Laser with optimized coupling of pump light to a gain medium in a side-pumped geometry

• US 6,157,663 A
• Filed: 04/16/1998
• Issued: 12/05/2000
• Est. Priority Date: 04/16/1998
• 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., Hemmati, Hamid, Wu, Xingkun
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Flores Ruiz, Delma R.
• Application Number:
  US09/061,796
• Time in Patent Office: 964 Days
• Field of Search: 372/75, 372/34, 372/78, 372/10, 372/70, 372/72, 372/69, 372/92, 372/101, 372/71, 372/19, 372/73
• US Class Current: 372/75
• CPC Class Codes: H01S 3/08072 Thermal lensing or thermally induced birefringence; Compensation thereof
• CPC Class Codes: H01S 3/091 using optical pumping
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation

Abstract

A solid-state laser includes a high-absorption coefficient solid-state gain medium such as Nd:YVO₄ that is side pumped with a semiconductor laser diode array. The resonant cavity of the solid-state laser is positioned so that the TEM₀₀ mode is spaced from the face of the laser through which the laser is pumped by a distance sufficient to reduce diffraction losses but sufficiently near to allow coupling of pump light into the gain mode. The gain medium, the doping level of the gain medium, and the operating temperature of the pump laser are selected to efficiently couple pump light into the gain mode. The pump laser is positioned to side pump the gain medium without collimating or focusing optics between the pump laser and the face of the gain medium. A gap between the pump laser and the gain medium is empirically selected to match the angular extent of the pump laser output light to the height of the gain mode at the position of the gain mode fixed to optimize coupling and diffraction losses.

Claims

1. A laser system comprising:

a laser cavity having an optical axis passing through the laser cavity;

a solid-state gain medium having a first transverse direction that is substantially perpendicular to the optical axis, the solid-state gain medium within the laser cavity and the optical axis passing through the solid-state gain medium; and

at least one semiconductor laser having an output, the at least one semiconductor laser positioned to direct a beam of light through a pump surface of the gain medium to pump the gain medium, with the beam of light diverging at least in the first transverse dimension, the beam of light from the at least one semiconductor laser pumping a laser mode within the gain medium to produce solid-state laser output,

the laser cavity defined so that the laser mode is spaced from the pump surface of the gain medium, and

the at least one semiconductor laser provided adjacent a face of the solid-state gain medium so that the beam of light output by the at least one semiconductor laser matches the laser mode.

2. The laser system of claim 1, wherein the at least one semiconductor laser is spaced from the face of the solid-state gain medium by a first distance.

3. The laser system of claim 2, wherein no focusing optics are provided between the at least one semiconductor laser and the face of the solid-state gain medium.

4. The laser system of claim 3, wherein the optical axis passes through the laser mode and through opposite ends of the gain medium, and wherein the laser cavity directs the laser mode along the optical axis in a direction parallel to the pump surface of the gain medium.

5. The laser system of claim 3, wherein the first distance provides a maximum output from the laser system for a particular output power of the at least one semiconductor laser.

6. The laser system of claim 3, wherein the first distance is within 50 μ

m of a position that corresponds to the maximum output from the laser system for a particular output power of the at least one semiconductor laser.

7. The laser system of claim 6, wherein the temperature of a surface of the gain medium is maintained at a temperature lower than a temperature of a surface of the at least one semiconductor laser.

8. The laser system of claim 3, wherein the first distance is within 100 μ

m of a position that corresponds to the maximum output from the laser system for a particular output power of the at least one semiconductor laser.

9. The laser system of claim 3, wherein the first distance is within 150 μ

m of a position that corresponds to the maximum output from the laser system for a particular output power of the at least one semiconductor laser.

10. The laser system of claim 8, wherein the temperature of the gain medium is maintained at a temperature approximately equal to a temperature of the at least one semiconductor laser.

11. The laser system of claim 3, wherein the first distance is such that an output of the solid-state laser is within 10% of the maximum output power for a given set of laser configuration and operational parameters.

12. The laser system of claim 1, wherein the beam of light output by the at least one semiconductor laser matches the laser mode to provide an output power from the solid-state laser within 50% of the maximum output power of the solid-state laser for a given set of laser configuration and operational parameters.

