JP2004333175A - Laser ultrasonic wave generating device by radiation of multiple beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute high-temperature, moving body, and nondestructive defect inspection by radiating a laser beam to a subject to generate ultrasonic waves, and contactlessly performing ultrasonic inspection using an optical interferometer. <P>SOLUTION: This device is a combined lens mechanism provided with a pulse Nd-YAG laser (pulsed Nd-YAG laser) to generate the laser beam, and a number of beam branching mechanisms to separate one high-output laser beam into multiple beams, in which distance between the laser beams and radiation cross sectional area of radiation of each laser beam can be freely adjusted. By separating one laser beam into multiple beams to be radiated to the subject, high-intensity multiple pulse laser ultrasonic waves are generated at the subject in this laser ultrasonic wave generating device by radiation of multiple beams. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention irradiates a measuring object with a laser beam to generate ultrasonic waves, performs a non-contact inspection of a material by ultrasonic waves using an optical interferometer, and can be applied to a high-temperature object or a moving object. This is a non-destructive inspection device.More specifically, in order to improve the generation efficiency of laser ultrasonic waves, by generating multiple laser beams and appropriately irradiating the measurement object, high intensity ultrasonic waves are generated and measured. Laser ultrasound by multiple beam irradiation improved to accurately evaluate various physical properties such as flaw detection and crystal grain size inside the target object, and to enable reliable measurement of crystal grain size and evaluation of internal defects The present invention relates to a device for generating the above.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a method using a piezoelectric element in a method of transmitting and receiving ultrasonic waves has been often used in a laser ultrasonic generator.
However, in a high-temperature environment or when the measurement object moves as in the iron making process, the use of the contact ultrasonic method utilizing a couplant is limited. As alternatives, an EMAT (Electro-Magnetic Acoustic Transducer) using the Lorentz principle and a MsS (Magnetostrictive sensor) technology using a magnetostriction phenomenon of a ferromagnetic material have been proposed in a non-contact ultrasonic generation and reception method. However, since the distance between the object to be measured and the transmitting / receiving probe is only a few millimeters, it is difficult to apply the method without a breakthrough in peripheral technology.
[0003]
On the other hand, when the measurement object is irradiated with the laser, an ultrasonic wave is generated in the measurement object by thermoelasticity and an ablative mechanism. In particular, when the laser beam reaches a high output, a fusion phenomenon occurs from the surface of the medium by the incident laser, and high-intensity ultrasonic waves, which are vibration waves, are generated in the medium due to the repulsive stress.
[0004]
Since the laser ultrasonic wave generated in the ablation region can be used in an environment where the separation distance (lift-off) from the measurement target is large, the physical properties of the measurement target can be remotely evaluated.
[0005]
However, no matter how much the intensity of the laser is increased during generation of the ultrasonic waves using the laser, the generated ultrasonic waves are not increased. This is because, as shown in the graph of FIG. 10, a phenomenon occurs in which the intensity of the generated ultrasonic wave is saturated at a laser intensity of 300 MJ. Therefore, in order to generate high-intensity ultrasonic waves, it is necessary to avoid such a generation phenomenon of ultrasonic waves.
[0006]
Therefore, in order to increase the generation intensity of laser-applied ultrasonic waves, it is necessary to develop a technique and a device for separating a laser beam emitted from a high-intensity laser generator into a number of laser beams and making the laser beam incident on a measurement target. is there. Further, the conventional pulse laser energy transmission intensity per optical fiber is about 250 MJ / pulse. However, in the measurement field requiring a high energy laser, the intensity is insufficient with such a single laser. However, it is necessary to provide an optical system using various laser beams and a large number of optical fibers suitable for this.
[0007]
Conventional nondestructive inspection using laser ultrasonic waves is effective for evaluating material properties in a high-temperature iron-making process. However, in order to obtain a signal with a high signal-to-noise ratio (S / N), it is necessary to use a laser for generating high-power ultrasonic waves. It is necessary to increase the effective signal.
