JP2014106127A - Terahertz wave measurement instrument and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate cooling or heat dissipation of a generation element for generating a terahertz wave while suppressing the increase in size and cost of a terahertz wave measurement instrument.SOLUTION: A terahertz wave measurement instrument (100) includes: generation means (110) which is irradiated with a first laser beam (LB1) to generate a terahertz wave (T Hz); detection means (130) which is irradiated with a second laser beam (LB2) to detect a terahertz wave radiated to a measurement object; delay means (120) which gives a desired optical path length difference between an optical path length of the first laser beam and that of the second laser beam; and control means (143) which reduces the light intensity of the terahertz wave generated in a non-detection period other than a detection period determined in accordance with the optical path length difference given by the delay means, in which the detection means detects a terahertz wave, by the generation means in comparison with the light intensity of the terahertz wave generated in the detection period by the generation means.

Description

  The present invention relates to a technical field of a terahertz wave measuring apparatus and method for analyzing characteristics of a measurement object using, for example, a terahertz wave.

  As a terahertz wave measuring apparatus, an apparatus using terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy) is known. The terahertz wave measuring apparatus analyzes the characteristics of the measurement object according to the following procedure. First, pump light (in other words, excitation light), which is one laser light obtained by branching ultrashort pulse laser light (for example, femtosecond pulse laser light), generates terahertz waves to which a bias voltage is applied. The element is irradiated. As a result, the terahertz wave generating element generates a terahertz wave. The terahertz wave generated by the terahertz wave generating element is irradiated to the measurement object. The terahertz wave irradiated to the measurement object is another laser light obtained by branching the ultrashort pulse laser light as reflected light or transmitted light from the measurement object, and is optically delayed with respect to the pump light. In other words, the terahertz wave detecting element irradiated with the probe light (in other words, excitation light) to which the (optical path length difference) is applied is irradiated. As a result, the terahertz wave detecting element detects a current signal corresponding to the intensity of the terahertz wave reflected or transmitted by the measurement object. The detected terahertz wave (that is, a terahertz wave in the time domain and a current signal) is Fourier-transformed to obtain a spectrum (that is, frequency response characteristics of amplitude and phase) of the terahertz wave. As a result, the characteristics of the measurement object are analyzed by analyzing the spectrum of the terahertz wave.

  By the way, if the terahertz wave generating element is used for a relatively long time, the current that flows in the gap portion between two conductive elements (for example, a dipole antenna) included in the terahertz wave generating element increases abruptly. A problem occurs (for example, see Patent Document 1). One cause of the occurrence of such a technical problem is, for example, an increase in carriers that are thermally excited in the terahertz wave generating element. In order to solve such a technical problem, Patent Document 1 discloses a terahertz wave generating element that employs a cooling mechanism that cools the terahertz wave generating element or a heat dissipation mechanism that promotes heat dissipation of the terahertz wave generating element. A technique for suppressing a rapid increase in current flowing in a gap between two conductive elements provided is disclosed.

  In addition, there is Patent Document 2 as a document related to the present invention.

Japanese Patent Laid-Open No. 2004-22766 JP 2008-122306 A

  However, the technique disclosed in Patent Document 1 requires a new physical structure such as a cooling mechanism or a heat dissipation mechanism. Therefore, a new technical problem that leads to an increase in the size and cost of the terahertz wave measuring apparatus arises.

  Examples of problems to be solved by the present invention include the above. The present invention provides a terahertz wave measuring apparatus and method that can promote the cooling or heat dissipation of a generating element that generates a terahertz wave while suppressing an increase in the size and cost of the terahertz wave measuring apparatus. Let it be an issue.

  A terahertz wave measuring apparatus that solves the above-described problems is a generation unit that generates a terahertz wave by irradiating a first laser beam, and a measurement object from the generation unit by irradiating a second laser beam. Detecting means for detecting the terahertz wave irradiated to the optical path; adjusting means for adjusting an optical path length difference between the optical path length of the first laser light and the optical path length of the second laser light; and the detecting means Compared with the light intensity of the terahertz wave generated by the generating means during the detection period for detecting the terahertz wave and determined according to the optical path length difference adjusted by the adjusting means, other than the detection period And control means for reducing the light intensity of the terahertz wave generated by the generating means during a non-detection period that is a period of.

  In the terahertz wave measuring method for solving the above-described problem, the first laser beam is irradiated to generate a terahertz wave, and the second laser beam is irradiated to the target object from the generating unit. Terahertz wave measurement comprising detection means for detecting the terahertz wave irradiated to the terahertz wave, and adjustment means for adjusting a difference in optical path length between the optical path length of the first laser light and the optical path length of the second laser light A terahertz wave measuring method in an apparatus, wherein the detection means is a detection period for detecting the terahertz wave, and is a non-detection period that is a period other than the detection period determined according to the optical path length difference adjusted by the adjustment means And a step of setting the terahertz wave generated by the generating means during the non-detection period as compared to the light intensity of the terahertz wave generated by the generating means during the detection period. And a control step of reducing the strength.

