Inspection Equipment

Abstract

To provide an inspection device which enables the inspection of an inspection object positioned in a lower layer of a hardly permeable material.SOLUTION: An inspection device includes: a light source for outputting pulsed excitation light having a time width from 10 picoseconds to 10 nanoseconds; a nonlinear optical crystal for generating a terahertz wave by the optical wavelength conversion of the pulsed excitation light; a polarizing part for reflecting at least a part of a reflected wave of the terahertz wave reflected by an inspection object; and a detector for detecting the reflected wave reflected by the polarizing part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an inspection apparatus. [Background technology]

[0002] Patent Document 1 discloses a reflection-type terahertz wave measuring device (inspection device) configured to be able to irradiate the surface of a structure with terahertz waves, a type of electromagnetic wave, and to detect terahertz waves reflected by the structure. This terahertz wave measuring device includes a terahertz wave transmitter as a terahertz wave transmitting means and a terahertz wave detector as a terahertz wave detecting means. In this terahertz wave measuring device, a terahertz wave generating element including a resonant tunneling diode (RTD) or a photoconductive antenna (PCA) is used as the terahertz wave transmitter, and a terahertz wave detecting element consisting of an RTD is used as the terahertz wave transmitter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-26991 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional configuration shown in Patent Document 1, the terahertz wave transmitter is composed of semiconductor elements such as an RTD or PCA, so the terahertz waves emitted by the terahertz wave transmitter are weak and have a small S / N ratio (signal-to-noise ratio), making it difficult to inspect an object located under a difficult-to-permeate material.

[0005] On the other hand, if the light source is a beam light source such as a chip laser, the terahertz waves will be more powerful (high output) than those emitted from semiconductor elements, making it possible to inspect objects located below a difficult-to-penetrate material. However, because the backscattered components (unwanted components) reflected from the surface of the difficult-to-penetrate material are stronger than the reflected components (signal components) reflected from the object, the reflected components (signal components) are hidden by the backscattered components (unwanted components) reflected from the surface of the difficult-to-penetrate material, making it difficult to inspect the object.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide an inspection device that enables inspection of an inspection object located under a difficult-to-permeate material. [Means for solving the problem]

[0007] An inspection device according to at least one embodiment of the present invention comprises: An inspection device for inspecting an inspection object coated with a coating material, a light source that outputs pulsed excitation light with a time width of 10 picoseconds to 10 nanoseconds; a nonlinear optical crystal that generates terahertz waves by optical wavelength conversion of the pulsed excitation light; The terahertz wave From the reflected wave reflected by the object under test, a backscattered component of the terahertz wave reflected by the surface of the coating material, which is a backscattered component having the same polarization plane as the terahertz wave, and a signal component of the terahertz wave reflected by the object under test located below the coating material, which is a signal component having a polarization plane different from that of the terahertz wave, are separated. a polarizing unit; The aforementioned signal components A detector that detects Equipped with 、 the polarizing unit includes a polarizer that reflects the signal component, The polarizer is positioned to remove the backscattered component from the reflected wave. do. [Effects of the Invention]

