Flexoelectric liquid crystal composition, liquid crystal element, laser inspection system, and method for analyzing specimen

Abstract

A flexoelectric liquid crystal composition that comprises at least one type of smectic liquid crystal compound, a chiral dopant, and a charge scavenger, and exhibits photoconductivity.

Description

[Technical Field]

[0001] The present disclosure relates to a flexoelectric liquid crystal composition, a liquid crystal device, a laser inspection system, and a method for analyzing a specimen. [Background technology]

[0002] Ultrasonic testing is a non-destructive inspection method. Ultrasonic testing is widely used in various fields because it can detect material characteristics and deterioration. A well-known method for ultrasonic testing is to use a laser.

[0003] For example, Patent Document 1 proposes a laser ultrasonic inspection device for non-destructively inspecting the surface of an object to be inspected for defects, etc. by irradiating the surface with laser light. The laser ultrasonic inspection device described in Patent Document 1 includes a photorefractive crystal for receiving the irradiated laser light and the reference laser light to perform interference measurement, and an inorganic BSO (Bismuth Silicon Oxide) crystal is used as the photorefractive crystal. Furthermore, Non-Patent Documents 1 and 2 propose a laser ultrasonic inspection device that uses a photorefractive material containing a polymer material instead of a photorefractive crystal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-038880 [Non-patent literature]

[0005] [Non-Patent Document 1] Zamiri, S., et al. "Employing 532 nm Wavelength in a Laser Ultrasound Interferometer Based on Photorefractive Polymer Composites." Open Access Library Journal, 2, e1247 (2015). DOI:10.4236 / oalib.1101247. [Non-patent document 2] Zamiri, S., et al. "Laser ultrasonic receivers based on organic photorefractive polymer composites" Appl. Phys. B (2014). 114:509-515 DOI 10.1007 / s00340-013-5554-7. Summary of the Invention [Problem to be solved by the invention]

[0006] The photorefractive effect is a phenomenon in which a refractive index grating (hologram) is formed in a medium that exhibits photoconductivity and electro-optic effects when laser light interferes in the medium. By using a photorefractive material that exhibits the photorefractive effect and an ultrasonic laser, it is possible to detect defects inside an object or measure the thickness of a plate-like object without contact.

[0007] Specifically, a continuous wave laser is irradiated onto the specimen, and the reflected light is incident on an element containing a photorefractive material (hereinafter also referred to as a "photorefractive element") and interferes with the reference light, resulting in two-wave coupling. Two-wave coupling occurs due to a phase mismatch between the interference fringes and the refractive index grating. As a result, the reflected light detected after passing through the photorefractive element is amplified, and the reference light is attenuated, so that the intensities of the reflected light and reference light approach a constant value. At this time, a pulsed laser with a pulse width of less than a nanosecond is irradiated onto the specimen, generating ultrasound waves on the surface of the specimen. The ultrasound waves propagate inside the specimen and are reflected by each surface of the specimen and by defects, structures, etc. within the specimen. Reflected ultrasound waves appear on the surface irradiated by the continuous wave laser, This causes fluctuations in the reflected light. This modulates the phase of the reflected light, which in turn changes the phase of the interference fringes in the photorefractive material, causing fluctuations in the light intensity of the reflected light and reference light due to two-wave coupling. Therefore, by measuring the time from when the pulsed light is irradiated onto the specimen until a change occurs in the reflected light or reference light, information can be obtained about the thickness of the specimen, as well as defects and structure within the specimen.

[0008] In conventional ultrasonic flaw detection measurements using a photorefractive material and an ultrasonic laser, inorganic crystals are used as the photorefractive material as in Patent Document 1, or polymers are used as in Non-Patent Documents 1 and 2. However, when inorganic crystals such as barium titanate or lithium niobate or polymers are used in the photorefractive element, there is a problem in that the response speed of the photorefractive effect is slow.

[0009] When the response of the photorefractive effect is slow, it is necessary to perform measurements using the photorefractive element in a quiet environment. This is because vibrations can shift the refractive index grating, modulating the two-beam coupling and making ultrasonic flaw detection impossible. For example, the frequency of vibrations generated by automobiles in a normal environment is 0.1 Hz to several tens of Hz, which is close to the response time (several seconds to several tens of milliseconds) of the photorefractive effect of inorganic crystals or polymers. Under normal conditions, ultrasonic flaw detection measurements are hindered. Therefore, it is necessary to apply a voltage of several kilovolts to the photorefractive element to increase the response speed, or to use a large-scale device equipped with a vibration isolation system for ultrasonic flaw detection measurements. For example, in Non-Patent Document 1, a voltage of 5 kV is applied to a photorefractive material containing a polymer material. On the other hand, Non-Patent Document 2 shows that the response speed can be increased by increasing the voltage applied to the photorefractive element. However, the technology of Non-Patent Document 2 merely shows that a response time of 195 ms or 60 ms was obtained by applying a voltage of 5 kV to the photorefractive material, and further improvement in the response speed is desirable.

[0010] The present disclosure has been made in consideration of the above-described circumstances, and aims to provide a flexoelectric liquid crystal composition having an excellent response speed of the photorefractive effect, a liquid crystal element and a laser inspection system including the same, and a method for analyzing a specimen using the laser inspection system. [Means for solving the problem]

[0011] The means for solving the above problems include the following embodiments. <1> at least one smectic liquid crystal compound; a chiral dopant; a charge scavenger; A flexoelectric liquid crystal composition exhibiting photoconductivity. <2> The chiral dopant comprises a photoconductive chiral dopant. <1> 1. The flexoelectric liquid crystal composition according to claim 1. <3> The photoconductive chiral dopant contains at least one of a compound represented by the following general formula (1) and a compound represented by the following general formula (2): <2> 1. The flexoelectric liquid crystal composition according to claim 1.

