JPH10260163A - Laser ultrasonic wave inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser ultrasonic wave inspecting device which, based on a new method, detects the ultrasonic wave reflected or scattered at a defective place with high SN ratio, without damaging an object to be inspected. SOLUTION: Laser beam 11 emitted from a laser light source 10 is split into, for example, ten parallel laser beams with a beam separator 12. The respective split laser beam is made incident on, respective channel of a multi- channel acoustic optical element 13 comprising, at least, the same number of channels as the beam. The laser beam coming out of each channel is made incident on a beam expander 14, and expanded in lateral direction to be such beam whose cross section vertical to advancing direction is almost straight line. The beam is line-focused linearly on the surface of a steel material 16, with these straight irradiation lines being irradiated almost in parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser ultrasonic wave for irradiating an object with a laser beam to generate ultrasonic waves, and detecting the ultrasonic waves propagated through the object to inspect the state of the object. Related to inspection equipment.

[0002]

2. Description of the Related Art As one of methods for detecting internal defects and the like in various materials, there is a so-called laser ultrasonic method. For this, for example, "Ultrasonic TECHNO
May issue "(vol.5, No.5, p38 (1993) Nippon Kogyo Shuppan). Since this method detects an ultrasonic wave using a laser beam, it can be used for a non-contact inspection for examining an internal state of a material or the like that cannot be inspected by contact. Therefore, application to quality inspection in the iron making process, inspection of welding in steel processing, quality inspection of ceramic materials, internal inspection of aircraft parts, quality inspection of other metals and composite materials, etc. are expected.

A typical laser ultrasonic inspection apparatus is, for example, a laser light source (for example, a Q-switched YAG laser) for exciting ultrasonic waves inside an inspection object, and a probe for detecting ultrasonic waves propagating in the inspection object. Laser light source (for example, He-Ne laser). When an appropriate excitation laser beam is applied to the test object, ultrasonic waves are generated in the test object due to thermal stress or evaporation reaction force. When the ultrasonic wave propagates through the inspection object, if there is a defect inside, the ultrasonic wave is reflected or scattered there. The detection of the ultrasonic wave propagating in the inspection object can be performed by observing the phase change and the Doppler shift of the probe laser beam. Then, it is possible to estimate the presence or absence of the internal defect or the position where the defect exists from the change of the time and amplitude required for the ultrasonic wave to propagate from the generation position of the ultrasonic wave to the detection position.

[0004]

By the way, the intensity of the ultrasonic wave reflected or scattered by the defect is very weak, and it is difficult to detect this signal at a high SN ratio. In order to increase the intensity of the ultrasonic wave reflected or scattered by the defect, it is conceivable to increase the intensity of the ultrasonic wave generated by increasing the output of the excitation laser. However, increasing the output of the excitation laser beam, which irradiates the laser beam in one location on the surface of the inspection target, may cause damage to the surface of the inspection target due to the laser beam. Has limitations.

When an excitation laser beam is applied to one portion of the surface of the inspection object to generate an ultrasonic wave, the ultrasonic wave spreads spherically from that point and propagates inside the inspection object. . For this reason, the ratio of the energy of the ultrasonic wave excited by the laser which contributes to the ultrasonic wave reflected or scattered by the defect becomes extremely low. As described above, when a weak ultrasonic wave is detected, the SN ratio is reduced, so that special consideration is required for the detection means, which is accompanied by difficulty.

[0006] The present invention has been made based on the above circumstances, and is based on a new method of detecting ultrasonic waves reflected or scattered from a defect at a high SN ratio without damaging the inspection object. It is an object to provide an inspection device.

[0007]

According to a first aspect of the present invention, there is provided an excitation laser light source, and a laser beam emitted from the excitation laser light source is provided as a plurality of laser beams. A splitting means, an acousto-optic means having at least the same number of channels as the plurality of laser beams, and passing the plurality of laser beams through an acousto-optic element provided independently for each channel; and Beam expansion means for extending the laser beam emitted from each channel in parallel so that the cross section perpendicular to the traveling direction becomes linear, and a predetermined electric power to the acousto-optic element of each channel of the acousto-optic means. At least one of the intensity and direction of the laser beam emitted from each channel of the acousto-optic means by supplying a signal; A signal generating means for controlling the ultrasonic wave generated in the inspection object by the laser light applied to the inspection object through the beam extending means or an ultrasonic detection means for detecting the ultrasonic wave reflected or scattered by the defect and It is characterized by having.

