JP3294148B2 - Laser ultrasonic flaw detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser ultrasonic inspection apparatus for non-destructively inspecting a defect inside a subject.

[0002]

2. Description of the Related Art Ultrasonic flaw detectors are widely used for transmitting ultrasonic waves inside a subject and observing reflected waves from the inside of the subject on the surface thereof to non-destructively inspect the inside of the subject for flaws. .

[0003] Rather than directly applying an ultrasonic wave to this type of ultrasonic flaw detector, the surface of the object is irradiated with a laser beam, thereby generating an ultrasonic wave on the object and irradiating the laser beam. There is a laser ultrasonic flaw detector for observing a reflected wave from inside a subject. The principle of the laser ultrasonic flaw detector will be briefly described with reference to FIG. In FIG. 7, 1
Is a laser light source for generating ultrasonic waves, 13 is a subject, and 110
Is a scratch, 15 is a laser light source for receiving ultrasonic waves, 111 is a lens for receiving light, 112 is an optical fiber, and 22 is a laser interferometer.

First, generation of an ultrasonic wave by a laser beam will be described. When the surface of the subject 13 is irradiated with laser light from the laser light source 1 for generating an ultrasonic wave, the surface of the subject 13 is heated and its temperature rises. Then, as the temperature rises, volume expansion occurs and stress is generated on the surface of the subject 13, and this stress becomes a vibration generation source and generates ultrasonic waves.

Next, reception of ultrasonic waves by laser light will be described. When the surface of the vibrating subject 13 is irradiated with laser light from the ultrasonic receiving laser light source 15,
The reflected light from the surface of the subject 13 causes a Doppler shift in the optical frequency domain. The reflected light having the Doppler shift is reflected by the light receiving lens 111 into the optical fiber 1.
Light is condensed on 12. Then, the reflected light condensed in the optical fiber 112 is guided to the laser interferometer 22, and the frequency component of the reflected light is extracted by the laser interferometer 22 and photoelectrically converted to obtain a vibration velocity waveform, thereby obtaining an ultrasonic wave. Can be received.

Further, there is an ultrasonic flaw detector using an oblique method in which ultrasonic waves are obliquely incident on the surface of a subject. Then, a faced array method is generally used in order to make ultrasonic waves obliquely incident on the surface of the subject.

FIG. 8 shows the principle of the faced array method when ultrasonic waves are directly applied to a subject using a piezoelectric element. 120 is an ultrasonic signal generation circuit, 121 is a time delay circuit, 122 is a piezoelectric element, and each piezoelectric element 122 is arranged at a distance L apart. When applying the ultrasonic wave generation signal from the ultrasonic signal generation circuit 120 to the piezoelectric element 122, the transmission of the signal to each piezoelectric element 122 by passing through the time delay circuit 121 is delayed every T seconds. Then, the ultrasonic waves generated from the piezoelectric element 122 are sequentially delayed, and the ultrasonic waves are obliquely incident on the subject 13. Note that the incident angle θ of the ultrasonic wave is expressed by the following equation.

Θ = sin ⁻¹ (T / L) There is a laser ultrasonic flaw detector using this faced array method. FIG. 9 schematically shows the concept of the ultrasonic wave generating section of the laser ultrasonic flaw detector using the faced array method. 130 is a laser light source, 131 is a half mirror, 132 is a condenser lens for incidence, 133 is an optical fiber, and 134 (134a to 134c) are optical fiber type delay units. The optical fiber type delay unit 134 is wound with an optical fiber of several tens to several hundreds of meters, and delays the irradiation of the subject with the laser light by increasing the length of the transmission path.

The ultrasonic generator generates a laser beam emitted from a laser light source 130 by a half mirror 131.
Each of the condenser lenses 132 is irradiated with uniform power. Then, the laser light is incident on each optical fiber 133 by the condenser lens 132, and the optical fiber type delay device 13
The irradiation is sequentially delayed at 4 to irradiate the object surface.

FIG. 10 shows a configuration of a laser beam irradiation / reception unit of a conventional ultrasonic reception unit. A laser irradiation optical fiber 140 to which the laser light from the laser light source is guided, a laser light receiving optical fiber 141 to guide the reflected laser light reflected on the surface of the subject 13 to the laser light interferometer, and condensing the laser light And a condenser lens 142.