[0012] [ka]

[0013] (In general formula (1) and general formula (2), R 1 and R 2 are each independently a hydrocarbon group having an asymmetric carbon atom. <4> In the general formula (1) and the general formula (2), R 1 and R 2 is a 2-methylbutyl group <3> 1. The flexoelectric liquid crystal composition according to claim 1. <5> The smectic liquid crystal compound includes a liquid crystal compound exhibiting a smectic C phase. <1> or <1> ~ <4> 10. The flexoelectric liquid crystal composition according to claim 9, wherein the flexoelectric liquid crystal composition is a flexoelectric liquid crystal composition having a wavelength of 100 nm or more. <6> The content of the chiral dopant is 0.1 parts by mass to 10 parts by mass with respect to 100 parts by mass of the total amount of the smectic liquid crystal compound. <1> ~ <5> 10. The flexoelectric liquid crystal composition according to claim 9, wherein the flexoelectric liquid crystal composition is a flexoelectric liquid crystal composition having a wavelength of 100 nm or more. <7> <1> ~ <6> a liquid crystal film formed from the flexoelectric liquid crystal composition according to any one of the above items; a pair of transparent substrates sandwiching the liquid crystal film; A liquid crystal element comprising: <8> The thickness of the liquid crystal film is 5 μm to 15 μm. <7> The liquid crystal element according to claim 1. <9> a first laser emission unit that irradiates a pulsed laser onto an object to generate ultrasonic vibrations on a surface of the object; a second laser emission unit that emits a continuous wave laser; a beam splitter that splits the continuous wave laser emitted from the second laser emission unit into an irradiation light that is irradiated onto the surface of the subject and a reference light; A reflected light, which is the irradiation light that is irradiated onto the surface of the object and reflected from the object, and a reference light are received, and the reflected light and the reference light are made to interfere with each other. <7> or <8> a liquid crystal element according to a detection unit that detects at least one of the irradiation light and the reference light emitted from the liquid crystal element; A laser inspection system comprising: <10> a first laser emission unit that irradiates a pulsed laser onto an object to generate ultrasonic vibrations on a surface of the object; a second laser emission unit that emits a continuous wave laser; a beam splitter that splits the continuous wave laser emitted from the second laser emission unit into an irradiation light that is irradiated onto the surface of the subject and a reference light; Reflected light, which is the irradiation light that is irradiated onto the surface of the object and reflected from the object; and a liquid crystal element that receives the reference light and causes the reflected light and the reference light to interfere with each other; a detection unit that detects at least one of the irradiation light and the reference light emitted from the liquid crystal element; Equipped with The liquid crystal element includes a liquid crystal film formed from a ferroelectric liquid crystal composition and a pair of transparent substrates sandwiching the liquid crystal film. <11> <9> or <10> 10. A method for analyzing properties of an object using the laser inspection system according to claim 9, A method for analyzing a test subject, which analyzes the properties of the test subject based on a change in the intensity of light detected by the detection unit due to interference within the liquid crystal element between the reflected light, which is the irradiation light that is irradiated onto a surface of the test subject where ultrasonic vibrations are generated and reflected from the test subject, and the reference light. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a flexoelectric liquid crystal composition having an excellent response speed of the photorefractive effect, a liquid crystal element and a laser inspection system including the same, and a method for analyzing a specimen using the laser inspection system. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic configuration diagram illustrating a laser inspection system according to an embodiment of the present disclosure. [Figure 2] 1 is a schematic configuration diagram illustrating a liquid crystal element according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a schematic configuration diagram showing a laser inspection system according to another embodiment (first embodiment) of the present disclosure. [Figure 4] FIG. 1 is a schematic configuration diagram showing a laser inspection system used in Example 1. [Figure 5] 10 is a graph showing the change in transmitted light intensity when an aluminum plate having a thickness of 2 mm, 3 mm, or 5 mm is used as the specimen. [Figure 6] 1 is a graph showing the relationship between longitudinal waves and transverse waves in ultrasonic vibration and changes in transmitted light intensity. [Figure 7] 10 is a graph showing the relationship between the measurement position on the aluminum plate and the change over time in the intensity of transmitted light of reflected light. [Figure 8] 1 is a graph showing the relationship between the measurement position of the thickness of an aluminum plate and the thickness measurement results. [Figure 9] FIG. 10 is a schematic configuration diagram showing a laser inspection system according to another embodiment (embodiment 2) of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.

[0017] [Flexoelectric Liquid Crystal Composition] The flexoelectric liquid crystal composition of the present disclosure contains at least one smectic liquid crystal compound, a chiral dopant, and a charge trapping agent, and exhibits photoconductivity. The use of a liquid crystal composition exhibiting the flexoelectric effect provides an excellent response speed of the photorefractive effect. Furthermore, flexoelectric liquid crystal compositions containing a smectic liquid crystal compound exhibit reduced light scattering.

[0018] The flexoelectric liquid crystal composition of the present disclosure has an excellent response speed of the photorefractive effect, eliminating the need to apply a high voltage to a liquid crystal element formed using the composition to increase the response speed. Furthermore, data on the amplification and attenuation of light intensity due to two-wave coupling can be obtained within a time frame shorter than the tens of milliseconds at which vibration noise becomes a problem, e.g., within microseconds to several milliseconds. Therefore, the liquid crystal element is virtually unaffected by vibration noise of 0.1 Hz to several tens of Hz. The use of a liquid crystal element allows measurement of properties such as thickness, internal defects, and structure of an object even in a vibrating environment, with minimal influence from air vibrations. This eliminates the need for a vibration isolation device, enabling the miniaturization of the device used to measure the properties of the object. Furthermore, the device for measuring the properties of the object can be carried outdoors to perform non-contact diagnosis of objects such as steel frames and concrete.

[0019] The use of a liquid crystal element formed using the flexoelectric liquid crystal composition of the present disclosure enables the measurement of properties of a moving object, and therefore, the use of a near-infrared laser enables the exploration of tissue beneath the skin.

[0020] By using a liquid crystal element formed using the flexoelectric liquid crystal composition of the present disclosure, a photorefractive effect can be obtained, and the mechanism by which the properties of a test object can be measured is as follows.

