JP2011169639A - Terahertz spectroscopic device, method for manufacturing the same, and terahertz spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To well measure the terahertz transmission spectrum of a substance highly absorbent for terahertz waves, without using an extremely thin liquid cell, a prism optical system, a silicon rod, and the like. <P>SOLUTION: The terahertz spectroscopic device is equipped with the gap part formed in a substrate 30 and an air clad type wave guide 34 circumferentially surrounded by the gap part so as to propagate terahertz waves between an input terminal 35 and an output terminal 33 in the substrate 30. A housing part (first and second housing parts 31A and 31B) for housing a measuring target is formed to a region, which contains a region through which the terahertz waves propagating through the waveguide 34 propagate as evanescent waves, in the periphery of the waveguide 34. Further, the gap part forming the air clad type waveguide 34 also has the function as the housing part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a terahertz spectroscopic device suitable for performing spectrum analysis of a liquid sample using terahertz waves, a manufacturing method thereof, and a terahertz spectroscopic apparatus.

  In recent years, technology using terahertz waves has attracted attention, and spectroscopy and imaging using terahertz waves are expected as industrial applications. For example, as a field of application of terahertz waves, a technology that performs terahertz imaging as a safe fluoroscopic inspection device using the fact that photon energy is extremely small compared to X-rays, and substances caused by molecular vibrational levels and rotational levels There is a spectroscopic technique for determining the state and identification of substances by obtaining the absorption spectrum and complex permittivity. Further, techniques for evaluating the carrier concentration and mobility of a semiconductor substrate and detecting a wiring defect position from terahertz generated by irradiating an LSI chip with a femtosecond laser have been developed.

  In particular, as disclosed in Patent Documents 1 to 3, a method for analyzing a substance by a spectroscopic technique using a terahertz wave is known. This analysis is performed by irradiating a sample to be measured with a terahertz wave and obtaining a spectrum of the transmitted or reflected terahertz wave.

Japanese Patent No. 4154388 Japanese Patent No. 4002173 JP 2007-71610 A

Hideki Hirori, et al., "Attenuated total reflection spectroscopy in time domain using terahertz coherent pulses," Jpn.J.Appl.Phys, 43, L1287 (2004). Li Cheng, et al., "Terahertz-wave absorption in liquids measured using the evanescent filed of a silicon waveguide," Appl. Phys. Lett, 92, 181104 (2008).

  By the way, since water has a very strong absorption spectrum in the frequency range of 0.3 THz to 30 THz among terahertz waves, a very thin liquid cell of about several μm to several tens of μm is used for terahertz spectroscopy of a sample containing a lot of water. Must be prepared. Furthermore, when performing terahertz spectroscopy in the time domain, it is necessary to take into account the effects of reflection at the sample interface and interference within the sample, and to accurately measure the sample thickness. For this reason, it has been difficult to obtain a terahertz transmission spectrum of a sample containing water.

  Therefore, as a method for obtaining an absorption spectrum and a complex dielectric constant of molecules contained in a substance having a very strong absorption spectrum such as water in the terahertz region, total reflection attenuation spectroscopy as disclosed in Non-Patent Document 1 is used. A method called law is known. This is a method using a terahertz evanescent wave generated at the time of total reflection in an optical system using a prism. An evanescent wave is an electromagnetic field that decays exponentially in the direction of the wave vector, and this method effectively reduces the terahertz absorption coefficient, allowing spectroscopic analysis of molecules in very strong terahertz absorbing materials such as water. It has become. However, the method using the prism optical system has a complicated apparatus configuration and requires a highly accurate assembly technique.

  On the other hand, as disclosed in Non-Patent Document 2, a method has been proposed in which a silicon rod is used as a terahertz waveguide and an evanescent wave generated around the waveguide is also used. However, this method has problems that it requires high-precision machining of the silicon rod, that the conditions for generating the evanescent wave cannot be adjusted easily, and that it is difficult to hold the silicon rod. High precision of technology is inevitable.

  Further, a method for obtaining a terahertz wave transmission spectrum of a liquid sample filled in a channel using a combination of a waveguide structure and a channel as disclosed in Patent Document 1 is known. Since the thickness of the flow path must be accurately adjusted, a highly accurate assembly technique is required.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a terahertz transmission spectrum of a substance having a large absorption with respect to a terahertz wave without using an ultrathin liquid cell, a prism optical system, and a silicon rod. An object of the present invention is to provide a terahertz spectroscopic device and a method for manufacturing the same, and a terahertz spectroscopic device that can perform measurement satisfactorily.

