Material identification device, material identification method, and terahertz light source

Abstract

A substance identification device comprising: an irradiation unit that simultaneously irradiates an object with a plurality of terahertz waves having different wavelengths; a detection unit that detects the terahertz waves transmitted through or reflected on the object; and an identification unit that identifies a substance constituting the object on the basis of transmittances and / or reflectances of the respective terahertz waves.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The disclosure of Japanese Patent Application No. 2021-122665, filed on July 27, 2021, is incorporated by reference in its entirety into this specification. [Technical field]

[0002] The present invention relates to a material identification device, a material identification method, and a terahertz light source. [Background technology]

[0003] In recent years, revisions to international treaties have restricted the export of waste plastics to China and other countries. In addition, government policy goals, such as achieving 100% recycling of plastics by 2035 and reducing CO2 emissions, have led to restrictions on fuel use and landfilling. This has greatly increased the need to convert waste plastics discharged from ordinary households and businesses into recycled plastics. In addition, the COVID-19 pandemic has led to increased stay-at-home demand and increased use of mail-order shopping, further increasing the amount of waste plastics such as food trays and packaging, which is also putting a strain on the processing capacity of processing companies.

[0004] In order to reuse waste plastics, it is first necessary to separate them by material. Today's waste plastics are made up of a wide variety of plastics, including colored plastics and plastics containing additives, making separation difficult. Traditionally, methods such as visual sorting, sorting by combustion or smell, electrostatic sorting, and gravity sorting have been used to separate waste plastics. However, using traditional sorting methods, it is extremely difficult to accurately separate waste plastics with complex compositions. For this reason, conversion to recycled plastics has not progressed, and the processing capacity of waste disposal companies is becoming increasingly strained.

[0005] In recent years, the application of technology related to optical identification of substances using infrared light, near-infrared light, and terahertz waves to the separation of waste plastics has been considered. For example, Japanese Patent Application Laid-Open No. 2015-83964 discloses an information acquisition device that acquires information about a specimen by irradiating a terahertz wave through a plate-shaped member to a specimen placed between the plate-shaped member and a reflecting member having a reflecting surface that reflects terahertz waves. Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in JP 2015-83964 A also uses pulsed terahertz waves to acquire information about a specimen. Ultrashort pulse lasers are unstable, with variations in pulse intensity. Therefore, there is a problem that it is difficult to acquire accurate information with an information acquisition device using an ultrashort pulse laser. In addition, ultrashort pulse lasers are expensive and large.

[0007] An object of the present disclosure is to provide a material identification device and a material identification method that are capable of identifying a plurality of materials at high speed and with high accuracy by using terahertz waves.

[0008] Another object of the present disclosure is to provide a terahertz light source capable of simultaneously generating a plurality of terahertz waves with different wavelengths. [Means for solving the problem]

[0009] The object identification device disclosed herein includes an irradiation unit that irradiates an object with multiple terahertz waves of different wavelengths at one time, a detection unit that detects the multiple terahertz waves that have passed through the object or been reflected by the object, and an identification unit that identifies the material that makes up the object from at least one of the transmittance and reflectance for each of the multiple terahertz waves.

[0010] The object identification method disclosed herein irradiates an object with multiple terahertz waves of different wavelengths at one time, detects the multiple terahertz waves that have passed through the object or been reflected by the object, and identifies the material that makes up the object from at least one of the transmittance and reflectance for each of the multiple terahertz waves.

[0011] The terahertz light source disclosed herein comprises a plurality of nonlinear optical crystals and a plurality of fiber lasers having different oscillation wavelengths, where the number of combinations when two fiber lasers are selected from the plurality of fiber lasers is equal to or greater than the number of the plurality of nonlinear optical crystals, and each of the plurality of nonlinear optical crystals is irradiated with two types of laser light having different wavelengths from the fiber laser of a corresponding combination, thereby simultaneously generating a plurality of terahertz waves having different wavelengths from the plurality of nonlinear optical crystals. Effect of the Invention

[0012] According to the material identifying device and material identifying method of the present invention, a plurality of materials can be identified at high speed and with high accuracy by irradiating a plurality of terahertz waves having different wavelengths at once.

[0013] According to the terahertz light source of the present invention, a plurality of terahertz waves having different wavelengths can be generated simultaneously. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing an overview of object identification according to the present disclosure. [Diagram 2] 1 is a schematic diagram illustrating an example of a configuration of an object identification device according to the present disclosure. [Diagram 3] 1 is a flowchart illustrating an example of a procedure of an object identification method according to the present disclosure. [Figure 4] 1 is a graph showing an example of changes in transmittance of plastic with respect to frequency. [Diagram 5] FIG. 1 is a schematic diagram showing an example of a method for separating plastics. [Figure 6]11 is a graph showing another example of the change in transmittance of plastic with respect to frequency. [Figure 7] 1 is a schematic diagram showing an example of the configuration of a terahertz light source according to the present disclosure. [Figure 8] 1 is a schematic diagram showing another example of the configuration of a terahertz light source according to the present disclosure. [Figure 9] 11 is a plan view showing yet another example of the configuration of the terahertz light source according to the present disclosure. FIG. [Figure 10] 10 is a side view of the terahertz light source shown in FIG. [Figure 11] 11 is a schematic diagram showing a modified example of the configuration of the object identification device according to the present disclosure. [Figure 12] 13 is a schematic diagram showing another modified example of the configuration of the object identification device according to the present disclosure. [Figure 13] FIG. 2 is a schematic diagram showing an example of the configuration of an optical system other than a light source. [Figure 14] FIG. 11 is a schematic diagram showing another example of the configuration of the optical system other than the light source. [Figure 15] FIG. 11 is a schematic diagram showing another example of the configuration of the optical system other than the light source. [Figure 16] FIG. 11 is a schematic diagram showing another example of the configuration of the optical system other than the light source. [Figure 17] FIG. 11 is a schematic diagram showing another example of the configuration of the optical system other than the light source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention will now be described in detail with reference to the drawings.

[0016] <Object Identification Overview> First, an overview of material identification according to the present disclosure will be described. In the material identification method disclosed herein, multiple terahertz waves with different wavelengths are irradiated onto an object at once, the multiple terahertz waves that have passed through the object or been reflected by the object are detected, and the material that makes up the object is identified from at least one of the transmittance and reflectance for each of the multiple terahertz waves.

[0017] Terahertz waves are in the frequency range between 100 GHz (gigahertz) and 10 THz (terahertz), which is intermediate between radio waves and light waves. Terahertz waves are electromagnetic waves with intermediate properties between radio waves and light waves, and have both the transparency of radio waves and the straightness of light waves. When terahertz waves are irradiated onto a material, they resonate with the material's inherent vibrations and absorb the electromagnetic wave energy, resulting in a spectrum unique to the material (the so-called fingerprint spectrum).

