Intracavity frequency-converted optically-pumped semiconductor laser

• US 6,370,168 B1
• Filed: 10/20/1999
• Issued: 04/09/2002
• Est. Priority Date: 10/20/1999
• Status: Expired due to Term

• Current Assignee: Coherent GmbH (Coherent Corp.)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Spinelli, Luis A.
• Primary Examiner(s): Davie, James W.
• Assistant Examiner(s): MONBLEAU, DAVIENNE N
• Application Number:
  US09/421,717
• Time in Patent Office: 902 Days
• Field of Search: 372/70, 372/71, 372/21, 372/75, 372/93, 372/97, 372/98, 372/105, 372/36, 372/22, 372/50
• US Class Current: 372/22
• CPC Class Codes: H01S 3/1062 using a controlled passive interferometer, e.g. a Fabry-Perot etalon
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 5/041 Optical pumping
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/183 having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]

Abstract

An intracavity, frequency-doubled, external-cavity, optically-pumped semiconductor laser in accordance with the present invention includes a semiconductor multilayer surface-emitting gain-structure surmounting a Bragg mirror. An external concave mirror and the Bragg-mirror define a stable laser-resonator including the gain-structure. A birefringent filter is located in the resonator, inclined at an angle to the resonator axis, for selecting a fundamental frequency of the laser-radiation within a gain bandwidth characteristic of semiconductor structure. An optically-nonlinear crystal is located in the laser-resonator between the birefringent filter and the gain-structure and arranged to double the selected frequency of laser-radiation. The gain-structure is coated with a dichroic coating which reflects the frequency-doubled radiation and transmits the fundamental radiation and optical pump-light. A surface of the birefringent filter facing the gain-structure includes a dichroic coating which reflects the frequency-doubled radiation and transmits the fundamental radiation. Frequency-doubled radiation generated on both forward and reverse passes of fundamental laser-radiation through the optically-nonlinear crystal is coupled out of the resonator by the dichroic coated birefringent filter.

Claims

1. A laser, comprising:

an OPS-structure including a multilayer gain-structure surmounting a multilayer mirror-structure, said gain-structure including a plurality of active layers spaced apart by spacer layers;

a straight laser-resonator having a resonator axis, said laser-resonator formed between said mirror structure of said OPS structure and a mirror spaced apart from said gain-structure;

a pump-light source arranged to deliver pump-radiation to said gain-structure for generating laser-radiation in said laser-resonator;

a transmissive wavelength-selective element located in said laser-resonator for selecting a frequency of said laser-radiation within a gain bandwidth characteristic of the composition of said gain-structure;

an optically-nonlinear crystal located in said laser-resonator between said transmissive wavelength-selective element and said gain-structure and arranged to double said selected frequency of laser-radiation, thereby providing frequency-doubled radiation; and

first and second dichroic filters, said first dichroic filter disposed between said gain-structure and said optically-nonlinear crystal at normal incidence to said resonator axis and arranged to reflect frequency-doubled radiation incident thereon and direct said frequency-doubled radiation away from said gain structure, through said optically nonlinear crystal toward said second dichroic filter, said second dichroic filter being located between said transmissive wavelength-selective element and said optically-nonlinear crystal and being inclined at an angle to said resonator axis and arranged to reflect frequency-doubled radiation out of said laser-resonator as output radiation.

2. The laser of claim 1, wherein said transmissive wavelength-selective element is a birefringent filter.

3. The laser of claim 2, wherein said birefringent filter is inclined to said resonator axis at about Brewster'"'"'s angle for the material of the birefringent filter.

4. The laser of claim 1, wherein said transmissive wavelength-selective element is an etalon.

5. The laser of claim 1, wherein said first dichroic filter is coated on said gain-structure.

6. The laser of claim 1, wherein said second dichroic filter is coated on a surface of said transmissive wavelength-selective element facing said optically-nonlinear crystal.

7. The laser of claim 1, wherein said first dichroic filter is coated on a substrate located between said gain-structure and said optically-nonlinear crystal.

8. The laser of claim 1, wherein said second dichroic filter is coated on a surface of a substrate located between said transmissive wavelength-selective element and said optically-nonlinear crystal.

9. The laser of claim 1, wherein said external mirror is a concave mirror having a radius of curvature greater than the optical length of said laser-resonator.

10. The laser of claim 9, wherein said laser-radiation has a mode-shape which is widest at said external mirror and narrowest proximate said OPS-structure and wherein said optically-nonlinear crystal is located at about said narrowest portion of said mode-shape.

11. The laser of claim 1, wherein said laser-radiation is in a single axial mode of said laser-resonator.

12. The laser of claim 1, wherein said active layers of said gain-structure are layers of a semiconductor material selected from the group of semiconductor materials consisting of In_xGa₁₋

xAs_yP<sub>1−

y</sub>, Al_xGa<sub>1−

x</sub>As_yP<sub>1−

y</sub>, and In_xGa<sub>1−

x</sub>N where 0.0≦

x≦

1.0 and 0≦

y≦

1.

13. The laser of claim 12, wherein said fundamental radiation has a wavelength between about 1800 and 425 nanometers.

14. The laser of claim 13, wherein said active layers of said gain-structure are layers of a semiconductor material having a composition In_0.18Ga_0.82As and said wavelength of fundamental radiation is 976 nm.

