Terahertz wave control element and method for manufacturing same

Abstract

A metamaterial (10) is a terahertz wave control element that optically controls terahertz waves, and has a matrix (20) and a plurality of dielectric fine particles (30) dispersed in the matrix (20). The size of the dielectric fine particles (30) is less than or equal to the wavelength of terahertz waves. The value of the relative refractive index of the matrix (20) for terahertz waves is smaller, by 2.0 or more, than the value of the relative refractive index of the dielectric fine particles (30) for terahertz waves.

Description

Terahertz Wave Control Element and Method for Manufacturing the Same

[0001] The present invention relates to a terahertz wave control element and a method for manufacturing the same.

[0002] As an electromagnetic wave being developed for the next generation, terahertz waves are known. Terahertz waves are electromagnetic waves having a frequency of about 0.1 to 10 THz and have high transparency and straightness. Terahertz waves are expected to be applied to various fields such as next-generation wireless communication, medical, security, and non-destructive inspection, and the development of elements capable of optically controlling terahertz waves has been advanced.

[0003] For example, Patent Document 1 and Non-Patent Document 1 disclose a metamaterial in which meta-atoms such as split ring resonators (SRRs) are dispersed in a transparent resin body such as a cycloolefin polymer (COP) as a candidate for a new optical material in the terahertz band. Further, Non-Patent Document 2 discloses a Si microparticle dispersion system in which microparticles of Si (silicon) are dispersed in a matrix of COP as a candidate for a new refractive index control material in the terahertz band.

[0004] Japanese Patent No. 7132660

[0005] Taiyu Okatani, Yuto Sunada, Kazuhiro Hane, Yoshiaki Kanamori, "Terahertz 3D bulk metamaterials with randomly dispersed split-ring resonators", Nanophotonics 2022; 11(9): 2065-2074Shun Wakiuchi, Taiyu Okatani, Naoki Inomata, Yoshiaki Kanamori, "Fabrication of silicon microparticle dispersion as terahertz wave refractive index control material", Optics & Laser Technology 181 (2025) 112051

[0006] While terahertz waves are expected to be applied in various fields as described above, there are currently not many materials that can be used as optical elements for terahertz waves. Therefore, there is a problem that it is difficult to obtain an element having desired optical characteristics for terahertz waves. In view of such circumstances, the development of a terahertz wave control element having new optical characteristics is required.

[0007] The present invention has been made to solve the above problems, and an object thereof is to provide a terahertz wave control element having new optical characteristics and a manufacturing method thereof.

[0008] In order to achieve the above object, a terahertz wave control element according to a first aspect of the present invention is a terahertz wave control element that optically controls terahertz waves, and includes a matrix and a plurality of dielectric fine particles dispersed in the matrix. The size of the dielectric fine particles is not more than the wavelength of the terahertz wave, and the value of the specific refractive index of the matrix with respect to the terahertz wave is 2.0 or more smaller than the value of the specific refractive index of the dielectric fine particles with respect to the terahertz wave.

[0009] In order to achieve the above object, a method for manufacturing a terahertz wave control element according to a second aspect of the present invention is a method for manufacturing the terahertz wave control element described above, and includes a mixing step of mixing a precursor of the matrix and the plurality of dielectric fine particles, and a curing step of irradiating ultraviolet rays to the precursor in a state of being mixed with the plurality of dielectric fine particles in the mixing step to cure the precursor.

[0010] According to the present invention, it is possible to provide a terahertz wave control element having new optical characteristics and a manufacturing method thereof.

[0011] This is a schematic diagram showing the structure of the metamaterial according to the embodiment. This is a schematic diagram showing the substantial structure of the metamaterial shown in Figure 1 with respect to terahertz waves. This is a flowchart showing the manufacturing process of the metamaterial according to the embodiment. This is the first schematic diagram showing the manufacturing process of the metamaterial according to the embodiment. This is the second schematic diagram showing the manufacturing process of the metamaterial according to the embodiment. This is the third schematic diagram showing the manufacturing process of the metamaterial according to the embodiment. This is the fourth schematic diagram showing the manufacturing process of the metamaterial according to the embodiment. This is a diagram showing the conditions under which the aerogel sample was manufactured in the optical properties measurement experiment. This is a diagram showing the measurement results of the specific refractive index of the aerogel sample manufactured under the conditions shown in Figure 5. This is a diagram showing the conditions under which the metamaterial sample was manufactured in the optical properties measurement experiment. This is a diagram showing the measurement results of the transmittance of the metamaterial sample manufactured under the conditions shown in Figure 7. This is a diagram showing the measurement results of the effective refractive index of the metamaterial sample manufactured under the conditions shown in Figure 7. This is a diagram showing the measurement results of the transmittance of the metamaterial sample with a volume occupancy of 13 vol% Si nanoparticles. This is a diagram showing the measurement results of the effective refractive index of the metamaterial sample with a volume occupancy of 13 vol% Si nanoparticles. This figure shows the phase delay measurement results for a metamaterial sample with a volume occupancy of 13 vol% Si nanoparticles. This figure shows the extinction coefficient measurement results for a metamaterial sample with a volume occupancy of 13 vol% Si nanoparticles. This figure shows the transmittance measurement results for a metamaterial sample with a volume occupancy of 44 vol% Si nanoparticles. This figure shows the effective refractive index measurement results for a metamaterial sample with a volume occupancy of 44 vol% Si nanoparticles. This figure shows the phase delay measurement results for a metamaterial sample with a volume occupancy of 44 vol% Si nanoparticles. This figure shows the extinction coefficient measurement results for a metamaterial sample with a volume occupancy of 44 vol% Si nanoparticles. This figure shows the transmittance and effective refractive index of a metamaterial sample with a volume occupancy of 13 vol% Si nanoparticles. This is a schematic diagram of a prism fabricated to demonstrate the dispersion spectroscopic performance of the metamaterial. This figure shows the beam profile of the output wave when a terahertz wave is incident on air.This figure shows the beam profile of the output wave when a terahertz wave is incident on a prism made of aerogel. This figure also shows the beam profile of the output wave when a terahertz wave is incident on a prism made of aerogel and Si nanoparticles. TiO. ２ This figure shows the results of transmittance measurements for a metamaterial sample using fine particles. ２ This figure shows the measurement results of the phase delay of a metamaterial sample using fine particles. ２ This figure shows the measurement results of the effective refractive index of a metamaterial sample using fine particles. ２ This figure shows the measurement results of the extinction coefficient of a metamaterial sample using fine particles.