[0018] It is preferable that each of the multiple terahertz waves having different wavelengths is a continuous wave. By using a continuous wave, the wavelength of the terahertz wave can be fixed, and the transmittance of the terahertz wave of each wavelength can be obtained. Therefore, the type of material can be identified based on the difference in the transmittance of the terahertz wave of each wavelength, and it is possible to identify the material in a shorter time than when comparing spectral spectra.

[0019] FIG. 1 is a schematic diagram showing an overview of material identification according to the present disclosure. Terahertz waves can be generated by various methods, but in this embodiment, for example, a terahertz light source including a plurality of fiber lasers 10, 12, 14 with different oscillation wavelengths and a plurality of nonlinear optical crystals 18, 22, 26 is used to generate a plurality of terahertz waves with different wavelengths by a difference frequency generation method or the like. Note that in this disclosure, the source of the terahertz waves may be referred to as a "terahertz light source", and the terahertz waves may be expressed as light waves.

[0020] When the pumping light from the fiber laser 10 and the pumping light from the fiber laser 12 are irradiated onto the nonlinear optical crystal 18, a terahertz wave of 2.18 THz is generated according to the difference frequency between the two types of pumping light. Similarly, when the pumping light from the fiber laser 12 and the pumping light from the fiber laser 14 are irradiated onto the nonlinear optical crystal 22, a terahertz wave of 1.06 THz is generated, and when the pumping light from the fiber laser 10 and the pumping light from the fiber laser 14 are irradiated onto the nonlinear optical crystal 26, a terahertz wave of 3.25 THz is generated.

[0021] The multiple terahertz waves are simultaneously irradiated onto object 28. The multiple terahertz waves that have passed through object 28 are detected by one of multiple detectors 30, 32, 34, each of which corresponds to a different wavelength. The transmittance of the terahertz waves at each wavelength is calculated from the intensity of the irradiated terahertz waves and the intensity of the detected terahertz waves. Since different types of substances have different transmission characteristics for terahertz waves, the substances that make up the object can be identified from the difference in the transmittance of the terahertz waves at each wavelength through object 28.

[0022] If two types of excitation light with different wavelengths are required to generate one type of terahertz wave, simple calculations would dictate that six types of excitation light with different wavelengths are required to generate three types of terahertz waves. However, in this embodiment, by generating three combinations of two types of excitation light from three types of excitation light with different wavelengths, it is possible to generate three types of terahertz waves from the three types of excitation light with different wavelengths.

[0023] In other words, it is possible to obtain terahertz waves from a limited number of fiber lasers in the number of combinations. The number of combinations in which two types of excitation light are selected from three different types of excitation light is expressed as 3C2=, which is 3. Similarly, since 4C2=6, six types of terahertz waves can be generated from four types of excitation light with different wavelengths, and since 5C2=10, ten types of terahertz waves can be generated from five types of excitation light with different wavelengths.

[0024] In this embodiment, an example in which three types of terahertz waves are used will be described, but the number of types of terahertz waves to be used is determined according to the number of types of materials to be separated. As the number of types of terahertz waves increases, more types of materials can be separated.

[0025] In this embodiment, a material identification procedure based on the relative intensity of transmittance will be described, but the method is not limited to transmittance, and an optimal standard may be selected by acquiring a trend based on measurements of an actual sample. For example, material identification based on the relative intensity of transmitted light or reflected light, material discrimination based on the relative intensity of transmittance or reflectance, or material identification based on a comparison of an absorption coefficient calculated based on a film thickness measured in advance may be used. For film thickness measurement, white light interference method, femtosecond laser transit time, etc. may be used.

[0026] In the following, an embodiment of the present invention will be described taking as an example a case where the object is waste plastic and the type of plastic that constitutes the object is identified.

[0027] [First embodiment] <Object Identification Device> Next, the configuration of the object identification device will be described. Fig. 2 is a schematic diagram showing an example of the configuration of an object identification device of the present disclosure. The object identification device 100 is a device that identifies the type of plastic material that constitutes an object 28. As shown in Fig. 2, the object identification device 100 includes an irradiation unit 102, a detection unit 104, a sorting processing unit 106, a control unit 108, and a transport device 110.

[0028] The irradiation unit 102 and the detection unit 104 are disposed to face each other across a transport path for the objects 28. The transport device 110 is configured to sequentially transport the plurality of objects 28 to a predetermined position between the irradiation unit 102 and the detection unit 104. The separation processing unit 106 is disposed downstream of the irradiation unit 102 and the detection unit 104 in the transport direction.

[0029] The conveying device 110 is, for example, a belt conveyor. The conveying device 110 includes a pair of rollers 110A and a belt 110B. The belt 110B moves in the conveying direction by the rotation of the pair of rollers 110A. The pair of rollers 110A are driven by a motor (not shown), which is controlled by the control unit 108. The belt 110B is made of a material that is highly transparent to terahertz waves. Examples of such materials include plastics such as polytetrafluoroethylene, polypropylene, and polycarbonate.

[0030] The irradiation unit 102 includes a terahertz light source, which will be described later, and simultaneously irradiates the object 28 with a plurality of terahertz waves having different wavelengths generated by the terahertz light source.

[0031] The detection unit 104 includes a plurality of detectors, and detects the intensities of a plurality of terahertz waves transmitted through the object 28. The plurality of detectors are provided corresponding to a plurality of terahertz waves with different wavelengths, and each of them detects the intensity of the terahertz wave of the corresponding wavelength (see FIG. 1). For example, a DTGS [Deuterium Tri-Glycine Sulfate] detector can be used as the plurality of detectors. The DTGS detector is a pyroelectric type photodetector in which the hydrogen atoms of triglycine sulfate are replaced with deuterium.

[0032] The control unit 108 is composed of an information processing device (computer) equipped with a CPU, ROM, RAM, and memory, and controls each part of the device and performs various calculations. For example, the control unit 108 stores the intensity of the irradiated terahertz waves (hereinafter referred to as "irradiation intensity") in a memory. When the control unit 108 acquires the intensity of the terahertz waves detected by the detection unit 104 (hereinafter referred to as "detection intensity"), it reads the irradiation intensity of the terahertz waves from the memory and calculates the transmittance of the terahertz waves from the irradiation intensity and the detection intensity. The control unit 108 identifies the type of plastic using the transmittance of the terahertz waves of each wavelength for the object 28. That is, the control unit 108 corresponds to the "identification unit" of the present invention.

[0033] The separating unit 106 is a sorting mechanism, etc. The separating unit 106 separates the objects 28 into types of plastic materials based on the identification results obtained by the control unit 108.

[0034] (Operation of object identification device) Next, the operation of the object identification device, that is, the procedure of the object identification method will be described. FIG. 3 is a flowchart showing an example of the procedure of the object identification method of the present disclosure. First, the transport device 110 transports the object 28 to a predetermined position (step S10). Next, the irradiation unit 102 generates a plurality of terahertz waves having different wavelengths and simultaneously irradiates the object 28 with the terahertz waves (step S12). Next, the detection unit 104 detects the plurality of terahertz waves that have passed through the object 28 (step S14).