  A device for terahertz spectroscopy according to the present invention includes a substrate including an input end to which a terahertz wave is input and an output end from which the terahertz wave is output, a gap formed in the substrate, and an input end and an output end in the substrate. An air-clad waveguide formed by being surrounded by an air gap so that a terahertz wave is propagated between the terahertz wave and the terahertz wave propagating through the waveguide as an evanescent wave around the waveguide. It is formed in a region including a propagating region, and is provided with a storage unit that stores a measurement target object.

A terahertz spectrometer according to the present invention includes a generating unit that generates a terahertz wave, a terahertz spectroscopic device that receives the terahertz wave generated by the generating unit, and a detection that detects the terahertz wave after propagating through the terahertz spectroscopic device Means.
Then, the terahertz spectroscopy device is constituted by the terahertz spectroscopy device of the present invention.

  In the terahertz spectroscopic device or the terahertz spectroscopic device according to the present invention, an evanescent wave is generated in the vicinity of the waveguide by propagating the terahertz wave through the air-clad waveguide. A housing part is formed in a region including a region where the evanescent wave propagates, and the object to be measured is accommodated, whereby the terahertz wave interacts with the object to be measured. This makes it possible to effectively reduce the terahertz absorption coefficient of strong terahertz absorbers such as water without using a prism optical system or silicon rod, and absorption spectra of molecules in strong terahertz absorbers such as water. Can be obtained satisfactorily.

  The method for producing a terahertz spectroscopy device according to the present invention is such that the terahertz spectroscopy device of the present invention is produced by imprint molding or stereolithography using a material containing an ultraviolet curable resin.

  In the method for manufacturing a terahertz spectroscopy device according to the present invention, the terahertz spectroscopy device of the present invention can be mass-produced by imprint molding or stereolithography. The terahertz spectroscopic device of the present invention can be manufactured by imprint molding or stereolithography. For example, a substrate manufacturing error of several μm does not have a great influence on spectral performance, and depends on a dimensional tolerance at the time of manufacturing the substrate. This is because the structure can reduce the influence on the spectral performance. The air clad type waveguide structure in the terahertz region used in the terahertz spectroscopy device of the present invention has a core diameter of several tens to several hundreds of times compared with, for example, a photonic crystal structure in an optical communication band. Since it is twice, mass production and production by stereolithography or imprint molding using a material containing an ultraviolet curable resin is possible.

  According to the terahertz spectroscopic device or the terahertz spectroscopic device of the present invention, the terahertz wave is propagated in the air-clad type waveguide, and the accommodating portion is formed in a region including the region where the evanescent wave generated thereby propagates. Since the terahertz wave interacts with the object to be measured, it is possible to effectively reduce the terahertz absorption coefficient by a strong terahertz absorbing material such as water without using a prism optical system or a silicon rod. . This makes it possible to satisfactorily perform terahertz transmission spectrum measurement of a substance having a large absorption with respect to terahertz waves without using an extremely thin liquid cell, prism optical system, silicon rod, or the like.

  According to the method for manufacturing a terahertz spectroscopic device of the present invention, the terahertz spectroscopic device of the present invention is manufactured by imprint molding or stereolithography using a material containing an ultraviolet curable resin. Is possible. This is due to the fact that the terahertz spectroscopy device of the present invention does not require high-precision manufacturing tolerances compared to, for example, a photonic crystal structure for optical communication.

It is a top view which shows the structural example of the device for terahertz spectroscopy which concerns on one embodiment of this invention. It is a top view which shows an example of the dimension of the device for terahertz spectroscopy shown in FIG. It is a block diagram which shows an example of the terahertz spectroscopy apparatus incorporating the device for terahertz spectroscopy shown in FIG. It is a perspective view which shows an example of the installation method in the case of introduce | transducing the terahertz spectroscopy device shown in FIG. 1 into a terahertz spectroscopy apparatus. (A) is a waveform diagram showing an example of the detection result of the terahertz wave detected by the terahertz spectrometer shown in FIG. 4, and (B) shows the spectrum waveform of the terahertz wave obtained based on the waveform of (A). FIG. FIG. 2 is a waveform diagram illustrating an example of a spectrum waveform of a terahertz wave obtained in a state where an object to be measured is not accommodated in the accommodating portion of the terahertz spectroscopy device illustrated in FIG. 1. It is a wave form diagram which shows an example of the spectrum waveform of the terahertz wave obtained in the state which accommodated the to-be-measured object in the accommodating part of the device for terahertz spectroscopy shown in FIG. FIG. 8 is a waveform diagram showing an absorption spectrum waveform for a terahertz wave of an object to be measured obtained from the spectrum waveform of FIG. 6 and the spectrum waveform of FIG. 7.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Configuration of Terahertz Spectroscopy Device 1]
FIG. 1 shows a configuration example of a terahertz spectroscopy device 1 according to an embodiment of the present invention. FIG. 2 shows an example of specific dimensions of the terahertz spectroscopy device 1. The terahertz spectroscopy device 1 includes a substrate 30 made of a material that is transparent or has a predetermined transmittance with respect to the wavelength of the terahertz wave to be measured. The substrate 30 is made of, for example, a single material (such as a material containing an ultraviolet curable resin) as a whole. The board | substrate 30 is flat form as a whole, and as shown in FIG. 2, thickness is about 0.1 mm-10 mm, and the length of a horizontal direction and a vertical direction is about 10 mm-300 mm.