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[0013] The terahertz wave control element according to the present invention is an element capable of optically controlling terahertz waves. Here, terahertz waves are electromagnetic waves having a frequency between 100 GHz and 10 THz, or a wavelength between 3 mm and 30 μm. Terahertz waves are electromagnetic waves that have properties intermediate between radio waves such as microwaves and millimeter waves, and light such as visible light. Specifically, terahertz waves, like other radio waves, have penetrating properties that allow them to pass through paper, wood, plastic, etc. On the other hand, terahertz waves have higher directivity than microwaves and millimeter waves, and are susceptible to the influence of obstacles such as buildings, trees, and people. Terahertz waves are expected to be applied in various fields such as next-generation wireless communication, medicine, security, and non-destructive testing.

[0014] As an example of a terahertz wave control element according to the present invention, the metamaterial 10 shown in Figure 1 will be described below. The metamaterial 10 is a substance that has optical properties such as refractive index and transmittance unique to terahertz waves, and can be used as an optical element for terahertz waves. For example, by periodically arranging the metamaterial 10 to form a periodic structure of a desired size, optical elements such as lenses and prisms for terahertz waves can be manufactured.

[0015] As shown in Figure 1, the metamaterial 10 comprises a matrix 20 and a plurality of dielectric nanoparticles 30. The matrix 20 is the base material component of the metamaterial 10. The material of the matrix 20 is selected from materials capable of fixing and holding a large number of dielectric nanoparticles 30 within it, although this will be described in detail later. The plurality of dielectric nanoparticles 30 are components dispersed within the matrix 20. Each of the plurality of dielectric nanoparticles 30 is a dielectric nanoparticle having a size smaller than the wavelength of a terahertz wave, and is isotropically dispersed and embedded within the matrix 20. Here, isotropic means that there is no three-dimensional directional dependence. In other words, in the metamaterial 10, the plurality of dielectric nanoparticles 30 are dispersed and fixed in positions within the matrix 20 without spatial bias.

[0016] When the size of each dielectric nanoparticle 30 in the matrix 20 is smaller than the wavelength of a terahertz wave, i.e., sub-wavelength size, the terahertz wave incident on the metamaterial 10 cannot distinguish each dielectric nanoparticle 30 contained in the matrix 20. Therefore, as shown in Figure 2, the metamaterial 10 behaves as a uniform material with a constant refractive index with respect to the incident terahertz wave. The specific refractive index of the metamaterial 10 with respect to the terahertz wave at this time is the effective refractive index n ｅｆｆ This is what is called the specific refractive index. The specific refractive index refers to the ratio to the refractive index of air.

[0017] If we denote the relative refractive index values ​​of the matrix 20 and the dielectric nanoparticles 30 in the terahertz frequency band as n1 and n2, respectively, then when n1 and n2 are different, the effective refractive index of the metamaterial 10 is n ｅｆｆ This value is generally different from both n1 and n2. In other words, the metamaterial 10 behaves as a material with a specific refractive index different from both the specific refractive index n1 of the matrix 20 and the specific refractive index n2 of the dielectric nanoparticles 30 with respect to terahertz waves. In this way, by dispersing subwavelength-sized dielectric nanoparticles 30 in a matrix 20 with a specific refractive index different from that of the dielectric nanoparticles 30, a metamaterial 10 with a new specific refractive index for terahertz waves can be manufactured. This makes it possible to manufacture an element with new optical properties for terahertz waves.

[0018] Taking into consideration the characteristics of the metamaterial 10 as described above, this embodiment describes a metamaterial 10 having a high refractive index contrast by employing a material having a relatively small specific refractive index as the material for the matrix 20. Here, a metamaterial 10 having a high refractive index contrast means a metamaterial 10 in which the difference between the specific refractive index n1 of the matrix 20 contained in the metamaterial 10 and the specific refractive index n2 of the dielectric nanoparticles 30 is large. A metamaterial 10 having a high refractive index contrast has an effective refractive index n in a specific frequency band, as will be described in more detail later. ｅｆｆ It exhibits peculiar behavior, such as becoming close to 1.0 or falling below 1.0. Currently, there are not many materials that can be used as terahertz wave optical elements. Therefore, in this embodiment, with the aim of increasing the selection of candidate materials that can be used as terahertz wave optical elements, we will describe an element having novel optical properties for terahertz waves that have not been previously known, and a method for manufacturing the same.

[0019] <Material of Matrix 20> The material of the matrix 20 is required to be a substance capable of fixing and holding multiple dielectric nanoparticles 30 inside the matrix 20. In addition, the material of the matrix 20 is required to be a substance with the smallest possible specific refractive index in the terahertz band so that the difference between the specific refractive index n1 of the matrix 20 and the specific refractive index n2 of the dielectric nanoparticles 30 is large in the metamaterial 10.

[0020] As an example of a material for the matrix 20 that satisfies these conditions, a porous material can be mentioned. A porous material is a substance that has many pores and generally has a relatively small specific refractive index. In the following, we will explain using the case where the matrix 20 is formed of a porous material as an example. Here, "X is formed of Y" means that X contains Y as its main component, and it is not limited to the case that X consists only of Y, but X may also contain substances other than Y as long as it does not affect the function of X. The same applies below. More specifically, aerogel can be used as one of the porous materials. Aerogel is a porous substance in which the solvent contained in the gel has been replaced with a gas. The specific refractive index of aerogel in the terahertz band is a relatively small value of about 1.0 to 1.1.

[0021] More specifically, as the aerogel, an organic aerogel having repeating units derived from a polyfunctional acrylate having three or four acrylic groups in one molecule can be used. Below, we will describe the case in which the organic aerogel described below is used as the material for the matrix 20.

[0022] The organic aerogel exhibits excellent mechanical strength. Because the organic aerogel possesses the above characteristics, the gel formed in the solvent can be dried under normal pressure without the pores collapsing, resulting in an aerogel with a high pore volume. While the reason for this effect is not entirely clear, it can be inferred, for example, that the use of a polyfunctional acrylate having three or four acrylic groups per molecule results in a high-strength gel, which suppresses shrinkage during drying.

[0023] The organic aerogel is a polymer obtained by radical polymerization of the above-mentioned polyfunctional acrylate, and has a three-dimensional network structure (crosslinked structure) and pores. The organic aerogel can be produced using the aerogel-forming composition described later.

[0024] In this specification, "polyfunctional" is used to mean having multiple acrylic groups; for example, "bifunctional acrylate" means a compound having two acrylic groups. Conversely, "monofunctional" is used to mean having one acrylic group.