According to a seventh aspect of the present invention, there is provided an excitation laser light source, beam splitting means for converting a laser beam emitted from the excitation laser light source into a plurality of laser beams, and at least the same number of channels as the plurality of laser beams. Acousto-optic means for passing the plurality of laser beams through the acousto-optic element provided independently for each channel, and a laser beam emitted from each channel of the acousto-optic means, perpendicular to the traveling direction Optical means for making the various cross-sections annular with different radii and irradiating them in a plurality of concentric rings on the surface to be inspected; and acousto-optical elements in each channel of the acousto-optical means. Are supplied in order from the outside to the inside of the plurality of concentric rings at predetermined timing. Signal generation means for controlling so as to detect an ultrasonic wave generated in the inspection object by a laser beam applied to the inspection object through the optical means or an ultrasonic wave reflected or scattered by a defect. Means.

According to the first aspect of the present invention, the characteristics of the laser beam emitted from the channel can be controlled by changing the electric signal supplied to the acousto-optic element. Specifically, the emission and non-emission of the laser beam can be switched by turning on / off the supplied signal, and the frequency of the ultrasonic wave generated in the acousto-optic medium can be changed by changing the frequency of the supplied signal. And thereby the diffraction angle of the emitted laser beam can be controlled. For example, the laser beam emitted from each channel of the acousto-optic means is set to have a constant line interval on the surface of the inspection target, and the surface ultrasonic wave of the substance to be inspected propagates over a distance of one line interval. When the laser beam is sequentially irradiated as the timing of the time required, the amplitude of the surface ultrasonic wave can be gradually increased each time a laser beam is irradiated. If this is used for defect detection, a high SN
The ratio can be realized. In addition, laser beams from a plurality of channels are simultaneously irradiated on the inspection object, and the refraction angle of the laser beam emitted from the acousto-optic means is changed by changing the frequency of the supplied electric signal. The beam can be scanned over the surface to be inspected. If this scanning speed is set to an appropriate value, an ultrasonic wave propagating on the surface or a directional ultrasonic wave propagating in the material can be generated in the inspection object, and if this is used for defect detection, A high SN ratio can be realized.

According to a seventh aspect of the present invention, an electric signal supplied to the acousto-optic element is appropriately changed, and a plurality of concentric annular laser beams irradiated on the surface of the inspection object are directed from the outside to the inside. By controlling the irradiation in order at a predetermined timing, it is possible to generate an ultrasonic wave that converges at one point of the inspection target. If there is a defect at this point, an ultrasonic wave that is largely reflected or scattered is generated from the defect, and it is possible to check for the presence or absence of the defect by detecting the ultrasonic wave.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the entire configuration of a laser ultrasonic inspection apparatus according to a first embodiment of the present invention, FIG. 2 is a schematic diagram of a multi-channel acousto-optic device, and FIG. FIG. 4 is a schematic perspective view showing the state of a laser beam obtained, FIG. 4 is a view for explaining light diffraction in an acousto-optic device, and FIG. 5 is a diagram showing the amplitude of ultrasonic waves gradually increased by sequentially irradiating a plurality of laser beams. It is the figure which showed the mode that it was going on typically.

As shown in FIG. 1, the laser ultrasonic inspection apparatus according to the first embodiment includes an ultrasonic generator 1 for generating ultrasonic waves on the surface of a steel material 16 to be inspected and an ultrasonic wave propagating on the surface of the steel material 16. It has an ultrasonic detector 2 for detecting sound waves. The ultrasonic generator 1 includes a laser light source 10, a beam separator 12, a multi-channel acousto-optic device 13, a beam expander 14, and a multi-channel acousto-optic device 1.
3 has an oscillator 15 for supplying a predetermined signal. The ultrasonic detection unit 2 uses a laser interferometer 20 or the like to
The ultrasonic displacement of the surface of the object is detected.