[0035] Next, the control unit 108 calculates the transmittance of the terahertz waves of each wavelength (step S16). Next, the control unit 108 uses the calculated transmittance to identify the type of plastic material that constitutes the object 28 (step S18). Next, the separation processing unit 106 separates the object 28 based on the identification result (step S18). These procedures are repeated for each object 28.

[0036] (Material identification based on transmittance) Here, a procedure for identifying a material based on its transmittance will be described with a specific example.

[0037] -Example 1- Specific example 1 is an example of identifying four types of plastics: polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polystyrene (PS).

[0038] Figure 4 is a graph showing an example of the change in transmittance of plastics versus frequency. The graph shows the change in transmittance versus terahertz wave frequency for a 1.5 mm thick polypropylene plate, a 1.5 mm thick polyethylene plate, and a 1.5 mm thick polystyrene plate. Polypropylene is shown by a solid line, polyethylene by a dotted line, and polystyrene by a dashed-dotted line.

[0039] The optical spectra of polypropylene, polyethylene, and polystyrene are significantly different. The transmittance of 2.2 THz terahertz waves is approximately 83% for polypropylene, approximately 73% for polyethylene, and approximately 2% for polystyrene. The transmittance of 3.3 THz terahertz waves is approximately 70% for polypropylene, approximately 80% for polyethylene, and approximately 3% for polystyrene. The transmittance of 2.2 THz terahertz waves is higher for polypropylene than for polyethylene, and the transmittance of 3.3 THz terahertz waves is higher for polyethylene than for polypropylene. Also, although not shown in the figure, polyethylene terephthalate barely transmits terahertz waves.

[0040] Figure 5 is a schematic diagram showing an example of a method for separating plastics. As shown in Figure 5, separation is performed using two types of terahertz waves, 2.2 THz and 3.3 THz. In the first stage, objects that do not transmit 2.2 THz and 3.3 THz terahertz waves are identified as polyethylene terephthalate. In the second stage, the transmittance for 2.2 THz terahertz waves (T@2.2 THz) is compared with the transmittance for 3.3 THz terahertz waves (T@3.3 THz).

[0041] Objects with similar T@2.2THz and T@3.3THz are identified as polystyrene. Objects with T@2.2THz greater than T@3.3THz are identified as polyethylene. Objects with T@2.2THz less than T@3.3THz are identified as polypropylene. In this way, four types of plastics can be distinguished.

[0042] It is also possible to add a 1.1 THz terahertz wave to the 2.2 THz and 3.3 THz terahertz waves. Higher discrimination capability can be achieved by using three types of terahertz waves. If the transmittance for the 1.1 THz terahertz wave is T@1.1 THz, discrimination is performed using more complex criteria, as shown below, improving discrimination capability.

[0043] An object with T@1.1THz>T@2.2THz>T@3.3THz is identified as polypropylene. An object with T@1.1THz ≒ T@3.3THz>T@2.2THz is identified as polyethylene. An object with T@1.1THz>T@2.2THz ≒ T@3.3THz is identified as polystyrene. An object that does not transmit any terahertz waves is identified as polyethylene terephthalate.

[0044] -Example 2- Example 2 is an example of identifying two types of plastics: polypropylene (PP) and polypropylene containing talc (PP+Talc). Polypropylene containing talc as a reinforcing agent is used in food trays, vehicle bumpers, and interior parts.

[0045] Figure 6 is a graph showing another example of the change in plastic transmittance versus frequency. It shows the change in transmittance versus terahertz wave frequency for a 0.1 mm thick polypropylene sheet and a 0.1 mm thick polypropylene sheet containing talc. The polypropylene is shown by the solid line, and the polypropylene containing talc is shown by the dotted line.

[0046] As shown in Figure 6, in polypropylene containing talc, the spectrum of talc clearly appears in the frequency range of 4 THz to 6 THz. Therefore, from the transmittance of terahertz waves of a specific wavelength in the frequency range of 4 THz to 6 THz, it is possible to identify polypropylene containing talc, and also to investigate the quantity and distribution of talc.

[0047] <Terahertz light source> Next, the terahertz light source constituting the irradiation unit 102 in FIG. 2 will be described. 7 is a schematic diagram showing an example of the configuration of a terahertz light source according to the present disclosure. As shown in FIG 7, the terahertz light source includes fiber lasers 10, 12, and 14, nonlinear optical crystals 18, 22, and 26, lenses 16, 20, 24, 42, and 50, beam splitters 40, 44, 48, 52, and 58, a mirror 54, a half-wave plate 56, collimators 36, 38, and 46, and dampers 60 and 62.

[0048] The fiber laser 10 includes a pumping light source 10A and an amplifying optical fiber 10B whose core is doped with rare earth elements. The laser light emitted from the pumping light source 10A enters the optical fiber 10B, propagates through the optical fiber 10B while being amplified, and oscillates at a predetermined wavelength. Similarly, the fiber laser 12 includes a pumping light source 12A and an optical fiber 12B, and the fiber laser 14 includes a pumping light source 14A and an optical fiber 14B.

[0049] Examples of the nonlinear optical crystals 18, 22, and 26 include GaP crystals, GaSe crystals, ZnGeP2 crystals, LiNbO3 crystals, and CdSe crystals. In the terahertz light source of the present disclosure, nonlinear optical crystals that have low absorption of the excitation light are preferred, and GaP crystals are the most preferred among the nonlinear optical crystals exemplified. By using GaP crystals as the nonlinear optical crystals 18, 22, and 26, the excitation light is transmitted through the nonlinear optical crystals with almost no absorption, as described below, making it possible to reuse the transmitted excitation light with high efficiency.

[0050] Lenses 16, 20, and 24, which are arranged upstream of the nonlinear optical crystal, are focusing lenses that focus the two types of pump light into the nonlinear optical crystal. In the case of nonlinear optical crystals with optical isotropy, such as GaP crystals and LiNbO3 crystals, terahertz waves are generated by difference frequency generation through angular phase matching. Lenses 16, 20, and 24 provide a slight angle between the two types of pump light, and phase matching is achieved by making the two types of pump light enter the nonlinear optical crystal.

[0051] The lenses 42 and 50 arranged downstream of the nonlinear optical crystal are also condensing lenses. The lens 42 forms a pair with the lens 16, and the lens 50 forms a pair with the lens 24. These pairs of lenses, with their symmetrical lens arrangement, condense the excitation light transmitted through the nonlinear optical crystal and reduce the beam divergence.

[0052] The beam splitters 40, 44, 48, 52, and 58 transmit one of the two types of incident excitation light and reflect the other, separating it into each excitation light. In this example, the two types of incident laser light differ not only in wavelength but also in polarization direction. The beam splitters 40, 44, 48, 52, and 58 are polarizing beam splitters, and transmit one of the two types of incident excitation light with different wavelengths and polarization directions and reflect the other, separating it into two excitation lights with different wavelengths and polarization directions.

[0053] The half-wave plate 56 is a wave plate that provides an optical path difference of half a wavelength between orthogonal linearly polarized components, and rotates the polarization direction of the incident excitation light by 90°.