[0025] Examples of polyfunctional acrylates (trifunctional acrylates) having three acrylic groups in one molecule include trimethylolpropane triacrylate, pentaerythritol triacrylate, tris(2-acryloyloxyethyl) isocyanurate, glyceryl triacrylate, and succinic acid-modified pentaerythritol triacrylate.

[0026] Examples of polyfunctional acrylates (tetrafunctional acrylates) having four acrylic groups in one molecule include pentaerythritol tetraacrylate and ditrimethylolpropane tetraacrylate.

[0027] As a polyfunctional acrylate having three or four acrylic groups in one molecule, a tetrafunctional acrylate is preferred, and pentaerythritol tetraacrylate is more preferred. In this case, a higher crosslinking density is achieved, which improves the mechanical strength of the gel.

[0028] Preferably, the organic aerogel further comprises repeating units derived from at least one selected from the group consisting of monofunctional acrylates having one acrylic group per molecule and difunctional acrylates having two acrylic groups per molecule. In this case, in addition to imparting functionalities such as hydrophobicity, the physical properties can be adjusted.

[0029] Examples of monofunctional acrylates having one acrylate group in one molecule include 1,1,1,3,3,3 - hexafluoroisopropyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, cyclohexyl acrylate, hexyl acrylate, octyl acrylate, 2 - ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, stearyl acrylate, trifluoroethyl acrylate, heptadecafluorodecyl acrylate, trimethylsilyl acrylate, tetrahydrofurfuryl acrylate, ethoxydiethylene glycol acrylate, benzyl acrylate, phenoxyethyl acrylate, polyethylene glycol monoacrylate, and polypropylene glycol monoacrylate.

[0030] Examples of bifunctional acrylates having two acrylate groups in one molecule include ethylene glycol diacrylate, 1,3 - propanediol diacrylate, 1,4 - butanediol diacrylate, neopentyl glycol diacrylate, 3 - methyl - 1,5 - pentanediol diacrylate, 1,6 - hexanediol diacrylate, 1,9 - nonanediol diacrylate, 1,10 - decanediol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tricyclo[5.2.1.0 ２，６ decane dimethanol diacrylate, polyethylene glycol diacrylate (the number of repeating units of ethylene glycol is 4 to 15), and polypropylene glycol diacrylate (the number of repeating units of propylene glycol is 4 to 15).

[0031] The density of the organic aerogel is preferably 0.05 g / cm ３ or more and 0.30 g / cm ３ or less. When the density is within the above range, the value of the specific refractive index of the organic aerogel in the terahertz band becomes smaller, and the difference difference of the specific refractive index difference between the dielectric particles and the organic aerogel in the terahertz band becomes larger.

[0032] The pore volume of the organic aerogel is preferably 0.5 cm ３ / g or more and 1.5 cm３ It is preferable that the pore volume is less than or equal to / g. When the above pore volume is within the above range, the specific refractive index of the organic aerogel in the terahertz band becomes smaller, and the difference in specific refractive index in the terahertz band between it and the dielectric fine particles becomes larger.

[0033] Preferably, the decomposition initiation temperature of the organic aerogel by TG-DTA (differential thermal-thermogravimetric analysis) under nitrogen is between 250°C and 400°C. In this case, it can be applied as a component usable in high-temperature environments.

[0034] The diameter of the pores in the organic aerogel is preferably between 1 nm and 500 nm.

[0035] <Aerogel Forming Composition> The aerogel forming composition contains a polyfunctional acrylate having three or four acrylic groups in one molecule (hereinafter also referred to as "[A] polyfunctional acrylate"), a radical photopolymerization initiator (hereinafter also referred to as "[B] radical photopolymerization initiator"), and a solvent having a boiling point of 100°C or higher and 300°C or lower at atmospheric pressure (hereinafter also referred to as "[C] solvent"). The aerogel forming composition may optionally contain other components other than [A] polyfunctional acrylate, [B] radical photopolymerization initiator, and [C] solvent (hereinafter simply referred to as "other components"), to the extent that it does not impair the effects of the present invention.

[0036] The above aerogel-forming composition makes it possible to form a low-density aerogel while maintaining mechanical strength. The reason for this is not entirely clear, but it can be inferred, for example, as follows: [A] The polyfunctional acrylate having three or four acrylic groups in one molecule of the aerogel-forming composition can be radically polymerized in a relatively low-boiling point solvent to obtain a gel with few defects in the crosslinking structure. It is thought that the solvent in this gel is replaced with air, thereby forming a low-density aerogel while maintaining mechanical strength.

[0037] The solid content concentration of the aerogel-forming composition is preferably 5% by mass or more and 35% by mass or less. When the solid content concentration is within the above range, an aerogel with a high pore volume can be obtained. The lower limit of the solid content concentration is preferably 5% by mass, more preferably 10% by mass, and still more preferably 15% by mass. The upper limit of the solid content concentration is preferably 35% by mass, more preferably 30% by mass, and still more preferably 25% by mass. The solid content concentration refers to the concentration of all components other than the [C] solvent contained in the aerogel-forming composition.

[0038] <Material of dielectric nanoparticles 30> The material of the dielectric nanoparticles 30 is required to be a substance that can be dispersed and embedded in the matrix 20 as nanoparticles with a size smaller than the wavelength of terahertz waves. In addition, the material of the dielectric nanoparticles 30 is required to be a substance with the largest possible specific refractive index in the terahertz band so that the difference between the specific refractive index n1 of the matrix 20 and the specific refractive index n2 of the dielectric nanoparticles 30 is large in the metamaterial 10.

[0039] As an example of a material for dielectric nanoparticles 30 that satisfy these conditions, silicon (Si) nanoparticles can be cited. Si is an inexpensive and readily available material and has a relatively high specific refractive index of about 3.4 in the terahertz band. In the following explanation, we will use the case where the dielectric nanoparticles 30 are Si nanoparticles formed from Si as an example.

[0040] The size of the dielectric nanoparticles 30 must be less than or equal to the wavelength of the terahertz waves incident on the metamaterial 10, so that the dielectric nanoparticles 30 become indistinguishable from the matrix 20 to the terahertz waves. For example, if the frequency band of the terahertz waves incident on the metamaterial 10 is assumed to be between 0.1 THz and 0.5 THz, the corresponding wavelengths will be between 3 mm and 600 μm. In this case, the size of the dielectric nanoparticles 30 is preferably around 300 μm or less, which is half of 600 μm. Alternatively, if terahertz waves of 0.5 THz or higher are assumed, the size of the dielectric nanoparticles 30 is preferably smaller than 300 μm. For example, if terahertz waves of 1.0 THz are assumed, the size of the dielectric nanoparticles 30 is preferably 150 μm or less, and if terahertz waves of 10.0 THz are assumed, the size of the dielectric nanoparticles 30 is preferably 15 μm or less. The shape of the dielectric nanoparticles 30 can be any shape, such as cubic or spherical. If the dielectric nanoparticles 30 are cubic in shape, the size of the dielectric nanoparticles 30 corresponds to one side of the cube, and if the dielectric nanoparticles 30 are spherical, the size of the dielectric nanoparticles 30 corresponds to the diameter of the sphere.