The laser light source 10 of the ultrasonic generator 1 is a laser light source for exciting an ultrasonic wave, and in this embodiment, Nd:
A YAG laser is used. A laser beam 11 emitted from a laser light source 10 enters a beam separator 12, where it is split into, for example, ten parallel laser beams. As the beam separator 12, a commercially available optical element that splits a laser beam into a plurality of parts by reflection and transmission by a film in which a dielectric or metal body is coated on both surfaces of an optically polished parallel flat substrate can be used. . As shown in FIG. 2, each of the split laser beams is a multi-channel acousto-optical element 13 having at least the same number of channels as the number of beams.
Incident on each channel. The multi-channel acousto-optic element 13 is composed of, for example, 10 independent acousto-optic elements, and a predetermined signal is supplied to each acousto-optic element from the oscillator 15 which is a signal generating means, so that The element exerts various actions described later on the laser beam incident on the channel.

The laser beam emitted from each channel of the multi-channel acousto-optic device 13 enters a beam expander 14 which is an expanding means. Before the laser beam enters the beam expander 14, the cross section perpendicular to the traveling direction is substantially circular.
When the beam is incident on the beam, the beam is expanded in the lateral direction, and when the beam is emitted, the beam has a substantially straight cross section perpendicular to the traveling direction. Each laser beam having a substantially linear cross section is linearly focused on the surface of the steel material 16 to be inspected as shown in FIG. 3, and these linear irradiation lines are parallel to each other. Irradiation.

When the laser beam is irradiated, the steel 16
Ultrasonic waves are generated in the irradiation line portion by thermal stress or evaporation reaction force. The ultrasonic waves include those that propagate inside the steel material 16 and those that propagate on the surface of the steel material 16. In the present embodiment, the ultrasonic wave propagating on the surface is used for detecting a defect. When the ultrasonic wave propagating on the surface of the steel material 16 scatters upon hitting a defect on the surface of the steel material 16, the ultrasonic wave originating therefrom is generated and propagates on the surface of the steel material 16. This ultrasonic wave is detected by the ultrasonic wave detection unit 2. Since the geometric arrangement of the ultrasonic wave generating unit 1 and the ultrasonic wave detecting unit 2 is known in advance, it is determined whether or not the surface of the steel material 16 has a defect from the timing when the ultrasonic wave is detected by the ultrasonic wave detecting unit 2. If there is a defect, its position is known.

Next, the principle of the multi-channel acousto-optic device 13 will be briefly described with reference to FIGS. Acousto-optical element is obtained by bonding the piezoelectric element to the acoustic-optic medium, such as tellurite glass or lead molybdate single crystals, acousto-optic and supplies an electric signal to the piezoelectric element from the oscillator 15 _{1-15 10} for each channel When an ultrasonic wave is generated in the medium, a periodic change in the refractive index occurs in the acousto-optic medium due to the photoelastic effect, which acts as a diffraction grating. The interaction distance between light and ultrasonic L (see FIG. 4), ₀ the wavelength of light λ in vacuum, the acoustic velocity of the medium V, and ultrasonic frequency (driving frequency) f _a, the refractive index of the medium n ^{_{when, 2πλ 0 Lf a 2 / nV}} 2> Bragg diffraction occurs when 4π (1) is satisfied, other zero-order light which is not subjected to diffraction, obtaining the first-order diffracted light of high light intensity shown in FIG. The direction of the first-order diffracted light (diffraction angle) θ _B is given by θ _B = sin ⁻¹ (λ ₀ f _a / 2V) (2) in consideration of the refraction at the light entrance / exit surface of the medium. Obtained or highest diffraction efficiency when a light incident angle is theta _B in Bragg diffraction.

The intensity I ₁ of the primary diffracted light depends on the power P _a of the ultrasound in the medium, the relationship ^{_{is, I 1 α sin 2 (K}} 1 (MeP a) 1/2 / λ 0) (3 ). Here, Me is a constant determined by the physical property value of the acousto-optic medium, and the larger this value is, the higher the diffraction efficiency is obtained, which is called the index of performance of the medium. Also, K ₁ is a constant dependent element. The above description of the acousto-optic device is based on the catalog of optical applied products of HOYA-SCHOTT Co., Ltd.

