JPH11271280A - Laser ultrasonic inspection device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of a laser beam source, a Fabry-Perot interferometer required and the like up to the minimum, and to efectively observe an ultrasonic wave at two or more of observation points on one specimen at the same Lime. SOLUTION: A laser beam radiated from a laser beam source 11 for ultrasonic observation is divided into two by a poralization beam splitter 12 to guided into acoustic optical elements 14, 15. The elements 14, 15 converts a light frequency of the incicent laser beam from f0 into f1 and f2 , where f1 represents a light frequency to make a differentiated value of transmitted light intensity by the light frequency get maximum locally, or its neighboring frequency, and f2 represents a light frequency to make the differentiated value get minimum locally, or its neighboring value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a test object with a laser beam to generate ultrasonic waves on the test object.
The present invention relates to a laser ultrasonic inspection apparatus and a laser ultrasonic inspection method for detecting the state of an inspection object by detecting the ultrasonic waves transmitted through the inspection object.

[0002]

2. Description of the Related Art As one of methods for inspecting internal defects or the like of 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). In this method, an ultrasonic wave generated by irradiating a test object (subject) with a laser beam for generating an ultrasonic wave is detected using another laser beam for detecting an ultrasonic wave. The defect can be inspected for defects inside the object. Therefore, application to quality inspection in an iron making process, inspection of a welded part in a steel frame processing process, quality inspection of a ceramic material, internal inspection of an aircraft part, and quality inspection of a metal and a composite material are expected.

FIG. 6 is a block diagram showing one configuration example of a laser ultrasonic inspection apparatus using the laser ultrasonic method. In the figure, a laser light source 5 for ultrasonic wave generation
Numeral 0 denotes a laser light source for generating ultrasonic waves on the surface of the subject 55, and a Q-switched YAG laser capable of emitting a pulse laser beam having a relatively large output is used. A part of the laser beam emitted from the ultrasonic wave generation laser light source 50 is branched by the beam splitter 52 toward the photodetector 56, but the other laser beams are reflected on the surface of the subject 55 by mirrors 53 and 54. Is irradiated. When the laser beam is irradiated, the subject 5
Ultrasonic waves are generated in 5 due to thermal stress or evaporation reaction force. This ultrasonic wave propagates inside the subject, reaches the back surface of the subject, is reflected, and returns to the front surface of the subject again as an echo. When a defect exists inside the subject, the ultrasonic wave is also reflected by the defect and returns to the front surface as an echo. Further, some of the generated ultrasonic waves propagate on the surface of the subject.

The light split by the beam splitter 52 toward the photodetector 56 is converted into an electric signal by the photodetector 56 and used as a trigger signal for an oscilloscope 57. On the other hand, the ultrasonic observation laser light source 60 provided separately from the ultrasonic generation laser light source 50 is provided with an ultrasonic echo returning to the surface of the subject 55 or an irradiation position of the ultrasonic generation laser beam. Is a laser light source for irradiating different positions and observing the ultrasonic waves propagated on the surface of the subject. Laser light source for ultrasonic observation 6
As 0, for example, a He-Ne laser having a stable frequency is used. The linearly polarized laser beam emitted from the laser light source 60 is reflected by a mirror 62 and a polarizing beam splitter (PBS) 63, and is applied to the surface of the subject 55 via a 波長 wavelength plate 64. This reflected light is applied to a quarter-wave plate 64 and a polarizing beam splitter 63.
Pass through the lens 65 and enter the Fabry-Perot interferometer 66. Light transmitted through the Fabry-Perot interferometer 66 is converted into an electric signal by a photodiode 67. This signal is amplified by an amplifier 68, passed through a high-pass filter 69 for removing low-frequency noise, and supplied to an oscilloscope 57.