[0041] <Method for Manufacturing Metamaterial 10> The method for manufacturing the metamaterial 10 described above will be explained with reference to Figures 3 and 4A to 4D. In the method for manufacturing the metamaterial 10 shown in Figure 3, first, a powdered matrix 20 and a plurality of dielectric nanoparticles 30 are inserted into a mold 40 (step S1). Specifically, the manufacturer prepares in advance the powdered matrix 20 and a plurality of dielectric nanoparticles 30, which are the materials necessary for manufacturing the metamaterial 10. Then, as shown in Figure 4A, the powdered matrix 20 and the plurality of dielectric nanoparticles 30 are placed inside the mold 40 and mixed.

[0042] Here, the powdered matrix 20 is a powdered version of the matrix 20, and is prepared in advance before starting the manufacturing method shown in Figure 3. Specifically, the manufacturer inserts the liquid precursor 21 of the matrix 20 into a suitable mold, cures it by irradiating it with ultraviolet light, and dries it. The manufacturer then grinds the matrix 20 obtained in this way into a powder (for example, a size of about 50 μm) using a mortar and pestle to produce the powdered matrix 20. In addition, multiple dielectric nanoparticles 30 can be produced, for example, by microfabrication of an FZ (Floating Zone)-Si wafer. The mold 40 is, for example, a silicone mold. The manufacturer prepares molds 40 of the size and shape corresponding to the element to be manufactured in advance. Step S1 is an example of an insertion step.

[0043] Returning to Figure 3, next, in step S2, a liquid precursor 21 of the matrix 20 containing a solvent is poured into the mold 40, which is in the state where the powdered matrix 20 and the plurality of dielectric nanoparticles 30 have been inserted and mixed in step S1, and mixed. Specifically, as shown in Figure 4B, the manufacturer pours the liquid precursor 21 of the matrix 20 into the mold 40 in which the powdered matrix 20 and the plurality of dielectric nanoparticles 30 have been inserted. This mixes the liquid precursor 21 with the powdered matrix 20 and the plurality of dielectric nanoparticles 30. Through this mixing, as shown in Figure 4C, the plurality of dielectric nanoparticles 30 and the powdered matrix 20 are dispersed isotropically, that is, evenly, three-dimensionally, within the liquid precursor 21. Step S2 is an example of a mixing step.

[0044] Returning to Figure 3, next, ultraviolet light is irradiated onto the precursor 21, which has been mixed with the plurality of dielectric nanoparticles 30 in step S2, to cure the precursor 21 (step S3). Specifically, as shown in Figure 4D, ultraviolet light is irradiated from above the mold 40 by the ultraviolet irradiation device 50 onto the liquid precursor 21, the plurality of dielectric nanoparticles 30, and the powdered matrix 20 mixed in the mold 40. The irradiation time of the ultraviolet light can be short, for example, several tens of seconds. As a result, the liquid precursor 21 hardens into a gel. The plurality of dielectric nanoparticles 30 are then fixed in a state of isotropically dispersed within the gelled precursor 21. Step S3 is an example of a curing step.

[0045] Returning to Figure 3, the next step is to dry the gelled precursor 21 in step S3 at atmospheric pressure (step S4). Specifically, for example, the solvent is removed from the gelled precursor 21 inside the mold 40 by heating it from below using a hot plate. This generates a matrix 20 from the precursor 21. As a result, a metamaterial 10 is produced in which multiple dielectric nanoparticles 30 are fixed in an isotropically dispersed state within the matrix 20. Step S4 is an example of a drying step.

[0046] By the manufacturing method described above, a metamaterial 10 is produced in which multiple dielectric nanoparticles 30 are isotropically dispersed and fixed in a matrix 20. Since the above-mentioned organic aerogel is used as the material for the matrix 20, the UV irradiation time in the curing step can be short, and drying in the drying step can be done at atmospheric pressure. Therefore, the metamaterial 10 can be manufactured in a very simple manner.

[0047] Furthermore, the powdered matrix 20 becomes indistinguishable from the matrix 20 generated during the process in which the precursor 21 is transformed into the matrix 20 by curing and solvent removal. Here, the powdered matrix 20 plays a role in facilitating the isotropically dispersed multiple dielectric nanoparticles 30 within the matrix 20 generated from the precursor 21. Specifically, by mixing the powdered matrix 20 with the multiple dielectric nanoparticles 30 within the mold 40 before pouring the liquid precursor 21 into the mold 40, it is possible to avoid the multiple dielectric nanoparticles 30 being unevenly distributed in certain areas within the mold 40. As a result, even after pouring and mixing the liquid precursor 21 into the mold 40, the multiple dielectric nanoparticles 30 are dispersed without bias in the liquid precursor 21. Therefore, the effect is obtained that the precursor 21 is also more easily dispersed isotropically in the matrix 20 generated by curing.

[0048] <Measurement Results of Optical Properties of Metamaterial 10> A measurement experiment was conducted to measure the optical properties of the metamaterial 10 according to this embodiment. The results of the measurement experiment are described below.

[0049] Firstly, the aforementioned organic aerogel was manufactured, and its optical properties were measured. Figure 5 shows the conditions under which the organic aerogel was manufactured. Specifically, three types of organic aerogel samples with different thicknesses were manufactured. In addition, two samples were manufactured for each thickness to confirm reproducibility. That is, organic aerogel samples were manufactured for six cases, 1a to 1c and 2a to 2c, as shown in Figure 5. Specifically, a liquid precursor 21 with the mass shown in the "Aerogel Mass" column of Figure 5 was irradiated with ultraviolet light and dried to manufacture organic aerogel samples with the thickness shown in the "Aerogel Thickness" column of Figure 5. The ultraviolet irradiation intensity was 48 mW / cm². ２ The ultraviolet irradiation time was set to 60 seconds.