As can be seen from the above equation (2), the diffraction angle θ _B of the first-order diffracted light depends on the frequency f _a of the ultrasonic wave. Therefore, by changing f _a , the angle θ _B of the first-order diffracted light can be controlled. By utilizing this, by selecting the appropriate f _a for each channel, a plurality of laser beams on the steel 16 as shown in FIG. 3, that the irradiation line is irradiated to a predetermined distance Can be.

Next, as can be seen from equation (3), when the value in ultrasonic power P _a in the acoustooptic medium, i.e. when during the acoustooptic medium, ultrasonic waves generated primary diffraction has an intensity I ₁ is also a value corresponding to P _a to the ultrasonic power of the light, when ultrasound power P _a is zero, or primary when no ultrasonic wave is generated in the acoustooptic medium The intensity I _{1 of the} diffracted light is also zero. Ultrasonic waves in the acousto-optic medium are generated by supplying electric power to the piezoelectric element. Therefore, by turning on / off the power supplied to the piezoelectric element of each channel of the multi-channel acousto-optic element 13, it is possible to switch on / off of the laser beam applied to the surface of the steel material 16. This makes it possible to irradiate the surface of the steel material 16 with a laser beam corresponding to each channel of the multi-channel acousto-optic element 13 in a desired order.

[0020] In this embodiment, by controlling the ultrasonic frequency f _a and the ultrasonic power P _a to be generated during the acoustooptic medium for each channel of the multi-channel acousto-optic device 13, irradiation of each laser beam The surface of the steel material 16 is irradiated with a laser beam in order so that the time interval between the irradiations becomes Δt and the interval between the irradiation lines becomes d ₀ . Here, Δt and d ₀ satisfy the relationship of d ₀ = v · Δt (4). Here, v is the sound speed of the ultrasonic wave propagating on the surface of the steel material 16.

When each laser beam is sequentially irradiated at such a line interval and a time interval, the ultrasonic wave propagating on the surface of the steel material 16 absorbs its energy every time the laser beam is irradiated, and FIG. a), (b),
(C), (d),..., The amplitude gradually increases and the energy increases. Regarding the stepwise increase in the amplitude of the ultrasonic wave by irradiating the laser beam at a predetermined line interval and time interval in this way, Ul.
Experimental studies are shown in trasonics, Vol. 31, No. 6, 1993, pp387-394.

By the way, a laser ultrasonic inspection device detects a surface displacement caused by ultrasonic waves scattered by a defect.
The ultrasonic waves scattered by the defect are very weak and require the use of a high-resolution laser interferometer. However, even if a high-resolution laser interferometer is used, a sufficient signal-to-noise ratio cannot be obtained if the signal intensity is almost equal to the noise intensity, and it is difficult to detect defects with high accuracy. In order to increase the intensity of the ultrasonic wave scattered by the defect, the energy of the ultrasonic wave generated by the excitation laser may be increased, but for that purpose, the output of the excitation laser must be increased. However, when the beam from the high-power excitation laser is irradiated on the steel material 16, serious damage occurs on the surface portion irradiated with the laser beam. For this reason, conventionally, an excitation laser having an output that does not damage the inspection target has to be used, and as a result, the energy of the ultrasonic wave is small, and a sufficient SN ratio cannot be obtained.

On the other hand, if a plurality of laser beams are used as in this embodiment and the output of each laser beam is kept within a certain range, the steel material 16 will not be damaged. In addition, the energy of the ultrasonic wave can be gradually increased by sequentially irradiating the plurality of laser beams at predetermined line intervals and time intervals, so that the SN ratio for defect detection is improved. Further, since the laser beam applied to the steel material 16 is a linear irradiation line parallel to each other, only ultrasonic waves propagating on the surface that propagate perpendicular to the irradiation line continue. Thereby, the ultrasonic wave propagating on the surface of the steel material 16 can be given directivity, so that the accuracy of determining the position of the defect is improved.

Next, a second embodiment of the present invention will be described. In the present embodiment, the apparatus shown in FIG.
A plurality (for example, 10) of line-focused laser beams are simultaneously irradiated in parallel to the surface of
6 are simultaneously scanned at a predetermined speed in the arrangement direction of the laser beams. FIG. 6 shows one laser beam L line-focused on the steel material 16. In the figure, point P is a point at which this laser beam is emitted from the multi-channel acousto-optic element 13, and point O is a point from the point P to the steel material 1.
6 is a perpendicular leg lowered on the surface, and 1 represents the length from point P to point O. Further, on the surface of the steel material 16, the arrangement direction of the laser beams is defined as the X direction, and the distance from the point O to the laser beam L measured along the X direction is defined as x. Here, for simplicity, a beam expander is not considered.