[0054] The collimators 36, 38, and 46 are fiber-connected collimator lenses that collimate the light emitted from the optical fiber and cause the parallel light to enter the optical fiber. The dampers 60 and 62 are attenuators that guide unnecessary light thereinto and attenuate it.

[0055] Next, the operation of the terahertz light source will be described. Here, the excitation light from fiber laser 10 is referred to as the "first excitation light" and is represented by a solid line in each figure. The excitation light from fiber laser 12 is referred to as the "second excitation light" and is represented by a dotted line in each figure. The excitation light from fiber laser 14 is referred to as the "third excitation light" and is represented by a dashed-dotted line in each figure. In this example, the wavelength of the first excitation light is 1072.3 nm, the wavelength of the second excitation light is 1064 nm, and the wavelength of the third excitation light is 1060.0 nm.

[0056] The first excitation light emitted from one end of the optical fiber 10B of the fiber laser 10 is collimated by the collimator 36 and enters the beam splitter 40, is reflected by the beam splitter 40 and enters the lens 16. On the other hand, the second excitation light emitted from one end of the optical fiber 12B of the fiber laser 12 is collimated by the collimator 38 and enters the beam splitter 40, passes through the beam splitter 40 and enters the lens 16.

[0057] The first and second excitation lights are focused by lens 16 into nonlinear optical crystal 18. At this time, lens 16 causes the first and second excitation lights to intersect at a slight angle within nonlinear optical crystal 18. When the first and second excitation lights, which have different wavelengths, are irradiated onto nonlinear optical crystal 18, a first terahertz wave is generated according to the difference frequency between the first and second excitation lights. In this example, the wavelength of the first terahertz wave is 2.18 THz.

[0058] The first and second excitation lights transmitted through the nonlinear optical crystal 18 are collected by the lens 42 and enter the beam splitter 44. The first excitation light is reflected by the beam splitter 44 and enters the beam splitter 48, and is reflected by the beam splitter 48 and enters the lens 24. The second excitation light is transmitted through the beam splitter 44 and enters the beam splitter 58, and is transmitted through the beam splitter 58 and enters the lens 20.

[0059] Since nonlinear optical crystals hardly absorb pump light, the first pump light transmitted through the nonlinear optical crystal 18 is reused to pump another nonlinear optical crystal 26, and the second pump light transmitted through the nonlinear optical crystal 18 is reused to pump another nonlinear optical crystal 22.

[0060] The third excitation light emitted from one end of the optical fiber 14B of the fiber laser 14 is collimated by the collimator 46 and enters the beam splitter 48, then passes through the beam splitter 48 and enters the lens 24. The first excitation light and the third excitation light are focused in the nonlinear optical crystal 26 by the lens 24. When the first excitation light and the third excitation light, which have different wavelengths, are irradiated onto the nonlinear optical crystal 26, a second terahertz wave is generated according to the difference frequency between the first excitation light and the third excitation light. In this example, the wavelength of the second terahertz wave is 3.25 THz.

[0061] The first and third pumping lights transmitted through the nonlinear optical crystal 26 are collected by the lens 50 and enter the beam splitter 52. The first pumping light is reflected by the beam splitter 52 and enters the damper 60, where it is attenuated. The third pumping light is transmitted through the beam splitter 52 and enters the mirror 54, where it is reflected and its optical path is folded. The third pumping light reflected by the mirror 54 passes through the half-wave plate 56 and enters the beam splitter 58, where it is reflected and enters the lens 20.

[0062] For example, if the first pump light is S-polarized, the second pump light is P-polarized, and the third pump light is P-polarized, the two types of pump light with different polarization directions can be separated, but the second pump light and the third pump light are the same P-polarized light and cannot be separated by the beam splitter 58. Therefore, the third pump light is converted from P-polarized to S-polarized light by the half-wave plate 56 so that it can be separated by the beam splitter 58.

[0063] The second pumping light and the third pumping light are focused in the nonlinear optical crystal 22 by the lens 20. When the second pumping light and the third pumping light, which have different wavelengths, are irradiated onto the nonlinear optical crystal 22, a third terahertz wave is generated according to the difference frequency between the second pumping light and the third pumping light. In this example, the wavelength of the third terahertz wave is 1.06 THz. The second pumping light and the third pumping light transmitted through the nonlinear optical crystal 22 enter the damper 62 and are attenuated within the damper 62.

[0064] As described above, the terahertz light source of the present disclosure can simultaneously generate a plurality of terahertz waves, each of which is a continuous wave and has different wavelengths, by continuously oscillating the fiber lasers 10, 12, and 14.

[0065] Moreover, the terahertz light source of the present disclosure has the characteristics of being easy to maintain and capable of continuous operation with low power consumption, similar to the fiber lasers 10, 12, and 14. Moreover, the terahertz light source of the present disclosure has the advantages of being inexpensive, small, and stable, compared to light sources that generate pulsed terahertz waves.

[0066] In addition, the terahertz light source of the present disclosure can generate three combinations of two types of excitation light from three types of excitation light with different wavelengths, thereby generating three types of terahertz waves from three types of excitation light with different wavelengths. In other words, it is possible to obtain terahertz waves from a limited number of excitation light sources, the number of which is equal to the number of combinations.

[0067] In addition, the terahertz light source disclosed herein can reduce the number of excitation light sources by reusing the transmitted excitation light that has passed through the nonlinear optical crystal, which has the advantage of requiring fewer excitation light sources than the semiconductor method in which one terahertz wave is generated from one semiconductor laser.

[0068] Furthermore, the object identification device of the present disclosure can use the terahertz light source of the present disclosure to irradiate multiple terahertz waves onto an object at once, thereby enabling multiple substances to be identified quickly and with high accuracy. That is, since an object is identified using the transmittance of multiple terahertz waves with different wavelengths, identification is possible at a higher speed than when identifying a substance by measuring a spectroscopic spectrum, and identification is possible with a high accuracy similar to identification using a spectroscopic spectrum. This allows the object identification device of the present disclosure to identify objects one after another at the same speed as the transport speed of the objects.

[0069] In addition, the object identification device of the present disclosure can directly enjoy the advantages of the terahertz light source of the present disclosure.

[0070] [Second embodiment] The second embodiment is similar to the first embodiment except for the change in the configuration of the terahertz light source, so only the differences will be described.

[0071] The configuration of the terahertz light source is not limited to that shown in Fig. 7. As described above, the pumping light transmitted through the nonlinear optical crystal is reused to pump another nonlinear optical crystal. The pumping light transmitted through the nonlinear optical crystal may be re-injected into an optical fiber for transmission and reused to pump another nonlinear optical crystal located at a distance.

[0072] Fig. 8 is a schematic diagram showing another example of the configuration of the terahertz light source of the present disclosure. The terahertz light source shown in Fig. 8 has the same main configuration as the terahertz light source shown in Fig. 7, so the same components are given the same reference numerals and their explanations are omitted, and only the differences are explained. First, nonlinear optical crystals 18, 22, and 26 are arranged at positions separated from each other.

