and output optics assembly, and to provide a visual indication of the location where laser ablation is taking place.

13. A laser ablation system in accordance with claim 11 and further comprising a helium-neon laser oriented to transmit a laser beam through the laser head, the fiber optic cable, and the output optics assembly.

14. A laser ablation system in accordance with claim 11 wherein the fiber optic cable is a metal jacketed fiber optic cable.

15. A laser ablation system in accordance with claim 11 wherein the fiber optic cable is an armor coiled, metal jacketed, step-indexed fused silica fiber optic cable that has a core diameter of 1000 μ

m and an energy threshold of 1×

10⁸ W/cm².

16. A laser ablation system in accordance with claim 11 and further comprising a window downstream of the focusing lens and shielding the focusing lens from ablated particles.

17. A laser ablation system in accordance with claim 16 and further comprising holes through the particle collection cell, transverse to the direction through which laser light passes, providing for air flow to impede ablated particles from settling on the window.

18. A laser ablation system in accordance with claim 11 and further comprising a robotic positioning system controllably moving the output optics assembly relative to a workpiece.

19. A laser ablation system in accordance with claim 18 wherein the robotic positioning system controllably moves the output optics assembly relative to a workpiece along a first direction at a speed between 5 and 20 cm/sec.

20. A laser ablation system in accordance with claim 18 wherein the robotic positioning system controllably moves the output optics assembly relative to a workpiece along a first direction at a speed greater than 8 cm/sec.

21. A laser ablation system in accordance with claim 18 wherein the robotic positioning system controllably moves the output optics assembly relative to a workpiece along a first direction at a speed of at least 10 cm/sec.

22. A laser ablation system in accordance with claim 20 wherein the robotic positioning system controllably moves the output optics assembly relative to a workpiece along a second direction, perpendicular to the first direction, in increments of 0.5 mm.

23. A laser ablation system in accordance with claim 22 wherein the robotic positioning system controllably moves the output optics assembly relative to a workpiece along the first direction more than once per step.

24. A laser ablation system in accordance with claim 18 wherein the output optics assembly produces a laser output having a focal point, and wherein the robotic positioning system locates the output optics assembly above a workpiece such that the workpiece is ±

2 mm from the focal point.

25. A laser ablation system in accordance with claim 18 wherein the output optics assembly produces a laser output which has a spot size when the laser output intersects a workpiece, and wherein the robotic positioning system locates the output optics assembly above a workpiece such that the spot size is between 0 and 2 mm.

26. A laser ablation system in accordance with claim 18 wherein the output optics assembly produces a laser output which has a spot size when the laser output intersects a workpiece, and wherein the robotic positioning system locates the output optics assembly above a workpiece such that the spot size is between 0.5 and 1.5 mm.

27. A laser ablation system in accordance with claim 18 wherein the output optics assembly produces a laser output which has a spot size when the laser output intersects a workpiece, and wherein the robotic positioning system locates the output optics assembly above a workpiece such that the spot size is 1 mm.

28. A laser ablation system in accordance with claim 18 wherein the robotic positioning system angles the output optics assembly ±

20°

from perpendicular to a work piece.

29. A laser ablation system in accordance with claim 18 wherein the robotic positioning system angles the output optics assembly ±

10°

from perpendicular to a work piece.

30. A laser ablation system in accordance with claim 18 wherein the robotic positioning system angles the output optics assembly perpendicularly to a work piece.

31. A laser ablation system in accordance with claim 11 and further comprising a particle collection cell telescoped to the second end of the output optic s assembly, the particle collection cell including a nozzle through which laser light passes an exhaust tube in communication with the nozzle, and a blower generating a vacuum on the exhaust tube.

32. A method of decontaminating a surface comprising the following steps:

providing a Nd;

YAG laser light ablation system having a laser head, a fiber optically coupled output optics assembly coupled to the laser head, and

an acousto-optic Q-switch to the laser head; and

operating the laser light ablation system with a repetition rate between 3 and 7 kHz, a pulse width between 100 and 140 ns, and an irradiance greater than 1×

10⁷ w/cm².

33. A method in accordance with claim 32 wherein the laser light ablation system is operated with a repetition rate between 4 and 6 kHz.

34. A method in accordance with claim 32 wherein the laser light ablation system is operated with a repetition rate of 5 kHz.

35. A method in accordance with claim 32 and further comprising the step of rastering the output optics assembly relative to the surface along a first direction at a speed between 5 and 20 cm/sec.

36. A method in accordance with claim 35 and further comprising the step of moving the output optics assembly relative to the surface along a second direction, perpendicular to the first direction, in increments of 0.5 mm every certain number of rasters.

37. A method in accordance with claim 36 wherein the number of rasters per movement in the second direction is more than one.

38. A method in accordance with claim 32 and further comprising the step of rastering the Output optics assembly relative to the surface along a first direction at a speed greater than 8 cm/sec.

39. A method in accordance with claim 32 and further comprising the step of rastering the output optics assembly relative to the surface along a first direction at a speed of at least 10 cm/sec.

40. A method in accordance with claim 32 wherein the output optics assembly produces a laser output having a focal point, and further comprising the step of maintaining the surface within 2 mm from the focal point.

41. A method in accordance with claim 32 wherein the output optics assembly produces a laser output having a spot size, and further comprising the step of maintaining the spot size at a selected size between 0 and 2 mm.

42. A method in accordance with claim 32 wherein the output optics assembly produces a laser output having a spot size, and further comprising the step of maintaining the spot size at a selected size between 0.5 and 1.5 mm.

43. A method in accordance with claim 32 wherein the output optics assembly produces a laser output having a spot size, and further comprising the step of maintaining the spot size at 1 mm.

44. A method in accordance with claim 32 and further comprising the step of maintaining the output optics assembly at a selected angle ±

20°

from perpendicular to the surface.

45. A method in accordance with claim 32 and further comprising the step of maintaining the output optics assembly at a selected angle ±

10°

from perpendicular to the surface.

46. A method in accordance with claim 32 and further comprising the step of maintaining the output optics assembly perpendicularly to the surface.

47. A method in accordance with claim 32 wherein the operating step comprises the step of operating the laser light ablation system to produce an irradiance between 2.2×

10⁷ and 3.2×

10⁷ W/cm².

48. A method in accordance with claim 32 wherein the operating step comprises the step of operating the laser light ablation system to produce an irradiance of 2.7×

10⁷ W/cm².

49. A laser system comprising:

a Nd;

YAG laser head providing a laser output;

a flexible fiber optic cable having a first end optically coupled to the laser output, and having a second end;

an acousto-optic Q-switch coupled between the laser head and the first end of the fiber optic cable and configured to switch the laser output of the laser head to provide a controlled laser output to the first end of the fiber optic cable with a repetition rate between 3 and 7 kHz, and an irradiance greater than 1×

10⁷ w/cm² ; and

an output optics assembly optically coupled to the second end of the fiber optic cable.