In FIG. 6, the direction θ _B of the first-order diffracted light is given by the equation (2). Here, if θ _B is sufficiently small, θ _B becomes θ _B = λ ₀ f _a / 2V (5) Can be saved. That is, the diffraction angle θ _B depends on the frequency f _a of the ultrasonic wave in the acousto-optic medium. Therefore,
By changing f _a , the diffraction angle θ _{B of the} laser beam
Can be controlled. Further, from FIG. 6, there is a relation of x = l tan θ _B (6). Here, as in the above, if θ _B is sufficiently small, (6) can be set as x = lθ _B (7). Assuming that the scanning speed of the laser beam on the surface of the steel material 16 is v, v = dx / dt. By substituting the equations (7) and (5), v = l (dθ _B / dt) = (λ ₀ l / 2V) · df _a / dt (8) Therefore, the multi-channel acousto-optic device 1
When the frequency f _a of the ultrasonic wave in the acousto-optic medium 3 is temporally changed according to the equation (8), the laser beam irradiated on the surface of the steel material 16 scans at the speed v.

When a plurality of line-focused parallel laser beams are irradiated on the sample surface, a very narrow band surface ultrasonic wave, that is, a surface ultrasonic wave having a tone burst signal waveform is generated on the sample surface. It is known to Further, it is known that when the plurality of line-focused parallel laser beams are scanned on the sample surface in the arrangement direction at the same speed as the sound speed of the surface ultrasonic wave, the intensity of the tone versatile ultrasonic wave can be increased. Have been. Regarding this, for example, Yamanaka, Nagata and Koda, “Generation of Single Mode Ultrasound by Laser Phase Velocity Scanning” (Journal of the Acoustical Society of Japan, 48, 8 (1992), p. 56).
4-571) and Jin Huang, Sridhar Krishnaswamy, and Ja
n D. Achenbach “Laser generation of narrow-band s
urface waves "(J. Acourst. Soc. Am., 92 (5) p.2527
-2531) can be referred to.

Therefore, the temporal change rate of f _{a in} the equation (8) is set to an appropriate value, and the speed v of the laser beam scanning the surface of the steel material 16 is the same as the sound speed of the ultrasonic wave propagating on the surface of the steel material 16. By setting the value, it is possible to generate a tone-burst ultrasonic wave propagating on the surface of the steel material 16 and to increase the intensity thereof. It can be used for the detection of defects on the surface.

In the present embodiment, what is necessary for scanning the laser beam is to change the frequency of the ultrasonic wave in the acousto-optic medium of the multi-channel acousto-optic element 13 with time. The frequency of the driving AC signal supplied from the oscillator 15 to each channel of the channel acousto-optic element 13 may be changed at a desired rate. That is, the scanning speed of the laser beam applied to the surface of the steel material 16 can be changed by electrical control. Moreover, it is possible to change the frequency of the AC signal at a desired frequency by a known technique,
Relatively simple. The desired frequency can be obtained by modifying the equation (8) to obtain df _a / dt = (2V / λ ₀ l) · v (9). In the equation (9), when the inspection target is a steel plate, v is about 3000 m / sec, and V when the acousto-optic medium of the multi-channel acousto-optic element to be used is tellurium dioxide (TeO ₂ ) single crystal.
Is about 4200 m / sec.

Next, a third embodiment of the present invention will be described. FIG. 7 is a schematic cross-sectional view showing a state where a plurality of irradiated laser beams 30 are scanned rightward on the surface of the steel material 16 to be inspected. In the second embodiment, ultrasonic waves that propagate on the surface of the steel material 16 are generated by scanning a plurality of line-focused laser beams at the same speed as the propagation speed of the surface ultrasonic waves. On the other hand, in the present embodiment, an ultrasonic wave that propagates from the surface of the steel material 16 to the inside thereof is generated. In this case, assuming that the scanning speed of the laser beam is v and the sound speed in the bulk of the steel material 16 is c, the angle θ represented by θ = sin ⁻¹ (c / v) (10) as shown in FIG. Directional ultrasonic waves propagate in the direction of. The scanning of the laser beam may be performed by changing the frequency of the AC signal supplied to each channel of the multi-channel acousto-optic device 13 in FIG. 2 at a predetermined time change rate, as in the second embodiment. If the rate of change is changed, the scanning speed of the laser beam is changed, so that the above θ is also changed. That is, the multi-channel acousto-optic device 13
The direction of propagation of the ultrasonic wave can be controlled by the electric signal supplied to the.