It is a block diagram which shows the structure of the terahertz wave measuring device of 1st Example. It is a perspective view which shows each structure of a terahertz wave generation element and a terahertz wave detection element. It is a flowchart which shows the flow of adjustment operation | movement of the light intensity of the terahertz wave by the terahertz wave measuring apparatus of 1st Example. 3 shows the waveform of the measurement interval signal and the bias voltage observed when the adjustment operation shown in FIG. 3 is performed, together with the optical path length difference between the optical path of the pump light and the optical path of the probe light set by the optical delay device. It is a graph. The measurement interval signal and the waveform of the bias voltage observed when the adjustment operation shown in FIG. 3 is performed under the situation where the bias voltage is a direct current voltage, the optical path of the pump light set by the optical delay device and the probe light It is a graph shown with the optical path length difference between optical paths. It is a top view which shows the structure of the optical delay device with which the terahertz wave measuring device of 2nd Example is provided. The measurement interval signal and the bias voltage waveform observed when the terahertz wave measuring apparatus according to the second embodiment performs the adjustment operation shown in FIG. 3 are used as the optical path of the pump light and the optical path of the probe light set by the optical delay device. It is a graph shown with the optical path length difference between and. It is a block diagram which shows the structure of the terahertz wave measuring device of 3rd Example. It is a flowchart which shows the flow of adjustment operation | movement of the light intensity of the terahertz wave by the terahertz wave measuring apparatus of 3rd Example. The waveform of the measurement section signal drive current and the average light intensity of the pulsed laser light observed when the adjustment operation shown in FIG. 9 is performed is calculated between the optical path of the pump light and the optical path of the probe light set by the optical delay device. It is a graph shown with the optical path length difference between. It is a block diagram which shows the structure of the terahertz wave measuring device of 4th Example. It is a flowchart which shows the flow of adjustment operation | movement of the light intensity of the terahertz wave by the terahertz wave measuring apparatus of 4th Example. The waveform of the measurement section signal drive current and the average light intensity of the pump light observed when the adjustment operation shown in FIG. 12 is performed is determined between the optical path of the pump light and the optical path of the probe light set by the optical delay device. It is a graph shown with the optical path length difference. It is a block diagram which shows the structure of the terahertz wave measuring device of 5th Example. It is a flowchart which shows the flow of adjustment operation | movement of the light intensity of the terahertz wave by the terahertz wave measuring apparatus of 5th Example. The measurement interval signal, the bias voltage drive current, and the average light intensity waveform of the pulsed laser beam observed when the adjustment operation shown in FIG. It is a graph shown with the optical path length difference between optical paths. It is a block diagram which shows the structure of the terahertz wave measuring device of 6th Example. It is a flowchart which shows the flow of adjustment operation | movement of the light intensity of the terahertz wave by the terahertz wave measuring apparatus of 6th Example. 18 shows the waveform of the measurement interval signal and the bias voltage observed when the adjustment operation shown in FIG. 18 is performed, together with the optical path length difference between the optical path of the pump light and the optical path of the probe light set by the optical delay device. It is a graph.

  Hereinafter, embodiments of the terahertz wave measuring apparatus and method will be described in order.

(Embodiment of terahertz wave measuring apparatus)
<1>
The terahertz wave measuring apparatus according to the present embodiment is configured to generate a terahertz wave by irradiating the first laser beam and irradiate the second laser beam to the measurement target from the generating unit. Detecting means for detecting the terahertz wave irradiated in step, adjusting means for adjusting an optical path length difference between the optical path length of the first laser light and the optical path length of the second laser light, and the detecting means Compared with the light intensity of the terahertz wave generated by the generating means during the detection period for detecting the terahertz wave and determined according to the optical path length difference adjusted by the adjusting means, other than the detection period Control means for reducing the light intensity of the terahertz wave generated by the generating means during a non-detection period that is a period.

  According to the terahertz wave measuring apparatus of this embodiment, the operation of the generating unit, the detecting unit, and the adjusting unit causes the terahertz wave irradiated to the measurement object using the terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy). Detected. The detected terahertz wave is used for analyzing the characteristics of the measurement object. Note that an existing detection method may be used as the terahertz wave detection method itself using the terahertz time domain spectroscopy. An outline of a terahertz wave detection method using terahertz time domain spectroscopy will be briefly described below.

  Specifically, the generation unit generates a terahertz wave by irradiating the generation unit with the first laser light as excitation light (for example, pump light). The terahertz wave generated by the generating means is irradiated to the measurement object.

  The detection means detects the terahertz wave reflected by the measurement object or transmitted through the measurement object by irradiating the detection means with the second laser light as excitation light (for example, probe light).

  At this time, the adjusting means adjusts the optical path length difference between the optical path of the first laser beam and the optical path of the second laser beam. In other words, the adjusting means sets the optical path length difference between the optical path of the first laser beam and the optical path of the second laser beam to a desired value. In order to adjust the optical path length difference, the adjusting unit may adjust, for example, at least one of the optical path length of the first laser light and the optical path length of the second laser light. Such adjustment of the optical path length difference is performed in order to suitably detect the waveform of the terahertz wave that appears in the order of sub-picoseconds.

  Particularly in the present embodiment, the control means adjusts the light intensity of the terahertz wave generated by the generation means. Specifically, the control means generates the terahertz wave generated by the generating means so that the light intensity of the terahertz wave generated by the generating means during the detection period is different from the light intensity of the terahertz wave generated by the generating means during the non-detection period. Adjust the light intensity. More specifically, the control means reduces the light intensity of the terahertz wave generated by the generating means during the non-detection period (in other words, smaller than the light intensity of the terahertz wave generated by the generating means during the detection period. As described above, the light intensity of the terahertz wave generated by the generating means is adjusted.

  Here, the “detection period” means a period during which the detection unit detects the terahertz wave. Typically, such a detection period is preferably set to coincide with a period during which the detection unit can detect the terahertz wave with high accuracy. Alternatively, it is preferable that such a detection period is typically set to coincide with a period during which the detection unit should detect the terahertz wave. Alternatively, it is preferable that such a detection period is typically set so as to coincide with a period during which the detection unit preferably detects the terahertz wave.

  On the other hand, the “non-detection period” means a period other than the detection period (that is, a period in which the detection period does not detect the terahertz wave). Typically, such a non-detection period is preferably set to coincide with a period during which the detection means cannot detect the terahertz wave with high accuracy. Alternatively, it is preferable that such a non-detection period is typically set to coincide with a period during which the detection unit should not detect the terahertz wave. Alternatively, such a non-detection period is typically set so as to coincide with a period during which it is not preferable for the detection means to detect the terahertz wave.

  In particular, in the present embodiment, the detection period is determined according to the optical path length difference that can affect the detection timing or detection accuracy of the terahertz wave (that is, the optical path length difference adjusted by the adjusting means). In consideration of the fact that the period other than the detection period is the non-detection period, it can be said that the non-detection period is determined according to the optical path length difference that defines the detection timing of the terahertz wave.

  Here, during the non-detection period, the generating means generates a terahertz wave having a relatively low light intensity. For this reason, in the non-detection period, compared with the detection period in which the terahertz wave having a relatively high light intensity is generated, heat generation by the generation unit accompanying the generation of the terahertz wave is suppressed. In other words, in the non-detection period, cooling or heat dissipation of the generating means is promoted compared to the detection period. Therefore, in the non-detection period, an increase in carriers thermally excited in the generating means is suppressed as compared with the detection period. For this reason, in this embodiment, the light intensity of the terahertz wave is fixed (in other words, it does not intentionally or actively decrease). A rapid increase in the current flowing through (for example, as will be described in detail later with reference to the drawings) can be suppressed.

  On the other hand, during the detection period, the generating means generates a terahertz wave having a relatively high light intensity. That is, the decrease in the light intensity of the terahertz wave that may affect the analysis of the characteristics of the measurement object using the terahertz wave is performed in a non-detection period in which the detection unit does not detect the terahertz wave. Therefore, even if the light intensity of the terahertz wave decreases during the non-detection period, the analysis of the characteristics of the measurement object using the terahertz wave is preferably performed.

