JPH1078415A - Method and device for noncontact and non-destructive material evaluation, and method and device for elastic wave excitation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic wave exciting method for exciting a bulk elastic wave foucused in the inside of a specimen and a non-contact and non-destructive method and device for evaluating defects and characteristics of material with high space resolution and in a non-contact and non-destructive state by using the bulk elastic wave. SOLUTION: A coherent parallel energy beam 1 and a focusing energy beam 2 different in frequencies are emitted from a laser beam light source 13, a specimen 3 is irradiated by overlapping them, and an interference fringe 5 is formed on the surface 4 thereof. The interference fringe 5 excites a bulk elastic wave 7 focusing toward the point 8 of the inside of the specimen 3. The specimen 3 is irradiated with probe light 10 from a laser beam light source 18a for detection while the specimen 3 is scanned with a specimen moving device 19a, and defects and characteristics of material of the specimen 3 can be evaluated by detecting and analyzing the reflection light 11 with a detection and analysis means. In addition, if an aspherical lens is used as a beam irradiation means, the bulk elastic wave can be focused without aberration on one point of the specimen 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for exciting a bulk acoustic wave converging from a surface of an object to a small area inside the object, and a method of using the elastic wave to change material properties inside the object. The present invention relates to a non-contact non-destructive material evaluation method for detecting and evaluating a material by contact non-destructive, and an apparatus therefor.

[0002]

2. Description of the Related Art Ultrasonic microscopes (SAM) and lasers using ultrasonic waves having a frequency of 50 to 100 MHz or more are used as a method for detecting minute defects that impair the strength and reliability of materials and structures, such as ceramic micro-cracks and IC package voids. Defect imaging using a scanning ultrasonic microscope (SLAM) is useful ([1] I, R, Smith, R, A, Harve).
y and D, J, Fathers, IEEE, Tr
an, Skinks and Ultrason, SU
−32 (1985) 274, [2] L, W, Kessse
lav, J, Acoustic, Soc, Am, 55 (19
74) 909), and evaluation by fringe generated when a crack is observed by SAM is known ([3] K,
Yamanaka and Y, Enomoto, J,
Appl, Phys, 53 (1982) 846).

In order to develop an ultrasonic microscope that does not use a coupler, the laser ultrasonic method is extended to scan a laser beam at the phase velocity of an ultrasonic wave, so that a large-amplitude single-mode surface wave can be obtained. Phase velocity scanning (P
The VS) method has been proposed. ([4] X, Ymanak
a, Y, Nagata and J, Koda; App
1, Phys, Latt, 58 (1991) 1591;
[5] K, Ymanaka, Y, Nagata and
T, Koda; Review of Progress
in Quantitative Non est
activeEvaluation, ads, D,
O, Thompson and D, E, Chimen
ti (Plenum, New York, 1992) V
ol, 11, P, 633). Laser ultrasonic wave generation method by thermoelastic effect used in nondestructive inspection ([6] D,
A, Hutchine; Physical Acous
tics, ads, W, P, Mason and R,
N, Thuraton (Academic, San D
iego, 1988) Vol, XVIII, P, 21) generally produces only ultrasound with small amplitude, but the above method solves this.

When the frequency is 100 MHz or higher, a scanning interference fringe (SIF) system for scanning an interference fringe at a phase speed instead of a single beam has been developed ([7] H, Nisi).
no, Y, Tsukahara, Y, Nagata,
T, Koda and K, Yamanaka; App
1, Phys, Lett, 62 (1993) 2036;
[8] K, Yamanaka, O, V, Koloso
v, Y, Nagata, T, Koda, H, Nishi
no and Y, Tsukahara; J, App
1, Phys, 74 (1993) 6511, [9] H,
Nishino, Y, Tsukahara, Y, Nag
ata, T, Koda and K, Yamanak
a; Tpn, Appl, Phys, 33 (1994) 3
26. reference). In addition, there is an extension of the scanning interference fringe (SIF) method to the excitation of bulk ultrasonic waves having directivity (Heisei 4).
Patent Application No. 355522). In this bulk ultrasonic excitation method, the phase velocity scanning method is particularly useful in this method, and it is possible to control the radiation direction of the generated elastic wave, and also to reduce the energy density on the sample surface, and damage the sample. There is an advantage that it is difficult to occur and an elastic wave of an arbitrary frequency can be excited, and independent control of frequency and directivity is possible.

As a method of exciting a surface acoustic wave to the surface of a sample, one of the two laser beams is passed through a conical (AXICON) lens, and the frequency of either laser beam is slightly reduced. Then, the two laser beams interfere with each other on the sample surface, form equidistant interference fringes moving toward the center of the concentric circle, and excite a surface acoustic wave focused on one point on the sample surface. It is described in the literature. (United States Pat
ent, (Patent Number 4,541,
280 Date of Patent Sep. 1
7, 1985) "EFFICIENT LASER G
ENERATION OF SURFACEACOUS
TIC WAVES ”). However, in this case, only excitation of surface acoustic waves propagating only on the surface of the sample is assumed, and the evaluation of defects in the material and the inspection for flaws cannot be performed.

[0006]

In the above-mentioned prior arts, the inspection with a high resolution cannot be performed because the inspection of the object is performed using mostly parallel beams. In addition, there is a problem that even when a focused beam is used, only surface acoustic waves that are focused only on the surface of the subject can be excited. This means that it is difficult to achieve high spatial resolution particularly when performing nondestructive inspection of the inside of the subject using a parallel beam. It is necessary to use a laser beam with a certain spot size to form interference fringes on the surface of the subject. However, there is a problem that a high spatial resolution cannot be obtained even if detection is performed by using the method, and a minute defect or the like inside the material cannot be accurately detected.

SUMMARY OF THE INVENTION The present invention solves the above problems, and provides a focused elastic wave excitation method and apparatus capable of focusing and exciting an elastic wave in a minute area inside a subject. To provide a non-contact non-destructive material evaluation method and apparatus capable of precisely evaluating a defect, a structure, a film thickness, and the like of a minute region inside a subject by changing a depth position at which an elastic wave is focused at a high speed. Further, an object of the present invention is to provide an elastic wave excitation device capable of exciting a bulk elastic wave focused on one point of a subject and measuring the inside of the subject with a high spatial resolution of about the wavelength of an ultrasonic wave. .

[0008]

According to the present invention, in order to achieve the above object, a coherent parallel energy beam and a focused energy beam having different frequencies from each other are irradiated onto a surface portion of an object in a superimposed manner. Generates an interference fringe that travels concentrically inward at a speed that is faster than the natural sound velocity of the subject, and the thermal action of the interference fringes causes the same spacing as the interference fringes on the surface portion of the subject. An elastic wave that excites an elastic wave that converges toward a minute area inside the subject, which is determined by the inherent sound velocity of the subject and the traveling speed of the interference fringes, according to the strain distribution. It is characterized by an excitation method. Also, a coherent parallel energy beam and a focused energy beam of different frequencies are superimposed on the surface of the subject and irradiated concentrically inward at a traveling speed higher than the inherent sound velocity of the subject. Generating a strain distribution having the same interval as the interference fringes on the surface of the subject due to the thermal action of the interference fringes, and according to the strain distribution, a characteristic sound of the subject. While exciting an elastic wave converging toward a minute region inside the subject determined by a velocity and a traveling speed of the interference fringes, the elastic wave reflected from or passed through the minute region to reach the front or back surface of the subject. The wave is detected in a non-contact and non-destructive manner by a probe light, and the elasticity is sequentially obtained by scanning the subject relatively to the parallel energy beam and the focused energy beam or the probe light. Based on the detection result, and wherein the non-contact non-destructive material evaluation method of analyzing material characteristics of the subject. Further, a non-contact non-destructive material evaluation method for detecting the elastic wave using the probe light by an optical knife edge method, a heterodyne interferometry, a Fabry-Perot interferometry, a homodyne interferometry, or a method using an electromagnetic ultrasonic transducer is characterized. I do.

