JP2015155843A - Terahertz wave measurement device, terahertz wave measurement method, computer program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a terahertz wave measurement device and a terahertz wave measurement method capable of suitably separating a plurality of terahertz waves and detecting the separated waves, as well as a computer program and a recording medium.

SOLUTION: A terahertz wave measurement device 1 comprises: emission means 100 for emitting terahertz waves equal in polarization; polarization state change means 230 for changing the polarization state by causing a phase difference to occur in the terahertz waves; separation means 250 for separating the terahertz waves whose polarization states were changed by the polarization state change means; and detection means 310, 320 for detecting each of the terahertz waves separated by the separation means.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a technical field of a terahertz wave measuring apparatus and a terahertz wave measuring method capable of performing various measurements by detecting a terahertz wave reflected or transmitted by an object to be measured, for example, and a computer program and a recording medium.

  In recent years, research and development of terahertz wave imaging has been activated, and there are expectations for its application to nondestructive inspection and the like. The nondestructive inspection is realized by the technique disclosed in Patent Document 1, for example. Specifically, Patent Document 1 proposes a technique of measuring the thickness of a coating film based on a time difference at which a plurality of terahertz waves reflected on the coating film are detected.

  On the other hand, Patent Document 2 proposes a technique of canceling the polarization rotation due to birefringence by changing the polarization state of the terahertz wave by an electric field changing portion (photonic crystal plate).

Japanese Patent No. 4046158 JP 2010-2214 A

  When measuring the thickness of a measurement sample, it is required to detect a plurality of reflected terahertz waves separately. However, when the thickness of the measurement sample becomes smaller than a certain width with respect to the pulse width of the terahertz wave (for example, when the thickness of the measurement sample becomes smaller than the half width of the terahertz wave), it becomes difficult to separate the plurality of terahertz waves. End up. On the other hand, the techniques described in Patent Documents 1 and 2 described above do not exhibit the effect of increasing the resolution in the depth direction of the measurement sample, and as a result, a plurality of terahertz waves cannot be separated, resulting in thickness measurement. This creates a technical problem that cannot be done.

  Examples of problems to be solved by the present invention include the above. An object of the present invention is to provide a terahertz wave measuring apparatus, a terahertz wave measuring method, a computer program, and a recording medium that are capable of suitably separating and detecting a plurality of terahertz waves.

  A terahertz wave measuring apparatus that solves the above problems includes an emitting unit that emits a terahertz wave with uniform polarization, a polarization state changing unit that changes a polarization state by causing a phase difference in the terahertz wave, and the polarization state change Separating means for separating the terahertz wave whose polarization state has been changed by means, and detecting means for detecting each of the terahertz waves separated by the separating means.

  A terahertz wave measuring method that solves the above problems includes an emission step of emitting terahertz waves with uniform polarization, a polarization state changing step of changing a polarization state by causing a phase difference in the terahertz wave, and the polarization state change A separation step of separating the terahertz wave whose polarization state has been changed in the step; and a detection step of detecting each of the terahertz waves separated in the separation step.

  A computer program for solving the above problems includes an emission step of emitting a terahertz wave with uniform polarization, a polarization state changing step of changing a polarization state by causing a phase difference in the terahertz wave, and the polarization state changing step. A computer executes a separation step of separating the terahertz wave whose polarization state has been changed, and a detection step of detecting each of the terahertz waves separated in the separation step.

  The computer program described above is recorded on a recording medium that solves the above problems.

It is the schematic which shows the whole structure of the terahertz wave measuring device which concerns on 1st Example. It is a side view which shows the reflected light in each interface with the laminated structure of a sample. It is a transition diagram which shows the change of the polarization state of a terahertz wave. It is a wave form diagram which shows the signal detected in the terahertz wave measuring device which concerns on a comparative example. It is a wave form diagram which shows the signal detected with the 2nd terahertz wave detection element of the terahertz wave measuring device which concerns on 1st Example. It is a wave form diagram which shows the signal detected by the 1st terahertz wave detection element of the terahertz wave measuring device which concerns on 1st Example. It is the schematic which shows the whole structure of the terahertz wave measuring device which concerns on 2nd Example.

