JP2012127897A - Internal flaw inspection method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect an internal flaw at high sensitivity in a non-destructive state and in a non-contact state with a compact configuration without an operating part by performing ultrasonic excitation to a sample surface in non-contact state, and by observing a sample interior in non-contact state by means for optical interference measurement of a point exciting an ultrasonic wave.SOLUTION: An internal flaw inspection method and a device therefor are so devised that an ultrasonic wave is emitted from a place distant from a sample to be inspected and the sample is irradiated with the ultrasonic wave; that a place irradiated with the ultrasonic wave on the sample surface is irradiated with polarized light whose polarized state is controlled; that light having the same polarization property as that of the irradiation polarized light among reflected and scattered light from the sample surface irradiated with the polarized light is detected by a photodetector; and that a signal detected by the photodetector is processed to detect an internal flaw inside the sample.

Description

  The present invention relates to a method for inspecting a defect inside a sample, and in particular, propagates an ultrasonic wave inside a sample using an air-propagating ultrasonic wave, and vibrates or transmits ultrasonic waves reflected or scattered from the defect. The present invention relates to an internal defect inspection method and apparatus for observing vibrations of sound waves with an optical interferometer.

At present, a contact ultrasonic method, a laser ultrasonic method, an X-ray CT method, and the like are widely used as a defect inspection method inside a sample.
As described in Non-Patent Document 1, the ultrasonic method propagates the ultrasonic wave generated by the ultrasonic oscillator to the sample and observes the reflection and scattering of the ultrasonic wave on the sample to perform the internal inspection. Is the method. In particular, the contact-type ultrasonic method is a method in which an ultrasonic transmitter is directly contacted with a sample, or is contacted with a sample through a medium for achieving acoustic matching, or the sample is immersed in an ultrasonic propagation medium such as a liquid. This refers to the method of propagating ultrasonic waves. Since the ultrasonic wavelength is as short as about 1 mm to about 1 μm, there is an advantage that the internal inspection can be performed with high accuracy.

  In the laser ultrasonic method, as described in Non-Patent Document 2, the sample is irradiated with light to excite the ultrasonic wave inside the sample, and the propagation of the ultrasonic wave is measured by the light. This is a method of inspecting the inside of the sample from the appearance. The laser ultrasonic method has an advantage that an internal inspection can be performed without contacting the sample, and an advantage that a high-frequency ultrasonic wave exceeding MHz can be used relatively easily.

  As described in Non-Patent Document 3, the X-ray CT method irradiates a sample with X-rays while changing the incident angle, measures transmitted X-rays in each direction, and transmits X-rays in each direction. In this method, the internal structure is reconstructed from the image and the internal inspection of the sample is performed. The X-ray CT method has high permeability and allows detailed observation of the internal structure and can be applied to many samples. Therefore, the X-ray CT method is widely used from industrial applications to medical uses. However, the application range is limited by the relatively large measuring equipment and the relatively long time required for measurement. There are also application areas where the invasiveness of X-rays themselves is a concern.

  As for displacement measurement using light, as described in Non-Patent Document 4, an optical interference method, a Time of Flight method (TOF method), and the like are known. The optical interferometry has the disadvantage of being relatively large-scale measurement, but has been applied in various fields because of its advantage of high sensitivity and two-dimensional observation. Recently, as described in Patent Document 1, an ultra-small high-sensitivity optical interferometer using a photonic crystal has been proposed.

JP 2008-286518 A

Japan Nondestructive Inspection Association, “Nondestructive Inspection Technology Series Ultrasonic Flaw Detection” I, II, III Hisashi Yamawaki, “Laser Ultrasound and Non-contact Material Evaluation”, Journal of the Japan Welding Society Vol. 64 (1995) No. 2, page 104 Seiji Ogawa and Teruo Ueno, “Non-invasive Visualization Handbook”, NTS Corporation Toyohiko Yatakai, “Applied Optics -Introduction to Optical Measurement”, Maruzen

  In the contact ultrasonic method, an ultrasonic transducer is brought into contact with a sample directly or through a medium, and ultrasonic waves are directly propagated to the sample. Detection is often done by a transducer in contact in the same way. While non-destructive internal inspection is possible, there is a problem that the sample must be in contact with the sample or immersed in the sample, causing the sample to be contaminated or changing from the original state. It has not been widely used in the inspection of goods. Moreover, when the unevenness | corrugation of a sample surface is large etc., the subject that the efficiency of ultrasonic excitation and detection falls remarkably.

  Even in the laser ultrasonic method, problems such as the need for a relatively large device to excite and detect sufficient ultrasonic waves for measurement and the risk of damage to the sample during ultrasonic excitation Therefore, the industrial spread is not progressing.

  There is an aerial ultrasonic method as a method for overcoming the above problems. In the aerial ultrasonic method, ultrasonic waves are radiated into the air from an ultrasonic transducer that is acoustically matched with air to the sample to propagate the ultrasonic wave to the sample, and a similar contacted transducer is used inside the sample. This is a method for detecting reflected or scattered ultrasonic waves.

  The aerial ultrasonic method is expected to be applied to pre-shipment inspection and the like because it allows ultrasonic excitation and ultrasonic detection in contact with a sample. However, in the air ultrasonic method, the attenuation by the air is large while propagating from the sample into the air and being detected by the transducer. Furthermore, coupled with the low detection sensitivity of the transducer, there is a problem that a large gain is required for the circuit on the detection side, and a long time is required for measurement. Furthermore, there is a problem that an excitation signal is superimposed on the detection circuit and a dead zone exists.

  In order to overcome these problems, it is effective to perform detection optically using an optical interference measurement method. This is because detection by optical interference measurement is more sensitive than detection by a transducer, and the dead zone can be greatly reduced.

  When using optical interferometry, the measurement light needs to be incident perpendicular to the sample surface, and the transducer and the photodetector cannot be the same in nature. For this reason, excitation and light detection by airborne ultrasonic waves cannot be performed coaxially, and it is necessary to make the ultrasonic waves obliquely incident. However, when the ultrasonic wave is obliquely incident on the sample, the relative position between the ultrasonic irradiation position on the sample surface and the detection position is determined in order to know the defect depth by the refraction of the ultrasonic wave at the interface between the air and the sample. Need to scan. This state will be briefly described with reference to FIGS.

  In FIG. 1, 101 is a sample, 201 is an ultrasonic transducer, and 205 is an optical sensor. Ultrasonic waves are propagated from the ultrasonic transducer 201 to the surface 102 of the sample 101 that is the object to be inspected, and the defects 103 inside the sample 101 are excited. The ultrasonic wave 203 scattered by the defect 103 vibrates or displaces the sample surface 102 (204). This surface displacement 204 is measured using an optical sensor 205. 2 shows the same defect detection principle as in FIG. 1, but the depth 106 of the defect 103 and the distance between the transducer 201 and the optical sensor 205 are different from those in FIG.

  In FIG. 1, the defect 103 is at a position of depth D1: 104, and the displacement 204 of the surface 102 of the sample 101 caused by the scattered ultrasonic wave 203 from the defect 103 is detected by the detection light 206 of the optical sensor 205. Since the ultrasonic wave 202 emitted from the transducer 201 is refracted by the sample surface 102, the distance between the transducer 201 and the optical sensor 205 needs to be 207 determined by the incident angle of the ultrasonic wave and the depth of the defect. On the other hand, as shown in FIG. 2, in order to detect the defect 105 located at a depth D2: 106 deeper than the defect 103 in FIG. 1, the distance L2: 208 between the transducer 201 and the optical sensor 205 is set as shown in FIG. It is necessary to set the distance 208 away from the distance L1: 207 in FIG.

  When performing ultrasonic measurement using common optical path optical interferometry, the measurement light must be incident perpendicularly to the sample surface, and the transducer and photodetector should be the same in nature. Can not. For this reason, conventionally, excitation and light detection by airborne ultrasonic waves cannot be performed coaxially, and it is necessary to make the ultrasonic waves obliquely incident. However, when the ultrasonic wave is obliquely incident on the sample, the relative position between the ultrasonic irradiation position on the sample surface and the detection position is determined in order to know the defect depth by the refraction of the ultrasonic wave at the interface between the air and the sample. Need to scan.