[0011]

The optical fiber type delay device of the ultrasonic generator of the conventional laser ultrasonic flaw detector requires an optical fiber length corresponding to the light propagation speed in order to delay the optical signal. . Since the light propagation speed is high, the length of the optical fiber becomes enormous. Therefore, the light intensity is attenuated while the optical signal propagates through the optical fiber. Since the lengths of the four optical fibers are different from each other, there is a problem that the intensity of the laser light emitted from the optical fibers becomes uneven.

Further, in order to accurately control the incident angle of the ultrasonic wave, fine adjustment for increasing or decreasing the delay time is required. However, in the optical fiber type delay device, the length of the optical fiber is reduced. There is a problem that the delay time cannot be adjusted since the delay time cannot be changed.

[0013] Further, in the ultrasonic receiving section of the laser ultrasonic flaw detector, when receiving ultrasonic waves with laser light, two optical fibers for laser irradiation and light receiving are used, so that the focal position of the condenser lens is changed. There has been a problem that the light is slightly displaced and light cannot be received efficiently.

An object of the present invention is to provide a laser ultrasonic inspection apparatus capable of irradiating the surface of a subject with a delay time being adjusted without attenuating the intensity of a laser beam. Another object of the present invention is to provide a laser ultrasonic flaw detector capable of efficiently condensing light reflected from the surface of a subject.

[0015]

The laser ultrasonic flaw detector according to the present invention has the following arrangement to solve the above-mentioned problems. (1) In order to non-destructively inspect a flaw inside a subject, the laser ultrasonic flaw detector of the present invention sequentially delays laser light from a laser light source from a plurality of generation-side optical fibers to different positions on the subject surface. In a laser ultrasonic flaw detector that includes an ultrasonic generator for irradiating an ultrasonic wave to the subject,
The ultrasonic generator includes an optical switch that sequentially switches and guides the laser light to the plurality of generation-side optical fibers one by one, and controls a delay time. ( 2 ) In order to non-destructively inspect a flaw inside a subject, the laser ultrasonic flaw detector of the present invention sequentially delays laser light from a laser light source from a plurality of generation-side optical fibers to different positions on the subject surface. And an ultrasonic generator for generating ultrasonic waves to the subject, and irradiating the surface of the subject with laser light from a laser light source and guiding reflected light from the subject to a laser interferometer to generate an ultrasonic wave on the subject surface. In a laser ultrasonic inspection device including an ultrasonic receiving unit that measures sound waves, the ultrasonic generator,
An optical switch for sequentially switching and guiding the laser light oscillated from the laser light source to the plurality of generation-side optical fibers one by one to control a delay time, and the ultrasonic receiving unit includes: Irradiation light applied to the specimen, and one receiving optical fiber which becomes an optical transmission path of the reflected light from the subject, and the laser light emitted from the receiving optical fiber is guided to the subject, and A light projecting / receiving lens for guiding the reflected light from the subject to the optical fiber, and guiding the laser light from the first optical fiber connected to the laser light source to the receiving optical fiber; An optical multiplexer / demultiplexer for guiding the optical fiber from the receiving optical fiber to a second optical fiber connected to the laser interferometer is provided. ( 3 ) The optical switch according to (1) or ( 2 ), wherein a rotary drum on which an optical fiber, which is an optical transmission path of laser light from the electro-optical element, is arranged on a central axis, and a concentric circle of the rotary drum. And a plurality of generation-side optical fibers having one end disposed thereon. ( 4 ) The optical multiplexer / demultiplexer according to (2) includes a receiving optical fiber, a first optical fiber connected to a laser light source, and a laser interferometer, which are optical transmission paths of irradiation light and reflected light to the subject. Three optical fibers of the second optical fiber to be connected are formed by fusion bonding. ( 5 ) In the laser ultrasonic inspection device according to (2), the projection / reception lens that irradiates the subject with the laser beam from the laser light source and guides the reflected light from the subject to the receiving-side optical fiber is provided. Are located. An interference filter is arranged in the optical path between the light projecting / receiving lens and the subject. ( 6 ) The laser interferometer uses Fabry-Perot interferometry. ( 7 ) In the ultrasonic generator according to (1) or ( 2 ), an electro-optical element that controls laser beam irradiation timing is connected between the laser light source and the optical switch. ( 8 ) The electro-optical element controls the intensity and pulse width of the laser light. ( 9 ) The electro-optical element according to ( 7 ) or ( 8 ) includes a crystal that controls a polarization angle of light by an applied voltage, and a polarizer that transmits only light in a unidirectional polarization state. Become.

