Far-infrared spectrometer and sample adapter

Abstract

Provided are a far-infrared spectroscopy device and sample adapter that make it possible to highly accurately measure a sample that is not flat. A far-infrared spectroscopy device according to this invention comprises an illumination optical system for concentrating far-infrared light onto a sample and a detector for detecting light that has passed through the sample. Sample adapters are placed on the optical path of the far-infrared light between the illumination optical system and the sample and on the optical path between the sample and a detection optical element. The front surfaces of the sample adapters are roughly flat, and the shapes of the sample-side surfaces of the sample adapters roughly match the shape of the sample. The surface of the sample that the far-infrared light is concentrated on and the surface that the far-infrared light passes through are curved.

Description

[Technical Field]

[0001] The present invention relates to a far-infrared spectrometer for analyzing a sample using light in the far-infrared region, and a sample adapter. [Background technology]

[0002] Far-infrared light in the wavelength range of approximately 25 μm to 4 mm is also called terahertz waves. Terahertz waves are highly penetrating to materials, and many materials have their own absorption spectrum peaks in this wavelength range. For this reason, it is expected that terahertz waves can be used to analyze materials that have low transparency to visible light or infrared light, or materials that are enclosed by a shield, by irradiating them with terahertz waves and obtaining the absorption spectrum of the material.

[0003] Time Domain Spectroscopy (TDS) is a well-known technology in this field. While TDS is useful for identifying pharmaceutical ingredients and quantitatively analyzing active ingredients, it suffers from a narrow dynamic range. Another method to address this issue is the injection-seeded THz parametric generator (is-TPG), which has a high peak power. This is-TPG method has the potential to enable measurements of tablet-shaped samples with a thickness of several mm, for example.

[0004] Patent Document 1 below discloses a far-infrared spectrometer using the is-TPG method. In the is-TPG method, when generating far-infrared light, two near-infrared laser beams (a high-pulse-energy pump beam and a single-wavelength seed beam) are introduced into a generating nonlinear optical crystal to parametrically oscillate pulsed single-wavelength far-infrared light (is-TPG light). The frequency of the generated is-TPG light can be changed by changing the wavelength of the seed beam and adjusting the angle of incidence on the nonlinear optical crystal. The generated is-TPG light is irradiated onto a sample, and the transmitted light is introduced into a detecting nonlinear optical crystal, where it is converted back into near-infrared light. The near-infrared light is then detected by a detector, allowing the sample to be analyzed.

[0005] However, in a spectroscopic device such as that disclosed in Patent Document 1, when the sample S has a non-planar (e.g., curved) shape, the is-TPG light is refracted at the interface and cannot be properly introduced into the nonlinear optical crystal for detection, resulting in a decrease in the conversion efficiency to near-infrared light and affecting the measurement accuracy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 116461 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a far-infrared spectrometer and a sample adapter that are capable of measuring a non-planar sample with high accuracy. [Means for solving the problem]

[0008] In order to solve the above problems, the far-infrared spectrometer according to the present invention includes an illumination optical system that focuses the far-infrared light on a sample, and a detector that detects the far-infrared light transmitted through the sample. A sample adapter is installed on the optical path of the far-infrared light between the illumination optical system and the sample, and on the optical path between the sample and the detection optical element. The surface of the sample adapter is substantially flat, and the surface shape of the sample adapter facing the sample is substantially the same as the shape of the sample. The surface of the sample that focuses the far-infrared light and the surface that transmits the far-infrared light are curved. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a far-infrared spectrometer and a sample adapter that are capable of measuring a non-flat sample with high accuracy. [Brief explanation of the drawings]