[0073] In the terahertz light source shown in FIG. 8, a collimator 70, an optical fiber 72, and a collimator 74 are inserted between the beam splitter 44 and the beam splitter 48, and a collimator 64, an optical fiber 66, and a collimator 68 are inserted between the beam splitter 44 and the beam splitter 58.

[0074] 7, a collimator 76, an optical fiber 78, and a collimator 80 are inserted between the beam splitters 52 and 58. Furthermore, dampers 82 and 84 are added to absorb stray light. The reason why the half-wave plate 56 is not necessary is that the polarization cannot be maintained when the pump light transmitted through the nonlinear optical crystal is returned to the optical fiber. If the polarization can be maintained, the half-wave plate 56 may be added to separate each pump light.

[0075] In the terahertz light source shown in Figure 8, the first excitation light reflected by the beam splitter 44 is collimated by a collimator 70 and enters one end of an optical fiber 72, is transmitted through the optical fiber 72 and exits from the other end of the optical fiber 72, is collimated by a collimator 74, and enters the beam splitter 48.

[0076] In addition, the second excitation light that has passed through the beam splitter 44 is collimated by a collimator 64 and enters one end of an optical fiber 66, is transmitted through the optical fiber 66 and exits from the other end of the optical fiber 66, is collimated by a collimator 68, and enters the beam splitter 58.

[0077] In addition, the third excitation light that has passed through the beam splitter 52 is collimated by a collimator 76 and enters one end of an optical fiber 78, is transmitted through the optical fiber 78 and exits from the other end of the optical fiber 78, is collimated by a collimator 80, and enters the beam splitter 58.

[0078] According to the second embodiment, it is possible to obtain the same effect as the first embodiment. Moreover, according to the second embodiment, when the pumping light transmitted through the nonlinear optical crystal is reused, the transmitted light is again input to the optical fiber and transmitted, so that the pumping light can be output from a position away from the input position to the optical fiber. This increases the degree of freedom in the layout when arranging each component, and it is also possible to arrange other nonlinear optical crystals at distant positions.

[0079] [Third embodiment] The third embodiment is similar to the first and second embodiments except that a plurality of nonlinear optical crystals are arranged side by side in a direction intersecting the transport direction, and therefore only the differences will be described.

[0080] Fig. 9 is a plan view showing yet another example of the configuration of the terahertz light source of the present disclosure. Fig. 10 is a side view of the terahertz light source shown in Fig. 9. In this example, a plurality of nonlinear optical crystals which are generators of a plurality of terahertz waves are arranged side by side in an intersecting direction which intersects with the conveying direction (indicated by an arrow) of conveying device 110 which conveys object 28. For example, nonlinear optical crystals 18, 22, and 26 of the terahertz light source shown in Fig. 8 are arranged side by side in the intersecting direction.

[0081] By transmitting the excitation light that has passed through the nonlinear optical crystal by being input again into the optical fiber, the degree of freedom in layout when arranging each component is increased, making it possible to arrange them as shown in Figures 9 and 10. The terahertz light source shown in Figure 9 has the same main configuration as the terahertz light source shown in Figures 7 and 8, so the same components are given the same reference numerals and their explanations are omitted, and only the differences will be explained.

[0082] A unit including the nonlinear optical crystal 18 shown in Fig. 10 will be described as an example. Here, the direction toward the transport device 110 is defined as "down" and the direction away from the transport device 110 is defined as "up". In this unit, the collimator 38, the beam splitter 40, the lens 16, the nonlinear optical crystal 18, the lens 42, the beam splitter 44, and the collimator 64 are arranged in the transport direction in the order listed.

[0083] The beam splitters 40 and 44 are disposed in such a manner that their reflecting surfaces intersect at 45° with a perpendicular line to the surface 110C of the belt 110B of the conveying device 110 and also intersect at 45° with the conveying direction of the conveying device 110. The collimator 36 is disposed above the beam splitter 40, and the collimator 70 is disposed above the beam splitter 44.

[0084] 10, the first excitation light emitted from one end of the optical fiber 10B of the fiber laser 10 is collimated by a collimator 36 and enters the beam splitter 40 from above, is reflected by the beam splitter 40 to the downstream side in the transport direction, and enters the lens 16. On the other hand, the second excitation light emitted from one end of the optical fiber 12B of the fiber laser 12 is collimated by a collimator 38 and enters the beam splitter 40 from the horizontal direction, transmits through the beam splitter 40, and enters the lens 16 located downstream in the transport direction.

[0085] The first and second excitation lights are focused in the nonlinear optical crystal 18 by the lens 16. A second terahertz wave is generated according to the difference frequency between the first and second excitation lights. The first and second excitation lights transmitted through the nonlinear optical crystal 18 are focused by the lens 42 and enter the beam splitter 44 from the horizontal direction.

[0086] The first excitation light is reflected upward by the beam splitter 44 and enters the collimator 70, is collimated by the collimator 70, and enters one end of the optical fiber 72. The second excitation light is transmitted horizontally through the beam splitter 44 and enters the collimator 64 located downstream in the transport direction, is collimated by the collimator 64, and enters one end of the optical fiber 66.

[0087] 9, the third pumping light emitted from one end of the optical fiber 14B of the fiber laser 14 is incident on the beam splitter 48 from the horizontal direction, and the first pumping light emitted from one end of the optical fiber 72 is incident on the beam splitter 48 from above. The third pumping light transmitted through the nonlinear optical crystal 26 is transmitted through the beam splitter 52 in the horizontal direction, and the first pumping light transmitted through the nonlinear optical crystal 26 is reflected upward by the beam splitter 52.

[0088] In the example shown in Figure 8, the first excitation light reflected by the beam splitter 52 is incident on the damper 60, while in the example shown in Figure 9, the first excitation light reflected by the beam splitter 52 is incident on the optical fiber 88 by the collimator 86 and reused.

[0089] Similarly, in the unit including the nonlinear optical crystal 22 shown in Figure 9, the third excitation light emitted from one end of the optical fiber 78 enters the beam splitter 58 from the horizontal direction, and the second excitation light emitted from one end of the optical fiber 66 enters the beam splitter 58 from above.

[0090] In the example shown in Fig. 8, the second and third pumping lights transmitted through the nonlinear optical crystal 22 enter the damper 62, whereas in the example shown in Fig. 9, the second and third pumping lights transmitted through the nonlinear optical crystal 22 are collected by a lens 90 and irradiated onto a beam splitter 96. The third pumping light passes through the beam splitter 96 in the horizontal direction and is made incident on an optical fiber 99 by a collimator 98 and is reused. The second pumping light is reflected upward by the beam splitter 96 and made incident on an optical fiber 92 by a collimator 94 and is reused.

[0091] According to the third embodiment, it is possible to obtain the same effects as those of the first embodiment. Also, according to the third embodiment, it is possible to simultaneously irradiate a plurality of terahertz waves onto an object conveyed by a conveying device.