The laser ultrasonic flaw detector according to the present invention has the following functions and effects due to the above configuration. The ultrasonic generator of the laser ultrasonic inspection apparatus according to the present invention sequentially switches laser light to a plurality of generation-side optical fibers while delay-controlling the laser light. Then, the object is irradiated from the generation side optical fiber. Therefore, the delay time of the laser beam irradiated on the surface of the subject can be controlled by sequentially switching the incidence side optical fiber while controlling the delay with the optical switch, thereby controlling the incident angle of the ultrasonic wave. be able to.

In the ultrasonic receiving unit, the optical transmission of the irradiation light irradiating the subject and the optical transmission of the reflected light from the subject are performed as shown in FIG.
It is done in. Then, the light from the laser light source is guided to the optical fiber 150 by the optical multiplexer / demultiplexer, and is irradiated on the subject. Also, the reflected light from the subject is
0 and is guided to a laser interferometer by an optical multiplexer / demultiplexer.
Therefore, the focal position of the condenser lens 151 does not shift, and light can be received efficiently.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an outline of a laser ultrasonic flaw detector according to one embodiment of the present invention. FIG. 2 is an enlarged view of a part of FIG.

First, the ultrasonic generator will be described. A laser light source 1 for generating an ultrasonic wave is connected to an electro-optical element 3 via an optical fiber 2. A controller 4 for performing control is connected to the electro-optical element 3. The electro-optical element 3 is connected to an optical switch 6 via an optical fiber 5. The optical switch 6 is connected to one ends of the plurality of generation-side optical fibers 7. The other ends of the plurality of generation-side optical fibers 7 are held by an optical fiber folder 9 in the flaw detection head 8.

Then, a laser beam from the ultrasonic wave generation laser light source 1 is emitted from the other end of the generation side optical fiber 7.
The emitted laser light is transmitted to the generating side
The light is focused. The condensed laser light is applied to the mirror 1
After being reflected by the sample 1, the sample 1
Irradiated on 3 surfaces. Further, the measuring device 14 is connected to the controller 4 and the optical switch 6, and controls the controller 4 and the optical switch 6.

Next, the ultrasonic receiving section of the present apparatus will be described. The ultrasonic light receiving laser light source 15 is
Through an optical coupler (optical multiplexer / demultiplexer) 17. The optical coupler 17 has the receiving optical fiber 1
8 is connected to one end. The other end of the receiving optical fiber 18 is disposed in the flaw detection head 8, and a laser beam from the ultrasonic receiving laser light source 15 is emitted. The emitted laser light is transmitted to the receiving-side light projecting / receiving lens 19, the interference filter 2.
Then, the light is reflected by the mirror 11 and irradiates the subject 13 via the light condensing window 12. The irradiated laser light is reflected on the surface of the subject 13 and travels along the same path to form an optical coupler 17.
Is input to

Here, the interference filter 20 is attached to transmit only the laser light of a specific wavelength and prevent the laser light from the laser light source 1 for generating an ultrasonic wave from entering the optical fiber 18 on the receiving side.

The optical coupler 17 is connected to a laser interferometer 22 via an optical fiber 21. The reflected laser light guided from the optical fiber 21 enters a laser interferometer 22. Then, the ultrasonic waves are received by the laser interferometer 22. Then, the laser interferometer 22 is
A measuring device 14 for measuring and recording an ultrasonic reception signal from the apparatus and confirming the presence or absence of a flaw in the subject is connected.

The structure of the electro-optical element will be described with reference to the schematic diagram of FIG. An optical fiber 2 for guiding a laser beam from a laser light source for generating an ultrasonic wave, a crystal 30 and a polarizer 31
And the optical fiber 5 are arranged on a straight line, so that laser light from the optical fiber 2 can enter the optical fiber 5. A power supply 3 for applying a voltage is applied to both ends of the crystal 30.
2 are connected.

The crystal 30 has a function of changing the polarization direction of light when a voltage is applied to both ends. That is, as shown in FIG. 3B, when the applied voltage is zero, the polarization direction of the light passing through the crystal 30 does not change, but the polarization direction of the light gradually tilts as the applied voltage value increases. To go. When the voltage exceeds a certain voltage, the polarization direction of the light is different from that at the time of incidence by 90 degrees.

