Solid-state laser source of tunable narrow-bandwidth ultraviolet radiation

• US 5,745,284 A
• Filed: 05/01/1996
• Issued: 04/28/1998
• Est. Priority Date: 02/23/1996
• Status: Expired due to Term

• Current Assignee: Harvard University, Navy The USA As Represented By The Secretary of The
• Original Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Inventors: Koplow, Jeffrey P., Kliner, Dahv A.V., Goldberg, Lew
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/640,568
• Time in Patent Office: 727 Days
• Field of Search: 372/22, 359/341, 359/344, 359/328, 359/329
• US Class Current: 359/344
• CPC Class Codes: G02F 1/3507 Arrangements comprising two or more nonlinear optical devices
• CPC Class Codes: G02F 1/354 Third or higher harmonic generation
• CPC Class Codes: G02F 1/37 for second-harmonic generation G02F1/3532 takes precedence
• CPC Class Codes: G03F 7/704 Scanned exposure beam, e.g. raster-, rotary- and vector scanning mask projection exposure involving relative movement of patterned beam and workpiece during imaging G03F7/70358
• CPC Class Codes: H01S 2301/03 Suppression of nonlinear conversion, e.g. specific design to suppress for example stimulated brillouin scattering [SBS], mainly in optical fibres in combination with multimode pumping
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/10 Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
• CPC Class Codes: H01S 5/0064 Anti-reflection components, e.g. optical isolators
• CPC Class Codes: H01S 5/0085 for modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 5/1014 Tapered waveguide, e.g. spotsize converter H01S5/1064 takes precedence
• 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 5/146 using a fiber as external cavity
• CPC Class Codes: H01S 5/4006 Injection locking
• CPC Class Codes: H01S 5/50 Amplifier structures not provided for in groups H01S5/02 - H01S5/30

Abstract

A solid-state laser source of tunable and narrow-bandwidth UV light is disclosed. The system relies on light from a diode laser that preferably generates light at infrared frequencies. The light from the seed diode laser is pulse amplified in a light amplifier, and converted into the ultraviolet by frequency tripling, quadrupling, or quintupling the infrared light. The narrow bandwidth, or relatively pure light, of the seed laser is preserved, and the pulse amplifier generates high peak light powers to increase the efficiency of the nonlinear crystals in the frequency conversion stage. Higher output powers may be obtained by adding a fiber amplifier to power amplify the pulsed laser light prior to conversion.

Claims

1. A solid-state tunable ultraviolet laser system, comprising:

a tunable diode laser which generates laser light;

a pulsed optical amplifier which pulse amplifies the laser light and is isolated from the tunable diode laser; and

a frequency conversion stage which converts the pulsed laser light into ultraviolet light.

2. A laser system as described in claim 1, wherein the diode laser is a continuous wave laser.

3. A laser system as described in claim 1, further comprising a pulse generator which drives the optical amplifier.

4. A laser system as described in claim 1, wherein the optical amplifier is a tapered amplifier.

5. A laser system as described in claim 1, wherein the frequency conversion stage doubles and triples the laser light.

6. A laser system as described in claim 5, wherein the frequency conversion stage comprises KNbO₃ and ADA crystals.

7. A laser system as described in claim 1, wherein the frequency conversion stage doubles and quadruples the laser light.

8. A laser system as described in claim 7, wherein the frequency conversion stage comprises KNbO₃ and BBO crystals.

18. A laser system as described in claim 1, wherein the diode laser amplitude and/or frequency modulates the laser light.

43. A laser system as described in claim 1, further comprising an isolator between the diode laser and the pulsed optical amplifier.

51. A laser system as described in claim 1, further comprising a pulse generator that drives the optical amplifier with a duty cycle less than 20%.

9. A solid-state tunable ultraviolet laser system, comprising:

a tunable diode laser which generates laser light;

a pulsed optical amplifier which pulse amplifies the laser light;

a frequency conversion stage which converts the pulsed laser light into ultraviolet light; and

a power optical amplifier which amplifies the pulsed laser light from the pulsed optical amplifier prior to reception by the frequency conversion stage.

10. A laser system as described in claim 9, wherein the power amplifier is a fiber amplifier.

11. A laser system as described in claim 10, further comprising a beam splitter for coupling the pulsed laser light from the pulsed optical amplifier into the fiber amplifier, and for output coupling the beam from the fiber amplifier to the frequency conversion stage.

12. A laser system as described in claim 10, further comprising an acousto-optic filter for the fiber amplifier, which is synchronized to the pulsed optical amplifier.

13. A laser system as described in claim 10, further comprising a laser diode array for pumping the fiber amplifier.

14. A laser system as described in claim 10, wherein the frequency conversion stage frequency quintuples the light from the fiber amplifier.

44. A laser system as described in claim 9, further comprising an isolator between the diode laser and the pulsed optical amplifier.