<1>
The terahertz wave measuring apparatus according to the present embodiment includes an emitting unit that emits a terahertz wave with uniform polarization, a polarization state changing unit that changes a polarization state by causing a phase difference in the terahertz wave, and the polarization state change. Separating means for separating the terahertz wave whose polarization state has been changed by means, and detecting means for detecting each of the terahertz waves separated by the separating means.

According to the terahertz wave measuring apparatus of the present embodiment, a terahertz wave is emitted from the emission means during the operation. A terahertz wave is an electromagnetic wave belonging to a frequency region (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). The emitting means includes a generating element configured as, for example, a photoconductive antenna (PCA) or a resonant tunneling diode (RTD), and emits a terahertz wave with uniform polarization. . Here, “alignment of polarized light” may be a state aligned with linearly polarized light or a state aligned with circularly polarized light, and may be substantially uniform temporally and spatially (ie, The polarization is not necessarily random).

  The polarization state of the emitted terahertz wave is changed by the polarization state changing means. The polarization state changing means is configured as an optical member such as a quarter-wave plate whose angle can be adjusted, for example. According to the polarization state changing means, for example, the polarization state can be adjusted for each of a plurality of terahertz waves having different phase differences caused by reflection at different interfaces of the object to be measured. For example, the polarization state changing unit changes the polarization state so that the terahertz wave can be appropriately separated by the separation unit described later.

  The terahertz wave whose polarization state has been changed is separated by the separation means according to, for example, a difference in polarization state (in other words, a phase difference). That is, when a plurality of terahertz waves having different polarization states are generated, they are separated as at least two terahertz waves. Separation of terahertz waves can be realized by, for example, reflecting or transmitting a plurality of terahertz waves in different directions using a polarizer. Alternatively, the state of emitting only one of the plurality of terahertz and the state of emitting only the other may be switched and separated on the time axis.

  The separated terahertz waves are detected by detection means including a photoconductive antenna and a resonant tunnel diode, for example. A plurality of detection means may be provided so as to correspond to each of a plurality of separated terahertz waves, or a plurality of terahertz waves may be detected by one detection means. The terahertz wave detected by the detection means is converted into an electric signal and used for various measurements. Specifically, the thickness of the object to be measured can be measured based on the peak widths of a plurality of terahertz waves.

  As described above, according to the terahertz wave measuring apparatus according to the present embodiment, a plurality of terahertz waves can be separated and detected. In particular, in this embodiment, since the separation of terahertz waves can be realized by the difference in polarization state, for example, even when the pulse intervals of a plurality of terahertz are narrow and the peak positions overlap, the separation can be suitably performed. .

<2>
In one aspect of the terahertz wave measuring apparatus according to the present embodiment, the emitting unit emits the terahertz wave toward the object to be measured, and the separating unit separates the terahertz wave reflected by the object to be measured. The polarization state changing means is arranged at least one between the emitting means and the object to be measured, or between the object to be measured and the separating means.

  According to this aspect, the terahertz wave emitted from the emitting means is emitted toward the object to be measured, and the terahertz wave reflected (scattered) by the object to be measured is separated by the separating means. If a plurality of terahertz waves separated in this way are detected, the shape, properties, etc. of the object to be measured can be measured.

  Here, in particular, the polarization state changing unit according to the present embodiment is disposed between at least one of the emission unit and the measurement object, or between the measurement object and the separation unit. Thereby, for example, when the polarization state changing means is arranged between the emitting means and the object to be measured, the terahertz wave emitted from the emitting means is changed to the object to be measured after the polarization state is changed by the polarization state changing means. Will be irradiated. On the other hand, when the polarization state changing means is arranged between the object to be measured and the separating means, the terahertz wave emitted from the emitting means is reflected by the object to be measured and then the polarization state is changed in the polarization state changing means. Is done.

  As described above, the timing at which the polarization state of the terahertz wave is changed varies depending on the arrangement position of the polarization state changing means. However, the effect on the terahertz wave (that is, the effect of changing the polarization state) does not change regardless of the position of the polarization state changing means. Therefore, the arrangement position of the polarization state changing means can be appropriately determined according to various specifications such as the device configuration and design items.