[0005] In the Fabry-Perot interferometer, when the resonator length is changed, the optical frequency at which the transmitted light intensity peaks changes accordingly. In such a Fabry-Perot interferometer,
If the resonator length is changed while a He-Ne laser beam (wavelength is 682.8 nm) having a constant optical frequency ν is incident, the transmittance of the He-Ne laser beam changes. FIG. 7 is a view showing the result of measuring the transmitted light intensity (vertical axis) of a He—Ne laser beam by sweeping the resonator length (horizontal axis) of the Fabry-Perot interferometer, and FIG. FIG. 9 is a diagram showing how transmitted light intensity (vertical axis) changes depending on optical frequency (horizontal axis) when the resonator length of the Perot interferometer is fixed. As shown in FIG.
Changing the resonator length of the Perot interferometer changes the optical frequency at which the transmitted light intensity peaks. Here, the change in the transmitted light intensity with respect to the change in the optical frequency (the value obtained by differentiating the transmitted light intensity with the optical frequency) is the most significant. The resonator length of the Fabry-Perot interferometer 66 is adjusted in advance so that the optical frequency ν of the He-Ne laser beam comes to the large point A, and the reflected light from the subject 55 is incident on the Fabry-Perot interferometer 66. Let it.

When the surface of the object 55 is ultrasonically vibrated by an ultrasonic echo reflected on the back surface or the defect of the object or by an ultrasonic wave propagating on the surface of the object, the spatial position of the surface of the object becomes It is displaced with the period of this ultrasonic wave. Therefore, when the laser beam from the ultrasonic observation laser light source 60 is reflected on the surface of the subject, it undergoes a Doppler shift accompanying this displacement, and the optical frequency fluctuates. As shown in FIG. 8, the reflected light from the subject 55 is
When the frequency is changed by ± Δν due to the Doppler shift, the transmitted light intensity is changed by ± ΔI as shown in the figure. Thus, by passing the reflected light from the subject 55 through the Fabry-Perot interferometer, a change in wavelength can be converted into a change in intensity.

When this signal is displayed on the oscilloscope 57 with the horizontal axis representing time and the vertical axis representing signal intensity, in the case of ultrasonic waves propagating inside the subject, if there is no defect inside the subject, the subject The signal intensity changes at fixed time intervals determined by the internal sound speed and the thickness of the subject. On the other hand, if there is a defect such as a cavity or an impurity inside the subject, the ultrasonic wave is reflected by the defect, and the signal intensity changes in a time shorter than the above time. Therefore, by examining this time interval, the presence or absence of a defect inside the object can be examined.
Also, in the case of ultrasonic waves propagating on the surface of the subject, if the position where the laser beam for generating ultrasonic waves is irradiated and the position where the laser beam for ultrasonic observation are irradiated are known, the time until the ultrasonic waves reach From the time, the sound speed of the subject can be obtained.

[0008]

By the way, in addition to detecting defects inside a material, the speed at which ultrasonic waves propagate through the material,
That is, various information can be obtained by measuring the sound speed. In particular, in the case of steel products, there is a correlation between the grain size of the crystal grains and the sound speed, and the grain size can be evaluated by examining the sound speed. Further, for example, in the case of a rolled steel product, by observing the anisotropy of this sound velocity, that is, how the sound velocity differs between the longitudinal direction and the width direction when rolling, the homogeneity of the product, other materials You can know various features. The above-described laser ultrasonic method can also be used for material inspection in such an embodiment.

When examining the anisotropy of the speed of sound, for example,
The position at which the laser beam for ultrasonic wave generation is irradiated is defined as the origin, and a point separated by a certain distance in the x-axis direction from this origin is irradiated with one laser beam for ultrasonic observation, and a point separated by a certain distance in the y-axis direction By irradiating another ultrasonic observation laser beam, the anisotropy of sound speed can be measured from the time difference between the observation times.

