Laser clamping assembly and method

• US 6,385,220 B1
• Filed: 04/21/1999
• Issued: 05/07/2002
• Est. Priority Date: 04/21/1999
• Status: Expired due to Fees

• Current Assignee: GSI Lumonics, Inc.
• Original Assignee: GSI Lumonics, Inc.
• Inventors: Liao, Yan, Armstrong, Michael Robert, Walker, David Ronald, Miller, Robert John Dwayne
• Primary Examiner(s): Davie, James W.
• Application Number:
  US09/295,338
• Time in Patent Office: 1,112 Days
• Field of Search: 372/34, 372/33, 372/36, 372/66, 372/67
• US Class Current: 372/34
• CPC Class Codes: H01S 3/025 of solid state lasers, e.g. housings or mountings
• CPC Class Codes: H01S 3/0407 Liquid cooling, e.g. by water
• CPC Class Codes: H01S 3/042 for solid state lasers H01S3/0401 takes precedence
• CPC Class Codes: H01S 3/0604 in the form of a plate or disc
• CPC Class Codes: H01S 3/08072 Thermal lensing or thermally induced birefringence; Compensation thereof
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping

Abstract

A laser clamping system for a disc laser medium that includes two heat conductive members (one of which is optically transparent) positioned on either side of a disc laser. Pressure is applied to the conductive members to restrain the disc from deforming under pumping conditions to reduce the lensing effect. Thin disc geometry allows the thermal load of laser material to be much closer to the heat conductive members so that heat dissipation is generally more efficient than that of other geometric configurations (e.g. rod or slab). In disc lasers each part of the laser beam experiences the same temperature gradient so that there is no lensing effect caused by radial temperature distribution. It has been discovered that any resulting lensing effect is disc lasers is mainly from the thermo-mechanical deformation of the disc itself. Consequently, a disc laser with clamped boundary conditions using the system as described above reduces the lensing effect and enables scaling laser power to a much higher level compared to unclamped disc laser systems. The clamping system and method of the present invention also improves performance in rod and slab type laser medium geometries.

Claims

1. A laser clamping system for a laser medium in a solid state laser comprising:

(a) a first member made from a heat conductive material;

(b) a second member constructed to allow a laser beam to pass therethrough substantially unattenuated, the laser medium being disposed between and in contact with the first and second member; and

(c) means for applying pressure to the laser medium through the first and second members to inhibit thermo-deformation of the laser medium.

2. The laser clamping system of claim 1, wherein the second member is made from a heat conductive material.

3. The laser clamping system of claim 1, wherein the second member is made from a material transparent to the laser beam.

4. The laser clamping system of claim 1, wherein the second member includes an aperture to allow the laser beam to pass through the second member to the laser medium.

5. The laser clamping system of claim 1, wherein at least one of the first and second members is a pressure body being harder than the laser medium.

6. The laser clamping system of claim 5, wherein the means for applying pressure includes a bolt assembly for attaching the first member to the second member.

7. The laser clamping system of claim 1, further comprising a conformable heat conductive material disposed intermediate the laser medium and at least one of the first and second members.

8. The laser clamping system of claim 1, further comprising at least one reflecting surface formed on at least one of the first and second members and configured to reflect pumping radiation transmitted through one of the first and second members and the laser medium to enhance pumping of the solid state laser.

9. The laser clamping system of claim 1, wherein the laser medium is a rod.

10. The laser clamping system of claim 1, wherein the laser medium is a slab.

11. The laser clamping system of claim 1, wherein the laser medium is a disc.

12. The laser clamping system of claim 11, wherein the means for applying pressure applies a pressure that exceed approximately 50 pounds per square inch.

13. The laser clamping system of claim 1, further comprising an index matching fluid disposed intermediate the laser medium and at least one of the first and second members.

14. The laser clamping system of claim 1, further comprising a cooling channel disposed in one of the members.

15. The laser clamping system of claim 1, wherein the heat conductive material is selected from the group consisting of:

copper, brass, aluminum and nickel.

16. The laser clamping system of claim 1, wherein the heat conductive material is selected from the group consisting of:

diamond and silicon carbide.