The polarizer 31 has a function of transmitting only a polarized light component in a certain direction. And crystal 3
The polarizer 31 is arranged so as to transmit light in a direction different from the polarization direction by 90 degrees before entering the zero. Therefore, the crystal 30
The transmission and non-transmission of light to the polarizer 31 can be controlled by controlling the voltage applied to the polarizer 31 to control the polarization direction of the laser light.

That is, when the voltage applied to the crystal 30 is zero, the polarization direction of the light passing through the crystal 30 is the same as that of the incident light, so that the light does not pass through the polarizer 31 and the amount of transmitted light becomes zero. When the applied voltage is maximum, the polarization direction of the light passing through the crystal 30 is different by 90 degrees, so that the light passes through the polarizer 31 and the amount of transmitted light is maximized.

Therefore, by controlling the value, pulse time, and timing of the applied voltage, it becomes possible to control the amount of transmitted laser light, pulse time, and timing output from the electro-optical element.

The configuration of the optical switch will be described with reference to the schematic diagram of FIG. One optical fiber 5 is mounted on the diameter of the rotatable rotating drum 40. Then, the light emitted from one end of the optical fiber 5 is arranged so as to be able to enter each of the generation-side optical fibers 7 when the rotating drum 40 is rotated. Source-side optical fiber 7
Are arranged on concentric circles of the rotating drum 40 so that the light intensity of each optical fiber 7 does not change. In the operation, the measuring device controls the rotation of the rotary drum 40 and causes the light from the optical fiber 5 to sequentially enter the generation-side optical fiber 7.

The structure of the optical coupler will be described with reference to the schematic diagram of FIG. In the optical coupler, an optical fiber 16 connected to an ultrasonic receiving laser light source and an optical fiber 21 connected to a laser interferometer are fusion-bonded to one receiving optical fiber 18. The laser light from the ultrasonic receiving laser light source is transmitted from the optical fiber 16 to the receiving optical fiber 1.
It is led to 8. Further, the laser light reflected by the subject can be guided from the receiving optical fiber 18 to the optical fiber 21 and can be incident on the laser interferometer.

The case where the Fabry-Perot interferometry is used as the configuration of the laser interferometer will be described. FIG. 6 is a schematic diagram showing the principle of Fabry-Perot interferometry. Two spherical mirrors 50 and 51 having a constant transmittance are arranged with their concave surfaces facing each other. Then, the reflected light oscillated from the ultrasonic receiving laser 15 and reflected on the surface of the subject enters from the convex surface of the spherical mirror 50. The photoelectric conversion element 52 is arranged on the convex side of the spherical mirror 51.

The reflected light from the subject 13 is reflected by the spherical mirror 5
0, and the reflected light is applied to two spherical mirrors 5
Multiple reflections occur between 0 and 51. Then, the reflected lights interfere with each other due to the multiple reflection, and work as a band-pass filter for the light of an extremely narrow band. Then, the amount of emitted light is converted into an electric signal by the photoelectric conversion element 52 disposed on the side opposite to the incident side, and transmitted to the measuring device as an ultrasonic reception signal.

The operation of the laser ultrasonic flaw detector according to the present embodiment will be described by dividing the operation into generation of ultrasonic waves and reception of ultrasonic waves.
First, generation of ultrasonic waves will be described. When continuous laser light is oscillated from the ultrasonic wave generating laser 1, the laser light is guided to the electro-optical element 3 by the optical fiber 2.

Then, the measuring device 14 sequentially switches the generating side optical fibers 7 in the optical switch 6 at time intervals in consideration of the delay time. Then, in synchronism with this, a pulse-like laser controlled to an arbitrary pulse width and laser light amount by the electro-optical element 3 is emitted. The laser light is incident on one end of the generation-side optical fiber 7 with an arbitrary delay time.

Then, a laser beam is emitted from the other end of the generation-side optical fiber 7 into the flaw detection head 8 and focused by the generation-side projection lens 10. After being reflected by the mirror 11, the laser light is applied to the subject 13 via the light condensing window 12. The surface of the subject 13 is heated by the irradiation of the laser beam, and the volume of the subject 13 is increased due to a rise in temperature, thereby generating stress. Then, this becomes a vibration source, and an ultrasonic wave is generated. Then, since the subject 13 is sequentially irradiated with laser light from the plurality of generation-side optical fibers 7 with a delay, the ultrasonic wave propagates inside the subject 13 at a certain angle.