13. The laser system of claim 1, wherein the beam of light output by the at least one semiconductor laser matches the laser mode to provide an output power from the solid-state laser within 20% of the maximum output power of the solid-state laser for a given set of laser configuration and operational parameters.

14. The laser system of claim 1, wherein the beam of light output by the at least one semiconductor laser matches the laser mode to provide an output power from the solid-state laser within 10% of the maximum output power of the solid-state laser for a given set of laser configuration and operational parameters.

15. The laser system of claim 1, wherein a height of the beam of light output by the at least one semiconductor laser matches a vertical extent of the laser mode at a position of the laser mode within the gain medium.

16. The laser system of claim 15, wherein no focusing optics are provided between the at least one semiconductor laser and the face of the solid-state gain medium.

17. The laser system of claim 1, further comprising a harmonic generating apparatus that receives the laser mode output and outputs a shorter wavelength output.

18. The laser system of claim 17, wherein the harmonic generating apparatus is a frequency doubling crystal and the shorter wavelength output is a frequency doubled laser beam.

19. The laser system of claim 18, wherein the frequency doubling crystal is LBO.

20. The laser system of claim 17, wherein the laser system is pulsed at a pulsed repetition frequency (PRF).

21. The laser system of claim 20, wherein the laser system is a stereolithographic apparatus.

22. The laser system of claim 21, wherein the PRF is greater than or equal to about 40 kHz.

23. The laser system of claim 21, wherein the PRF is greater than or equal to about 22.2 kHz.

24. The laser system of claim 18, wherein the first distance provides a maximum power for the frequency doubled laser beam for a particular output power of the at least one semiconductor laser.

25. The laser system of claim 18, wherein the first distance is within 50 μ

m of a position that corresponds to a maximum power for the frequency doubled laser beam for a particular output power of the at least one semiconductor laser.

26. The laser system of claim 25, wherein the temperature of the gain medium is maintained at a temperature lower than a temperature of the at least one semiconductor laser.

27. The laser system of claim 18, wherein the first distance is within 100 μ

m of a position that corresponds to the maximum power in the frequency doubled laser beam for a particular output power of the at least one semiconductor laser.

28. The laser system of claim 18, wherein the first distance is within 150 μ

m of a position that corresponds to the maximum power in the frequency doubled laser beam for a particular output power of the at least one semiconductor laser.

29. The laser system of claim 27, wherein the temperature of the gain medium is maintained at a temperature approximately equal to a temperature of the at least one semiconductor laser.

30. The laser system of claim 18, wherein the first distance is such that an output of the solid-state laser is within 10% of the maximum power in the frequency doubled laser beam for a given set of laser configuration and operational parameters.

31. The laser system of claim 18, wherein the beam of light output by the at least one semiconductor laser matches the laser mode to provide an output power in the frequency doubled laser beam within 50% of the maximum for a given set of laser configuration and operational parameters.

32. The laser system of claim 18, wherein the beam of light output by the at least one semiconductor laser matches the laser mode to provide an output power in the frequency doubled laser beam within 20% of the maximum for a given set of laser configuration and operational parameters.

33. The laser system of claim 18, wherein the beam of light output by the at least one semiconductor laser matches the laser mode to provide an output power in the frequency doubled laser beam within 10% of the maximum for a given set of laser configuration and operational parameters.

34. The laser system of claim 3, wherein the first distance is selected to provide a maximum output in a lowest order laser mode of the laser system for a particular output power of the at least one semiconductor laser.

35. The laser system of claim 2, wherein the first distance is selected to provide a maximum output in a TEM₀₀ mode from the laser system for a particular output power of the at least one semiconductor laser.

36. The laser system of claim 3, wherein the first distance is between approximately 100-10,000 μ

m.

37. The laser system of claim 3, wherein the first distance is between approximately 100-500 μ

m.

38. The laser system of claim 1, wherein the gain medium receives pump light only from one side.

39. The laser system of claim 4, wherein the laser mode is spaced from the pump surface of the gain medium by a distance that reduces diffraction losses through the pump surface to a sufficient level to allow at least ten percent optical to optical efficiency from the gain medium.

40. The laser system of claim 4, wherein the laser mode is spaced from the pump surface of the gain medium by a distance that reduces diffraction losses through the pump surface to a sufficient level to allow at least twenty percent slope efficiency within the gain medium.