  The substrate 30 is provided with an input end 35 and an output end 33, and an air-clad waveguide 34 (core) that propagates terahertz waves between the input end 35 and the output end 33. For example, a terahertz wave 36 generated by using a femtosecond laser and a photoconductive antenna is input to the input terminal 35. A terahertz wave 32 after being propagated through the waveguide 34 is output from the output end 33.

  The substrate 30 is provided with a first accommodating portion 31A and a second accommodating portion 31B in which an object to be measured (for example, a liquid sample) is accommodated. A liquid sample is injected into the first storage unit 31A and the second storage unit 31B using, for example, a syringe. 31 A of 1st accommodating parts and the 2nd accommodating part 31B are formed in the area | region including the area | region where the terahertz wave which propagates the waveguide 34 propagates as an evanescent wave around the waveguide 34. FIG. In the example of FIG. 1, an example of a structure in which a container having a rectangular planar shape and cross-sectional shape is provided, it is sufficient that the space for filling the object to be measured is provided. It is not limited to a rectangular shape.

  31 A of 1st accommodating parts and the 2nd accommodating part 31B are the area | regions where the 2nd surface (back surface) side facing the 1st surface was closed while the 1st surface (front surface) side in the board | substrate 30 was open | released. It has a digging-type structure. It is preferable that the thickness of the second surface side in the first housing portion 31A and the second housing portion 31B is less than the wavelength of the terahertz wave. By setting the thickness to less than the wavelength of the terahertz wave, the radiation loss of the terahertz wave in the first housing portion 31A and the second housing portion 31B can be minimized.

  The first accommodating portion 31A and the second accommodating portion 31B also function as a gap for forming the air-clad waveguide 34. For this reason, in the first accommodating portion 31A and the second accommodating portion 31B, an air-clad waveguide 34 through which the terahertz wave is propagated is formed between the input end 35 and the output end 33 in the substrate 30. Thus, it is provided so as to surround (pinch) the periphery of the waveguide 34.

In order to propagate the terahertz wave, the waveguide 34 is a rectangular rod-shaped core having a cross-sectional area (area of a cross section perpendicular to the traveling direction of the terahertz wave) of less than 100 mm ² as shown in FIG. Yes. The waveguide 34 is connected to the substrate 30 in the vicinity of the input end 35 and the output end 33, thereby having a doubly supported beam structure held by the substrate 30. In order for the waveguide 34 to function as an air-clad terahertz waveguide, a material having a necessary refractive index and a core shape such as a core diameter are determined according to the wavelength of the terahertz wave used for measurement. For example, the design is performed by a numerical calculation method such as a beam propagation method or a time domain finite difference method. In the present embodiment, since the purpose is to generate a terahertz evanescent wave by a waveguide structure having no cladding, the shape and dimensions are not limited to those described above.

[Operation and Effect of Terahertz Spectroscopy Device 1]
In the terahertz spectroscopy device 1, an evanescent wave is generated in the vicinity of the waveguide 34 by propagating the terahertz wave through the air clad type waveguide 34 existing in the single substrate 30. The first accommodating portion 31A and the second accommodating portion 31B are formed in a region including the region where the evanescent wave propagates, and the terahertz wave interacts with the measurement target object by accommodating the measurement target object. . The terahertz evanescent wave generated here is an electromagnetic wave that decays exponentially in the direction of the wave vector, but the core shape and core diameter, which are the design parameters of the air-clad waveguide, and the attenuation distance are controlled by the material used. Is possible. For this reason, it is possible to control the magnitude of the interaction between the terahertz wave and the object to be measured that occurs in the first housing portion 31A and the second housing portion 31B.

