High power laser devices

• US 6,243,407 B1
• Filed: 07/07/1997
• Issued: 06/05/2001
• Est. Priority Date: 03/21/1997
• Status: Expired due to Term

• Current Assignee: Necsel Intellectual Property Inc. (Ushio Incorporated)
• Original Assignee: Novalux, Inc. (LionHub Group Ltd.)
• Inventors: Mooradian, Aram
• Primary Examiner(s): ZAHN, JEFFREY N
• Assistant Examiner(s): Wise, Robert E.
• Application Number:
  US08/888,533
• Time in Patent Office: 1,429 Days
• Field of Search: 372/82, 372/83, 372/92, 372/43, 372/50
• US Class Current: 372/92
• CPC Class Codes: H01S 2301/166 Single transverse or lateral mode
• CPC Class Codes: H01S 3/1022 by controlling the optical pumping
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 5/041 Optical pumping
• CPC Class Codes: H01S 5/04256 characterised by the configuration
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/18308 having a special structure for lateral current or light confinement
• CPC Class Codes: H01S 5/18394 Apertures, e.g. defined by the shape of the upper electrode
• CPC Class Codes: H04N 9/315 Modulator illumination systems general applications of lighting devices F21V; general optical systems G02B; lamp houses for projectors not peculiar to the presence of an electronic spatial light modulator G03B21/20

Abstract

In an apparatus and method for generating high power laser radiation, the geometry of the resonant laser cavity defines a fundamental spatial or transverse cavity mode. A gain medium is disposed within the resonant cavity and an energy source energizes the gain medium within a first volume. This causes spontaneous and stimulated energy emission to propagate in the gain medium in a direction transverse to the fundamental cavity mode. The transverse emission in turn optically pumps a second volume of the gain medium about the first volume. When the intensity of the emission is sufficiently high, inversion and gain are produced in the second volume. By optimizing the geometry of the cavity such that the fundamental cavity mode is coupled to both the first and the second volumes encompassing the first pumped volume, the transversely-directed energy of the first volume which would otherwise be wasted is instead captured by the fundamental beam, improving the overall power efficiently of the laser. When configured in an external cavity, the high-power laser of the present invention is especially amenable to frequency conversion of the output beam, as it provides beam intensities suitable for efficient nonlinear frequency conversion.

Claims

1. A laser comprising:

first and second reflectors defining a resonant cavity;

a gain medium disposed within said resonant cavity; and

an energy source for energizing said gain medium within a first volume, wherein

said resonant cavity defines a fundamental cavity mode of an associated laser beam;

said energy source causes optical energy emission to propagate in said gain medium in a direction substantially transverse to said fundamental cavity mode;

said transverse energy emission optically pumps a second volume of said gain medium about said first volume;

the energy within said first and second volumes is coupled into said fundamental cavity mode; and

said energy source energizes the gain medium by optical excitation.

2. The laser of claim 1 further comprising a nonlinear material disposed in the path of the laser beam for adjusting the frequency of the beam.

3. The laser of claim 2 wherein the non-linear material is disposed within the laser cavity.

4. The laser of claim 2 wherein the non-linear material is disposed external to the laser cavity.

5. The laser of claim 2 wherein the non-linear material is selected from the group consisting of KTP, LiNbO₃, periodically-poled LiNbO₃, KTN, and KNbO₃.

6. The laser of claim 1 further comprising an intracavity tuning element selected from the group consisting of an etalon, a birefringent element, a prism, and a grating.

7. The laser of claim 1 further comprising a conductive material transparent to the fundamental wavelength and absorbent of second harmonic radiation grown adjacent to the gain region such that second harmonic light is absorbed in said conductive material and electrons and holes diffuse into the gain region to increase the efficiency of second harmonic radiation emitted in a forward direction.

8. The laser of claim 1 further comprising a conductive material transparent to the fundamental wavelength and absorbent of second harmonic radiation grown adjacent to the gain region such that second harmonic light is absorbed in said conductive material and electrons and holes diffuse into the gain region to increase the efficiency of second harmonic radiation emitted in a forward direction.