[0008]
In addition, various types of patents have been proposed by a number of inventors for a conventional method and apparatus for non-contact flaw detection of an internal defect of an object using a laser. These inventions about the laser ultrasonic wave, mainly irradiate the laser to one surface of the measurement object, to generate an ultrasonic wave inside the measurement object, as a non-contact ultrasonic probe on the opposite side, For example, the present invention relates to a method and an apparatus for receiving a signal using an optical interferometer, an acoustic microphone, an aerial ultrasonic probe, an EMAT, and the like, and evaluating an internal defect or the like.
[0009]
Further, as a conventional technique relating to a field of utilizing a laser beam related to ultrasonic flaw detection, there is “Laser beam aiming apparatus for ultrasonic inspection” in Patent Document 1. This is a laser sighting device that irradiates the measurement object with a visible laser beam coaxially with the ultrasonic probe, generates a cross on the surface of the measurement object, and complements it so that you can check the flaw detection position. It is.
[0010]
There is a “Multi-beam optical system” in Patent Document 2 that utilizes the concept of a multiple laser beam, which is introduced to solve the bending of a beam spot line when a semiconductor circuit is formed. It is a patent on the use of multiple laser beams, and is not a technical content related to ultrasonic flaw detection or physical property evaluation by ultrasonic waves. Therefore, conventionally, a single laser beam was used, and there was no way to generate high-intensity ultrasonic waves on the measurement target, and as a result, internal defects of the measurement target could not be detected with high reliability. There was a point.
[0011]
[Patent Document 1]
US Pat. No. 5,773,721 [Patent Document 2]
US Patent No. 6,466,351
[Problems to be solved by the invention]
The present invention has been made to solve the above-described conventional problems, and has an object to achieve the optimum increase in the intensity of laser-induced ultrasonic waves without a saturation phenomenon of laser ultrasonic waves. By generating and appropriately irradiating the object to be measured, high-intensity ultrasonic waves are generated, and various physical properties such as flaw detection and crystal grain size inside the object to be measured are accurately evaluated to obtain highly reliable crystal grains. It is an object of the present invention to provide a laser ultrasonic wave generating apparatus using multiple beam irradiation, which is improved so as to be utilized for diameter measurement and internal defect evaluation.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention irradiates a laser beam to a measurement object (100) to generate ultrasonic waves, and performs an internal inspection by ultrasonic waves without contact using an optical interferometer. In a device for performing a nondestructive inspection of a material, a pulsed Nd-YAG laser (10) for generating a laser beam and one high-power output from the pulsed Nd-YAG laser (10) A plurality of beam splitters for splitting a laser beam into a plurality of laser beams; a large diameter for adjusting a distance between beams (d) of the plurality of laser beams formed by the beam splitter and an irradiation sectional area of each laser beam; A combination lens mechanism (60) composed of a focusing lens (62a) and a wedge-shaped window focusing lens (62b); An apparatus for generating laser ultrasonic waves by multiple beam irradiation, wherein high-intensity multi-pulse laser ultrasonic waves are generated from the measurement object (100) by irradiating the fixed object (100). is there.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. The multi-beam laser ultrasonic wave generator (1) of the present invention can independently adjust the distance between the multi-laser beams and the beam size for generating the multi-pulse laser ultrasonic waves. Generate five laser beams arranged in a letter shape.
[0015]
As shown in FIG. 1, the apparatus (1) for generating a laser ultrasonic wave by irradiating multiple beams according to the present invention includes a plurality of concave and convex lenses (22a) behind a pulse YAG laser (10). ) (22b) comprising a beam reducer set (20).
[0016]
The beam size reduction device (20) is a device for reducing the size of a high-power laser beam (PO) by a combination of convex-concave lenses made of quartz. This means that when a high-energy laser beam (PO) for generating an ultrasonic wave enters through the concave lens (22a) and passes through the convex lens (22b), the beam is formed as a quartz lens set of convex and concave. Is to reduce the size of.
[0017]
Further, a beam splitter (32) is provided at the rear side of the beam size reducing device (20) so as to divide the laser beam (PO) at a ratio of 40:60, as shown in detail in FIG. A first beam splitting mechanism is arranged, and a second beam splitting mechanism (40) and a third beam splitting mechanism (50) are arranged behind the first beam splitting mechanism.
[0018]
The beam splitter (32) is a lens that appropriately coats a glass surface to transmit light at a certain ratio, and reflects the rest.