  This method makes it possible to effectively reduce the terahertz absorption coefficient of a strong terahertz absorbing material such as water without using a prism optical system or a silicon rod, and molecules in a strong terahertz absorbing material such as water. It is possible to obtain a good absorption spectrum. In this case, for example, a substrate manufacturing error of several μm does not greatly affect the spectral performance, and the influence on the spectral performance due to the dimensional tolerance at the time of manufacturing the substrate can be reduced. Further, the air clad type waveguide structure in the terahertz region used in the terahertz spectroscopy device 1 has a core diameter of several tens of times to several tens of times as compared with, for example, a photonic crystal structure in an optical communication band. Since it is 100 times, relatively high-precision manufacturing tolerances are not required, and mass production and production by optical modeling or imprint molding using a material containing an ultraviolet curable resin is possible.

  As described above, according to the terahertz spectroscopy device 1 according to the present embodiment, a terahertz transmission of a substance having a large absorption with respect to a terahertz wave can be achieved without using an extremely thin liquid cell, a prism optical system, a silicon rod, or the like. It becomes possible to perform spectrum measurement satisfactorily.

[Example of application to terahertz spectrometer]
FIG. 3 shows an example of a terahertz spectrometer using the terahertz spectrometer device 1. This terahertz spectrometer includes a femtosecond laser 90, a beam splitter 91, photoconductive antennas 92A and 92B, silicon lenses 93A and 93B, parabolic mirrors 94 and 96, silicon lenses 95A and 95B, and a reflecting mirror. 97 and a time delay unit 98 are provided.
The femtosecond laser 90 and the photoconductive antenna 92A correspond to a specific example of “generating means” in the present invention. The photoconductive antenna 92B mainly corresponds to a specific example of “detecting means” in the present invention.

  FIG. 4 shows an example of an installation method when the terahertz spectroscopy device 1 shown in FIG. 1 is introduced into the terahertz spectroscopy apparatus shown in FIG. Since the terahertz spectroscopy device 1 performs the measurement using the evanescent wave, for example, if the measurement is performed in a state where the bottom surface of the device is in close contact with or in close contact with the floor surface, the measurement may be adversely affected by radiation loss. Therefore, it is preferable to perform measurement in the state where there are no obstacles on the bottom surface and the vicinity of the surface of the device. For example, it is preferable to perform measurement in a state where the terahertz spectroscopy device 1 is floated in the space by partially supporting the substrate 30 at a position away from the waveguide 34 and the accommodating portions 31A and 31B. In the example of installation shown in FIG. 4, the terahertz spectroscopy device 1 is partially supported at four corners by columnar support portions 41 on the base substrate 40, so that the entire device is floated in space. . The support portion 41 is installed at a sufficient distance (for example, 10 mm or more) that the evanescent wave generated by the terahertz wave propagating through the waveguide 34 does not reach. In addition, in the installation example of FIG. 4, although it is the structure supported by the support part 41 from the lower side of a device, the structure which supports a device from the upper side may be sufficient. For example, a structure in which the base substrate 40 is disposed on the uppermost side and the entire device is suspended through the support portion 41 may be used upside down from the installation example of FIG.

[Measurement operation by terahertz spectrometer]
In the terahertz spectrometer shown in FIG. 3, a laser pulse having a pulse width of about 100 fs (femtosecond) is generated from the femtosecond laser 90. The laser pulse is divided by a beam splitter 91, one of which is made of GaAs (gallium arsenide) or the like grown at low temperature, and irradiated to a gap portion of a biased photoconductive antenna 92A to generate a terahertz wave. The terahertz waves are collected by a silicon lens 93A installed immediately after the photoconductive antenna 92A, and incident on the input end 35 (FIG. 1) of the terahertz spectroscopy device 1 through the parabolic mirror 94 and the silicon lens 95A. The waveguide 34 is coupled. While propagating through the waveguide 34, the terahertz wave input to the terahertz spectroscopy device 1 is interacted with the object to be measured by the evanescent wave as described above, and is output from the output end 33. The terahertz wave output from the terahertz spectroscopy device 1 is coupled to the photoconductive antenna 92B through the silicon lens 95B, the parabolic mirror 96, and the silicon lens 93B.

  On the other hand, the other laser pulse divided by the beam splitter 91 passes through the time delay unit 98 and the reflecting mirror 97 and is coupled to the photoconductive antenna 92B in a state where the arrival time is shifted. By measuring the photocurrent from the photoconductive antenna 92B at each delay time shifted in arrival time, for example, a terahertz electric field time waveform 100 as shown in FIG. 5A can be obtained. By performing a Fourier transform on this, for example, a terahertz wave spectrum 101 as shown in FIG. 5B can be obtained.