[0092] [Fourth embodiment] The fourth embodiment is similar to the first embodiment except that the object identification device includes a pressing mechanism, so only the differences will be described.

[0093] Fig. 11 is a schematic diagram showing a modified example of the configuration of the object identification device of the present disclosure. In this example, the object identification device 100 is provided with a pressing mechanism 112 for pressing an object 28. The identification device shown in Fig. 11 has the same main configuration as the identification device shown in Fig. 2, so the same components are denoted with the same reference numerals and their explanations are omitted, and only the differences are described.

[0094] Similar to the conveying device 110, the pressing mechanism 112 includes a pair of rollers 112A and a belt 112B. The length of the pressing mechanism 112 in the conveying direction is shorter than the length of the conveying device 110 in the conveying direction. The pair of rollers 112A are driven by a motor (not shown), which is controlled by the control unit 108. Similar to the belt 110B, the belt 112B is made of a material that is highly transparent to terahertz waves, such as plastic.

[0095] The pressing mechanism 112 is disposed above the conveying device 110, and sandwiches the object 28 between the surface of the belt 112B of the pressing mechanism 112 and the surface of the belt 110B of the conveying device 110, and presses the object 28. As the belt 110B moves in the conveying direction due to the rotation of the roller 110A of the conveying device 110, the roller 112A of the pressing mechanism 112 rotates and moves the belt 112B. As a result, the object 28 is conveyed in a pressed state.

[0096] For example, since the target 28 such as waste plastic is provided in various forms, the distance from the target 28 to the detection unit 104 varies depending on the irradiated portion, causing interference of the terahertz wave. When interference of the terahertz wave occurs, the detection accuracy of the transmitted light or reflected light decreases.

[0097] In the fourth embodiment, the object 28 is pressed by the pressing mechanism 112 to keep the distance from the object 28 to the detection unit 104 constant, thereby avoiding interference, which is a drawback specific to terahertz waves. This improves the detection accuracy of transmitted light or reflected light and also improves the identification accuracy of the object, compared to a case in which the pressing mechanism 112 is not provided.

[0098] [Fifth embodiment] The fifth embodiment is similar to the first embodiment except that the irradiation unit and the detection unit are arranged on the same side of the object and a reflective member is provided on the transport device, and therefore only the differences will be described.

[0099] Fig. 12 is a schematic diagram showing another modified example of the configuration of the object identification device of the present disclosure. In this example, the irradiation unit 102 and the detection unit 104 are disposed above the transport device 110. The identification device shown in Fig. 12 has the same main configuration as the identification device shown in Fig. 2, so the same components are denoted with the same reference numerals and their explanations are omitted, and only the differences will be described.

[0100] A reflecting member 114 is provided on the rear surface of the belt 110B of the transport device 110. The reflecting member 114 is made of a material having a high reflectance to terahertz waves, such as a metal such as gold, silver, or aluminum, or a semiconductor. The reflecting member 114 may be in the form of a thin film.

[0101] In the fifth embodiment, as shown in FIG. 14, for example, a portion of the terahertz waves irradiated from a nonlinear optical crystal 18 included in an irradiation unit 102 passes through an object 28, is reflected by a reflecting member 114 on the rear surface of a belt 110B, passes through the object 28 again, and is detected by a detector 30 included in a detection unit 104 arranged above a conveying device 110.

[0102] According to the fifth embodiment, the irradiation unit 102 and the detection unit 104 can be arranged on the same side of the object 28, thereby making it possible to reduce the size of the entire object identification device 100. In addition, there is an advantage that transmitted light that has passed through the object 28 multiple times can be detected, improving the detection accuracy of the transmittance, and therefore the identification accuracy of the material.

[0103] [Variations] It should be noted that the configurations of the material identifying device, material identifying method, and terahertz light source described in the above embodiment are merely examples, and it goes without saying that the configurations may be changed without departing from the spirit of the present invention.

[0104] (Optical system other than the light source) Below, modified examples of the configuration of the optical system other than the light source will be described. In the configuration shown in FIG. 2, the irradiation unit 102 and the detection unit 104 are arranged symmetrically on either side of the object 28, and the terahertz waves emitted from the irradiation unit 102 are directly irradiated onto the object 28 directly below, and the transmitted light that passes through the object 28 is directly detected by the detection unit 104 directly below. However, the arrangement of the irradiation unit 102 and the detection unit 104, the optical path of the terahertz waves emitted from the irradiation unit 102, and the optical path of the transmitted light emitted from the object 28 may be changed as appropriate.

[0105] 13 to 17, object 28 is sandwiched between the surface of belt 112B of pressing mechanism 112 and the surface of belt 110B of conveying device 110. As belts 110B and 112B move in the conveying direction indicated by the arrows, object 28 also moves in the conveying direction indicated by the arrows. In addition, irradiation unit 102 is represented by "nonlinear optical crystal 18," and detection unit 104 is represented by "detector 30."

[0106] Fig. 13 is a schematic diagram showing an example of the configuration of the optical system other than the light source. In the example shown in Fig. 13, nonlinear optical crystal 18 is disposed below transport device 110, and detector 30 is disposed above transport device 110. Parabolic mirrors 116 and 118 are disposed above transport device 110 to change the optical path of the terahertz wave transmitted through object 28 and guide it to detector 30. In this example, the terahertz wave emitted from nonlinear optical crystal 18 transmits through object 28, is reflected by parabolic mirrors 116 and 118, and enters detector 30.

[0107] Fig. 14 is a schematic diagram showing another example of the configuration of the optical system other than the light source. In the example shown in Fig. 14, nonlinear optical crystal 18 and detector 30 are arranged above conveyor device 110. Parabolic mirrors 116 and 118 are arranged above conveyor device 110 to change the optical path of the terahertz wave transmitted through object 28 and guide it to detector 30. A reflecting member 114 is provided on the back surface of belt 110B of conveyor device 110.

[0108] In this example, the terahertz waves emitted from the nonlinear optical crystal 18 pass through the object 28 , are reflected by the reflecting member 114 , pass through the object 28 again, are reflected by the parabolic mirrors 116 and 118 , and are incident on the detector 30 .

[0109] Fig. 15 is a schematic diagram showing another example of the configuration of the optical system other than the light source. In the example shown in Fig. 15, nonlinear optical crystal 18 and detector 30 are arranged above conveyor 110. Above conveyor 110, parabolic mirrors 120 and 122 for changing the optical path of the terahertz wave emitted from nonlinear optical crystal 18 and guiding it to object 28, and parabolic mirrors 124 and 126 for changing the optical path of the terahertz wave transmitted through object 28 and guiding it to detector 30 are arranged. A reflecting member 114 is provided on the back surface of belt 110B of conveyor 110.

[0110] In this example, the terahertz waves emitted from nonlinear optical crystal 18 are reflected by parabolic mirrors 120 and 122, and are irradiated onto object 28. The terahertz waves transmitted through object 28 are reflected by reflecting member 114, transmitted through object 28 again, and reflected by parabolic mirrors 124 and 126 to enter detector 30.