15. The laser of claim 1, wherein said dichroic filters are transmissive at the wavelength selected by the wavelength selected element.

16. A laser, comprising:

an OPS-structure including a multilayer gain-structure surmounting a multilayer mirror-structure, said gain-structure including a plurality of active layers spaced apart by spacer layers said active layers being layers of an indium gallium arsenide composition having a composition selected such that said active layers have a characteristic emission wavelength for laser-radiation in the region of 976 nanometers;

a straight laser-resonator having a resonator axis, said laser-resonator formed between said mirror structure of said OPS structure and a concave mirror spaced-apart from said OPS structure;

a pump-light source arranged to deliver pump-radiation to said gain-structure for generating laser-radiation having said characteristic emission wavelength in said laser-resonator;

a birefringent filter located in said laser-resonator for maintaining said laser-radiation at said characteristic emission wavelength, said birefringent filter inclined at an angle to said resonator axis;

an optically-nonlinear crystal located in said laser-resonator between said birefringent filter said gain-structure and arranged to double the frequency of said characteristic emission wavelength of laser-radiation, thereby providing frequency-doubled radiation having a wavelength of about 488 nanometers; and

first and second dichroic filters, configured to have high reflectivity at about 488 nanometers, said first dichroic filter being in the form of a coating on said gain-structure arranged to reflect said frequency doubled radiation incident thereon away from said gain-structure, through said optically nonlinear crystal toward said second dichroic filter, and said second dichroic filter being in the form of a coating on a surface of said birefringent filter facing said optically-nonlinear crystal and arranged to reflect frequency-doubled radiation out of said laser-resonator as output radiation.

17. The laser of claim 16, wherein said OPS-structure is in thermal contact with a heat-sink, said heat-sink being of a material having a thermal expansion coefficient which matches the thermal expansion coefficient of gallium arsenide.

18. The laser of claim 17, wherein said heat-sink material is a copper-tungsten material.

19. The laser of claim 16, wherein said optically-nonlinear crystal is an LBO crystal.

20. The laser of claim 16, wherein said concave mirror is spaced apart from said OPS-structure by a distance less than the radius of curvature of said concave mirror.

21. The laser of claim 20, wherein said birefringent filter is in the form of a crystal quartz plate inclined to said resonator axis at an angle of about 57 degrees.

22. The laser of claim 16, wherein said dichroic filters are highly transmissive at 976 nanometers.

23. A laser, comprising:

a straight laser resonator formed between two opposed mirrors;

an OPS-structure located in said resonator, said OPS structure including a multilayer gain-structure have a plurality of active layers spaced apart by spacer layers;

a pump-light source arranged to deliver pump-radiation to said gain-structure for generating fundamental laser-radiation in said laser-resonator;

a transmissive wavelength-selective element located in said laser-resonator for selecting a frequency of said fundamental laser-radiation within a gain bandwidth characteristic of the composition of said gain-structure;

an optically-nonlinear crystal located in said laser-resonator between said transmissive wavelength-selective element and said gain-structure and arranged to double said selected frequency of laser-radiation, thereby providing frequency-doubled radiation; and

first and second dichroic filters configured to reflect the frequency doubled radiation and transmit the fundamental radiation, said first dichroic filter disposed between said gain-structure and said optically-nonlinear crystal and arranged to reflect said frequency doubled radiation away from said gain-structure, through said optically-nonlinear crystal toward said second dichroic filter, said second dichroic filter being located between said transmissive wavelength-selective element and said optically-nonlinear crystal and being inclined at an angle to said resonator axis and arranged to reflect frequency-doubled radiation out of said laser-resonator as output radiation.

24. The laser of claim 23, wherein said transmissive wavelength-selective element is a birefringent filter.

25. The laser of claim 24, wherein said birefringent filter is inclined to said resonator axis at about Brewster'"'"'s angle for the material of the birefringent filter.

26. The laser of claim 25, wherein said second dichroic filter is coated on a surface of said birefringent filter facing said optically-nonlinear crystal.

27. The laser of claim 26, wherein said first dichroic filter is coated on said gain-structure.

28. The laser of claim 27 wherein one of said mirrors of said laser is a multilayer mirror structure formed with said OPS-structure.

29. The laser of claim 28, wherein said external mirror is a concave mirror having a radius of curvature greater than the optical length of said laser-resonator.

30. The laser of claim 29, wherein said laser-radiation has a mode-shape which is widest at said external mirror and narrowest proximate said OPS-structure and wherein said optically-nonlinear crystal is located at about said narrowest portion of said mode-shape.

31. The laser of claim 30, wherein said laser-radiation is in a single axial mode of said laser-resonator.

32. The laser of claim 27, wherein said active layers of said gain-structure are layers of a semiconductor material selected from the group of semiconductor materials consisting of In_xGa₁₋

xAs_yP<sub>1−

y</sub>, Al_xGa<sub>1−

x</sub>As_yP<sub>1−

y</sub>, and In_xGa<sub>1−

x</sub>N where 0.0≦

x≦

1.0 and 0≦

y≦

1.

33. The laser of claim 32, wherein said fundamental radiation has a wavelength between about 1800 and 425 nanometers.

34. The laser of claim 33, wherein said active layers of said gain-structure are layers of a semiconductor material having a composition In_0.18Ga_0.82As and said wavelength of fundamental radiation is 976 nm.