17. The laser clamping system of claim 16, wherein the heat conductive material is selected from the group consisting of:

gold coated diamond, nickel-coated diamond, gold-coated silicon carbide and nickel-coated silicon carbide.

18. The laser clamping system of claim 3, wherein the material transparent to the laser beam is selected from the group consisting of:

fused silica, sapphire and diamond.

19. The laser clamping system of claim 7, wherein the conformable heat conductive material is selected from the group consisting of:

soft solder and indium.

20. The laser clamping system of claim 8, wherein the at least one reflecting surface includes a high reflectivity coating material at lasing and pumping wavelengths.

21. The laser clamping system of claim 1, wherein the laser medium includes a neodymium-doped material.

22. The laser clamping system of claim 1, wherein the laser medium includes a heat sink side and a pressure side, the heat sink side including a reflector layer, a metal layer and a contact layer;

and the pressure side including an anti-reflective coating.

23. The laser clamping system of claim 22, wherein the pressure side includes a contact layer.

24. The laser clamping system of claim 23, wherein the contact layer is transparent at lasing and pumping wavelengths.

25. The laser clamping system of claim 22, wherein the reflector layer includes a high reflectivity coating material at lasing and pumping wavelengths.

26. The laser clamping system of claim 22, wherein the metal layer is selected from the group consisting of gold and copper.

27. The laser clamping system of claim 23, wherein the contact layer is selected from the group consisting of soft solder and indium.

28. The laser clamping system of claim 14, wherein a cooling medium is arranged to pass through the cooling channel.

29. The laser clamping system of claim 28, wherein the cooling medium is water.

30. The laser clamping system of claim 9, wherein the means for applying pressure includes a pressure body that surrounds the rod, a pair of compression sleeves mounted at ends of the rod for exerting pressure on the pressure body and the rod.

31. The laser clamping system of claim 30, wherein each of the compression sleeves includes an aperture arranged to permit pumping light access at one end of the rod and laser mode output at another end of the rod.

32. The laser clamping system of claim 10, wherein the means for applying pressure includes a pair of pressure plates mounted along two edges of the slab perpendicular to a lasing direction and clamps for applying pressure to the pressure plates and the slab.

33. A laser clamping system for a laser medium in a solid state laser comprising:

(a) two heat conducting members, each heat conducting member having a generally planar surface, the two heat conducting members being oriented to receive the laser medium such that the laser medium contacts the generally planar surfaces of the two heat conducting members;

(b) at least one of the heat conducting members allows the laser beam to pass therethrough substantially unattenuated and unchanged; and

(c) pressure means for holding both heat conducting members in contact against the laser medium, whereby the heat conducting members and the pressure means remove heat from the laser medium under pumping conditions.

34. The laser clamping system of claim 33, wherein the heat conducting members induce a temperature gradient in the laser medium that is substantially parallel to the a propagation axis of a laser beam.

35. The laser clamping system of claim 34, wherein the at least one of the heat conducting members is made from a material transparent to the laser beam.

36. The laser clamping system of claim 34, wherein the at least one of the heat conducting members includes an aperture in communication with the laser medium for receiving the laser beam.

37. The laser clamping system of claim 33, wherein the pressure means includes a bolt assembly for attaching the two heat conducting members together.

38. The laser clamping system of claim 33, further comprising a conformable heat conductive material disposable intermediate the laser medium and at least one of the heat conducting members.

39. The laser clamping system of claim 33, further comprising at least one reflecting surface formed upon at least one of the heat conducting members and configured to reflect pumping radiation transmitted through at least one of the heat conducting members and the laser medium.

40. The laser clamping system of claim 33, wherein the laser medium is a rod.

41. The laser clamping system of claim 33, wherein the laser medium is a slab.

42. The laser clamping system of claim 33, wherein the laser medium is a disc.

43. A thin-plate laser comprising:

(a) a solid state laser medium configured as a thin-plate;

(b) two heat conductive members capturing the solid state laser medium therebetween, the two heat conductive members each generally conforming to one of a pair of opposed surfaces of the solid state laser medium to facilitate heat transfer from the solid state laser medium to the two heat conductive members;

(c) at least one of the heat conductive members being optically transparent to transmit pumping light from a source to the solid state laser medium; and

(d) force applying means for applying pressure to the heat conductive members to restrain the solid state laser medium from mechanical deformation under pumping conditions.