  For this reason, in the ultrasonic internal inspection apparatus combining the optical interference measurement with the aerial ultrasonic method, there is a problem that the apparatus has an operating part and has to be a relatively large apparatus.

  The purpose of the present invention is to perform non-contact ultrasonic excitation on the sample surface, and by observing the inside of the sample non-contact using means for optical interference measurement of the point where the ultrasonic wave is excited, there is no moving part, An object of the present invention is to provide an internal defect inspection method and apparatus using a non-destructive and non-contact means with a compact configuration and high sensitivity.

  In order to solve the above-described problems, in the present invention, an ultrasonic wave is emitted from a location away from the sample to be inspected, and this ultrasonic wave is irradiated to the sample. Irradiate polarized light whose polarization state is controlled, and detect light with the same polarization characteristics as the irradiated polarized light from the reflected / scattered light from the surface of the sample irradiated with this polarized light, An internal defect inspection method for detecting a defect inside the sample by processing a signal detected by the photodetector.

  In order to solve the above-described problems, in the present invention, the internal defect inspection apparatus includes an ultrasonic irradiation unit that irradiates a sample to be inspected with ultrasonic waves, and a sample irradiated with ultrasonic waves by the ultrasonic irradiation unit. An optical detection unit that irradiates light on the surface and detects reflected / scattered light from the surface, and a signal processing unit that detects a defect inside the sample by processing a signal output from the optical detection unit The ultrasonic irradiation unit has an ultrasonic transducer that irradiates ultrasonic waves toward the sample from a location away from the sample, and the optical detection unit has a light source means and light emitted from the light source means. A polarization control means for controlling the polarization state, a light irradiation means for irradiating the polarized light whose polarization state is controlled by the deflection control unit to the portion of the sample surface irradiated with the ultrasonic wave, and the light irradiation means Sample irradiated with polarized light It has a light detection means for detecting light having the same polarization characteristics as the irradiated polarized light out of the reflected / scattered light from the surface, and the signal processing unit processes the signal output from the optical detection means to A defect was detected.

  According to the present invention, the active part is obtained by performing non-contact ultrasonic excitation on the surface of the sample and enabling non-contact observation of the inside of the sample using means for optical interference measurement of the point where the ultrasonic wave is excited. In addition, it is possible to provide an internal defect inspection method and apparatus using a non-destructive and non-contact means with high sensitivity and a compact configuration.

It is a schematic diagram explaining aerial ultrasonic excitation and internal observation by an optical sensor when a defect is shallow. It is a schematic diagram explaining aerial ultrasonic excitation and internal observation by an optical sensor when a defect is deep. It is a perspective view of an ultrasonic transducer with a through hole. It is a perspective view of an ultrasonic transducer with a step through hole. It is sectional drawing of the ultrasonic measuring device which has arrange | positioned the common optical path optical interferometer in the through-hole provided in the ultrasonic transducer. It is a block diagram which shows the structural example of the common optical path optical interferometer using the linearly polarized light introduced from the outside as a light source. FIG. 6 is a perspective view showing the structure of photonic crystal arrays 618 and 619. It is a block diagram which shows the structure of the common optical path optical interferometer which incorporated the light source. It is a block diagram which shows the structure of the line focus type common optical path light interferometer using the linearly polarized light introduced from the outside as a light source. It is a perspective view which shows the structure of the photonic crystal arrays 635 and 636. FIG. It is sectional drawing of the ultrasonic transducer with a through-hole incorporating the common optical path optical interferometer explaining the measuring method of the ultrasonic measurement using a through-hole ultrasonic transducer and a common optical path optical interferometer. It is sectional drawing of an ultrasonic transducer which shows the structure of the ultrasonic measuring device which has arrange | positioned the reference mirror and focusing lens of a common optical path optical interferometer to the through-hole provided in the ultrasonic transducer. It is sectional drawing of the ultrasonic transducer which shows the structural example of the ultrasonic measuring device which has arrange | positioned the reference mirror of a common optical path optical interferometer to the step through-hole provided in the ultrasonic transducer. It is sectional drawing of an ultrasonic transducer which shows the structure of the ultrasonic measuring device which has arrange | positioned the common optical path optical interferometer to the step through-hole provided in the ultrasonic transducer. It is sectional drawing of the ultrasonic transducer for demonstrating the ultrasonic measurement at the time of using a non-convergent type transducer for an ultrasonic transducer. It is sectional drawing of the ultrasonic transducer which shows the structural example of the ultrasonic measuring device using an ultrasonic transducer and a grazing incidence Sagnac interferometer. It is sectional drawing of the ultrasonic transducer which shows the structural example of the ultrasonic measuring device using the oblique incidence Sagnac interferometer which has an ultrasonic transducer and a variable optical delay path. It is sectional drawing of the ultrasonic transducer which shows the structural example of the ultrasonic measuring device using an ultrasonic transducer and a fiber type oblique incidence Sagnac interferometer. It is a block diagram of a duplexer showing a configuration of a duplexer used in an ultrasonic measurement apparatus using an ultrasonic transducer and a fiber-type oblique incidence Sagnac interferometer. It is sectional drawing of the ultrasonic transducer which shows the structural example of the ultrasonic measuring device using the oblique incidence Sagnac interferometer which used the ultrasonic transducer and parallel measurement light. It is a block diagram which shows the structure of the whole ultrasonic measuring device. It is a schematic diagram of the data obtained by scanning an ultrasonic measuring device. It is a front view of the display screen which shows the example which calculated the depth distribution of the defect from the data obtained by scanning an ultrasonic measuring device, and displayed it two-dimensionally.

  Embodiments of the present invention will be described with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the sample 101 is ultrasonically excited on the sample surface 102 without contact, and the surface displacement of the ultrasonic excitation point is measured by the optical sensor 205, and the inside of the sample is observed without contact. Can perform aerial ultrasonic internal measurements. In such non-contact measurement, in order to realize a compact measurement system in which the relative position between the ultrasonic transducer 301 and the optical sensor 205 is fixed, the ultrasonic transducer 301 or 303 as shown in FIGS. Is used.

  The ultrasonic transducer 301 illustrated in FIG. 3 is an “ultrasonic transducer with a through hole” in which a through hole 302 for disposing the optical sensor 205 or a part of the optical sensor 205 is provided at the center thereof. The ultrasonic transducer 303 illustrated in FIG. 4 has a counterbore 304 in which the optical sensor 205 or a part of the optical sensor 205 is arranged at the center, a counterbore 304 for passing a signal to the optical sensor 205 and detection light, and a diameter. This is a “stepped through-hole ultrasonic transducer” provided with different through-holes 305.

  The through hole 302 in FIG. 3 to the counterbore 304 in FIG. 4 may be a through hole or counterbore that is large enough to arrange the entire optical sensor 205, and is large enough to dispose only a part of the optical sensor 205. It may be. 3 to 4, the cross-sectional shapes of the through hole 302, the through hole 305, and the counterbore 304 are circular, but they are not necessarily circular and may be other shapes such as a rectangle.

  The ultrasonic transducer 301 shown in FIG. 3 has a shape suitable when the length of the optical sensor 205 to be used is approximately the same as the length of the ultrasonic transducer. On the other hand, the ultrasonic transducer 303 shown in FIG. 4 is suitable when the length of the optical sensor 205 is sufficiently shorter than the ultrasonic transducer, or when only a part of the optical sensor 205 is arranged. In addition, since the ultrasonic transducer 303 has a smaller amount of processing on the transducer than the ultrasonic transducer 301, it is possible to suppress a decrease in the excitation performance of the ultrasonic transducer, and the ultrasonic transducer machine. There is an advantage that it is possible to suppress a decrease in the mechanical strength.