[0008] According to at least one embodiment of the present invention, backscattered components (unwanted components) reflected from the surface of the difficult-to-permeate material are transmitted through the polarizing unit, while reflected components (signal components) reflected from the object to be inspected located below the difficult-to-permeate material are reflected by the polarizing unit. This allows the backscattered components (unwanted components) reflected from the surface of the difficult-to-permeate material to be separated from the reflected components (signal components) reflected from the object to be inspected. Therefore, the reflected components (signal components) from the object to be inspected can be detected by the detector, enabling inspection of the object to be inspected. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram schematically illustrating the configuration of an inspection device according to a first embodiment. [Figure 2] FIG. 10 is a diagram schematically illustrating the configuration of an inspection device according to a second embodiment. [Figure 3] FIG. 10 is a diagram schematically illustrating the configuration of an inspection device according to a third embodiment. [Figure 4] FIG. 10 is a diagram schematically illustrating the configuration of an inspection device according to a fourth embodiment. [Figure 5] FIG. 10 is a diagram schematically illustrating the configuration of a main part of an inspection device according to a fifth embodiment. [Figure 6] FIG. 10 is a diagram schematically illustrating the configuration of a main part of an inspection device according to a sixth embodiment. [Figure 7] FIG. 1 is a diagram illustrating an inspection principle. [Figure 8] FIG. 1 is a diagram schematically illustrating an example of an inspection of a test piece. [Figure 9] FIG. 13 is a diagram schematically illustrating the configuration of a main part of an inspection device according to a seventh embodiment. [Figure 10] FIG. 13 is a diagram schematically illustrating the configuration of an inspection device according to an eighth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0011] [Embodiment 1] [Configuration of inspection device according to embodiment 1] As shown in FIG. 1, the inspection device 1A according to the first embodiment inspects an inspection target TG that is covered with a difficult-to-permeate material RM. The difficult-to-permeate material RM is, for example, black rubber. The inspection device 1A includes a light source 12 that outputs pulsed excitation light LB with a time width of 10 picoseconds to 10 nanoseconds, a nonlinear optical crystal 14 that generates terahertz waves TH by optical wavelength conversion of the pulsed excitation light LB, a polarizing unit 16 that reflects at least a portion of reflected waves RW that are generated when the terahertz waves TH are reflected by the inspection target TG, and a detector 18 that detects the reflected waves RW reflected by the polarizing unit 16.

[0012] The light source 12 outputs pulsed excitation light LB, and the pulsed excitation light LB is output with a pulse time width of, for example, 1 microsecond or less, preferably 1 nanosecond or less. The light source 12 is, for example, a beam light source such as a chip laser. The nonlinear optical crystal 14 is, for example, a periodically poled lithium niobate (LiNbO3) crystal, which generates terahertz waves TH by backward terahertz wave TH oscillation. The terahertz waves TH have a frequency of 10 12 It is an electromagnetic wave in the range of 0.1 to 100 THz (1 trillion hertz).

[0013] The polarization unit 16 separates the backscattered components (unwanted components) NC reflected from the surface of the low-permeability material RM from the reflected components (signal components) SC reflected from the test object TG located below the low-permeability material RM, taking advantage of the difference in polarization (birefringence). For example, black rubber, which is manufactured using a stretching process and solidified in a stretched state in one direction, has different in-plane refractive indices (a transmission axis and an absorption axis). As a result, the polarization plane of the backscattered components NC reflected from the surface of the black rubber is the same as that of the incident terahertz wave TH, while the polarization plane of the reflected components SC reflected from the test object TG is rotated from that of the incident terahertz wave TH. Therefore, the polarization unit 16 positions a polarizer to remove the backscattered components (unwanted components) NC reflected from the surface of the black rubber, thereby extracting the reflected components (signal components) SC reflected from the test object TG.

[0014] For example, the polarization unit 16 is configured with a polarizer such as a wire grid. The wire grid is configured to transmit p-polarized components and reflect s-polarized components by forming fine metal grids (slits), and in this embodiment, the grid is arranged so that backscattered components (unwanted components) NC transmit through the grid and reflected components (signal components) SC are reflected, thereby extracting the reflected components (signal components) SC reflected by the inspection target TG.

[0015] [Operation of inspection device 1A] In the inspection device 1A according to the first embodiment, when inspecting an inspection object TG, a pulsed excitation light LB having a time width of 10 picoseconds to 10 nanoseconds is output from the light source 12. The pulsed excitation light LB is wavelength-converted to a terahertz wave TH by passing through a nonlinear optical crystal 14, and is then irradiated onto a low-transmission material RM and an inspection object TG located below the low-transmission material RM. Backscattered components (unwanted components) NC reflected from the surface of the low-transmission material RM pass through the polarizing unit 16, and reflected components (signal components) SC reflected from the inspection object TG located below the low-transmission material RM are reflected by the polarizing unit 16. As a result, the backscattered components (unwanted components) NC reflected from the surface of the low-transmission material RM are removed, and the reflected components (signal components) SC from the inspection object TG are extracted. Therefore, the reflected components (signal components) SC from the inspection object TG are detected by the detector 18 and used for inspection of the inspection object TG.