[0050] Figure 6 shows the results of measuring the specific refractive index in the terahertz band of the organic aerogel samples manufactured in this manner. Terahertz time-domain spectroscopy (THz-TDS; Time-Domain Spectroscopy, manufactured by Nippon Precision Co., Ltd.) was used to measure the specific refractive index. As shown in Figure 6, the specific refractive index of the six manufactured samples was around 1.10 (more specifically, between 1.09 and 1.12) in the terahertz band from 0.1 THz to 0.5 THz. In particular, for the six manufactured samples, the minimum specific refractive index at 0.3 THz was 1.099 and the maximum was 1.108. Therefore, the error in specific refractive index due to manufacturing was limited to a maximum of about 0.01. Although not shown in the figure, the specific refractive index of each sample in the terahertz band above 0.5 THz gradually decreased to around 1.09 as the frequency increased up to 1.0 THz.

[0051] Secondly, a sample of the metamaterial 10 was actually manufactured using the manufacturing method described above, and a measurement experiment was conducted to measure the optical properties of the manufactured sample. In the measurement experiment, the organic aerogel described above was used as the matrix 20. In addition, as the dielectric nanoparticles 30, Si (silicon) nanoparticles with a size of approximately 300 μm, which were fabricated by microfabrication of an FZ-Si wafer, were used.

[0052] Figure 7 shows the conditions under which the metamaterial 10 sample was manufactured in the measurement experiment. As shown in Figure 7, in the measurement experiment, the volume occupancy rate ρ of the Si nanoparticles used as dielectric nanoparticles 30 was Ｓｉ For each of the eight cases (1) to (8) in which the parameter was changed, a sample of metamaterial 10 was manufactured using the manufacturing method shown in Figure 3.

[0053] Here, the volume occupancy rate of Si nanoparticles ρ Ｓｉ This corresponds to the ratio to the volume of the manufactured metamaterial 10. ρ is the volume occupancy of Si nanoparticles. Ｓｉ To control this, the mass of the Si nanoparticles inserted into the mold 40 in the insertion step (step S1 in Figure 3) was varied in eight ways, from 0.02 g to 0.24 g. This resulted in the volume occupancy rate ρ of the Si nanoparticles. ＳｉThe concentration was varied in eight ways, from 4 vol% to 44 vol%. Then, for each of these eight cases, the steps of the manufacturing method shown in Figure 3 were performed to produce eight different samples of the metamaterial 10.

[0054] The mass of the powdered matrix 20 inserted into the mold 40 along with the Si fine particles in the insertion step (step S1 in Figure 3) was fixed at 0.01 g in all cases (1) to (8). The liquid precursor 21 injected into the mold 40 in the mixing step (step S2 in Figure 3) was fixed at 0.20 g in all cases (1) to (8). The ultraviolet irradiation conditions in the curing step (step S3 in Figure 3) were set to an ultraviolet irradiation intensity of 40 mW / cm². ２ The ultraviolet irradiation time was set to 90 seconds. In the drying step (step S4 in Figure 3), a commercially available hot plate was used. The thickness of the metamaterial 10 sample produced in this way is shown in Figure 7.

[0055] Thus, the optical properties of the metamaterial 10 samples manufactured for each of the cases (1) to (8) are the transmittance to terahertz waves and the effective refractive index n. ｅｆｆ The following were measured. Terahertz time-domain spectroscopy (THz-TDS) was used for the measurement, as described above. Figures 8A and 8B show the transmittance and effective refractive index n when samples of metamaterial 10 manufactured for each of the eight cases (1) to (8) were irradiated with terahertz waves in the frequency band of 0.1 THz to 0.5 THz. ｅｆｆ The measurement results are shown below.

[0056] In addition, Figures 8A and 8B also show, as reference data, the measurement results for the metamaterial 10 without Si nanoparticles (represented as "no Si" in Figures 8A and 8B). Here, the metamaterial 10 without Si nanoparticles is a metamaterial 10 manufactured using only the liquid precursor 21 as the material, without including Si nanoparticles, and has a volume occupancy ρ Ｓｉ This corresponds to the case where the value is 0. The other conditions are the same as those in cases (1) to (8) shown in Figure 7.

[0057] In the transmittance measurement results shown in Figure 8A, first, the transmittance of the metamaterial 10 without Si nanoparticles was close to 100%. In contrast, when the metamaterial 10 contained Si nanoparticles, the transmittance to terahertz waves tended to decrease significantly, especially on the high-frequency side. In particular, the volume occupancy rate ρ of the Si nanoparticles Ｓｉ As the value increased, the transmittance decreased, and at higher frequencies, the transmittance tended to become almost zero.

[0058] Next, the effective refractive index n in Figure 8B ｅｆｆ The measurement results showed that the volume occupancy rate of Si nanoparticles ρ Ｓｉ As n increases, the effective refractive index n ｅｆｆ The volume occupancy ρ increases, especially at higher frequencies. Ｓｉ The difference tended to become larger due to this. The effective refractive index n at high frequencies was such that ｅｆｆ The difference is the volume occupancy rate ρ Ｓｉ The volume occupancy ρ increased, with the boundary being between 15 vol% and 20 vol%. Ｓｉ If the effective refractive index is 15 vol% or less, ｅｆｆ However, it was observed that the specific refractive index of the metamaterial 10, which does not contain Si nanoparticles, was smaller than that of the organic aerogel (approximately 1.1).

[0059] To examine these characteristics in more detail, the volume occupancy ρ Ｓｉ = Case of 13 vol% and volume occupancy ρ Ｓｉ The measurement results for each case, including the case of 44 vol%, are shown separately. Figures 9A to 9D show the volume occupancy ρ. Ｓｉ Transmittance and effective refractive index n of metamaterial 10 manufactured in a case of 13 vol% = ｅｆｆ The measured results for the phase lag ΔΦ and extinction coefficient are shown below. In this case, as shown in Figure 9A, the transmittance was relatively large at frequencies below 0.2 THz, but decreased at frequencies above 0.2 THz. In particular, the transmittance was close to 0 between 0.25 THz and 0.32 THz, and responses due to the lowest-order ED (Electric Dipole) mode and MD (Magnetic Dipole) mode were observed.

[0060] Volume occupancy ρ Ｓｉ Effective refractive index n in the case of = 13 vol% ｅｆｆ As shown in Figure 9B, the effective refractive index n was relatively large at frequencies lower than 0.3 THz, but in the frequency range of 0.3 THz to 0.4 THz, it was close to 1.0, i.e., smaller than the specific refractive index of organic aerogel, which is approximately 1.1. In particular, in the frequency range of 0.31 THz to 0.33 THz, the effective refractive index n was smaller than 1.0. ｅｆｆ It was observed.

