PRE-AMPLIFIER FOR DETECTION LASERS WITHIN LASER ULTRASONIC INSPECTION SYSTEMS

• US 20080181268A1
• Filed: 03/20/2007
• Published: 07/31/2008
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Dubois, Marc, Drake, Thomas E., Yawn, Kenneth R.
• Granted Patent: US 7,916,307 B2
• Time in Patent Office: Days
• US Class Current: 372/30
• CPC Class Codes: G01H 9/008 by using ultrasonic waves measuring position using ultrasonic waves G01S15/02
• CPC Class Codes: G01N 2021/1706 in solids
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/0231 Composite or layered materials
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046

Abstract

A pulse detection laser is provided. The pulse detection laser includes a single frequency oscillator, a continuous pre-amplifier, and a pulsed amplifier. The single frequency oscillator generates a seed laser beam and is optically coupled to the continuous preamplifier. The continuous pre-amplifier amplifies the seed laser to produce an intermediate power laser beam. A pulsed amplifier optically coupled to the continuous pre-amplifier receives the intermediate power laser beam and amplifies the intermediate power laser beam to produce a pulse detection laser beam. One task of this pulse detection laser is to illuminate ultrasonic displacements. Light from the laser is scattered, collected, and analyzed with an interferometer to demodulate the ultrasonic displacements caused by the return echoes of the ultrasound at the surface of the part.

Claims

1. A method to generate a pulsed detection laser beam comprising:

generating a seed laser;

amplifying the seed laser with a continuous pre-amplifier to produce an intermediate power laser beam; and

amplifying the intermediate power laser beam with a pulsed amplifier to produce the pulsed detection laser beam.

2. The method of claim 1, wherein:

the pulsed detection laser beam is directed to a surface of a remote target;

the pulsed detection laser beam illuminates a portion of the surface of the remote target;

ultrasonic surface displacements within the illuminated portion of the surface of the remote target phase modulate the pulsed detection laser beam;

optics collect phase modulated light produced by the detection laser beam being scattered or reflected by the surface of the remote target; and

the phase modulated light is processed to obtain data representative of the ultrasonic surface displacements at the surface and structures within the remote target.

3. The method of claim 1, wherein the continuous pre-amplifier comprises:

diode pumped fiber;

diode pumped rod lasing material;

diode pumped slab lasing material;

diode pumped thin disc lasing material;

lamp pumped thin disc lasing material;

lamp pumped rod lasing material;

or

lamp pumped slab lasing material.

4. The method of claim 1, wherein the pulsed amplifier comprises:

diode pumped fiber;

or

diode pumped solid-state lasing material.

5. The method of claim 1, wherein:

the seed laser is fiber coupled to the continuous pre-amplifier; and

the continuous pre-amplifier is fiber coupled to the pulsed amplifier.

6. The method of claim 1, wherein:

the seed laser is optically coupled via free space to the continuous pre-amplifier; and

the continuous pre-amplifier is optically coupled via free space to the pulsed amplifier.

7. The method of claim 1, wherein the seed laser is generated by a single frequency oscillator.

8. The method of claim 7, wherein the single frequency oscillator comprises:

non-planar ring oscillator;

linear cavity oscillator;

or

fiber oscillator.

9. The method of claim 1, wherein the continuous pre-amplifier comprises a single pass amplifier or a multi-pass amplifier.

10. A pulsed detection laser comprising:

a single frequency oscillator operable to generate a seed laser beam;

a continuous pre-amplifier optically coupled to the single frequency oscillator, the continuous pre-amplifier operable to amplify the seed laser to produce an intermediate power laser beam; and

a pulsed amplifier optically coupled to the continuous pre-amplifier, the pulsed amplifier operable to amplify the intermediate power laser beam to produce a pulsed detection laser beam.

11. The pulsed detection laser of claim 10, wherein:

the pulsed detection laser beam is directed to a surface of a remote target;

the pulsed detection laser beam illuminates a portion of the surface of the remote target;

ultrasonic surface displacements within the illuminated portion of the surface of the remote target phase modulate the pulsed detection laser beam;

optics collect phase modulated light produced by the detection laser beam being scattered or reflected by the surface of the remote target; and

the phase modulated light is processed to obtain data representative of the ultrasonic surface displacements at the surface and structures within the remote target.

12. The pulsed detection laser of claim 10, wherein the continuous pre-amplifier comprises:

diode pumped fiber;

diode pumped rod lasing material;

diode pumped slab lasing material;

diode pumped thin disc lasing material;

lamp pumped thin disc lasing material;

lamp pumped rod lasing material;

or

lamp pumped slab lasing material.

13. The pulsed detection laser of claim 10, wherein the pulsed amplifier comprises:

diode pumped fiber;

or

diode pumped solid-state lasing material.

14. The pulsed detection laser of claim 10, wherein:

the seed laser is fiber coupled to the continuous pre-amplifier; and

the continuous pre-amplifier is fiber coupled to the pulsed amplifier.

15. The pulsed detection laser of claim 10, wherein:

the seed laser is optically coupled via free space to the continuous pre-amplifier; and

the continuous pre-amplifier is optically coupled via free space to the pulsed amplifier.

16. The pulsed detection laser of claim 10, wherein the seed laser is generated by a single frequency oscillator.

17. The pulsed detection laser of claim 16, wherein the single frequency oscillator comprises:

non-planar ring oscillator;

linear cavity oscillator;

or

fiber oscillator.

18. The pulsed detection laser of claim 10, wherein the continuous pre-amplifier comprises a single pass amplifier or a multi-pass amplifier.