[0021] Flexoelectric liquid crystal compositions are made of smectic liquid crystal compounds and The flexoelectric liquid crystal composition includes a chiral dopant, a photoconductive compound, and a charge trapping agent. As described below, the chiral dopant may also be a photoconductive chiral dopant, which eliminates the need for a separate photoconductive compound. When light is interfered in a liquid crystal film obtained from such a flexoelectric liquid crystal composition, the photoconductive compound absorbs the light in the bright areas of the interference fringes, generating positive and negative charges. Negative charges (electrons) are trapped by the charge trapping agent, while positive charges (holes) diffuse throughout the liquid crystal film. The bright areas of the interference fringes are negatively charged, and the dark areas are positively charged. As a result, an electric field (internal electric field) is generated due to the potential difference between the bright and dark areas. This internal electric field generates an electro-optic effect, changing the refractive index and forming a refractive index grating. Specifically, the internal electric field changes the polarization direction of the liquid crystal film, forming lattice fringes in which the liquid crystal alignment is periodically changed. These lattice fringes function as a refractive index grating. The refractive index grating is generated between the bright and dark areas of the interference fringes.

[0022] The refractive index grating due to the photorefractive effect has a specific effect on the transmission of interfering laser beams. When a refractive index grating that is out of phase with the light and dark phase of the interference fringes is formed, only one of the interfering beams is diffracted and the other is not diffracted, resulting in contrasting changes in the transmission intensity of each laser beam. Of the two interfering laser beams, the transmission intensity of one increases and the transmission intensity of the other decreases. This phenomenon is called photorefractive two-wave coupling.

[0023] Since photorefractive two-wave coupling occurs due to the interference of two laser beams, even a slight phase shift in one of the laser beams will deviate from the two-wave coupling conditions and cause a change in the intensity of the light transmitted through the liquid crystal element. Therefore, this phenomenon can be used to detect the phase modulation of light.

[0024] For example, a continuous wave (CW) laser beam is split into two beams, one of which is incident on a liquid crystal element as a reference beam, and the other is incident on an object being examined as an object under test, and the reflected light from the object is then incident on the liquid crystal element. The reference and reflected beams are made to interfere with each other, and the intensity of each beam passing through the liquid crystal element is measured. Photorefractive two-wave coupling occurs, amplifying the reflected beam and attenuating the reference beam, and both beams approach a constant value.

[0025] Next, a pulsed laser with a pulse width of less than a nanosecond is irradiated onto the object, generating ultrasonic waves on the object's surface. The ultrasonic waves travel through the object and are reflected by the object's surfaces and by defects and structures within the object. The reflected waves that appear on the object's surface cause fluctuations in the reflection of the irradiated light. Fluctuations in the reflection of the irradiated light cause modulation in the phase of the reflected wave of the irradiated light, which in turn changes the phase of the interference fringes in the liquid crystal film. This deviates from the condition for two-wave coupling, causing changes in the amplification and attenuation of light. By measuring the time from when the pulsed laser light is irradiated onto the object until a change in the irradiated light occurs, information about the object's properties, such as its thickness, internal defects, and structure, can be obtained.

[0026] Hereinafter, each component contained in the flexoelectric liquid crystal composition of the present disclosure will be described in detail.

[0027] (Smectic liquid crystal compounds) The flexoelectric liquid crystal composition (hereinafter also referred to as "liquid crystal composition") of the present disclosure contains at least one smectic liquid crystal compound. The smectic liquid crystal compound contained in the liquid crystal composition may be a single type or a mixture of two or more types.

[0028] The smectic liquid crystal compound is preferably a liquid crystal compound exhibiting a smectic C phase, from the viewpoints of easily obtaining an alignment state with few defects, high transparency, and favorably exhibiting a flexoelectric effect. The liquid crystal compound exhibiting a smectic C phase may be a single compound. It may be a mixture of two or more kinds.

[0029] Examples of liquid crystal compounds exhibiting a smectic C phase include mesogen compounds having a phenylpyrimidine skeleton, a phenylpyridine skeleton, a biphenyl skeleton, etc. The liquid crystal compound exhibiting a smectic C phase preferably contains at least one of a 2-phenylpyrimidine derivative, a 2-phenylpyridine derivative, and a biphenyl ester derivative.

[0030] The 2-phenylpyrimidine derivative is preferably, for example, an alkoxy-substituted 2-phenylpyrimidine derivative, and more preferably a compound represented by the following chemical formula: The 2-phenylpyrimidine derivative may be one type alone or a mixture of two or more types, for example, a mixture of compounds represented by the following chemical formula:

[0031] [ka]

[0032] The 2-phenylpyridine derivative is preferably, for example, an alkoxy-substituted 2-phenylpyrimidine derivative, and more preferably a compound represented by the following chemical formula: The 2-phenylpyridine derivative may be one type alone or a mixture of two or more types, for example, a mixture of compounds represented by the following chemical formula:

[0033] [ka]

[0034] The biphenyl ester derivative is preferably, for example, a compound in which a biphenyl skeleton and a phenyl skeleton are bonded via an ester bond, and more preferably a compound represented by the following chemical formula: The biphenyl ester derivative may be a single type or a mixture of two or more types, for example, a mixture of two or more types of compounds represented by the following chemical formula:

[0035] [ka]

[0036] The liquid crystal composition of the present disclosure contains a chiral dopant. The chiral dopant is a compound with an asymmetric structure, and the chiral moiety of the chiral dopant causes the smectic liquid crystal compound to exhibit an excellent flexoelectric effect. The use of a smectic liquid crystal compound provides a greater photorefractive effect than liquid crystals exhibiting ferroelectricity.

[0037] The chiral dopant preferably includes a photoconductive chiral dopant. By using the photoconductive chiral dopant, the liquid crystal composition can exhibit photoconductivity without using a separate compound exhibiting photoconductivity. The photoconductive chiral dopant may be used alone or in combination of two or more.

[0038] The photoconductive chiral dopant preferably contains at least one of a compound represented by the following general formula (1) and a compound represented by the following general formula (2). [ka]

[0039] In general formula (1) and general formula (2), R 1 and R 2 are each independently a hydrocarbon group having an asymmetric carbon atom.