[0010] [Figure 1A] 1 is a schematic diagram illustrating the overall configuration of a far-infrared spectroscopic device 1 according to a first embodiment of the present invention. [Figure 1B] 2 is a vector diagram showing the relationship between the various lights in the device of FIG. 1. [Figure 2A] 1 is a schematic diagram illustrating how far-infrared light FIR is collected by a detection optical system 300 when the sample S has a planar shape. [Figure 2B] 1 is a schematic diagram illustrating how far-infrared light FIR is collected by a detection optical system 300 when the sample S has a planar shape. [Figure 2C] 1 is a schematic diagram illustrating how far-infrared light FIR is collected by a detection optical system 300 when the sample S has a planar shape. [Figure 3A] 1 is a schematic diagram illustrating how far-infrared light FIR is collected by a detection optical system 300 when the sample S has a curved surface. [Figure 3B] 1 is a schematic diagram illustrating how far-infrared light FIR is collected by a detection optical system 300 when the sample S has a curved surface. [Figure 3C] 1 is a schematic diagram illustrating how far-infrared light FIR is collected by a detection optical system 300 when the sample S has a curved surface. [Figure 4A] 1A and 1B are schematic diagrams illustrating the effects of the far-infrared spectrometer 1 and the sample adapter 800 according to the first embodiment. [Figure 4B] 1A and 1B are schematic diagrams illustrating the effects of the far-infrared spectrometer 1 and the sample adapter 800 according to the first embodiment. [Figure 4C] 1A and 1B are schematic diagrams illustrating the effects of the far-infrared spectrometer 1 and the sample adapter 800 according to the first embodiment. [Figure 5] FIG. 8 is a schematic diagram illustrating a sample adapter 800 according to a second embodiment of the present invention. [Figure 6A] FIG. 8 is a schematic diagram illustrating a sample adapter 800 according to a second embodiment of the present invention. [Figure 6B] FIG. 8 is a schematic diagram illustrating a sample adapter 800 according to a second embodiment of the present invention. [Figure 7A] FIG. 10 is a schematic diagram illustrating a sample adapter 800 according to a third embodiment of the present invention. [Figure 7B] FIG. 10 is a schematic diagram illustrating a sample adapter 800 according to a third embodiment of the present invention. [Figure 7C] FIG. 10 is a schematic diagram illustrating a sample adapter 800 according to a third embodiment of the present invention. [Figure 7D] FIG. 10 is a schematic diagram illustrating a sample adapter 800 according to a third embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram illustrating an example of the configuration of a far-infrared spectrometer using a THz-TDS method. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In the accompanying drawings, functionally identical elements may be designated by the same numerals. Note that the accompanying drawings show embodiments and implementation examples according to the principles of the present disclosure, but these are for understanding the present disclosure and are not to be used to interpret the present disclosure in a limiting manner. The descriptions in this specification are merely typical examples and are not intended to limit the scope or application of the present disclosure in any way.

[0012] Although the present embodiment has been described in sufficient detail to enable those skilled in the art to implement the present disclosure, it should be understood that other implementations and forms are possible, and that changes in configuration and structure and substitutions of various elements are possible without departing from the scope and spirit of the technical ideas of the present disclosure. Therefore, the following description should not be interpreted as being limited thereto.

[0013] [First embodiment] The overall configuration of a far-infrared spectroscopic instrument 1 according to a first embodiment of the present invention will be described with reference to the schematic diagram of FIG. 1A. The far-infrared spectroscopic instrument 1 is an instrument for analyzing a sample S by irradiating the sample S with far-infrared light. The far-infrared spectroscopic instrument 1 includes, for example, a tunable far-infrared light source 100, an illumination optical system 200, a detection optical system 300, a detection nonlinear optical crystal holder 400, a photodetector 500, a control unit 600, and a signal processing unit 700. As will be described later, the sample S to be measured by the far-infrared spectroscopic instrument 1 is stored in a sample adapter 800. The sample adapter 800 is disposed after the illumination optical system 200 and before the detection optical system 300.

[0014] The wavelength-tunable far-infrared light source 100 includes a nonlinear optical crystal LN1 therein for generating far-infrared light used in measuring a sample S, and is configured to be able to change the wavelength of the far-infrared light. The illumination optical system 200 is an optical system that irradiates the far-infrared light onto the sample S. The detection optical system 300 is an optical system that guides the far-infrared light that has passed through the sample S to a detection nonlinear optical crystal holder 400. The detection nonlinear optical crystal holder 400 holds a detection nonlinear optical crystal LN2 therein and converts the incident far-infrared light into near-infrared light. The photodetector 500 is a detector for detecting this near-infrared light. The control unit 600 is a control device that controls the illumination optical system 200 and the like, and the signal processing unit 700 performs predetermined signal processing on the signal detected by the photodetector 500.

