Laser ultrasonic detection method and device

Abstract

The present application relates to a laser ultrasonic detection method and device, which generates and emits a detection light field with a longitudinal phase singularity to a slit diaphragm, uses the slit diaphragm to diffract the detection light field to obtain a diffracted light field, blocks the diffracted light field into a single diffraction spot, and determines the laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface based on the energy of the single diffraction spot. This solves the problem of low detection accuracy of laser ultrasonic detection for tiny material structures in related technologies and improves the accuracy of laser ultrasonic detection.

Description

Technical Field

[0001] The present application relates to the field of laser ultrasonic detection, and in particular to a laser ultrasonic detection method and device. Background Art

[0002] Laser ultrasonic microscopy is similar to XRD (X-ray diffraction) testing, a method with a large field of view, low resolution, and high speed. It has important applications in material structure testing, such as inspecting turbine blades. Its principle is to focus a pulsed laser beam on the surface of an alloy, locally heating the alloy. Due to the alloy's thermal expansion and contraction, acoustic surface waves (SAWs) are generated at the heated area and propagate along the alloy. A second continuous laser beam is then used to detect these SAWs. By analyzing the detected SAW signals (frequency, velocity, etc.), defects and cracks in the alloy can be detected.

[0003] Related technologies for laser ultrasonic detection offer a "knife-edge detection" method, which involves irradiating a Gaussian beam on the surface of a material, converting the acoustic surface wave signal into the displacement of the Gaussian beam. A knife-edge is then used to partially block the Gaussian beam, causing the energy of the Gaussian beam passing through the knife-edge to change when the beam undergoes a slight displacement. This allows detection of the Gaussian beam displacement, and thus of the acoustic surface wave. However, when the material structure of the object being detected is relatively small, the accuracy of laser ultrasonic detection for detecting surface deformation is reduced.

[0004] Currently, no effective solution has been proposed for the problem of low detection accuracy of laser ultrasonic detection for tiny material structures in related technologies. Summary of the Invention

[0005] The embodiments of the present application provide a laser ultrasonic detection method and device to at least solve the problem of low detection accuracy of laser ultrasonic detection for tiny material structures in the related art.

[0006] In a first aspect, an embodiment of the present application provides a laser ultrasonic detection method, characterized by comprising:

[0007] Generate and transmit a detection light field to the slit aperture, wherein the detection light field is a longitudinal phase singular point light field;

[0008] diffracting the detection light field using the slit aperture to obtain a diffracted light field;

[0009] Blocking the diffracted light field into a single diffraction spot;

[0010] A laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface is determined according to the energy of the single diffraction spot.

[0011] In some embodiments, generating the probe light field includes:

[0012] The original light field is expanded, the expanded original light field is converted into circularly polarized laser light, and the circularly polarized laser light is modulated into a longitudinal phase singular point light field as the detection light field.

[0013] In some embodiments, before shielding the diffracted light field into a single diffraction spot, the method includes:

[0014] The diffracted light field is focused to generate double long strip diffraction spots.

[0015] In some embodiments, after shielding the diffracted light field into a single diffraction spot, the method includes:

[0016] shaping the single diffraction spot into a quasi-circular spot;

[0017] The quasi-circular light spots are coupled, and the energy of the coupled quasi-circular light spots is detected.

[0018] In some embodiments, determining, based on the energy of the single diffraction spot, a laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface includes:

[0019] By detecting the energy of a single diffraction spot, the displacement of the singular point of the detection light field in the slit is determined;

[0020] The laser ultrasonic detection signal is determined according to the displacement of the singular point in the slit.

[0021] In a second aspect, the present application provides a laser ultrasonic detection device, characterized in that it comprises: a light field generator, a slit aperture, a knife edge and a detector; wherein,

[0022] The light field generator is used to generate and transmit a detection light field to the slit aperture, wherein the detection light field is a longitudinal phase singular point light field;

[0023] The slit diaphragm has a slit center located on the same horizontal line as the center of the detection light field, and is used to diffract the detection light field to obtain a diffracted light field;

[0024] The knife edge is used to block the diffracted light field into a single diffraction spot;

[0025] The detector is used to detect the energy of the single diffraction spot and determine the laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface based on the energy of the single diffraction spot.