  An example of an actual usage pattern of the through-hole ultrasonic transducer 301 shown in FIG. 3 is schematically shown in FIG. That is, the optical sensor 306 is arranged in the through hole 302 of the ultrasonic transducer 301 with a through hole, and a signal is taken out by the input / output cable 307. When the light source of the detection light is separated from the optical sensor 306, it is necessary to guide light from the outside to the optical sensor 306. In this case, the input / output cable 307 may incorporate an optical fiber or the like.

  In the present invention, the optical sensor 205 or the optical sensor 306 uses, for example, an optical sensor composed of an optical interferometer in which the measurement light and the reference light pass through the optical paths that are optically the same or optically approximately the same. Since the interferometer is constituted by a common optical path, it is advantageous in that it is resistant to disturbances and can perform highly sensitive measurement. Hereinafter, the optical sensor 206 to the optical sensor 306 are referred to as a common optical path optical interferometer.

  The configuration and function of the common optical path optical interferometer 306 will be described with reference to FIGS. 6A to 8. The detailed configuration and operation of the common optical path optical interferometer 306 are the same as those described in, for example, Japanese Patent Application Laid-Open No. 2008-286518. As shown in FIG. 6A, the common optical path optical interferometer 306 guides light from a laser light source (not shown) provided outside by a polarization plane preserving fiber 601. A linearly polarized laser beam having a polarization direction of 45 ° emitted from the polarization-preserving fiber 601 is converted into parallel light 603 by a collimator 602, further transmitted through a polarizing element 604 such as a Glan-Thompson prism, and transmitted light 605 is transmitted through a prism mirror 606 and a non-transmitted light. The light is reflected by the polarization beam splitter 607 and is incident on the reference mirror 608. The reference mirror 608 uses a planar polarizing element such as a photonic crystal or a wire grid polarizer.

Of the laser light incident on the reference mirror 608, the P polarization component is transmitted through the reference mirror 608, and the S polarization component is reflected by the reference mirror 608.
The P-polarized beam 609 that has passed through the reference mirror 608 is collected by the condenser lens 610 as the convergent light 611 on the ultrasonic excitation unit 612 on the surface 102 of the sample 101. That is, the interval between the condenser lens 610 and the surface 102 of the sample 101 is adjusted so that the focal position of the condenser lens 610 coincides with the sample surface 102. An ultrasonic wave is irradiated to the region 612 of the surface 102 of the sample 101 from the ultrasonic transducer 301 shown in FIG. The reflected light from the region 612 irradiated with this ultrasonic wave passes through the condenser lens 610 and then becomes P-polarized parallel light 609 again and passes through the reference mirror 608. The S-polarized beam previously reflected by the reference mirror 608 and the P-polarized beam 609 reflected from the region 612 irradiated with ultrasonic waves on the surface 102 of the sample 101 and transmitted through the reference mirror 608 are combined as an orthogonally polarized beam 614. Then, it passes through the non-polarizing beam splitter 607.

  After passing through the opening 613 for removing stray light, the orthogonally polarized beam 614 is divided into four orthogonally polarized beams 617 by two opposing pyramid-shaped square pyramid prisms 615 and 616. The beam splitting method may be implemented as a combination of a diffractive optical element and a cube-shaped beam splitter. The four orthogonally polarized beams 617 are transmitted through the phase shift element composed of the photonic crystal arrays 618 and 619, so that phase shifts of 0, π / 2, π, and 3π / 2 are generated between the orthogonally polarized components. Polarization interference occurs in the given state, and four phase shift interference lights 620 are generated.

  The four phase shift interference lights 620 are condensed on the light receiving surfaces of four photoelectric conversion elements 623 such as photodiodes as four convergent lights 622 by passing through the four imaging lenses 621 corresponding thereto. Received light. Output signals from the four photoelectric conversion elements 623 that have received the four convergent lights 622 are amplified by the amplifier 624 and then output as four phase shift interference signals 307.

  As is apparent from FIG. 6A, the focal positions of the four imaging lenses 621 coincide with the light receiving surface of the photoelectric conversion element 623. Accordingly, the sample surface 102 and the light receiving surface of the photoelectric conversion element 623 are in a conjugate relationship, that is, an imaging relationship via the condenser lens 610 and the imaging lens 621. Therefore, even if the sample surface 102 is inclined or has minute irregularities, or the sample surface 102 is rough, the reflected light from the sample surface 102 is accurately collected on the light receiving surface of the photoelectric conversion element 623. Four stable phase-shift interference signals are obtained with the S-polarized light component received by light and reflected by the reference mirror 608.

  The phase shift element described above is composed of, for example, two photonic crystal arrays 618 and 619. The photonic crystal array 618 is composed of two regions as shown in FIG. 6B, and the upper half region 618a is composed of a photonic crystal having a function as a quarter wavelength plate, and the lower half region. 618b is constituted by a substrate having the same optical path length as that of the photonic crystal. That is, among the four orthogonally polarized beams 617, a phase difference of π / 2 is generated between the orthogonally polarized beam transmitted through the region 618a and the orthogonally polarized beam transmitted through the region 618b.

  The photonic crystal array 619 is also composed of two regions as shown in FIG. 6B. The region 619a is composed of a photonic crystal having a crystal axis direction of 0 °, and the region 619b is a photo having a crystal axis direction of 90 ° orthogonal to each other. Consists of nick crystals. The photonic crystals in the two regions have a function as a polarizing element. Of the four orthogonally polarized beam beams 617, two orthogonally polarized beams that pass through the photonic crystal in the region 619a and the photonic crystal in the region 619b are used. A relative phase difference of π is given between two orthogonally polarized beams that are transmitted.

  After passing through the photonic crystal arrays 618 and 619, four orthogonal polarization beams composed of S-polarized reference light reflected by the reference mirror 608 and detection light composed of P-polarized light transmitted through the reference mirror 608 and reflected by the sample surface 102. Four orthogonally polarized beams interfere.

  In the photonic crystal arrays 618 and 619, for example, a line & space diffraction grating having a pitch smaller than the wavelength of incident light is formed on a synthetic quartz substrate, and a plurality of dielectric thin films having different refractive indexes are formed thereon. It is constructed by stacking.

  FIG. 7 shows another configuration example of the common optical path optical interferometer 306. In the configuration shown in FIG. 7, instead of guiding the laser light from the laser light source shown in FIG. 6A to the interferometer by the polarization-maintaining fiber 601, a small laser diode 626 such as a semiconductor laser is used as a common optical path optical interferometer. Built in 306. The linearly polarized laser light 627 emitted from the laser diode 626 is converted into parallel light 603 by the collimating lens 628 and further transmitted through a polarizing element 604 such as a Glan-Thompson prism, and the transmitted light 605 is converted into a prism mirror 606 and a non-polarizing beam splitter 607. And is incident on the reference mirror 608. Since the configuration and function of each part thereafter are the same as those of the embodiment shown in FIG. 6 except for the presence or absence of the laser light source and the polarization plane preserving fiber 601, description thereof will be omitted.

  FIG. 8 shows an example having an optical system that emits linear measurement light 632 as still another configuration example of the common optical path optical interferometer 306. As shown in FIG. 8, the common optical path optical interferometer 306 is configured to guide light from a laser light source (not shown) provided outside by a polarization plane preserving fiber 601. The 45 ° direction linearly polarized laser light emitted from the polarization plane preserving fiber 601 is converted into parallel light 603 by a collimator 602, further transmitted through a polarizing element 604 such as a Glan-Thompson prism, and the transmitted light 605 is converted into a diffraction grating, a hologram element, or It is converted into a rectangular beam 630 by a beam shaping element 629 such as an anamorphic prism pair. The rectangular beam 630 is reflected by the prism mirror 606 and the non-polarizing beam splitter 607 and is incident on the reference mirror 608.

  The reference mirror 608 is made of the above-described photonic crystal, for example. For example, the photonic crystal reflects a polarization component orthogonal to the photonic crystal optical axis and transmits a polarization component orthogonal to the photonic crystal optical axis. The linearly polarized beam reflected by the reference mirror 608 is used as reference light, and the transmitted linearly polarized beam 631 is used as measurement light. Instead of the photonic crystal, it is also possible to use a planar polarizing element such as a wire grid polarizer.