[0015] The wavelength-tunable far-infrared light source 100 includes a pulsed laser light source 110 (pump light source) that emits pump light 11, a wavelength-tunable light source 120 that emits seed light 12, and an automatic translation stage 130. The pump light 11 and the seed light 12 have different wavelengths. A portion of the pump light 11 is incident on the automatic translation stage 130 via a branching element such as a half mirror 123, and the remaining portion becomes the pump light that is incident on a detection nonlinear optical crystal described below. The seed light 12 is incident on the automatic translation stage 130 via an incident angle adjustment mechanism 121 and a mirror 122. The incident angle adjustment mechanism 121 adjusts the incident angle at which the seed light 12 is incident on the generation nonlinear optical crystal LN1.

[0016] The automatic translation stage 130 is equipped with a generating nonlinear optical crystal LN1 inside. When pump light 11 and seed light 12, which are laser beams with different wavelengths, are incident on this generating nonlinear optical crystal LN1, far-infrared FIR light is generated by parametric generation. This method is called the is-TPG method. Here, far-infrared light generated by the is-TPG method is called is-TPG light. For example, if MgO:LiNbO3 is used as the generating nonlinear optical crystal LN1, a pulsed Q-switched YAG laser (wavelength: 1064 nm) is used as the pulsed laser light source 110, and seed light 12 emitted by the wavelength-tunable light source 120 is input into the generating nonlinear optical crystal LN1, far-infrared FIR light can be obtained by parametric generation. The wavelength-tunable light source 120 may also be a continuous wave laser.

[0017] A generating Si prism 132 is attached to the side of the generating nonlinear optical crystal LN1. This allows the generated far-infrared light FIR to be extracted efficiently. By changing the wavelength of the seed light 12, for example, between about 1066 nm and 1084 nm, and further adjusting the incident angle of the seed light 12 with respect to the generating nonlinear optical crystal LN1, the frequency of the generated far-infrared light FIR (is-TPG light) can be changed, for example, between about 0.5 THz and 5 THz.

[0018] Figure 1B is a vector diagram showing the relationship between each light. The frequency of the generated far-infrared light FIR is expressed as ω T , the frequency of the pump light 11 is ω P , the frequency of the seed beam 12 is ω S Then, ω T =ω P -ω S (Equation 1) holds. Furthermore, the wave vectors of the far-infrared light FIR, the pump light 11, and the seed light 12 are →k T , →k P , →k S Then, →k T =→k P -→k SThe following equation (2) holds: The generated far-infrared light FIR (0.5 THz to 5 THz) is extracted into the air via the generating Si prism 132 at an angle of approximately 48° to 36° with respect to the pump light 11.

[0019] LiNbO3, an example of a material for the generating nonlinear optical crystal LN1, strongly absorbs far-infrared light of 3 THz or higher. For this reason, in order to shorten the distance that the generated far-infrared light FIR travels inside the generating nonlinear optical crystal LN1 as much as possible, it is known that the pump light 11 and the seed light 12 are introduced as close as possible to the end face (the face connected to the generating Si prism 132) of the generating nonlinear optical crystal LN1. The shorter the distance that the far-infrared light FIR travels inside the generating nonlinear optical crystal LN1, the more effectively the amount of far-infrared light FIR absorbed by the generating nonlinear optical crystal LN1 can be suppressed.

[0020] However, when the pump light 11 and seed light 12 are incident as close to the end face of the generating nonlinear optical crystal LN1 as possible, another problem occurs: far-infrared light cannot be generated efficiently. That is, when far-infrared light with a low frequency of 1 THz or less is generated, absorption of the low-frequency far-infrared light inside the generating nonlinear optical crystal LN1 can be suppressed, but on the other hand, the pump light 11 is vignetted at the crystal end, making it impossible to introduce all of the energy into the crystal. In addition, the optical path length over which the interaction between the pump light 11 and the far-infrared light FIR occurs is shortened, reducing the generation efficiency of the far-infrared light FIR. This results in another problem: the far-infrared light FIR cannot be generated efficiently.

[0021] Therefore, in the far-infrared spectroscopic device of this embodiment, when generating far-infrared light with a low frequency of 1 THz or less, the pump light 11 and seed light 12 are irradiated near the center of the generating nonlinear optical crystal LN1. The pump light 11 is not vignetted at the crystal edges, and all of its energy can be introduced into the generating nonlinear optical crystal LN1. This increases the distance that the far-infrared light FIR travels inside the generating nonlinear optical crystal LN1 induced by the pump light 11 before it is emitted from the generating nonlinear optical crystal LN1. This increases the distance over which the interaction between the pump light 11 and the far-infrared light FIR occurs, thereby increasing the generation efficiency of the far-infrared light FIR. Since absorption of far-infrared light with a frequency of 1 THz or less within the generating nonlinear optical crystal LN1 is small, generating far-infrared light at the center of the crystal does not pose a problem.