A forming means for forming a parallel energy beam having a predetermined frequency and a focused energy beam having a different frequency from the parallel energy beam; and causing the parallel energy beam and the focused energy beam to interfere with each other on a surface portion of the subject. At least irradiate,
Beam irradiating means for exciting an elastic wave directed to a minute region inside the subject; and detecting the elastic wave reaching the front or back surface of the subject from the minute region in a non-contact and non-destructive manner by using probe light. A non-contact non-destructive material evaluation apparatus including a detection / analysis unit for analyzing a material property of a specimen and a scanning unit for relatively scanning the specimen with respect to the parallel energy beam and the focused energy beam or the probe light. Make up. In addition, a non-contact non-destructive material evaluation apparatus is provided in which the irradiation means is provided with an adjusting means for making the energy densities of the parallel energy beam and the focused energy beam the same in order to completely interfere with each other.

Further, a parallel energy beam having a wavelength λ and a focused energy beam having a frequency difference of f and a focused energy beam are superposed on the surface of the subject having a natural sound velocity of V, and the focused energy beam is irradiated with the focused energy beam. F · (λ ² +2
By setting the focal point at a depth (a) that satisfies the relational expression of λa) ^1/2 > V, an interference fringe traveling inward concentrically is generated on the surface of the subject, and the thermal interference of this interference fringe is generated. An elasticity that forms a strain having the same distribution as the interference fringes on the surface portion of the subject by the action, and excites an elastic wave focused toward a specific minute region in the deep part of the subject according to the strain distribution. It features a wave excitation method. Further, in order to change the depth direction position of the minute region inside the subject where the focused elastic wave excited toward the inside of the subject is focused, the focal position of the focused energy beam applied to the subject surface is changed. The method is characterized by an elastic wave excitation method that changes along the depth direction of the elastic wave. Further, in order to change the depth direction position of the minute region inside the subject where the focused elastic wave excited toward the inside of the subject is focused, the frequency difference between the focused energy beam and the parallel energy beam applied to the subject surface is changed. It is characterized by an elastic wave excitation method for changing f. In addition, the focused elastic wave excited toward the inside of the subject irradiates the subject surface to change the position of the minute region inside the subject that is focused inside the subject along a direction parallel to the subject surface. An elastic wave excitation method for changing the incident angle of the parallel energy beam is characterized.

A parallel laser beam and a focused laser beam having a frequency difference f with respect to the parallel laser beam are formed at a wavelength λ. Laser irradiating means for irradiating the focused laser beam with the laser beam. The laser irradiating means focuses the focused laser beam on the surface of the object with respect to a depth satisfying a relational expression of f · (λ ² + 2λa) ^1/2 > V The laser irradiation means is positioned at (a) to excite and focus an elastic wave in a minute area inside the subject, and the laser irradiating means moves the focal position a in a depth direction in a path through which the focused laser beam passes. Acoustic wave excitation device having means for changing the position in the depth direction of a minute region in the subject on which the elastic wave is focused by having an optical system consisting of a lens or a set of reflectors changing along And it constitutes. Further, a parallel laser beam and a focused laser beam having a frequency difference f with respect to the parallel laser beam are formed at a wavelength λ, and the parallel laser beam and the focused laser beam have a natural sound velocity of V.
Laser irradiation means for irradiating the surface portion of the object with interference with each other, and the laser irradiation means focuses the focused laser beam on the surface of the object by f · (λ ² + 2λa)
^The laser irradiation means is located at a depth (a) satisfying the relational expression of ^1/2 > V to excite and focus an elastic wave in a minute area inside the subject, and the laser irradiation means includes a focused laser beam and The elastic wave excitation device is configured to change the position in the depth direction of a minute region inside the subject where the elastic wave is focused by means for changing the relative frequency difference f of the parallel laser beams. In addition, the parallel laser beam and the focused laser beam interfere with each other to irradiate the surface portion of the object to excite an elastic wave focused toward the inside of the object, and the frequency difference between the two laser beams is temporally changed. Has a laser irradiation means that changes in the direction, and observes the displacement of the surface of the subject when the elastic wave excited in the subject passes or reflects inside the subject and propagates again to the surface of the subject, and converts the signal into an electric signal. It has a receiving means for converting, and an analyzing means for frequency-analyzing an electric signal representing the surface displacement outputted from the receiving means, and evaluates the structure and elasticity at different depth positions in the subject continuously or stepwise. This constitutes an elastic wave excitation device that performs the following.

Further, a coherent parallel energy beam and a focused energy beam having different frequencies are superimposed on the surface of the subject and irradiated concentrically at a traveling speed higher than the natural sound speed of the subject. Beam irradiating means for generating an interference fringe that travels toward the surface, and forms a strain distribution having the same interval as the interference fringe on the surface portion of the subject due to the thermal action of the interference fringe. An elastic wave excitation device that excites an elastic wave converging toward a minute region inside the subject, which is determined by the inherent sound speed of the subject and the traveling speed of the interference fringes accordingly, wherein the beam irradiation unit includes: An elastic wave excitation device comprising a focusing lens formed of an aspherical lens, wherein the focused energy beam is shaped so that the elastic wave can be substantially point-focused toward a minute area inside the non-sample. It is intended to formed. Further, the aspheric lens may be such that an extension line of the incident direction of the component of the focused energy beam at a position away from the point c at the center of the concentric circle on the surface of the subject by x along the surface of the subject is c. Depth a that satisfies at least the following formula from just below the point
And the point of the elastic wave is focused on a minute region located at a depth _az from the point c of the subject made of an isotropic material. 17. An elastic wave excitation device according to item 17. x = a _z tan [sin ^-1 (V x / λ f (a ² +
x ^{2) 1/2)]} where, f is the frequency difference between the parallel energy beam and focused energy beam, lambda is the wavelength of the focused energy beam, V is a specific sound velocity of the subject. Further, the aspherical lens has an extension line in the incident direction of the component of the focused energy beam at a point R at a position R away from the point c at the center of the concentric circle on the surface of the subject by x along the surface of the subject. A depth a that satisfies at least the following equation from immediately below the point c.
, And the point is focused on a point Q in the minute region located at a depth _az from the point c of the subject made of an anisotropic material. An elastic wave excitation device according to claim 17 is characterized. x = a _z tan [sin ^-1 (V ′ · x / λ · f · (a ²
+ X ² ) ^1/2 )] where f is the frequency difference between the parallel energy beam and the focused energy beam, λ is the wavelength of the focused energy beam, and V ′ is the direction connecting the R point and the Q point of the subject. Sound velocity.