In this case, if two laser light sources for ultrasonic observation and two Fabry-Perot interferometers are provided,
In order to increase the cost of the apparatus, it is conceivable that a laser beam emitted from a single laser light source is split into two by a beam splitter or the like, and each is separately irradiated on the surface of the subject. However, when the reflected light is made incident on the same Fabry-Perot interferometer, when the time difference between the ultrasonic source and the ultrasonic wave at the subject reaches the two ultrasonic observation points is small, two oscilloscopes are used. Waveforms indicating changes in transmission intensity overlap, making it impossible to accurately determine the time difference between the two arrival times.

At this time, it is conceivable that the distance from the origin to the two ultrasonic observation points is greatly shifted. However, in the case of a material whose sound velocity anisotropy is completely unknown, how much should it be shifted? Sometimes I don't know. It is also conceivable to sequentially change the irradiation position of the ultrasonic observation laser beam while observing the observation results by trial and error.However, since the laser ultrasonic device is composed of many precise optical parts, every time the irradiation position is changed In addition, precise adjustment of the optical components is required, resulting in poor work efficiency.

The present invention has been made based on the above circumstances, and minimizes the number of necessary laser light sources, Fabry-Perot interferometers, and the like, and efficiently uses two or more observation points for one subject. An object of the present invention is to provide a laser ultrasonic inspection apparatus and a laser ultrasonic inspection method capable of simultaneously observing ultrasonic waves.

[0013]

According to the first aspect of the present invention, there is provided a laser ultrasonic inspection apparatus, comprising: a first laser for emitting a laser beam for generating an ultrasonic wave on a subject; A light source, a second laser light source that emits a laser beam for observing an ultrasonic wave that has propagated through the subject, and a first laser beam that splits the laser beam emitted from the second laser light source into at least two laser beams. Branching means, an optical frequency converting means for converting an optical frequency of each laser beam split into at least two beams by the first splitting means to predetermined different optical frequencies, and converting the optical frequency to the predetermined optical frequency. Each of the laser beams is irradiated to a predetermined position of the subject, and each of the laser beams reflected from the subject is converted into a single optical beam. Optical means for integrating the laser beam into a path, a Fabry-Perot interferometer for injecting the laser beam integrated into a single optical path by the optical means, and a laser beam output from the Fabry-Perot interferometer by an optical frequency. A second branching means for branching each laser beam, and a light detecting means for detecting a change in intensity by making each of the laser beams branched by the second branching means incident; The absolute value of the value obtained by differentiating the transmitted light intensity by the optical frequency in the light transmission characteristics of the Fabry-Perot interferometer with respect to the predetermined optical frequency of each laser beam after passing through the conversion means is locally maximum. A characteristic light frequency (maximum change frequency) or its vicinity.

According to a second aspect of the present invention, in the first aspect of the invention, when the number of the laser beams is two, the predetermined optical frequency is changed to a single peak of the light transmission characteristic of the Fabry-Perot interferometer. Adjacent to the maximum change frequency located before and after, and when there are at least three laser beams, the predetermined optical frequency is positioned before and after a plurality of peaks of light transmission characteristics of the Fabry-Perot interferometer. Or at or near the maximum change frequency.

According to a third aspect of the present invention, in the first or second aspect, the optical frequency conversion means is an acousto-optical element. The invention according to claim 4 is
The invention according to any one of claims 1, 2 and 3, further comprising means for obtaining sound speeds of ultrasonic waves in a plurality of directions of the subject based on an output of the light detecting means.