[0061] Volume occupancy ρ Ｓｉ In the case of =13 vol%, the phase delay ΔΦ is as shown in Figure 9C, where n is the effective refractive index. ｅｆｆ It exhibited similar characteristics to the above. In particular, the effective refractive index n ｅｆｆ In the frequency range from 0.31 THz to 0.33 THz, where the value was less than 1.0, the extinction coefficient showed a value less than 0. Furthermore, as shown in Figure 9D, the extinction coefficient showed a relatively large value in the frequency range from 0.25 THz to 0.35 THz.

[0062] Note that the values ​​at the positions indicated by dashed lines in Figures 9A to 9D represent corresponding measured values. Specifically, the transmittance for terahertz waves at 0.3376 THz is 15.39%, and the effective refractive index n ｅｆｆ The coefficient of decay was 1.010, and the coefficient of extinction was 0.1637.

[0063] Next, from Figure 10A to Figure 10D, the volume occupancy rate ρ Ｓｉ Transmittance and effective refractive index n of metamaterial 10 manufactured in a 44 vol% case. ｅｆｆ The measured results for the phase lag ΔΦ and extinction coefficient are shown. In this case, the transmittance was 0.3624% at 0.2747 THz, as shown in Figure 10A, and was almost 0 at higher frequencies. Effective refractive index n ｅｆｆ As shown in Figure 10B, the values ​​ranged from 1.8 to 3.0. In other words, the effective refractive index n in this case... ｅｆｆ This is the volume occupancy rate ρ mentioned above. ＳｉNo phenomena were observed where the value was smaller than 1.0 or close to 1.0, such as in the case of 13 vol%. Furthermore, the phase lag ΔΦ and extinction coefficient were measured as shown in Figures 10C and 10D, respectively.

[0064] Based on the measurement results above, the volume occupancy rate of Si nanoparticles ρ Ｓｉ When the effective refractive index n is 15 vol% or less, the effective refractive index n is at the higher frequency side. ｅｆｆ It was found that the effective refractive index n at a specific frequency was close to 1.0. ｅｆｆ A peculiar phenomenon occurred in which the effective refractive index n became smaller than 1.0. Since the specific refractive index of organic aerogel in the terahertz band is approximately 1.1 and the specific refractive index of Si nanoparticles is approximately 3.4, such measurement results indicate that for combinations of materials with a specific refractive index of 1.0 or higher, the effective refractive index n ｅｆｆ This means that it is possible to manufacture metamaterial 10 with a specific refractive index less than 1.0. Since materials with a specific refractive index less than 1.0 are rare, they are expected to have applications in a variety of uses.

[0065] <Dispersive Spectroscopic Performance of Metamaterial 10> Next, a demonstration experiment was conducted to prove that the metamaterial 10 according to this embodiment has high dispersion spectroscopic performance. The results of the demonstration experiment are described below. Figure 11A shows the volume occupancy rate ρ of Si fine particles among the measurement results shown in Figures 8A and 8B as an example of estimating the spectroscopic performance of the metamaterial 10. Ｓｉ Transmittance and effective refractive index n in the case where n is 13 vol% ｅｆｆ This is shown. From Figure 11A, the effective refractive index n from 0.1 THz to 0.2 THz is shown. ｅｆｆ It was confirmed that there is a dispersion spectroscopic characteristic in which the value increases by 0.104.

[0066] To demonstrate the high-dispersion spectral performance of metamaterial 10, a prism having a right-angled triangular shape with vertex angles of 30°, 60°, and 90° was designed and fabricated, as shown in Figure 11B. Specifically, two types of prisms were fabricated: "prism-0," which does not contain Si nanoparticles, and "prism-A," which contains Si nanoparticles. Here, prism-0 is a prism made using only the aforementioned organic aerogel as the material, without containing Si nanoparticles, and represents the "no Si" case in Figures 8A and 8B (volume occupancy ρ Ｓｉ This corresponds to the case where = 0. In contrast, prism-A has a volume occupancy rate of Si nanoparticles ρ Ｓｉ This is a prism made of metamaterial 10 in the case where the concentration is 13 vol% (i.e., case (4) shown in Figure 7). In the demonstration experiment, for each of these two types of prisms, an incident wave was incident perpendicular to the incident plane of the side with an apex angle of 30°–90° in the prism. Three types of terahertz waves with frequencies of 0.10 THz, 0.15 THz, and 0.20 THz were incident as incident waves. The design was such that these incident waves would be refracted at the interface between the air and the prism and emitted from the exit plane of the side with an apex angle of 30°–60°, and the exit angle θ of the emitted wave was ｅ The following was measured. Also, for reference, the emission angle θ of the emitted wave when terahertz waves are incident on air without using a prism was measured. ｅ We also measured it.

[0067] Figures 12A to 12C show polar coordinate plots of the beam profiles of the output waves when terahertz waves with frequencies of 0.10 THz, 0.15 THz, and 0.20 THz are incident. Specifically, Figure 12A shows the beam profile of the output wave when terahertz waves are incident on air, Figure 12B shows the beam profile of the output wave when terahertz waves are incident on prism-0, and Figure 12C shows the beam profile of the output wave when terahertz waves are incident on prism-A. In Figures 12A to 12C, the axis of rotation is the detection angle (i.e., the output angle θ of the output wave). ｅ) represents the normalized intensity of the emitted wave. Air shown in Figure 12A and prism-0 shown in Figure 12B do not have wavelength dispersion characteristics, so at any frequency of 0.10 THz, 0.15 THz, and 0.20 THz, the emitted angle θ ｅ These were almost the same. In contrast, in prism-A shown in Figure 12C, the emission angle θ increases as the frequency increases. ｅ The angle transitioned in the direction of increasing. Specifically, the exit angle θ ｅ The spectral angle was 100.8° at 0.10 THz, but transitioned to 108.7° at 0.20 THz. In other words, a spectral angle of 7.9° was obtained between 0.10 THz and 0.20 THz. These results confirm that the metamaterial 10, in which Si nanoparticles are dispersed in an aerogel matrix, possesses high-dispersion spectral performance due to its wavelength dispersion characteristics.

[0068] As described above, the metamaterial 10 according to this embodiment has a matrix 20 formed of organic aerogel and a plurality of dielectric nanoparticles 30 which are subwavelength-sized Si nanoparticles dispersed in the matrix 20. Thus, because the metamaterial 10 according to this embodiment uses aerogel with a low specific refractive index as the matrix 20, it has a high refractive index contrast between the matrix 20 and the dielectric nanoparticles 30. This makes it possible to provide an element with novel optical properties for terahertz waves that have not been known before.