When it is assumed that an elastic wave having a frequency f is generated at one point inside the object, the phase distribution of the elastic wave propagating on the surface of the object is estimated, and whether the phase distribution is equal to the phase distribution of the elastic wave on the surface of the object. Alternatively, in order to generate an approximated strain distribution, a parallel energy beam and a focused energy beam having coherence and having a frequency difference f are superimposed on the surface of the object to irradiate the interference fringes traveling inward. Elasticity that generates and forms a distortion having the same distribution as the phase distribution on the surface portion of the subject due to the thermal action of the interference fringes, and excites an elastic wave focused toward the one point inside the subject. It features a wave excitation method. Further, the focal position of the focused energy beam applied to the surface of the object is changed in order to change the position in the depth direction of a point at which the focused elastic wave excited toward the inside of the object is focused inside the object. The method is characterized by an elastic wave excitation method that changes along the vertical direction. Further, in order to change the position in the depth direction of one point where the focused elastic wave excited toward the inside of the subject is focused inside the subject, the frequency difference f between the focused energy beam and the parallel energy beam applied to the subject surface is changed. Is characterized by an elastic wave excitation method for changing Further, in order to change a point at which the focused elastic wave excited toward the inside of the subject is focused inside the subject along a direction parallel to the subject surface, the incident angle of the parallel energy beam applied to the subject surface is changed. It is characterized by an elastic wave excitation method to be changed.

According to the first aspect of the present invention, for example, two coherent laser beams are irradiated to an intended portion on a subject as a parallel energy beam and a focused energy beam having a slightly different frequency from the parallel energy beam. As a result, an interference fringe that is scanned concentrically is generated, and a strain distribution having the same interval as the interference fringe is formed on the surface of the subject by the action of the interference fringe. This strain distribution excites a bulk acoustic wave that converges toward a minute region in the subject determined by the natural sound velocity of the elastic wave propagating through the subject and the traveling speed of the interference fringes. In general, a solid has two waves, shear wave velocity and longitudinal wave velocity. Here, the intrinsic sound velocity refers to the transverse sound velocity when the bulk acoustic wave to be excited inside the subject is the transverse wave, and the longitudinal sound velocity Denotes longitudinal wave sound velocity. Furthermore, non-contact and non-destructive detection of bulk acoustic waves emitted from the subject by the probe light radiated toward the front or back surface of the subject, among the subject or the coherent energy beam and the probe light By scanning at least one, the non-contact detection point is moved, and a detection signal which is extremely sensitive to a defect or a change in material near the focus of the ultrasonic wave excited inside the subject can be obtained. Further, according to the second aspect of the present invention, by changing the focal position of the focused energy beam or the frequency difference between the parallel energy beam and the focused energy beam, the depth direction of the minute region inside the subject where the bulk acoustic wave is focused is changed. The position can be adjusted continuously or stepwise. Thereby, the internal flaw detection can be realized at high speed. Furthermore, according to the third aspect of the present invention, even when the subject has elastic anisotropy, it is assumed that an elastic wave is generated at one point inside the subject, and the calculation is performed in consideration of the anisotropy. The phase distribution of the elastic wave on the surface of the subject is estimated. In addition, a method of irradiating a wavefront generated by a sound wave generated from a specific point in an anisotropic medium on the surface, or a method of irradiating a laser beam having a phase distribution with a shape other than concentric circles on the surface of an object is known in elasticity and optics, Not discussed here. By generating an interference fringe corresponding to this phase distribution, it is possible to excite a bulk acoustic wave converging on the one point. That is, even if the material has anisotropy, by generating interference fringes corresponding to the material, the bulk acoustic wave can be freely directed to a desired depth position.
As described above, the present invention can excite a bulk acoustic wave that focuses on a minute area inside a subject at a pinpoint, and can freely change the focus position of the bulk elastic wave, which is a practical problem, at a high speed. Originally, material inspection with high spatial resolution can be performed in a non-contact and non-destructive manner.

In the above-described apparatus, the use of an aspherical lens designed under specific conditions as a beam irradiation means enables focusing to one point at a pinpoint, thereby further improving the accuracy of material evaluation.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-contact non-destructive material evaluation method and apparatus, an elastic wave excitation method and a focused laser elastic wave excitation apparatus according to the present invention will be described below in detail with reference to the drawings. First,
A method of exciting a converging bulk acoustic wave will be described with reference to FIGS. As shown in FIGS. 1A and 1B, a parallel energy beam 1 having an angular frequency ω and a focused energy beam 2 having an angular frequency ω ′ are radiated from, for example, a laser beam source, and as shown in FIG. Is irradiated onto the surface portion of the subject 3 in a perpendicular and overlapping manner, for example. Parallel energy beam 1 and focused energy beam 2
Each line schematically represents a wavefront having the same phase. As shown in FIG. 2, the parallel energy beam 1 and the focused energy beam 2 interfere with each other on the surface 4 of the subject 3. Concentric interference fringes 5 as shown in FIG. 3 are generated. Bright and dark portions of the interference fringe 5, for example, 5a
The amount of thermal energy applied to the subject 3 differs between the light portion of the light beam 5b and the dark portion of the light beam 5b. This causes a difference in the amount of expansion, and a mechanical distortion occurs along the concentric circle of the interference fringe 5. Note that the interference fringes 5 progress from the outer periphery to the inner center, and in the case of an isotropic material, the pattern becomes larger as it approaches the center. As shown in FIG. 4, a region 6 (schematically shown in the figure) that has been heated and expanded by the energy beam is generated on the surface 4 of the subject 3, and a mechanical strain distribution is generated, and from the surface toward the inside. The bulk acoustic wave 7 oscillating at the angular frequency | ω′−ω | is excited. This bulk acoustic wave 7 is
This is an elastic wave that is focused toward the focusing point 8 which is an internal minute region.

FIG. 5 schematically shows the above operation. In the figure, the surface 4 of the subject 3 is set to y = 0 and the surface 4
Is the distance from the focal point 8 'of the focused energy beam to
And As described above, the bulk acoustic wave 7 traveling from the surface 4 toward the inside of the subject 3 is excited and focused toward the focusing point 8. Assuming that x = 0 on the surface 4 where y = 0 and just above the focal point 8, a bulk acoustic wave 7 with a radiation angle φ is directed from each x point to the focal point 8 inside the subject 3. Irradiated. As described above, when the angular frequencies of the parallel energy beam 1 and the focused energy beam 2 are ω and ω ′, and the wavelength of the focused energy beam is λ, the interval b between the interference fringes 5 is expressed by the following equation (1).

◎

(Equation 1)

Since the interference fringe 5 has a frequency of f = | ω'-ω | / 2π, the scanning speed (traveling speed) v from the outside to the center of the interference fringe 5 at x is expressed by the following equation (2).

◎

(Equation 2)

Next, assuming that the natural sound velocity of the subject 3 itself is V, v> V between the scanning speed v of the interference fringe 5 shown in the equation (2) and the aforementioned natural sound velocity V. When the condition (1) is satisfied, the bulk acoustic wave 7 traveling toward the inside of the subject 3 is emitted. Radiation angle φ at each x point of this bulk acoustic wave 7
Is obtained from the following equation (3) according to Snell's law.