[0111] Fig. 16 is a schematic diagram showing another example of the configuration of the optical system other than the light source. In addition to the configuration shown in Fig. 15, a reflecting member 128 is provided above the pressing mechanism 112. The length of the reflecting member 128 in the transport direction is shorter than the length of the reflecting member 114 in the transport direction.

[0112] In this example, the terahertz waves emitted from nonlinear optical crystal 18 are reflected by parabolic mirrors 120, 122 and irradiated onto object 28. The terahertz waves that have passed through object 28 propagate along the conveyance direction while being reflected between reflecting member 114 and reflecting member 128, and pass through object 28 many times. Finally, the terahertz waves reflected by reflecting member 114 are reflected by parabolic mirrors 124, 126 and enter detector 30.

[0113] Fig. 17 is a schematic diagram showing another example of the configuration of the optical system other than the light source. In the example shown in Fig. 17, unlike Fig. 16, the nonlinear optical crystal 18 is arranged below the transport device 110, and the parabolic mirrors 120 and 122 are also arranged below the transport device 110. A reflecting member 128 is provided above the pressing mechanism 112. The length of the reflecting member 128 in the transport direction is approximately equal to the length of the reflecting member 114 in the transport direction.

[0114] In this example, similar to the example shown in FIG. 16, the terahertz waves that pass through the object 28 propagate along the conveying direction while being reflected between the reflecting member 114 and the reflecting member 128, and pass through the object 28 many times. However, since the length of the reflecting member 128 in the conveying direction is longer, the number of times that the terahertz waves pass through the object 28 increases.

[0115] As described above, the entire object identification device 100 can be made smaller by arranging the nonlinear optical crystal 18 (i.e., the irradiation unit 102) and the detector 30 (i.e., the detection unit 104) on the same side of the object 28. Furthermore, the more times the light passes through the object 28, the more the accuracy of detecting the transmittance and therefore the accuracy of identifying the material improves.

[0116] <Other Modifications> In this embodiment, a material identification device and a material identification method using a terahertz light source according to the present disclosure that generates terahertz waves by a difference frequency generation method will be described, but as long as a plurality of terahertz waves with different wavelengths can be generated simultaneously, the terahertz waves are not limited to those generated by a difference frequency generation method, and are also not limited to continuous waves.

[0117] For example, multiple terahertz waves may be generated simultaneously by combining multiple terahertz light sources. Examples of terahertz light sources that can be used include quantum cascade lasers, semiconductor lasers, Tannet, Impatt, Gunn diodes, resonant tunneling diodes, photoconductive antennas, and uni-traveling carrier photodiodes (UTC-PDs).

[0118] In addition, in the present embodiment, a material identification device and a material identification method using a terahertz light source according to the present disclosure that generates a terahertz wave that is a continuous wave will be described, but the terahertz wave is not limited to a continuous wave. It is sufficient to be able to simultaneously generate a plurality of terahertz waves with different wavelengths, and for example, a pulse wave can also be used.

[0119] Furthermore, the material identification device and the material identification method of the present invention can be applied not only to the identification of waste plastics, but also to a wide range of applications requiring the identification of materials. For example, the material identification device and the material identification method of the present invention can be applied to the quality control of plastic products.

[0120] A first aspect of the present disclosure is a material identification device comprising: an irradiation unit that irradiates an object with a plurality of terahertz waves having different wavelengths at once; a detection unit that detects the plurality of terahertz waves that have passed through the object or been reflected by the object; and an identification unit that identifies a material that constitutes the object from at least one of the transmittance and the reflectance for each of the plurality of terahertz waves. A second aspect of the present disclosure is the material identifying device of the first aspect, wherein the plurality of terahertz waves are continuous waves. A third aspect of the present disclosure is the material identifying device according to the first or second aspect, wherein the irradiating unit generates terahertz waves by a difference frequency generation method using a nonlinear optical crystal. A fourth aspect of the present disclosure is a material identification device according to any of the first to third aspects, wherein the irradiation unit includes a plurality of nonlinear optical crystals and a plurality of fiber lasers having different oscillation wavelengths, where the number of combinations when selecting two fiber lasers from the plurality of fiber lasers is equal to or greater than the number of the plurality of nonlinear optical crystals, and each of the plurality of nonlinear optical crystals is irradiated with two types of laser light having different wavelengths from a corresponding combination of fiber lasers, and a plurality of terahertz waves having different wavelengths are simultaneously generated from the plurality of nonlinear optical crystals by a difference frequency generation method. A fifth aspect of the present disclosure is the material identifying device according to the third or fourth aspect, wherein the nonlinear optical crystal is a GaP crystal. A sixth aspect of the present disclosure is the material identifying device according to the fourth or fifth aspect, wherein the irradiating unit irradiates laser light transmitted through one nonlinear optical crystal onto another nonlinear optical crystal. A seventh aspect of the present disclosure is the material identification device of the fourth or fifth aspect, wherein the irradiation unit is configured to transmit laser light that has passed through one nonlinear optical crystal to another nonlinear optical crystal using an optical fiber. An eighth aspect of the present disclosure is a material identification device according to any of the first to seventh aspects, further comprising a transport device for transporting the object, and the irradiation unit simultaneously irradiates the multiple terahertz waves onto the object transported by the transport device. A ninth aspect of the present disclosure is the material identification device of the eighth aspect, wherein the multiple nonlinear optical crystals of the irradiation unit are arranged in a line in an intersecting direction that intersects with the conveying direction of the conveying device, and the irradiation unit simultaneously irradiates multiple terahertz waves from the multiple nonlinear optical crystals onto the object conveyed by the conveying device. A tenth aspect of the present disclosure is a material identification device according to any of the first to ninth aspects, wherein the identification unit compares optical characteristics of at least one of transmittance and reflectance of a known material with corresponding optical characteristics of the object at each of a plurality of different wavelengths of terahertz waves to identify the material constituting the object. An eleventh aspect of the present disclosure is a material identification device according to any of the first to tenth aspects, further comprising a pressing mechanism for pressing the object, and the irradiation unit simultaneously irradiates the plurality of terahertz waves onto the object while it is pressed by the pressing mechanism. A twelfth aspect of the present disclosure is a material identification device according to any of the first to eleventh aspects, further comprising a reflecting member that reflects each of the multiple terahertz waves that have passed through the object, and the detection unit detects the multiple terahertz waves that have been reflected by the reflecting member and passed through the object multiple times. A thirteenth aspect of the present disclosure is a material identification method, which includes irradiating an object with a plurality of terahertz waves having different wavelengths at once, detecting the plurality of terahertz waves that have passed through the object or been reflected by the object, and identifying a material that constitutes the object from at least one of the transmittance and the reflectance for each of the plurality of terahertz waves. A fourteenth aspect of the present disclosure is a terahertz light source comprising: a plurality of nonlinear optical crystals; and a plurality of fiber lasers having different oscillation wavelengths, where the number of combinations when two fiber lasers are selected from the plurality of fiber lasers is equal to or greater than the number of the plurality of nonlinear optical crystals, and irradiates each of the plurality of nonlinear optical crystals with two types of laser light having different wavelengths from the fiber laser of a corresponding combination, thereby simultaneously generating a plurality of terahertz waves having different wavelengths from the plurality of nonlinear optical crystals. A fifteenth aspect of the present disclosure is a terahertz light source according to the fourteenth aspect, comprising: two fiber lasers in a corresponding combination for each of the plurality of nonlinear optical crystals; a focusing lens that focuses the two types of laser light with different wavelengths emitted from the two fiber lasers and causes the light to enter the nonlinear optical crystal; and a beam splitter that separates the two types of laser light with different wavelengths that have passed through the nonlinear optical crystal, and causes the laser light separated by the beam splitter to enter a nonlinear optical crystal different from the nonlinear optical crystal that has passed through. A sixteenth aspect of the present disclosure is the terahertz light source of the fifteenth aspect, in which the laser light separated by the beam splitter is input into an optical fiber, transmitted through the optical fiber, and input into a nonlinear optical crystal different from the nonlinear optical crystal through which the laser light passed.