[0016] [Effects of Inspection Device 1A] According to the inspection device 1A of the first embodiment, the backscattered components (unwanted components) NC reflected from the surface of the difficult-to-transmit material RM are transmitted through the polarizing unit 16, and the reflected components (signal components) SC reflected from the test object TG located below the difficult-to-transmit material RM are reflected by the polarizing unit 16, thereby removing the backscattered components (unwanted components) NC reflected from the surface of the difficult-to-transmit material RM and extracting the reflected components (signal components) SC from the test object TG. This makes it possible for the detector 18 to detect the reflected components (signal components) SC reflected from the test object TG that are hidden behind the backscattered components (unwanted components) reflected from the surface of the difficult-to-transmit material RM, thereby enabling inspection of the test object TG.

[0017] [Embodiment 2] [Configuration of inspection device according to embodiment 2] 2, the inspection device 1B according to the second embodiment includes a condenser lens 20 that condenses the terahertz wave TH between the nonlinear optical crystal 14 and the inspection object TG and irradiates the terahertz wave TH onto the inspection object TG. The other configurations are the same as those of the inspection device 1A according to the first embodiment.

[0018] [Operation of inspection device 1B] In the inspection device 1B according to the second embodiment, when inspecting an inspection object TG, the terahertz waves TH are focused by the focusing lens 20 and irradiated onto the inspection object TG. Therefore, the terahertz waves TH are focused on the inspection object TG, and the detector 18 can detect the reflected components (signal components) SC with high resolution. Other operations, that is, operations until the terahertz waves TH are incident on the focusing lens 20 and operations until the reflected components (signal components) SC are detected by the detector 18 and used to inspect the inspection object TG, are the same as those of the inspection device 1A according to the first embodiment.

[0019] [Embodiment 3] [Configuration of inspection device according to embodiment 3] 3, the inspection device 1C according to the third embodiment includes a data logger 22 that stores data on the reflection component (signal component) SC detected by the detector 18. A trigger signal TS is transmitted to the data logger 22 simultaneously with the output of the pulsed excitation light LB from the light source 12, and the data logger 22 is configured to store the data on the reflection component (signal component) SC upon receiving the trigger signal TS. The other configurations are the same as those of the inspection device 1A or 1B according to the first or second embodiment.

[0020] [Operation of inspection device 1C] In the inspection device 1C according to the third embodiment, when inspecting the inspection target TG, the data logger 22 stores data on the reflection component (signal component) SC detected by the detector 18 upon receiving a trigger signal TS transmitted simultaneously with the output of the pulsed excitation light LB from the light source 12. Therefore, the amount of data on the reflection component (signal component) SC stored in the data logger 22 can be reduced compared to when the data logger 22 continuously stores data on the reflection component (signal component) SC. Other operations, i.e., operations until the reflection component (signal component) SC is detected by the detector 18, are the same as those of the inspection device 1A or 1B according to the first or second embodiment.

[0021] [Embodiment 4] [Configuration of inspection device according to embodiment 4] As shown in FIG. 4, in the inspection device 1D according to the fourth embodiment, the terahertz wave TH is linearly polarized, and the polarization unit 16 includes a first polarizer 24 that reflects a component of the reflected wave RW having a polarization plane different from that of the terahertz wave TH, and a second polarizer 26 that transmits the component reflected by the first polarizer 24. The first polarizer 24 is configured based on the same principle as the polarization unit 16 described above, to extract a reflected component (signal component) SC reflected by the inspection target TG, and the second polarizer 26 transmits the extracted reflected component (signal component) SC. For example, the first polarizer 24 and the second polarizer 26 are configured as wire grids. The other configurations are the same as those of any of the inspection devices 1A, 1B, and 1C according to the first to third embodiments.