<3>
In the aspect of separating the terahertz waves reflected by the object to be measured as described above, the object to be measured has the first layer, the second layer, and the third layer having different refractive indexes stacked in order as viewed from the emitting unit side. And the separation means is reflected at the interface between the first layer and the second layer and the interface between the second layer and the third layer. The terahertz wave may be separated.

  In this case, the object to be measured has a first layer, a second layer, and a third layer having different refractive indexes. And these three layers are laminated | stacked in order of the 1st layer, the 2nd layer, and the 3rd layer seeing from the radiation | emission means side. Therefore, the terahertz wave emitted from the emission means first enters the first layer, then enters the second layer, and finally enters the third layer. Note that the three layers of the object to be measured are configured to contact each other, and there are interfaces between the first layer and the second layer, and interfaces between the second layer and the third layer.

In the separation unit according to the present embodiment, the terahertz wave reflected from the object to be measured is reflected at the interface between the first layer and the second layer and the interface between the second layer and the third layer. Are separated from each other. Therefore, it is possible to separately detect the terahertz wave reflected at the interface between the first layer and the second layer and the terahertz wave reflected at the interface between the second layer and the third layer.
<4>
In the aspect in which the terahertz wave is irradiated to the measurement object having the laminated structure as described above, the measurement of measuring the thickness of the second layer based on the difference between the peak positions of the terahertz waves separated by the separation unit. Means may further be provided.

  In this case, based on the difference between the peak position of the terahertz wave reflected at the interface between the first layer and the second layer and the peak position of the terahertz wave reflected at the interface between the second layer and the third layer by the measuring means. Then, the thickness of the second layer is measured. For example, the physical thickness can be obtained by dividing the optical thickness obtained from the difference between the peak values of two terahertz waves by the refractive index.

  In the present embodiment, for example, terahertz waves can be separated depending on the polarization state, so that each terahertz wave can be appropriately detected even when the peak positions of the terahertz waves reflected by the two interfaces are very close. Therefore, even if the thickness of the second layer is extremely thin, thickness measurement can be suitably performed.

<5>
In another aspect of the terahertz wave measuring apparatus according to this embodiment, the separation unit separates the terahertz waves having different polarization states by emitting the terahertz waves in different directions.

  According to this aspect, the separating unit includes, for example, a wire grid polarizer and the like, and emits terahertz waves having different polarization states in different directions. For example, the separating unit reflects one terahertz wave and transmits the other terahertz wave. Thus, one terahertz wave and the other terahertz follow different optical paths, and as a result, a plurality of terahertz waves can be separated.

<6>
In another aspect of the terahertz wave measuring apparatus according to the present embodiment, the separating unit switches between a state of emitting one of the terahertz waves having different polarization states and a state of emitting the other of the terahertz waves and separates them.

  According to this aspect, the state of emitting one of the terahertz waves having different polarization states and the state of emitting the other are selectively realized by the separating unit. Thereby, in a state where one terahertz wave is emitted, it is possible to detect one terahertz wave by the detecting means. In the state where the other terahertz wave is emitted, the other terahertz wave can be detected by the detecting means. Thus, in this aspect, it is possible to separate a plurality of terahertz waves on the time axis.

<7>
The terahertz wave measuring method according to the present embodiment includes an emission step of emitting terahertz waves with uniform polarization, a polarization state changing step of changing a polarization state by causing a phase difference in the terahertz wave, and the polarization state change A separation step of separating the terahertz wave whose polarization state has been changed in the step; and a detection step of detecting each of the terahertz waves separated in the separation step.

  According to the terahertz wave measuring method according to the present embodiment, a plurality of terahertz waves can be separated and detected as in the above-described terahertz wave measuring apparatus.

  Note that the terahertz wave measuring method according to the present embodiment can also adopt various aspects similar to the various aspects of the terahertz wave measuring apparatus according to the present embodiment described above.

<8>
The computer program according to the present embodiment includes an emission step of emitting terahertz waves with uniform polarization, a polarization state changing step of changing a polarization state by causing a phase difference in the terahertz waves, and the polarization state changing step. A computer executes a separation step of separating the terahertz wave whose polarization state has been changed, and a detection step of detecting each of the terahertz waves separated in the separation step.