  Furthermore, in this embodiment, the heat generation of the generating means accompanying the generation of the terahertz wave is suppressed without using a new physical structure such as a cooling mechanism or a heat dissipation mechanism. Therefore, cooling or heat dissipation of the generating means is promoted while suppressing an increase in the size and cost of the terahertz wave measuring apparatus.

<2>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the control unit does not cause the generation unit to generate the terahertz wave during the non-detection period.

  According to this aspect, the control unit can reduce the light intensity of the terahertz wave generated by the generation unit until the light intensity becomes zero. Therefore, in this aspect, compared with the aspect in which the light intensity of the terahertz wave generated by the generating means is decreased until the light intensity becomes a value greater than zero, the heat generated by the generating means accompanying the generation of the terahertz wave is more increased. It is further suppressed. For this reason, it is possible to further suppress an abrupt increase in the current flowing in the generating means (for example, the current flowing in the gap between two conductive parts provided in the generating means as will be described in detail later with reference to the drawings). .

<3>
In another aspect of the terahertz wave measuring apparatus according to the present embodiment, the generating unit includes two conductive units that sandwich a gap portion and to which a bias voltage is applied, and the control unit is configured to detect the detection period. The bias voltage applied during the non-detection period is decreased compared to the applied bias voltage.

  According to this aspect, the control unit can relatively easily and suitably reduce the light intensity of the terahertz wave generated by the generation unit by reducing the bias voltage applied to the generation unit.

<4>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the control unit generates the generation in the non-detection period as compared with the light intensity of the first laser light irradiated on the generation unit in the detection period. The light intensity of the first laser light irradiated on the means is reduced.

  According to this aspect, the control means reduces the light intensity of the first laser light (for example, the average light intensity) irradiated to the generation means, so that the light intensity of the terahertz wave generated by the generation means is relatively easy. And can be preferably reduced.

<5>
In the aspect of the terahertz wave measuring apparatus that reduces the light intensity of the first laser light irradiated to the generating means as described above, the terahertz wave measuring apparatus further includes light source means for generating the first laser light in accordance with a drive current, and the control The means reduces the drive current in the non-detection period as compared to the drive current in the detection period.

  According to this aspect, the control unit reduces the drive current output to the light source unit in order to generate the first laser beam, so that the light intensity of the first laser beam applied to the generation unit is relatively easy. And can be preferably reduced.

<6>
In the aspect of the terahertz wave measuring apparatus that reduces the light intensity of the first laser beam irradiated to the generating unit as described above, the first laser beam is disposed on the optical path of the first laser beam toward the generating unit. The control unit further includes a blocking unit that blocks part or all of the propagation of light, and the control unit compares the amount of blocking of the first laser light by the blocking unit in the detection period with respect to the non-detection period. The blocking amount of the first laser beam by the blocking means is increased.

  According to this aspect, the control unit irradiates the generation unit by increasing the blocking amount of the first laser light on the optical path on the way from the light source unit to the generation unit (in other words, decreasing the transmission amount). The light intensity of the first laser beam can be reduced relatively easily and suitably.

<7>
As described above, in the aspect of the terahertz wave measuring apparatus that does not generate the terahertz wave in the non-detection period, the generation unit includes two conductive portions to which a bias voltage is applied with a gap portion interposed therebetween. The control means sets the bias voltage applied during the non-detection period to zero.

  According to this aspect, by setting the bias voltage applied to the generation unit to zero, the control unit can relatively easily and suitably realize a state in which the generation unit does not generate the terahertz wave.

<8>
As described above, in the aspect of the terahertz wave measuring apparatus in which the generation unit does not generate the terahertz wave in the non-detection period, the control unit has the light intensity of the first laser light irradiated to the generation unit in the non-detection period. Is set to zero.

  According to this aspect, the control means sets the light intensity of the first laser light applied to the generation means to zero, so that the generation means does not generate a terahertz wave relatively easily and suitably. be able to.

<9>
In the aspect of the terahertz wave measuring apparatus that sets the light intensity of the first laser light irradiated to the generating means as described above to zero, the terahertz wave measuring device further includes a light source means that generates the first laser light according to a driving current, The control means sets the drive current to zero during the non-detection period.

  According to this aspect, the control means compares the light intensity of the first laser light applied to the generating means by setting the drive current output to the light source means to zero to generate the first laser light. It can be set to zero easily and preferably.

<10>
In the aspect of the terahertz wave measuring apparatus that sets the light intensity of the first laser beam irradiated to the generating unit to zero as described above, the terahertz wave measuring device is disposed on the optical path of the first laser beam toward the generating unit, and The apparatus further includes a blocking unit that blocks part or all of the propagation of one laser beam, and the control unit causes the blocking unit to block all propagation of the first laser beam during the non-detection period.

  According to this aspect, the control means blocks the entire first laser beam on the optical path on the way from the light source means to the generation means (in other words, sets the transmission amount to zero), thereby irradiating the generation means. The light intensity of the first laser light can be set to zero relatively easily and preferably.

<11>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the detection period is a period including a period in which the optical path length difference provided by the delay unit changes linearly.

  According to this aspect, since the generation means generates a terahertz wave having a relatively high light intensity in such a detection period, the characteristics of the measurement object using the terahertz wave are preferably analyzed. On the other hand, in the non-detection period other than such a detection period, cooling or heat dissipation of the generating means is promoted.

(Embodiment of terahertz wave measuring method)
<12>
In the terahertz wave measuring method of the present embodiment, the first laser light is irradiated as excitation light, thereby generating terahertz waves, and the second laser light is irradiated as excitation light, so that the generation means Detecting means for detecting the terahertz wave irradiated to the measurement object from the adjustment means, adjusting means for adjusting the optical path length difference between the optical path length of the first laser light and the optical path length of the second laser light; A terahertz wave measuring method in a terahertz wave measuring apparatus comprising: a detection period in which the detection unit detects the terahertz wave, and a period other than the detection period determined according to the optical path length difference adjusted by the adjustment unit Compared with a setting step for setting a non-detection period and the light intensity of the terahertz wave generated by the generation means during the detection period, the generation means is generated during the non-detection period. And a control step of reducing the light intensity of the serial terahertz wave.

  According to the terahertz wave measuring method of the present embodiment, the same effects as the various effects that can be enjoyed by the above-described terahertz wave measuring apparatus of the present embodiment can be suitably received.