  The polarized beam 631 that has passed through the reference mirror 608 is focused in the y-axis direction while maintaining a parallel light state in the x-axis direction by the condenser lens 610, and is converged linearly on the surface 102 of the sample 101 as the convergent light 632. (633). That is, the focal position of the condensing lens 610 coincides with the sample surface 102. The reflected light from the sample surface 102 passes through the condenser lens 610 and then becomes linearly polarized rectangular parallel light again and passes through the reference mirror 608. A polarized beam of reference light reflected by the reference mirror 608 and reflected light from the sample surface 102 that has passed through the reference mirror 608 is combined as an orthogonally polarized beam 634 and transmitted through the non-polarized beam splitter 607.

  This orthogonally polarized beam 634 is transmitted through a phase shift element formed by two photonic crystal arrays 635 and 636, for example, so that phase shifts of 0, π / 2, π, and 3π / 2 between orthogonal polarization components are obtained. , And four phase shift interference lights 637 divided in the direction orthogonal to the longitudinal direction of the focused spot 633 are generated.

  The phase shift element is composed of two photonic crystal arrays 635 and 636, for example. The photonic crystal array 635 includes two regions divided in a direction orthogonal to the longitudinal direction of the focused spot 633. The upper half region is composed of a photonic crystal that functions as a quarter-wave plate, and the lower half is composed of a substrate having the same optical path length as the photonic crystal. That is, a phase difference of π / 2 is generated between the orthogonally polarized beams transmitted through the upper half and the lower half of the rectangular orthogonally polarized beams 634.

  The photonic crystal array 636 is divided into four in a direction orthogonal to the longitudinal direction of the focused spot 633, and a photonic crystal having a crystal axis direction of 0 ° and a photonic crystal having a crystal axis direction of 90 °. They are lined up alternately. Each photonic crystal has a function as a polarizing element, and two polarization components constituting an orthogonally polarized beam that transmits a photonic crystal having a crystal axis direction of 0 ° out of the rectangular orthogonally polarized beam 634, and A relative phase difference of π is given between two polarization components constituting an orthogonal polarization beam transmitted through a photonic crystal having a crystal axis direction of 90 °, and both polarization components interfere with each other.

  That is, between each orthogonal polarization component in the direction orthogonal to the longitudinal direction of the rectangular orthogonal polarization beam 634 transmitted through the phase shift element composed of the two photonic crystal arrays 635 and 636, 0, π / 2, π, Polarization interference occurs in a state where a phase shift of 3π / 2 is given, and is divided into four in a direction perpendicular to the longitudinal direction of the focused spot 633, and phase shift interference light 637 conjugate to the longitudinal direction of the focused spot 633 is obtained. Generated.

  The phase shift interference light 637 is received by N pixels × 4 as N × 4 converged lights 639 by N × 4 lens arrays 638 corresponding to the longitudinal direction of the focused spot 633 and the four regions of the phase shift element. The light is collected and received on a light receiving surface of a split photoelectric conversion element 640 such as a photodiode array composed of regions, amplified by an amplifier 641, and then output as N × 4 phase shift interference signals.

  As is clear from FIG. 8, the focal position of the lens array 639 coincides with the light receiving surface of the photoelectric conversion element 640. Therefore, the sample surface 102 and the light receiving surface of the photoelectric conversion element 640 are in a conjugate relationship, that is, an imaging relationship via the condenser lens 610 and the lens array 638. Therefore, even if the sample surface 102 is inclined or has minute irregularities, or even if the sample surface 102 is rough, the reflected light from the surface is accurately condensed on the light receiving surface of the photoelectric conversion element 640. And a stable phase shift interference signal is obtained.

  As shown in FIGS. 6 to 8, according to the present embodiment, the weak ultrasonic vibration on the order of picometers generated on the sample surface 102 by excitation of the aerial ultrasonic waves is suppressed while minimizing the influence of disturbance. Sensitivity can be detected, and internal defects of a sample having an inclined surface or minute irregularities on the surface or a sample having a rough surface can be stably detected without contact or nondestructively. Furthermore, according to the embodiment shown in FIG. 8, since the common optical path optical interferometer 306 is scanned only in one direction at a certain distance from the sample, a three-dimensional ultrasonic image of the sample 101 can be obtained. The scanning mechanism has a simple configuration and at the same time, the time required for internal defect inspection is shortened.

  An actual measurement method in the embodiment shown in FIG. 5 will be briefly described with reference to FIG. The ultrasonic wave 308 emitted from the ultrasonic transducer 301 propagates in the air, and a part of the ultrasonic wave 308 passes through the sample surface 102 and propagates inside the sample 101 (309). When, for example, a defect 310 exists in the sample 101, a part of the ultrasonic wave 309 is reflected or scattered and returns to the sample surface 102 (311). Since the reflected or scattered ultrasonic wave 311 displaces the sample surface 102, the surface displacement caused by the ultrasonic wave is measured by the measurement light 312 of the common optical path light interferometer 306.

  When the surface displacement is measured by the common optical path optical interferometer 306 as described above, it can be seen that, for example, the defect 310 exists inside the sample 101 due to the surface displacement, and the surface displacement is detected by the measurement light 312 after emitting the ultrasonic wave 308. For example, the distance from the ultrasonic irradiation point on the sample surface 102 of the defect 310 can be known from the time until detection of the defect 310.

  In FIG. 10, a reference mirror 313 and a focusing lens 314 (part of the reference mirror 608 and the focusing lens 610 in FIGS. 6 to 8), which are part of a common optical path optical interferometer, are inserted into a through-hole 302 provided in the ultrasonic transducer 301. Corresponding) is shown in the configuration arranged in the through hole 302. In the configuration shown in FIG. 10, the detection light is guided from the common optical path optical interferometer 314 by the optical fiber 315 and emitted as parallel light by the output coupler 316. The output coupler 316 has a function of emitting the detection light guided by the optical fiber 315 as a parallel light beam and a function of introducing the detection light reflected by the sample surface 102 and returned to the optical fiber 315.

  Part of the detection light The S-polarized component of the emitted light is reflected by the reference mirror 3131 and is incident on the output coupler 316 again. On the other hand, the P-polarized component passes through the reference mirror 3131 and enters the condenser lens 3132, and converges on the measurement point on the sample surface 102 and is irradiated. The detection light reflected by the sample surface 102 is collected by the condenser lens 3132, passes through the reference mirror 3131, and returns to the output coupler 316. Thereafter, the detection light is guided to the common optical path optical interferometer 314 by the optical fiber 315.

  In the configuration shown in FIG. 10, when a polarization preserving fiber is used as the optical fiber 315 and a polarizing mirror capable of controlling reflection and transmission with the polarization of the incident light is used as the reference mirror 313, the detection light is efficiently guided to the sample 102. As a result, the detection efficiency can be increased. In FIG. 10, the reference mirror 3131 and the output coupler 316 are shown separately. However, the reference mirror 3131 is attached to the output coupler 316 or the same function as the reference mirror 313 is provided on the exit end face of the output coupler 316. An optical thin film may be formed and used.

  The advantage of the configuration shown in FIG. 10 is that the common optical path light interference system 306 is disposed in the through hole 302 in order to dispose the reference mirror 3131, the condenser lens 3132, and the output coupler 316 inside the ultrasonic transducer 301. Compared with the embodiment described in FIG. 5, the amount of processing on the ultrasonic transducer 301 can be reduced. If the amount of processing on the ultrasonic transducer 301 can be reduced, the influence on the excitation performance of the ultrasonic transducer 301 due to the through-hole 302 processing can be suppressed, and the mechanical strength of the ultrasonic transducer 301 can be impaired. Disappear.