The ultrasonic waves generated on the surface of the subject 13 propagate inside the subject 13. If there is a defect at the interface or inside, the light is reflected there and returns to the surface of the subject 13, and the reflected ultrasonic waves vibrate the surface of the subject 13.

Next, the operation of ultrasonic reception will be described.
The laser light emitted from the ultrasonic receiving laser light source 15 is
The light is guided to one end of the receiving optical fiber 18 via the optical fiber 16 and the optical coupler 17. The laser light is emitted from the other end of the receiving optical fiber 18 into the flaw detection head 8. Then, the laser beam is transmitted to the receiving side light emitting / receiving lens 19.
And the mirror 11 is irradiated via the interference filter 20. After being reflected by the mirror 11, the laser light is applied to the surface of the subject 13 through the converging window 12.

When the surface of the subject 13 vibrated by the irradiation of the laser beam from the ultrasonic generator is irradiated with the laser beam by the ultrasonic receiver, the laser beam reflected on the surface of the subject 13 is Doppler in the optical frequency range. A shift occurs and the frequency of the reflected light changes. Then, the reflected light having undergone the Doppler shift is guided to the optical coupler 17 by following a path reverse to that at the time of incidence from the ultrasonic receiving laser light source 15. Then, the laser reflected light is guided from the optical coupler 17 to the laser interferometer 22 via the optical fiber 21, and the frequency of the reflected light is measured.

If the inside of the subject 13 has a flaw, the frequency of the ultrasonic wave on the surface of the subject 13 changes, so that the amount of Doppler shift changes and the frequency of the laser reflected light changes. Therefore, the measurement device 1
The ultrasonic reception signal transmitted to 4 changes, and the presence or absence of a flaw can be inspected.

The laser ultrasonic flaw detector of this embodiment is provided with an optical switch for sequentially switching laser light to a plurality of optical fibers and controlling a delay time. Can be irradiated with laser light.

Further, one optical fiber which becomes a light transmission path of the irradiation light irradiated to the subject and the reflected light from the subject, a laser beam from the laser light source is guided to the optical fiber, and By providing an optical coupler for guiding the reflected light from the optical fiber to the laser interferometer, the laser light from the subject can be efficiently collected.

Further, since the stress generated on the surface of the subject can be controlled by controlling the irradiation power of the laser beam by the electro-optical element, the frequency of the ultrasonic wave can be controlled. Therefore, by controlling the irradiation power of the laser beam, it is possible to make the ultrasonic frequency optimal for the material of the subject.

The present invention is not limited to the above embodiment. For example, besides Fabry-Perot interferometry as a laser interferometer, homodyne interferometry, time difference interferometry,
Heterodyne interferometry is applicable. In addition, various modifications can be made without departing from the spirit of the present invention.

[0044]

According to the laser ultrasonic flaw detector of the present invention, an ultrasonic wave using the faced array method which can easily and accurately control the incident angle, irradiation pulse width and irradiation time of ultrasonic waves. An ultrasonic testing device can be provided.
In addition, the optical multiplexer / demultiplexer reduces the number of optical fibers for receiving ultrasonic waves to one, and the focus of the light emitting / receiving lens does not shift, so that the light receiving efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of a laser ultrasonic inspection device according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a part of the laser ultrasonic flaw detector of FIG. 1;

FIG. 3 is a schematic diagram showing an electro-optical element of the laser ultrasonic flaw detector.

FIG. 4 is a schematic diagram showing an optical switch of the laser ultrasonic inspection device.

FIG. 5 is a schematic view showing an optical coupler of the laser ultrasonic flaw detector.

FIG. 6 is a schematic diagram showing an outline of a Fabry-Perot interferometer.

FIG. 7 is a schematic view showing the concept of a laser ultrasonic flaw detector.

FIG. 8 is a schematic view showing the concept of the faced array flaw detection method.

FIG. 9 is a schematic view showing the concept of a conventional laser ultrasonic inspection device using the faced array method.

FIG. 10 is a schematic diagram showing the concept of a laser beam irradiation / light receiving unit of an ultrasonic receiving unit of a conventional laser ultrasonic flaw detector.

