Extended lifetime frequency conversion crystals

• US 6,532,100 B1
• Filed: 08/04/1999
• Issued: 03/11/2003
• Est. Priority Date: 08/04/1999
• Status: Expired due to Term

• Current Assignee: 3D Systems, Inc. (3D Systems Corporation)
• Original Assignee: 3D Systems, Inc. (3D Systems Corporation)
• Inventors: Partanen, Jouni P., Hug, William F., Wu, Xingkun, Reynolds, Gary
• Primary Examiner(s): Lee; John D.
• Application Number:
  US09/368,342
• Time in Patent Office: 1,315 Days
• Field of Search: 359/326-332 372/21,22
• US Class Current: 359/326
• CPC Class Codes: G02F 1/35 Non-linear optics
• CPC Class Codes: G02F 1/3505 Coatings; Housings; Supports

Abstract

Solid state lasers that use non-linear optical crystals to generate frequency tripled or quadrupled output in the ultraviolet have low lifetimes due to damage to the face of the non-linear crystal through which the ultraviolet signal exits. To prevent this damage, the tripling or quadrupling crystal is provided within a controlled environment that is maintained substantially free from contaminants such as silicon-bearing and organic compounds. The tripling or quadrupling crystal is enclosed within a tubular chamber with windows on the ends of the tube that provide optical access to the entrance and exit faces of the tripling or quadrupling crystal. All heating elements and alignment elements for the crystal are outside of the chamber. Because the crystal is stored within the hermetically sealed chamber, contaminants are not available within the environment of the crystal that could interact with the energetic photons of the ultraviolet output of the frequency multiplied solid state laser. The windows and walls of the chamber are preferably made of materials that can be cleaned effectively, such as sapphire or quartz for the windows and stainless steel for the walls and flanges of the chamber.

Claims

1. A laser system, comprising:

a solid state laser producing a fundamental laser output at a fundamental wavelength;

a frequency conversion crystal disposed along an optical path leading from the solid state laser, the frequency conversion crystal receiving light and outputting light at a second wavelength different from the fundamental wavelength; and

a chamber enclosing at least a portion of an exit face of the frequency conversion crystal within an environment hermetically sealed from an environment outside of the chamber, the chamber thermally coupled to heating elements used for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.

2. The laser system of claim 1, wherein the chamber is free of adjustment mechanisms usable to adjust a position of the frequency conversion crystal.

3. The laser system of claim 1, wherein all fixtures for moving or rotating the frequency conversion crystal are outside of the chamber.

4. The laser system of claim 1, further comprising a heater positioned outside of the chamber and thermally coupled to a wall of the chamber.

5. The laser system of claim 4, further comprising:

a thermally conductive mounting block, the frequency conversion crystal mounted to the thermally conductive mounting block; and

a temperature sensor thermally coupled to the thermally conductive mounting block.

6. The laser system of claim 4, further comprising a temperature sensor thermally coupled to a wall of the chamber.

7. The laser system of claim 6, wherein the temperature sensor is connected to the wall of the chamber.

8. The laser system of claim 1, wherein the chamber is free of insulation coated wires.

9. The laser system of claim 1, further comprising a first lens to converge light onto the frequency conversion crystal and a second lens to collect light diverging from the frequency conversion crystal.

10. The laser system of claim 9, wherein the first and the second lenses are outside of the chamber.

11. The laser system of claim 9, wherein at least one face of at least one of the first and second lenses faces on an environment within the chamber.

12. The laser system of claim 11, wherein a face of each of the first and second lenses faces on an environment within the chamber.

13. The laser system of claim 1, wherein the chamber is substantially free from organic contaminants.

14. The laser system of claim 13, wherein the chamber is sufficiently free from organic contaminants to provide over two thousand hours of operation without servicing the frequency conversion crystal.

15. The laser system of claim 13, wherein the chamber is sufficiently free from organic contaminants to provide over five thousand hours of operation without servicing the frequency conversion crystal.

16. The laser system of claim 1, wherein the chamber is sufficiently free from contaminants and sufficiently hermetically sealed to provide over one thousand hours of operation without servicing the frequency conversion crystal.

17. The laser system of claim 1, wherein the chamber is sufficiently free from contaminants and sufficiently hermetically sealed to provide over five thousand hours of operation without servicing the frequency conversion crystal.

18. The laser system of claim 1, wherein the chamber is substantially free from organic sealants.

19. The laser system of claim 1, wherein the chamber is evacuated.

20. The laser system of claim 1, wherein the chamber is filled with a functionally inert gas.

21. The laser system of claim 20, wherein the chamber is maintained at above atmospheric pressure.

22. The laser system of claim 1, wherein the second wavelength is in the range from about 325 to about 360 nanometers.

23. The laser system of claim 1, further comprising an exit window of the chamber positioned so that light of the second wavelength passes through the exit window, the frequency conversion crystal spaced from the exit window by a sufficient distance to substantially prevent plating of contaminants onto the exit window.

24. The laser system of claim 1, further comprising an exit window of the chamber positioned so that light of the second wavelength passes through the exit window, the frequency conversion crystal spaced from the exit window by a sufficient distance to substantially prevent ultraviolet light mediated damage of the exit window.

25. The laser system of claim 1, further comprising an exit window of the chamber positioned so that light of the second wavelength passes through the exit window, the frequency conversion crystal spaced from the exit window by a sufficient distance to provide at least five thousand hours of operation without replacing or servicing the exit window.

26. The laser system of claim 1, wherein the frequency conversion crystal is mounted on a translation stage so the frequency conversion crystal can be translated with respect to the optical path and wherein the frequency conversion crystal can be translated within the laser system to provide a new exit face from the frequency conversion crystal.