[0022] In the first embodiment, an automatic translation stage 130 is used to move the generating nonlinear optical crystal LN1 and the generating Si prism 132 in the y'-axis direction relative to the pump light 11 according to the frequency of the far-infrared light FIR to be generated. This changes the positions at which the pump light 11 and the seed light 12 are incident on the generating nonlinear optical crystal LN1. In this way, for far-infrared light FIR with a low frequency of 1 THz or less, a sufficiently long optical path length for interaction between the pump light 11 and the far-infrared light FIR can be ensured, and for far-infrared light FIR with a high frequency of 3 THz or more, far-infrared light can be efficiently generated without being absorbed inside the crystal.

[0023] Moreover, excess light emitted from generating nonlinear optical crystal 130 is collected and discarded by damper 134. Similarly, excess light is collected and discarded by damper 404 in detecting nonlinear optical crystal LN2, which will be described later.

[0024] The illumination optical system 200 includes, for example, a mirror 201, a condenser lens 202, an automatic translation stage 203, a slit 204, a rotation stage 205, and condenser lenses 207 and 208. The illumination optical system 200 is an optical system that guides the far-infrared light FIR emitted from the wavelength-tunable far-infrared light source 100 to the sample S.

[0025] The automatic translation stage 203 has a slit 204 therein, and the position of the slit 204 is adjusted by the control unit 600. When the emission angle of the far-infrared light FIR changes due to a change in the frequency of the far-infrared light FIR, the rotation stage 205 adjusts the amount of rotation thereof to adjust the angle of a mirror 206 included therein. The far-infrared light FIR reflected by the mirror 206 is converted into parallel light by a condenser lens 207 and is again condensed toward the sample S by a condenser lens 208.

[0026] The sample S is placed at a position where the far-infrared light FIR is focused by the focusing lens 208. The far-infrared light FIR that has passed through the sample S is directed by the detection optical system 300 toward the detection nonlinear optical crystal holder 400. The detection nonlinear optical crystal holder 400 includes therein a detection nonlinear optical crystal LN2 and a detection Si prism 402 connected to its side.

[0027] The far-infrared light FIR passes through the detection Si prism 402 and enters the detection nonlinear optical crystal LN2. The far-infrared light FIR intersects with the near-infrared light 13, which is branched by the half mirror 123 and the mirror 209, in the detection nonlinear optical crystal LN2, causing parametric oscillation of near-infrared light (detection light NIR) with a wavelength of approximately 1066 nm to 1084 nm. At this time, if the Rayleigh lengths of the near-infrared light 13 and the far-infrared light FIR are made the same near the intersection region within the detection nonlinear optical crystal LN2, the generation efficiency of the detection light NIR can be improved. The detection light NIR is photoelectrically converted by the photodetector 290, which is sensitive to near-infrared light, and detected as a detection signal.

[0028] 2A to 2C and 3A to 3C, the collection of far-infrared light FIR by the detection optical system 300 will be described. FIGS. 2A to 2C show the collection state of far-infrared light FIR when the surface of the sample S has a flat shape (flat sample S). FIGS. 3A to 3C show the collection state of far-infrared light FIR when the surface of the sample S' has a curved shape (curved sample S'). FIGS. 2A and 3A show the case where the samples S and S' coincide with the collection position of the collecting lens 208, FIGS. 2B and 3B show the case where the samples S and S' are placed in front of the collection position of the collecting lens 208, and FIGS. 2C and 3C show the case where the samples S and S' are placed behind the collection position of the collecting lens 208.

[0029] 2A to 2C, when the surface of the sample S is flat, the far-infrared light FIR is not significantly refracted by the sample S, regardless of whether the sample S is at the focusing position of the focusing lens 208, in front of the focusing position, or behind the focusing position. Therefore, the focusing position of the far-infrared light FIR in the detection nonlinear optical crystal LN2 does not change significantly.