Generation and Directivity Control of
Bulk Acoustic Waves by Phase Velocity Scanning of
Laser Interference Fringes (Hideo NISHINO et.al.,
Jpn.J. Appl. Vol. 34 (1995) pp.2874-2878)
By irradiating the sample surface with two laser beams having slightly different optical frequencies, the interference fringes are scanned on the sample surface, and the ultrasonic BAW (Bulk Acoustic Waves) propagates in a specific direction inside the sample. It is shown that it can be done. However, in this case, two laser beams having slightly different optical frequencies must be prepared, and these must be irradiated on the sample surface at a predetermined angle, which complicates the configuration of the apparatus. Also,
In order to change the direction of ultrasonic wave propagation, the angle of the laser beam applied to the sample surface must be changed.
It becomes difficult to control the propagation direction. On the other hand, in the device of the present embodiment, the propagation direction of the ultrasonic wave can be controlled only by the electrical control of the AC signal supplied to the multi-channel acousto-optic element 13 as described above. Therefore, the control of the propagation direction of the ultrasonic wave is greatly facilitated, and the ultrasonic wave can be easily propagated in a target direction with directivity.

FIG. 8 is a diagram schematically showing a modification of the present embodiment. That is, a plurality of laser beams that are separately line-focused on the left side and the right side of the surface of the steel material 16 are irradiated, and these are scanned at the same scanning speed in directions approaching each other. Then, as shown in the figure, the ultrasonic wave propagates from the right laser beam in the direction of angle θ, and the ultrasonic wave propagates from the left laser beam in the direction of angle −θ. These ultrasonic waves converge on the point Q, and the energy of the ultrasonic waves at the point Q becomes very large. If there is a defect at this point Q, a large scattered wave is generated therefrom, so that the presence of the defect can be known by detecting this. The position of the point Q where the ultrasonic wave converges is known in advance,
By changing the angle θ, it is possible to easily check the presence or absence of a defect at each point inside the steel material 16.
6 can be inspected with high detection accuracy.

Next, a fourth embodiment of the present invention will be described. FIG. 9 is a diagram schematically illustrating a laser ultrasonic inspection apparatus according to the fourth embodiment. In the first to third embodiments, the laser beam emitted from the multi-channel acousto-optical element 13 is expanded by a beam expander so that the cross section perpendicular to the traveling direction becomes a straight line, and these are line-focused to obtain a surface of the steel material 16. Irradiation. On the other hand, in the present embodiment, ten laser beams 40 ₁ , 40 ₂ ,.
40 ₁₀ respectively of the corresponding known axicon lens 50 _1, 50 _2, ..., 50 ₁₀ cross section perpendicular to a laser beam of an annular in the traveling direction by passing the these appropriate optics Is used to irradiate the surface of the steel material 16 concentrically. In the configuration of FIG.
0 ₁ to 40 ₁₀ and axicon lenses 50 ₁ to 50 ₁₀ are linearly arranged.

[0033] 10 sheets of each of the annular laser beam emitted from the axicon lens lens 50 ₁ and the like in order to irradiate the concentric annular around the specific point on the surface of the steel material 16, which also are arranged in a straight line Half mirror 51 ₁ , 5
1 _2, ..., can be used 51 _10. Among them, the half mirror 51 _{2-51 9} reflects the laser beam from the corresponding axicon lens, transmits the other laser beam. Half mirror 51 _1, the laser beam from the corresponding axicon lens 50 ₁ is transmitted through, the laser beam that has been reflected from the other of the half mirror reflects. Also, the half mirror 51 ₁₀
The laser beam from the axicon lens 50 ₁₀ is only reflected. Further, each optical system is adjusted so that each annular laser beam is irradiated concentrically around a point O on the surface of the steel material 16 to be inspected. Mirror 5 for irradiating laser beam for detection
5 is arranged above the point O. The mirror 55 also has a role of reflecting light reflected on the surface of the steel material 16 and guiding the light to an interferometer (not shown).