[0019]
The second beam splitting mechanism (40) adjusts the beam 40% reflected by the first beam splitting mechanism (30) with a number of mirrors (42a) so as to have an appropriate optical path, and then adjusts the beam by a beam splitter (40). 42b), split at 50:50 to generate two laser beams (P1) and (P2) which are irradiated on the x-axis of the measurement object (100).
[0020]
The third beam splitter (50), which receives the laser transmitted through the first beam splitter (30) at 60% and crosses the second beam splitter (40), A beam splitter (52a) that reflects 33.3% of the transmitted laser beam to 60% and irradiates one laser beam (P3) on the y-axis of the measurement object (100). Then, a beam splitter (54a) for reflecting and transmitting the remaining 66.7% of the transmitted laser beam at 50:50 is provided, and one laser beam (P4) is irradiated to the origin of the measurement object (100). Then, a mirror (52b) for reflecting the transmitted laser beam by a mirror and finally irradiating one beam (P5) on the y-axis of the measurement object (100) is provided.
[0021]
Further, a combination lens mechanism (60) for adjusting the distance between pulses on the surface of the measurement object (100) is arranged on the exit side of the second beam branching mechanism (40) and the third beam branching mechanism (50). The distance (d) between the beams can be adjusted efficiently by appropriately adjusting the distance between the beam and the object to be measured (100).
[0022]
On the other hand, as shown in FIGS. 4A and 4B, the combination lens mechanism (60) includes a large-diameter focal lens (62a) of a convex lens and an optical lens (62b) of a wedge-type window. It uses a union.
[0023]
If only a general focusing optical lens (62a), for example, a convex lens as shown in FIG. 4A) is used, a large number of laser beams may be interposed due to a change in the distance between the object (100) and the lens (62a). Not only the distance (d) but also the size of the irradiated beam changes at the same time, but after determining the appropriate distance (d) between the laser beams and the beam size, it is shown in FIG. The use of only such a large-aperture focal lens (62a) is also possible.
[0024]
However, when the size of the laser beam is reduced by passing through a beam size reduction device (20) to reduce only the distance (d) between the laser beams, a large-diameter focal lens (62a) whose beam size changes. 4), the distance (d) between the beams can be adjusted by using an optical lens (62b) having a wedge-shaped window as shown in FIG. 4b).
[0025]
The optical lens (62b) of the wedge-shaped window changes the distance (d) between the laser beams without changing the size of the laser beam when the distance to the object (100) changes. 4b), the distance (d) between the laser beams in the direction perpendicular to the arrow in FIG. 4b) automatically changes. Such a structure is a very simple and compact structure, and the distance (d) between the laser beams can be adjusted.
[0026]
Therefore, the combination of the large-diameter focal lens (62a) of the convex lens and the optical lens (62b) of the wedge-shaped window can be selected as needed, or can be used in these combinations. Things.
[0027]
The combination lens mechanism (60) efficiently and independently converts the large-diameter focal lens (62a) of a convex lens and the optical lens (62b) of a wedge-shaped window (z-axis) independently or simultaneously in the z-axis direction. As shown in FIG. 1, an automatic lens position controller (74) including a precision motor (Step motor) (70) and a controller (72) is provided.
[0028]
The pulse YAG laser (10) and the automatic lens adjuster (74) are electrically connected to a computer (80) so that they can be controlled through an image program (MMI) screen of a computer monitor.
[0029]
In the present invention configured as above, when five lasers are irradiated on the object to be measured (100), heat is generated by the laser intensity of each beam (P1) (P2) (P3) (P4) (P5). Ultrasonic waves are generated in the measurement object by elasticity (thermoelastic) or ablative mechanism (ablation mechanism). In particular, when the laser beam reaches a high output, the incident laser causes a fusion phenomenon from the surface of the medium, generates laser-induced plasma, and generates an ultrasonic wave in the medium by the reaction force. ), The displacement of the minute ultrasonic wave appearing on the surface of the measurement object (100) is measured by using a detection laser radiated on the back surface, that is, another laser radiated from an optical interferometer (110).
[0030]
For this reason, in the present invention, a beam size reduction device (Beam reducer set) (20) comprising a large number of concave and convex lenses (22a) (22b) is arranged from the back of the YAG laser generator (1), and is used. The laser beam emitted from the high-power pulse laser, that is, the beam (P0) having a diameter of 9 mm emitted from the YAG laser (10) of the present invention is suitable for generating laser ultrasonic waves from the measurement object (100). Is converted to have an appropriate laser intensity.