[0022] [Operation of inspection device 1D] In the inspection device 1D according to the fourth embodiment, when inspecting an inspection object TG, most of the backscattered components (unwanted components) NC reflected from the surface of the difficult-to-transmit material RM are transmitted through the first polarizer 24, while the reflected components (signal components) SC reflected from the inspection object TG located below the difficult-to-transmit material RM are reflected by the first polarizer 24. As a result, most of the backscattered components (unwanted components) NC reflected from the surface of the difficult-to-transmit material RM are removed by the first polarizer 24, and the reflected components (signal components) SC reflected from the inspection object TG are extracted. Then, the reflected components (SC) reflected from the inspection object TG are transmitted through the second polarizer 26, thereby removing the unwanted components (backscattered components) ΔNC that were not completely removed by the first polarizer 24. This reduces noise in the reflected components (signal components) SC reflected from the inspection object TG, improving the detection accuracy of the detector 18 and enabling highly accurate inspection. Other operations, i.e., the operations until the backscattered components (unwanted components) NC reflected on the surface of the difficult-to-transmit material RM and the reflected components reflected on the test object TG located in the lower layer of the difficult-to-transmit material RM are incident on the polarization unit 16 (first polarizer 24), are the same as the operations of any of the inspection devices 1A, 1B, and 1C according to embodiments 1 to 3.

[0023] [Embodiment 5] [Configuration of inspection device according to embodiment 5] As shown in FIG. 5, in the inspection device 1E according to the fifth embodiment, the terahertz wave TH is linearly polarized, and the polarization unit 16 includes a first polarizer 28 that reflects a component of the reflected wave RW having a polarization plane different from that of the terahertz wave TH, and a second polarizer 30 that reflects the component reflected by the first polarizer 28. The first polarizer 28 is configured based on the same principle as the polarization unit 16 described above to extract a reflected component (signal component) SC reflected by the inspection target TG, and the second polarizer 30 is configured to reflect the component (signal component) SC reflected by the first polarizer 28. For example, the first polarizer 28 and the second polarizer 30 are configured as wire grids. The other configurations are the same as those of any of the inspection devices 1A, 1B, and 1C according to the first to third embodiments.

[0024] [Operation of inspection device 1E] In the inspection device 1E according to the fifth embodiment, the unwanted component (backscattered component) ΔNC that was not completely separated by the first polarizer 28 is transmitted through the second polarizer 30, and the reflected component (signal component) SC reflected by the inspection object TG is reflected by the second polarizer 30. As a result, most of the backscattered component (unwanted component) NC reflected by the surface of the low-transmission material RM is removed by the first polarizer 24, and the reflected component (signal component) SC reflected by the inspection object TG is extracted. Then, the reflected component (SC) reflected by the inspection object TG is reflected by the second polarizer 26, thereby removing the unwanted component (backscattered component) ΔNC that was not completely removed by the first polarizer 24. Note that, with regard to the Mie scattered light (unwanted waves) generated by the first polarizer 28 (wire grid), backward scattering (corresponding to reflection from the second polarizer 30) is considered to be smaller than forward scattering (corresponding to transmission from the second polarizer 30). Therefore, the Mie scattered light generated by the first polarizer 28 can be made less likely to be picked up. Therefore, noise in the reflected components reflected by the test object TG is reduced, improving the detection accuracy of the detector 18 and enabling highly accurate testing. Other operations, that is, operations until the backscattered components (unwanted components) NC reflected by the surface of the difficult-to-transmit material RM and the reflected components reflected by the test object TG located in a layer below the difficult-to-transmit material RM are incident on the polarization unit 16 (first polarizer 28), are the same as the operations of any of the inspection devices 1A, 1B, and 1C according to the first to third embodiments.

[0025] [Embodiment 6] [Configuration of inspection device according to embodiment 6] 6, in the inspection apparatus 1F according to the sixth embodiment, the first polarizer 28 includes a first rotation unit 32 that rotates the first polarizer 28 so that the polarization plane of the terahertz wave TH rotates within a range of 90°, and the second polarizer 30 includes a second rotation unit 34 that rotates the second polarizer 30 so that the reflection component (signal component) SC reflected by the first polarizer 28 rotates within a range of 90°. For example, the first polarizer 28 is disk-shaped and is supported rotatably around the central axis of the first polarizer 28, and the first rotation unit 32 includes a gear 36 provided on the outer periphery of the first polarizer 28 and an actuator 40 such as a motor that rotates a gear 38 that meshes with the gear 36. Similarly, the second polarizer 30 is disk-shaped and supported rotatably around the rotation axis of the second polarizer 30, and the second rotating unit 34 is composed of a gear 42 provided on the outer periphery of the second polarizer and an actuator 46 such as a motor that rotates a gear 44 that meshes with the gear 42. The other configurations are the same as those of any of the inspection devices 1A, 1B, 1C, and 1E according to the first to third and fifth embodiments.