As described above, it is possible to irradiate each laser beam concentrically, and to irradiate the laser beam sequentially from the outer laser beam to the inner laser beam at a predetermined timing. 9
As shown in FIG. 5, the ultrasonic wave propagates so as to converge on a specific point inside the steel material 16. Therefore, if there is a defect at this point, a large scattered wave is generated from the defect. By detecting this, the existence of the defect can be known. The position of the point where the ultrasonic wave converges can be changed on a straight line perpendicular to the surface passing through the point O by the timing of switching the laser beam. This makes it possible to easily check the presence or absence of a defect at each point inside the inspection target, thereby enabling inspection inside the inspection target with high detection accuracy. As described above, detecting a defect inside an inspection object by irradiating a laser beam whose cross section perpendicular to the traveling direction is annular is described in Cielo P. 1985 In.
ternational Advances in NDT vol.11, ed WJMcGonna
gle, p-175 and P. Cielo and CK Jen, and T. Ko
da, Appl. Phys. Lett. 58, 1591-1593 (1991).

The present invention is not limited to the above embodiments, and various changes can be made within the scope of the invention. For example, in each of the above-described embodiments, the inspection target is a steel material, but it is possible to non-destructively inspect the presence or absence of a surface or internal defect and the position of various materials other than the steel material. In the fourth embodiment, an axicon lens,
Although a half mirror or the like is arranged linearly to irradiate a concentric annular laser beam, the arrangement of an optical system for irradiating a concentric annular laser beam is not limited to this, and a collection method may be considered.

[0036]

As described above, according to the present invention,
By controlling the characteristics of the laser beam emitted from each channel of the acousto-optic means by supplying a predetermined electrical signal to the acousto-optic element of each channel of the acousto-optic means, for example, at a predetermined time interval and on the surface of the inspection object By irradiating the laser beam sequentially at predetermined line intervals, even if the intensity of each laser beam is not so large, the intensity of the ultrasonic wave propagating on the surface of the inspection object can be gradually increased. Since it can be used for defect detection, a detection signal having a high SN ratio can be obtained without damaging the inspection object, and inspection accuracy can be improved.
In addition, by supplying a predetermined electric signal to the acousto-optic element, a laser beam having a predetermined line interval can be simultaneously irradiated on the surface of the inspection object, and these can be simultaneously scanned on the surface, thereby transmitting the surface. Ultrasonic waves and ultrasonic waves propagating inside can be generated, and these can be given directivity, so that a detection signal with a high SN ratio can be obtained without damaging the inspection object, and the inspection accuracy can be further improved. be able to.

Further, the laser beam emitted from each channel of the acousto-optic means is formed into an annular shape having different radii in cross sections perpendicular to the traveling direction thereof, and these are formed into a plurality of concentric annular shapes on the surface of the inspection object. Providing optical means for irradiating, appropriately changing an electric signal supplied to the acousto-optic element, and setting a predetermined timing from the outside to the inside for a plurality of concentric annular laser beams irradiated on the surface of the inspection object , It is possible to generate ultrasonic waves that converge on one point of the inspection target. When the ultrasound is converged in this way,
When there is a defect at this point, the ultrasonic wave reflected or scattered therefrom also becomes large, so that the SN ratio can be increased and the inspection accuracy can be increased. Moreover, the depth of the point where the ultrasonic wave converges can be changed by changing the electric signal supplied to the acousto-optic element.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an overall configuration of a laser ultrasonic inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a multi-channel acousto-optic device.

FIG. 3 is a schematic perspective view illustrating a state of a line-focused laser beam applied to a surface of an inspection target.

FIG. 4 is a diagram for explaining light diffraction in the acousto-optic element.

FIG. 5 is a diagram schematically showing a state in which the amplitude of an ultrasonic wave is gradually increased by sequentially irradiating a plurality of laser beams in the second embodiment.

FIG. 6 is a diagram showing one laser beam L line-focused on the surface of a steel material.