[0031]
The beam size reduction device (20) is a quartz lens set of convex and concave made of quartz. When a high-energy laser beam (P0) for generating an ultrasonic wave enters, the beam is reduced. Reduce size.
[0032]
Then, the beam size reducing device (20) is capable of transmitting the laser incident beams (P1) (P2) (P3) (P4) (P5) and the like incident on the measurement object (100) at the time of generating the laser ultrasonic waves. The size of the laser beam is adjusted so as to have a maximum laser intensity within a range that does not cause sound wave intensity saturation. The laser beam (P0) whose size has been adjusted in this way is split at a ratio of 40:60 by the first beam splitting mechanism (30) behind the beam size reduction device (20), and the rear side thereof is separated. The light is reflected and transmitted to the second beam splitting mechanism (40) and the third splitting mechanism (50) provided in the above.
[0033]
In the second beam splitting mechanism (40), the beam reflected by 40% from the first beam splitting mechanism (30) is adjusted by the mirror (42a) so as to have an appropriate path, and then adjusted from the beam splitter (42b). 50:50 to generate two laser beams (P1) and (P2) which are irradiated on the x-axis of the measurement object (100).
[0034]
The laser beam transmitted through the first beam splitting mechanism (30) having an intensity of 60% is crossed by the second beam splitting mechanism (40) so that the laser beam having the intensity of 60% is crossed by the third beam splitting mechanism (50). Is first reflected by the beam splitter (51a) by 33.3%, and one laser beam (P3) is irradiated on the y-axis of the measurement object (100). The remaining 66.7% is transmitted. The reflected laser beam is reflected and transmitted by a beam splitter (54a), and one laser beam (P4) is irradiated to the origin of the measurement object (100). The laser transmitted at the end is reflected by a mirror (52b). Then, one beam (P5) is finally irradiated on the y-axis of the measurement object (100).
[0035]
The five cross-shaped laser beams (P1), (P2), (P3), (P4), and (P5) formed on the x- and y-axes are irradiated on the measurement object (100) almost simultaneously. The optical elements and the like, that is, the beam splitting mechanisms (30), (40) and (50) are arranged so that the path difference between the beams is minimized.
[0036]
After obtaining the five separated laser beams (P1), (P2), (P3), (P4), and (P5) by the method described above, when irradiating the measurement object (100), the distance between the beams is reduced. The large-diameter focal point of the convex lens in the combination lens mechanism (60) provided on the exit side of the second beam splitting mechanism (40) and the third beam splitting mechanism (50) so that the distance (d) can be efficiently controlled. By adjusting the distance to the surface of the measurement object (100) by using one of the lens (62a) and the optical lens (62b) of a wedge-shaped window (wedge-type window), FIG. Efficiently adjust the distance between each beam of the five lasers as shown.
[0037]
At this time, when adjusting only the distance between the laser beams without changing the size of the laser beams, the combination lens mechanism (60) has a wedge-type window as shown in FIG. The present invention includes the use of only the optical lens (62b).
[0038]
Then, an optical lens (62b) of a wedge-type window for changing a distance between the laser beams is moved by a precision motor (70) and a controller so as to move efficiently in the z-axis direction. ) (72) constitutes an automatic lens position controller (74), and connects the YAG laser (10) and the automatic lens position controller (74) to a computer (80), and a computer monitor. Can be controlled through an image program (MMI) screen.
[0039]
As described above, in the present invention, when a pulse-shaped laser beam (PO) of about 1.6 joules / pulse is input, a loss occurs during transmission, and the five laser beams (P1) (P2) (P3) are lost. ) The surface of the measurement object (100) is irradiated with 250 to 300 mJ / pulse for each beam of (P4) and (P5). That is, a cross configuration with five laser beams (P1), (P2), (P3), (P4), and (P5), one in the center and four in the 90 ° direction are arranged in a cross (+) configuration. Obtained as multiple laser beams.