  Incidentally, the terahertz wave measuring method of the present embodiment may also take various aspects, corresponding to the various aspects that the terahertz wave measuring apparatus of the present embodiment can take.

  Such an operation and other advantages of the present embodiment will be further clarified from examples described below.

  As described above, the terahertz wave measuring apparatus according to the present embodiment includes the generation unit, the detection unit, the delay unit, and the control unit. The terahertz wave measuring method according to the present embodiment includes a setting process and a control process. Therefore, cooling or heat dissipation of the generating means for generating the terahertz wave can be promoted while suppressing an increase in the size and cost of the terahertz wave measuring apparatus.

  Hereinafter, examples will be described with reference to the drawings.

(1) First Embodiment First , a terahertz wave measuring apparatus 100 according to a first embodiment will be described with reference to FIGS.

(1-1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 100 of the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 100 according to the first embodiment.

  As shown in FIG. 1, the terahertz wave measuring apparatus 100 irradiates the measurement target with the terahertz wave THz and transmits the terahertz wave THz transmitted through or reflected from the measurement target (that is, irradiated to the measurement target). Detected terahertz wave THz).

The terahertz wave THz is an electromagnetic wave belonging to a frequency region (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). The terahertz region is a frequency region that combines light straightness and electromagnetic wave transparency. The terahertz region is a frequency region in which various substances have unique absorption spectra. Therefore, the terahertz wave measuring apparatus 100 can analyze the characteristics of the measurement object by analyzing the frequency spectrum of the terahertz wave THz applied to the measurement object.

  In order to acquire the frequency spectrum of the terahertz wave THz irradiated on the measurement object, the terahertz wave measuring apparatus 100 employs terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy). The terahertz time domain spectroscopy irradiates the measurement target with the terahertz wave THz and performs Fourier transform on the time waveform of the terahertz wave THz that has passed through the measurement target or reflected from the measurement target. This is a method for acquiring a spectrum (that is, amplitude and phase for each frequency).

  Here, since the period of the terahertz wave THz is a period on the order of subpicoseconds, it is technically difficult to directly detect the time waveform of the terahertz wave THz. Therefore, the terahertz wave measuring apparatus 100 indirectly detects the time waveform of the terahertz wave THz, which employs a pump-probe method based on time delay scanning.

  As shown in FIG. 1, a terahertz wave measuring apparatus 100 that employs such a terahertz time-domain spectroscopy method and a pump-probe method includes a pulse laser apparatus 101 that is a specific example of “light source means”, and “generating means”. A terahertz wave generating element 110, a beam splitter 161, a reflecting mirror 162, a reflecting mirror 163, an optical delay device 120, which is a specific example of “delay means”, and a “detection means”. Specific examples of the terahertz wave detection element 130, the bias voltage generation unit 141, the measurement interval signal generation unit 142, the terahertz wave generation control unit 143 that is a specific example of “control means”, and IV (current − A voltage) conversion unit 144 and an arithmetic processing unit 150 are provided.

  The pulse laser device 101 generates pulse laser light LB in the sub-picosecond order or femtosecond order having light intensity corresponding to the drive current input to the pulse laser device 101. The pulse laser beam LB generated by the pulse laser device 101 is incident on the beam splitter 161 via a light guide (not shown) (for example, an optical fiber).

  The beam splitter 161 splits the pulsed laser light LB into pump light LB1 which is a specific example of “first laser light” and probe light LB2 which is a specific example of “second laser light”. The pump light LB1 is incident on the terahertz wave generating element 110 through a light guide path (not shown). On the other hand, the probe light LB2 enters the optical delay device 120 via a light guide path and a reflecting mirror 162 (not shown).

  The optical delay device 120 adjusts the difference (that is, the optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Specifically, the optical delay device 120 adjusts the optical path length between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 by adjusting the optical path length of the probe light LB2. The timing at which the pump light LB1 enters the terahertz wave generation element 110 (or from the terahertz wave generation element 110) is adjusted by adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. The relative shift amount between the timing at which the outgoing terahertz wave THz enters the terahertz detection element 130) and the timing at which the probe light LB2 enters the terahertz wave detection element 130 can be adjusted. For example, when the optical path of the probe light LB2 is increased by 0.3 millimeters (however, the optical path length in the air) by the optical delay device 120, the timing at which the probe light LB2 enters the terahertz wave detection element 130 is delayed by 1 picosecond. Become. In this case, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is delayed by 1 picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the terahertz wave detecting element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is gradually shifted. Thus, the terahertz detection element 130 can indirectly detect the time waveform of the terahertz wave THz.

  However, the optical delay device 120 adjusts the optical path length of the pump light LB1 in addition to or in place of the optical path length of the probe light LB2, so that the optical path length between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 is adjusted. The optical path length difference may be adjusted. In this case, the optical delay device 120 is preferably disposed on the optical path of the pump light LB1 between the beam splitter 111 and the terahertz wave generating element 110.

  In order to adjust the optical path length of the probe light LB2, the optical delay device 120 includes a retroreflecting mirror 121, a feed screw mechanism 122, and a motor 123.

  The retroreflecting mirror 121 retroreflects the probe light LB2 incident on the retroreflecting mirror 121. That is, the retroreflective mirror 121 reflects the probe light LB2 incident on the retroreflective mirror 121 in a direction parallel to the incident direction of the probe light LB2. In the first embodiment, the retroreflecting mirror 121 includes a first reflecting surface 121a and a second reflecting surface 121b that intersect at an angle of 90 degrees. The first reflecting surface 121a reflects the probe light LB2 incident on the retroreflecting mirror 121 toward the second reflecting surface 121b. The second reflecting surface 121b reflects the probe light LB2 incident on the second reflecting surface 121b from the first reflecting surface 121a toward the outside of the retroreflecting mirror 120 (for example, the reflecting mirror 163).

  The retroreflective mirror 121 includes a feed groove that fits into the feed screw mechanism 122. As a result, the retroreflecting mirror 121 adjusts the optical path of the probe light LB2 (specifically, the optical path of the probe light LB2 when it enters the retroreflecting light 121 in accordance with the rotation of the feed screw mechanism 122 driven by the motor 123). Then, it moves along the vertical direction in FIG. By the movement of the retroreflecting mirror 121, the optical path length of the probe light LB2 is adjusted.

  The retroreflecting mirror 121 is moved under the control of the arithmetic processing unit 150. That is, the arithmetic processing unit 150 controls the operation of the motor 123 by outputting a control signal designating the drive amount of the motor 123 to the motor 123.

  The probe light LB2 emitted from the optical delay device 120 enters the terahertz wave detection element 130 via a light guide path and a reflecting mirror 163 (not shown).

  Here, the terahertz wave generating element 110 irradiated with the pump light LB1 and the terahertz detecting element 130 irradiated with the probe light LB2 will be described in more detail with reference to FIG. FIG. 2 is a perspective view showing the configuration of each of the terahertz wave generation element 110 and the terahertz wave detection element 130. The configurations of the terahertz wave generation element 110 and the terahertz wave detection element 130 illustrated in FIG. 2 are merely examples, and a photoconductive antenna or a photoconductive switch having a configuration different from the configuration illustrated in FIG. The terahertz wave detecting element 130 may be used.

  As shown in FIG. 2A, the terahertz wave generating element 110 includes a substrate 111, an antenna (in other words, a transmission line) 112, which is a specific example of “conductive portion”, and a specific example of “conductive portion”. Which is an antenna (in other words, a transmission line) 113.

  The substrate 111 is a semiconductor substrate such as a GaAs (Gallium Arsenide) substrate. Each of the antenna 112 and the antenna 113 is a monopole antenna having a shape extending in the longitudinal direction. The antenna 112 and the antenna 113 are arranged on the substrate 111 so as to be parallel in the short direction. A gap (that is, a gap) 114 of about several micrometers is secured between the antenna 112 and the antenna 113. Therefore, the antenna 112 and the antenna 113 as a whole constitute a dipole antenna.

  A bias voltage output from the bias voltage generation unit 141 is applied to the gap 114 via the antenna 112, the antenna 113, and the terahertz wave generation control unit 143. When the pump beam LB1 is irradiated to the gap 114 in a state where an effective bias voltage (for example, a bias voltage other than 0 V) is applied to the gap 114, the terahertz wave generation element 110 receives carriers by photoexcitation by the pump beam LB1. Occur. As a result, the terahertz wave generating element 110 generates a pulse-shaped current signal in the order of subpicoseconds or in the order of femtoseconds corresponding to the generated carrier. As a result, the terahertz wave generation element 110 generates a terahertz wave THz resulting from the pulsed current signal.

  As shown in FIG. 2B, the terahertz wave detecting element 130 also has the same configuration as the terahertz wave generating element 110. That is, the terahertz wave detecting element 130 includes the substrate 131, an antenna (in other words, a transmission line) 132 as a specific example of “conductive portion”, and an antenna (in other words, a transmission portion) as a specific example of “conductive portion”. Track) 133. The substrate 131, the antenna 132, and the antenna 133 have the same configuration as the substrate 111, the antenna 112, and the antenna 113, respectively.

  When the probe light LB2 is irradiated to the gap 134, carriers are generated in the terahertz detection element 130 by light excitation by the probe light LB2. When the terahertz detection element 130 is irradiated with the terahertz wave THz while the probe beam LB2 is irradiated on the gap 134, a current signal having a signal intensity corresponding to the light intensity of the terahertz wave THz is generated in the gap 134. . The current signal is output to the IV conversion unit 144 via the antenna 132 and the antenna 133.

  In FIG. 1 again, the terahertz wave THz emitted from the terahertz wave generating element 110 is irradiated onto the measurement object via an optical system (not shown) (for example, a lens). The terahertz wave THz applied to the measurement object is incident on the terahertz wave detection element 130 through a not-shown optical system (for example, a lens) as reflected light or transmitted light from the measurement object. As a result, the terahertz wave detection element 130 outputs a current signal having a signal intensity corresponding to the light intensity of the terahertz wave THz.

  The current signal output from the terahertz wave detection element 130 is converted into a voltage signal by the IV conversion unit 144. Thereafter, the arithmetic processing unit 150 performs synchronous detection on the voltage signal using the bias voltage as a reference signal. As a result, the arithmetic processing unit 150 detects a sample value of the terahertz wave THz. Thereafter, the same operation is repeated while appropriately adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2, so that the arithmetic processing unit 150 detects the time waveform of the terahertz waveform. be able to. In addition, the arithmetic processing unit 150 may acquire a frequency spectrum (that is, an amplitude and a phase for each frequency) of the terahertz wave by performing a Fourier transform on the detected time waveform of the terahertz waveform. Furthermore, the arithmetic processing unit 150 may analyze the characteristics of the measurement object by analyzing the frequency spectrum of the terahertz wave.

  Here, if the terahertz wave generating element 110 continues to emit the terahertz wave THz for a long time, a technical problem that the current flowing through the gap 114 of the terahertz wave generating element 110 becomes excessively or rapidly increased occurs. . One of the causes that the current flowing through the gap 114 becomes excessively or rapidly increased is an increase in carriers that are thermally excited in the terahertz wave generating element 110. Therefore, in the first embodiment, the terahertz wave generation control unit 143 appropriately adjusts the light intensity of the terahertz wave THz generated by the terahertz wave generation element 120 in order to suppress heat generation in the terahertz wave generation element 110. In particular, in the first embodiment, the terahertz wave generation control unit 143 appropriately adjusts the light intensity of the terahertz wave THz generated by the terahertz wave generation element 120 by adjusting the bias voltage generated by the bias voltage generation unit 141. .

  In addition, in the first embodiment, the terahertz wave generation control unit 143 appropriately adjusts the light intensity of the terahertz wave THz generated by the terahertz wave generation element 120 according to the measurement interval signal generated by the measurement interval signal generation unit 142. To do. The measurement interval signal generation unit 142 is at a high level (or the first level) while the terahertz wave detection element 130 detects the terahertz wave THz under the control of the arithmetic processing unit 150, while the terahertz wave detection element 142 During the period when 130 does not detect the terahertz wave THz, a measurement interval signal that is at a low level (or a second level different from the first level) is generated. The terahertz wave generation control unit 143 is configured so that the light intensity of the terahertz wave THz during the period when the measurement section signal is at a low level is smaller than the light intensity of the terahertz wave THz during the period when the measurement section signal is at a high level. The light intensity of the terahertz wave THz generated by the terahertz wave generating element 120 is appropriately adjusted.

  In the following, further description will be given of such an aspect of adjusting the light intensity of the terahertz wave THz (in the first embodiment, adjusting the light intensity of the terahertz wave THz by adjusting the bias voltage).

  In the above description, the bias voltage generation unit 141, the measurement interval signal generation unit 142, and the terahertz wave generation control unit 143 are configured as configuration requirements (for example, hardware circuits) that are independent from the arithmetic processing unit 150 that is a CPU. ing. However, the bias voltage generation unit 141, the measurement interval signal generation unit 142, and the terahertz wave generation control unit 143 may be logical processing blocks realized by a computer program inside the arithmetic processing unit 150 that is a CPU.

(1-2) Adjustment of the light intensity of the terahertz wave by the terahertz wave measuring apparatus Subsequently, the adjustment of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 100 of the first embodiment will be described with reference to FIGS. The description will proceed with the operation. FIG. 3 is a flowchart showing the flow of the adjustment operation of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 100 of the first embodiment. 4 shows the waveform of the measurement interval signal and the bias voltage observed when the adjustment operation shown in FIG. 3 is performed, between the optical path of the pump light LB1 and the optical path of the probe light LB2 set by the optical delay device 120. It is a graph shown with the optical path length difference between.

  As illustrated in FIG. 3, the measurement section signal generation unit 142 determines whether or not the current time is a time included in a measurement period in which the terahertz detection element 130 detects the terahertz wave THz (step S11). In other words, the measurement section signal generation unit 142 determines whether or not the current time is a time that is not included in the non-measurement period in which the terahertz detection element 130 does not detect the terahertz wave THz.

  In the first embodiment, the measurement period is defined according to the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 set by the optical delay device 120. The non-measurement period is a period other than the measurement period.

  As an example, an example in which a period during which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 is linearly changed is a measurement period will be described with reference to FIG. When adjusting the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2, the retroreflective mirror 121 moves while repeating acceleration and deceleration. As a result, as shown in the first graph in FIG. 4, a period during which the moving speed of the retroreflector 121 is fixed (for example, a period from time t1 to time t2 and a period from time t3 to time t4) and Periods in which the moving speed of the retroreflecting mirror 121 changes (for example, a period from time t2 to time t3 and a period from time t4 to time t5) alternately appear. Therefore, as shown in the second graph of FIG. 4, the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes linearly (for example, the period from time t1 to time t2 and (Period from time t3 to time t4) and a period in which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes nonlinearly (for example, from the time t2 to the time t3 and from the time t4) And the period between time t5) appear alternately. The period during which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes linearly is the period during which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes nonlinearly. As compared with, the terahertz wave detecting element 130 is easy to detect the terahertz wave THz. Therefore, for example, a period in which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes linearly may be used as the measurement period. On the other hand, a period in which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes nonlinearly may be used as the non-measurement period.

  However, even if the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes nonlinearly, a part or all of the period may be used as the measurement period.

  In addition, the control information directly indicating the period during which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes linearly is notified from the arithmetic processing unit 150 to the measurement section signal generation unit 142. May be. Alternatively, control information (for example, indirectly indicating a period during which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes linearly from the arithmetic processing unit 150 to the measurement interval signal generation unit 142. , The driving amount of the motor 123, etc.) may be notified. In any case, the measurement interval signal generation unit 142 refers to the information notified from the arithmetic processing unit 150, so that the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 changes linearly. The period can be recognized relatively easily.

  In FIG. 3 again, when it is determined as a result of the determination in step S11 that the current time is a time included in the measurement period in which the terahertz detection element 130 detects the terahertz wave THz (step S11: Yes), The measurement section signal generation unit 142 sets the signal level of the measurement section signal to a high level as shown in the third graph in FIG. 4 (step S12). The measurement interval signal generation unit 142 outputs the generated measurement interval signal to the terahertz wave generation control unit 143 as appropriate.

  The terahertz wave generation control unit 143 to which the high-level measurement interval signal is input, the bias voltage output from the bias voltage generation unit 141 (hereinafter, the bias voltage output from the bias voltage generation unit 141 is appropriately referred to as “reference voltage”. A voltage obtained by multiplying a predetermined coefficient A (where A is a real number of 1 or more) is output to the terahertz wave generating element 110 as a bias voltage (step S13).

  On the other hand, as a result of the determination in step S11, when it is determined that the current time is a time included in a non-measurement period in which the terahertz detection element 130 detects the terahertz wave THz (step S11: No), measurement is performed. The section signal generation unit 142 sets the signal level of the measurement section signal to a low level as shown in the third graph of FIG. 4 (step S14). The measurement interval signal generation unit 142 outputs the generated measurement interval signal to the terahertz wave generation control unit 143 as appropriate.

  The terahertz wave generation control unit 143 to which the low level measurement interval signal is input has a predetermined coefficient B with respect to the reference voltage output from the bias voltage generation unit 141 (where B is 0 or more and less than 1). A voltage obtained by multiplying the real number is output as a bias voltage to the terahertz wave generating element 110 (step S15). That is, in the first embodiment, the bias voltage output to the terahertz wave generation element 110 during the non-measurement period is smaller than the bias voltage output to the terahertz wave generation element 110 during the measurement period. Yes. In other words, in the first embodiment, the bias voltage output to the terahertz wave generation element 110 during the non-measurement period is compared with the bias voltage output to the terahertz wave generation element 110 during the measurement period. is decreasing.

  The above operation is repeated until the terahertz wave THz detection operation by the terahertz wave measuring apparatus 100 is completed (step S16).

  Here, the bias voltage will be described in more detail with reference to FIG. As shown in the graph in the fourth row of FIG. 4, a case where the bias voltage generation unit 141 generates a bias voltage that is an AC voltage will be described as an example.

  Here, if the predetermined coefficient A = 1 and the predetermined coefficient B = 0.5, the bias voltage generation unit 141 generates during the measurement period as shown in the graph of the fifth row in FIG. The bias voltage thus output is output to the terahertz wave generating element 110 as it is. On the other hand, as shown in the fifth graph of FIG. 4, during the non-measurement period, the voltage value of the bias voltage generated by the bias voltage generation unit 141 is reduced by half and then the terahertz wave generation element 110 is applied. Are output.

  Alternatively, if the predetermined coefficient A = 1 and the predetermined coefficient B = 0, the bias voltage generated by the bias voltage generation unit 141 is measured during the measurement period as shown in the graph of the fifth row in FIG. Is output to the terahertz wave generating element 110 as it is. On the other hand, as shown in the sixth graph in FIG. 4, the bias voltage is not output to the terahertz wave generating element 110 during the non-measurement period.

  As described above, in the terahertz wave measuring apparatus 100 according to the first embodiment, the bias voltage output to the terahertz wave generating element 110 during the non-measurement period is output to the terahertz wave generating element 110 during the measurement period. Smaller than the bias voltage to be applied. For this reason, the light intensity of the terahertz wave THz emitted from the terahertz wave generation element 110 during the non-measurement period is smaller than the light intensity of the terahertz wave THz emitted from the terahertz wave generation element 110 during the measurement period. For this reason, in the non-measurement period, heat generation of the terahertz wave generation element 110 due to the emission of the terahertz wave THz is suppressed as compared with the measurement period in which the terahertz wave THz having a relatively high light intensity is emitted. In other words, cooling or heat dissipation of the terahertz wave generating element 110 is promoted during the non-measurement period as compared with the measurement period. Therefore, in the non-measurement period, an increase in carriers that are thermally excited in the terahertz wave generation element 110 is suppressed as compared with the measurement period. For this reason, the terahertz wave measuring apparatus 100 of the first embodiment has a gap 114 of the terahertz wave generating element 110 as compared with the terahertz wave measuring apparatus of the comparative example in which the light intensity of the terahertz wave THz does not intentionally decrease. A rapid increase in the current flowing through can be suppressed.

  On the other hand, during the measurement period, the terahertz wave generating element 110 emits a terahertz wave THz having a relatively high light intensity. That is, the decrease in the light intensity of the terahertz wave THz that may affect the analysis of the characteristics of the measurement object using the terahertz wave THz is performed in the non-measurement period in which the terahertz detection element 130 does not detect the terahertz wave THz. Therefore, even if the light intensity of the terahertz wave THz decreases during the non-measurement period, the characteristics of the measurement object using the terahertz wave THz are preferably analyzed appropriately.

  Furthermore, in the terahertz wave measuring apparatus 100 of the first embodiment, heat generation of the terahertz wave generating element 110 due to generation of the terahertz wave THz is suppressed without using a new physical structure such as a cooling mechanism or a heat dissipation mechanism. . Therefore, cooling or heat dissipation of the terahertz wave generating element 110 is promoted while suppressing an increase in size and cost of the terahertz wave measuring apparatus 100.

  In the above description, the description has been made using an example in which the bias voltage is an AC voltage. However, the bias voltage may be a DC voltage. Hereinafter, the waveform of the bias voltage when the bias voltage is a DC voltage will be described with reference to FIG. FIG. 5 shows the pumping light LB1 set by the optical delay device 120 with the measurement interval signal and the waveform of the bias voltage observed when the adjustment operation shown in FIG. 3 is performed under the situation where the bias voltage is a DC voltage. It is a graph shown with the optical path length difference between this optical path and the optical path of probe light LB2.

  As shown in the third graph in FIG. 5, the measurement interval signal generator 142 outputs the measurement interval signal even when the bias voltage is a DC voltage, as in the case where the bias voltage is an AC voltage. Generate.

  Further, as shown in the fourth graph of FIG. 5, it is assumed that the bias voltage generation unit 141 generates a bias voltage that is a DC voltage. When the adjustment operation with the predetermined coefficient A = 1 and the predetermined coefficient B = 0.5 is performed with respect to such a bias voltage, the terahertz wave generating element 110 has a graph in the fifth row in FIG. The bias voltage shown in FIG. Alternatively, when an adjustment operation in which the predetermined coefficient A = 1 and the predetermined coefficient B = 0 is performed, the terahertz wave generation element 110 outputs the bias voltage shown in the sixth graph in FIG. .

  Therefore, even when the bias voltage is a DC voltage, the same effect as that obtained when the bias voltage is an AC voltage is preferably enjoyed.

  If the bias voltage is a DC voltage, the synchronous detection in the arithmetic processing unit 150 may not be performed. In other words, when the arithmetic processing unit 150 does not perform synchronous detection, since the bias voltage may be a DC voltage, the bias voltage may be adjusted in the manner shown in FIG.

(2) Second Example Next, a terahertz wave measuring apparatus 200 according to a second example will be described with reference to FIGS. FIG. 6 is a plan view showing the configuration of the optical delay device 220 provided in the terahertz wave measuring apparatus 200 of the second embodiment. FIG. 7 shows the pump light LB1 set by the optical delay device 220 with the measurement interval signal and the waveform of the bias voltage observed when the terahertz wave measuring apparatus 200 of the second embodiment performs the adjustment operation shown in FIG. It is a graph shown with the optical path length difference between this optical path and the optical path of probe light LB2.

  The terahertz wave measuring apparatus 200 according to the second embodiment is different from the terahertz wave measuring apparatus 100 according to the first embodiment in that the configuration of the optical delay device 220 is different. The other components of the terahertz wave measuring apparatus 200 of the second embodiment are the same as the other components of the terahertz wave measuring apparatus 100 of the first embodiment. Therefore, in the following, description focusing on the optical delay device 200 will be made.

  As shown in FIG. 6, the optical delay device 220 of the second embodiment includes a rotating substrate 221 that can be rotated by the operation of a motor 123 (not shown) and a plurality of (four in FIG. 6) retroreflecting mirrors 121. ing. The plurality of retroreflecting mirrors 121 are arranged at equal intervals on a circle C centered on the rotation axis of the rotating substrate 221. Accordingly, each of the plurality of retroreflecting mirrors 121 circulates on the circle C as the rotating substrate 221 rotates.

  In the terahertz wave measuring apparatus 200 including such an optical delay device 220, for example, as shown in the first graph in FIG. 7, the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 is The changing period may be the measurement period. In other words, a period during which the optical path length difference between the optical path of the pump light LB1 and the optical path of the probe light LB2 is not changed may be a non-measurement period.

  Here, the terahertz wave measuring apparatus 200 of the second embodiment performs the adjustment operation of the light intensity of the terahertz wave THz in the manner shown in FIG. 3, similarly to the terahertz wave measuring apparatus 100 of the first embodiment. That is, the measurement section signal generation unit 142 included in the terahertz wave measuring apparatus 200 of the second embodiment generates the measurement section signal shown in the second graph in FIG. 7 (Step S12 and Step S14 in FIG. 3). Furthermore, the terahertz wave generation control unit 143 included in the terahertz wave measuring apparatus 200 according to the second embodiment performs the fourth or fifth stage of FIG. 7 based on the measurement interval signal shown in the second stage graph of FIG. The bias voltage shown in the graph is output to the terahertz wave generating element 110 (step S13 or step S15 in FIG. 3).