[0030] On the other hand, if the surface of the sample S' is non-flat, for example, convexly curved, as shown in Figure 3A, even if the sample S' is at the focusing position of the focusing lens 208, due to the lens effect of the curved sample S', the focusing position in the detection nonlinear optical crystal LN2 will be closer than when the sample S is flat.

[0031] Furthermore, as shown in Figure 3B, when the sample S' has a convex curved surface and is located closer to the focusing position of the focusing lens 208, the focusing position in the detection nonlinear optical crystal LN2 is located much closer to the surface than when the sample S is flat (Figure 2B), and the difference in position is even greater than the difference between Figures 2A and 3A.

[0032] Furthermore, as shown in Figure 3C, when the sample S' has a convex curved surface and is located behind the focusing position of the focusing lens 208, the focusing position in the detection nonlinear optical crystal LN2 is located significantly closer than when the sample S is flat (Figure 2B), and the difference in position is even greater than the difference between Figures 2A and 3A.

[0033] In this way, if the far-infrared light FIR is not properly focused in the detection nonlinear optical crystal LN2, the detection light NIR cannot be efficiently generated in the detection nonlinear optical crystal LN2, It becomes impossible to observe the absorption spectrum correctly. This problem can be solved to some extent by placing the sample S with high positional precision, but the lens effect of the sample S means that the far-infrared light cannot be sufficiently focused on the nonlinear optical crystal LN2 used for detection. This problem occurs not only when the surface of the sample S is convex, but also when it is concave or has other non-planar shapes.

[0034] In a typical spectrometer that uses light in the wavelength range from deep ultraviolet to infrared as the measurement light, an integrating sphere is used, allowing light transmitted through the sample to be detected with a large numerical aperture (NA), so the surface shape of the sample is not a major issue. In contrast, an integrating sphere cannot be used in an instrument that uses far-infrared light as the measurement light. Therefore, when measuring a sample with a curved surface, it is difficult to detect the transmitted light with high efficiency. This is a problem not only in instruments that use the is-TPG method, such as the far-infrared spectrometer of this embodiment, but also in instruments that use the TDS method.

[0035] Therefore, the apparatus of the first embodiment employs a sample adapter 800, as shown in FIGS. 4A to 4C, in which the entrance and exit surfaces of far-infrared light FIR for a curved sample S' are flat. The sample adapter 800 may be divided so as to sandwich the sample S', or may have a hollow portion capable of accommodating the sample S'. The outer shape of the sample adapter 800 is sufficient as long as it is flat. The surface of the sample adapter 800 facing the sample S' has a shape that substantially matches the surface shape of the sample S'. Furthermore, it is preferable that the material of the sample adapter 800 has a refractive index of 1 or more for far-infrared light and a high transmittance for far-infrared light.

[0036] Furthermore, it is desirable that the curvature of the sample side (inner wall surface) of the sample adapter 800 and the curvature of the curved surface of the sample S' are approximately the same, but they may be different. Specifically, it is sufficient that the difference in curvature is small enough not to cause a lens effect on the passing far-infrared light FIR. Furthermore, the surface of the sample S' and the sample-side surface of the sample adapter 800 may or may not be in contact. It is preferable that the gap between them is shorter than the wavelength of the far-infrared light FIR. Note that it is not necessary to precisely polish the surface of the sample adapter 800; it is sufficient if the surface roughness is equal to or less than the wavelength of the far-infrared light FIR. Furthermore, the entrance surface and exit surface of the sample S' do not need to be parallel.

[0037] When using such a sample adapter with a typical spectrometer that uses light in the deep ultraviolet to infrared wavelength range as the measurement light, the wavelength of the measurement light is short, so the gap between the curved sample and the adapter must be small (for example, several hundred nm to several microns), and the adapter must be precisely adjusted to the curvature of the curved sample. Therefore, with instruments that use light in the deep ultraviolet to infrared wavelength range as the measurement light, measurements using a sample adapter are impossible, and a measurement method using an integrating sphere is considered to be the most suitable.

[0038] In the wavelength range (approximately 0.5 THz to 5 THz) targeted by the far-infrared spectrometer of the first embodiment, it is possible to fabricate the sample adapter using a material with high transmittance and a nearly constant refractive index within that range. Furthermore, since the wavelength of far-infrared light is several hundred microns, it is not a problem if there is a gap of approximately that wavelength between the sample S' and the sample adapter 800. Therefore, it is possible to use one sample adapter 800 to measure multiple curved samples with different curvatures.