  According to the computer program according to the present embodiment, a plurality of terahertz waves can be separated and detected as in the above-described terahertz wave measuring apparatus and terahertz wave measuring method.

  Note that the computer program according to the present embodiment can also adopt various aspects similar to the various aspects of the terahertz wave measuring apparatus according to the present embodiment described above.

<9>
The recording medium according to the present embodiment records the computer program according to the present embodiment described above.

  According to the recording medium according to the present embodiment, a plurality of terahertz waves can be separated and detected by executing a recorded computer program.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, a case where the terahertz wave measuring apparatus of the present invention is applied to an apparatus that measures the thickness of an object to be measured using terahertz waves will be described.

<First embodiment>
First, the configuration of the terahertz wave measuring apparatus 1 according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing the overall configuration of the terahertz wave measuring apparatus according to the first embodiment.

  In FIG. 1, the terahertz wave measuring apparatus 1 according to the first embodiment is configured to irradiate a sample 500 that is a measurement target with a terahertz wave and detect the terahertz wave reflected by the sample 500.

  Specifically, the terahertz wave measuring apparatus 1 includes an erbium-doped fiber laser 10, fiber beam splitters 20 and 30, a terahertz wave generating element 100, a collimator lens 210, an objective lens 220, and a quarter wavelength plate 230. A mirror 240, a polarizer 250, condenser lenses 260 and 270, a first terahertz wave detecting element 310, a second terahertz wave detecting element 320, and an optical delay mechanism 400.

  The erbium-doped fiber laser 10 is configured to emit laser light for generating a terahertz wave element. Laser light emitted from the erbium-doped fiber laser 10 enters the fiber beam splitter 20.

  The fiber beam splitter 20 separates the incident light and emits it toward each of the terahertz wave generating element 100 and the optical delay mechanism 400. The fiber beam splitter 30 separates the incident light and emits the light toward each of the first terahertz wave detection element 310 and the second terahertz wave detection element 320.

  The terahertz wave generating element 100 includes, for example, a photoconductive antenna and a resonant tunnel diode, and generates a terahertz wave according to incident laser light. The terahertz wave generating element 100 is an example of the “exiting means” in the present invention, and emits terahertz waves having a uniform polarization state.

  The collimating lens 210 guides the terahertz wave emitted from the terahertz wave generating element 100 to the sample direction as parallel light.

  The objective lens 220 collects the terahertz wave incident from the collimator lens 210 (that is, from the terahertz wave generating element 100 side) and irradiates the sample 500 with it. The objective lens 220 emits the terahertz wave reflected by the sample 500 toward ¼ as parallel light (that is, toward the first terahertz wave detection element 310 and the second terahertz wave detection element 320 side).

  The quarter-wave plate 230 is made of, for example, a birefringent crystal, and emits the incident terahertz wave with a predetermined phase difference. For this reason, the polarization state of the terahertz wave that has passed through the quarter-wave plate 230 changes. The quarter wavelength plate 230 is an example of the “polarization state changing unit” in the present invention.

  The mirror 240 is configured to include a material having a high reflectivity with respect to the terahertz wave, and reflects the terahertz wave emitted from the quarter wavelength plate 230 toward the polarizer 250.

  The polarizer 250 is configured as a wire grid polarizer, for example, and transmits a terahertz wave that is one polarization state and reflects a terahertz wave that is another polarization state. For this reason, of the terahertz waves incident on the polarizer 250, the terahertz wave in one polarization state is emitted toward the condenser lens 260 (that is, toward the first terahertz wave detection element 310). On the other hand, among the terahertz waves incident on the polarizer 250, terahertz waves having other polarization states are emitted toward the condenser lens 270 (that is, toward the second terahertz wave detection element 320). The polarizer 250 is an example of the “separating means” in the present invention.

  The condensing lenses 260 and 270 collect each of the terahertz separated in the polarizer 250 and irradiate the first terahertz wave detection element 310 and the second terahertz wave detection element 320, respectively.

