A prism member having an entrance surface for arranging a terahertz-wave generator for generating a terahertz wave in response to pump light incident thereon, an arrangement part for arranging an object to be measured, an exit surface for arranging a terahertz-wave detector for detecting a correlation between the terahertz wave transmitted through the object in the arrangement part and probe light, a first optical surface for collimating or condensing the terahertz wave incident thereon from the entrance surface toward the arrangement part, and a second optical surface for condensing the terahertz wave transmitted through the arrangement part toward the exit surface, the arrangement part forms a depression adapted to be filled with a liquid incapable of dissolving the object therein.

TECHNICAL FIELD

The present invention relates to a prism member for use in transmission spectrometry employing a terahertz wave and a terahertz-wave spectrometer and terahertz-wave spectrometric method using the same.

BACKGROUND ART

Conventionally known as an example of techniques relating to a spectrometer using a terahertz wave is a terahertz-wave spectrometer described in Patent Literature 1. In this terahertz-wave spectrometer, an entrance surface of an internal total reflection prism is integrally provided with a terahertz-wave generator, while an exit surface of the internal total reflection prism is integrally provided with a terahertz-wave detector. Using such an integral prism integrating the internal total reflection prism, terahertz-wave generator, and terahertz-wave detector together is advantageous in that it can detect terahertz waves at high efficiency while reducing the size of the total reflection spectrometer.

An example of detection devices for performing transmission spectrometry which detects the state of a terahertz wave transmitted through an object to be measured is one disclosed in Patent Literature 2. In this detection device, both end faces of a multilayer body formed by holding both sides of a polystyrene sheet with metal sheets are provided with a terahertz-wave generator and a terahertz-wave detector. A void having a rectangular cross section is formed at a center part of the polystyrene sheet, so as to be filled with an object to be measured.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

When measuring the state of a terahertz wave transmitted through an object to be measured, if the terahertz wave passes through air, the measurement accuracy may decrease under the influence of absorption by moisture in the air or the reflection loss at the interface between a waveguide member and the air. On the other hand, there is a case where the terahertz wave is transmitted through the object as collimated or condensed light. Hence, there has been a demand for contrivances for enabling measurement suppressing the above-mentioned influences of absorption and reflection loss regardless of the form of the part where the object is placed or the shape of the object.

It is an object of the present invention to provide a prism member which can improve the measurement accuracy of spectrometry regardless of the shape of the object and a terahertz-wave spectrometer and terahertz-wave spectrometric method using the same.

Solution to Problem

The prism member in accordance with the present invention is a prism member for use in transmission spectrometry of an object to be measured employing a terahertz wave, the prism member comprising an entrance surface for arranging a terahertz-wave generator for generating a terahertz wave in response to pump light incident thereon, an arrangement part for arranging the object, an exit surface for arranging a terahertz-wave detector for detecting a correlation between the terahertz wave transmitted through the object in the arrangement part and probe light, a first optical surface for collimating or condensing the terahertz wave incident thereon from the entrance surface toward the arrangement part, and a second optical surface for condensing the terahertz wave transmitted through the arrangement part toward the exit surface, while the arrangement part forms a depression adapted to be filled with a liquid incapable of dissolving the object therein.

In this prism member, the arrangement part for arranging the object is a depression which can be filled with a liquid incapable of dissolving the object therein. Therefore, in a path of the terahertz wave impinging on the first optical surface and then passing through the arrangement part toward the second optical surface, the terahertz wave can be kept from traveling through air. This can eliminate the influence of absorption by the moisture in the air, thereby improving the measurement accuracy in spectrometry. The depression may have various forms depending on the shape of the object and the like but can easily be filled with a liquid regardless of the forms, whereby the convenience of measurement is maintained.