◎

(Equation 3)

FIG. 6 shows a bulk acoustic wave 7 focusing on a focal point 8 simulated using the above equation.
The simulation conditions are as follows: energy beam wavelength λ
= 532nm laser beam, f = | ω'-ω |
/ 2π = 100 MHz modulation is performed. Where ω ′> ω
In the opposite case, radially diffused elastic waves are excited. The inherent sound velocity V in the subject 3 is set to 5
000 m / s. The focal point 8 ′ of the focused laser beam is located a = 10 cm below the surface of the subject 3. FIG.
Is a unit expressed in meters, and in the case of an interference fringe 5 having a beam radius of about 0.6 [mm] as shown in the figure, a width of about 150 [μm] at a focus position of a depth of about 1 [mm] Shows that the bulk acoustic waves are focused. In this calculation, a spherical wave having a perfectly spherical phase surface is assumed as the focused laser beam. However, as described later, an aspheric lens is used as a lens that converts a parallel beam from a laser light source into a focused beam. For example, it is possible to excite bulk ultrasonic waves that are almost completely focused on a minute area at one point. Even if the beam is not a perfect parallel laser beam but is formed by a lens having a long focal length to some extent, a focused bulk acoustic wave can be excited.

Further, if a focused laser beam and a parallel laser beam are applied to the surface of the subject, it is not always possible to sufficiently concentrate the bulk acoustic waves inside the subject. As shown in FIG. 7, it is necessary that the focal point O of the focused energy beam be located at a certain depth or more. When a wave is radiated from a finite and parallel oscillating surface and is focused at a certain position (focal point), the convergence can be approximately evaluated by how many phases of the wave in the oscillating surface are included. It is assumed that the focal point O of the focused energy beam having the wavelength λ is located at the position of the depth a from the subject surface, and the parallel energy beam is perpendicularly incident on the subject surface. Let f be the frequency difference between the focused energy beam and the parallel energy beam,
Assuming that the phase change of the strain wave in the oscillation plane where sufficient convergence is obtained for the excited elastic wave is at least one cycle, FIG.
As shown in the figure, the average phase velocity of the wavefront at the distance from the surface position directly above the point O to the position P of one cycle is f · (λ ² +
2λa) ^1/2 . When the phase velocity is higher than the inherent sound velocity V of the subject material, the elastic wave can enter the subject with sufficient convergence and be focused.
Elastic waves in general isotropic solid materials include two types of longitudinal waves and transverse waves, each having a different natural sound velocity.
V used for (λ ² + 2λa) ^1/2 > V is used by substituting according to the type of elastic wave to be focused.

By changing the depth a of the focus of the focused energy beam from the surface of the subject or the frequency difference f between the focused energy beam and the parallel energy beam, the focusing position of the elastic wave excited inside the subject is changed. You can do it. Table 1 below shows changes in the focal depth of the elastic wave excited when the focal depth (a) of the focused energy beam is changed. It is assumed that the sound velocity V of the subject is 3000 m / s and the frequency difference f is 100 MHz. As shown in Table 1, as the focal depth a of the focused energy beam increases, the focal depth of the elastic wave excited inside the subject increases accordingly. FIG. 8 illustrates the above.
That is, when the focal position of the focused energy beam is shallow, such as A, the focused position of the excited elastic wave comes to point A '. On the other hand, when the focal position of the focused energy beam is at point B, which is deeper than point A, the focused position of the elastic wave is excited at point B 'shown, which is deeper than point A'. As described above, the focal position of the elastic wave can be freely changed by changing the focal depth a of the focused energy beam.

◎

[Table 1]

As described above, in order to move the focus position of the elastic wave along the depth direction (vertical direction) of the subject, the focal depth of the focused energy beam may be changed. As shown in FIG. 9, the converging lens 26 of the means for forming a focused energy beam and the subject 3 may be moved mechanically. As a specific method, the focusing lens 26 may be moved in the direction of the arrow by the lens moving device 26a as shown in the drawing, or the subject 3 may be moved by the subject moving device 19a. In this case, these moving distances must be moved by several tens times the moving distance of the focal depth. However, if a focal length changing mechanism generally called a zoom lens is used, the focal position can be significantly changed by moving the lens over a very short distance, and high-speed multipoint measurement in the depth direction becomes possible.

Next, by changing the frequency difference f,
It is possible to change the focusing depth of the excited elastic wave. Table 2 shows the change in the focal depth of the elastic wave excited when the frequency difference f is changed when the sound velocity of the subject is 3000 m / s and the focal depth a of the focused energy beam is 10 cm.

◎

[Table 2]

As shown in FIG. 10, the frequency f can be changed, for example, by using an acousto-optic device (AO) introduced to create a frequency difference f between the parallel energy beam and the focused energy beam.
This can be achieved by changing the frequency of the electric signal input to the element. For example, if the frequency difference between the parallel energy beam and the focused energy beam is continuously changed during a single irradiation of the energy beam by using a chirp signal for the acousto-optic element, the elasticity focused to different depths can be obtained. The waves are excited at once. Furthermore, the displacement generated by the excited elastic wave on the surface of the subject is observed by, for example, an optical means, and the obtained surface displacement signal is subjected to frequency analysis to obtain a result reflecting the elastic characteristic of the subject. Can be done. That is, FIG. 11 (a) is a diagram showing a state where the focusing depth by a change in the frequency difference f is changed, shows the case where a defect occurs in the focusing depth of the location when the frequency difference f ₁ is there.
FIG. 11B shows the displacement frequency on the horizontal axis and the intensity reflecting the elasticity of the subject on the vertical axis. Since the displacement generated on the surface of the subject by the elastic wave from the defective part is different from the displacement generated on the surface of the subject from the part without the defect, the displacement is observed inside the subject by observing the displacement by optical means. The presence and depth of the generated defect can be detected by the frequency analysis shown in FIG.

Further, as shown in FIG. 12, the focusing position of the bulk acoustic wave inside the subject can be changed along the horizontal direction by causing the parallel energy beam to enter the subject surface at a certain inclination angle. According to this, the focus position or observation point of the elastic wave can be changed without moving the subject or the energy beam irradiation means. As shown in FIG. 13, when the area where interference fringes can be formed on the surface of the subject is narrow due to the surface unevenness, the advantage that the focusing position can be changed in the horizontal direction only by changing the incident angle of the parallel energy beam. There is.

Next, a non-contact non-destructive material evaluation method according to the present invention will be schematically described with reference to FIG. The bulk acoustic wave 7 that has passed through the minute region reaches the back side of the subject 3. When the back surface is irradiated with the probe light 10 from the laser light source 9, the reflected light 11 corresponding to the minute deformation of the back surface caused by the bulk acoustic wave 7 is reflected. This is detected and analyzed by various detection / analysis means 12 to be described later to analyze the material characteristics of the subject 3 and to detect anomalies such as material defects existing inside the subject 3 in a non-contact and non-destructive manner. Can be. Note that the probe light 10 may be applied to the front surface instead of the back surface to detect bulk ultrasonic waves reflected from a minute region.