  The first terahertz wave detection element 310 and the second terahertz wave detection element 320 are configured to include, for example, a photoconductive antenna and a resonant tunnel diode, detect terahertz waves and convert them into electrical signals, and a processing unit (not shown) Etc. Laser light is incident on the first terahertz wave detecting element 310 and the second terahertz wave detecting element 320 via the optical delay mechanism 400 and the beam fiber splitter 30. Each of the first terahertz wave detecting element 310 and the second terahertz wave detecting element 320 is an example of the “detecting means” in the present invention.

  The optical delay mechanism 400 generates an arbitrary delay in the incident terahertz wave, for example, by changing the position of the internal mirror, and emits it. As a result, a delay occurs between the laser light incident on the terahertz wave generating element 100 and the laser light incident on the first terahertz wave detecting element 310 and the second terahertz wave detecting element 320.

  Next, with reference to FIG. 2, the laminated structure of the sample 500 and the reflection of the terahertz wave in the sample 500 will be specifically described. FIG. 2 is a side view showing the reflected light at each interface together with the laminated structure of the sample.

  In FIG. 2, a sample 500 includes a first layer 510, a second layer 520, and a third layer 530 in order from the incident direction of the terahertz wave. The refractive index of the first layer 510 is n1, the refractive index of the second layer 520 is n2, and the refractive index of the third layer 530 is n3. That is, the first layer 510, the second layer 520, and the third layer 530 are configured as layers having different refractive indexes.

  In such a sample 500, the interface between the first layer 510 and the second layer 520 (hereinafter referred to as “first interface” as appropriate) and the interface between the second layer 520 and the third layer 530 (hereinafter referred to as appropriate). It is considered that the terahertz wave is reflected at the “second interface”). Then, in the terahertz wave reflected at the first interface, a phase difference δ1 corresponding to the refractive index n1 of the first layer 510 and the refractive index n2 of the second layer 520 is generated. Similarly, in the terahertz wave reflected at the second interface, a phase difference δ2 corresponding to the refractive index n2 of the second layer 520 and the refractive index n3 of the third layer 530 is generated. Therefore, the terahertz wave reflected at the first interface and the terahertz wave reflected at the second interface are in different polarization states.

  Next, a change in the polarization state of the terahertz wave will be specifically described with reference to FIG. FIG. 3 is a transition diagram showing changes in the polarization state of the terahertz wave.

  As shown in FIG. 3A, the terahertz wave generating element 100 generates linearly polarized terahertz waves. The terahertz waves are reflected at each interface of the sample 500, so that two terahertz waves having different polarization states are obtained. Specifically, the terahertz wave reflected at the first interface is in a polarization state as shown in FIG. 3B due to the phase shift of δ1. On the other hand, the terahertz wave reflected at the second interface is in a polarization state as shown in FIG. 3C due to the phase shift of δ2.

  The terahertz wave reflected by the sample 500 is further given a phase difference in the quarter-wave plate 230. For this reason, the polarization states of the two terahertz waves having different polarization states due to the reflection of the sample 500 are polarized. Specifically, the terahertz wave reflected by the first interface is in a polarization state (that is, linearly polarized light) as shown in FIG. On the other hand, the terahertz wave reflected by the second interface is in a polarization state as shown in FIG.

  Next, with reference to FIG. 4 to FIG. 6, the separation of the terahertz wave due to the difference in polarization state will be described in detail. FIG. 4 is a waveform diagram showing signals detected in the terahertz wave measuring apparatus according to the comparative example. FIG. 5 is a waveform diagram showing signals detected by the second terahertz wave detecting element of the terahertz wave measuring apparatus according to the first embodiment, and FIG. 6 is a waveform diagram of the terahertz wave measuring apparatus according to the first embodiment. It is a wave form diagram which shows the signal detected with a 1 terahertz wave detection element.

  As shown in FIG. 4, in the comparative example in which the terahertz wave is detected without being separated, the terahertz wave reflected by the first interface (solid line) and the terahertz wave reflected by the second interface are close to each other. Detected. In such a case, if the peak positions of the terahertz waves are closer than the half width of the pulse, it is difficult to separate the terahertz waves after detection. Therefore, when using a terahertz wave with a wide pulse width or measuring a thin object to be measured, it is desirable to separate each terahertz wave before detection.