The depression may include a first refractive surface for refracting the terahertz wave from the first optical surface toward the object and a second refractive surface for refracting the terahertz wave transmitted through the object toward the second optical surface. When refracting light at an interface between media having different refractive indexes, appropriately setting the angle of incidence with respect to the interface can reduce reflection loss as compared with the case where the light is perpendicularly incident on the interface and transmitted therethrough without refraction. Therefore, the reflection loss of the terahertz wave directed from the first optical surface to the object can be reduced when the depression includes the first refractive surface, while the reflection loss of the terahertz wave passing through the object toward the second optical surface can be reduced when the depression includes the second refractive surface. This can more securely eliminate the influence of the reflection loss of the terahertz wave, thereby further improving the measurement accuracy in spectrometry.

The object may be a solid, while the arrangement part may have a support part for supporting the object. This can stabilize the posture of the object within the arrangement part when the object is a solid, thereby further improving the measurement accuracy.

The object may be a liquid, while the arrangement part may have a support part for supporting a cell containing the object. This makes the object easy to arrange into and take out from the arrangement part when the object is a liquid.

The terahertz-wave spectrometer in accordance with the present invention is a terahertz-wave spectrometer for performing transmission spectrometry of an object to be measured by using a terahertz wave, the spectrometer comprising a light source for emitting laser light, a branching unit for splitting the laser light emitted from the light source into pump light and probe light, and a prism member; the prism member having an entrance surface for arranging a terahertz-wave generator for generating a terahertz wave in response to the pump light incident thereon, an arrangement part for arranging the object, an exit surface for arranging a terahertz-wave detector for detecting a correlation between the terahertz wave transmitted through the object in the arrangement part and the probe light, a first optical surface for collimating or condensing the terahertz wave incident thereon from the entrance surface toward the arrangement part, and a second optical surface for condensing the terahertz wave transmitted through the arrangement part toward the exit surface, while the arrangement part forms a depression adapted to be filled with a liquid incapable of dissolving the object therein.

In this terahertz-wave spectrometer, the arrangement part for arranging the object in the prism member is a depression which can be filled with a liquid incapable of dissolving the object therein. Therefore, in a path of the terahertz wave impinging on the first optical surface and then passing through the arrangement part toward the second optical surface, the terahertz wave can be kept from traveling through air. This can eliminate the influence of absorption by the moisture in the air, thereby improving the measurement accuracy in spectrometry. The depression may have various forms depending on the shape of the object and the like but can easily be filled with a liquid regardless of the forms, whereby the convenience of measurement is maintained.

The depression may include a first refractive surface for refracting the terahertz wave from the first optical surface toward the object and a second refractive surface for refracting the terahertz wave transmitted through the object toward the second optical surface. When refracting light at an interface between media having different refractive indexes, appropriately setting the angle of incidence with respect to the interface can reduce reflection loss as compared with the case where the light is perpendicularly incident on the interface and transmitted therethrough without refraction. Therefore, the reflection loss of the terahertz wave directed from the first optical surface to the object can be reduced when the depression includes the first refractive surface, while the reflection loss of the terahertz wave passing through the object toward the second optical surface can be reduced when the depression includes the second refractive surface. This can more securely eliminate the influence of the reflection loss of the terahertz wave, thereby further improving the measurement accuracy in spectrometry.

The object may be a solid, while the arrangement part may have a support part for supporting the object. This can stabilize the posture of the object within the arrangement part when the object is a solid, thereby further improving the measurement accuracy.

The object may be a liquid, while the arrangement part may have a support part for supporting a cell containing the object. This makes the object easy to arrange into and take out from the arrangement part when the object is a liquid.

