Efficient frequency-converted laser

• US 5,761,227 A
• Filed: 12/05/1996
• Issued: 06/02/1998
• Est. Priority Date: 08/23/1994
• Status: Expired due to Term

• Current Assignee: CVI Laser LLC
• Original Assignee: Laser Power Corp
• Inventors: Hargis, David E., Nelte, Sven E.
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US08/760,702
• Time in Patent Office: 544 Days
• Field of Search: 372/22, 372/92, 372/99, 372/98, 372/107, 372/108
• US Class Current: 372/22
• CPC Class Codes: G02F 1/3503 Structural association of optical elements, e.g. lenses, with the non-linear optical device
• CPC Class Codes: H01S 2302/00 Amplification / lasing wavelength
• CPC Class Codes: H01S 2303/00 Pumping wavelength
• CPC Class Codes: H01S 3/0405 Conductive cooling, e.g. by heat sinks or thermo-electric elements
• CPC Class Codes: H01S 3/042 for solid state lasers H01S3/0401 takes precedence
• CPC Class Codes: H01S 3/0602 Crystal lasers or glass lasers H01S3/063 takes precedence
• CPC Class Codes: H01S 3/0612 Non-homogeneous structure H01S3/07 takes precedence
• CPC Class Codes: H01S 3/0627 the resonator being monolithic, e.g. microlaser
• CPC Class Codes: H01S 3/0815 having 3 reflectors, e.g. V-shaped resonators
• CPC Class Codes: H01S 3/0816 having 4 reflectors, e.g. Z-shaped resonators
• CPC Class Codes: H01S 3/082 defining a plurality of resonators, e.g. for mode selection or suppression
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1611 neodymium
• CPC Class Codes: H01S 3/1671 vanadate, niobate, tantalate
• CPC Class Codes: H01S 3/1673 YVO4 [YVO]

Abstract

An intracavity frequency-converted laser having an intracavity reflector situated to reflect converted radiation at a nonzero angle with respect to the optical axis. The laser includes an optical cavity that defines an optical axis, a gain medium for providing a fundamental laser emission, a pump source for pumping the gain medium, and a nonlinear material for frequency converting the fundamental laser emission to provide first and second converted beams that propagate in opposite directions within the optical cavity. An angled reflector that reflects optical radiation at the converted wavelength, but is transmissive at the fundamental wavelength is situated within the optical cavity to reflect one of the converted beams along a path angled with respect to the optical axis. Advantageously, reflecting the converted radiation before it propagates through the gain medium avoids absorption losses. Furthermore, interference between the reflected beam and other converted beam is avoided due to the angle of reflection. In one embodiment, the gain medium comprises an Nd³⁺ doped material, the laser is designed to lase on the ⁴ F_3/2 →⁴ I_9/2 transition at about 870-960 nm, and a nonlinear crystal is situated to frequency-double the emission of the gain medium to produce blue light at about 435-480 nm.

Claims

1. A method of intracavity frequency conversion in a laser comprising the steps of:

a) pumping a gain medium situated within an optical cavity to provide a laser emission along an optical axis defined by the optical cavity;

b) frequency converting the laser emission within the optical cavity to generate a first converted beam propagating in a first direction along the optical axis and a second converted beam propagating in a second, opposite direction along the optical axis; and

c) reflecting said second converted beam at a predefined nonzero angle with respect to the optical axis to provide a reflected converted beam.

2. The method of claim 1 and further comprising the step of reflecting said second converted beam such that the reflected converted beam does not propagate through the gain medium.

3. The method of claim 1 wherein said reflecting step includes reflecting said second converted beam from an angled reflector situated within said optical cavity, said angled reflector being transmissive of the laser emission and reflective of the converted beam.

4. The method of claim 3, and further comprising the steps of:

outputting said first converted beam from the optical cavity through an output reflector that is substantially transmissive of the converted beam and substantially reflective of the laser emission; and

reflecting the second converted beam at an angle with respect to the first converted beam such that it exits the cavity through said output reflector.

5. The method of claim 1 wherein said pumping step comprises optically pumping a solid-state gain medium.

6. The method of claim 1, and further comprising the step of outputting the first converted beam and the reflected converted beam from the optical cavity, and imaging said beams to a common point.

7. The method of claim 1, and further comprising the step of re-combining said first and said reflected converted beams after said beams exit from the optical cavity, said re-combining causing said first and said reflected converted beams to overlap and propagate in a collinear direction.

8. A method of intracavity frequency conversion in a solid-state laser comprising the steps of:

a) optically pumping a solid-state gain medium situated within an optical cavity to provide a fundamental laser emission along an optical axis defined by the optical cavity;

b) frequency converting the fundamental laser emission in a nonlinear crystal within the optical cavity to generate a first converted beam propagating in a first direction along the optical axis and a second converted beam propagating in a second, opposite direction along the optical axis; and

c) reflecting said second converted beam from an angled reflector situated within said optical cavity to provide a reflected converted beam propagating at a predefined nonzero angle with respect to the optical axis.