  On the other hand, in this embodiment, as a result of passing through the quarter wavelength plate 230, the terahertz wave in the polarization state shown in FIG. 3D and the terahertz wave in the polarization state shown in FIG. It is incident on the child 250. Here, in particular, the polarization direction of the terahertz transmitted through the polarizer 250 is set to a direction indicated by a broken line in FIG. 3D (that is, a direction orthogonal to the polarization direction of the terahertz wave reflected by the first interface). Is set to For this reason, the terahertz wave reflected by the first interface is reflected almost entirely by the polarizer 250. In other words, the terahertz wave reflected by the first interface hardly transmits the polarizer 250. On the other hand, the terahertz wave reflected at the second interface has a polarization state that is relatively close to the polarization direction that the polarizer 250 transmits. For this reason, most of the terahertz waves reflected at the second interface are transmitted through the polarizer 250 and only a part is reflected.

  In FIG. 5, as a result of the above, in the reflection direction of the polarizer 250 (that is, in the direction of the second terahertz wave detection element 320), almost all of the terahertz waves reflected at the first interface and the second interface are reflected. A small part of the terahertz wave is guided. Therefore, the peak of the terahertz wave (solid line) reflected from the first interface can be obtained from the output of the second terahertz wave detecting element 320.

  In FIG. 6, in the transmission direction of the other polarizer 250 (that is, in the direction of the first terahertz wave detection element 310), the terahertz wave reflected at the first interface is hardly transmitted and the terahertz reflected at the second interface is reflected. Most of the waves are guided. Therefore, the peak of the terahertz wave (broken line) reflected at the second interface can be obtained from the output of the first terahertz wave detecting element 310.

  As a result, according to the terahertz wave measuring apparatus 1 according to the present embodiment, the terahertz wave reflected by the first interface and the terahertz wave reflected by the second interface can be suitably separated and detected. Note that the thickness of the second layer 520 is calculated from the detected peak position of each terahertz wave by arithmetic processing. Specifically, when the peak position of the terahertz wave reflected at the first interface is x and the peak position of the terahertz wave reflected at the second interface is y, the optical thickness d1 of the second layer 520 is as follows: It is obtained by the mathematical formula (1).

d1 = y−x (1)
Furthermore, if the refractive index n2 of the second layer 520 is used, the physical thickness d2 of the second layer 520 can be obtained by the following formula (2).

d2 = (y−x) / n2 (2)
As described above, according to the terahertz wave measuring apparatus 1 according to the present embodiment, the thickness of the object to be measured can be suitably measured by separating and detecting the terahertz wave using the difference in polarization state.

  In the above-described embodiments, the case where two terahertz waves are separated has been described. However, for example, by providing a plurality of polarizers 250, it is possible to separate three or more terahertz waves. In this case, three or more terahertz wave detection elements may be arranged.

<Second embodiment>
Next, the configuration of the terahertz wave measuring apparatus 2 according to the second embodiment will be described with reference to FIG. FIG. 7 is a schematic diagram showing the overall configuration of the terahertz wave measuring apparatus according to the second embodiment. The second embodiment differs from the first embodiment described above only in part of the configuration, and the other points are substantially the same. For this reason, below, a different part from 1st Example already demonstrated is demonstrated in detail, and description shall be abbreviate | omitted suitably about another overlapping part.

  In FIG. 7, in the terahertz wave measuring apparatus 2 according to the second embodiment, only one terahertz wave detecting element is provided. That is, only the first terahertz wave detecting element 310 is provided, and the second terahertz wave detecting element 320 shown in FIG. 1 is not provided.

  In addition, a polarizer 250b is provided in front of the first terahertz wave detection element 310. The polarizer 250b is configured to be able to adjust the polarization direction of the transmitted terahertz wave.

  The quarter wavelength plate 230 according to the second embodiment is provided on the forward path side with respect to the sample 500. In other words, the quarter wavelength plate 230 is provided to cause a phase difference in the terahertz wave before being irradiated on the sample 500. However, the arrangement position of the quarter-wave plate 230 does not affect its function. That is, even if the quarter wave plate 230 changes the polarization state of the terahertz wave reflected by the sample 500 as in the first embodiment, or the quarter wave plate 230 as in the second embodiment. Even when the polarization state of the terahertz wave before being reflected by the sample 500 is changed, the contribution to the separation of the terahertz wave is the same. In addition, you may comprise so that the quarter wavelength plate 230 may be passed through both before and after irradiation to the sample 500.