The terahertz-wave spectrometric method in accordance with the present invention is a terahertz-wave spectrometric method for performing transmission spectrometry of an object to be measured by using a terahertz wave, the method using a prism member having an entrance surface for arranging a terahertz-wave generator for generating a terahertz wave in response to pump light incident thereon, an arrangement part for arranging the object, an exit surface for arranging a terahertz-wave detector for detecting a correlation between the terahertz wave transmitted through the object in the arrangement part and probe light, a first optical surface for collimating or condensing the terahertz wave incident thereon from the entrance surface toward the arrangement part, and a second optical surface for condensing the terahertz wave transmitted through the arrangement part toward the exit surface, the arrangement part forming a depression adapted to be filled with a liquid incapable of dissolving the object therein; the method comprising arranging the object in a state where the depression is filled with the liquid incapable of dissolving the object therein; and measuring an optical constant concerning the object according to the terahertz wave transmitted through the object.

This terahertz-wave spectrometric method performs spectrometry by using a prism member whose arrangement part for arranging the object is a depression and filling the depression with a liquid incapable of dissolving the object. Therefore, in a path of the terahertz wave impinging on the first optical surface and then passing through the arrangement part toward the second optical surface, the terahertz wave can be kept from traveling through air. This can eliminate the influence of absorption by the moisture in the air, thereby improving the measurement accuracy in spectrometry. The depression may have various forms depending on the shape of the object and the like but can easily be filled with a liquid regardless of the forms, whereby the convenience of measurement is maintained.

The prism member having the arrangement part constituted by the depression including a first refractive surface for refracting the terahertz wave from the first optical surface toward the object and a second refractive surface for refracting the terahertz wave transmitted through the object toward the second optical surface may be used. When refracting light at an interface between media having different refractive indexes, appropriately setting the angle of incidence with respect to the interface can reduce reflection loss as compared with the case where the light is perpendicularly incident on the interface and transmitted therethrough without refraction. Therefore, the reflection loss of the terahertz wave directed from the first optical surface to the object can be reduced when the depression includes the first refractive surface, while the reflection loss of the terahertz wave passing through the object toward the second optical surface can be reduced when the depression includes the second refractive surface. This can more securely eliminate the influence of the reflection loss of the terahertz wave, thereby further improving the measurement accuracy in spectrometry.

The object may be a solid, and the prism member having a support part for supporting the object in the arrangement part may be used. This can stabilize the posture of the object within the arrangement part when the object is a solid, thereby further improving the measurement accuracy.

The object may be a liquid, and the prism member having a support part for supporting a cell containing the object may be used. This makes the object easy to arrange into and take out from the arrangement part when the object is a liquid.

As the liquid incapable of dissolving the object therein, a liquid incapable of absorbing the terahertz wave may be used. This inhibits the liquid from absorbing the terahertz wave and thus can measure the optical constant concerning the object more accurately.

As the liquid incapable of dissolving the object therein, a fluorine-based inert liquid may be used. In this case, using the fluorine-based inert liquid makes many substances insoluble to the liquid and inhibits the liquid from absorbing the terahertz wave. The fluorine-based inert liquid is hard to vaporize and thus prevents volatile ingredients from adversely affecting the surroundings, while suppressing environmental load.

As the liquid incapable of dissolving the object therein, a silicone oil may be used. In this case, using the silicone oil makes many substances insoluble to the liquid and inhibits the liquid from absorbing the terahertz wave. The silicone oil is hard to vaporize and thus prevents volatile ingredients from adversely affecting the surroundings, while suppressing environmental load.

Advantageous Effects of Invention

The present invention can improve the measurement accuracy of spectrometry regardless of the shape of the object.

DESCRIPTION OF EMBODIMENTS

In the following, preferred embodiments of the prism member, terahertz-wave spectrometer, and terahertz-wave spectrometric method in accordance with the present invention will be explained in detail with reference to the drawings.

FIG. 1is a diagram illustrating an embodiment of the terahertz-wave spectrometer in accordance with the present invention. As depicted, this terahertz-wave spectrometer1comprises a laser light source2for emitting laser light, an integral prism3in which a terahertz-wave generator32, a spectroscopic prism (prism member)31, and a terahertz-wave detector33are integrated together, and a detection unit4for detecting a terahertz wave. The terahertz-wave spectrometer1also comprises a controller5for controlling operations of the constituents mentioned above, a data analyzer6for analyzing data according to an output from the detection unit4, and a display unit7for displaying results of processing in the data analyzer6.