9. Multiple lasers of claim 1 configured as an array of addressable elements.

10. A laser comprising:

first and second reflectors defining a resonant cavity for an associated laser beam;

a semiconductor substrate;

a semiconductor gain medium on said substrate;

an energy source for energizing said gain medium within a first volume; and

a non-linear material disposed in the path of said laser beam for adjusting the frequency of the beam;

wherein

both said substrate and said gain medium are inside said resonant cavity;

said resonant cavity defines a fundamental cavity mode of said associated laser beam;

said energy source causes optical energy emission to propagate in said gain medium in a direction substantially transverse to said fundamental cavity mode;

said transverse emission optically pumps a second volume of said gain medium about said first volume; and

said energy within said first and second volumes is coupled into said fundamental cavity mode.

11. A laser comprising:

a resonant cavity between configured first and second reflectors, said resonant cavity defining a fundamental cavity mode;

a gain medium disposed within said resonant cavity; and

an energy source for energizing said gain medium within a first volume,

wherein

said resonant cavity defines a fundamental cavity mode of an associated laser beam;

said energy source causes optical energy emission to propagate in said gain medium in a direction substantially transverse to said fundamental cavity mode;

said transverse emission optically pumps a second volume of said gain medium about said first volume; and

said energy within said first and second volumes is coupled into said fundamental cavity mode.

12. The laser of claim 11 wherein said first volume is substantially cylindrical and of cross-sectional diameter D₁ and said second volume is substantially an annulus of outer cross-sectional diameter D₂ and inner cross-sectional diameter D₁, said first and second volumes being substantially cross-sectionally concentric.

13. The laser of claim 11 wherein the gain medium comprises a material selected from the group consisting of semiconductor, multiple-quantum-well semiconductor and solid state.

14. The laser of claim 11 further comprising an annular electrode and a circular electrode disposed on opposite sides of said gain medium which, when energized, electrically pumps said first volume of the laser with current.

15. The laser of claim 11 further comprising a substrate layer having a first face adjoining said gain medium and said first reflector, and a second face adjoining said second reflector that is configured with a preselected curvature.

16. A device for lasing, comprising:

first and second reflectors positioned at opposite ends of a resonant cavity,

an active region disposed within the resonant cavity; and

a first contact disposed on said first reflector,

wherein

said first and second reflectors are adapted to define a fundamental emission mode traveling through the resonant cavity;

said first contact defines a first volume in said active region;

said first contact is adapted to transmit electrical energy into said first volume of said active region;

said electrical energy causes optical energy emission in the first volume of said active region including transverse optical energy emission propagating in a direction substantially transverse to the fundamental emission mode;

said transverse optical energy emission optically pumps a second volume in said active region immediately surrounding the first volume; and

the optical energy emission in the first and second volumes is substantially coupled into the fundamental emission mode.

17. The device of claim 16, further comprising:

a semiconductor material disposed on said active region at a first end; and

a second contact disposed on said semiconductor material at a second end, opposite to the first, said second contact being adapted to transmit electrical energy into said semiconductor material.

18. The device of claim 17, wherein the first volume is of substantially cylindrical shape and the second volume is of substantially annular shape immediately surrounding the first volume, the first and second volumes being substantially cross-sectionally concentric.

19. The device of claim 17, wherein said first and second contacts are adapted to transmit electrical energy for electrically pumping the first volume of said active region, said first and second contacts defining an electrical energy path through said semiconductor material, said active region, and said first reflector.

20. The device of claim 19, wherein said first contact is of substantially circular shape, said second contact is of substantially annular shape, and the electrical energy path is defined by electrical current flowing between said first and second contacts.

21. The device of claim 17, wherein said second reflector is directly adjacent to said semiconductor material at the second end.

22. The device of claim 17, wherein said second reflector is external to said semiconductor material.

23. The device of claim 17, wherein said active region includes a solid state material.

24. The device of claim 23, wherein said solid state materials is chosen from a group of materials comprising Er:

glass, Yb;

glass, or Yb;

YAG.

25. The device of claim 17, wherein said active region includes a semiconductor material.

26. The device of claim 25, wherein said active region comprises at least one quantum-well semiconductor material structure.

27. The device of claim 17, further comprising a nonlinear material positioned within the resonant cavity for conversion of a frequency of the fundamental emission mode.

28. The device of claim 27, wherein said nonlinear material is selected from a group of materials comprising KTP, KTN, KNbO₃, LiNbO₃, or periodically-poled LiNbO₃.

29. The device of claim 27, wherein said nonlinear material is disposed on said semiconductor material at the second end.