According to a fifth aspect of the present invention, in the first, second or third aspect of the present invention, there is provided means for obtaining an attenuation rate of the ultrasonic wave based on an output of the light detecting means. The laser ultrasonic inspection method according to the invention according to claim 6, wherein a step of irradiating a subject with a laser beam emitted from a first laser light source to generate ultrasonic waves, and Emitting a laser beam for observation from a second laser light source, branching the laser beam into at least two laser beams, and changing the optical frequency of each of the at least two laser beams to a predetermined light different from each other. Frequency, and irradiating each laser beam converted to a predetermined optical frequency to a predetermined position on the subject, and each laser beam reflected from the subject to a single optical path Integrating the laser beam integrated into the single optical path into a Fabry-Perot interferometer; and The force has been laser beam,
Branching each laser beam by the optical frequency, and irradiating each laser beam branched by the optical frequency to the light detection means, and detecting a change in the intensity thereof, comprising: The predetermined optical frequency of each laser beam is
In the light transmission characteristics of the Perot interferometer, an optical frequency (maximum change frequency) at or near the optical frequency at which the absolute value of the value obtained by differentiating the transmitted light intensity with the optical frequency is locally maximum is characterized.

According to a seventh aspect of the present invention, in the case where the number of the laser beams is two, the predetermined optical frequency is set to a maximum value adjacent to a single peak of a light transmission characteristic of the Fabry-Perot interferometer. Change frequency or its vicinity,
When the number of the laser beams is at least three, the predetermined optical frequency is a maximum change frequency located before or after a plurality of peaks of the light transmission characteristic of the Fabry-Perot interferometer or a vicinity thereof.

According to an eighth aspect of the present invention, in the invention according to the sixth or seventh aspect, the step of converting the optical frequency of each of the at least two laser beams into a predetermined different optical frequency includes: It is characterized in that it is performed using an acousto-optic element. The invention according to claim 9 is the sixth invention.
The invention according to claim 7 or 8, further comprising measuring sound speeds of ultrasonic waves in a plurality of directions of the subject based on an output of the light detecting means.

According to a tenth aspect of the present invention, in addition to the sixth, seventh or eighth aspect of the present invention, it is preferable that an attenuation rate of an ultrasonic wave propagating through the subject is determined based on an output of the light detecting means. Features.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of one embodiment of a laser ultrasonic device according to the present invention.
In FIG. 1, a laser light source 10 for generating an ultrasonic wave is a laser light source that emits a laser beam for generating an ultrasonic wave on the surface of the subject 1, and a laser light source 11 for ultrasonic observation propagates through the subject 1. It is a laser light source that emits a laser beam for observing ultrasonic waves. As the laser light source 10 for generating ultrasonic waves, for example, Nd: Y
An AG laser is used, and as the ultrasonic observation laser light source 11, for example, a He-Ne laser whose frequency is stable is used.

The laser beam emitted from the ultrasonic wave generation laser light source 10 is irradiated onto the surface of the subject 1 directly or via an appropriate optical path (omitted in FIG. 1). When the laser beam is irradiated, ultrasonic waves are generated in that part of the subject by thermal stress or evaporation reaction force. There are two types of ultrasonic waves: one that propagates inside the subject and one that propagates on the surface of the subject around the point irradiated with the laser beam, just like a wave traveling on the water surface. In the present embodiment, the sound velocity of the subject is measured by observing the latter ultrasonic wave by means described later.

On the other hand, a laser beam emitted from the ultrasonic observation laser light source 11 (the optical frequency is f ₀ )
Are separated by a polarizing beam splitter (PBS) 12 into a laser beam that passes therethrough and a laser beam that is reflected here. The laser beam reflected by the PBS 12 enters the first acousto-optic element 14 via the mirror 13, and the laser transmitted through the PBS 12 enters the second acousto-optic element 15.

The acousto-optic devices 14 and 15 are devices utilizing an acousto-optic effect, and in this case, an acousto-optic frequency shifter (Acousto-Optical Frequency).
(Shifter: AOFS). That is, when an appropriate signal is supplied to the acousto-optic element from an oscillator or the like, the medium provided therein performs ultrasonic vibration, and the elastic strain and pressure change depending on the location. Due to this, a refractive index fluctuation having a cycle of the wavelength of the ultrasonic wave occurs in the medium, and the light incident on the fluctuation region causes diffraction. At this time, the diffracted light undergoes Doppler shift due to the ultrasonic wave, and the optical frequency of the first-order diffracted light has a value shifted from the optical frequency of the incident light by the frequency of the ultrasonic wave. That is, the optical frequency of the incident light is ν _i , the optical frequency of the first-order diffracted light is ν _d ,
When the frequency of the ultrasound and f _a, the _{ν d = ν i ± f a} . Here, the sign of ± is determined by the direction of diffraction.