  In the configuration shown in FIG. 10, since the constituent elements 314 other than the reference mirror 3131 and the condensing lens 3132 in the optical interferometer are separated from the ultrasonic transducer 301, it is possible to reduce the size of the measurement unit for exciting and detecting ultrasonic waves. There is. In addition, the optical detector and circuit of the optical interferometer can be separated from elements that generate an electric field by applying a high voltage like an ultrasonic transducer, thus avoiding electrical effects on the optical interference system. There are also benefits.

  If the reference mirror 3131, the condensing lens 3132, and the output coupler 316 are arranged in a through hole or counterbore provided in the ultrasonic transducer, the ultrasonic transducer has a stepped through hole perforation shown in FIG. A sonic transducer 303 is more suitable. A configuration example using the stepped through-holed ultrasonic transducer 303 is shown in FIG. In FIG. 11, the reference mirror 3131, the condenser lens 3132, and the output coupler 316 are disposed on the spot facing 304, and the through hole 305 is a hole through which only the optical fiber 315 is passed, and thus the diameter is smaller than the spot facing.

  When the configuration as shown in FIG. 11 is adopted, the amount of processing on the ultrasonic transducer 303 can be minimized, and therefore, there is an advantage that a decrease in the vibration performance and mechanical strength of the ultrasonic transducer 303 can be minimized. .

  In the configuration shown in FIG. 10 or FIG. 11, a configuration in which the condenser lens 3132 is omitted is also conceivable. In the case of this configuration, the detection light emitted from the output coupler 316 reaches the sample surface 102 as a parallel light beam, detects the surface displacement of the entire detection light irradiation region, reflects and returns to the output coupler 316. become. In this case, there is an advantage that the detection area can be widened compared with the case where the condensing lens 3132 is used, and the focal length adjustment of the condensing lens 3132 for focusing the detection light on the sample surface 102 can be omitted. is there. This is an effective means when the sample surface 102 is uneven.

  If the common optical path optical interferometer 306 can be suppressed sufficiently smaller than the ultrasonic transducer 303, a configuration as shown in FIG. 12 is also possible. That is, the common optical path light interferometer 306 is disposed in the spot facing 304 provided in the ultrasonic transducer 303, and only the input / output cable 307 is passed through the through hole 305. The advantage of the configuration shown in FIG. 12 is that the decrease in the vibration performance and mechanical strength of the ultrasonic transducer 303 can be minimized, and the ultrasonic transducer 303 and the common optical path optical interferometer 306 can be integrated. Therefore, the apparatus can be configured compactly as a whole.

  In the configuration shown in FIG. 5 or FIG. 9 to FIG. 12, an example in which the ultrasonic transducer 301 or 303 is a convergent ultrasonic transducer is shown. However, as shown in FIG. A non-convergent ultrasonic transducer that emits ultrasonic waves may be used. FIG. 13 shows a configuration example in which the common optical path optical interferometer 306 is disposed in the through hole 302 provided in the ultrasonic transducer 301.

  Although FIG. 13 illustrates a configuration in which the common optical path optical interferometer 306 is disposed in the through hole 302, a configuration in which only the reference mirror 313 and the output coupler 316 are disposed in the through hole as illustrated in FIG. 10 or FIG. As shown in FIGS. 11 and 12, a stepped through-hole ultrasonic transducer 303 may be used.

  In the configuration shown in FIG. 13, the ultrasonic wave begins to propagate as a substantially plane wave from the ultrasonic transducer 301 and propagates while gradually widening the wavefront due to the influence of diffraction (308). The ultrasonic wave 308 that has entered the inside of the sample 101 propagates in the sample 101 as a substantially plane wave, and is reflected or scattered if there is a defect 310, for example. For example, ultrasonic waves 311 reflected or scattered from the defect 310 reach the sample surface 102 and cause a surface displacement 317. This surface displacement 317 is measured by the detection light 312 of the common optical path optical interferometer 306.

  When the surface displacement of the surface 102 of the sample 101 is detected by measurement with the common optical path optical interferometer 306, it can be seen that there is, for example, a defect 310 inside the sample 101 in the vicinity of the detected position. From the time until the displacement 317 is measured with the measurement light 312, for example, the depth of the defect 310 from the sample surface 102 can be known.

  FIG. 5 or FIG. 9 to FIG. 12 show the configuration example using the converging ultrasonic transducer 301 or 303. The advantage of using the converging ultrasonic transducer 301 or 303 is that the ultrasonic wave is applied to the sample surface 102. Since it can converge to one point, ultrasonic excitation can be performed efficiently. On the other hand, when the non-converging ultrasonic transducer 3011 as shown in FIG. 13 is used, the ultrasonic wave propagating inside the sample 101 can be made into a substantially plane wave, so that the same excitation condition is always realized regardless of the depth of the defect 103. Being able to do so is an advantage.

  When exciting the ultrasonic wave using the convergent ultrasonic transducer 301 or 303, although the excitation efficiency is good, the ultrasonic wave propagating in the sample 101 becomes a spherical wave spreading from the excitation point and propagates in all directions. Therefore, the amplitude decreases to 1 / r ^ 2 at a position r from the excitation point.

  In the ultrasonic excitation using one of the non-convergent ultrasonic transducers 3011, although the excitation efficiency is inferior to that of the converging transducer 301 or 303, the sample 101 propagates as a plane wave, so that attenuation due to propagation can be almost ignored. . Therefore, the sensitivity is good when detecting foreign matters, defects, and interfaces located deep from the sample surface 102. Further, since the ultrasonic wave propagating in the sample 101 is a plane wave, it is also advantageous that the time from ultrasonic excitation to light detection corresponds purely to foreign matter, defects, and interface depth.

  On the other hand, since the ultrasonic wave excited by the convergent ultrasonic transducer 301 or 303 becomes a spherical wave inside the sample 101, the time from the ultrasonic excitation to the light detection is from the ultrasonic convergence point on the sample surface 102 to a foreign object or defect. Corresponds to the interface distance. Therefore, in order to investigate the depth of the foreign matter, defect, and interface from the sample surface 102, the point where ultrasonic excitation and light detection are performed is two-dimensionally scanned along the surface of the sample 101, and the time from excitation to detection is determined. It is necessary to create a distribution that changes, and to comprehensively evaluate the results measured from a plurality of directions to calculate the positions of foreign matter, defects, and interfaces.

  When the non-convergent ultrasonic transducer 3011 is used, the frequency f of the ultrasonic wave oscillated from the non-convergent ultrasonic transducer 3011 and the spread L of the surface that oscillates the ultrasonic wave of the non-convergent ultrasonic transducer 3011 are obtained. By selecting appropriately, the efficiency and accuracy of defect detection of size W can be improved. This is because when the velocity of sound in the air is v and the wavelength v / f is sufficiently larger than the oscillation surface L (v / f >> L), the ultrasonic wave is the oscillation surface of the non-convergent ultrasonic transducer 3011. If the wavelength is sufficiently small with respect to the oscillation surface (v / f << L), it is propagated in a beam shape with good directivity from the oscillation surface of the non-convergent ultrasonic transducer 3011.

  That is, when an ultrasonic wave that diverges from the oscillation surface of the non-convergent ultrasonic transducer 3011 is incident on the sample, not only the excitation efficiency is lowered, but also the wavefront of the ultrasonic wave excited by the sample is complicated. This makes it difficult to interpret the measurement results. However, when the scattering of ultrasonic waves inside the sample is strong, by increasing the wavelength of the ultrasonic waves (that is, by reducing the frequency), it is possible to suppress ultrasonic scattering and detect defects at deeper positions. There are advantages to doing.

  On the other hand, when ultrasonic waves propagating in the form of a beam from the oscillation surface of the convergent ultrasonic transducer 301 or 303 are incident on the sample, the excitation efficiency is improved and the ultrasonic wavefront propagating inside the sample becomes a plane wave, so that defect detection is possible. There is an advantage that the efficiency of the measurement is improved and an advantage that the measurement result is easy to understand. However, when the directivity of the beam-like ultrasonic wave is improved, only a defect directly under the oscillation surface of the convergent ultrasonic transducer 301 or 303 can be excited, and there is a concern that a defect directly under the optical sensor may be missed.