44. The laser clamping system of claim 43, wherein the heat conductive members are made of a material harder than the disc laser medium.

45. The laser clamping system of claim 43, wherein the generally planar surface of each heat conductive member includes a polished surface to enhance heat transfer at an interface thereof with the disc laser medium.

46. The laser clamping system of claim 43, further comprising a conformable, heat conductive material disposable intermediate the disc laser medium and at least one of the heat conductive members.

47. The laser clamping system of claim 46, wherein the heat conductive material is indium.

48. A method for enhancing an output of a laser having a solid state laser medium, the method comprising the steps of:

(a) pumping the solid state laser medium through at least one of two heat conductive members, one heat conductive member being disposed in thermal contact with each of two generally opposed surfaces of the solid state laser medium;

(b) removing heat from the solid state laser medium via the two heat conductive members; and

(c) applying pressure to the heat conductive members to restrain the solid state laser medium from mechanically deforming under pumping conditions to mitigate thermal focusing and depolarization of laser radiation stimulated with the solid state laser medium.

49. The method of claim 48, further comprising the step of disposing a conformable, heat conductive material intermediate the solid state laser medium and at least one of the heat conductive members.

50. The method of claim 48, further comprising the step of reflecting pumping radiation from at least one mirrored surface formed upon at least one of the heat conductive members such that the reflected pumping radiation is transmitted back through the solid state laser medium to enhance pumping thereof.

51. A laser clamping system for a laser medium in a solid state laser comprising:

(a) members arranged to sandwich the laser medium therebetween; and

(b) a device for applying pressure to the laser medium through the members to prevent thermally-induced mechanical distortion of the laser medium during operation.

52. The laser clamping system of claim 51, wherein the members include a first heat conductive body and a second body constructed to allow a laser beam to pass therethrough substantially unattenuated.

53. A thin-plate laser comprising:

(a) a solid state laser medium configured as a thin plate;

(b) two heat conductive members capturing the solid state laser medium therebetween, the two heat conductive members each generally conforming to one of a pair of opposed surfaces of the solid state laser medium to facilitate heat transfer from the solid state laser medium to the two heat conductive members;

(c) at least one of the heat conductive members being optically transparent to transmit pumping light from a source to the solid state laser medium; and

(d) a device for applying pressure to the heat conductive members to restrain the solid state laser medium from mechanical deformation under pumping conditions.

54. A method for operating a laser comprising the steps of:

(a) sandwiching the laser medium between two layers; and

(b) applying an anti-deformation force to the laser medium during operation, said anti-deformation force being sufficient to restrain thermally induced mechanical distortion in the laser medium.

55. The method of claim 54, further comprising the step selected at least one of the two layer to conduct heat away from the laser medium.

56. The method of claim 55, further comprising the step of disposing a conformable, heat conductive material intermediate the laser medium and at least one of the heat conductive members.

57. The method of claim 55, further comprising the step of reflecting pumping radiation from at least one mirrored surface formed upon at least one of the layers such that the reflected pumping radiation is transmitted back through the laser medium.

58. A solid state laser system comprising:

(a) a solid state laser medium that when irradiated or pumped produces lasing action and that is prone to thermally induced mechanical distortion under pumping conditions, said laser medium having two substantially opposing planar and parallel end surfaces which are substantially perpendicular to a propagation axis of a laser beam;

(b) two heat conducting members for conducting heat away from the laser medium, each heat conducting member having a generally planar surface placed in contact with one of the planar and parallel laser medium end surfaces;

(c) at least one of the heat conducting members allowing the laser beam to pass therethrough; and

(d) a clamping device for applying sufficient clamping pressure to the laser material through the two heat conducting members to restrain the laser material from deforming as a result of thermally induced mechanical distortion under pumping conditions.