[0069] In particular, as observed in the measurement experiment described above, the volume occupancy rate ρ of Si nanoparticles Ｓｉ When the effective refractive index n is 15 vol% or less, ｅｆｆ The effective refractive index n showed a value close to 1.0. Also, at a specific frequency, ｅｆｆ A unique phenomenon was observed in which the effective refractive index n in the terahertz band was less than 1.0. In this embodiment, the effective refractive index n in the terahertz band was observed. ｅｆｆIt is possible to provide an element having characteristic optical properties such that the volume occupancy ρ approaches 1.0 or is less than 1.0. Furthermore, the transmittance can be brought close to 0 in the range of 0.25 THz to 0.32 THz, for example, it is possible to provide an element having low-pass filter characteristics in the Beyond 5G / 6G communication band. In addition, the volume occupancy ρ of Si fine particles Ｓｉ Even when the concentration is greater than 15 vol%, the high refractive index contrast makes it possible to provide an element with previously unknown characteristic optical properties for terahertz waves. In this way, while there are currently not many materials that can be used as optical elements for terahertz waves, it is possible to increase the range of available options for optical elements for terahertz waves.

[0070] Although embodiments of the present invention have been described above, these embodiments are merely examples, and the scope of application of the present invention is not limited thereto. In other words, the embodiments of the present invention can be applied in various ways, and all embodiments fall within the scope of the present invention.

[0071] For example, in the above embodiment, the matrix 20 was formed of an organic aerogel. However, the material of the matrix 20 can be any material that can fix and hold dielectric nanoparticles 30 inside the matrix 20 and has a relatively small specific refractive index in the terahertz band. For example, the matrix 20 is not limited to an organic aerogel, but may also be formed of an inorganic aerogel. Furthermore, the matrix 20 may be formed of a porous material other than aerogel. Examples of porous materials other than aerogel include organic or inorganic porous materials such as mesoporous silica, zeolite, activated carbon, and diatomaceous earth.

[0072] More preferably, the value of the relative refractive index n1 of the matrix 20 with respect to terahertz waves is preferably less than or equal to a predetermined value. In the measurement results shown in Figure 6, the relative refractive index of the aerogel in the terahertz band ranged from 1.09 to 1.12. From these measurement results, if the relative refractive index n1 of the matrix 20 with respect to terahertz waves is 1.2 or less, the effective refractive index n in the above embodiment is less than or equal to n ｅｆｆIt can be inferred that similar results can be obtained as the characteristic of showing a value close to 1.0 or less than 1.0. However, such a characteristic is not seen in the metamaterials disclosed in Patent Document 1 and Non-Patent Documents 1 and 2. Considering that the specific refractive index value in the terahertz band of the cycloolefin polymer (COP) used in these documents is approximately 1.5, it can be inferred that in order to obtain results similar to those of the above embodiment, the specific refractive index n1 of the matrix 20 for terahertz waves must be less than 1.5 as a minimum condition.

[0073] Furthermore, in the above embodiment, the dielectric nanoparticles 30 were Si nanoparticles formed from Si. However, the material of the dielectric nanoparticles 30 can be any material that can be dispersed and embedded in the matrix 20 as nanoparticles with a size smaller than the wavelength of a terahertz wave, and that is a dielectric material with a relatively large specific refractive index in the terahertz band. Also, the material of the dielectric nanoparticles 30 may contain multiple types of materials. For example, the dielectric nanoparticles 30 may contain silicon, gallium phosphide, gallium arsenide, or at least one selected from alumina, zirconia, silicon carbide, aluminum nitride, yttrium oxide (yttria), and barium titanate. Alternatively, they may be formed from at least one of dielectrics with a relatively high refractive index, such as ceramics obtained by high-temperature treatment of yttrium oxide, barium titanate, etc., and compounds containing said ceramics. Furthermore, the dielectric nanoparticles 30 may contain titanium oxide (TiO ２ ) may be formed by the above. More preferably, the dielectric nanoparticles 30 are formed from a material having a specific refractive index of 3.0 or higher in the terahertz band, so as to maximize the difference in specific refractive index (n2-n1) between them and the matrix 20.

[0074] Furthermore, it is preferable that the value of the relative refractive index n1 of the matrix 20 with respect to terahertz waves is smaller than the value of the relative refractive index n2 of the dielectric nanoparticles 30 with respect to terahertz waves by a predetermined value or more. The relative refractive index of aerogel in the terahertz band was approximately 1.1 (a value between 1.09 and 1.12) in the measurement results shown in Figure 6. And, since the relative refractive index of Si nanoparticles in the terahertz band is approximately 3.4, the difference in relative refractive index in the above embodiment was approximately 2.3 (= 3.4 - 1.1). Given these measurement results and the difference in relative refractive index between COP and Si nanoparticles in the metamaterial disclosed in Non-Patent Literature 2 is approximately 1.9, considering the error, if the relative refractive index n1 of the matrix 20 with respect to terahertz waves is 2.0 or more smaller than the relative refractive index n2 of the dielectric nanoparticles 30 with respect to terahertz waves, then the effective refractive index in the above embodiment is n ｅｆｆ It can be inferred that similar results can be obtained as the characteristic of showing a value close to 1.0 or less than 1.0. More preferably, it can be inferred that the above effect can be obtained more reliably if the relative refractive index n1 of the matrix 20 with respect to terahertz waves is 2.2 or more smaller than the relative refractive index n2 of the dielectric nanoparticles 30 with respect to terahertz waves.

[0075] Furthermore, the terahertz wave control element may have subwavelength-sized nanoparticles formed from a material other than a dielectric instead of dielectric nanoparticles 30. In other words, the terahertz wave control element may have a matrix 20 and a plurality of nanoparticles formed from a material other than a dielectric dispersed in the matrix 20. For example, the nanoparticles may be nanoparticles formed from metal, i.e., metallic nanoparticles. In that case, as metallic nanoparticles, split-ring resonators (SRRs) made of materials such as gold (Au), silver (Ag), copper (Cu), and aluminum (Al), as disclosed in Patent Document 1 and Non-Patent Document 1, can be used. Even in such cases, a metamaterial 10 with high refractive index contrast can be obtained by ensuring that the value of the relative refractive index n1 of the matrix 20 with respect to terahertz waves is less than or equal to a predetermined value (preferably 1.2). This makes it possible to provide an element with characteristic optical properties with respect to terahertz waves that have not been previously known.