  When actually detecting defects using the non-convergent transducer 3011, the ultrasonic frequency and the size of the transducer are taken into account in consideration of the ultrasonic propagation characteristics of the sample, the size of the defect to be detected, and the purpose of the defect inspection. Select the size.

  In FIG. 5 or FIG. 9 to FIG. 13, an example in which the imaging optical system is assembled using detection light for light detection as convergent light is shown, but the detection light may be parallel light. An advantage of using detection light as parallel light is that a wider area can be measured at a time. On the other hand, when the imaging optical system is used, the detection light density is increased because the detection light is narrowed down to one point in space, and detection can be performed efficiently. Further, there is an advantage that the spatial resolution can be improved and an advantage that the measurement can be performed even when the sample surface 102 is inclined.

  Whether the detection light is collimated or condensed using an imaging optical system, if the final photoelectric conversion element is a monocular element such as a photodiode or photomultiplier tube, the irradiated area That is, the surface displacement in the visual field can be detected by averaging. In this case, since the change in the entire visual field is added and detected, there is an advantage that the detection sensitivity is improved.

  On the other hand, when a two-dimensional imaging device such as a CCD camera is used as the photoelectric conversion device, there is an advantage that spatial resolution is possible because the field of view is divided into pixels. Whether to use a monocular element or a two-dimensional imaging element as the photoelectric conversion element is selected depending on the measurement object and the object to be detected.

  In the first embodiment, an embodiment is described in which a common optical path optical interferometer 306 is used as an optical sensor and ultrasonic excitation is symmetric with respect to the detection optical axis of the optical sensor. The advantage of the configuration described in the first embodiment is that a very compact measurement system can be realized. On the other hand, a compact and high-sensitivity non-contact internal defect inspection can also be realized by using the configuration illustrated in FIG. 14 and performing optical measurement symmetrical to the propagation direction of the excitation ultrasonic wave. The advantage of the second embodiment is that the entire measurement system can be configured relatively compactly, and the configuration of the optical sensor used for detection can be simplified compared to the first embodiment.

A second embodiment of the present invention will be described with reference to FIGS.
FIG. 14 shows a configuration of a non-contact ultrasonic measurement apparatus in which an ultrasonic wave is excited on a sample 101 by an aerial ultrasonic excitation transducer 401, ultrasonic waves are detected through surface displacement by an oblique incident Sagnac interferometer, and the inside of the sample is observed. An example is shown.

  The ultrasonic wave irradiated from the ultrasonic transducer 401 passes through the sample surface 102 and propagates inside the sample 101. If a defect or an interface exists inside the sample 101, the ultrasonic wave is reflected or scattered there, and a part thereof returns to the sample surface 102 to displace the surface.

  The measurement light 402 in the Sagnac interferometer enters from the + z direction to the −z direction. The measuring light 402 is converted into linearly polarized light 4021 and 4022 in the (x + y) direction or the (x−y) direction by the polarizer 403, and is divided by orthogonal polarization components by the polarization beam splitter 404. The polarization beam splitter 404 can be separated into orthogonal polarization components, i.e., has a function of transmitting one polarized light and reflecting the other polarized light.

  The detection light 4021 that has passed through the polarization beam splitter 404 has its propagation direction changed by the mirror 405, and is condensed by the lens 406 onto the region where the ultrasonic transducer 401 excites the ultrasonic waves. The measurement light 402 reflected or scattered by the sample surface 102 is collected by the lens 407, the propagation direction is changed by the mirror 408 and the mirror 409, and is directed to the polarization beam splitter 404. The detection light 402 passes through the polarization beam splitter 404 and reaches the wave plate 410.

  On the other hand, the detection light 4022 converted into linearly polarized light by the polarizer 403 and reflected by the polarization beam splitter 403 is changed in the propagation direction by the mirror 409 and the mirror 408, and the ultrasonic transducer 401 excites the ultrasonic wave by the lens 407. Focused on the area where The measurement light 402 reflected or scattered by the sample surface 102 is collected by the lens 406, changed in direction by the mirror 405, reflected by the polarization beam splitter 404, and reaches the wave plate 410.

  The orthogonally polarized measurement lights 4021 and 4022 that have reached the wave plate 410 interfere with each other by providing a phase difference by the wave plate 410, and only a specific polarization component is extracted by the analyzer 411. The measurement light 402 that interferes and is extracted by the analyzer 411 reaches the photodetector 412 and is measured.

  Here, the photodetector 412 may be a monocular element such as a photodiode or a photomultiplier tube, or a two-dimensional imaging element such as a CCD camera. When light detection is performed using a monocular element, there is an advantage that it is advantageous for high speed and high sensitivity. However, when performing two-dimensional measurement, the entire optical interferometer or the sample 101 needs to be scanned. On the other hand, when a two-dimensional image sensor such as a CCD camera is used, there is an advantage that spatially-resolved measurement can be performed within the irradiation region of the measurement light 402. Here, the spatial resolution is determined by the magnification of the lens 406, the lens 407, and the imaging lens 438, and the size of the two-dimensional image sensor.

  In the case of using a monocular element, the focal length and aperture of the imaging lens 438 can be selected in consideration of the detection efficiency in the photodetector 412 based on the resolution and magnification. In the case of using a monocular element, the imaging lens 438 is not always necessary depending on the situation, and can be omitted.

  In the configuration shown in FIG. 14, the optical path of the measurement light 4021 propagating through the polarizer beam splitter 403 → mirror 405 → the lens 406 and the changed beam splitter 404 → from the time when the measurement light 402 is incident until it reaches the sample surface 102. There are two optical paths in the optical path of the measuring light 4022 that propagates from the mirror 409 to the mirror 408 to the lens 407, and the optical path length differs by an interval L: 413 between the changed beam splitter 404 and the mirror 409. Therefore, the measurement light reaches the sample surface 102 at a timing different by t0 = L0 / c0. However, the measurement beams 4021 and 4022 that have reached the polarization beam splitter 404 again and are reflected or transmitted are combined into one light beam when reaching the wave plate 410. Here, t0 is the difference in arrival time of the measuring light, L0 is the optical path difference 413 until reaching the sample surface 102, and c0 is the speed of light in vacuum.

  Eventually, the measuring light 402 measures the displacement d (t) of the surface of the sample surface 102 at a timing different by t0. In the optical interferometer having the configuration shown in FIG. 14, D (t) = {d (t + t0) -d (t)} / t0, that is, the surface vibration is measured. Here, d (t) is the surface displacement at time t, and D (t) is the difference in surface displacement detected by the interferometer at time t.

  When the optical interferometer configured as shown in FIG. 14 is used, the measurement light propagates in the opposite direction on the same optical path. Therefore, the influence of air fluctuations in the optical path and disturbance on each element of the interferometer can be reduced, and high sensitivity detection can be achieved. The advantage is that it can be achieved.

  In FIG. 14, it is assumed that the detection light 402 collected by the lens 408 is collected in a region close to the detection light 402 collected by the lens 406 and transmitted through the polarization beam splitter 404. The adjacent region includes being focused on the same region, and may be separated by about 100 μm. When the measurement light 4021 condensed by the lens 406 and the measurement light 4022 condensed by the lens 407 are irradiated on a closer area, the vibration D (t) of the sample surface 102 at the time t 0 corresponding to the optical path difference L: 413 is measured. Therefore, when the measurement light is irradiated to a more distant area, a physical quantity in which both vibration and spatial differentiation are superimposed is measured. The condensing area of the measuring beams 4021 and 4022 can be changed according to the purpose.