The laser light source2is a light source for generating a femtosecond pulsed laser. The laser light source2issues a femtosecond pulsed laser having an average power of 120 mW and a repetition rate of 77 MHz, for example. The femtosecond pulsed laser emitted from the laser light source2impinges on mirrors11,12in sequence and then is split into two, i.e., pump light48and probe light49, by a beam splitter13(seeFIG. 2). A probe light optical path C1 through which the probe light49propagates is provided with mirrors14,15and a lens16, so that the probe light49is condensed by the lens16, so as to be made incident on the terahertz-wave detector33which will be explained later.

On the other hand, a pump light optical path C2 through which the pump light48propagates is provided with a delay unit21and a modulator22. The delay unit21, which is constructed by a pair of mirrors23,24and a reflection prism25disposed on a movable stage26, can adjust a delay in the pump light48by moving the position of the reflection prism25back and forth with respect to the pair of mirrors23,24. The modulator22is a part which switches between transmitting and blocking the pump light48by an optical chopper, for example. According to a signal from the controller5, the modulator22modulates the switching between transmitting and blocking the pump light48at 1 kHz, for example.

The pump light48propagated through the pump light optical path C2 impinges on a mirror28and then is condensed by a lens27, so as to be made incident on the integral prism3. As illustrated inFIG. 2, the spectroscopic prism31constituting the integral prism3, which is formed by Si, for example, has an entrance surface31ato which the terahertz-wave generator32is integrally secured and an exit surface31bto which the terahertz-wave detector33is integrally secured. The upper face of the spectroscopic prism31forms an arrangement part31cto be arranged with an object to be measured34, from which various optical constants such as refractive index, dielectric constant, and absorption coefficient are measured.

In the bottom face of the spectroscopic prism31, as illustrated inFIG. 2, a first optical surface31dfor collimating a terahertz wave T generated in the terahertz-wave generator32toward the arrangement part31cis provided between the entrance surface31aand the arrangement part31c. A second optical surface31efor condensing the terahertz wave T from the arrangement part31ctoward the exit surface31bis provided between the arrangement part31cand the exit surface31b. The first and second optical surfaces31d,31eare formed by curving the bottom face of the spectroscopic prism31into a predetermined form.

Nonlinear optical crystals of ZnTe and the like, antenna elements such as optical switches using GaAs, semiconductors such as InAs, and superconductors, for example, can be used as the terahertz-wave generator32. The pulse of the terahertz wave T generated from these elements is in the order of several picoseconds in general. When a nonlinear optical crystal is used as the terahertz-wave generator32, the pump light48incident on the terahertz-wave generator32, if any, is converted into the terahertz wave T by a nonlinear optical effect.

Electrooptical crystals of ZnTe and the like and antenna elements such as optical switches using GaAs, for example, can be used as the terahertz-wave detector33. When the terahertz wave T and the probe light49are incident on the terahertz-wave detector33at the same time in the case where an electrooptical crystal is used as the terahertz-wave detector33, the probe light49incurs birefringence due to the Pockels effect. The amount of birefringence in the probe light49is in proportion to the electric field intensity of the terahertz wave T. Therefore, detecting the amount of birefringence of the probe light49makes it possible to detect the terahertz wave T.

For example, a thermosetting adhesive is used for securing the terahertz-wave generator32and the terahertz-wave detector33. Preferably, the adhesive used here is transparent at the wavelength of the terahertz wave T and has a refractive index in the middle between or equivalent to each of the respective refractive indexes of the terahertz-wave generator32and terahertz-wave detector33and the refractive index of the spectroscopic prism31.