[0026] In some embodiments, the field generator includes a continuous wave laser, a beam expander, a polarizer, a first glass slide, and a second glass slide;

[0027] The continuous wave laser is used to emit the original light field to the beam expander;

[0028] The beam expander is used to expand the original light field;

[0029] The polarizer is used to convert the expanded original light field into linearly polarized light;

[0030] The first glass slide is used to convert the linearly polarized light into circularly polarized light;

[0031] The second glass slide is used to modulate the circularly polarized laser into a detection light field.

[0032] In some embodiments, the laser ultrasonic detection device further includes a Fourier lens, which is placed between the slit aperture and the knife edge and is used to focus the diffraction light field into a double long strip diffraction spot.

[0033] In some embodiments, the laser ultrasonic detection device further includes a cylindrical lens, which is placed between the knife edge and the detector and is used to adjust the single diffraction spot into a quasi-circular spot.

[0034] In some embodiments, the laser ultrasonic detection device further includes a beam reduction system, which is placed between the cylindrical lens and the detector and is used to couple the quasi-circular light spot.

[0035] Compared with the related art, the laser ultrasonic detection device provided in the embodiment of the present application generates and emits a detection light field of a longitudinal phase singularity through a light field generator, the slit aperture diffracts the longitudinal phase singularity light field to obtain a diffraction light field, the knife edge blocks the diffraction light field, and blocks the diffraction spot of the diffraction light field into a single diffraction spot. The detector receives and measures the single diffraction spot blocked by the knife edge to measure the change in light beam energy, thereby solving the problem of low detection accuracy of laser ultrasonic detection for tiny material structures in the related art.

[0036] The details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0038] Figure 1is a flow chart of the laser ultrasonic detection method according to an embodiment of the present application;

[0039] Figure 2 Schematic diagram of the structure of the laser ultrasonic detection device according to an embodiment of the present application;

[0040] Figure 3 is a light field distribution diagram on the focal plane of the Fourier lens as the detection light field of an embodiment of the present application moves along with the longitudinal phase singular point;

[0041] Figure 4 This is a comparison chart of the displacement sensing accuracy of the laser ultrasonic detection device of the embodiment of the present application and the displacement sensing accuracy of the traditional blade detection device. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts are within the scope of protection of this application.

[0043] Obviously, the drawings described below are merely examples or embodiments of the present application. Those skilled in the art can, without inventive effort, apply the present application to other similar scenarios based on these drawings. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, changes in design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in this application.

[0044] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments unless there is a conflict.

[0045] Unless otherwise defined, the technical terms or scientific terms involved in this application should have the usual meaning understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "the" and similar words involved in this application do not indicate quantity restrictions and can represent the singular or plural. The terms "include", "include", "have" and any variations thereof involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The "multiple" involved in this application refers to two or more.

[0046] In this embodiment, a laser ultrasonic detection method is provided. Figure 1 is a flow chart of the laser ultrasonic detection method according to an embodiment of the present application. Figure 1 As shown, the method includes the following steps:

[0047] Step S101 : generating and transmitting a detection light field to a slit aperture, wherein the detection light field is a longitudinal phase singular point light field.

[0048] This application uses the diffraction law of the relative position of an optical longitudinal phase singularity and a slit for laser ultrasonic detection, replacing the diffraction law of the relative position of a Gaussian beam and a knife edge in traditional techniques. The longitudinal phase singularity light field contains an optical longitudinal phase singularity at its center, which exhibits extreme optical properties such as infinitesimal spatial scale, high phase gradient, phase step, and the ability to carry a toroidal energy flux.

[0049] Step S102: diffract the detection light field using a slit aperture to obtain a diffracted light field.