[0026] [Operation of inspection equipment 1F] As shown in Figure 7(a), when there is no crack CR in the test object TG, the polarization plane of the reflected component SC reflected from the test object TG is the same as the polarization plane of the incident terahertz wave TH (polarization does not change). However, as shown in Figure 7(b), when there is a crack CR in the test object TG, the polarization plane of the reflected component SC reflected from the test object TG is a polarization plane that is a changed version of the polarization plane of the incident terahertz wave TH (polarization changes).

[0027] From the results of testing and verification, the inventors of the present application have found that when a crack CR in an inspection object TG is irradiated with linearly polarized terahertz waves TH with a polarization plane of 45°, contrast with surrounding healthy areas can be obtained.

[0028] Therefore, in the inspection device 1F according to the sixth embodiment, when inspecting the inspection object TG, the first rotation unit 32 rotates the first polarizer 28 so that the polarization plane of the terahertz wave TH rotates within a range of 90°, while the second rotation unit 34 rotates the second polarizer 30 so that the reflection component (signal component) SC reflected by the first polarizer 28 rotates within a range of 90°. As a result, even if it is unknown whether or not a crack CR exists in the inspection object TG, it is possible to search for the crack CR by rotating the second polarizer 30 while rotating the first polarizer 28. Then, the maximum value of the reflection component (signal component) SC detected by the detector 18 is searched for (Max Hold measurement).

[0029] As shown in Figure 8, in an example where a test piece TP with slits SL1 to SL6 on a line LN was inspected, when the polarization was adjusted and incident light was obliquely 45 degrees relative to the slits SL1 to SL6, signals from the slits SL1 to SL6 were detected when the first polarizer 28 was in the range of 30 to 70 degrees from the reference position. On the other hand, when the first polarizer 28 was at 10 or 90 degrees (90) from the reference position, signals from the slits SL1 to SL6 could not be detected. Furthermore, since there is a large difference in signal strength between 30 and 50 degrees, and since the tilt of the actual crack CR is unknown, the maximum value of the reflection component (signal component) SC detected by the detector 18 is searched for.

[0030] By searching for the maximum value of the reflected component (signal component) SC in this manner, it is possible to measure the maximum value of the reflected component (signal component) SC having a polarization plane different from that of the terahertz wave TH, and to clearly identify cracks, as shown in FIG. 8. Therefore, even if the inspection object TG is coated with a thermal barrier coating such as ceramics, the inspection object TG can be inspected without removing the thermal barrier coating. Other operations, i.e., operations until the backscattered component (unwanted component) NC reflected from the surface of the low-permeability material RM and the reflected component reflected from the inspection object TG located below the low-permeability material RM are incident on the polarization unit 16 (first polarizer 28), are the same as those of any of the inspection devices 1A, 1B, 1C, and 1E according to the first to third and fifth embodiments.

[0031] [Embodiment 7] [Configuration of inspection device according to embodiment 7] 9, in the inspection device 1G according to the seventh embodiment, the detector 18 is a terahertz wave detector that is highly sensitive to circularly polarized light, and a quarter-wave plate 48 is provided between the second polarizer 30 and the detector 18. For example, the quarter-wave plate 48 is made of quartz or the like. The other configurations are the same as those of any of the inspection devices 1A, 1B, 1C, 1E, and 1F according to the first to third and fifth to sixth embodiments.

[0032] [Operation of inspection device 1G] In the inspection device 1G according to the seventh embodiment, the reflected component (signal component) SC reflected by the second polarizer 30 passes through the quarter-wave plate 48, becoming a circularly polarized terahertz wave TH, which is incident on the detector 18. The circularly polarized terahertz wave TH is detected by the detector 18, which has high sensitivity to circularly polarized light, and the value (signal value) of the reflected component (signal component) becomes large.