FIG. 7 is a schematic cross-sectional view showing a third embodiment in which a plurality of irradiated laser beams are scanned rightward on the surface of a steel material.

FIG. 8 is a diagram showing a modification of the third embodiment.

FIG. 9 is a diagram schematically illustrating a laser ultrasonic inspection apparatus according to a fourth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS ₁ Ultrasonic wave generation part 2 Ultrasonic wave detection part 10 Laser light source 11 Laser beam 12 Beam separator 13 Multichannel acousto-optic element 14 Beam expander 15, 15 1-15 ₁₀ oscillator 16 Steel material 20 Laser interferometer 40 ₁ , 40 ₂ Laser beam 50 _1, 50 ₂ axicon lens 51 _1, 51 ₂ a half mirror 55 mirror

Claims (7)

[Claims] 1. An excitation laser light source, beam splitting means for converting a laser beam emitted from the excitation laser light source into a plurality of laser beams, and at least the same number of channels as the plurality of laser beams. Acousto-optic means for passing the plurality of laser beams through an acousto-optic element provided independently for each laser beam, and a laser beam emitted from each channel of the acousto-optic means has a linear cross section perpendicular to its traveling direction. Beam expanding means for extending each laser beam in parallel so as to provide a predetermined electric signal to the acousto-optic element of each channel of the acousto-optic means, and the intensity and intensity of the laser beam emitted from each channel of the acousto-optic means A signal generating means for controlling at least one of the directions, and an inspection object via the beam extending means Reflected or scattered and an ultrasonic detecting means for detecting the ultrasonic wave, laser ultrasonic inspection apparatus characterized by comprising by ultrasound or which defects generated on the test object by irradiated laser beam. 2. The electric signal according to claim 1, wherein the signal generating means is configured to irradiate a laser beam emitted from each channel of the acousto-optic means on the surface of the inspection object in order at a predetermined time interval and a predetermined line interval. 2. The laser ultrasonic inspection apparatus according to claim 1, wherein the laser ultrasonic inspection apparatus supplies the laser beam to each of the acousto-optic elements of the acousto-optic means. 3. The signal generation means, wherein each laser beam emitted from a plurality of channels of the acousto-optic means,
The electrical signal of the acousto-optic means is applied to the surface of the inspection object at the same time at predetermined line intervals, and is scanned at a predetermined speed on the surface of the inspection object in a direction perpendicular to the line direction. 2. The laser ultrasonic inspection apparatus according to claim 1, wherein the apparatus is supplied to each acousto-optic element. 4. The laser ultrasonic inspection apparatus according to claim 3, wherein the predetermined velocity is the same velocity as a sound velocity of an ultrasonic wave propagating on a surface of a substance constituting the inspection object. 5. The laser ultrasonic inspection apparatus according to claim 3, wherein the predetermined velocity is a velocity determined by a sound velocity of an ultrasonic wave propagating inside a substance constituting the inspection target. 6. The predetermined speed is equal to a first speed determined by a sound speed of an ultrasonic wave propagating inside a substance constituting the inspection object and opposite in direction to the first speed. A second speed, wherein half of the laser beams emitted from the plurality of channels are the first speed, and the other half are the second speed, each of which scans the surface of the inspection object in a direction approaching each other. Claim 3
The laser ultrasound device as described. 7. An excitation laser light source, beam splitting means for converting a laser beam emitted from the excitation laser light source into a plurality of laser beams, and at least the same number of channels as the plurality of laser beams. Acousto-optic means for passing the plurality of laser beams through an acousto-optic element provided independently for each laser beam, and a laser beam emitted from each channel of the acousto-optic means having a different cross section perpendicular to the traveling direction. Optical means for forming a ring of a radius and irradiating them in a plurality of concentric rings on the surface of the object to be inspected; and supplying a predetermined electric signal to the acousto-optic element of each channel of the acousto-optic means. And controlling the plurality of concentric rings so that they are sequentially irradiated from the outside to the inside at a predetermined timing. Signal generating means, and ultrasonic detecting means for detecting ultrasonic waves generated in the inspection object by the laser light applied to the inspection object through the optical means or ultrasonic waves reflected or scattered by the defect. A laser ultrasonic inspection apparatus characterized in that: