JP2007271288A - Laser excitation ultrasonic image device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser excitation ultrasonic image device, capable of inspecting a defect in an inside of an inspection object and capable of analyzing structure thereof in nondestructive and noncontact manner, with nanometer order of spatial resolution. <P>SOLUTION: This laser excitation ultrasonic image device is provided with an ultrasonic wave exciting laser irradiation part 2 for irradiating the inspection object P with an ultrasonic wave exciting laser L1, and for exciting ultrasonic waves that propagate through its inside or the like; a reference light emitting part 2 for emitting a reference light L2 for detecting ultrasonic echo generated by the ultrasonic waves resulting from the defects in the inside of the inspection object P; a photoelectric face 4 for receiving reflected light or scattered light L3, including changes in the light intensity or the optical frequency or the like generated by an interaction between the reference light L2 and the ultrasonic echo on its surface, when the reference light L2 is reflected or scattered by the inspection object P, and for emitting electrons by the reflected light or scattered light L3; a sweeping part 5 provided with paired sweeping electrodes 51 for sweeping the orbits of the electrons emitted from the photoelectric face 4; a fluorescent face 7 for light-transforming the electron swept by the sweeping part 5; and an image output part 8 for forming a luminescent spot appeared in the fluorescent face 7 into an image to be output. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser-excited ultrasonic imaging apparatus for performing non-contact, non-destructive and high-accuracy inspection of cracks and defects or structural analysis for a measurement object that is difficult to contact or approach.

  2. Description of the Related Art Conventionally, there has been known a technique capable of non-destructively inspecting a crack or a defect of an inspection object by capturing a cross-sectional image of the inspection object using an ultrasonic echo (for example, Patent Document 1). reference).

  There is also known an inspection apparatus that can inspect internal defects such as cracks and defects to be inspected in a non-destructive and non-contact manner using a laser ultrasonic method.

  The inspection apparatus using this laser ultrasonic method is used as follows.

First, a laser beam is irradiated on the surface of the inspection object, and ultrasonic waves are excited on the surface of the inspection object or inside thereof. When this ultrasonic wave hits a defect in the process of propagating through the inspection object, an ultrasonic echo is generated there. The inspection object is irradiated with a laser beam for ultrasonic detection separately from the laser beam for generating ultrasonic waves. When an echo from a defect reaches this irradiation site, ultrasonic vibration is generated on the surface thereof, so that the reflected wave of the laser beam undergoes a Doppler shift and its optical frequency is displaced. This optical frequency displacement is converted into a transmitted light intensity displacement by a Fabry-Perot interferometer, for example, and is incident on a photodetector. As a result, the defect inside the inspection object can be detected as a change in the output signal of the photodetector (see, for example, Patent Document 2).
JP 2000-28589 A JP 2002-228639 A (2nd page)

  However, the configuration described in Patent Document 1 requires water as a medium for transmitting ultrasonic waves to the sample. For this reason, if the object to be inspected changes in shape or electrical characteristics due to moisture absorption or the like, for example, there is a problem that an accurate inspection cannot be performed. Further, since the upper limit of the frequency of ultrasonic waves that can be generated by the piezoelectric element is several hundred MHz, there is a problem that the resolution of the image is limited to about several tens of microns.

  Further, in the configuration described in Patent Document 2, for example, even if the pulse width of a beam for generating ultrasonic waves is narrowed, the response speed of the Fabry-Perot interferometer and the photodetector is limited, and the spatial resolution of nanometer order or less It is difficult to obtain an image. Furthermore, for zero-dimensional measurement, in order to inspect the entire sample, it is necessary to two-dimensionally scan the measurement point, which causes a problem that it takes a long time.

  Accordingly, the present invention provides a laser-excited ultrasonic imaging apparatus that can perform non-destructive and non-contact defect inspection and structural analysis inside an inspection target (1) with a spatial resolution of nanometer order and (2) high inspection speed. Doing this is the main challenge.

  That is, the laser-excited ultrasonic imaging apparatus according to the present invention emits a pulsed laser to an inspection object, and excites an ultrasonic wave propagating through the surface or inside of the inspection object; When the reference light is reflected or scattered to the inspection object, and the reference light emitting part that emits the reference light for detecting the ultrasonic echo generated due to the defect or the internal structure inside the inspection object. In addition, the surface receives reflected light or scattered light including a change in light intensity or optical frequency caused by the interaction between the reference light and the ultrasonic echo, and emits electrons by the reflected light or scattered light. A photocathode; a sweep unit comprising a pair of sweep electrodes for sweeping an orbit of electrons emitted from the photocathode; a phosphor screen for photoconverting electrons swept by the sweep unit; and the phosphor screen By comprising comprises an image output unit for a bright spot by imaging output appearing characterized.

  According to such a configuration, each electron emitted from the photocathode and arriving at a slight delay is displaced in the sweep portion in a slightly different direction in the sweep direction and reaches the phosphor screen. That is, by sweeping electrons at high speed by the sweep unit, the temporal and spatial light intensity change of reflected light or scattered light can be captured as an image on the fluorescent screen with high accuracy. Therefore, for example, if the pulse width of a pulse laser is set to several hundred picoseconds or less, an image with a nanometer spatial resolution of 5 nm at a time resolution of 1 picosecond and 500 nm at 100 picoseconds can be obtained in a solid. By using this image, it becomes possible to find very fine defects and to analyze the internal structure with high accuracy.

  That is, it is possible to provide a laser-excited ultrasonic imaging apparatus that can perform defect inspection and structural analysis inside an inspection object in a non-destructive and non-contact manner with a spatial resolution of nanometer order and a high inspection speed.

  If the reference light emitted from the reference light emitting unit is a laser, the above-described effects of the present invention become significant.

  If a slit having a longitudinal dimension is provided in a direction perpendicular to the sweep direction, the same direction as the sweep direction on the phosphor screen can be set as a time axis, and a direction perpendicular to the sweep direction can be set as a spatial axis. Measurement can be performed. Thereby, measurement time can be shortened.

  In order to double the weak light to a sufficient amount and contribute to high-accuracy analysis, the electrons swept by the sweep electrode are detected between the pair of sweep electrodes and the phosphor screen, and the gain is increased. It is desirable to provide an electron multiplier that outputs the doubled electrons to the phosphor screen.

  As described above, in the laser-excited ultrasonic imaging apparatus according to the present invention, each electron that is emitted from the photocathode and is gradually delayed is displaced in the sweep portion in a slightly different direction in the sweep direction, and is thus reflected on the phosphor screen. To reach. That is, by sweeping electrons at a high speed by the sweep unit, the temporal and spatial light intensity change of reflected light or scattered light can be captured as a two-dimensional image on the fluorescent screen. Therefore, for example, if the pulse width of the pulse laser is set to several hundred picoseconds or less, an image with a nanometer spatial resolution can be obtained, and this image can be used to find very fine defects. In addition, the internal structure can be analyzed with high accuracy.

  That is, it is possible to provide a laser-excited ultrasonic imaging apparatus that can perform defect inspection and structural analysis inside an inspection object in a non-destructive and non-contact manner with a spatial resolution of nanometer order and a high inspection speed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  The laser-excited ultrasonic imaging apparatus A of the present embodiment measures the modulation of the reference light intensity due to the variation in surface reflectance due to the pressure of the laser-excited ultrasonic wave of the inspection object P (for example, steel material) and the variation in the surface position. The inspection apparatus is used as an inspection apparatus for inspecting defects inside the inspection object P in a non-destructive and non-contact manner, an analysis apparatus for analyzing the internal structure of the inspection object P, and the like. As shown in FIGS. 1, 2, and 3, the laser-excited ultrasonic imaging apparatus A has an ultrasonic excitation laser L1 for exciting an ultrasonic wave in the inspection object P (the “pulse laser of the present invention”). And a reference laser radiation unit that emits a reference laser L2 as reference light for detecting an ultrasonic echo generated in the inspection object P by the ultrasonic wave. 2 (corresponding to the “reference light emitting part” of the present invention), the slit 3 for passing the reflected laser L3 as reflected light or scattered light obtained from the ultrasonic echo and the reference laser L2, and the received light as electrons A photoelectric surface 4 that is converted into an electron beam, a sweep unit 5 having a pair of sweep electrodes 51a and 51b, an electron multiplier unit 6 for doubling the swept electrons, and a phosphor screen for photoconverting the electrons 7 and this phosphor screen 7 In addition to an image output unit 8 (not shown) for outputting the obtained optical image, the operations of the ultrasonic excitation laser radiation unit 1, the reference laser radiation unit 2, and the sweep unit 5 are controlled. A control unit 9 is provided. In the present embodiment, the slit 3, the photocathode 4, the sweep unit 5, the electron multiplying unit 6, the phosphor screen 7, and the image output unit 8 are integrally assembled as a camera unit AU. Hereinafter, each part is demonstrated concretely.

  The ultrasonic excitation laser radiating unit 1 emits an ultrasonic excitation laser L1 to the inspection target P and excites ultrasonic waves propagating through the surface or inside of the inspection target P. Specifically, when the ultrasonic excitation laser L1 emitted from the ultrasonic excitation laser emitting unit 1 is irradiated onto the surface of the inspection target P, ultrasonic waves are generated at the irradiation point due to thermal stress or the like. By doing so, the ultrasonic wave propagating through the inspection object P is excited. In the present embodiment, the pulse width of the ultrasonic excitation laser L1 is set to several hundred picoseconds or less.

The reference laser emitting unit 2 emits a reference laser L2 for detecting an ultrasonic echo generated by the ultrasonic wave due to a defect or an internal structure inside the inspection target P. In the present embodiment, the radiation direction of the reference laser L2 and the radiation direction of the ultrasonic excitation laser L1 are set to be the same direction (see FIG. 2). Note that the radiation direction of the reference laser L2 and the radiation direction of the ultrasonic excitation laser L1 do not have to be the same, and the radiation angle of the ultrasonic excitation laser L1 is not substantially limited. Further, in the present embodiment, the reference laser L2, well although a continuous wave (CW) laser, not limited to this, in the light of the light or single wavelength that is mixture of a plurality of wavelengths such as white light and, Use of a pulsed laser is not prevented.

  The slit 3 has a horizontally long and substantially rectangular shape having a longitudinal dimension in a direction orthogonal to the sweep direction 5H. In the present embodiment, when the reference laser L2 is reflected by the inspection target P, the reflected laser includes a change in light intensity or optical frequency generated by the interaction between the reference laser L2 and the ultrasonic echo on the surface thereof. It is arranged at a position where L3 passes.

  The photocathode 4 receives the reflected laser L3 that has passed through the slit 3 and emits electrons.

  The sweep unit 5 includes sweep electrodes 51a and 51b (hereinafter collectively referred to as a sweep electrode 51) that form a pair for sweeping the trajectory of electrons emitted from the photocathode 4. In the present embodiment, one sweep electrode 51 is connected to the sweep circuit, while the other sweep electrode 51 is grounded. And the control part 9 mentioned later is comprised so that the sweep voltage between the sweep electrodes 51 may be controlled so that the electron which passes between the sweep electrodes 51 may be swung up or down.

  The electron multiplier 6 is arranged between the pair of sweep electrodes 51 and the phosphor screen 7, detects electrons swept by the sweep electrode 51, and multiplies the electrons with respect to the phosphor screen 7. What outputs is used, and what is generally called a microchannel plate (MCP) is used. In the present embodiment, the electron multiplying unit 6 is configured to double the number of electrons to about several thousand times, but is not limited thereto.

  The phosphor screen 7 receives and double-converts the electrons doubled by the electron multiplier 6.

  The image output unit 8 images the bright spots appearing on the phosphor screen 7 and outputs them as an optical image. The optical image output by the image output unit 8 is output in a state where it can be taken by an external video camera, but is not limited thereto.

  The controller 9 controls the emission timing of the ultrasonic excitation laser L1, the emission timing of the reference laser L2, and the application timing of the sweep voltage to the sweep electrodes 51a and 51b. For example, the emission timing of the ultrasonic excitation laser L1 and the emission timing of the reference laser L2 can be controlled synchronously, and the application timing of the sweep voltage can be controlled in a sweep time range of several tens of ps or less. .