A wax transparent at the wavelength of the terahertz wave T may be melted and coagulated in place of the adhesive, or marginal parts of the terahertz-wave generator32and terahertz-wave detector33may be secured with the adhesive while the terahertz-wave generator32and terahertz-wave detector33are in direct contact with the entrance surface31aand exit surface31b, respectively.

When the terahertz-wave detector33is an electrooptical crystal, the detection unit4for detecting the terahertz wave is constituted by a quarter wave plate41, a polarizer42, a pair of photodiodes43,43, a differential amplifier44, and a lock-in amplifier47, for example, as illustrated inFIG. 1. The probe light49reflected by the terahertz-wave detector33is guided by the mirror45toward the detection unit4, condensed by a lens46, so as to be transmitted through the quarter wave plate41, and then separated by the polarizer42, which is a Wollaston prism or the like, into vertical and horizontal linearly polarized light components. The vertical and horizontal linearly polarized light components of the probe light49are converted into their respective electric signals by the pair of photodiodes43,43, while the difference therebetween is detected by the differential amplifier44. The output signal from the differential amplifier44is amplified by the lock-in amplifier47and then fed to the data analyzer6.

The differential amplifier44outputs a signal having an intensity in proportion to the electric field intensity of the terahertz wave T when the terahertz wave T and the probe light49are incident on the terahertz-wave detector33at the same time, but no signal when not. The amplitude and phase of the terahertz wave T in the arrangement part31cof the spectroscopic prism31vary depending on the object34arranged in the arrangement part31c. Therefore, measuring the change in amplitude and phase of the terahertz wave T can evaluate the spectroscopic characteristic of the object34.

The data analyzer6is a part which performs data analysis processing of transmission spectrometry according to an analysis program exclusively used by the terahertz-wave spectrometer1, for example, and is physically a computer system having a CPU (central processing unit), a memory, an input device, the display unit7, and the like. The data analyzer6executes data analysis processing according to a signal fed from the lock-in amplifier47and causes the display unit7to display results of analysis.

The structure of the arrangement part31cof the above-mentioned integral prism3will now be explained further in detail.

As illustrated inFIG. 2, the arrangement part31cof the integral prism3is constructed by a depression51ahaving a triangular cross section formed between side faces of the integral prism3. The depression51ahas a first refractive surface52for refracting the terahertz wave T from the first optical surface31dtoward the object34and a second refractive surface53for refracting the terahertz wave T transmitted through the object34toward the second optical surface31e.

The depression51ais filled with a liquid50. The liquid50is required to be incapable of dissolving the object34therein and preferably does not absorb the terahertz wave T. As the liquid50, a fluorine-based inert liquid, a silicone oil, or the like is used. Examples of the fluorine-based inert liquid include perfluorocarbon, hydrofluorocarbon, and perfluoropolyether.

Among these liquids, perfluorocarbon is preferred in particular in its insolubility and absorbability. Fluorine-based inert liquids and silicone oils are preferred in that they are hard to vaporize and thus prevent volatile ingredients from adversely affecting the surroundings, while suppressing environmental load. By “incapable of absorbing the terahertz wave” is meant herein that the absorbing coefficient for terahertz waves at 0.1 THz to 10 THz is 20 cm−1or less, more preferably 10 cm−1or less, for example.

When the spectroscopic prism31is made of Si having a refractive index of 3.4, the refractive index of the liquid50filling the depression51ais 1.4, and the incidence angle θi of the terahertz wave T with respect to the spectroscopic prism31is 45°, the opening angle δ of the depression51ahaving the triangular cross section is 67.3°, for example. Any jig (not depicted) may be used for holding the object34within the depression51a. The object34is held substantially orthogonal to the terahertz wave T entering the arrangement part31c.