In the description of the present embodiment, the optical frequency of the laser beam emitted from the ultrasonic observation laser light source 11 is assumed to be f _0, and an appropriate signal is supplied to the acousto-optic devices 14 and 15 to thereby obtain the optical frequency f _0. Shift. Here, the optical frequency of the first-order diffracted light of the acousto-optic element 15 is f
_1, although the optical frequency of the first-order diffracted light of the acoustooptic device 14 and f _2, whether to what value the f ₁ and f ₂ specifically it will be described later.

The laser beam diffracted by the acousto-optic element 14 passes through a mirror 16 and a half mirror 18 to be inspected.
A laser beam applied to a predetermined position on the surface and reflected by the surface of the subject 1 is reflected by the half mirror 18 and the polarization beam splitter 19 and enters the Fabry-Perot interferometer 21. On the other hand, the laser beam diffracted by the acousto-optic element 15 is applied to a predetermined position on the surface of the subject 1 via a mirror 17 and a half mirror 18, and the laser beam reflected on the surface of the subject 1 is a half beam. The light is reflected by the mirrors 18 and 20, passes through the polarization beam splitter 19, and enters the Fabry-Perot interferometer 21.
Therefore, the two split laser beams are finally combined into a single optical path and then enter the Fabry-Perot interferometer 21.

FIG. 2 is a graph showing the characteristics of the Fabry-Perot interferometer 21, in which the horizontal axis represents the optical frequency of the incident light and the vertical axis represents the intensity of the emitted light (the intensity of the transmitted light). As shown in the figure, the Fabry-Perot interferometer, the emitted light intensity at a certain optical frequency f _p is the peak decreases greatly before and after. Such peaks of the emitted light intensity appear at substantially constant optical frequency intervals, but FIG. 2 shows only one peak.

As described above, the optical frequencies f ₁ and f ₂ depend on the frequencies of the signals supplied to the acousto-optic devices 14 and 15, respectively. ₁ an optical frequency or optical frequency of the vicinity thereof as a value obtained by differentiating the intensity of transmitted light at the optical frequency becomes locally maximum and f _1, the value obtained by differentiating the intensity of transmitted light in optical frequency and locally minimal Such an optical frequency or an optical frequency in the vicinity thereof is f ₂ . In this specification, the optical frequency at which the value obtained by differentiating the transmitted light intensity with the optical frequency is locally maximum or minimum is referred to as “maximum change frequency”. In addition,
As described above, the term “local” means that the peak of the emitted light intensity appears at a substantially constant optical frequency interval, and the maximum change frequency exists at the optical frequencies before and after each peak. It is.

As described above, by selecting the optical frequencies f ₁ and f _{2 so} that the change in the intensity of the emitted light is the largest, the slight change in the optical frequency can be used to change the intensity of the emitted light from the Fabry-Perot interferometer. Can be captured with high sensitivity. The laser beam emitted from the Fabry-Perot interferometer 21 enters the interference filter 22. The interference filter reflects incident light of a certain range of optical frequencies and transmits another range of incident light. Therefore, in the present embodiment, f ₁
The light passes through with a light frequency near centered, light having a light frequency near about the f ₂ uses an interference filter 22 reflecting. Therefore, the laser beam having the optical frequency f ₁ passes through the interference filter 22 and passes through the photodetector 23.
The laser beam having an optical frequency of f ₂ is reflected by the interference filter 22 and detected by the photodetector 24. The photodetectors 23 and 24 convert the intensity of the incident light into an electric signal and output the electric signal. In FIG. 1, FIG.
Although the photodiode 67, the amplifier 68, the high-pass filter 69, and the oscilloscope 57 which are specifically shown in FIG. 1 are simply shown as the photodetectors 23 and 24, essentially the same ones can be used.