Next, a non-contact non-destructive material evaluation apparatus according to the present invention will be described. FIG. 15 is a block diagram showing the overall configuration of the present apparatus. As shown in FIG.
The laser beam from 3 is converted into a parallel energy beam 1 having an angular frequency ω by a parallel energy beam forming means 15 and a focused energy beam forming means 16 via an optical system 14.
And a focused energy beam 2 having an angular frequency ω ′.
These parallel and focused energy beams 1 and 2 are irradiated on the surface 4 of the subject 3 via the beam irradiation means 17. As described above, the subject 3 generates the bulk acoustic wave 7 that is focused on the focusing point 8. On the other hand, the probe light 10 is emitted from the probe light forming means 18 and irradiates the subject 3. The reflected light 11 from the subject 3 is input to the detecting / analyzing means 12 for detecting and analyzing the material properties as described above, and predetermined detection and analysis are performed. The subject 3
Is provided with a scanning means 19 for moving it in the x and y axis directions. By appropriately moving the subject 3 by the scanning means 19, all parts of the subject 3 can be inspected. The beam irradiation means 17 is provided with an adjustment means 20 for making the energy densities of the parallel energy beam 1 and the focused energy beam 2 equal to each other so as to completely interfere with each other. With the above configuration, it is possible to excite an elastic wave focused on a minute area inside the subject 3 and to perform material evaluation for detecting and analyzing the characteristics of the material in a non-contact and non-destructive manner using the bulk elastic wave. be able to.

FIG. 16 is a block diagram showing a specific example of a non-contact non-destructive material evaluation apparatus according to the present invention. The laser beam 21 emitted from the laser beam light source 13 is split by the half mirror 22 into two laser beams 21a and 21b. The laser beam 21a is adjusted by the adjusting means 2 described above.
0, a parallel energy beam forming means 15 and a beam irradiating means 17 via a beam diameter adjusting mechanism 20a.
The beam becomes a parallel energy beam 1 via a beam splitter 23 which is one of them, and is irradiated on the subject 3. On the other hand, the laser beam 21b is frequency-modulated by a modulating element (AO element) M connected to the broadband signal generator S via a mirror 24, and is a mirror 25 which is one of the focused energy beam forming means 16 and the beam irradiating means 17. The focused energy beam 2 is irradiated to the surface 4 of the subject 3 via the condenser lens 26 and the beam splitter 23. As described above, the bulk acoustic waves 7 converged on the focal point 8 in the subject 3
Occurs. As shown in the figure, the subject 3 is provided with a subject moving device 19a, which is one of the scanning means 19 for scanning the subject 3 in the x direction, for example. Further, the focal point 8 can be moved in the vertical direction by changing the frequency of the control signal output from the wideband signal generator S.

On the other hand, the probe light 10 emitted from the detection laser beam light source 18a, which is one of the probe light forming means 18, is applied to the subject 3 via the condenser lens 27. The reflected light 11 is detected and analyzed by a knife edge method detection / analysis means 12a based on the principle of the knife edge method, which is an example of the detection / analysis means 12. The knife edge method detection / analysis means 12a includes a condenser lens 28, a knife edge 29, a photodiode 30, an oscilloscope 31, and the like. The reflected light 11 from the subject 3 slightly changes its reflecting direction due to the inclination caused by the vibration of the surface of the subject. This makes it possible to detect a change in the reflected wave 11 due to the unevenness of the surface of the subject according to the bulk acoustic wave, and to accurately measure the intensity of the bulk acoustic wave 7. Note that the oscilloscope 31 and the subject moving device 19a are
It is connected to. The computer C performs an analysis operation on material defects and material characteristics.

Next, the embodiment shown in FIG. 16 will be described. Subject 3
The beam radius on the surface 4 is about 0.5 [mm]. The test object 3 uses a copper plate having a thickness of 1 [mm].
In this case, the natural sound velocity (longitudinal wave) of copper is about 4700 m / s
It is. A completely polarized laser beam having a wavelength of 532 [nm] is converted to a second light of a Q-switched Nd: YAG pulse laser.
Oscillation was performed using harmonics, and the pulse width was set to 50 nsec. The beam was split into two paths by a beam splitter, and one of them was subjected to frequency modulation of the laser beam 21b by 100 MHz by an acousto-optic element M. In order for the two laser beams to completely interfere with each other, the energy densities of the parallel energy beam 1 and the focused energy beam 2 on the surface of the subject are adjusted to the same using the beam diameter adjusting mechanism 20a or the like. FIG. 17 shows the result of evaluating the convergence of the excited bulk acoustic waves. The x-coordinate is taken parallel to the surface of the subject, and only the detection and analysis means is moved, and the vertical axis indicates the relative intensity of bulk acoustic waves. As shown in FIG. 17, it was detected by the knife edge method that the bulk acoustic wave was focused and reached the back surface immediately below the focusing point 8.

In the above embodiment, the knife edge method detecting / analyzing means 12a has been described as the detecting / analyzing means 12, but other than the above, the heterodyne interferometry, Fabry-Perot interferometry, homodyne interferometry, and electromagnetic ultrasonic transducer may be used. Detection and analysis means are employed.

FIG. 18 shows the principle configuration of the heterodyne interferometry detection / analysis means 12b. Laser light source 3
3, light having a frequency F is oscillated, and is split into two by a half mirror 34, one of which is modulated to a frequency of F + f by an AO element 32, which is a frequency modulation element, to a displacement portion 35 of the subject 3. Irradiated. The other light passes through the half mirror 34. The transmitted light and the light reflected from the displacement portion 35 are combined into one light flux by the half mirror 36,
Since the frequencies are F and F + f, interference occurs. For this reason,
A "beat" occurs. The light intensity is converted into an electric signal by the photodiode 37 and can be observed by the oscilloscope 38. By the way, assuming that the sample surface is raised from its original height by one-fourth wavelength of the laser beam due to its vibration, half of the beat phase generated by the interference between the laser beam and the laser beam that does not pass through the other surface. That is, it is shifted by the wavelength. Since the beat signal itself is a signal having a frequency as low as the modulation frequency, the change in phase can be easily observed with the oscilloscope 38.
As described above, this method makes it possible to measure the phase change of the beat and observe a very small displacement of about the wavelength of light on the surface.

FIG. 19 shows the Fabry-Perot interferometry detection / analysis means 12c. This uses a Fabry-Perot interferometer and uses translucent mirrors 39 and 40 that extract and output light having a specific frequency (wavelength). When the light of frequency F emitted from the laser light source 41 strikes the displacement portion 42 vibrating at the frequency f of the subject 3, the reflected light emits a wave of frequency F 'different from the frequency F due to the Doppler effect. . The Fabry-Perot interferometer has a frequency other than F, for example.
By disposing the mirrors 39 and 40 so as to extract only the light having the frequency F ', the light having the frequency F'
3 and is converted into an electric signal. By observing this with the oscilloscope 44, it is possible to observe the wave generated in the subject 3. The description of the method using the homodyne interferometry and the electromagnetic ultrasonic transducer is omitted from the description, but is described in a publicly known document and is not described here.

In the above description, the case where the interference fringes 5 whose intervals change continuously as shown in FIG. 3 has been described, but this has a perfectly spherical phase surface as the focused energy beam 2. This is because a spherical wave was adopted. If a focused energy beam having a conical phase is adopted using a conical lens, for example, concentric interference fringes 5 'at equal intervals are formed as shown in FIG. However,
Assuming that the interval between interference fringes is h and f = (ω′−ω) 2t, a relationship of V <f · h is required. (As shown in FIG. 21, the bulk acoustic wave 7 is focused on a vertical linear focusing position 8a in accordance with the strain distribution generated on the surface 4 of the subject 3 due to the interference fringes 5 '. As a result, a wide range is obtained. Inspection of the material characteristics is performed in the vertical direction at a time, so that the efficiency of the material evaluation man-hour can be improved, and of course, interference fringes having other shapes can be formed by changing the shape of the focused energy beam. If a focused energy beam having a cylindrical phase surface is used, a bulk acoustic wave can be focused on a horizontal straight line.