[0050] Among them, due to the extreme optical properties of the longitudinal phase singularity, the extreme physical properties of the detection light field are partially resolved after passing through the diffraction element. This application uses a slit aperture as a diffraction element. After the extreme physical properties of the detection light field are resolved by the slit aperture, the generated diffraction stripes present a dual-spot structure. When the longitudinal singularity shifts in the slit aperture, the extreme physical properties blocked by the slit aperture also change, which in turn causes the energy of the two spots in the dual-spot structure to fluctuate, but the total energy of the two spots remains approximately unchanged. During the detection process, the dual-spot structure has a sensitive response characteristic to the spatial position of the longitudinal singularity, and can also have a relatively obvious energy change for a small displacement of the longitudinal singularity, so it can also have an accurate detection effect for tiny material structures.

[0051] Step S103: shielding the diffracted light field into a single diffraction spot.

[0052] The two spots of the diffraction light field are shielded into a single diffraction spot, so that the change of the longitudinal singular point displacement is reflected as the fluctuation of the energy of the single spot.

[0053] Step S104 : determining the laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface according to the energy of the single diffraction spot.

[0054] Focusing a laser on a metal surface heats it. Due to the metal's thermal expansion and contraction, the heated area generates acoustic surface waves (the laser ultrasonic detection signal) that propagate along the metal. Using continuous laser light to detect these acoustic surface waves, and analyzing the detected acoustic surface wave signals, it is possible to detect defects, cracks, and other metal information.

[0055] Compared to the related art, the longitudinal phase singular point light field used in the present application has an extremely high phase step. This phase step will be diffracted by the slit and divide the light field into two spot structures. The detection light field used in the related art is a Gaussian beam. When passing through the knife edge, half of the beam is covered, and the energy of the beam does not change significantly with displacement, resulting in low detection accuracy. However, when the longitudinal phase singular point light field in the present application passes through the knife edge, a circular spot is completely covered, the energy changes more significantly with displacement, and the detection accuracy is higher. In addition, when the Gaussian beam passes through the knife edge, it will diffract at the edge of the knife edge, causing interference with the energy detection of the beam and reducing the linearity of the measurement. However, when the longitudinal phase singular point light field in the present application passes through the slit, it is diffracted into two spots, avoiding the diffraction generated on the knife edge and improving the linearity of the beam energy detection. At the same time, the position of the Gaussian beam used in the prior art will change with the change of energy, so the measurement stability is low. The energy fluctuation form of the two light spots in the present application is essentially an interference phenomenon, so the positions of the two light spots remain unchanged, ensuring improved measurement accuracy while having extremely high measurement stability.

[0056] The present application uses the above-mentioned laser ultrasonic detection method to generate and emit a detection light field with a longitudinal phase singularity to a slit aperture, use the slit aperture to diffract the detection light field to obtain a diffracted light field, block the diffracted light field into a single diffraction spot, and determine the laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface based on the energy of the single diffraction spot. This solves the problem of low detection accuracy of laser ultrasonic detection for tiny material structures in related technologies and achieves the beneficial effect of improving the accuracy of laser ultrasonic detection.

[0057] In some embodiments, generating the detection light field includes: expanding the original light field, converting the expanded original light field into circularly polarized laser light, and modulating the circularly polarized laser light into a longitudinal phase singular point light field as the detection light field.

[0058] Among them, the original light field is a continuous laser beam. Beam expansion can change the diameter and divergence angle of the laser beam, making the laser beam into a collimated beam, so that a small high-power density light spot can be obtained by focusing subsequently.

[0059] In some embodiments, before shielding the diffracted light field into a single diffraction spot, the method further includes: focusing the diffracted light field to generate a double long strip diffraction spot.

[0060] Among them, a Fourier lens can be used to focus the diffracted light field, so that the light field distribution of the diffracted light field is Fourier transformed, thereby realizing the generation of double long strip diffraction spots.