[0033] In this way, when the detector 18 is a terahertz wave detector that is highly sensitive to circularly polarized light, providing the quarter-wave plate 48 between the second polarizer 30 and the detector 18 can increase the value (signal value) of the reflected component (signal component) detected by the detector 18. Other operations, that is, operations until the reflected component (signal component) SC reflected by the inspection object TG is reflected by the second polarizer 30, are the same as the operations of any of the inspection devices 1A, 1B, 1C, 1E, and 1G according to the first to third and fifth to sixth embodiments.

[0034] [Embodiment 8] [Configuration of inspection device according to embodiment 8] As shown in Fig. 10, in the inspection device 1H according to the seventh embodiment, the terahertz wave TH is a circularly polarized wave, and the polarizing unit 16 includes a half mirror 50 that reflects the reflected wave RW. The inspection device 1G includes a quarter-wave plate 52 at the output end of the nonlinear optical crystal 14, i.e., between the nonlinear optical crystal 14 and the half mirror 50. For example, the quarter-wave plate 52 is made of quartz or the like. The other configurations are the same as those of any of the inspection devices 1A, 1B, and 1C according to the first to third embodiments.

[0035] [Operation of inspection device 1H] In the inspection device 1H according to the seventh embodiment, when inspecting an inspection object TG, the linearly polarized terahertz wave TH, which has been optically wavelength-converted by the nonlinear optical crystal 14, passes through the quarter-wave plate 52 to become a circularly polarized terahertz wave THc, which is then irradiated onto the inspection object TG. The reflected wave RW reflected by the inspection object TG is reflected by the half mirror 50, detected by the detector 18, and used to inspect the inspection object. In the sixth and seventh embodiments, it is required to irradiate a crack in the inspection object with a linearly polarized wave having a polarization plane of 45°. However, the circularly polarized terahertz wave THc can be expected to have a constant sensitivity to cracks in the inspection object TG, regardless of the polarization plane. Therefore, since it is not necessary to search for the maximum value of the reflection component (signal component) SC, it is expected that the measurement time will be shorter than in the sixth and seventh embodiments. The other operations are the same as those of any of the inspection devices 1A, 1B, and 1C according to the first to third embodiments.

[0036] The contents described in each of the above embodiments can be understood, for example, as follows.

[0037] The inspection device (1A to 1H) according to the aspect of [1] is a light source (12) that outputs pulsed excitation light having a time width of 10 picoseconds to 10 nanoseconds; a nonlinear optical crystal (14) that generates terahertz waves by optical wavelength conversion of the pulsed excitation light; a polarizing unit (16) that reflects at least a part of a reflected wave (RW) that is generated when the terahertz wave (TH) is reflected by an object to be inspected (TG); a detector (18) for detecting a reflected wave (RW) reflected by the polarizing unit (16); Equipped with.

[0038] With this configuration, the backscattered components (unwanted components) (NC) reflected from the surface of the difficult-to-permeate material (RM) are transmitted through the polarizing unit (16), while the reflected components (signal components) (SC) reflected from the test object (TG) located below the difficult-to-permeate material (RM) are reflected by the polarizing unit (16). This separates the backscattered components (unwanted components) (NC) reflected from the surface of the difficult-to-permeate material (RM) from the reflected components (signal components) (SC) from the test object (TG). Therefore, the detector (18) can detect the reflected components (signal components) (SC) from the test object (TG), enabling the test object (TG) to be inspected.

[0039] [2] The inspection device (1D) according to another aspect is the inspection device according to [1], The terahertz wave (TH) is a linearly polarized wave, The polarizing unit (16) a first polarizer (24) that reflects a component of the reflected wave (RW) that has a polarization plane different from that of the terahertz wave; a second polarizer (26) that transmits the component reflected by the first polarizer (24); Equipped with.

[0040] With this configuration, most of the backscattered components (unwanted components) (NC) reflected from the surface of the difficult-to-permeate material (RM) are transmitted through the first polarizer, and the reflected components (signal components) (SC) reflected from the test object (TG) located below the difficult-to-permeate material (RM) are reflected by the first polarizer (24), thereby separating the backscattered components (unwanted components) (NC) reflected from the surface of the difficult-to-permeate material (RM) from the reflected components (signal components) (SC) reflected from the test object (TG). The unwanted components (backscattered components) that were not completely separated by the first polarizer (24) are reflected by the second polarizer (26), and the reflected components (signal components) (SC) reflected from the test object (TG) are transmitted through the second polarizer (26), thereby separating the unwanted components that were not completely separated by the first polarizer (24) from the reflected components (signal components) (SC) reflected from the test object (TG). Therefore, noise in the reflected component (signal component) (SC) from the inspection object (TG) is reduced, the detection accuracy of the detector (18) is improved, and highly accurate inspection is possible.