15. A solid-state tunable ultraviolet laser system, comprising:

a tunable diode laser which generates laser light;

a pulsed optical amplifier which pulse amplifies the laser light;

a frequency conversion stage which converts the pulsed laser light into ultraviolet light;

a detector which senses the ultraviolet light; and

a controller which tunes the diode laser on and off an absorption band of a species of interest and determines a presence of the species in response to light detected by the detector.

16. A laser system as described in claim 15, wherein the detector is tuned to a wavelength of the laser light.

17. A laser system as described in claim 15, wherein the detector is tuned to a wavelength of light that the species generates by fluorescence.

19. A method for generating ultraviolet light, comprising:

generating laser light with a tunable diode laser;

pulse amplifying the laser light;

isolating the laser light generation from the pulse amplification; and

frequency converting the pulsed laser light into ultraviolet light.

20. A method as described in claim 19, further comprising pulse amplifying the laser light with a tapered optical amplifier.

21. A method as described in claim 19, further comprising driving the pulse amplifier with a pulse generator.

22. A method as described in claim 19, wherein the step of frequency converting the pulse laser light comprises:

frequency doubling the laser light; and

then

frequency tripling the laser light.

23. A method as described in claim 19, wherein the step of frequency converting the pulse laser light comprises:

frequency doubling the laser light; and

then

frequency quadrupling the laser light.

30. A method as described in claim 19, wherein the step of frequency converting the laser light comprises frequency quintupling the pulsed laser light.

31. A method as described in claim 30, wherein the step of frequency quintupling comprises:

generating a second harmonic of a fundamental of the pulsed laser light;

generating a fourth harmonic of the fundamental; and

mixing the fundamental with the fourth harmonic to generate a fifth harmonic.

24. A method for generating ultraviolet light, comprising:

generating laser light with a tunable diode laser;

pulse amplifying the laser light;

frequency converting the pulsed laser light into ultraviolet light; and

tuning a frequency of the laser light on an off of an absorption feature of a chemical species.

25. A method as described in claim 24, further comprising detecting light absorbed by the chemical species.

26. A method as described in claim 24, further comprising detecting light generated by fluorescence by the chemical species.

27. A method for generating ultraviolet light, comprising:

generating laser light with a tunable diode laser;

pulse amplifying the laser light;

frequency converting the pulsed laser light into ultraviolet light; and

power amplifying the pulsed laser light prior to the frequency conversion.

28. A method as described in claim 27, wherein the step of amplifying the pulsed laser light comprises amplifying the pulsed laser light in a fiber amplifier.

29. A method as described in claim 27, further comprising time-domain filtering the pulsed laser light from the fiber amplifier to suppress amplified spontaneous emission.

32. A solid-state tunable ultraviolet laser system, comprising:

a tunable diode laser which generates laser light;

a pulsed optical amplifier which pulse amplifies the laser light;

a frequency conversion stage which converts the pulsed laser light into ultraviolet light;

a detector which senses the ultra-violet light; and

a controller which tunes the diode laser on and off an absorption band of a species of interest and determines a presence of the species in response to light detected by the detector.

33. A laser system comprising:

a pulsed seed laser source, which generates amplitude modulated laser light;

a fiber amplifier, which power amplifies the amplitude modulated laser light; and

a frequency conversion stage, which converts the amplified laser light into ultraviolet light.

34. A laser system as described in claim 33, wherein the pulsed seed laser source comprises:

a continuous wave diode seed laser, which generates laser light; and

an amplitude modulator, which amplitude modulates the laser light.

35. A laser system as described in claim 34, wherein the amplitude modulator comprises an electro-optic or acousto-optic modulator.

36. A laser system as described in claim 33, wherein the pulsed seed laser source comprises a pulsed distributed feedback laser.

39. A laser system as described in claim 33, wherein the frequency conversion stage comprises three frequency conversion crystals for successively receiving the light from the fiber amplifier.

40. A laser system as described in claim 33, further comprising a saturable absorber for suppressing amplified spontaneous emission.

41. A laser system as described in claim 33, wherein the pulsed seed laser source is a pulsed diode laser.

42. A laser system as described in claim 34 wherein the amplitude modulator is a Mach-Zehnder interferometer.

45. A laser system as described in claim 34, further comprising an optical isolator between the continuous wave diode seed laser and the amplitude modulator.

46. A laser system as described in claim 33, further comprising a filter which suppresses amplified spontaneous emission in the fiber amplifier.

47. A laser system as described in claim 46, wherein the filter is a frequency-domain filter.

48. A laser system as described in claim 46, wherein the filter is a time-domain filter.

49. A laser system as described in claim 46, wherein the filter is an saturable absorber filter.

50. A laser system as described in claim 46, wherein the filter is an acousto-optic filter.

37. A laser system, comprising:

a pulsed seed laser source, which generates amplitude modulated laser light;

a fiber amplifier, which power amplifies the amplitude modulated laser light;

a frequency conversion stage, which converts the amplified laser light into ultraviolet light; and

an acousto-optic filter, which suppresses amplified spontaneous emission in the fiber amplifier.

38. A laser system as described in claim 37, wherein the acousto-optic filter is synchronized with the pulsed seed laser source.