[0061] In some embodiments, after the diffraction light field is blocked into a single diffraction spot, the method further includes: shaping the single diffraction spot into a quasi-circular spot, coupling the quasi-circular spots, and detecting the energy of the coupled quasi-circular spots.

[0062] After coupling the light field, its energy needs to be measured. Specifically, the energy signal can be received by a high-sensitivity oscilloscope and sent to an electronic computer for analysis and processing, so as to obtain the change in the singularity position and then the ultrasonic frequency.

[0063] In some embodiments, determining the laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface based on the energy of a single diffraction spot includes: determining the displacement of the singular point of the detection light field in the slit by detecting the energy of the single diffraction spot; and determining the laser ultrasonic detection signal based on the displacement of the singular point in the slit.

[0064] Among them, the optical longitudinal phase singularity will form a double-spot diffraction pattern when passing through the slit. The position of the singularity in the slit determines the energy fluctuation between the two spots. Therefore, the singularity displacement can be measured by detecting the energy of a single spot. The singularity displacement contains the laser ultrasonic detection signal, thereby realizing the detection of laser ultrasound.

[0065] In a second aspect, this embodiment provides a laser ultrasonic detection device, Figure 2 is a structural diagram of the laser ultrasonic detection device according to an embodiment of the present application. Figure 2 As shown, the device includes:

[0066] The light field generator 21 is used to generate and transmit a detection light field to the slit aperture, wherein the detection light field is a longitudinal phase singular point light field.

[0067] Among them, the light field generator 21 is used to generate a longitudinal phase singularity light field as the detection light field of the acoustic surface wave signal. The longitudinal phase singularity has an extremely high phase step, and the energy of the light beam changes significantly with the displacement. It is used in the field of laser detection and has high detection accuracy.

[0068] The slit aperture 22 is used to diffract the detection light field to obtain a diffracted light field.

[0069] Among them, the detection light field passes through the slit aperture 22 after being reflected by the metal sample to be detected. The slit aperture 22 needs to be placed at the exact center of the detection light field during the optical path calibration stage to ensure that the longitudinal phase singularity is at the center of the slit of the slit aperture 22, thereby retaining the passage of the light field near the longitudinal phase singularity. Since the phase step of the longitudinal phase singularity itself is extremely high, this phase step is greatly stretched by the diffraction of the slit aperture 22, and the original light field is stretched into a linear structure, and the light field is divided into two light spot structures. As the longitudinal phase singularity moves in the middle of the slit aperture 22, the energy of the two divided light spots also fluctuates, thereby achieving the redistribution of the energy of the two light spots. In addition, since the fluctuation of the energy of the two light spots is essentially an interference phenomenon, the position of the two light spots does not change with the movement of the longitudinal phase singularity in the middle of the slit aperture 22. In this way, on the basis of improving the measurement accuracy, the stability of the measurement process is also guaranteed.

[0070] The knife edge 23 is used to block the diffraction spots of the diffraction light field into a single diffraction spot.

[0071] The knife-edge technique used during the detection process, utilizing blade 23, is a non-interferometric detection technique. The specific principle is that when the size of the probe light spot incident on the surface of the probe material is smaller than the ultrasonic wavelength, the reflected light is deflected. The light flux intercepted by blade 23 is used to measure the amount of deflection of the reflected light. This deflection can reflect the propagation of acoustic surface waves, as well as the structure and defects of the sample surface. In this application, the diffracted light field of the longitudinal phase singularity is blocked by blade 23 to form a single diffraction spot. The other diffraction spot is completely blocked by blade 23 and used to measure the deflection of the reflected light.

[0072] The detector 24 is used to receive and measure the diffraction spot of the diffracted light field after being blocked by the knife edge.

[0073] The detector 24 receives the light spot after a series of processing, and obtains the displacement change of the detection light field by measuring the change in the energy of the light beam, thereby realizing the detection of higher frequency sound wave signals.

[0074] In some embodiments, the light field generator 21 includes a continuous wave laser, a beam expander, a polarizer, a first glass plate, and a second glass plate.