41. The laser system of claim 40, wherein the laser mode is disposed symmetrically around the optical axis.

42. The laser system of claim 1, wherein a 1/e² point of the laser mode is spaced from the pump surface of the gain medium by a distance of at least approximately two hundred microns.

43. The laser system of claim 1, wherein a 1/e² point of the laser mode is spaced from the pump surface of the gain medium by a distance of between approximately two hundred and three hundred microns.

44. The laser system of claim 1, wherein the gain medium is Nd:

YVO₄.

45. The laser system of claim 44, wherein the gain medium incorporates approximately 1% neodymium.

46. The laser system of claim 44, wherein the gain medium incorporates about 0.6-1.0% neodymium.

47. The laser system of claim 44, wherein the gain medium incorporates about 0.5-1.5% neodymium.

48. The laser system of claim 4, wherein the gain medium has top and bottom surfaces defining the vertical dimension of the gain medium, and wherein the laser mode is spaced from the top and bottom surfaces by second and third distances that are each larger than a fourth distance separating the laser mode from the pump surface.

49. The laser system of claim 46, wherein the gain medium has an inverse of an absorption coefficient for radiation in the beam of light that is shorter than a width of the gain medium in a second transverse direction that is perpendicular to the first transverse direction and the optical axis.

50. The laser system of claim 47, wherein fourth distance is such that diffraction losses through the pump surface are sufficiently low to allow at least ten percent optical to optical efficiency for the solid-state laser output.

51. The laser system of claim 47, wherein fourth distance is such that diffraction losses through the pump surface are sufficiently low to allow at least twenty percent slope efficiency for the solid-state laser output.

52. The laser system of claim 50, wherein the laser mode is disposed symmetrically around the optical axis.

53. The laser system of claim 51, wherein at least 90% of the solid-state laser output power is in the TEM₀₀ mode.

54. The laser system of claim 49, wherein a 1/e² point of the laser mode is spaced from the pump surface of the gain medium by the fourth distance of at least approximately two hundred microns.

55. The laser system of claim 54, wherein a 1/e² point of the laser mode is spaced from the pump surface of the gain medium by the fourth distance of between approximately two hundred and three hundred microns.

97. The system of claim 1 wherein the laser mode is positioned at a depth along a second transverse direction that is substantially perpendicular to the optical axis and to the first transverse direction.

56. A laser system comprising:

a laser cavity having an optical axis passing through the laser cavity;

a solid-state gain medium having a first transverse direction that is substantially perpendicular to the optical axis, the solid-state gain medium within the laser cavity and the optical axis passing through the solid-state gain medium; and

at least one semiconductor laser emitting a beam of light wider than a height of the beam at an output of the at least one semiconductor laser, the at least one semiconductor laser positioned to direct the beam of light through a pump surface of the gain medium to pump the gain medium, with the beam of light diverging in the first transverse direction, the beam of light from the at least one semiconductor laser pumping a laser mode within the gain medium to produce solid-state laser output,

the laser cavity positions the laser mode so that the optical axis is parallel to the pump surface, and

the at least one semiconductor laser provided adjacent the pump surface so that the beam of light matches the laser mode.

57. The laser system of claim 56, wherein a width of the beam of light is at least half of a length of the laser mode within the gain medium.

58. The laser system of claim 56, wherein the at least one semiconductor laser is spaced from the face of the solid-state gain medium by a first distance.

59. The laser system of claim 58, wherein no focusing optics are provided between the at least one semiconductor laser and the face of the solid-state gain medium.

60. The laser system of claim 58, wherein the first distance provides a maximum output from the laser system for a particular output power of the at least one semiconductor laser.

61. The laser system of claim 58, wherein the first distance is within 50 μ

m of a position that corresponds to the maximum output from the laser system for a particular output power of the at least one semiconductor laser.

62. The laser system of claim 61, wherein the temperature of the gain medium is maintained at a temperature lower than a temperature of the at least one semiconductor laser.

63. The laser system of claim 61, wherein the first distance is within 100 μ

m of a position that corresponds to the maximum output from the laser system for a particular output power of the at least one semiconductor laser.

64. The laser system of claim 58, wherein the first distance is within 150 μ

m of a position that corresponds to the maximum output from the laser system for a particular output power of the at least one semiconductor laser.