[0029] Figure 3, which shows the output signal of the photodetector 23 and 24, (a) the signal center frequency based on the laser beam f _1, (b) the center frequency of f ₂ laser It is a signal based on the beam. In FIG. 3, the output signal greatly changes due to a change in the output light intensity of the Fabry-Perot interferometer, and the change in the output light intensity is caused by the ultrasonic wave reflected on the surface of the subject. This is because the detection laser beam has undergone Doppler shift due to ultrasonic vibration of the surface of the subject. here,
Figure 3 t ₁ shown in (a) is a time from the irradiation of a laser beam for ultrasonic generation in the subject 1 to the laser beam of the optical frequency f ₁ is subjected to Doppler shift,
T ₂ shown in FIG. 3 (b) is a time from the irradiation of a laser beam for ultrasonic generation in the subject 1 to the laser beam of the optical frequency f ₂ is subjected to Doppler shift.

Therefore, for example, as shown in FIG. 4, a point G irradiated with a laser beam for generating an ultrasonic wave and a point O irradiated with a laser beam for ultrasonic observation having an optical frequency of f _1.
If the mutual positional relationship between the point O ₂ and the point O ₂ irradiated with the laser beam for ultrasonic observation whose optical frequency is f ₂ is known, the direction from the point G to the point O ₁ can be calculated by a simple calculation (this is sound velocity v _{x in} the x-axis direction) and sound velocity v in the direction from point G to point O ₂ (this is the y-axis direction).
You can find _y .

In the case of a steel plate manufactured by rolling, by examining how the sound speed differs between the longitudinal direction and the width direction when rolling, that is, by examining the anisotropy of the sound speed, the homogeneity of the product and various other materials are examined. You can know the characteristics of. At this time, using the laser ultrasonic apparatus of the present embodiment, for example, the sound velocity v _x is measured by matching the width direction when rolling to the x-axis direction, and the sound velocity v _y by matching the width direction to the y-axis. Can be measured.

In this embodiment, the laser beam emitted from one ultrasonic observation laser light source 11 is divided into two parts, and the optical frequency f of each laser beam is further divided.
_p is shifted by the acousto-optic elements 14 and 15 to the frequencies f ₁ and f ₂ that are optimal for observing the Doppler shift, and ultrasonic waves are generated using laser beams having two different optical frequencies f ₁ and f ₂ after the shift. Are observed using separate photodetectors. By this, even if the time when the two ultrasonic waves are observed are very close,
The time difference between the two can be obtained with high accuracy.

In this embodiment, two laser beams for ultrasonic observation are obtained by splitting a laser beam emitted from a single laser light source 11. Further, the two laser beams reflected by the subject 1 are detected using a single Fabry-Perot interferometer 21. Thus, the relatively expensive laser light source 1
1 and one Fabry-Perot interferometer 21, which is advantageous in terms of cost.

As another example of the inspection performed using the laser ultrasonic device of the present embodiment, the attenuation rate of the ultrasonic wave can be obtained. 5, in the case of performing the inspection point is irradiated with a laser beam for ultrasonic generator G, O ₁ point light frequency is irradiated with a laser beam for ultrasonic observation of f _1, and the optical frequency f ₂ in is a diagram showing the positional relationship between the point O ₂ for irradiating a laser beam for ultrasonic observation. As shown in FIG. 5, when the points G, O ₁ , and O ₂ are arranged so as to be on the same straight line (here, the x-axis) and an output signal as shown in FIG. The positions of points and points O ₁ and O ₂
The attenuation rate of the ultrasonic wave in this direction can be measured from the magnitude of the peak of the output signal at. In materials such as steel plates, the attenuation rate of ultrasonic waves is closely related to the grain size of crystal grains, and it is generally known that the attenuation rate increases as the grain size increases. The crystal grain size is an important factor that governs various physical properties depending on the material, and obtaining information on this is important in performing product inspection. According to the present embodiment, the attenuation rate of the subject can be efficiently measured by using two ultrasonic waves.