  In the configuration shown in FIG. 14, the timing at which the measurement beams 4021 and 4022 reach the sample surface 102 is fixed at t0 = L0 / c0 when the optical interferometer is configured. Therefore, as shown in FIG. 15, the irradiation timing of the measurement light 402 can be made variable by adding a delay optical path constituted by a corner mirror 417 or the like to the interferometer. That is, the measurement light 4024 that is incident on the measurement beam 402 and reflected by the polarization beam splitter 404 passes through the mirror 418 and the corner mirror 417, is collected by the lens 418, and is irradiated on the sample surface 102. Compared with the polarized light component 4023 that passes through the mirror 414 and is collected by the lens 415 and reaches the sample surface 102, the sample surface is delayed by t1 = 2L1 / c0. By moving the corner mirror 417, L1 is changed, and t1 can be controlled to make the timing of reaching the sample surface 102 variable.

  Here, the corner mirror 417 may be an optical element that reflects light in parallel with incident light. In addition to the corner mirror, the corner mirror 417 may be configured by a combination of a retro reflector, a corner cube, a cat's eye, a mirror, and the like. good.

  In the configuration examples shown in FIGS. 14 and 15, the Sagnac interferometer is configured by arranging optical elements such as mirrors so that the detection light 402 propagates through the space. As described above, the structure propagates in the same optical path at different timings, and thus has a strong characteristic against disturbance. However, in order to make it more stable against disturbance, a configuration as shown in FIG. 16 can be considered.

  The configuration shown in FIG. 16 is a configuration in which the optical path is configured by an optical fiber, and only the portion where the measurement light 402 is irradiated onto the sample surface 102 is emitted from the optical fiber. In FIG. 16, measurement light oscillated by the light source 420 is introduced into a polarization preserving fiber 421 (hereinafter referred to as fiber 421). A linear polarizer 422 is disposed on the fiber 421 so that the polarization propagating through the fiber 421 can be adjusted. The measurement light propagating through the fiber 421 is separated into orthogonal polarization components by a demultiplexer 423, and each polarization component is divided into a polarization preserving fiber fiber 424 (hereinafter referred to as a fiber 424) and a polarization preserving fiber fiber 429 (hereinafter referred to as a fiber 424). ).

  The detection light guided to the fiber 424 is emitted by the output coupler 425 and condensed on the sample surface 102 by the lens 426. The measurement light reflected or scattered by the sample surface 102 is collected by the lens 427, introduced into the fiber 429 by the output coupler 428, and reaches the branching filter 423. On the other hand, the detection light guided from the splitter 423 to the fiber 429 passes through the output coupler 428 and is collected on the sample surface 102 by the lens 427. The detection light reflected or scattered by the sample surface 102 is collected by the lens 426, introduced into the fiber 424 through the output coupler 425, and returns to the duplexer 423.

  Here, the measurement light guided from the duplexer 423 to the fibers 424 and 429 reaches the sample surface 102 at different timings due to the different lengths of the fibers 424 and 429.

  The polarization components returned to the demultiplexer 423 are combined by the demultiplexer 423 and guided to the fiber 430. A wave plate 431 and an analyzer 432 are incorporated in the fiber 430. The phase difference is adjusted by the wave plate 431 so that the orthogonal polarization components interfere with each other, and a specific polarization is obtained from the measurement light interfered by the analyzer 432. The components are extracted, and the detection light collected by the condenser lens 438 is detected by the photodetector 410, and displacement is measured based on the detection signal.

  The demultiplexer 423 shown in FIG. 17 separates the measurement light incident from the fiber 421 by polarization and branches each polarization component to the fibers 424 and 429, and the light incident from the fibers 424 and 429. Any element having a function of guiding all of the light to the fiber 430 while preserving the polarized light may be used. For example, the duplexer 423 can be configured by combining the circulator 433 and the polarization coupler 434 as illustrated in FIG.

  The configuration using the optical fiber shown in FIG. 16 has an advantage that the entire apparatus can be configured more compactly by winding the optical fibers 424 and 429 and the like than the configurations shown in FIGS.

  In the optical interferometer shown in FIGS. 14 to 16, the measurement light is condensed on the sample surface 102 by the lens 406 or the lens 407, the lens 415, the lens 416, the lens 426, and the lens 427. The advantages of condensing the detection light 402 on the sample surface 102 using a lens or the like are that high sensitivity detection is possible by improving the light density in detection and that spatial resolution can be improved.

  However, since the light density of the detection light is improved, there is a risk of damaging the sample surface 102, and in order to perform a two-dimensional measurement, it is necessary to scan the optical interferometer or the sample. Therefore, a configuration in which the measurement light is not condensed on the sample surface 102 as illustrated in FIG. 18 is also conceivable. In the configuration shown in FIG. 18, similarly to FIG. 14, the light split into the orthogonal polarization components by the polarization beam splitter 404 is changed in its propagation direction by the element 435 such as a prism, and the ultrasonic transducer 401 Irradiates the region where the sound wave is excited as parallel light.

  The detection light reflected or scattered by the sample surface 102 has its propagation direction changed by an element 436 such as a prism and a mirror 437, passes through the polarization beam splitter 404, and reaches the wave plate 410. On the other hand, the measurement light reflected by the polarizing beam splitter 404 propagates in the mirror 437 → element 436 → sample surface 102 → element 435, reaches the polarizing beam splitter 404, is reflected by the polarizing beam splitter 404, and reaches the wave plate 410.

  The advantage of using the configuration of irradiating the sample surface 102 with the measurement light 402 in the state of parallel light as shown in FIG. 18 is that the sample 101 is less likely to be damaged by lowering the light density of the detection light. A wide area can be measured at a time. Further, since the sample 101 is irradiated with the detection light as parallel light, there is an advantage that the detection light 402 always reaches the photodetector 412 even when the distance between the elements 435 and 436 and the sample 101 changes.

  In the configuration using an interferometer that does not collect the measurement light as shown in FIG. 18, spatially resolving measurement is possible by using the photodetector 412 as a two-dimensional image sensor, and a large area can be measured in one measurement. Since it can be covered, high-speed and large-area measurement is possible. In addition, when a monocular photodetector is used, there is an advantage that high-sensitivity detection can be performed because surface displacement over a wide area can be measured.

  The ultrasonic wave is excited on the sample 101 by the aerial ultrasonic wave excitation transducer 401 described in the first and second embodiments, and the ultrasonic wave is detected via the surface displacement by the common optical path light interferometer or the oblique incidence Sagnac interferometer. The non-contact ultrasonic measurement means for observing the inside of the 101 can be realized by the configuration shown in FIGS. However, the configurations shown in FIGS. 5 to 18 can only realize observation in the depth direction of the sample 101 in a limited area irradiated with measurement light or a single spatial point collected by the lens. Therefore, it is necessary to scan the measurement unit including the components shown in FIGS. 5 to 18 along the sample surface by some means.

  FIG. 19 shows an example of an apparatus configuration in which a scanning device 503 on which a measurement unit 501 and a light source 502 for detection light are mounted scans a sample 101 mounted on a sample stage 507. The scanning device 503 can move, for example, the measurement unit 501 in the orthogonal three-axis direction and rotate around the three orthogonal axes by the scanning control unit 506, and can move the measurement point on the sample 101. In the configuration shown in FIG. 19, the light source 502 is also mounted on the scanning device 503. However, the light source 502 is not necessarily mounted on the scanning device 503, and a configuration in which measurement light is guided to the measurement unit 501 by using an optical fiber or the like. But you can. Further, the sample stage 507 on which the sample 101 is mounted may have a function of moving or rotating.

  An analog output signal from the photodetector 412 in the measurement unit 501, that is, a signal corresponding to the surface displacement of the sample 101 is transmitted to the control unit 505 after the analog signal is converted into a digital signal by the analog-digital converter 504, for example. . The control unit 505 controls the scanning control unit 506 to change the position on the sample 101 and collect surface displacement signals at each point on the sample surface 102. As shown in FIG. 20, the collected result is a data set 2002 in which the displacement 2001 of the sample surface 102 at each point in space is observed on the time axis.

  The control unit 505 processes data obtained by observing the displacement of the surface 102 of the sample 101 at each point in the space as shown in FIG. 20, and displays it as a two-dimensional image 2102 on the display screen 2101 as shown in FIG. 21, for example. It may have a function. 21 reads the data shown in FIG. 20, calculates the depth, position, and distribution of defects, interfaces, and the like in the sample 101 from the time until the sample surface is displaced after exciting the ultrasonic wave. It is an example plotted with points.