Further, in the case of anisotropic materials, the natural sound velocity varies depending on the direction and the incident angle, and the pattern of interference fringes necessary for the excited elastic wave to be focused inside the subject is not concentric, but the focused energy beam Alternatively, it is possible to excite a desired bulk acoustic wave by distorting the parallel energy beam. That is, in this case, as shown in FIG. 22, a deformed phase distribution is formed on the surface of the subject by the elastic wave radiated from the point S inside the anisotropic subject. Therefore, in the case of an anisotropic material, it is assumed that an elastic wave having a frequency f is generated at one point (point S) inside the subject, and an elastic wave having a phase distribution as shown in FIG. Presumed to have been propagated. The surface area of the subject is irradiated with a parallel energy beam and a focused energy beam having a coherent and frequency difference from each other to generate a strain distribution equal to or approximate to the phase distribution of the elastic wave, from the periphery to the inside. An interference fringe traveling toward the target is generated, and a distortion having the same phase distribution as the above-mentioned phase distribution can be formed on the surface of the subject by the thermal action of the interference fringes. As a result, a bulk acoustic wave focused toward the point S inside the subject can be excited. FIG. 23 is a reference diagram showing another example of a surface phase distribution having elastic anisotropy.

Next, an embodiment in which an aspheric lens is used as the beam irradiation means will be described with reference to FIGS. In the above embodiment, since a spherical lens is used as the beam irradiating means, the focused bulk ultrasonic waves excited by the spherical lens are not completely focused and converge at one point with some aberration as shown in FIG. . When measuring the inside of a subject with a high spatial resolution of about the wavelength of an ultrasonic wave, it is sometimes necessary to achieve almost perfect point focusing. Therefore, in this embodiment, the phase distribution of the focused beam on the surface of the subject is adjusted by using an aspherical lens as a beam irradiation means instead of the spherical lens, thereby achieving perfect point focusing of the excited elastic wave.

FIG. 24 shows the principle of excitation of a point-focused bulk ultrasonic wave. The illustrated point C of the subject 3 ′ is the origin in the vertical direction Z, and the direction along the surface of the subject 3 ′ horizontally from the point C is the r axis. The parallel energy beam 1 'having passed through the beam splitter 23' is incident on the surface of the subject 3 'at an incident angle of 0 degree. On the other hand, another parallel energy beam 47 whose frequency is higher by f than the parallel energy beam 1 'passes through a condenser lens 46 composed of an aspherical lens, becomes a focused energy beam 48, and focuses a component reflected by the beam splitter 23'. The energy beam 2 'is incident on the surface of the subject 3'. The parallel energy beam 1 'and the focused energy beam 2' intersect at the surface of the subject 3 ', and form an interference fringe (hereinafter, a converging-type scanning interference fringe 5') concentrically traveling inward on the plane. I do. This focused scanning interference fringe 5 'excites a focused bulk ultrasonic wave 7' (bulk elastic wave) which is focused on a focal point 8 'inside the subject 3'.

As shown in FIG. 24, the component of the focused energy beam 48 incident on the point R which is x away from the point c along the surface of the object with the point c as the origin is the object 3 'at the angle φ shown in the above equation (3). To excite bulk acoustic waves 7 'radiated therein. Further, assuming that the position 8 of the bulk acoustic wave 7 'is converged and the position 8 is a point at a depth _az just below the point c, there must be a relation of x = _az · tanφ as shown in the following equation (4). No. The depth a at which the component of the focused energy beam 48 incident at a position x away from the point c satisfies the equation 4 from immediately below the point c.
By designing the aspherical lens 46 so as to be incident in the direction passing through the point 8 ', the minute region 8 located at a point at a depth _az from the point c of the subject 3' made of an isotropic material.
The point (Q point) of the bulk acoustic wave 7 'must be focused.

◎

(Equation 4) Here, f is the frequency difference between the parallel energy beam and the focused energy beam, and λ is the wavelength V of the focused energy beam, which is the natural sound velocity in the direction connecting the points R and Q of the subject 3 ′.

Next, the same discussion can be made when the subject 3 'is an anisotropic material, and the following equation (5) is satisfied.

◎

(Equation 5) Here, V 'is the sound velocity of the subject 3' in the direction connecting the points R and Q of the subject 3 '.

The above-mentioned V 'can be theoretically obtained from the anisotropic elastic constant by actually measuring the sample material, but this is a well-known theory of elasticity and will not be described further. Also, a method of designing an aspheric lens for forming an energy beam incident on an arbitrary position (for example, point R) of the subject 3 'in an intended direction is optically known and will not be further described.

Next, a specific configuration of a non-contact non-destructive material evaluation apparatus using an aspherical focusing lens 46 is shown in FIG. A laser beam 21 'emitted from a laser beam light source 13' is split into two laser beams 21a 'and 21b' by a beam splitter 22 '. The diameter of the laser beam 21a 'is adjusted by the beam system adjusting mechanism 20a' to the diameter for irradiating the subject 3 '. The adjusted laser beam 1 ′ that has passed through the beam splitter 23 ′ is applied to the subject 3 ′. On the other hand, the laser beam 21b '
After passing through the 4 ', is introduced into the acousto-optic device 45 of the TeO _2, frequency by the drive frequency of the acousto-optic device 45 of TeO ₂ is shifted to a higher side. The frequency-shifted laser beam 21b 'passes through an aspherical focusing lens 46 via a mirror 25' to become a focused laser beam 48, and the component reflected by the beam splitter 23 'is a laser beam 2'
Becomes The laser beams 1 ′ and 2 ′ intersect and interfere with each other on the surface of the subject 1 to form an interference fringe which is scanned inward, thereby forming a focused bulk ultrasonic wave 7 having a desired point as a focal point 8 ′. 'Is generated. On the other hand, the generated focused bulk ultrasonic wave 7 'is detected by, for example, the following optical system using an optical knife edge method. The probe beam 10 'emitted from the detection laser beam light source 18a' is condensed by the condenser lens 27 'to the wavelength of the focused bulk ultrasonic wave. The probe beam 11 'reflected by the subject 3' is adjusted by the condenser lens 28 'and guided to the light receiving surface of the avalanche photodiode 30'. By adjusting the knife edge provided in front of the avalanche photodiode 30 ', the focused bulk ultrasonic wave 7' is measured and observed with the oscilloscope 31 '. By moving the subject 3 'using the subject moving device 19a' as necessary,
It is possible to measure a plurality of parts to be measured. In the above-described embodiment, the optical knife edge method is used as a method for detecting the focused bulk ultrasonic wave. However, the present invention is not limited to this, and any general method for detecting the ultrasonic wave without contact may be used. . In this example, the acousto-optic device 45 is used as a means for shifting the frequency of the laser beam, but the invention is not limited to this.