It should be noted that the present invention is not limited to the above embodiment, and various changes can be made within the scope of the gist. For example, in the above embodiment, two laser beams for ultrasonic observation are provided, and therefore, only one peak is shown in the characteristic diagram of the Fabry-Perot interferometer shown in FIG. However, in an actual Fabry-Perot interferometer, when the range of the horizontal axis (optical frequency) in FIG. 2 is expanded, the peak of the transmitted light intensity appears repeatedly at a constant optical frequency interval. Therefore, the number of optical frequencies at which the value obtained by differentiating the transmitted light intensity with respect to the optical frequency becomes the largest is not only two as shown in FIG. If a large number of ultrasonic observation laser beams having such an optical frequency are generated by the acousto-optic device, observation using three or more ultrasonic observation laser beams becomes possible. Even in that case, only one laser light source for ultrasonic observation and one Fabry-Perot interferometer may be used.

[0036]

As described above, according to the present invention,
After splitting a laser beam emitted from a single ultrasonic observation laser light source into a plurality of beams, the optical frequencies are different from each other, and the optical frequency of each converted laser beam is determined by the Fabry-Perot interferometer. Since the light frequency of each laser beam is converted so that the absolute value of the value obtained by differentiating the transmitted light intensity with respect to the light frequency in the light transmission characteristics becomes a value near the maximum so that the object is irradiated. Even when the reflected light from the subject is incident on a single Fabry-Perot interferometer and the Doppler shift of each reflected light is observed, each can be reliably identified. To provide a laser ultrasonic apparatus and a laser ultrasonic method capable of efficiently and surely examining the sound velocity and its anisotropy of ultrasonic waves and the attenuation rate of ultrasonic waves. Door can be.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing characteristics of a Fabry-Perot interferometer 21.

FIG. 3 is a diagram showing an output signal of a photodetector.

FIG. 4 irradiates a laser beam for generating an ultrasonic wave;
FIG. 5 is a diagram showing a positional relationship between two points for irradiating two ultrasonic observation laser beams.

FIG. 5 is a diagram showing a positional relationship between a point irradiated with a laser beam for generating an ultrasonic wave and a point irradiated with two laser beams for ultrasonic observation.

FIG. 6 is a diagram showing an example of a conventional laser ultrasonic device.

FIG. 7 is a diagram showing the result of measuring the transmitted light intensity (vertical axis) of a He—Ne laser beam by sweeping the resonator length (horizontal axis) of the Fabry-Perot interferometer.

FIG. 8 shows the transmitted light intensity (vertical axis) depending on the optical frequency (horizontal axis) when the resonator length of the Fabry-Perot interferometer is fixed.
FIG. 7 is a diagram showing how the color changes.

[Explanation of symbols]

 1,55 object 10,50 laser light source for ultrasonic wave generation 11,60 laser light source for ultrasonic observation 12,19,63 polarizing beam splitter (PBS) 13,16,17,20,53,54,62 mirror 14, Reference Signs List 15 acousto-optic element 18 half mirror 21, 66 Fabry-Perot interferometer 22 interference filter 23, 24, 56 photodetector 52 beam splitter 57 oscilloscope 64 quarter-wave plate 65 lens 67 photodiode 68 amplifier 69 high-pass filter

Claims (10)