[0040] R 1 and R 2are each independently preferably an alkyl group having an asymmetric carbon, more preferably an alkyl group having an asymmetric carbon and having 4 to 10 carbon atoms, and even more preferably an alkyl group having an asymmetric carbon and having 5 to 8 carbon atoms. 1 and R 2 In view of the flexoelectric effect of the smectic liquid crystal compound, R is particularly preferably a 2-methylbutyl group. 1 and R 2 The compound where is a 2-methylbutyl group is represented by the following chemical formula:

[0041] [ka]

[0042] The content of the chiral dopant may be 0.1 to 10 parts by mass, or 0.1 to 5 parts by mass, relative to 100 parts by mass of the total amount of the smectic liquid crystal compounds.

[0043] When a non-photoconductive chiral dopant is used as the chiral dopant, the liquid crystal composition may contain a compound exhibiting photoconductivity in order to impart photoconductivity to the liquid crystal composition.

[0044] Examples of compounds exhibiting photoconductivity include oligothiophene compounds such as terthiophene compounds and quatrothiophene compounds, thianocene compounds, carbazole compounds, squaraine compounds, etc. The photoconductive compounds may be used alone or in combination of two or more.

[0045] Examples of oligothiophene compounds include compounds represented by the following chemical formula:

[0046] [ka]

[0047] Examples of thianocene compounds include compounds represented by the following chemical formula:

[0048] [ka]

[0049] The carbazole-based compound is more preferably a compound represented by the following chemical formula:

[0050] [ka]

[0051] (charge trapping agent) The liquid crystal composition of the present disclosure contains a charge trapping agent. The charge trapping agent is added to trap negative charges and to shift the wavelength of absorbed light to a longer wavelength by charge transfer absorption. Examples of the charge trapping agent include trinitrofluorenone (TNF), tetracyanoquinodimethane (TCNQ), and fullerene derivatives.

[0052] The content of the charge capturing agent may be 0.1 to 1 part by mass, or may be 0.1 to 0.3 parts by mass, relative to 100 parts by mass of the total amount of the smectic liquid crystal compounds.

[0053] (Other ingredients) The liquid crystal composition of the present disclosure may contain other components in addition to the smectic liquid crystal compound, the chiral dopant, the compound exhibiting photoconductivity, or the charge trapping agent. The other components are not particularly limited as long as they exhibit the effects of the liquid crystal composition of the present disclosure, and examples thereof include surfactants, polymerization inhibitors, antioxidants, and ultraviolet absorbers.

[0054] The liquid crystal composition of the present disclosure may or may not contain a liquid crystal compound other than a smectic liquid crystal compound. From the viewpoint of suppressing light scattering, the content of the liquid crystal compound other than a smectic liquid crystal compound in the liquid crystal composition may be 10 parts by mass or less, 5 parts by mass or less, or even 0 part by mass relative to 100 parts by mass of the smectic liquid crystal compound.

[0055] [Liquid crystal element] The liquid crystal element of the present disclosure includes a liquid crystal film formed from the flexoelectric liquid crystal composition of the present disclosure and a pair of transparent substrates sandwiching the liquid crystal film. By using the flexoelectric liquid crystal composition described above to form the liquid crystal film, light scattering is suppressed, resulting in a liquid crystal element with excellent response speed of the photorefractive effect. By using this liquid crystal element and an ultrasonic laser, it is possible to measure properties such as internal defects and structures of a test object even in a vibrating environment as described above.

[0056] The thickness of the liquid crystal film is preferably 5 μm to 15 μm, more preferably 6 μm to 13 μm, and even more preferably 8 μm to 12 μm. When the thickness of the liquid crystal film is 5 μm or more, a refractive index grating tends to be easily formed, and when the thickness of the liquid crystal film is 15 μm or less, the smectic liquid crystal tends to be aligned appropriately.

[0057] The area of ​​the main surface of the liquid crystal film is set to 0.5 cm2 in order to suppress alignment defects. 2 ~5cm 2 Preferably, it is 0.5 cm 2 ~1cm 2 It is more preferable that:

[0058] The liquid crystal film is sandwiched between a pair of transparent substrates. The transparent substrate is not particularly limited and can be appropriately selected. Examples of the transparent substrate include a glass substrate and a plastic substrate (e.g., a polyethylene naphthalate (PEN) substrate, a polyethylene terephthalate (PET) substrate, a polycarbonate (PC) substrate, a polyimide (PI) substrate, etc.). The thickness and shape of the transparent substrates are not particularly limited as long as they can sandwich the liquid crystal film.

[0059] The pair of transparent substrates may have an alignment film on the surface facing the liquid crystal film, or the liquid crystal film may be sandwiched between the pair of transparent substrates via the alignment film.

[0060] The material of the alignment film is not particularly limited and may be the same as that of a conventionally known alignment film, such as polyimide, polyvinyl alcohol, or polyester.

[0061] The alignment film may be subjected to a rubbing treatment. The rubbing treatment can be performed by rubbing the surface of the alignment film in a certain direction with a rod, roller, or the like wrapped in paper or cloth. As an example, when the alignment film is a polyimide film, a polyimide solution may be applied by spin coating to a transparent substrate with transparent electrodes (e.g., a glass substrate with transparent electrodes) and dried, and the polyimide-coated surface may be rubbed with a roller wrapped in velvet cloth. The rubbing strength when performing the rubbing treatment is expressed by the following formula:

[0062]

number

[0063] In the formula, R s is the rubbing strength (mm), N is the number of rubbings, M is the length of the contact area between the rubbing cloth and the substrate (mm), r is the radius of the rubbing cloth roll (mm), n is the rotation speed of the roller (rpm: revolutions per minute), and V is the moving speed of the alignment film-coated substrate (mm s -1 The rubbing strength is preferably 200 mm to 250 mm. This tends to form an alignment layer with few alignment defects and high transparency.

[0064] From the viewpoint of promoting separation of positive and negative charges by light irradiation, a transparent electrode may be provided on each of the pair of transparent substrates, or a transparent electrode may be provided on each of the pair of transparent substrates on the liquid crystal film side. When the pair of transparent substrates have alignment films, a transparent electrode may be provided between the transparent electrodes and the alignment films.