[0040]
FIG. 5 shows the intensity change of the generated laser ultrasonic wave when the distance (d) between the centers of the laser sources is changed in the case of the cross configuration of 5 sources in the cross (+) form. Shown in a graph. The unit on the vertical axis indicates the relative intensity when the intensity during single beam irradiation is set to 1.
[0041]
As shown in FIG. 5, it can be seen that the intensity of the ultrasonic wave (longitudinal wave) generated by the cross-shaped multiple beam incidence changes depending on the incidence condition of the multiple laser beam. That is, as the distance between the laser beams decreases (d), the intensity of the generated ultrasonic waves increases, and as the frequency increases, the effect of increasing the ultrasonic intensity due to multiple incidence within the distance between the beams of several mm or less appears.
[0042]
FIG. 6 shows an irradiation state of a multiple incident laser beam generated by utilizing the present invention. This means that while keeping the diameter of the beam constant at 4.5 mm, the focusing lens (62b) of the wedge-shaped window is moved in the axial direction, and the distance (d) between the beams is reduced to 0,5. It is an example of the result adjusted to 10, 15, and 20 mm.
[0043]
FIG. 7 shows that while keeping the beam diameter constant at 3.0 mm, the focusing lens (62b) of the wedge-type window is moved in the axial direction, and the distance (d) between the beams is reduced to 0. , 4.5, 8.5, and 13 mm.
[0044]
As described above, according to the present invention, a high intensity ultrasonic wave is generated from the measurement object (100) by the five laser beams irradiated to the measurement object (100), and the detection is performed on the back surface of the measurement object (100). The ultrasonic displacement appearing from the surface of the measuring object (100) can be measured by the laser for use and the optical interferometer (110).
[0045]
FIG. 8 shows a laser ultrasonic signal generated according to the present invention. As a result, as shown in FIG. 8A, a peak signal of a portion to be analyzed from an acquired signal on a time-domain plane (time-domain) is obtained. Fast Fourier Transform processing is performed to convert the data into a frequency domain as shown in FIG.
[0046]
FIG. 9 shows an example of the result of showing the ultrasonic intensity of the obtained laser ultrasonic signal while changing the distance (d) between the laser beams while the diameter of the laser beam is 3.0 mm.
[0047]
As described above, according to the present invention, there is a distance between laser beams, and five laser beams are made incident at separately close positions to generate ultrasonic waves at each laser beam irradiation point. The generated ultrasonic wave causes an interference phenomenon of the ultrasonic wave in the process of being propagated from the measurement object (100), and the intensity of the ultrasonic wave is significantly higher than that of the conventional ultrasonic wave generated by a single laser beam. Ultrasonic output can be generated.
[0048]
【The invention's effect】
According to the present invention, a high-intensity ultrasonic output can be obtained from the measurement object (100) and the ultrasonic inspection can be performed in a non-contact manner, so that the non-destructive inspection can be easily performed on a high-temperature and moving object. . That is, high-intensity ultrasonic waves are generated at a high-temperature continuous casting slab or a rolling target (100), and various physical properties such as a defect detection and a crystal grain size inside the measuring target (100) are measured online. Can be evaluated.
[0049]
In addition, the apparatus for generating a laser ultrasonic wave by irradiating multiple beams according to the present invention can be used to produce high value-added steel such as ultrafine grained steel. In addition, since high-power ultrasonic waves can be generated and incident on the object to be measured (100), a signal having a high noise-to-signal ratio (S / N) can be obtained, and a reliable crystal grain size measurement and internal measurement can be performed. Defects can be evaluated. When the evaluation result is fed back to the rolling or continuous casting process, there are effects such as remarkably improving the quality of the continuous casting slab and the rolled product.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a laser ultrasonic wave generating apparatus using multiple beam irradiation according to the present invention.
FIG. 2 is a configuration diagram of a divided portion of a laser beam in the apparatus for generating a laser ultrasonic wave by irradiating multiple beams according to the present invention.
FIG. 3 is an explanatory diagram showing a trajectory of a laser beam obtained from a laser ultrasonic wave generating apparatus using multiple beam irradiation according to the present invention.
FIG. 4 is a detailed view of a combination lens provided in the apparatus for generating laser ultrasonic waves by multiple beam irradiation according to the present invention.