[Claims] A first laser light source that emits a laser beam for generating an ultrasonic wave on the subject; a second laser light source that emits a laser beam for observing the ultrasonic wave propagated through the subject; A first branching unit that branches a laser beam emitted from the second laser light source into at least two laser beams, and an optical frequency of each laser beam branched into at least two by the first branching unit. An optical frequency converting means for converting each of the laser beams into a predetermined optical frequency different from each other, and irradiating each of the laser beams converted to the predetermined optical frequency to a predetermined position of the subject, and each laser reflected from the subject. Optical means for integrating the beam into a single optical path; and said laser beam integrated by said optical means into a single optical path. A Fabry-Perot interferometer to be emitted, a second branching unit that branches a laser beam output from the Fabry-Perot interferometer into respective laser beams according to an optical frequency, and a second branching unit. Light detecting means for irradiating each of the laser beams and detecting a change in the intensity thereof, wherein the predetermined optical frequency of each of the laser beams after passing through the optical frequency converting means is converted into the Fabry
A laser ultrasonic wave characterized in that the optical frequency (maximum change frequency) is such that the absolute value of the value obtained by differentiating the transmitted light intensity with respect to the optical frequency in the light transmission characteristics of the Perot interferometer is locally maximum, or near it. Inspection equipment. 2. In the case where there are two laser beams, the predetermined optical frequency is the adjacent maximum change frequency located before or after a single peak of the light transmission characteristic of the Fabry-Perot interferometer or in the vicinity thereof. In the case where the number of the laser beams is at least three, the predetermined optical frequency is a maximum change frequency located before or after a plurality of peaks of the light transmission characteristic of the Fabry-Perot interferometer or the vicinity thereof. Laser ultrasonic inspection equipment. 3. The laser ultrasonic inspection apparatus according to claim 1, wherein said optical frequency conversion means is an acousto-optic device. 4. The laser ultrasonic inspection according to claim 1, further comprising: means for obtaining sound speeds of ultrasonic waves in a plurality of directions of said subject based on an output of said light detecting means. apparatus. 5. The laser ultrasonic inspection apparatus according to claim 1, further comprising means for obtaining an ultrasonic attenuation rate based on an output of said light detecting means. 6. A step of irradiating an object with a laser beam emitted from a first laser light source to generate an ultrasonic wave, and a step of applying a laser beam for observing the ultrasonic wave propagated through the object to a second state. A step of emitting light from a laser light source and splitting the same into at least two laser beams; a step of converting the optical frequency of each of the at least two split laser beams into a different predetermined optical frequency; Irradiating each laser beam converted to a frequency to a predetermined position on the subject; integrating each laser beam reflected from the subject into a single optical path; and Injecting the laser beam integrated into the path into the Fabry-Perot interferometer; and transmitting the laser beam output from the Fabry-Perot interferometer to an optical frequency. Branching each laser beam according to a number, and irradiating each laser beam branched according to an optical frequency to a light detection unit, and detecting a change in intensity thereof. An optical frequency (the maximum change frequency) at which the absolute value of the value obtained by differentiating the transmitted light intensity with the optical frequency in the optical transmission characteristics of the Fabry-Perot interferometer is locally maximized with respect to the predetermined optical frequency of each laser beam. ) Or in the vicinity thereof. 7. When the number of the laser beams is two, the predetermined optical frequency is the adjacent maximum change frequency located before or after a single peak of the light transmission characteristic of the Fabry-Perot interferometer or in the vicinity thereof. In the case where the number of the laser beams is at least three, the predetermined optical frequency is a maximum change frequency located before or after a plurality of peaks of the light transmission characteristic of the Fabry-Perot interferometer or a vicinity thereof. The method according to claim 6, wherein the method is performed. 8. The step of converting the optical frequency of each of the at least two branched laser beams into a predetermined different optical frequency is performed using an acousto-optic element. 7. The laser ultrasonic inspection method according to 7. 9. The laser ultrasonic inspection method according to claim 6, wherein sound speeds of ultrasonic waves in a plurality of directions of the subject are measured based on an output of the light detecting means. 10. The laser ultrasonic inspection method according to claim 6, wherein an attenuation rate of an ultrasonic wave propagating through the subject is obtained based on an output of the light detecting means.