9. The method of claim 8 and further comprising the step of reflecting said second converted beam without propagating through the gain medium.

10. The method of claim 9 further comprising the step of propagating said reflected converted beam through said nonlinear material without substantially overlapping with said first converted beam.

11. The method of claim 9, and further comprising the steps of:

outputting said first converted beam from the optical cavity through an output reflector that is substantially transmissive of the converted beam and substantially reflective of the fundamental laser emission; and

reflecting the second converted beam at an angle with respect to the first converted beam such that it exits the cavity through said output reflector.

12. The method of claim 8 wherein said optical pumping step includes longitudinally pumping said solid-state gain medium with a laser diode.

13. A method of intracavity frequency conversion to produce blue light in a laser having an optical cavity that defines an optical axis, said method comprising the steps of:

a) optically pumping an anisotropic neodymium-doped gain crystal in an longitudinal direction;

b) generating a polarized fundamental laser emission in said gain crystal corresponding to the ⁴ F_3/2 →

⁴ I_9/2 laser transition, said gain crystal defining an ordinary axis and an extraordinary axis situated within said optical cavity in an orthogonal relationship to the optical axis so that the polarized fundamental laser emission propagates along the optical axis with a predetermined polarization aligned parallel with one of said ordinary and extraordinary axes;

c) frequency doubling said polarized fundamental laser emission within said optical cavity in a nonlinear crystal to generate a first converted beam propagating in a first direction along the optical axis and a second converted beam propagating in a second, opposite direction along the optical axis; and

d) reflecting said second converted beam from an angled reflector situated within said optical cavity to provide a reflected converted beam propagating at a predefined nonzero angle with respect to the optical axis.

14. The method of claim 13, wherein said gain crystal comprises Nd:

YVO₄, said fundamental laser emission is generated at approximately 914 nm, and said frequency doubling step includes generating blue light at approximately 457 nm.

15. The method of claim 13, and further comprising the step of Type I phase matching.

16. The method of claim 13, wherein said optical pumping step includes longitudinally pumping said solid-state gain medium with a laser diode.

17. The method of claim 13, and further comprising the step of narrowing the linewidth of said fundamental laser emission by use of a spectral filter situated within the optical cavity.

18. The method of claim 13, and further comprising the step of propagating said reflected converted beam through said nonlinear material without substantially overlapping with said first converted beam.

19. The method of claim 13, and further comprising the steps of:

outputting said first converted beam from the optical cavity through an output reflector that is substantially transmissive of the converted beams and substantially reflective of the fundamental laser emission; and

reflecting the second converted beam at an angle with respect to the first converted beam such that it exits the cavity through said output reflector.

20. The method of claim 13, and further comprising the step of outputting the first converted beam and the reflected converted beam from the optical cavity, and imaging said beams to a common point.

21. The method of claim 13, and further comprising the step of re-combining said first and said reflected converted beams after said beams exit from the optical cavity, said re-combining causing said first and said reflected converted beams to overlap and propagate in a collinear direction.

22. A frequency-converted laser comprising:

an optical cavity that defines an optical axis;

a gain medium situated within said optical cavity;

a pump source for pumping said gain medium to excite a laser emission within the optical cavity;

a nonlinear material situated within the optical cavity for converting said laser emission to a converted wavelength; and

an angled reflector situated within the optical cavity for reflecting optical radiation at the converted wavelength along a path at a nonzero angle with respects to the optical axis.

23. The laser of claim 22 wherein said angled reflector is situated between said gain medium and said nonlinear material.

24. The laser of claim 22, and further comprising a spectral filter positioned within the laser cavity.

25. The laser of claim 22, wherein the optical cavity has a linear configuration.

26. A solid-state frequency-converted laser comprising:

an optical cavity that defines an optical axis;

a solid-state gain medium situated within said optical cavity;

a pump source for optically pumping said gain medium to excite a fundamental laser emission at a fundamental wavelength within the optical cavity;

a nonlinear crystal situated within the optical cavity for converting the fundamental laser emission to a converted wavelength; and

an angled reflector situated within the optical cavity for reflecting optical radiation at the converted wavelength along a path at a nonzero angle with respect to the optical axis.

27. The laser of claim 26 wherein said angled reflector is situated between said gain medium and said nonlinear material.

28. The laser of claim 26, wherein the gain medium is selected from a group consisting of:

Nd;

YVO₄, Nd;

GdVO₄, Nd;

YAlO₃, Nd;

YLiF₄, Nd;

LSB, Cr;

LiSAF, Cr;

LiCAF, Cr⁴⁺ ;

Mg₂ SiO₄, and Cr⁴⁺ ;

Ca₂ GeO₄.