  During operation of the terahertz wave measuring apparatus 2 according to the second embodiment, the angles of the quarter-wave plate 230 and the polarizer 250 are adjusted so that the terahertz wave reflected at the first interface is almost transmitted through the polarizer 250b. Is done. In this case, the terahertz wave reflected by the first interface and the terahertz wave reflected by the second interface having a different polarization state hardly pass through the quarter-wave plate. Therefore, the first terahertz wave detecting element 310 can suitably detect the peak of the terahertz wave reflected by the first interface.

  Subsequently, the angles of the quarter-wave plate 230 and the polarizer 250 are adjusted so that the terahertz wave reflected by the second interface is almost transmitted through the polarizer 250b. In this case, the terahertz wave reflected by the second interface and the terahertz wave reflected by the first interface having a different polarization state hardly pass through the quarter wavelength plate. Therefore, the first terahertz wave detecting element 310 can suitably detect the peak of the terahertz wave reflected by the second interface.

  As described above, in the terahertz wave measuring apparatus 2 according to the second embodiment, similarly to the terahertz wave measuring apparatus 1 according to the first embodiment, terahertz waves having different polarization states can be suitably separated and detected. it can. Accordingly, the thickness of the sample 500 can be suitably measured based on the detected peak position of each terahertz wave.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification, and terahertz wave measurement with such a change is possible. An apparatus, a terahertz wave measuring method, a computer program, and a recording medium are also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1, 2 Terahertz wave measuring apparatus 10 Erbium dope fiber laser 20, 30 Fiber beam splitter 100 Terahertz wave generating element 210 Collimating lens 220 Objective lens 230 1/4 wavelength plate 240 Mirror 250 Polarizer 260, 270 Condensing lens 310 1st terahertz Wave detection element 320 Second terahertz wave detection element 400 Optical delay mechanism 500 samples

Claims (9)

Emitting means for emitting terahertz waves with uniform polarization;
Polarization state changing means for changing the polarization state by causing a phase difference in the terahertz wave;
Separating means for separating the terahertz wave whose polarization state has been changed by the polarization state changing means;
A terahertz wave measuring apparatus comprising: a detecting unit that detects each of the terahertz waves separated by the separating unit. The emitting means emits the terahertz wave toward the object to be measured,
The separation means separates the terahertz wave reflected by the object to be measured,
The polarization state changing means is arranged at least one between the emitting means and the object to be measured, or between the object to be measured and the separating means. Terahertz wave measuring device. The object to be measured has a laminated structure in which a first layer, a second layer, and a third layer having different refractive indexes are laminated in order from the emitting means side,
The separating means separates the terahertz wave reflected at the interface between the first layer and the second layer and the terahertz wave reflected from the interface between the second layer and the third layer. The terahertz wave measuring apparatus according to claim 2.   The terahertz wave measuring apparatus according to claim 3, further comprising a measuring unit that measures the thickness of the second layer based on a difference in peak positions of the terahertz waves separated by the separating unit. .   5. The terahertz wave measuring apparatus according to claim 1, wherein the separation unit separates the terahertz waves having different polarization states by emitting the terahertz waves in different directions. 6.   5. The separation unit according to claim 1, wherein the separation unit performs separation by switching between a state of emitting one of the terahertz waves having different polarization states and a state of emitting the other of the terahertz waves. Terahertz wave measuring device. An emission process for emitting terahertz waves with uniform polarization;
A polarization state changing step of changing a polarization state by causing a phase difference in the terahertz wave;
A separation step of separating the terahertz wave whose polarization state has been changed in the polarization state changing step;
And a detection step of detecting each of the terahertz waves separated in the separation step. An emission process for emitting terahertz waves with uniform polarization;
A polarization state changing step of changing a polarization state by causing a phase difference in the terahertz wave;
A separation step of separating the terahertz wave whose polarization state has been changed in the polarization state changing step;
A computer program causing a computer to execute a detection step of detecting each of the terahertz waves separated in the separation step.   A recording medium in which the computer program according to claim 8 is recorded.

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