65. The laser system of claim 58, wherein the laser system includes a stereolithographic apparatus and wherein the stereolithographic apparatus receives as input a frequency multiplied laser beam.

66. The laser system of claim 65, wherein the laser system operates at a pulsed repetition frequency (PRF).

67. The laser system of claim 66, wherein the PRF is at least about 40 kHz.

68. The laser system of claim 67, wherein an ellipticity of the frequency multiplied laser beam is less than about 1.3.

69. The laser system of claim 66, wherein an ellipticity of the frequency multiplied laser beam is about 1.

70. The laser system of claim 56, wherein the laser cavity is defined in part by a high reflectivity mirror, an output coupler and a thermal lens formed within the gain medium.

71. The laser system of claim 70, wherein the thermal lens is the strongest focussing element within the laser cavity.

72. The laser system of claim 56, wherein the thermal lens stabilizes the laser cavity.

73. The laser system of claim 56, further comprising a frequency multiplying apparatus that receives the solid-state laser output and outputs a shorter wavelength output.

74. The laser system of claim 73, wherein the frequency multiplying apparatus is a frequency doubling crystal and the shorter wavelength output is a frequency doubled laser beam.

75. The laser system of claim 73, wherein the frequency multiplying apparatus includes two harmonic generating crystals and the shorter wavelength output is a frequency tripled laser beam.

76. A laser system, comprising:

a lasing medium for producing a laser beam of a desired wavelength;

at least one diode laser for directing a pumping beam along a pumping optical path for side pumping the lasing medium and producing a population inversion in the lasing medium; and

optical elements for forming a resonant cavity around the lasing medium defining a set of modes and for producing the laser beam,

wherein the optical elements are disposed to position the set of modes within the lasing medium and the at least one diode laser provides a pump wavelength different from a peak of absorption of the lasing medium,

the at least one diode laser provided adjacent a face of the lasing medium so that the pumping beam is matched to a lasing mode of the laser system.

77. The laser system of claim 76, wherein the lasing medium has a high-absorption coefficient.

78. The laser system of claim 77, wherein the output power in the laser beam is a maximum for a selected power level of the pumping beam.

79. The laser system of claim 78, wherein the set of modes consists of a TEM₀₀ mode.

80. The laser system of claim 78, wherein at least 90% of the output power of the laser is in a TEM₀₀ mode.

81. The laser system of claim 76, wherein the beam of light has an angular divergence in a direction along a first transverse direction that is substantially perpendicular to the optical axis.

82. The laser system of claim 81, wherein the at least one diode laser is spaced from the face of the lasing medium by a first distance to match the angular divergence of the beam of light to a height of the set of modes of the laser system.

83. The laser system of claim 82, wherein no focusing optics are provided between the at least one diode laser and the face of the lasing medium.

84. The laser system of claim 83, wherein the first distance is selected to provide a maximum output from the laser system for a particular output power of the at least one diode laser.

85. A laser system, comprising:

a lasing medium for producing a laser beam of a desired wavelength;

at least one diode laser for directing a pumping beam along a pumping optical path for side pumping the lasing medium and producing a population inversion in the lasing medium;

optical elements for forming a resonant cavity around the lasing medium defining a set of modes and for producing a the laser beam; and

wherein the optical elements are disposed to position the optical set of modes within the lasing medium, spaced from all sides of the lasing medium,

wherein the pumping optical path contains no focusing optics between the at least one diode laser and the lasing medium, and

wherein the at least one diode laser is spaced from the side face of the lasing medium by a first distance to match an angular divergence of the pumping beam to a height of the set modes of the laser system.

86. The laser system of claim 85, wherein the lasing medium has first and second end faces and wherein the laser beam passes through the first and second end faces.

87. The laser system of claim 86, wherein the set of modes is spaced from and parallel to a side face of the lasing medium.

88. The laser system of claim 87, wherein a 1/e² point of the set of modes is spaced from the side face of the lasing medium by a distance of at least approximately two hundred microns.

89. The laser system of claim 87, wherein a 1/e² point of the set of modes is spaced from the side face of the gain medium by a distance of between approximately two hundred and three hundred microns.

90. The laser system of claim 87, wherein the set of modes is spaced from the side face of the lasing medium by a distance that reduces diffraction losses through the side face to a sufficient level to allow at least ten percent optical to optical efficiency for the laser system.