As illustrated inFIG. 3, blocks35,35are bonded to both side faces of the integral prism3, respectively. The blocks35,35form walls on both sides of the depression51aopening to both side faces of the integral prism, thereby allowing the depression51ato be filled with the liquid50. For securely preventing the liquid50from leaking out of the depression51afilled therewith, it is preferred for the integral prism3and the block35to be bonded together with an adhesive made of silicone rubber or the like interposed therebetween.

FIG. 4is a flowchart illustrating a procedure of deriving an optical constant of the object34by transmission spectrometry using the above-mentioned terahertz-wave spectrometer1.

First, as illustrated in the flowchart, the terahertz-wave spectrometer1is used for performing reference measurement and sample measurement (steps S01and S02). In the reference measurement, the depression51ais filled with the liquid50, and a substance (the liquid50here) having a known optical constant is measured. In the sample measurement, the object34is arranged in the depression51afilled with the liquid50, so as to measure a substance to obtain an optical constant. Subsequently, a reference measurement result Trefand a sample measurement result Tsigare Fourier-transformed, so as to determine a reference amplitude Rref, a reference phase φref, a sample amplitude Rsig, and a sample phase φsig(step S03).

Next, a transmittance T is determined by the following expression (1) according to the reference amplitude Rrefand sample amplitude Rsig, and a phase difference Δ between the reference phase φrefand the sample phase φsigare determined by the following expression (2) (step S04).

These values are represented by using the complex refractive index of the object34(expression (3)) as the following expression (4). In expression (4), tref sigand tsig refare transmission Fresnel coefficients which are represented by the following expressions (5) and (6), respectively.

Therefore, the complex refractive index of the object34can be determined from the simultaneous equations of the following expressions (7) and (8), whereby a desirable optical constant of the object34is derived (step S05).

In the terahertz-wave spectrometer1, as explained in the foregoing, the arrangement part31cto be arranged with the object34in the spectroscopic prism31is the depression51a, which is filled with the liquid50incapable of dissolving the object34therein. Therefore, in a path of the terahertz wave T impinging on the first optical surface31dand then passing through the arrangement part31ctoward the second optical surface31e, the terahertz wave T can be kept from traveling through air.

This can eliminate the influence of absorption by the moisture in the air, thereby improving the measurement accuracy in spectrometry. The depression51amay have various forms but can easily be filled with the liquid50regardless of the forms, whereby the convenience of measurement is maintained.

The depression includes the first refractive surface52for refracting the terahertz wave T from the first optical surface31dtoward the object34and the second refractive surface53for refracting the terahertz wave T transmitted through the object34toward the second optical surface31e. When refracting P-polarized light at an interface between media having different refractive indexes, appropriately setting the angle of incidence with respect to the interface can reduce reflection loss as compared with the case where the light is perpendicularly incident on the interface and transmitted therethrough without refraction. This is clear from the fact that the reflectance of light transmitted through the interface between media having different refractive indexes is calculated by the following expressions (9) and (10):

Therefore, the reflection loss of the terahertz wave T directed from the first optical surface31dto the object34can be reduced when the depression51aincludes the first refractive surface52, while the reflection loss of the terahertz wave T passing through the object34toward the second optical surface31ecan be reduced when the depression includes the second refractive surface53. For example, in the case where the refractive index of the spectroscopic prism31and the liquid50filling the depression51ahave refractive indexes of 3.4 and 1.4, respectively, the reflection loss occurring when the terahertz wave is made perpendicularly incident on the interface between the spectroscopic prism31and the liquid50reaches 31.8% on the entrance and exit sides of the liquid50in total. When the depression51aincludes the first and second refractive surfaces52,53, by contrast, appropriately setting the angles of the first and second refractive surfaces52,53can cut down the reflection loss to about 0.1%. This can more securely eliminate the influence of the reflection loss of the terahertz wave, thereby further improving the measurement accuracy in spectrometry.

FIG. 5is a set of charts illustrating results of measuring absorption coefficients of the object34by using the terahertz-wave spectrometer.FIG. 5(a)is a chart when using glucose anhydrate as the object34, andFIG. 5(b)is a chart when using glucose hydrate as the object34. The plotted conventional example was acquired when the object arranged in air without using the integral prism3was irradiated with the terahertz wave.