[0076] <Measurement results of the optical properties of the metamaterial 10 using titanium oxide> Below, as one example, titanium oxide (TiO2) is used as dielectric nanoparticle 30. ２ Let's explain the case where ( ) is used. First, regarding the refractive index n of titanium dioxide, according to Japanese Journal of Applied Physics Vol.45, No.9B, 2006, pp.7499-7502, the dielectric constant ε of titanium dioxide in the terahertz band is approximately 100. And the relationship is that the dielectric constant ε is the square of the refractive index n (ε = n ２ From this, it can be calculated that the specific refractive index of titanium dioxide in the terahertz band is approximately 10. Therefore, the specific refractive index of titanium dioxide in the terahertz band satisfies the above-mentioned condition for dielectric nanoparticles 30, which is 3.0 or greater. Furthermore, when titanium dioxide is used as dielectric nanoparticles 30, the condition that the specific refractive index of the matrix 20 for terahertz waves is 2.0 or less than the specific refractive index of the dielectric nanoparticles 30 for terahertz waves is also satisfied. For this reason, titanium dioxide is one of the candidates that can be used as dielectric nanoparticles 30.

[0077] In fact, TiO is used as the dielectric nanoparticle 30. ２ Samples of metamaterial 10 using fine particles were prepared, and the optical properties of the prepared samples were measured. The measurement results are described below. In the measurement, samples of metamaterial 10 were prepared using "TIO13PB" (particle size = approximately 2 μm), a product of Kojun Chemical Laboratory Co., Ltd., as dielectric fine particles 30. At that time, an organic aerogel was used as the matrix 20, as in the measurement experiment using Si fine particles as dielectric fine particles 30 as described above. Other conditions were also the same, with Si fine particles being TiO ２ Aside from replacing the particles with fine particles, the measurement experiment is the same as described above.

[0078] More specifically, the TiO used as dielectric nanoparticle 30 ２ Concentration of fine particles (by weight) ρ ＴｉＯ２ Samples of metamaterial 10 were fabricated for each of seven cases ranging from 4.9 wt% to 40 wt%. Then, terahertz waves in the frequency band of 0.1 THz to 0.5 THz were irradiated onto the fabricated samples, and the optical properties such as transmittance, phase delay, and effective refractive index n were measured. ｅｆｆ The extinction coefficient was also measured. Figures 13A to 13D show the transmittance, phase lag, and effective refractive index n, respectively. ｅｆｆ The results of the extinction coefficient measurement are also shown. Note that in Figures 13A to 13D, TiO is used as reference data. ２ Metamaterial 10 that does not contain (concentration ρ ＴｉＯ２ The measurement results for the case where = 0 (represented as "no TiO2" in Figures 13A to 13D) are also shown.

[0079] As shown in Figure 13C, the effective refractive index n ｅｆｆ It exhibits a nearly flat frequency response, and TiO ２ concentration of fine particles ρ ＴｉＯ２ The higher the effective refractive index n, the higher the effective refractive index n ｅｆｆ It showed a characteristic of increasing TiO ２ When using fine particles, the overall trend is that the effective refractive index n is higher compared to when using Si fine particles for the dielectric fine particles 30. ｅｆｆThe following was obtained. Furthermore, the transmittance, phase lag, and extinction coefficient were measured as shown in Figures 13A, 13B, and 13D, respectively. From these measurement results, it was confirmed that the metamaterial 10 using titanium oxide as dielectric nanoparticles 30 can be a candidate for a terahertz wave control element with new optical properties. In addition, the metamaterial 10 in which the dielectric nanoparticles 30 described above are dispersed in the matrix 20 has an effective refractive index n in the terahertz region. ｅｆｆ It has been shown to be effective in controlling [the phenomenon].

[0080] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of the invention is indicated not by the embodiments, but by the claims. Various modifications made within the scope of the claims and the equivalent scope of the meaning of the invention are considered to be within the scope of this invention.

[0081] This application is based on Japanese Patent Application No. 2025-25012, filed on 19 February 2025. The entire specification, claims, and drawings of Japanese Patent Application No. 2025-25012 are incorporated herein by reference.

[0082] 10 Metamaterial 20 Matrix 21 Precursor 30 Dielectric nanoparticles 40 Mold 50 Ultraviolet irradiation device

Claims

1. A terahertz wave control element for optically controlling terahertz waves, comprising a matrix and a plurality of dielectric nanoparticles dispersed in the matrix, wherein the size of the dielectric nanoparticles is less than or equal to the wavelength of the terahertz wave, and the relative refractive index of the matrix with respect to the terahertz wave is 2.0 or less than the relative refractive index of the dielectric nanoparticles with respect to the terahertz wave.

2. The terahertz wave control element according to claim 1, wherein the matrix is ​​formed of a porous material.

3. The terahertz wave control element according to claim 2, wherein the porous material is aerogel.

4. The terahertz wave control element according to claim 2, wherein the porous material is an organic aerogel.

5. The terahertz wave control element according to any one of claims 1 to 4, wherein the relative refractive index of the matrix with respect to the terahertz wave is 1.2 or less.

6. The terahertz wave control element according to any one of claims 1 to 5, wherein the volume occupancy of the plurality of dielectric nanoparticles in the terahertz wave control element is 15 vol% or less.

7. The terahertz wave control element according to any one of claims 1 to 6, wherein the dielectric nanoparticles are formed from at least one of silicon, gallium phosphide, gallium arsenide, alumina, zirconia, silicon carbide, aluminum nitride, yttrium oxide, barium titanate, and titanium oxide.

8. The terahertz wave control element according to claim 7, wherein the dielectric nanoparticles are formed of silicon.

9. The terahertz wave control element according to any one of claims 1 to 8, wherein the value of the relative refractive index of the dielectric nanoparticles with respect to the terahertz wave is greater than 3.

0.

10. A terahertz wave control element for optically controlling terahertz waves, comprising a matrix and a plurality of fine particles dispersed in the matrix, wherein the size of the fine particles is less than or equal to the wavelength of the terahertz wave, and the relative refractive index of the matrix with respect to the terahertz wave is 1.2 or less.

11. The terahertz wave control element according to claim 10, wherein the fine particles are formed of metal.

12. A method for manufacturing a terahertz wave control element according to any one of claims 1 to 9, comprising: a mixing step of mixing a matrix precursor with a plurality of dielectric nanoparticles; and a curing step of curing the precursor, which has been mixed with the plurality of dielectric nanoparticles in the mixing step, by irradiating it with ultraviolet light.

13. A method for manufacturing a terahertz wave control element according to claim 12, further comprising a drying step of drying the precursor cured in the curing step at atmospheric pressure.

14. The method for manufacturing a terahertz wave control element according to claim 12 or 13, wherein in the mixing step, the precursor is mixed with the plurality of dielectric fine particles that are mixed with the powdered matrix.

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