30. The device of claim 27, wherein said nonlinear material is disposed external to said semiconductor material.

31. A method for improving efficiency of a laser device, comprising the following steps:

positioning first and second reflectors to thereby define a fundamental emission mode of the laser device;

positioning a first contact on the first reflector to thereby define a first volume in an active region of the laser device;

electrically energizing the active region through the first contact to thereby generate optical energy emission in the first volume;

propagating optical energy along the active region from the first volume into a second volume immediately adjacent to the first volume, to thereby optically stimulate said second volume; and

adapting the first and second reflectors to couple the optical energy emission in both of the first and second volumes into the fundamental emission mode.

32. The method of claim 31, further comprising the following steps:

positioning a semiconductor material layer directly adjacent to the active region at a side remote from the first reflector; and

positioning a second contact on the semiconductor material layer to thereby define an electrical energy path through the semiconductor material layer between the first contact and the second contact within the laser device.

33. The method of claim 31, further comprising a step of converting a frequency of the fundamental emission mode by positioning a nonlinear material between the first and second reflectors.

34. A vertical cavity surface emitting laser comprising:

a resonant cavity between first and second reflectors, said resonant cavity defining a fundamental cavity mode;

a gain medium disposed within said resonant cavity; and

an optical energy source for optically exciting said gain medium within a first volume of said gain medium and thereby producing a population inversion and stimulated optical emission, the transverse extent of said first volume being substantially greater than the thickness of said gain medium,

wherein

stimulated optical emission from the first volume propagates substantially in a direction transverse to the direction of the fundamental cavity mode and optically excites the gain medium in an annular second volume surrounding said optically pumped first volume, thereby producing a population inversion in the gain medium within said second volume, and

substantially all of the excitation energy from the first said volume that is absorbed in the second said volume is emitted by stimulated emission into the fundamental cavity mode.

35. The vertical cavity surface emitting laser of claim 34, further comprising a non-linear material disposed within the resonant cavity for conversion of a frequency of the optical emission of the laser.

36. The vertical cavity surface emitting laser of claim 34, wherein the first volume is substantially cylindrical and the second volume is substantially annular in shape, and the first and second volumes are substantially cross-sectionally concentric.

37. The vertical cavity surface emitting laser of claim 34, further comprising a semiconductor material wherein said gain medium is directly adjacent to said semiconductor material at a first end and said second reflector is directly adjacent to said semiconductor material at a second end, opposite to the first.

38. The vertical cavity surface emitting laser of claim 34, further comprising a semiconductor material wherein said gain medium is directly adjacent to said semiconductor material at a first end and said second reflector is external to said semiconductor material at a second end, opposite to the first.

39. A vertical cavity surface emitting laser comprising:

a resonant cavity between first and second reflectors, said resonant cavity

defining a fundamental cavity mode;

a gain medium disposed within said resonant cavity; and

an electrical energy source for electrically exciting said gain medium within a first volume and thereby producing a population inversion and stimulated optical emission, the transverse extent of said first volume being substantially greater than the thickness of said gain medium,

wherein

stimulated optical emission from the first volume propagates substantially in a direction transverse to the direction of the fundamental cavity mode and optically excites the gain medium in an annular second volume surrounding said optically pumped first volume, thereby producing a population inversion in the gain medium within said second volume, and

substantially all of the excitation energy from the first said volume that is absorbed in the second said volume is emitted by stimulated emission into the fundamental cavity mode.

40. The vertical cavity surface emitting laser of claim 39, further comprising a non-linear material disposed within the resonant cavity for conversion of a frequency of the optical emission of the laser.

41. The vertical cavity surface emitting laser of claim 39, wherein the first volume is substantially cylindrical and the second volume is substantially annual, the first and second volumes are substantially cross-sectionally concentric.

42. The vertical cavity surface emitting laser of claim 39, further comprising a semiconductor material directly adjacent to said gain medium at a first end.

43. The vertical cavity surface emitting laser of claim 42, wherein said second reflector is directly adjacent to said semiconductor material at a second end, opposite to the first.

44. The vertical cavity surface emitting laser of claim 42, wherein said second reflector is external to said semiconductor material at a second end, opposite to the first.

45. The vertical cavity surface emitting laser of claim 42, wherein said electrical energy source comprises:

a first contact directly adjacent to the first reflector for electrically exciting the first volume within said gain medium; and

a second contact directly adjacent to said semiconductor material at the second end for defining an electrical energy path between said first and second contacts.