[0065] The liquid crystal film is formed by applying the liquid crystal composition described above to one transparent substrate, preferably to the alignment film of one transparent electrode, and sandwiching the applied liquid crystal composition between the other transparent substrate. Examples of methods for applying the liquid crystal material to the transparent substrate include coating methods such as spin coating and spraying; inkjet printing; and screen printing. The liquid crystal composition applied to the transparent substrate may be subjected to a drying treatment, if necessary.

[0066] As an example, a liquid crystal element having a liquid crystal film may be formed by bonding two rubbed transparent substrates with transparent electrodes (e.g., glass substrates with transparent electrodes) via 10 μm glass bead spacers, etc. It is preferable to bond the pair of transparent substrates so that the rubbing directions are opposite to each other, i.e., so that the liquid crystal is aligned in an antiparallel manner.

[0067] [Laser inspection system] The laser inspection system of the present disclosure includes a first laser emitting unit that generates ultrasonic vibrations on a surface of an object by irradiating the object with a pulsed laser, a second laser emitting unit that emits a continuous wave laser, a beam splitter that splits the continuous wave laser emitted from the second laser emitting unit into irradiation light that is irradiated onto the surface of the object and reference light, a liquid crystal element of the present disclosure that receives reflected light that is the irradiation light that is irradiated onto the surface of the object and reflected from the object, and the reference light, and causes the reflected light and the reference light to interfere with each other, and a detection unit that detects at least one of the irradiation light and the reference light emitted from the liquid crystal element.

[0068] In the laser inspection system of the present disclosure, a liquid crystal element having a liquid crystal film formed from a ferroelectric liquid crystal composition may be used instead of the aforementioned liquid crystal element having a liquid crystal film formed from a flexoelectric liquid crystal composition. Even when a liquid crystal element having a liquid crystal film formed from a ferroelectric liquid crystal composition is used, a photorefractive effect can be obtained, resulting in a laser inspection system with excellent response speed. On the other hand, from the viewpoint of suitably suppressing light scattering, it is preferable to use the aforementioned liquid crystal element having a liquid crystal film formed from a flexoelectric liquid crystal composition and a laser inspection system including such a liquid crystal element.

[0069] The ferroelectric liquid crystal composition is not particularly limited, and examples thereof include conventionally known liquid crystal compositions exhibiting ferroelectricity, such as the ferroelectric liquid crystal material described in JP-A-2008-216679, the ferroelectric liquid crystal composition described in JP-A-2009-108233, and other known ferroelectric liquid crystal materials or ferroelectric liquid crystal compositions.

[0070] [Testing method for subjects] The inspection method for a specimen disclosed herein is a method for analyzing the properties of a specimen using the laser inspection system disclosed herein (including the case where a liquid crystal element having a liquid crystal film formed from a ferroelectric liquid crystal composition is used), and is a method for analyzing the properties of the specimen based on a change in the intensity of light detected by the detection unit due to interference within the liquid crystal element between the reflected light, which is the irradiated light that is irradiated onto the surface of the specimen where ultrasonic vibrations are generated and reflected from the specimen, and the reference light.

[0071] The laser inspection system and the inspection method for an object of the present disclosure use the liquid crystal element of the present disclosure described above, and therefore can measure internal defects, structural properties, and the like of the object of the object even in a vibrating environment as described above. Hereinafter, one embodiment of the laser inspection system of the present disclosure and an inspection method for an object of the present disclosure using the same will be described. Note that the laser inspection system of the present disclosure is not limited to the specific configuration described below, and the inspection method for an object of the present disclosure is not limited to the method described below.

[0072] Fig. 1 shows a laser inspection system according to one embodiment of the present disclosure. The laser inspection system 100 shown in Fig. 1 includes a first laser emission unit 1, a second laser emission unit 2, beam splitters 3A and 3B, mirrors 4A and 4B, condenser lenses 5A to 5E, detectors 6A to 6C, voltage application means 7, a display unit 8, a control unit 9, and a liquid crystal element 10. An object to be inspected is placed in an area 20 indicated by a dotted line in Fig. 1.

[0073] The first laser emitting unit 1 is a laser irradiation device that emits a pulsed laser toward an object to be examined. The pulsed laser emitted by the first laser emitting unit 1 is reflected by a mirror 4A, and the reflected pulsed laser is collected by a collecting lens 5A and then irradiated onto the surface (e.g., the back surface) of the object placed in an area 20. When the pulsed laser is irradiated onto the surface of the object, ultrasonic vibrations are generated on the surface of the object.

[0074] The wavelength of the pulsed laser emitted from the first laser emission unit 1 is preferably in the infrared to visible light range and may be selected appropriately depending on the subject. As the first laser emission unit 1, for example, a nanosecond Q-switched pulsed laser may be used.

[0075] The second laser emitting unit 2 is a laser irradiation device that emits a continuous wave laser. The continuous wave laser emitted from the second laser emitting unit 2 is split by a beam splitter 3A into an irradiation light that is irradiated onto the surface of the subject and a reference light. The irradiation light split by the beam splitter 3A passes through a condenser lens 5B, the beam splitter 3B, and a condenser lens 5C in this order, and is irradiated onto the surface (e.g., the front surface) of the subject placed in region 20. At this time, the surface of the subject irradiated with the pulsed laser and the surface of the subject irradiated with the irradiation light face each other, and the irradiation area of ​​the subject with the irradiation light is located on an extension of the irradiation position of the pulsed laser.

[0076] The wavelength of the continuous wave laser emitted from the second laser emission unit 2 is preferably in the ultraviolet to visible light range, and may be appropriately selected depending on the absorption wavelength range of the specimen, the compound exhibiting photoconductivity, or the photoconductive chiral dopant, etc. Furthermore, from the viewpoint of favorably forming interference fringes by the light reflected from the specimen, it is preferable to select a continuous wave laser having a coherence length (coherence length) of 1 cm or more.

[0077] The light irradiated onto the surface of the subject and reflected from the subject passes through the condenser lens 5C, the beam splitter 3B and the condenser lens 5D in this order, and is then irradiated onto the liquid crystal film 12 of the liquid crystal element 10 as reflected light.

[0078] The reference light split by the beam splitter 3A is reflected by a mirror 4B, and is condensed by a condenser lens 5B, after which the liquid crystal film 12 of the liquid crystal element 10 is irradiated with the light.