  Next, the operation of the laser excitation ultrasonic imaging apparatus A having the above configuration will be described.

  First, when the surface of the inspection object P (for example, steel) shown in FIG. 4A is irradiated with the ultrasonic excitation laser L1 emitted from the ultrasonic excitation laser radiation unit 1 under the control of the control unit 9, An ultrasonic wave is generated at the irradiation point due to thermal stress or the like, and the ultrasonic wave S1 propagating through the inspection object P is excited.

  When there is a defect in the inspection target P (for example, defect K), the ultrasonic wave S1 propagating through the defect is reflected by the defect K and an ultrasonic echo S2 is generated.

  On the other hand, when the reference laser L2 radiated from the reference laser radiation unit 2 under the control of the control unit 9 is reflected by the inspection target P, it is generated by the interaction between the reference laser L2 and the ultrasonic echo S2 on the surface thereof. A reflected laser L3 including a change in the light intensity or optical frequency is generated.

  The reflection laser L3 generated in this way reaches the photocathode 4 through the slit 3. Specifically, as shown in FIG. 5, the light reaches the photocathode 4 through the slit 3 in the order of the reflected lasers L3a, L3b, L3c, L3d, and L3e.

  The reflected laser L3 that has reached the photocathode 4 is emitted as electrons.

  Then, the electrons Ea, Eb, Ec, Ed, and Ee emitted from the photocathode 4 are swept between the sweep electrodes 51 of the sweep unit 5 and displaced in the order as shown in FIG. Reach 6

  The electrons that have reached the electron multiplier 6 in this way are multiplied and reach the phosphor screen 7.

  Thus, the electrons that have reached the phosphor screen 7 are converted into light and appear as bright spots F (Fa, Fb, Fc, Fd, Fe), and are output as an image Z by the image output unit 8. In this way, an image Z having information on the spatial resolution of nano-order can be obtained (see FIG. 4B).

  Therefore, according to such a laser-excited ultrasonic imaging apparatus A, the electrons Ea, Eb, Ec, Ed, and Ee emitted from the photocathode 4 and arriving little by little are swept at a high speed in the sweep unit 5. It is displaced in slightly different directions in the sweep direction 5H, reaches the phosphor screen 7 and appears as a bright spot F. That is, the temporal and spatial light intensity change of the reflected laser L3 can be captured as an image (optical image) on the fluorescent screen 7 with high accuracy.

  That is, an excellent laser-excited ultrasonic imaging apparatus A that is capable of non-destructive and non-contact inspection and structural analysis of very fine defect K inside the inspection target P with a spatial resolution of nanometer order and high inspection speed. Can be provided.

  Since the slit 3 having a longitudinal dimension is provided in a direction orthogonal to the sweep direction 5H, the same direction as the sweep direction 5H on the phosphor screen 7 can be set as a time axis, and a direction orthogonal to the sweep direction 5H can be set as a spatial axis. Simultaneous point measurement can be performed. Thereby, measurement time can be shortened.

  An electron multiplying unit 6 for detecting electrons swept by the sweep electrode 51 and outputting the multiplied electrons to the phosphor screen 7 is provided between the pair of sweep electrodes 51 and the phosphor screen 7. Therefore, the weak light can be doubled to a sufficient amount of light and used for highly accurate analysis.

  The present invention is not limited to the above embodiment.

  For example, configuration zero-dimensional measurement without using the slit 3 can be performed.

  Moreover, as shown in FIG. 6, it can also be set as the structure which does not use the electron multiplication part 6. FIG.

  Further, instead of the reference laser radiation unit 2, for example, a reference light radiation unit that emits incoherent white light as reference light may be used.

  The inspection object is not limited to steel.

  The laser-excited ultrasonic imaging apparatus A can be used not only for defect inspection but also for analysis of internal structures.

  Further, the type of each part that is integrally assembled as the camera unit AU is not limited to that of the present embodiment, and may not be integrally assembled.

  In addition, the pulse width of the ultrasonic excitation laser L1 emitted from the ultrasonic excitation laser radiation unit 1 is set to several hundred picoseconds or less, but the present invention is not limited thereto, and it is not prevented from being set to nanoseconds or more.

  Further, an embodiment in which a photomultiplier for bright spots appearing on the fluorescent screen 7 is provided by arranging an image intensifier after the fluorescent screen 7 is also conceivable.

  In addition, another embodiment of the present invention shown in FIGS. 1, 3, and 7, that is, the surface displacement of the inspection target P is measured by laser-excited ultrasonic waves using an optical interference optical system. It can also be used as an inspection device for inspecting defects inside the target P in a non-destructive / non-contact manner, an analysis device for analyzing the internal structure of the inspection target P, or the like.

  In this case, as shown in FIG. 7, the camera unit AU is disposed facing the piezo stage PS via the half mirror HM. Then, when the surface position of the inspection target P fluctuates due to the pressure of the laser excitation ultrasonic wave generated in the inspection target P, the optical path difference between the reflected light path from the surface of the inspection target P and the reflected light path from the piezo stage PS is increased. What is necessary is just to measure the fluctuation | variation of the light intensity of the light interference which arises in camera unit AU by changing.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

1 is a functional configuration diagram of a laser excitation ultrasonic imaging apparatus according to an embodiment of the present invention. Explanatory drawing for demonstrating the radiation | emission and reflection aspect of each laser in the embodiment. The schematic block diagram which shows the structure of the AU principal part in the embodiment. The explanatory view for explaining the generation mode of the ultrasonic echo etc. in the embodiment, and the figure showing the example of the image obtained. Explanatory drawing for demonstrating operation | movement of the laser excitation ultrasonic imaging device in the embodiment. The schematic block diagram which shows the structure of the principal part in other embodiment of this invention. The figure which shows the optical interference measurement system using the laser excitation ultrasonic imaging device which concerns on other embodiment of this invention.

Explanation of symbols

A ... Laser-excited ultrasonic imaging device F (Fa to Fe) ... Bright spot K ... Defect L1 ..... Pulse laser (ultrasonic excitation laser)
L2 ... Reference light (reference laser)
L3 ..... Reflected light or scattered light (reflected laser)
P ... Inspection object S1 ... Ultrasonic S2 ... Ultrasonic echo Z ········ Image 1 ············································· Part (reference laser radiation part)
3 ... slit 4 ... photocathode 5 ... sweep part 5H ... ····························································································· Phosphor screen ..... Image output unit 51 (51a, 51b) ... Sweep electrode

Claims (5)

A laser emitting unit for ultrasonic excitation that emits a pulsed laser to the inspection object and excites ultrasonic waves propagating through the surface or inside of the inspection object;
A reference light emitting unit that emits reference light for detecting an ultrasonic echo generated due to a defect or an internal structure of the ultrasonic wave inside the inspection target; and
When the reference light is reflected or scattered on the inspection object, the surface receives reflected or scattered light including a change in light intensity or optical frequency generated by the interaction between the reference light and the ultrasonic echo on the surface. A photocathode that emits electrons by this reflected or scattered light,
A sweep unit comprising a pair of sweep electrodes for sweeping the trajectory of electrons emitted from the photocathode;
A phosphor screen for photoconverting electrons swept by the sweep unit;
A laser-excited ultrasonic imaging apparatus, comprising: an image output unit that images and outputs bright spots appearing on the phosphor screen.   The laser-excited ultrasonic imaging apparatus according to claim 1, wherein the pulse width of the pulse laser is several hundred picoseconds or less.   The laser excitation ultrasonic imaging apparatus according to claim 1 or 2, wherein the reference light emitted from the reference light emitting unit is a laser.   The laser-excited ultrasonic imaging apparatus according to any one of claims 1 to 3, wherein a slit having a longitudinal dimension is provided in a direction orthogonal to the sweep direction. An electron multiplier for detecting electrons swept by the sweep electrode and outputting the multiplied electrons to the phosphor screen is provided between the pair of sweep electrodes and the phosphor screen. The laser-excited ultrasonic imaging apparatus according to any one of claims 1 to 4.