FIG. 5 is a graph showing the intensity of laser ultrasonic waves when the center distance of the laser beam changes in the apparatus for generating laser ultrasonic waves by multiple beam irradiation according to the present invention.
FIG. 6 is a photograph showing an irradiation mode of a multiple laser beam or the like generated by a laser ultrasonic wave generator by multiple beam irradiation according to the present invention.
FIG. 7 is a photograph showing an irradiation mode of a multiple laser beam adjusted by using a wedge-shaped focal lens in a laser ultrasonic wave generation apparatus using multiple beam irradiation according to the present invention.
FIG. 8A is a graph showing an ultrasonic intensity waveform obtained by the apparatus for generating a laser ultrasonic wave by multiple beam irradiation according to the present invention, and FIG. 8B is a diagram showing a signal obtained from FIG. FIG. 7 is a graph showing the magnitude of amplitude for each frequency obtained by the above method.
FIG. 9 is a graph showing the intensity of ultrasonic waves when the distance between beams is changed by the apparatus for generating laser ultrasonic waves by multiple beam irradiation according to the present invention.
FIG. 10 is a graph showing an ultrasonic saturation phenomenon according to a general laser irradiation intensity density.
[Explanation of symbols]
10 pulse YAG laser 20 beam size reduction device (Beam reducer set)
Reference numeral 22a: concave lens 22b: convex lens 30: first beam splitting mechanism (Beam splitter module)
32 ... beam splitter 40 ... second beam splitter module
42a ... mirror
42b: Beam splitter 50: Third beam splitter mechanism
52a, 54a... Beam splitter 60... Combination lens mechanism (pulse distance controlling focusing lenses)
62a: large-diameter focal lens 62b: wedge-type window optical lens 70: precision motor (step motor)
72 ... controller
74 ... automatic lens position controller
80 Computer 100 Measurement object 110 Optical interferometer
P1, P2, P3, P4, P5 ... Laser beam

Claims (5)

An apparatus for performing non-destructive inspection of a material in which a measurement object (100) is irradiated with a laser beam to generate an ultrasonic wave and performs an internal inspection by an ultrasonic wave in a non-contact manner using an optical interferometer. A pulsed Nd-YAG laser (10); a plurality of beam splitting mechanisms for splitting one high-power laser beam emitted from the pulsed YAG laser (10) into a plurality of laser beams; A combined lens comprising a large-diameter focal lens (62a) and a wedge-shaped window focal lens (62b) for adjusting the inter-beam distance (d) of a plurality of laser beams produced by the beam splitting mechanism and the irradiation sectional area of each laser beam. A high-intensity multi-beam by irradiating a single ray beam in various ways and irradiating the object to be measured (100). The laser ultrasonic generator according to multiple beam irradiation, characterized in that the pulsed laser ultrasonic configured as to cause the measured object (100). A beam size reducing device (20) comprising a number of concave and convex lenses (22a) (22b) behind the pulse YAG laser to reduce the beam size. 2. A laser ultrasonic generator using multiple beam irradiation according to claim 1. The laser beam splitter according to claim 1, wherein the first beam splitting mechanism (30) includes a beam splitter (32) so as to split the laser beam (PO) at a ratio of 40:60. Sound wave generator. In the second beam splitting mechanism (40), a number of mirrors (42a) for adjusting a beam reflected by 40% by the first beam splitting mechanism (30) so as to have an appropriate optical path; 2. A beam splitter (42b) for separating two laser beams (P1) and (P2) irradiated on the x-axis of an object to be measured (100). A laser ultrasonic generator using multiple beam irradiation. The third beam splitting mechanism (50) receives the laser transmitted through the first beam splitting mechanism (30) at 60%, and is disposed so as to cross the second beam splitting mechanism (40). And a beam splitter (52a) for reflecting the transmitted laser beam by 33.3% to irradiate one laser beam (P3) on the y-axis of the measurement object (100). A beam splitter (54a) for reflecting and transmitting the laser beam transmitted by 66.7% at 50:50 is provided to irradiate one laser beam (P4) to the origin of the measurement object (100), and And a mirror (52b) for finally irradiating the laser beam transmitted through the laser beam (P5) onto the y-axis of the measurement object (100). The laser ultrasonic generator according to claim 4, wherein the laser ultrasonic wave is generated by multiple beam irradiation.

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