Claims

1. an irradiation unit that generates multiple terahertz waves with different wavelengths, the number of which is the same as the number of combinations of two types of excitation light sources selected from multiple excitation light sources, by a difference frequency generation method based on angle phase matching using a nonlinear optical crystal, and irradiates a target object with the multiple terahertz waves at once; a detection unit that detects the plurality of terahertz waves that have passed through the object or that have been reflected by the object; an identification unit that identifies a material constituting the object based on at least one of a transmittance and a reflectance for each of the plurality of terahertz waves; A material identification device comprising:

2. The irradiation unit includes: a first excitation light source; a second excitation light source; a first lens for providing a slight angle between the light of the first and second excitation light sources; a first nonlinear optical crystal that transmits light from the first and second excitation light sources irradiated from the first lens and generates a first terahertz wave; a third excitation light source; and a second lens for providing a slight angle between the light of the third pumping light source and one of the light of the first and second pumping light sources transmitted through the first nonlinear optical crystal; a second nonlinear optical crystal that transmits the light of the third excitation light source and one of the light of the first and second excitation light sources irradiated from the second lens and generates a second terahertz wave; a third lens for providing a slight angle between the other of the light beams from the first and second pumping light sources transmitted through the first nonlinear optical crystal and the light beam from the third pumping light source; a third nonlinear optical crystal that transmits the light of a third excitation light source irradiated from the third lens and the other of the light of the first and second excitation light sources and generates a third terahertz wave. The material identification device according to claim 1 .

3. a half-wave plate for converting the polarization direction of the light from the third excitation light source transmitted through the second nonlinear optical crystal; the third lens provides a slight angle between the other of the light from the first and second excitation light sources transmitted through the first nonlinear optical crystal and the light from the third excitation light source transmitted through the half-wave plate; The material identification device according to claim 2 .

4. The nonlinear optical crystals are all GaP crystals. The material identification device according to claim 1 or 2.

5. The irradiation unit is configured to transmit the laser light transmitted through one nonlinear optical crystal to another nonlinear optical crystal using an optical fiber. The material identification device according to claim 2 .

6. A conveying device for conveying the object is further provided, The irradiation unit simultaneously irradiates the object transported by the transport device with the plurality of terahertz waves. The material identification device according to claim 1 or 2.

7. The plurality of nonlinear optical crystals of the irradiation unit are arranged so as to be aligned in a cross direction intersecting a conveying direction of the conveying device, and the irradiation unit simultaneously irradiates the object conveyed by the conveying device with a plurality of terahertz waves from the plurality of nonlinear optical crystals. The material identification device according to claim 6 which recites claim 2.

8. The identification unit is comparing a characteristic of at least one of optical properties of a transmittance and a reflectance of a known substance with a characteristic of a corresponding optical property of the object at each of a plurality of terahertz waves having different wavelengths, thereby identifying a substance constituting the object; The material identification device according to claim 1 or 2.

9. Further comprising a pressing mechanism for pressing the object, The irradiation unit simultaneously irradiates the plurality of terahertz waves onto the object in a state pressed by the pressing mechanism. The material identification device according to claim 1 or 2.

10. a reflecting member that reflects each of the plurality of terahertz waves that have passed through the object; The detection unit detects the plurality of terahertz waves that have been reflected by the reflecting member and transmitted through the object a plurality of times. The material identification device according to claim 1 or 2.

11. A difference frequency generation method using angle phase matching with a nonlinear optical crystal is used to generate a plurality of terahertz waves with different wavelengths, the number of which is the same as the number of combinations of two types of excitation light sources selected from a plurality of excitation light sources, and the plurality of terahertz waves is irradiated onto an object at one time; Detecting the plurality of terahertz waves that have been transmitted through the object or reflected by the object; identifying a material constituting the object based on at least one of a transmittance and a reflectance for each of the plurality of terahertz waves; Material identification method.

12. A plurality of nonlinear optical crystals; A plurality of excitation light sources; a difference frequency generation method using the nonlinear optical crystal based on angle phase matching to generate a plurality of terahertz waves having different wavelengths, the number of which is the same as the number of combinations of two types of excitation light sources selected from the plurality of excitation light sources, and the plurality of terahertz waves are irradiated onto an object at one time; Terahertz light source.

13. a first excitation light source; a second excitation light source; a first lens for providing a slight angle between the light of the first and second excitation light sources; a first nonlinear optical crystal that transmits light from the first and second excitation light sources irradiated from the first lens and generates a first terahertz wave; a third excitation light source; and a second lens for providing a slight angle between the light of the third pumping light source and one of the light of the first and second pumping light sources transmitted through the first nonlinear optical crystal; a second nonlinear optical crystal that transmits the light of the third excitation light source and one of the light of the first and second excitation light sources irradiated from the second lens and generates a second terahertz wave; a third lens for providing a slight angle between the other of the light beams from the first and second pumping light sources transmitted through the first nonlinear optical crystal and the light beam from the third pumping light source; a third nonlinear optical crystal that transmits the light of a third excitation light source irradiated from the third lens and the other of the light of the first and second excitation light sources and generates a third terahertz wave; The terahertz light source according to claim 12.

14. a half-wave plate for converting the polarization direction of the light from the third excitation light source transmitted through the second nonlinear optical crystal; the third lens provides a slight angle between the other of the light from the first and second excitation light sources transmitted through the first nonlinear optical crystal and the light from the third excitation light source transmitted through the half-wave plate; The terahertz light source according to claim 13.

15. a plurality of beam splitters for splitting the light from the excitation light source transmitted through the plurality of nonlinear optical crystals; The terahertz light source according to claim 13 or 14.

16. The light from the excitation light source separated by the plurality of beam splitters is input into an optical fiber, transmitted through the optical fiber, and input into a nonlinear optical crystal different from the nonlinear optical crystal through which the light has passed. The terahertz light source according to claim 15.

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