[0075] The continuous wave laser is used to emit a light beam to the beam expander, the beam expander is used to expand the light beam, the first glass slide is used to convert linearly polarized light into circularly polarized light, and the second glass slide is used to modulate the circularly polarized laser into a detection light field.

[0076] Among them, the continuous wave laser can continuously output laser of a certain duration. The light beam emitted by the continuous wave laser is expanded by a beam expander. The expanded light beam passes through the polarizer and the first glass slide once to be converted into a circularly polarized laser. The circularly polarized laser is irradiated onto the second glass slide and modulated into a longitudinal phase singular point light field as the detection light field of the acoustic surface wave signal.

[0077] Illustratively, the first glass slide used in this application is a 1 / 4 glass slide, and the second glass slide is a 1st-order glass slide. The 1 / 4 glass slide utilizes the anisotropic characteristics of the material to have different refractive indices and propagation speeds for light in different polarization directions, thereby generating a phase difference between the two components, thereby converting linearly polarized light into circularly polarized light, or converting circularly polarized light into linearly polarized light.

[0078] In some embodiments, the laser ultrasonic detection device further includes a Fourier lens 25 , which is placed between the slit aperture 22 and the knife edge 23 and is used to focus the diffracted light field into a double long strip diffraction spot.

[0079] Among them, the function of the Fourier lens 25 is that the light field distribution of the incident diffracted light field on the focal plane after passing through the Fourier lens 25 is equivalent to the Fourier transform of the incident light field, thereby completing the focusing of the diffracted light field and realizing the generation of double long strip diffraction spots.

[0080] Exemplarily, the knife edge 23 should be placed at the focal plane of the Fourier lens 25 to ensure that one of the light spots can be completely covered.

[0081] In some embodiments, the laser ultrasonic detection device further includes a cylindrical lens 26 , which is placed between the knife edge 23 and the detector 24 and is used to adjust a single diffraction spot into a quasi-circular spot.

[0082] Among them, the cylindrical lens 26 is an aspherical lens with a one-dimensional magnification function. In this application, it is used to shape the single long strip diffraction spot after being blocked by the knife edge 23 into a quasi-circular spot.

[0083] Exemplarily, the axis of the cylindrical lens 26 is perpendicular to the single diffraction spot, and the focal length is determined according to the aspect ratio of the single diffraction spot, thereby ensuring that the long strip-shaped spot can be transformed into a quasi-circular spot through the cylindrical lens 26.

[0084] In some embodiments, the laser ultrasonic detection device further includes a beam reduction system 27 , which is placed between the cylindrical lens 26 and the detector 24 and is used to couple a quasi-circular light spot.

[0085] The beam reduction system 27 comprises a 4-f beam reduction system. The 4-f system is a special optical system that, when two coherent polarized beams are input, continuously changes the phase difference between the diffraction orders of the two beams, thereby achieving the purpose of subtracting or adding the diffracted light intensity. In this application, the beam reduction system 27 includes two lenses. The focal length ratio of the two lenses should be selected based on the size of the incident aperture of the detector 24 to ensure that the light beam can be coupled into the detector 24.

[0086] Figure 3 is a light field distribution diagram on the focal plane of the Fourier lens as the detection light field of the embodiment of the present application moves along with the longitudinal phase singular point, such as Figure 3 As shown, the detection light field passes through the Fourier lens 25, the slit aperture 22, and the knife edge 23, and is gradually shaped from the detection light field into a double long strip diffraction spot, and finally becomes a single long strip diffraction spot after being blocked.