35. The pulsed detection laser of claim 16, wherein the single frequency oscillator comprises:

non-planar ring oscillator;

linear cavity oscillator;

or

fiber oscillator.

19. A method to generate a pulsed detection laser beam operable to detect ultrasonic surface displacements within a surface of a remote target comprising:

generating a seed laser with a master oscillator;

amplifying the seed laser with a continuous pre-amplifier to produce an intermediate power laser beam;

amplifying the intermediate power laser beam with a pulsed amplifier to produce the pulsed detection laser beam; and

wherein;

the pulsed detection laser beam is directed to the surface of the remote target;

the pulsed detection laser beam illuminates a portion of the surface of the remote target;

ultrasonic surface displacements within the illuminated portion of the surface of the remote target phase modulate the pulsed detection laser beam;

optics collect phase modulated light produced by the detection laser beam being scattered or reflected by the surface of the remote target; and

the phase modulated light is processed to obtain data representative of the ultrasonic surface displacements at the surface and structures within the remote target.

20. The method of claim 19, wherein the continuous pre-amplifier comprises:

diode pumped fiber;

diode pumped rod lasing material;

diode pumped slab lasing material;

diode pumped thin disc lasing material;

lamp pumped thin disc lasing material;

lamp pumped rod lasing material;

or

lamp pumped slab lasing material.

21. The method of claim 19, wherein the pulsed amplifier comprises:

diode pumped fiber;

or

diode pumped solid-state lasing material.

22. The method of claim 19, wherein:

the seed laser is fiber coupled to the continuous pre-amplifier; and

the continuous pre-amplifier is fiber coupled to the pulsed amplifier.

23. The method of claim 19, wherein:

the seed laser is optically coupled via free space to the continuous pre-amplifier; and

the continuous pre-amplifier is optically coupled via free space to the pulsed amplifier.

24. The method of claim 19, wherein the seed laser is generated by a single frequency oscillator.

25. The method of claim 24, wherein the single frequency oscillator comprises:

non-planar ring oscillator;

linear cavity oscillator;

or

fiber oscillator.

26. The method of claim 19, wherein the continuous pre-amplifier comprises a single pass amplifier or a multi-pass amplifier.

27. The method of claim 19, further comprising processing the data to assess the structural integrity of the remote target.

28. The method of claim 19, wherein the master oscillator comprise Ytterbium doped fibers operable to produce radiation at a wavelength of about 1000 nm.

29. The method of claim 19, wherein the master oscillator comprise Erbium doped or co-doped fibers operable to produce radiation at a wavelength of about 1550 nm.

30. The method of claim 19, wherein the master oscillator comprise fiber lasers having side cladding pumping wherein pumping diodes are coupled to active fiber through pumping fibers.

31. The method of claim 19, wherein the pulsed amplifier comprises pumping diodes, the pumping diodes comprise single emitters, a group of single emitters, diode bars, and/or a group of diode bars.

32. A pulsed detection laser operable to generate a pulsed detection laser beam to detect ultrasonic surface displacements within a surface of a remote target comprising:

a single frequency oscillator operable to generate a seed laser beam;

a continuous pre-amplifier optically coupled to the single frequency oscillator, the continuous pre-amplifier operable to amplify the seed laser to produce an intermediate power laser beam;

a pulsed amplifier optically coupled to the continuous pre-amplifier, the pulsed amplifier operable to amplify the intermediate power laser beam to produce a pulsed detection laser beam; and

wherein;

the pulsed detection laser beam is directed to the surface of the remote target;

the pulsed detection laser beam illuminates a portion of the surface of the remote target;

ultrasonic surface displacements within the illuminated portion of the surface of the remote target scatter the pulsed detection laser beam to produce phase modulated light; and

the phase modulated light is processed to obtain data representative of the ultrasonic surface displacements at the surface and structures within the remote target.

33. The pulsed detection laser of claim 32, wherein:

the seed laser is fiber coupled to the continuous pre-amplifier; and

the continuous pre-amplifier is fiber coupled to the pulsed amplifier.

34. The pulsed detection laser of claim 32, wherein:

the pulsed detection laser beam is directed to a surface of a remote target;

the pulsed detection laser beam illuminates a portion of the surface of the remote target;

ultrasonic surface displacements within the illuminated portion of the surface of the remote target phase modulate the pulsed detection laser beam;

optics collect phase modulated light produced by the detection laser beam being scattered or reflected by the surface of the remote target; and

the phase modulated light is processed to obtain data representative of the ultrasonic surface displacements at the surface and structures within the remote target.

36. A large area composite inspection apparatus for measuring ultrasonic surface displacements on a surface of a remote target comprising:

an ultrasound generation system operable to produce ultrasonic surface displacements at the remote target;

a detection laser operable to illuminate ultrasonic surface displacements on the surface of the remote target with a pulsed detection laser beam, wherein the detection laser comprises;

a single frequency oscillator operable to generate a seed laser beam;

a continuous pre-amplifier optically coupled to the single frequency oscillator, the continuous pre-amplifier operable to amplify the seed laser to produce an intermediate power laser beam; and

a pulsed amplifier optically coupled to the continuous pre-amplifier, the pulsed amplifier operable to amplify the intermediate power laser beam to produce a pulsed detection laser beam;

a scanning assembly operable to create relative motion between an illumination spot of the pulsed detection laser beam and the surface of the remote target;

collection optics for collecting phase modulated light from the pulsed detection laser beam either reflected or scattered by the remote target;

an optical processor to process the phase modulated light collected by the collection optics and produce an output signal; and

a processor operable to process the output signal to obtain data representative of the ultrasonic surface displacements on the surface of the remote target.