[0079] As shown in Fig. 2, a liquid crystal element 10 includes a pair of transparent substrates 11 and a liquid crystal film 12 sandwiched between the pair of transparent substrates. An ITO transparent electrode 13 and an alignment film 14 are provided between the transparent substrate 11 and the liquid crystal film 12, in this order from the transparent substrate 11 side. The ITO transparent electrode 13 is electrically connected to a voltage application means 7, and an electric field is formed in the liquid crystal film 12 by applying a voltage to the ITO transparent electrode 13. From the viewpoint of promoting positive and negative charge separation by light irradiation, it is preferable to apply a voltage so that an electric field of about several V / µm is formed in the liquid crystal film 12.

[0080] The liquid crystal film 12 in the liquid crystal element 10 receives the reflected light and the reference light and causes them to interfere with each other, thereby forming a refractive index grating that is out of phase with the light and dark phase of the interference fringes, and the reflected light is amplified and the reference light is attenuated by photorefractive two-wave coupling.

[0081] The light absorption transition moment of the photoconductive chiral dopant in the liquid crystal film is in the direction of the molecular long axis, and the photoconductive chiral dopant aligns in the same direction as the smectic liquid crystal. Therefore, it is preferable to increase the light absorption efficiency by aligning the polarization of the laser nearly parallel to the alignment direction of the smectic liquid crystal.

[0082] The detectors 6A and 6B detect the irradiated light and the reference light emitted from the liquid crystal element 10. The light intensities of the irradiated light and the reference light detected by the detectors 6A and 6B are output to the display unit 8.

[0083] After the light intensities of the irradiated light and reference light output by the display unit 8 approach a constant value, the control unit 9 controls the first laser emitting unit 1 to emit a pulsed laser beam toward the specimen from the first laser emitting unit 1. The emitted pulsed laser beam is irradiated onto the surface of the specimen. The detector 6C detects the timing of the pulsed laser beam irradiation, and the detected irradiation timing is output by the display unit 8. The pulsed laser beam irradiated onto the surface of the specimen generates ultrasonic waves on the surface of the specimen. The ultrasonic waves propagate through the interior of the specimen and are reflected by defects, structures, and other components of the specimen. The reflected waves from the surface of the specimen cause fluctuations in the reflection of the irradiated light. This causes a phase modulation of the reflected wave of the irradiated light, as described above, which in turn changes the phase of the interference fringes in the liquid crystal film 12, resulting in a change in the amplification and attenuation of the light. By measuring the time from when the pulsed laser beam is irradiated onto the specimen to when a change in the irradiated light occurs, information about the properties of the specimen, such as the thickness of the specimen, internal defects, and structure of the specimen, can be obtained.

[0084] Furthermore, by changing the irradiation position of the pulsed laser on the object and the irradiation area of ​​the irradiation light based on the continuous wave laser, information on the properties of the object, such as the thickness of the object at a plurality of locations, defects inside the object, and structure, etc. For example, by obtaining information on the thickness of the object or defects inside the object at a plurality of locations, the structure of the object, the structure of the defects, etc. can be grasped.

[0085] The laser inspection system of the present disclosure does not need to include all of the components, devices, etc. configured as shown in Fig. 1, and may also include components, devices, etc. other than those configured as shown in Fig. 1. For example, the laser inspection system of the present disclosure may include optical components other than those configured as shown in Fig. 1, and may also include an ND filter, a wave plate, a quarter wave plate, a half wave plate, a polarizing plate, a filter, a lens other than a condenser lens, etc.

[0086] The laser inspection system of the present disclosure is not limited to a configuration in which an object to be inspected is placed in the laser inspection system, and may be a system in which, for example, a structure such as a tunnel or a bridge is used as the object to be inspected for internal defects, structural characteristics, and the like of the object to be inspected. For example, by configuring the laser inspection system of the present disclosure as shown in FIG. 3, a pulsed laser and a continuous wave laser can be coaxially irradiated onto the object to be inspected from the same direction, thereby analyzing the properties of the object to be inspected. This configuration enables non-contact measurement of the thickness of steel frames or the like located at a distance, internal flaw detection of tunnels, bridges, and the like, and the like. Furthermore, when the laser inspection system of the present disclosure is mounted on a vehicle body, mobile equipment, or the like, the properties of the object to be inspected while the vehicle body, mobile equipment, or the like is moving.

[0087] (Laser inspection system of embodiment 1) 3 includes a first laser emitting unit 21, a second laser emitting unit 22, beam splitters 23A and 23B, a mirror 24, a filter 25, a detector 26, a quarter-wave plate 27, half-wave plates 28A and 28B, and a liquid crystal element 30. The pulsed laser emitted from the first laser emitting unit 21 and the continuous wave laser emitted from the second laser emitting unit 22 are irradiated onto an object 40 coaxially and in the same direction. Note that in the present disclosure, a black circle in the figure represents vertically polarized light, and a double-headed arrow represents horizontally polarized light.

[0088] The laser inspection system 200 is configured to include only the detector 26 that detects the reference light emitted from the liquid crystal element 30, but may also include a detector that detects the reflected light emitted from the liquid crystal element 30. Furthermore, the laser inspection system 200 may also include members, devices, etc. other than the configuration shown in FIG.

[0089] (Laser inspection system of embodiment 2) The laser inspection system 300 shown in FIG. 9 includes a liquid crystal element 30, a first laser emitting unit 31, a second laser emitting unit 32, beam splitters 33A and 33B, a dichroic mirror 34A, a mirror 34B, a filter 35, detectors 36A and 36B, and a quarter-wave plate 37A.

[0090] In the laser inspection system 200 of the first embodiment, it is necessary to use a non-polarizing beam splitter as the beam splitter 23B. When the continuous wave laser passes through the beam splitter 23B, the laser intensity is halved, and when the light reflected by the object 50 is split by the beam splitter 23B, the laser intensity is further halved (total of one-fourth).

[0091] On the other hand, the laser inspection system 300 of the second embodiment uses polarizing beam splitters as the beam splitters 33A and 33B, and further uses a dichroic mirror 34A that reflects light of a specific wavelength and transmits light of other wavelengths.