[0087] Figure 4 : is a comparison chart of the displacement sensing accuracy of the laser ultrasonic detection device of the embodiment of the present application and the displacement sensing accuracy of the traditional blade detection device, such as Figure 4 As shown, Figure 4 The dots in the figure are the results of the traditional blade detection technology, and the square dots are the results of the laser ultrasonic detection device for the optical longitudinal phase singularity of embodiment 1. The horizontal axis is the displacement, and the vertical axis is the relative change rate of the intensity. It can be seen that Figure 4 The data slope of the laser ultrasonic detection device for optical longitudinal phase singularity in the embodiment of the present application is significantly higher than that of the traditional blade detection device, that is, the energy of the light beam of the laser ultrasonic detection device for optical longitudinal phase singularity in the embodiment of the present application changes more obviously with displacement, and the measurement accuracy is higher, which proves that the detection sensitivity of the laser ultrasonic detection device in the embodiment of the present application is higher than that of the related technology, so that the laser ultrasonic detection device of the present application can realize the detection of higher-frequency sound wave signals and realize the improvement of the imaging resolution of laser ultrasonic microscopy technology.

[0088] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A laser ultrasonic detection method, characterized in that: include: Generate and transmit a detection light field to be reflected by the metal sample to be detected to the slit aperture, wherein the detection light field is a longitudinal phase singular point light field; diffracting the detection light field using the slit aperture to obtain a diffracted light field; Blocking the diffracted light field into a single diffraction spot; A laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface is determined according to the energy of the single diffraction spot.

2. The laser ultrasonic detection method according to claim 1, characterized in that: Generating the detection light field includes: The original light field is expanded, the expanded original light field is converted into circularly polarized laser light, and the circularly polarized laser light is modulated into a longitudinal phase singular point light field as the detection light field.

3. The laser ultrasonic detection method according to claim 1, characterized in that: Before shielding the diffracted light field into a single diffraction spot, the method includes: The diffracted light field is focused to generate double long strip diffraction spots.

4. The laser ultrasonic detection method according to claim 1, characterized in that: After shielding the diffracted light field into a single diffraction spot, the method includes: shaping the single diffraction spot into a quasi-circular spot; The quasi-circular light spots are coupled, and the energy of the coupled quasi-circular light spots is detected.

5. The laser ultrasonic detection method according to claim 1, characterized in that: Determining, based on the energy of the single diffraction spot, a laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface includes: By detecting the energy of a single diffraction spot, the displacement of the singular point of the detection light field in the slit is determined; The laser ultrasonic detection signal is determined according to the displacement of the singular point in the slit.

6. A laser ultrasonic detection device, characterized in that: include: A light field generator, a slit aperture, a knife edge, and a detector; wherein, The light field generator is used to generate and emit a detection light field that is reflected by the metal sample to be detected to the slit aperture, wherein the detection light field is a longitudinal phase singular point light field; The slit aperture, wherein the center position of the slit is on the same horizontal line as the center position of the detection light field, is used to diffract the detection light field to obtain a diffracted light field; The knife edge is used to block the diffracted light field into a single diffraction spot; The detector is used to detect the energy of the single diffraction spot and determine the laser ultrasonic detection signal generated when the detection light field is emitted to the metal surface based on the energy of the single diffraction spot.

7. The laser ultrasonic detection device according to claim 6, characterized in that: The light field generator includes a continuous wave laser, a beam expander, a polarizer, a first glass slide, and a second glass slide; The continuous wave laser is used to emit the original light field to the beam expander; The beam expander is used to expand the original light field; The polarizer is used to convert the expanded original light field into linearly polarized light; The first glass slide is used to convert the linearly polarized light into circularly polarized laser light; The second glass slide is used to modulate the circularly polarized laser into a detection light field.

8. The laser ultrasonic detection device according to claim 6, characterized in that: The laser ultrasonic detection device further comprises a Fourier lens, which is placed between the slit aperture and the knife edge and is used to focus the diffracted light field into a double-strip diffraction light spot.

9. The laser ultrasonic detection device according to claim 6, characterized in that: The laser ultrasonic detection device further includes a cylindrical lens, which is placed between the knife edge and the detector and is used to adjust the single diffraction spot into a quasi-circular spot.

10. The laser ultrasonic detection device according to claim 9, characterized in that: The laser ultrasonic detection device further includes a beam reduction system, which is placed between the cylindrical lens and the detector and is used to couple the quasi-circular light spot.

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