27. The laser system of claim 26, wherein the translation stage is translated from outside the chamber.

28. The laser system of claim 1, wherein the chamber provides an hermetic environment consisting essentially of one or more of glass, fused silica, sapphire, quartz, ceramic and metal.

29. The laser system of claim 1, wherein the chamber provides an hermetic environment consisting of inorganic materials.

30. The laser system of claim 1, wherein the second wavelength is an ultraviolet wavelength.

31. The laser system of claim 30, wherein the laser system comprises a doubling crystal and a tripling crystal.

32. The laser system of claim 1, wherein the solid state laser comprises a Nd:

YVO₄ gain medium.

33. The laser system of claim 32, wherein the laser system comprises a stereolithography system.

34. The laser system of claim 1, further comprising a second frequency conversion crystal, wherein the second frequency conversion crystal is enclosed within the chamber.

35. The laser system of claim 1, wherein the laser system comprises a stereolithography system.

36. A method for producing a laser system, comprising:

providing a mounting fixture and a chamber adapted for holding the mounting fixture;

cleaning the mounting fixture and the chamber;

cleaning at least a surface of a frequency conversion crystal to be protected by the chamber;

assembling the frequency conversion crystal, the mounting fixture and the chamber to define an assembly and sealing the chamber to enclose the surface of the frequency conversion crystal to be protected by the chamber, providing the chamber with heating elements used for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.;

providing a laser outputting light of a fundamental wavelength; and

aligning the frequency conversion crystal with respect to an optical path of the laser.

37. The method of claim 36, further comprising the step of adjusting a temperature of the frequency conversion crystal to an operation temperature prior to aligning the frequency conversion crystal.

38. The method of claim 36, further comprising filling the chamber with a gas consisting essentially of large, slow diffusing molecules.

39. The method of claim 38, wherein the gas is sulfur hexaflouride.

40. A method for producing a laser system, comprising:

providing a mounting fixture and a chamber adapted for holding the mounting fixture;

cleaning the mounting fixture and the chamber;

cleaning at least a surface of a frequency conversion crystal to be protected by the chamber;

assembling the frequency conversion crystal, the mounting fixture and the chamber to define an assembly and sealing the chamber to enclose the surface of the frequency conversion crystal to be protected by the chamber, providing the chamber with heating elements used for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.; and

adjusting a temperature of the frequency conversion crystal to identify an operating temperature.

41. The method of claim 40, wherein the act of cleaning the mounting fixture and the chamber is performed before the act of assembling.

42. The method of claim 40, wherein the act of cleaning the mounting fixture and the chamber is performed after the act of assembling.

43. The method of claim 40, wherein the act of cleaning the mounting fixture and the chamber includes baking the mounting fixture and the chamber in an oven.

44. A method for producing a laser system, comprising:

providing a mounting fixture and a chamber adapted for holding the mounting fixture;

cleaning the mounting fixture and the chamber;

cleaning at least a surface of a frequency conversion crystal to be protected by the chamber;

assembling the frequency conversion crystal, the mounting fixture and the chamber to define an assembly and sealing the chamber to enclose the surface of the frequency conversion crystal to be protected by the chamber, providing the chamber with heating elements used for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.; and

adjusting a temperature of the frequency conversion crystal to verify an operating temperature of the frequency conversion crystal is within a desired range.

45. A method for producing a laser system, comprising:

providing a mounting fixture and a chamber adapted for holding the mounting fixture;

cleaning the mounting fixture and the chamber;

cleaning at least a surface of a frequency conversion crystal to be protected by the chamber;

assembling the frequency conversion crystal, the mounting fixture and the chamber to define an assembly, providing the chamber with heating elements used for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.;

sealing the chamber to enclose the surface of the frequency conversion crystal to be protected by the chamber; and

applying a laser beam to the frequency conversion crystal after sealing the chamber.

46. A method for producing a laser system, comprising:

providing a mounting fixture and a chamber adapted for holding the mounting fixture;

cleaning the mounting fixture and the chamber;

cleaning at least a surface of a frequency conversion crystal to be protected by the chamber;

assembling the frequency conversion crystal, the mounting fixture and the chamber to define an assembly;

sealing the chamber to enclose the surface of the frequency conversion crystal to be protected by the chamber, providing the chamber with heating elements for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.; and

aligning the frequency conversion crystal after the step of sealing.

47. The method of claim 46, wherein assembling and sealing the chamber are performed before any alignment of the frequency crystal in the laser system.

48. A method for replacing a frequency conversion crystal in a laser system, comprising:

providing a laser system that uses a frequency conversion crystal to generate light of a converted wavelength;

removing the frequency conversion crystal from the laser system; and

installing a new frequency conversion crystal into the laser system, wherein the new frequency conversion crystal has at least one surface maintained in an hermetically sealed environment prior to and throughout installation, wherein the chamber is thermally coupled to heating elements for adjusting an operating temperature of the frequency conversion crystal, where all the heating elements are provided outside of the chamber and where the chamber is stable to baking at 300°

C.

49. The method of claim 48, wherein the frequency conversion crystal to be replaced has at least one surface maintained in a hermetically sealed environment defined by a structure and that structure is removed to replace the frequency conversion crystal to be replaced.

50. The method of claim 48, wherein the laser system includes a solid state laser.

51. The method of claim 48, further comprising the step of aligning the frequency conversion crystal with respect to a laser beam.

52. The method of claim 48, further comprising the step of heating the frequency conversion crystal to an operating temperature while aligning the frequency conversion crystal.