  By displaying in a two-dimensional manner like the two-dimensional image 2102 in FIG. 21, there is an advantage that the distribution of, for example, defects and interfaces in the sample 101 can be intuitively known. When a two-dimensional imaging device is used for the photodetector 412, the scanning device 503 is scanned to connect the two-dimensional images picked up at each point in the space, so that two areas of a wider area than the field of view of the two-dimensional imaging device can be obtained. For example, it is possible to know the dimensional distribution of defects and interfaces in the sample 101.

DESCRIPTION OF SYMBOLS 101 ... Sample 102 ... Sample surface 103 ... Defect 201 ... Ultrasonic transducer 205 ... Common optical path optical interferometer 301 ... Ultrasonic transducer 302 ... Through-hole 303 ... Ultrasonic transducer 304 ... Spot facing 305 ... Through hole 306 ... Common optical path optical interferometer 310 ... Defect 313 ... Reference mirror 314 ... Common optical path optical interferometer 315 ... Optical fiber 316: Output coupler 401 ... Ultrasonic transducer 403 ... Polarizer 404 ... Polarizing beam splitter 405, 408, 409, 414, 418 ... Mirror 406, 407, 415, 416 ... Lens 410: Wave plate 411: Analyzer 412 ... Photodetector 417 ... Corner mirror 420 ... Light source 421, 424, 430 ... Optical fiber 422 ... Polarizer 423 ... Demultiplexer 425, 428 ... Output coupler 426, 427 ... Lenses 429, 430 ... Optical fiber 431 ... Wave plate 432 ... Analyzer 433 ... Circulator 434 ... Polarizing coupler 435, 436 ... Prism 437 ... Mirror 501 ... Measurement unit 502 ... Light source 503 ... Scanning device 504 ... Analog / digital converter 505 ... Control unit 601 ... Polarization plane preserving fiber 602 ... Collimator 604 ... Polarizing element 606 ... Prism mirror 607 ... Non-polarizing beam splitter 608 ・Reference mirror 610 ... Condensing lens 613 ... Aperture 615 ... Square pyramid prism 616 ... Square pyramid prism 618 ... Photonic crystal array 619 ... Photonic crystal array 621 ... Connection Image lens 623 ... Photoelectric conversion element 624 ... Amplifier 626 ... Laser diode 628 ... Collimating lens 629 ... Beam shaping element 635 ... Photonic crystal array 636 ... Photonic crystal Array 639 ... Lens array 640 ... Photoelectric conversion element.

Claims (14)

  Ultrasound is emitted from a location away from the sample to be inspected to irradiate the sample with the ultrasonic wave, and the polarized light whose state of polarization is controlled is irradiated to the surface of the sample irradiated with the ultrasonic wave. The light having the same polarization characteristics as the irradiated polarized light out of the reflected / scattered light from the surface of the sample irradiated with the polarized light is detected by a photodetector, and the signal detected by the photodetector is detected. An internal defect inspection method characterized by processing to detect defects inside the sample.   The internal defect inspection method according to claim 1, wherein the ultrasonic wave is irradiated while being converged toward a surface of the sample from a location away from the sample.   The optical image by light having the same polarization characteristics as the irradiated polarized light out of the reflected / scattered light from the surface of the sample irradiated with the polarized light is detected by a photodetector. 2. The internal defect inspection method according to 2.   The light detector has light having the same polarization characteristics as the irradiated polarized light among the reflected / scattered light from the inspection spot irradiated with the ultrasonic wave on the surface of the sample irradiated with the polarized light; The internal defect inspection method according to any one of claims 1 to 3, further comprising detecting light obtained by combining light having a polarization component different from the polarized light irradiated on the surface of the sample.   5. The polarized light having a polarization component different from the polarized light irradiated on the surface of the sample shares at least a part of an optical path with the polarized light irradiated on the surface of the sample. Internal defect inspection method.   The polarized light whose state of polarization is controlled is branched into two optical paths, and one of the polarized lights branched into the two optical paths is irradiated with the ultrasonic wave on the surface of the sample. And the second polarized light of the polarized light branched into the two optical paths is applied to the inspection site irradiated with the ultrasonic wave on the surface of the sample. Condensed and irradiated by the irradiation means, light incident on the second irradiation means out of the light irradiated by the first irradiation means and reflected / scattered from the inspection location, and the second irradiation means 2. The internal defect inspection method according to claim 1, wherein the light that is incident on the first irradiation means among the light that is irradiated and reflected / scattered from the inspection location is detected by the photodetector.   The internal defect inspection method according to claim 6, wherein an optical path length of the first irradiation unit is different from an optical path length of the second irradiation unit.   An ultrasonic irradiation unit that irradiates a sample to be inspected with ultrasonic waves, and an optical device that detects reflected / scattered light from the surface by irradiating light onto the surface of the sample irradiated with ultrasonic waves by the ultrasonic irradiation unit A non-destructive non-contact internal inspection apparatus including a detection unit and a signal processing unit that processes a signal output from the optical detection unit and detects a defect inside the sample, wherein the ultrasonic irradiation unit includes: An ultrasonic transducer that irradiates the sample with ultrasonic waves from a location remote from the sample, and the optical detection unit controls the state of polarization of light emitted from the light source means and the light source means. Means, a light irradiating means for irradiating the surface of the sample irradiated with the polarized light whose polarization state is controlled by the deflection controller, and the polarized light is irradiated by the light irradiating means. Reflected / scattered light from the surface of the sample Among them, it has a light detection means for detecting light having the same polarization characteristics as the irradiated polarized light, and the signal processing section detects a defect inside the sample by processing the signal output from the optical detection means. An internal defect inspection apparatus characterized by that.   The internal defect inspection according to claim 8, wherein the ultrasonic transducer of the ultrasonic irradiation unit converges and irradiates the ultrasonic wave from a location away from the sample toward an inspection location on the surface of the sample. apparatus.   The irradiating means of the optical detection unit condenses and irradiates light on the inspection portion irradiated with the ultrasonic wave on the surface of the sample, and reflects and scatters the image of the reflected and scattered light from the condensed and irradiated portion. The internal defect inspection device according to claim 8 or 9, wherein the internal defect inspection device is detected.   The light detection means of the optical detection unit is the same polarized light as the irradiated polarized light out of the reflected / scattered light from the inspection location irradiated with the ultrasonic wave on the surface of the sample irradiated with the polarized light by the irradiation means. Detecting light combining light having characteristics and light having a polarization component different from the polarized light irradiated on the surface of the sample by the irradiation unit among the light emitted from the light source unit. The internal defect inspection apparatus according to any one of claims 8 to 10.   Polarized light having a polarization component different from the polarized light irradiated on the surface of the sample is reflected by the polarized light irradiated on the surface of the sample, the optical path from the light source means to the irradiation means, and the surface of the sample. The internal defect inspection apparatus according to claim 11, wherein at least a part of each of the scattered light and the optical path to the light detection means is shared.   The light irradiating means of the optical detection unit includes a polarization branching unit that branches the polarized light whose polarization state is controlled by the deflection control unit into two optical paths, and a polarized light that is branched into two optical paths by the polarization branching unit. A first irradiating means for condensing and irradiating one of the polarized light to the inspection site irradiated with the ultrasonic wave on the surface of the sample, and polarized light branched into two optical paths by the polarization branching means A second irradiating means for condensing and irradiating the other polarized light on the surface of the sample irradiated with the ultrasonic wave, and the light detecting means comprises the first irradiating means. Of the light irradiated by the means and reflected / scattered from the inspection location, the light incident on the second irradiation means and the light irradiated by the second irradiation means and reflected / scattered from the inspection location Detecting light incident on the first irradiation means. Inner defect inspection device according to claim 8, wherein the symptom.   14. The internal defect inspection apparatus according to claim 13, wherein the optical path length of the first irradiation unit and the optical path length of the second irradiation unit are different.

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