[0050]

According to the present invention, the following remarkable effects are obtained. 1) The surface of the subject is irradiated with coherent parallel energy beams and focused energy beams having different frequencies to form interference fringes, and the elasticity is provided on condition that the traveling speed of the interference fringes is higher than the inherent sound speed of the subject. Excitation of a wave (bulk elastic wave) inside the subject can be easily realized. 2) The bulk acoustic wave can be focused on a specific portion inside the subject depending on the shape of the focused energy beam, and in some cases, can be easily focused on each of the focusing positions along a straight line. 3) By irradiating the probe light and scanning the object, it is possible to accurately detect a defect, a material, a characteristic, and the like of a material in a minute region inside the object in a non-contact and non-destructive manner. 4) Material evaluation with high accuracy, high spatial resolution, and high efficiency as compared with the prior art is enabled. 5) By changing the focal position of the focused energy beam or the frequency difference between the parallel energy beam and the focused energy beam, the depth position of the minute region inside the subject where the bulk acoustic wave is focused can be adjusted continuously or stepwise. Flaw detection can be performed at high speed. 6) Assuming that an elastic wave is generated at one point inside the object even when the object has anisotropic elasticity, the surface phase distribution of the elastic wave is estimated by performing a calculation in consideration of the anisotropy. By generating the interference fringes corresponding to the above, it is possible to excite the bulk acoustic wave focused on the one point. Thus, an anisotropic subject can be handled in the same manner as a non-anisotropic subject. 7) According to the elastic wave excitation device of the present invention using the aspherical lens, since the bulk ultrasonic wave can be focused at one point, the amplitude at the focal point becomes large and the detection can be performed with a high signal-to-noise ratio. Become. Also, it is possible to evaluate acoustic materials with a resolution comparable to that of an ultrasonic microscope. In addition, since the above effects can be obtained in a non-contact manner, acoustic measurement and evaluation at the level of an ultrasonic microscope can be performed in any environment and in an extreme atmosphere.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a parallel energy beam and a focused energy beam used in the present invention.

FIG. 2 is a schematic diagram showing an interference state between a parallel energy beam and a focused energy beam.

FIG. 3 is a plan view showing interference fringes of the present invention.

FIG. 4 is a schematic diagram showing bulk acoustic waves generated in a subject by the interference fringes of the present invention.

FIG. 5 is a schematic diagram for theoretically obtaining a focused state and a radiation angle of a bulk acoustic wave of the present invention.

FIG. 6 is a diagram showing a focus position of a bulk acoustic wave of the present invention.

FIG. 7 is a schematic diagram for obtaining a phase velocity of a wavefront generated on the surface of a subject.

FIG. 8 is a schematic diagram showing a change in a focusing position of a focal energy beam.

FIG. 9 is a configuration diagram for explaining movement of a focus position of a laser beam.

FIG. 10 is a diagram showing a chirp signal.

FIG. 11 is a diagram illustrating a result in which elastic characteristics of a subject are reflected on a frequency corresponding to a depth position of the subject.

FIG. 12 is a schematic diagram showing a change in a focusing position when a parallel energy beam is incident on the surface of a subject at an angle.

FIG. 13 is a schematic diagram showing a beam irradiation method when an interference fringe formation region is narrow.

FIG. 14 is a schematic diagram for explaining a non-contact non-destructive material evaluation method of the present invention using bulk acoustic waves.

FIG. 15 is a block diagram showing a schematic configuration of a non-contact and non-destructive material evaluation device of the present invention.

FIG. 16 is a configuration diagram showing an example of a non-contact and non-destructive material evaluation device of the present invention.

FIG. 17 is a relative intensity diagram showing a detection result of the present invention.

FIG. 18 is a configuration diagram illustrating an example of a detection / analysis unit according to the present invention.

FIG. 19 is a configuration diagram showing another example of the detection / analysis means in the present invention.

FIG. 20 is a plan view showing equally spaced concentric interference fringes in the present invention.

FIG. 21 is a schematic diagram showing a linear focusing state of bulk acoustic waves in FIG. 20;

FIG. 22 is a schematic diagram showing a phase distribution generated by an elastic wave radiated from the inside of the subject.

FIG. 23 is a schematic diagram showing another example of the phase distribution on the surface of the subject having elastic anisotropy.

FIG. 24 is a schematic diagram for explaining the principle of exciting a point-focused bulk ultrasonic wave using an aspheric lens.

FIG. 25 is a configuration diagram showing a specific configuration of a non-contact non-destructive material evaluation device of the present invention using an aspheric lens.

[Explanation of symbols]

1,1 'parallel energy beam 2,2', 47,48 focused energy beam 3,3 'subject 4 surface 5,5' interference fringe 5a bright part of interference fringe 5b dark part of interference fringe 6 area 7,7 ' Bulk elastic wave 8 Focusing point 8 'Focus of focused energy beam 8a Focusing position 9,33,41 Laser light source 10 Probe light 11 Reflected light 12,12a, 12b, 12c Detecting and analyzing means 13 Laser beam light source 14 Optical system 15 Parallel energy Beam forming means 16 Focused energy beam forming means 17, 17a Beam irradiating means 18 Probe light forming means 18a Detection laser beam light source 19 Scanning means 19a Subject moving device 20 Adjusting means 20a Beam diameter adjusting mechanism 21, 21a, 21b Laser beam 22 , 34,36 Half mirror 23,23 'Beam split 24,25 mirror 26,27,28 condenser lens 29 knife edge 30,37,43 photodiode 30 'avalanche photodiode 31,38,44 oscilloscope 32 AO element (frequency modulation element) 35,42 displacement part 39,40 mirror 45 Acousto-optic element 46 Aspherical focusing lens

Claims (19)