[0041] [3] The inspection device (1E) according to another aspect is the inspection device according to [1], the terahertz waves are linearly polarized waves, The polarizing unit (16) a first polarizer (28) that reflects a component of the reflected wave (RW) having a polarization plane different from that of the terahertz wave (TH); a second polarizer (30) that reflects the component reflected by the first polarizer (28); Equipped with.

[0042] With this configuration, most of the backscattered components (unwanted components) (NC) reflected from the surface of the difficult-to-transmit material (RM) are transmitted through the first polarizer (28), and the reflected components (signal components) (SC) reflected from the test object (TG) located below the difficult-to-transmit material (RM) are reflected by the first polarizer (28), making it possible to separate the backscattered components (unwanted components) (NC) from the surface of the difficult-to-transmit material (RM) from the reflected components (signal components) (SC) from the test object (TG).The reflected components (signal components) (SC) from the test object (TG) reflected by the first polarizer (28) are reflected by the second polarizer (30).However, since the amount of Mie-scattered light (unwanted waves) generated by the first polarizer (28) (wire grid) is considered to be smaller in backscatter (equivalent to reflection from the second polarizer) than in forward scattering (equivalent to transmission from the second polarizer), it is possible to make it difficult for the first polarizer (28) to pick up the Mie-scattered light. Therefore, noise in the reflected component reflected by the test object (TG) is reduced, the detection accuracy of the detector (18) is improved, and highly accurate testing is possible.

[0043] [4] The inspection device (1F) according to another aspect is the inspection device according to [3], the first polarizer (28) includes a first rotation unit (32) that rotates the first polarizer (28) so that the polarization plane of the terahertz wave rotates within a range of 90°; The second polarizer (30) includes a second rotation section (34) that rotates the second polarizer (30) so that the component reflected by the first polarizer (28) is rotated through a range of 90°.

[0044] With this configuration, it is possible to measure the maximum value of the reflected component having a polarization plane different from that of the terahertz wave (TH), and to clarify cracks whose direction is unknown.

[0045] [5] The inspection device (1G) according to another aspect is the inspection device according to [3] or [4], A quarter wave plate (48) is provided between the second polarizer (30) and the detector (18).

[0046] According to this configuration, when the detector (18) is a terahertz wave detector that is highly sensitive to circularly polarized light, by providing a quarter-wave plate (48) between the second polarizer (30) and the detector (18), the value (signal value) of the reflected component (signal component) detected by the detector 18 can be increased.

[0047] [6] The inspection device (1H) according to another aspect is the inspection device according to [1], the terahertz waves (TH) are circularly polarized waves, The polarization unit (16) includes a half mirror (50) that reflects the reflected wave (RW). The inspection device (1G) includes a quarter-wave plate (52) at the output end of the nonlinear optical crystal (14).

[0048] According to this configuration, the linearly polarized terahertz waves (TH) converted in wavelength by the nonlinear optical crystal (14) are transmitted through the quarter-wave plate (52) to become circularly polarized terahertz waves (TH) and are then irradiated onto the test object (TG). The circularly polarized terahertz waves (TH) can be expected to have a constant sensitivity regardless of the crack direction in the test object (TG), and therefore a reduction in measurement time can also be expected.

[0049] [7] The inspection device (1B to 1G) according to another aspect is the inspection device according to any one of [1] to [6], The apparatus includes a condenser lens (20) that condenses the terahertz waves and irradiates the terahertz waves onto the test object (TG).

[0050] According to this configuration, the terahertz waves (TH) irradiated from the nonlinear optical crystal (14) are focused by the focusing lens (20) and then irradiated onto the test object (TG), so that the terahertz waves (TH) are collected on the test object (TG), and the detector (18) can detect the reflected components (signal components) (SC) with high resolution.