[0092] In the second embodiment, the continuous wave laser reflected by the dichroic mirror 34A is irradiated onto the beam splitters 33A and 33B. The beam splitter 33A splits the laser into vertically polarized and horizontally polarized laser beams, and the vertically polarized laser beam is reflected toward the subject 50 by the beam splitter 33B. The vertically polarized laser beam reflected toward the subject 50 passes through the quarter-wave plate 37A, is reflected by the subject 50, and then passes through the quarter-wave plate 37A again. The reflected light reflected by the subject 50 and transmitted through the quarter-wave plate 37A is horizontally polarized, and the horizontally polarized reflected light passes through the beam splitter 33B and is irradiated onto the liquid crystal element 30. Furthermore, the horizontally polarized laser beam split by the beam splitter 33A is also irradiated onto the liquid crystal element 30 as a reference light. The reflected light and reference light transmitted through the liquid crystal element 30 are detected by the detectors 36A and 36B, respectively. By using beam splitters 33A and 33B, which are polarizing beam splitters, the loss of intensity of the continuous wave laser when the laser passes through and reflects off the beam splitter is suppressed, which makes it possible to reduce the intensity of the continuous wave laser required for high-precision detection. [Example]

[0093] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the following description, all "%" refers to mass unless otherwise specified. do.

[0094] Example 1 [Preparation of Liquid Crystal Composition] A liquid crystal mixture of three 2-phenylpyrimidine derivatives represented by the following chemical formulas was used as a liquid crystal compound exhibiting a smectic C phase, a compound having a terthiophene skeleton represented by the following chemical formula was used as a photoconductive chiral dopant, and trinitrofluorenone represented by the following chemical formula was used as a charge capture agent. A liquid crystal composition was prepared by mixing the liquid crystal compounds, photoconductive chiral dopant, and charge capture agent in the following mixing ratios. Liquid crystal compound: 100 parts by mass Photoconductive chiral dopant: 5 parts by mass Charge trapping agent: 0.1 parts by mass

[0095] [ka]

[0096] [Fabrication of liquid crystal elements] A polyimide was applied to the surface of a transparent substrate with an ITO (indium tin oxide) transparent electrode, and a rubbing treatment was performed with a rubbing strength of 200 mm to 250 mm to form an alignment film. The liquid crystal composition described above was applied to the surface of the transparent substrate with the alignment film, and a liquid crystal element with a liquid crystal film was fabricated by sandwiching the liquid crystal composition between a pair of transparent substrates so that the surface with the alignment film was located on the liquid crystal composition side. The liquid crystal film had a thickness of 10 μm.

[0097] [Preparing the laser inspection system] Using the liquid crystal element fabricated as described above, a laser inspection system was prepared as shown in Figure 4. As will be described later, a test object was placed in the dotted line area in Figure 4 and the thickness of the test object was measured.

[0098] [Measurement of specimen thickness] The thickness of a flat aluminum plate (the test object) was measured by placing it within the dotted line in Figure 4. A 473 nm wavelength light was output from a CW laser and separated into an irradiated light beam and a reference light beam using a polarizing beam splitter. The 473 nm wavelength irradiated the front side of the aluminum plate, and the reflected light was allowed to interfere with the reference light within the liquid crystal film. The transmitted light intensity of the reflected light and the transmitted light intensity of the reference light were detected by detectors 1 and 2 and confirmed on the display. The voltage applied to the liquid crystal film by the DC power supply was 20 V or less, and the electric field applied to the liquid crystal film was 2 V / μm.

[0099] Next, a nanosecond pulsed laser with a wavelength of 1064 nm was irradiated onto the back surface of the aluminum plate, and changes in the irradiated light and reference light were examined. The timing of the pulsed laser irradiation was detected by detector 3 and confirmed on the display. The irradiation positions of the irradiated light and the pulsed laser on the aluminum plate were accurately recorded.

[0100] The ultrasonic vibrations generated on the surface of an aluminum plate by pulsed laser irradiation include longitudinal and shear waves. The propagation speed within the aluminum plate is 6420 m / s for longitudinal waves and 3040 m / s for shear waves. As the ultrasonic vibrations propagate from the back surface to the front surface, fluctuations occur in the reflection of the irradiated light. The inter-surface distance of the aluminum plate, i.e., its thickness, can be measured by measuring the time from pulsed laser irradiation to a change in the reflection of the irradiated light. Figure 5 shows the change in the intensity of the transmitted light of the reference beam when aluminum plates with thicknesses of 2 mm, 3 mm, and 5 mm are used as specimens. The arrows in Figure 5(1) indicate the longitudinal wave arrival time for each thickness, and the arrows in Figure 5(2) indicate the shear wave arrival time for each thickness. Table 1 shows the thickness of the aluminum plate calculated from the longitudinal wave arrival time, shear wave arrival time, and longitudinal wave propagation speed and shear wave propagation speed.

[0101] [Table 1]

[0102] As shown in Table 1, the measurements using longitudinal waves and shear waves corresponded accurately to the thickness of the aluminum plate, confirming that the thickness of the specimen could be measured using the method of this example. Note that although many signals were observed in the measurement results, these were ultrasonic vibrations that were reflected from the front and back surfaces of the aluminum plate, as shown in Figure 6, for example. As described in the aforementioned Non-Patent Documents 1 and 2, when a polymer material is used as the photorefractive material, it is necessary to apply a high voltage of about 5 kV to the photorefractive material to measure the thickness of the object. On the other hand, when a liquid crystal film is formed using a flexoelectric liquid crystal composition as in this example, the thickness of the object can be measured with high accuracy by applying a low voltage of 20 V or less to the liquid crystal film. Furthermore, in this example, a high response speed was ensured even when the above-mentioned constant voltage was applied to the liquid crystal film.