[0039] The combination of the sample adapter 800 and the curved sample S' is equivalent to measuring a flat sample S with respect to the far-infrared light FIR. Therefore, the transmitted far-infrared light FIR is appropriately focused on the detection nonlinear optical crystal LN2 using lenses 301 and 302, etc., and the near-infrared light 13 and the far-infrared light FIR are merged to efficiently generate detection light NIR. That is, as shown in Figures 4B and 4C, even if the sample adapter 800 is positioned forward or backward from the focusing position of the far-infrared light FIR by the focusing lens 208, the far-infrared light FIR can be appropriately introduced into the detection nonlinear optical crystal LN2, thereby constructing a robust optical system. Furthermore, even if the sample S' and the sample adapter 800 are tilted relative to the far-infrared light FIR, the focal position of the lenses 301 and 302 does not change in the optical axis direction but only shifts in the y direction in Figure 4, so the detection efficiency is not significantly affected. As described above, the far-infrared spectrometer 1 and the sample adapter 800 of the first embodiment make it possible to measure a non-flat sample with high accuracy.

[0040] [Second embodiment] Next, a far-infrared spectrometer according to a second embodiment will be described with reference to FIG. 5. The far-infrared spectrometer according to the second embodiment differs from the sample adapter 800 according to the first embodiment in the structure of the sample adapter 800. The rest of the structure of the far-infrared spectrometer is the same as that of the first embodiment, so redundant description will be omitted below. This second embodiment is suitable for a small sample S2, for example, a sample having a size equivalent to the beam diameter of the irradiated far-infrared light FIR when focused.

[0041] The sample adapter 800 comprises a main body 810 and an absorber 811 formed on the front and back surfaces of the main body 810. The main body 810 may be divided so that the sample S2 can be sandwiched therebetween, or may have a hollow portion through which the sample can be inserted. The absorber 811 is made of a material that has the property of absorbing far-infrared light FIR. The absorber 811 has an opening 813 near its center that allows the far-infrared light FIR to pass through (without absorbing it). The surface shape of the main body 810 is approximately flat. The surface shape of the absorber 811 may be approximately flat or curved.

[0042] The size of the opening 813 approximately coincides with the position of the sample S2 placed in the main body 810, and the far-infrared light FIR that passes through the opening 813 passes through the sample S2 and then passes through the opening 813 on the back surface to enter the detection optical system 300. The size of the opening 813 is not limited to a specific size, but as an example, it is preferable that the size of the opening 813 be approximately the same as the size of the sample S2. For example, if the size of the sample S2 is several mm, the size of the opening 813 is also set to be approximately several mm.

[0043] As described above, this second embodiment is suitable for measuring a small sample S2 whose beam diameter is approximately the same as the focused beam diameter of the irradiated far-infrared light FIR. When such a small sample S2 is directly irradiated with far-infrared light FIR, most of the far-infrared light FIR, which has a Gaussian distribution, passes through the sample S2 and enters the detection nonlinear optical crystal LN2, where it is converted into near-infrared light NIR. However, some of the far-infrared light FIR, for example, light at the tail of the Gaussian distribution, may not be irradiated onto the sample S2 but may be introduced directly into the detection nonlinear optical crystal LN2 and converted into near-infrared light. The far-infrared light FIR that passes through the sample 202 is absorbed or scattered by the sample S2, resulting in a very low intensity, whereas the far-infrared light FIR that does not pass through the sample S2 is not attenuated.

[0044] Depending on the absorption coefficient of sample S2 for far-infrared light, the intensity of near-infrared light obtained without passing through sample S2 may be stronger than the intensity of near-infrared light obtained by converting far-infrared light FIR after passing through sample S2. In this case, the absorption spectrum is strongly influenced by the near-infrared light obtained without passing through sample S2, making it difficult to accurately measure the transmission absorption spectrum. This phenomenon occurs whether the surface of sample S2 is flat or curved. As shown in FIG. 5, if the surface of sample S2 is curved, the efficiency of generation of detection light decreases, as described in the first embodiment, making it even more difficult to accurately observe the absorption spectrum.