  Next, with reference to FIGS. 6-8, the measurement procedure in which the spectrum of a to-be-measured object is obtained is demonstrated. 6 shows a spectrum waveform of the terahertz wave obtained by the terahertz spectrometer of FIG. 3 in a state where the measurement target object is not accommodated in the first accommodation unit 31A and the second accommodation unit 31B of the terahertz spectroscopy device 1. 20 is shown schematically. FIG. 7 schematically shows a spectrum waveform 21 of a terahertz wave obtained in a state where the measurement target is accommodated in the first accommodating portion 31A and the second accommodating portion 31B of the terahertz spectroscopy device 1.

  Thus, the spectrum waveform 20 obtained in a state where the measurement target object is not accommodated and the spectrum waveform 21 obtained in a state where the measurement target object is accommodated are measured, and the ratio thereof is obtained. Thereby, for example, as shown in FIG. 8, an absorption spectrum waveform 22 for the terahertz wave of the measurement object can be obtained.

  When measuring the spectral waveform 21 shown in FIG. 7, the measurement object may be accommodated in both the first accommodating portion 31A and the second accommodating portion 31B, or one accommodating portion. The object to be measured may be accommodated only in the area.

<Other embodiments>
The present invention is not limited to the above embodiment, and various modifications can be made.
For example, the terahertz wave generating means is not limited to the one using the femtosecond laser 90 and the photoconductive antenna 92A as shown in FIG. For example, a laser generated by a quantum cascade laser or optical parametric oscillation may be used.

  DESCRIPTION OF SYMBOLS 1 ... Terahertz spectroscopy device, 30 ... Board | substrate, 31A ... 1st accommodating part (gap part), 31B ... 2nd accommodating part (gap part), 33 ... Output end, 34 ... Waveguide (core), 35 ... Input end, 32, 36 ... terahertz wave, 40 ... base substrate, 41 ... support, 90 ... femtosecond laser, 91 ... beam splitter, 92A, 92B ... photoconductive antenna, 93A, 93B ... silicon lens, 94, 96 ... Parabolic mirror, 95A, 95B ... Silicon lens, 97 ... Reflector, 98 ... Time delay.

Claims (8)

A substrate including an input end to which a terahertz wave is input and an output end from which the terahertz wave is output;
A void formed in the substrate;
In the substrate, an air-cladding type waveguide formed by being surrounded by the gap so that the terahertz wave is propagated between the input end and the output end;
A terahertz spectroscopic device comprising: a housing portion that is formed in a region including a region where a terahertz wave propagating through the waveguide propagates as an evanescent wave around the waveguide, and that accommodates an object to be measured. The device for terahertz spectroscopy according to claim 1, wherein the gap portion also functions as the housing portion. The device for terahertz spectroscopy according to claim 1, wherein the waveguide has a cross-sectional area of less than 100 mm ² . The accommodating portion has a digging-type structure in which a first surface side of the substrate is opened and a second surface side facing the first surface is a closed region;
The device for terahertz spectroscopy according to claim 1, wherein a thickness of the housing portion on a side of the second surface is less than a wavelength of the terahertz wave. The device for terahertz spectroscopy according to any one of claims 1 to 4, wherein the substrate is made of a single material that transmits the terahertz wave. Generating means for generating terahertz waves;
A terahertz spectroscopic device to which the terahertz wave generated by the generating means is input;
Detecting means for detecting a terahertz wave after propagating through the terahertz spectroscopic device;
The terahertz spectroscopy device is
A substrate including an input end to which the terahertz wave is input and an output end from which the terahertz wave is output;
A void formed in the substrate;
In the substrate, an air-cladding type waveguide formed by being surrounded by the gap so that the terahertz wave is propagated between the input end and the output end;
A terahertz spectrometer having a housing portion that is formed in a region including a region where a terahertz wave propagating through the waveguide propagates as an evanescent wave around the waveguide, and that accommodates an object to be measured. The terahertz spectrometer according to claim 6, wherein measurement is performed in a state where the terahertz spectroscopy device is floated in a space by partially supporting the substrate at a position away from the waveguide and the housing portion. A substrate including an input end to which a terahertz wave is input and an output end from which the terahertz wave is output;
A void formed in the substrate;
In the substrate, an air-cladding type waveguide formed by being surrounded by the gap so that the terahertz wave is propagated between the input end and the output end;
A terahertz spectroscopic device comprising: a housing portion in which a terahertz wave propagating in the waveguide is formed in a region including a region in which the terahertz wave propagating through the waveguide is propagated as an evanescent wave and in which the measurement target is accommodated.
A method for manufacturing a terahertz spectroscopic device manufactured by imprint molding or stereolithography using a material containing an ultraviolet curable resin.

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