# US 7,612,894 B2 · Fiber laser for ultrasonic testing

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- Number: US 7,612,894 B2
- Document ID: US7612894B2
- Status: Granted
- Kind: B2
- Application number: 11/458,377
- Filed: 2006-07-18
- Published: 2008-01-24
- Granted: 2009-11-03
- Earliest claimed: 2006-07-18
- Assignees: Lockheed Martin Corporation
- Inventors: Thomas E. Drake; Marc Dubois
- Web page: https://patentgrep.com/patent/US7612894B2

## CPC

- 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)}
- G01H 9/004: {using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125)}
- G01N 29/265: by moving the sensor relative to a stationary material
- G01N 2291/0231: Composite or layered materials
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES

## Abstract

Embodiments of the present invention relates to an improved laser for the optical detection of ultrasound. The primary task of this “first” detection laser is to illuminate the spot where a “second” laser is used to generate ultrasound in the part under test. The scattered light from the first laser is collected and analyzed with an interferometer to demodulate the surface vibrations caused by the return echoes of the ultrasound at the surface of the part. The improved detection laser (first laser) is constructed using a diode-pumped fiber laser to produce a high power single-frequency laser source.

## Claims

### Claim 1

A method to detect ultrasonic surface displacements at a remote target comprising:
generating ultrasonic displacements at a surface of the remote target;
providing a diode pumped detection fiber laser comprising:
a master oscillator comprising a diode pumped fiber laser;
a diode pumped laser pre-amplifier comprising a diode pumped fiber laser amplifier; and
a diode pumped laser amplifier comprising a diode pumped fiber laser amplifier;
generating a seed laser beam using the master oscillator;
amplifying the seed laser beam to generate an output laser beam using the diode pumped laser pre-amplifier;
amplifying the output laser beam using the diode pumped laser amplifier to thereby generate a detection laser beam;
directing the detection laser beam to the surface of the remote target;
scattering the detection laser beam with the ultrasonic surface displacements at the surface to produce phase modulated light;
collecting the phase modulated light;
processing the phase modulated light to obtain data representative of the ultrasonic surface displacements at the surface; and
collecting the data with the information to analyze structures within the remote target.

### Claim 2 (depends on 1)

The method of claim 1, wherein generating ultrasonic displacements at a surface of the remote target further comprises:
directing a generation laser beam to illuminate a portion of a surface of the remote target, wherein the ultrasonic surface displacements occur within the illuminated portion of the surface of the remote target.

### Claim 3 (depends on 1)

The method of claim 1, further comprising processing the data to assess the structural integrity of the remote target.

### Claim 4 (depends on 1)

The method of claim 1, wherein the master oscillator or the at least one diode pumped laser amplifier comprises a diode pumped slab laser.

### Claim 5 (depends on 1)

The method of claim 1, wherein the master oscillator and/or the at least one diode pumped laser amplifier comprise Ytterbium doped fibers operable to produce radiation at a wavelength of about 1000 nm.

### Claim 6 (depends on 1)

The method of claim 1, wherein the master oscillator and/or the at least one diode pumped laser amplifier comprise Erbium doped or co-doped fibers operable to produce radiation at a wavelength of about 1550 nm.

### Claim 7 (depends on 1)

The method of claim 1, wherein the master oscillator and/or the at least one diode pumped laser amplifier comprise fiber lasers having side cladding pumping wherein pumping diodes are coupled to active fiber through pumping fibers.

### Claim 8 (depends on 7)

The method of claim 7, wherein the pumping fibers couple to the active fiber through side cladding or an inner cladding of the active fiber.

### Claim 9 (depends on 7)

The method of claim 7, wherein the pumping diodes comprise single emitters a group of single emitters diode bars, and/or a group of diode bars.

### Claim 10

An apparatus operable to detect ultrasonic surface displacements on a remote target comprising:
an ultrasound generation system operable to produce ultrasonic surface displacements at the remote target;
a diode pumped detection fiber laser operable to generate a detection laser beam that substantially illuminates the ultrasonic surface displacements at the remote target;
collection optics operable to collect phase modulated light from the diode pumped detection fiber laser either reflected or scattered by the remote target; and
a processor operable to: process the phase modulated light from the diode pumped detection fiber laser either reflected or scattered by the remote target to obtain data representative of the ultrasonic displacements at the remote target; and
process the data representative of the ultrasonic displacements to assess the structural integrity of the remote target;
wherein the diode pumped detection fiber laser comprises:
a master oscillator operable to generate a seed laser beam, wherein the master oscillator comprises a diode pumped fiber laser;
at least one diode pumped laser pre-amplifier operable to amplify the seed laser beam, wherein the at least one diode pumped laser pre-amplifier comprises a diode pumped fiber laser amplifier; and
at least one diode pumped laser amplifier operable to amplify an output laser beam produced by the at least one diode pumped laser pre-amplifier, wherein the at least one diode pumped laser amplifier comprises a diode pumped fiber laser amplifier.

### Claim 11 (depends on 10)

The apparatus of claim 10, wherein the ultrasound generation system is operable to:
direct a generation laser beam to illuminate a portion of a surface of the remote target, wherein the ultrasonic surface displacements occur within the illuminated portion of the surface of the remote target.

### Claim 12 (depends on 10)

The apparatus of claim 10, wherein the master oscillator and/or the at least one diode pumped laser amplifier comprise Ytterbium doped fibers operable to produce a radiation at a wavelength around 1000 nm.

### Claim 13 (depends on 10)

The apparatus of claim 10, wherein the master oscillator and/or the at least one diode pumped laser amplifier comprise Erbium doped or co-doped fibers operable to produce radiation at a wavelength of about 1550 nm.

### Claim 14 (depends on 10)

The apparatus of claim 10, wherein the master oscillator and/or the at least one diode pumped laser amplifier comprise fiber lasers having side cladding pumping wherein pumping diodes are coupled to active fiber through pumping fibers.

### Claim 15 (depends on 14)

The apparatus of claim 14, wherein the pumping fibers couple to the active fiber through side cladding or an inner cladding of the active fiber.

### Claim 16 (depends on 14)

The apparatus of claim 14, wherein the pumping diodes comprise single emitters a group of single emitters diode bars, and/or a group of diode bars.

### Claim 17 (depends on 10)

The apparatus of claim 10, wherein diode pumped detection fiber laser comprises:
at least two parallel diode pumped laser amplifiers operable to amplify the seed laser beam, wherein the at least two parallel diode pumped laser amplifiers comprise diode pumped fiber laser, wherein an output of the at least two parallel diode pumped laser amplifiers are combined within a single optical fiber.

### Claim 18 (depends on 10)

The apparatus of claim 10, wherein the master oscillator or the at least one diode pumped laser amplifier comprises a diode pumped slab laser.