[0045] In the second embodiment, absorbers 811 having openings 813 of approximately the same size as the sample S2 are installed on the front and back surfaces of the main body 810 of the sample adapter 800. This allows for blocking of far-infrared light FIR that does not pass through the sample S2. The shape of the openings 813 is not particularly limited and may be, for example, circular, elliptical, square, rectangular, etc. The absorbers 811 are not limited to any particular material as long as they are capable of absorbing far-infrared light FIR. The attenuation rate is preferably such that the incident far-infrared light FIR is attenuated to less than half its intensity. When a material with a small attenuation rate is used as the absorber 811, it is possible to combine the absorber 811 with a shielding material 812 capable of blocking far-infrared light FIR, as shown in Figures 6A and 6B.

[0046] The shielding material 212 can be made of a metal material such as aluminum, which can reflect far-infrared light with a high reflectance. In this case, the light reflected by the shielding material 812 may be further reflected by other optical systems or structures, becoming stray light, which may then be introduced into the detection nonlinear optical crystal LN2 and observed as detection light. To prevent this, it is preferable to install an absorbing material 811, rather than a shielding material 812, on the outermost surface on the input / output side of the far-infrared light FIR, as shown in Figures 6A and 6B. Note that with the arrangement shown in Figure 6A, it is possible that the far-infrared light may be reflected by the metal shielding material 812 behind the sample S2, and then reflected by the metal shielding material 812 in front of the sample S2, before being observed. Therefore, it is also possible to sandwich the metal shielding material 812 between absorbing materials 811, as shown in Figure 6B.

[0047] [Third embodiment] Next, a far-infrared spectrometer according to a third embodiment will be described with reference to FIG. 7A. The far-infrared spectrometer of this third embodiment differs from the sample adapter 800 of the previous embodiment in the structure of the sample adapter 800. The remaining structure of the far-infrared spectrometer is the same as that of the previous embodiment, so redundant description will be omitted below. This third embodiment is suitable for a sample S3, such as a pharmaceutical caplet tablet, which has a different aspect ratio and whose short-side length is approximately equal to the beam diameter of the far-infrared light FIR when focused.

[0048] Similar to the sample adapter 800 of the second embodiment, this sample adapter 800 includes a main body 810, an absorber 811 formed on the front and back surfaces of the main body 810, and a light-shielding material 812. The main body 800 may be divided so as to sandwich the sample S3 therebetween, or may have a hollow portion through which the sample S3 can be inserted. The absorber 811 is made of a material that has the property of absorbing far-infrared light FIR. The absorber 811 has an opening 813 near its center that allows the far-infrared light FIR to pass through. The surface shape of the main body 810 is substantially planar, and the surface shape of the absorber 811 is also substantially planar. The opening 813 has long sides corresponding to the longitudinal length of the sample S3 and short sides aligned with the lateral length of the sample S3.

[0049] In the is-TPG system, the generation angle of far-infrared light (FIR) relative to near-infrared light (NIR) (180-γ in Figure 1B) varies depending on the frequency of the light. Therefore, as shown in Figure 7B, by placing the sample S3 with its long axis aligned in the x direction, even if the frequency of the far-infrared light (FIR) is changed, there is no need to precisely position the sample S3 using an automatic sample translation stage (not shown) or to precisely determine the mirror angle. In this case, the shape of the holes in the absorbing material 211 and the blocking material 212 through which the far-infrared light passes can be circular or square, similar to the far-infrared beam shape, as shown in Figure 7C, or rectangular or elliptical, as shown in Figure 7D. Using a rectangular or elliptical shape eliminates the need for highly accurate positioning, allowing for the construction of a robust optical system.

[0050] [others] In the above-described embodiments of the present invention, an apparatus using the is-TPG method has been described as an example. However, the present invention is not limited to this and can also be applied to an apparatus using terahertz time domain spectroscopy (THz-TDS). FIG. 8 is a schematic diagram illustrating an example of the configuration of a far-infrared spectroscopic apparatus using the THz-TDS method. In this apparatus, near-infrared light emitted from a femtosecond laser 901 is split into pump light 11 and probe light 13 by a beam splitter 902. The pump light 11 is introduced into a far-infrared light generating element 905, which generates far-infrared light FIR based on the pump light 11. The far-infrared light FIR is focused by a silicon lens 906 and then irradiated onto a sample adapter 800 containing a curved sample S' using an off-axis parabolic mirror 911. The far-infrared light transmitted through the curved sample S' and sample adapter 800 passes through an off-axis parabolic mirror 911' and is irradiated onto the detecting element 907. The probe light 13 passes through a movable mirror 921, which provides a time delay, and is introduced into the detecting element 907. The detection signal from the detecting element 907 is amplified by a preamplifier 931, and then its frequency spectrum is analyzed by a lock-in amplifier 932. A control unit 932 controls the entire apparatus. By moving the movable mirror 921 on the optical path of the probe light 13, the timing at which the probe light 13 reaches the detecting element 907 is shifted, and the time waveform of the oscillating electric field of the pulse wave of far-infrared light FIR is measured.