[Claims] 1. A coherent parallel energy beam and a focused energy beam having different frequencies are superimposed on a surface portion of a subject and radiated concentrically inside at a traveling speed higher than a natural sound speed of the subject. An interference fringe is generated, and a thermal distribution of the interference fringes is formed on the surface of the subject by the thermal action of the interference fringes. An elastic wave exciting method which excites an elastic wave converging toward a minute area inside the subject, which is determined by a natural sound velocity of the subject and a traveling speed of the interference fringes. 2. A coherent parallel energy beam and a focused energy beam having different frequencies are superimposed on a surface portion of a subject and radiated concentrically inside at a traveling speed higher than a natural sound speed of the subject. An interference fringe is generated, and a thermal distribution of the interference fringes is formed on the surface of the subject by the thermal action of the interference fringes. While exciting an elastic wave converging toward a minute region inside the subject determined by the inherent sound velocity of the subject and the traveling speed of the interference fringes, the acoustic wave is reflected from or passes through the minute region to reach the front or back surface of the subject. Before the elastic wave is detected in a non-contact and non-destructive manner by the probe light, and the object is scanned relative to the parallel energy beam and the focused energy beam or the probe light before being sequentially obtained. A non-contact, non-destructive material evaluation method, comprising analyzing material properties of the subject based on a detection result of the elastic wave. 3. An optical knife edge method, a heterodyne interferometer, a Fabry-Perot interferometer,
The non-contact non-destructive material evaluation method according to claim 2, wherein the elastic wave is detected by a method using a homodyne interferometry or an electromagnetic ultrasonic transducer. 4. A forming means for forming a parallel energy beam having a predetermined frequency and a focused energy beam having a different frequency from the parallel energy beam, and causing the parallel energy beam and the focused energy beam to interfere with each other on a surface portion of a subject. A beam irradiating means for irradiating at least and exciting an elastic wave directed to a minute region inside the subject, and the elastic wave reaching the front surface or the back surface of the subject from the minute region in a non-contact and non-destructive manner with probe light. Detection and analysis means for detecting and analyzing the material properties of the subject,
A non-contact non-destructive material evaluation apparatus, comprising: a scanning unit that relatively scans the subject with respect to the parallel energy beam, the focused energy beam, or the probe light. 5. The apparatus according to claim 4, wherein said irradiating means is provided with an adjusting means for equalizing the energy densities of the parallel energy beam and the focused energy beam in order to completely interfere the two energy beams. Non-contact non-destructive material evaluation device. 6. A coherent parallel energy beam having a wavelength λ and a frequency difference of f and a focused energy beam are irradiated onto a surface portion of a subject having a natural sound velocity of V in a superimposed manner, and the focused energy beam is irradiated with the focused energy beam. By placing the focal point at a depth (a) that satisfies the following relational expression from the surface of the specimen, an interference fringe traveling concentrically toward the inside is generated on the surface of the object, and the thermal action of the interference fringes generates the above-mentioned interference fringes. Forming a strain having the same distribution as the interference fringes on the surface portion of the subject, and exciting an elastic wave focused toward a specific minute region in the deep part of the subject according to the strain distribution. Elastic wave excitation method. f · (λ ² + 2λa) ^1/2 > V 7. A focal position of a focused energy beam applied to a surface of a subject is changed in order to change a position in a depth direction of a minute region inside the subject where a focused elastic wave excited toward the inside of the subject is focused. The method according to claim 6, wherein the change is performed along the depth direction of the surface of the subject. 8. A focused energy beam and a parallel energy beam applied to a surface of a subject in order to change a position in a depth direction of a minute region inside the subject where a focused elastic wave excited toward the inside of the subject is focused. The elastic wave excitation method according to claim 6, wherein the frequency difference f is changed. 9. A parallel irradiating surface of a subject to change a position of a minute region inside the subject where a focused elastic wave excited toward the inside of the subject converges along a direction parallel to the surface of the subject. The elastic wave excitation method according to claim 6, wherein an incident angle of the energy beam is changed. 10. A parallel laser beam and a focused laser beam having a frequency difference f with respect to the parallel laser beam are formed at a wavelength λ, and the parallel laser beam and the focused laser beam are surface portions of a subject having a natural sound velocity of V. Laser irradiating means for irradiating the focused laser beam at a depth (a) that satisfies the following relational expression with respect to the surface of the object, A laser or irradiating means for exciting and converging an elastic wave in a minute area, and wherein the laser irradiating means is a set of lenses or reflectors for changing a focal position a along a depth direction in a path through which the focused laser beam passes. An elastic wave excitation apparatus having means for changing a depth direction position of a minute region in a subject where the elastic wave is focused by having an optical system comprising: f · (λ ² + 2λa) ^1/2 > V 11. A parallel laser beam and a focused laser beam having a frequency difference f with respect to the parallel laser beam are formed at a wavelength λ, and the parallel laser beam and the focused laser beam are surface portions of an object having a natural sound velocity of V. Laser irradiating means for irradiating the focused laser beam at a depth (a) that satisfies the following relational expression with respect to the surface of the object, An object that excites and focuses an elastic wave on a minute region, and wherein the laser irradiation means is configured to change the relative frequency difference f between the focused laser beam and the parallel laser beam so that the elastic wave is focused on the subject. An elastic wave excitation device that changes the position in the depth direction of a small area inside. f · (λ ² + 2λa) ^1/2 > V 12. A parallel laser beam and a focused laser beam are irradiated on a surface portion of an object by interfering with each other to excite an elastic wave focused toward the inside of the object and a frequency difference between the two laser beams. Has a laser irradiation means that changes with time, and observes the displacement of the subject surface when the elastic wave excited in the subject passes or reflects inside the subject and propagates again to the subject surface. Receiving means for converting to an electric signal, and having an analyzing means for frequency-analyzing the electric signal representing the surface displacement output from the receiving means, the structure of the depth direction position continuously or stepwise different inside the subject or An elastic wave material evaluation device that evaluates elasticity. 13. Assuming that an elastic wave having a frequency f is generated at one point inside the object, the phase distribution of the elastic wave propagating on the surface of the object is estimated, and the phase distribution of the elastic wave on the surface of the object is estimated. In order to generate an equal or approximate strain distribution, a coherent parallel energy beam and a focused energy beam having a frequency difference f from each other are irradiated on the surface of the subject in a superimposed manner, and the interference proceeds inward. Generate a fringe, form a distortion having the same distribution as the phase distribution in the surface portion of the subject by the thermal action of the interference fringes,
An elastic wave excitation method comprising: exciting an elastic wave converging toward the one point inside the subject. 14. The focal position of a focused energy beam applied to a surface of a subject to change a depth position of a point at which a focused elastic wave excited toward the inside of the subject is focused inside the subject. 14. The method according to claim 13, wherein the change is performed along a depth direction of the surface. 15. A focused energy beam and a parallel energy beam applied to a surface of a subject to change a depth position of a point at which a focused elastic wave excited toward the inside of the subject is focused inside the subject. 14. The elastic wave excitation method according to claim 13, wherein the frequency difference f is changed. 16. A parallel energy beam applied to a subject surface to change a point at which a focused elastic wave excited toward the inside of the subject converges inside the subject along a direction parallel to the subject surface. 14. The method according to claim 13, wherein the incident angle is changed. 17. A coherent parallel energy beam and a focused energy beam having mutually different frequencies are radiated on a surface portion of a subject so as to be concentrically inward at a traveling speed higher than a natural sound speed of the subject. Beam irradiating means for generating an interference fringe that travels toward the surface, and forms a strain distribution having the same interval as the interference fringe on the surface portion of the subject due to the thermal action of the interference fringe. An elastic wave excitation device that excites an elastic wave converging toward a minute region inside the subject, which is determined by the inherent sound speed of the subject and the traveling speed of the interference fringes accordingly, wherein the beam irradiation unit includes:
An acoustic wave excitation comprising a focusing lens comprising an aspherical lens, wherein the focused energy beam is shaped so that the elastic wave can be substantially point-focused toward a minute area inside the non-analyte. apparatus. 18. The aspheric lens according to claim 1, wherein the component of the focused energy beam is an extension of the incident direction of the focused energy beam at a position away from the point c of the center of the concentric circle on the surface of the object by x along the surface of the object. Is designed to pass through a point having a depth a that satisfies at least the following expression from immediately below the c point, and is located at a point having a depth _az from the c point of the subject made of an isotropic material. The elastic wave excitation device according to claim 17, wherein the elastic wave is point-focused on a minute area. x = a _z tan [sin ^-1 (V x / λ f (a ² +
x ^{2) 1/2)]} where, f is the frequency difference between the parallel energy beam and focused energy beam, lambda is the wavelength of the focused energy beam, V is a specific sound velocity of the subject. 19. The aspherical lens according to claim 1, wherein the focus energy beam component at the point R at a position R away from the center point c of the concentric circle on the surface of the subject by x along the surface of the subject. The extension line is designed to pass through a point having a depth a that satisfies at least the following equation from immediately below the point c, and a point having a depth _az from the point c of the subject made of an anisotropic material. 18. The elastic wave excitation device according to claim 17, wherein the elastic wave is point-focused at a located minute region Q. x = a _z tan [sin ^-1 (V ′ · x / λ · f · (a ²
+ X ² ) ^1/2 )] Here, f is the frequency difference between the parallel energy beam and the focused energy beam, λ is the wavelength of the focused energy beam, and V ′ is the direction connecting the R point and the Q point of the subject. Sound velocity.