[0103] <Example 2> The same operations as in Example 1 were carried out, except that the flat aluminum plate to be tested was changed to an aluminum plate having a curved depression. For the aluminum plate having a curved depression, the thickness of the flat portion without the depression was 5 mm, and the thickness of the center of the depression was 3 mm. Figure 7 shows the relationship between the measurement position on the aluminum plate and the time change in the intensity of transmitted light of the reflected light. As shown in Figure 7, the measurement position on the aluminum plate corresponding to the irradiation position of the pulsed laser was determined by dividing the aluminum plate into five equal parts in the length direction from the reference point to the center of the depression, as shown in Figure 7, and irradiating the five equally divided positions with pulsed laser as indicated by the arrows, to evaluate the thickness of the aluminum plate corresponding to the irradiation position of the pulsed laser. Note that the measurement position on the aluminum plate corresponding to the irradiation position of the pulsed laser was determined by dividing the aluminum plate into five equal parts in the length direction from the reference point to the center of the depression. The distance in the longitudinal direction was 4 mm, and the distance between adjacent irradiation positions of the pulsed laser was 1 mm. The relationship between the measurement position of the aluminum plate thickness and the thickness measurement results when using longitudinal waves is shown in Figure 8. The measurement position of 0 mm in Figure 8 is the reference point.

[0104] As shown in Figure 8, the peak position of the transmitted light intensity varied depending on the measurement position of the aluminum plate thickness. As a result, it was possible to determine the shape of the depression by checking the variation in the aluminum plate thickness at the measurement position of the depression.

[0105] The disclosure of Japanese Patent Application No. 2021-123643, filed on July 28, 2021, is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0106] 1, 21, 31 First laser emission unit 2, 22, 32 Second laser emission unit 3A, 3B, 23A, 23B, 33A, 33B Beam Splitters 4A, 4B, 24, 34B mirrors 5A~5E Condenser Lens 6A~6C, 26, 36A, 36B detectors 7. Voltage application means 8 Display 9 Control Unit 10, 30 Liquid crystal element 11 Transparent substrate 12 Liquid crystal film 13 ITO transparent electrode 14 Alignment film 25, 35 filters 27, 37A 1 / 4 wavelength plate 28A, 28B, 38 1 / 2 wave plate 34A Dichroic Mirror 40, 50 subjects 100, 200, 300 Laser Inspection Systems

Claims

9. a first laser emission unit that irradiates a pulsed laser onto an object to generate ultrasonic vibrations on a surface of the object; a second laser emission unit that emits a continuous wave laser; a first polarizing beam splitter that is irradiated with a pulsed laser beam emitted from a first laser emitting unit and a continuous wave laser beam emitted from a second laser emitting unit, and that splits the continuous wave laser beam emitted from the second laser emitting unit into irradiation light that is irradiated onto the surface of the subject and reference light; a liquid crystal element that receives the reference light and the reflected light, which is the irradiation light that is irradiated onto the surface of the subject and reflected from the subject, and causes the reflected light and the reference light to interfere with each other; a detection unit that detects at least one of the irradiation light and the reference light emitted from the liquid crystal element; a second polarizing beam splitter located between the subject and the liquid crystal element, which reflects the irradiation light split by the first polarizing beam splitter toward the subject and transmits the reflected light reflected by the subject toward the liquid crystal element; Equipped with the liquid crystal element comprises a liquid crystal film formed of a flexoelectric liquid crystal composition and a pair of transparent substrates sandwiching the liquid crystal film; The flexoelectric liquid crystal composition exhibits photoconductivity and comprises at least one smectic liquid crystal compound, a chiral dopant, and a charge trapping agent; The content of the chiral dopant is 0.1 to 5 parts by mass with respect to 100 parts by mass of the total amount of the smectic liquid crystal compound.

10. a first laser emission unit that irradiates a pulsed laser onto an object to generate ultrasonic vibrations on a surface of the object; a second laser emission unit that emits a continuous wave laser; a first polarizing beam splitter that is irradiated with a pulsed laser beam emitted from a first laser emitting unit and a continuous wave laser beam emitted from a second laser emitting unit, and that splits the continuous wave laser beam emitted from the second laser emitting unit into irradiation light that is irradiated onto the surface of the subject and reference light; a liquid crystal element that receives the reference light and the reflected light, which is the irradiation light that is irradiated onto the surface of the subject and reflected from the subject, and causes the reflected light and the reference light to interfere with each other; a detection unit that detects at least one of the irradiation light and the reference light emitted from the liquid crystal element; a second polarizing beam splitter located between the subject and the liquid crystal element, which reflects the irradiation light split by the first polarizing beam splitter toward the subject and transmits the reflected light reflected by the subject toward the liquid crystal element; Equipped with The liquid crystal element includes a liquid crystal film formed from a ferroelectric liquid crystal composition and a pair of transparent substrates sandwiching the liquid crystal film.

11. A method for analyzing properties of an object using the laser inspection system according to claim 9, comprising: A method for analyzing a test subject, which analyzes the properties of the test subject based on a change in the intensity of light detected by the detection unit due to interference within the liquid crystal element between the reflected light, which is the irradiation light that is irradiated onto a surface of the test subject where ultrasonic vibrations are generated and reflected from the test subject, and the reference light.

12. A method for analyzing properties of an object using the laser inspection system according to claim 10, comprising: A method for analyzing a test subject, which analyzes the properties of the test subject based on a change in the intensity of light detected by the detection unit due to interference within the liquid crystal element between the reflected light, which is the irradiation light that is irradiated onto a surface of the test subject where ultrasonic vibrations are generated and reflected from the test subject, and the reference light.

13. The laser inspection system of claim 9 , wherein the chiral dopant comprises a photoconductive chiral dopant.

14. 14. The laser inspection system of claim 13, wherein the photoconductive chiral dopant includes at least one of a compound represented by the following general formula (1) and a compound represented by the following general formula (2): [Chemical formula 1] (In general formula (1) and general formula (2), R １ and R ２ are each independently a hydrocarbon group having an asymmetric carbon atom.

15. In the general formula (1) and the general formula (2), R １ and R ２ 15. The laser inspection system of claim 14, wherein is a 2-methylbutyl group.

16. The laser inspection system of claim 9 , wherein the smectic liquid crystal compound comprises a liquid crystal compound exhibiting a smectic C phase.

17. The laser inspection system according to any one of claims 9 and 13 to 16, wherein the liquid crystal film has a thickness of 5 μm to 15 μm.

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