[0051] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, or the configuration of another embodiment can be added to the configuration of one embodiment. Furthermore, part of the configuration of each embodiment can be added, deleted, or replaced with other configurations. Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be implemented in hardware, in part or in whole, by designing, for example, an integrated circuit. Furthermore, the above-described configurations, functions, etc. may be implemented in software, by a processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files that realize each function can be stored in memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD. [Explanation of symbols]

[0052] 1...far-infrared spectroscopic device, 100...wavelength-tunable far-infrared light source, 200...illumination optical system, 300...detection optical system, 400...detection nonlinear optical crystal holder, 500...photodetector, 600...control unit, 700...signal processing unit, 110...pulse laser light source, 120...wavelength-tunable light source, 121...incident angle adjustment mechanism, 122...mirror, 123...half mirror, 11...pump light, 12...seed light, LN1...generating nonlinear optical crystal, 130...automatic translation stage, 132...generating Si prism, 134...damper, 201...mirror, 202...condensing lens, 203...automatic translation stage, 204...slit, 205...rotating stage, 206...mirror, 207, 208...condensing lens, 301, 302...lens, LN2...nonlinear optical crystal for detection, 402...Si prism for detection, 404...damper, 800...sample adapter, 810...main body, 811...absorber, 812...shielding material, 901...femtosecond laser, 902...beam splitter, 905...far-infrared light generating element, 906...silicon lens, 907...detection element, 911, 911'...parabolic mirror, 921...movable mirror.

Claims

1. an illumination optical system that focuses far-infrared light onto a sample; a detector for detecting far-infrared light transmitted through the sample; Equipped with a sample adapter is installed on an optical path of the far-infrared light between the illumination optical system and the sample, and on an optical path between the sample and a detection optical element; the surface of the sample adapter opposite to the sample side is substantially flat; the surface shape of the sample adapter on the sample side has a shape that substantially matches the shape of the sample; the surface of the sample that collects and transmits the far-infrared light is a curved surface, the sample adapter has a constant refractive index of 1 or more in a band of the far-infrared light, the sample adapter is configured such that, when the sample adapter is installed, a distance between the sample-side surface of the sample adapter and the sample is equal to or less than the wavelength of the far-infrared light. A far-infrared spectroscopic device characterized by:

2. a pump light source that emits pump light that is near-infrared light; a wavelength-tunable light source that emits seed light; a first nonlinear optical crystal that generates far-infrared light by parametric generation of the pump light and the seed light; a second nonlinear optical crystal that converts the far-infrared light that has passed through the sample into near-infrared light; The far-infrared spectroscopic device of claim 1 further comprising:

3. The sample adapter comprises: an absorber provided on the surface of the main body and having an opening for passing the far-infrared light; The far-infrared spectroscopic device of claim 1 further comprising:

4. The far-infrared spectroscopic device according to claim 3 , further comprising a light-shielding material made of metal and arranged in contact with the absorbing material.

5. The far-infrared spectroscopic device according to claim 4 , wherein the light-shielding material is disposed so as to be sandwiched between the light-absorbing materials.

6. A sample adapter to be placed around a sample to be measured by far-infrared spectroscopy, the surface of the sample adapter opposite to the sample side is substantially flat; the surface of the sample adapter facing the sample has a shape that substantially matches the shape of the sample; the surface of the sample that collects and transmits the far-infrared light is a curved surface, the sample adapter has a constant refractive index of 1 or more in a band of the far-infrared light, the sample adapter is configured such that, when the sample adapter is installed, a distance between the sample-side surface of the sample adapter and the sample is equal to or less than the wavelength of the far-infrared light. A sample adapter comprising:

7. an absorbent material and a light-shielding material that are installed on the surface of the sample adapter and that absorb far-infrared light; 7. The sample adapter according to claim 6, wherein the absorbent material and the light-shielding material have openings in parts thereof.

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