The results illustrated in the charts show that, in each sample, the example eliminates the influences of absorption by moisture in the air and the influence of the reflection loss, so as to improve the S/N ratio as compared with the conventional example, thereby yielding vivid absorption peaks in the absorption curve. In the example, the object34is insoluble to the liquid50, from which it can be determined that the obtained absorption coefficient is an absorption coefficient inherent in the substance of the object34. This also makes it possible to reuse the object34after the measurement.

The present invention is not limited to the above-mentioned embodiment.FIGS. 6 and 7are diagrams illustrating modified examples of the spectroscopic prism. In the example illustrated inFIG. 6, the solid object34is formed into a disk, for instance. The apex of the bottom portion of the depression51aforming the arrangement part31cis provided with a recess for fitting the lower part of the object34, whereby the spectroscopic prism31is formed with a support part54for supporting the object34. This can stabilize the posture of the object34within the arrangement part31c, thereby further improving the measurement accuracy. The solid object34may be secured to a holder, whose bottom part is supported by the support part54.

In an example illustrated inFIG. 7, a disk-shaped cell55is filled with the liquid object34, for instance. The spectroscopic prism31is formed with the support part54similar to that inFIG. 6, and the lower part of the cell55is fitted into the recess, whereby the cell55is supported. This makes the object34easy to arrange into and take out from the arrangement part31cwhen the object34is a liquid.

The apex of the bottom portion of the arrangement part31cmay also be formed with a flat part as the support part54for the object34or cell55. As illustrated inFIG. 8, an opening56amay be formed in a plate-like member56larger than the width of the depression51a, and the plate-like member56having the object34or cell55inserted in the opening56amay cover the depression51a, so as to support the object34or cell55. The plate-like member56may be provided with a slide mechanism which can adjust the width of the opening56a.

FIG. 9is a diagram illustrating yet another modified example of the spectroscopic prism. In a spectroscopic prism36illustrated inFIG. 9, a side face36aserving as both entrance and exit surfaces is provided on one side, the first and second optical surfaces36c,36dare provided on both flanks of a side face36bopposite from the side face36a, and an arrangement part36eis provided at the center of the side face36b. The terahertz-wave generator32and terahertz-wave detector33are integrally secured to the side face36aso as to be juxtaposed horizontally. The first optical surface36cis disposed such as to reflect and collimate the terahertz wave T generated in the terahertz-wave generator32within the spectroscopic prism36. The second optical surface36dis disposed such as to reflect the terahertz wave T collimated by the first optical surface36c, so as to condense it toward the terahertz-wave detector33.

The arrangement part36eis constituted by a depression57formed at the center of the side face36b. The depression57opens not only to the side face36bof the spectroscopic prism36, but also to its upper face36f, thereby exhibiting a rectangular form in planar view. A plate material37is bonded to the side face36bof the spectroscopic prism36. This forms a wall on the side face36bside of the depression57, thereby allowing the depression57to be filled with the liquid50from thereabove. Two side faces57a,57aof the depression57opposing each other are disposed perpendicular to the path of the terahertz wave T directed from the first optical surface36cto the second optical surface36d.

In this spectroscopic prism36, the terahertz wave T is perpendicularly incident on the two side faces57a,57aserving as the interfaces between the spectroscopic prism36and the liquid50and passes through the liquid50without refraction. In place of the depression57in the example ofFIG. 9, a depression58opening to only the upper face36fof the spectroscopic prism36may be provided as illustrated inFIG. 10. This enables the depression58to be filled with the liquid50without bonding the plate material37to the spectroscopic prism36.

INDUSTRIAL APPLICABILITY

The present invention can be utilized in transmission spectrometry.

REFERENCE SIGNS LIST