29. The laser of claim 26, wherein the gain medium comprises a Nd³⁺ doped laser crystal.

30. The laser of claim 29, wherein the laser cavity is designed to lase within the range of about 870-960 nm in order to lase on the ⁴ F_3/2 →

⁴ I_9/2 transition of Nd³⁺.

31. The laser of claim 29, wherein the laser cavity is designed to lase at about 1064 nm in order to lase on the ⁴ F_3/2 →

⁴ I_11/2 transition of Nd³⁺.

32. The laser of claim 26, wherein the gain medium comprises a Cr⁴⁺ doped material designed to lase within a range between about 1150 and 1400 nm.

33. The laser of claim 26, wherein the gain medium comprises a Cr³⁺ doped material designed to lase within a range between about 800 and 1000 nm.

34. The laser of claim 33 wherein said gain medium comprises Cr:

LiSAF.

35. The laser of claim 26, wherein said pump source comprises a laser diode for longitudinally pumping said gain medium.

36. The laser of claim 26, wherein said gain medium comprises an anisotropic material having a first crystal axis and a second crystal axis situated orthogonal to the optical axis, said first crystal axis defining a predetermined polarization of the fundamental laser emission, said first crystal axis being aligned with respect to the nonlinear material in an orientation to provide a predetermined frequency conversion process.

37. The laser of claim 36 and further comprising an optical coating on said anisotropic gain medium that has greater transmissivity for said fundamental laser emission than for emission along said second crystal axis.

38. The laser of claim 26, wherein the optical cavity has a linear configuration.

39. A frequency-doubled laser comprising:

an optical cavity, said optical cavity defining an optical axis;

a gain medium including an anisotropic neodymium-doped crystal for generating a substantially polarized fundamental laser emission corresponding to the ⁴ F_3/2 →

⁴ I_9/2 laser transition, said crystal defining an ordinary axis and an extraordinary axis situated within said optical cavity in an orthogonal relationship to the optical axis so that the polarized fundamental laser emission propagates along the optical axis with a predetermined polarization aligned parallel to one of said ordinary axis and extraordinary axis;

an optical pump source situated to longitudinally pump said gain medium with optical radiation;

a nonlinear crystal situated within said optical cavity to frequency double the polarized fundamental emission to generate blue light; and

an angled reflector situated within the optical cavity for reflecting optical radiation at said blue light along a path at a nonzero angle with respect to the optical axis.

40. The laser of claim 39, wherein said optical pump source comprises a laser diode.

41. The laser of claim 39, wherein said gain medium is selected from the group comprising Nd:

YVO₄ and Nd;

GdVO₄.

42. The laser of claim 41 wherein said gain medium comprises Nd:

YVO₄ and has a dopant concentration-length product ranging between 0.1 at. %-mm and 0.5 at. %-mm and a length less than 2.0 mm.

43. The laser of claim 42 wherein said gain medium has a length along the optical axis of approximately 0.3 mm and a dopant concentration of approximately 1.0 at. %.

44. The laser of claim 41 wherein said gain medium comprises Nd:

GdVO₄ and has a dopant concentration-length product ranging between 0.05 at. %-mm and 0.3 at. %-mm and a length less than 2.0 mm.

45. The laser of claim 39, wherein said nonlinear crystal is selected from a group comprising KNbO₃ and BBO.

46. The laser of claim 39, and further comprising a spectral filter situated within the optical cavity for narrowing the linewidth of said fundamental laser emission.

47. The laser of claim 39 wherein said angled reflector is situated between said gain medium and said nonlinear material.

48. The laser of claim 39, and further comprising a spectral filter positioned within the laser cavity.

49. The laser of claim 39, wherein the optical cavity has a linear configuration.

50. A frequency-converted laser comprising:

means for providing an optical cavity that defines an optical axis;

a gain medium situated within said optical cavity;

pump means for pumping said gain medium to provide a laser emission along the optical axis;

frequency-conversion means for frequency converting the laser emission within the optical cavity means to generate a first converted beam propagating in a first direction along the optical axis and a second converted beam propagating in a second, opposite direction along the optical axis; and

reflector means for reflecting said second converted beam at a predefined nonzero angle with respect to the optical axis to provide a reflected converted beam.

51. The laser of claim 50, and further comprising means for reflecting said second converted beam such that the reflected converted beam does not propagate through the gain medium.

52. The laser of claim 50, and further comprising means for propagating said reflected converted beam through said frequency-conversion means without substantially overlapping with said first converted beam.

53. The laser of claim 50 wherein said reflector means includes an angled reflector situated within said optical cavity, said angled reflector being transmissive of the laser emission and reflective of the converted beam.

54. The laser of claim 50, and further comprising means for outputting the first converted beam and the reflected converted beam from the optical cavity, and means for imaging said beams to a common point.

55. The laser of claim 50, and further comprising a means for re-combining said first and said reflected converted beams after said beams exit from the optical cavity, so that said first and said reflected converted beams overlap and propagate in a collinear direction.