91. The laser system of claim 90, wherein the set of modes consists only of a substantially TEM₀₀ mode of the resonant cavity.

92. The laser system of claim 91, wherein the lasing medium is Nd:

YVO₄.

93. The laser system of claim 92, wherein the lasing medium incorporates approximately 1% neodymium.

94. The laser system of claim 85, wherein the first distance is selected to provide a maximum output from the laser system for a particular output intensity of the at least one diode laser.

95. A laser system, comprising:

a lasing medium for producing a laser beam of a desired wavelength;

at least one diode laser for directing a pumping beam along a pumping optical path for side pumping the lasing medium and producing a population inversion in the lasing medium; and

optical elements for forming a resonant cavity around the lasing medium, the optical elements defining a set of modes and for producing the laser beam,

wherein the optical elements are disposed to position the set of modes within the lasing medium,

the at least one diode laser provided adjacent a face of the lasing medium so that the pumping beam is matched to a lasing mode of the laser system.

96. A laser system, comprising:

a lasing medium for producing a laser beam of a desired wavelength;

at least one diode laser for directing a pumping beam along a pumping optical path for pumping the lasing medium at a pumping surface and producing a population inversion in the lasing medium; and

optical elements for forming a resonant cavity around the lasing medium, the optical elements defining a set of modes and for producing the laser beam,

wherein the optical elements are disposed to space the set of modes from the pumping surface of the lasing medium,

the at least one diode laser provided adjacent to a face of the lasing medium so that the pumping beam is matched to a lasing mode of the laser system.

98. A method for manufacturing a laser system, comprising the steps of:

providing a lasing medium for producing a laser beam of a desired wavelength;

providing at least one diode laser for directing a pumping beam along a pumping optical path for side pumping the lasing medium and producing a population inversion in the lasing medium; and

providing optical elements for forming a resonant cavity around the lasing medium, the optical elements defining a set of modes and for producing the laser beam;

locating the optical elements to position the set of modes within the lasing medium;

locating the at least one diode laser at a distance spaced from a face of the lasing medium to supply the pumping beam to the lasing medium;

relatively moving the lasing medium and the diode laser a plurality of times to a plurality of relative positions and noting an output power of the laser beam for each of the plurality of relative positions; and

fixing the relative position of the diode laser and the lasing medium at a selected a position so that the output power is at least 50% of a maximum output power as determined in the moving step.

99. A method for preparing a laser system for operation, comprising:

a. providing a laser system, comprising;

i. a lasing medium for producing a laser beam of a desired wavelength;

ii. at least one diode laser for directing a pumping beam along a pumping optical path for side pumping the lasing medium and producing a population inversion in the lasing medium; and

iii. providing optical elements for forming a resonant cavity around the lasing medium, the optical elements defining a set of modes and for producing the laser beam,

wherein the optical elements are located to position the set of modes within the lasing medium;

wherein the at least one diode laser is spaced at a distance from a face of the lasing medium to supply the pumping beam to the lasing medium;

b. relatively moving the lasing medium and the diode laser a plurality of times to a plurality of relative positions and noting the output power of the laser beam for each of the plurality of relative positions; and

c. fixing the relative position of the diode laser and the lasing medium at a selected a position so that the output power is at least 50% of a maximum output power as determined in the moving step.

100. A method for preparing a laser system for operation, comprising:

a. providing a laser system, comprising;

i. a lasing medium for producing a laser beam of a desired wavelength;

ii. at least one diode laser for directing a pumping beam along a pumping optical path for side pumping the lasing medium and producing a population inversion in the lasing medium; and

iii. providing optical elements for forming a resonant cavity around the lasing medium, the optical elements defining a set of modes and for producing the laser beam,

wherein the optical elements are located to position the set of modes within the lasing medium;

wherein the at least one diode laser is spaced at a distance from a face of the lasing medium to supply the pumping beam to the lasing medium;

b. providing a frequency conversion crystal that converts said laser beam of desired wavelength into a laser beam of second desired wavelength;

b. relatively moving the lasing medium and the diode laser a plurality of times to a plurality of relative positions and noting the output power of the laser beam of second desired wavelength for each of the plurality of relative positions; and

c. fixing the relative position of the diode laser and the lasing medium at a selected a position so that the output power is at least 50% of a maximum output power of the laser beam of second desired wavelength as determined in the moving step.