[0051] [8] An inspection device according to another aspect is the inspection device according to any one of [1] to [7], a data logger (22) for storing the reflected waves (RW) detected by the detector (18); A trigger signal is transmitted to the data logger (22) simultaneously with the output of the excitation light from the light source (12), and the data logger (22) is configured to store the reflected wave (RW) when the trigger signal is received.

[0052] According to this configuration, the data logger (22) stores the data of the reflected component (signal component) (SC) when it receives the trigger signal (TS), so the amount of data of the reflected component (signal component) (SC) stored in the data logger (22) can be reduced compared to when the data logger (22) continuously stores the data of the reflected component (signal component) (SC). [Explanation of symbols]

[0053] 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H Inspection equipment 12 light source 14 Nonlinear optical crystals 16 Polarization section 18 detectors 20 Condenser lens 22 Data logger 24 First polarizer 26 Second polarizer 28 First polarizer 30 Second polarizer 32 First Rotating Section 34 Second Rotating Section 36,42 gears 38,44 gears 40,46 Motor 48 1 / 4 wave plate 50 Half Mirror 52 1 / 4 wave plate LB pulsed excitation light RM impermeable material TG Inspection object CR crack TH Terahertz waves THc Circularly polarized terahertz waves TS trigger signal RW reflected wave SC signal component NC unnecessary components CR crack TP test specimen LN Line SL1~SL6 slits

Claims

1. An inspection device for inspecting an object coated with a coating material, comprising: a light source that outputs pulsed excitation light having a time width of 10 picoseconds to 10 nanoseconds; a nonlinear optical crystal that generates terahertz waves by optical wavelength conversion of the pulsed excitation light; a polarization unit that separates, from the reflected waves of the terahertz waves reflected by the object under test, backscattered components of the terahertz waves reflected by the surface of the coating material, the backscattered components having the same plane of polarization as the terahertz waves, and signal components of the terahertz waves reflected by the object under test located below the coating material, the backscattered components having the same plane of polarization as the terahertz waves; a detector for detecting the signal component; Equipped with the polarizing unit includes a polarizer that reflects the signal component, The polarizer is positioned to remove the backscattered component from the reflected wave.

2. the terahertz waves are linearly polarized waves, The polarizer is a first polarizer that reflects the signal component; a second polarizer that transmits the signal component reflected by the first polarizer; and The inspection device of claim 1 , comprising:

3. the terahertz waves are linearly polarized waves, The polarizer is a first polarizer that reflects the signal component; a second polarizer that reflects the signal component reflected by the first polarizer; and The inspection device of claim 1 , comprising:

4. the first polarizer includes a first rotation unit that rotates the first polarizer so that the polarization plane of the terahertz wave rotates within a range of 90°; the second polarizer includes a second rotation unit that rotates the second polarizer so that the signal component reflected by the first polarizer is rotated within a range of 90°. The inspection device according to claim 3 .

5. The inspection device according to claim 3 or 4, further comprising a quarter-wave plate between the second polarizer and the detector.

6. A light source that outputs pulsed excitation light having a time width of 10 picoseconds to 10 nanoseconds; a nonlinear optical crystal that generates terahertz waves by optical wavelength conversion of the pulsed excitation light; a polarizing unit that reflects at least a portion of the terahertz wave reflected by an object to be inspected; a detector for detecting the reflected wave; Equipped with the terahertz waves are linearly polarized waves, The polarizing unit is a first polarizer that reflects a component of the reflected wave having a polarization plane different from that of the terahertz wave; a second polarizer that reflects the component reflected by the first polarizer; and Equipped with The inspection device further comprises a quarter wave plate between the second polarizer and the detector.

7. 7. The inspection device according to claim 1, further comprising a condenser lens that condenses the terahertz waves and irradiates the terahertz waves onto the object to be inspected.

8. a data logger for storing the reflected waves detected by the detector; 8. The inspection device according to claim 1, wherein a trigger signal is transmitted to the data logger simultaneously with the output of the pulsed excitation light from the light source, and the data logger is configured to store the reflected wave upon receiving the trigger signal.

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