FIG. 11 is a schematic view showing the concept of a laser beam irradiation / light receiving unit of the ultrasonic receiving unit of the laser ultrasonic flaw detector according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser light source for ultrasonic wave generation 2 optical fiber 3 electro-optical element 4 controller 5 optical fiber 6 optical switch 7 generating optical fiber 8 flaw detection head 9 optical fiber folder 10 half-moon lens for emitting light on projection side 11 mirror 12 focusing window DESCRIPTION OF SYMBOLS 13 Subject 14 Measuring apparatus 15 Laser light source for ultrasonic reception 16 Optical fiber 17 Optical coupler 18 Reception side optical fiber 19 Reception side light emitting / receiving lens 20 Interference filter 21 Optical fiber 22 Laser interferometer 30 Crystal 31 Polarizer 32 Power supply Reference Signs List 40 rotating drum 50 spherical mirror 51 spherical mirror 52 photoelectric conversion element

Continued on the front page (73) Patent holder 000230940 Japan Atomic Power Co., Ltd. 1-6-1, Otemachi, Chiyoda-ku, Tokyo (73) Patent holder 000006208 Mitsubishi Heavy Industries, Ltd. 2-5-1 Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Tomoya Matsunaga 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture Inside Kansai Electric Power Company (72) Inventor Katsuaki Yamaoka 2-5 Marunouchi, Takamatsu City, Kagawa Prefecture Shikoku Electric Power Company (72) Invention Person Masakazu Tanaka 2-1-282 Watanabe-dori, Chuo-ku, Fukuoka City Inside Kyushu Electric Power Co., Inc. (72) Inventor Takayuki Aoki 1-6-1 Otemachi, Chiyoda-ku, Tokyo Japan Atomic Power Company (72) Inventor Kunio Shibaike 2-1-1, Shinaihama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. 72) Inventor Shuji Tanioka Hyogo, Kobe City, Hyogo Prefecture 1-1-1, Wadazakicho, Mitsubishi Heavy Industries, Ltd., Kobe Shipyard (72) Inventor Hirofumi Tanaka 1-1-1, Wadazakicho, Hyogo-ku, Kobe, Hyogo, Japan Mitsubishi Heavy Industries, Ltd., Kobe Shipyard (72) Inventor Hiroaki Ikeda 6-22, Kannonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Prefecture, Hiroshima Laboratory, Mitsubishi Heavy Industries, Ltd. (56) References JP-A-63-11135 (JP, A) JP-A-9-61261 (JP, A) Kaihei 3-128851 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 29/00-29/28 G01N 21/00-21/74

Claims (2)

(57) [Claims] In order to non-destructively inspect a flaw inside a subject,
A laser including an ultrasonic generator for sequentially irradiating laser light from a laser light source oscillated from the laser light source from a plurality of generation-side optical fibers to different positions on the surface of an object to generate ultrasonic waves on the object. In the ultrasonic flaw detector, the ultrasonic generator includes an optical switch that sequentially switches and guides the laser light from the laser light source to the plurality of generation-side optical fibers one by one, and controls a delay time. A laser ultrasonic flaw detector. 2. A method for non-destructively inspecting a flaw inside a subject,
A laser light from a laser light source is sequentially delayed from a plurality of generation-side optical fibers to irradiate different positions on the subject surface to generate ultrasonic waves on the subject, and an ultrasonic generator from the laser light source on the subject surface. A laser ultrasonic flaw detector including an ultrasonic receiving unit that irradiates a laser beam and guides reflected light from the object to a laser interferometer to measure ultrasonic waves on the surface of the object, wherein the ultrasonic generating unit includes the laser An optical switch that sequentially switches and guides the laser light emitted from the light source to the plurality of generation-side optical fibers one by one, and controls a delay time. Irradiation light to be irradiated,
And one receiving optical fiber which becomes an optical transmission path of the reflected light from the subject, and guides the laser light emitted from the receiving optical fiber to the subject, and transmits the reflected light from the subject to the subject. A light projecting / receiving lens for guiding the optical fiber, a laser beam from a first optical fiber connected to the laser light source to the receiving optical fiber, and the reflected light from the receiving optical fiber to the laser. A laser ultrasonic flaw detector comprising an optical multiplexer / demultiplexer for guiding to a second optical fiber connected to an interferometer.