  Even in the terahertz wave measuring apparatus 200 of the second embodiment, it is possible to suitably enjoy the same effects as those that can be enjoyed by the terahertz wave measuring apparatus 100 of the first embodiment. In addition, in the second embodiment, as compared to the first embodiment, the period during which the measurement interval signal is at a low level is relatively long as shown in the second graph of FIG. Therefore, in the second embodiment, heat generation of the terahertz wave generating element 110 due to the emission of the terahertz wave THz is further suppressed as compared with the first embodiment. In other words, in the second embodiment, cooling or heat dissipation of the terahertz wave generating element 110 is further promoted as compared with the first embodiment. For this reason, in the second example, compared with the first example, it is possible to further suppress the rapid increase in the current flowing through the gap 114 of the terahertz wave generating element 110.

  In the third to sixth embodiments described below, the optical delay device 220 of the second embodiment may be used in addition to or instead of the optical delay device 120.

(3) Third Example Next, a terahertz wave measuring apparatus 300 of a third example will be described with reference to FIGS. In addition, about the same structure and operation | movement as the terahertz wave measuring apparatus 100 of 1st Example, the detailed description is abbreviate | omitted by attaching | subjecting the same referential mark and step number.

(3-1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 300 of the third embodiment will be described with reference to FIG. FIG. 8 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 300 according to the third embodiment.

  As shown in FIG. 8, in the terahertz wave measuring apparatus 300 of the third embodiment, the arrangement position and operation of the terahertz wave generation control unit 343 are different from the arrangement position and operation of the terahertz wave generation control unit 143 of the first embodiment. In this respect, it differs from the terahertz wave measuring apparatus 100 of the first embodiment. Other configurations of the terahertz wave measuring apparatus 300 of the third embodiment may be the same as other configurations of the terahertz wave measuring apparatus 100 of the first embodiment.

  Specifically, in the third embodiment, the terahertz wave generation control unit 343 adjusts the drive current output to the pulse laser apparatus 101 based on the measurement interval signal, so that the terahertz wave generating element 120 generates the terahertz wave. The light intensity of the wave THz is adjusted as appropriate. Further, in the third embodiment, the bias voltage generation unit 141 outputs the bias voltage to the terahertz generation element 110 without passing through the terahertz wave generation control unit 343. That is, the bias voltage generated by the bias voltage generation unit 141 is output to the terahertz generation element 110 without being adjusted (in other words, the bias voltage generated by the bias voltage generation unit 141 is used as it is).

  In the following, further description will be given of such an aspect of adjusting the light intensity of the terahertz wave THz (in the third embodiment, adjusting the light intensity of the terahertz wave THz by adjusting the driving current).

(3-2) Adjustment of the light intensity of the terahertz wave by the terahertz wave measuring apparatus Subsequently, the adjustment of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 300 of the third embodiment will be described with reference to FIGS. The description will proceed with the operation. FIG. 9 is a flowchart showing the flow of the adjustment operation of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 300 of the third embodiment. FIG. 10 shows the waveform of the measurement interval signal, the drive current, and the average light intensity of the pulsed laser light LB observed when the adjustment operation shown in FIG. 9 is performed, for the pump light LB1 set by the optical delay device 120. It is a graph shown with the optical path length difference between an optical path and the optical path of probe light LB2.

  As shown in FIG. 9, also in the third embodiment, as in the first embodiment, the measurement section signal generation unit 142 generates a measurement section signal (step S11, step S12, and step S14).

  Thereafter, the terahertz wave generation control unit 143 to which the high-level measurement interval signal is input drives the current obtained by multiplying the reference current by a predetermined coefficient C (where C is a real number of 1 or more). It outputs to the pulse laser apparatus 101 as an electric current (step S33).

  On the other hand, the terahertz wave generation control unit 143, to which the low-level measurement interval signal is input, multiplies the reference current by a predetermined coefficient D (where D is a real number less than 1 and greater than or equal to 0). Is output to the pulse laser device 101 as a drive current (step S35). That is, in the third embodiment, the drive current output to the pulse laser apparatus 101 during the non-measurement period is smaller than the drive current output to the pulse laser apparatus 101 during the measurement period. In other words, in the third embodiment, the drive current output to the pulse laser apparatus 101 during the non-measurement period is reduced compared to the drive current output to the pulse laser apparatus 101 during the measurement period. ing.

  The above operation is repeated until the terahertz wave THz detection operation by the terahertz wave measuring apparatus 100 is completed (step S16).

  Here, the drive current and the average light intensity of the pulsed laser beam LB will be described in more detail with reference to FIG.

  Assume that an adjustment operation in which a predetermined coefficient C = 1 and a predetermined coefficient D = 0.5 is performed with respect to a reference current (for example, a direct current) shown in the fourth graph of FIG. In this case, as shown in the fifth graph of FIG. 10, a relatively large drive current (in other words, larger than the drive current in the non-measurement period) is output to the pulse laser apparatus 101 during the measurement period. Is done. As a result, as shown in the sixth graph of FIG. 10, the pulse laser apparatus 101 is relatively large during the measurement period (in other words, the average light intensity of the pulse laser beam LB generated during the non-measurement period. The pulsed laser beam LB having an average light intensity (greater than) is generated. On the other hand, as shown in the graph of the fifth row in FIG. 10, a relatively small drive current (in other words, smaller than the drive current in the measurement period) is not applied to the pulse laser device 101 in the non-measurement period. Is output. As a result, as shown in the sixth graph in FIG. 10, the pulse laser device 101 is relatively small during the non-measurement period (in other words, the average light intensity of the pulse laser beam LB generated during the measurement period). The pulsed laser beam LB having an average light intensity (smaller than that) is generated.

  Alternatively, it is assumed that an adjustment operation in which a predetermined coefficient C = 1 and a predetermined coefficient D = 0 is performed with respect to a reference current (for example, direct current) shown in the fourth graph of FIG. In this case, as shown in the seventh graph in FIG. 10, a drive current that matches the reference current is output to the pulse laser device 101 during the measurement period. As a result, as shown in the graph in the eighth stage of FIG. 10, during the measurement period, the pulse laser device 101 generates pulsed laser light LB having an average light intensity corresponding to the reference current. On the other hand, as shown in the seventh graph in FIG. 10, the drive current is not output to the pulse laser device 101 during the non-measurement period. As a result, as shown in the sixth graph of FIG. 10, the pulse laser apparatus 101 does not generate the pulse laser beam LB during the non-measurement period.

  As described above, in the terahertz wave measuring apparatus 300 according to the third embodiment, the drive current output to the pulse laser apparatus 101 during the non-measurement period is the drive output to the pulse laser apparatus 101 during the measurement period. It is smaller than the current. Therefore, the average light intensity of the pulse laser beam LB output from the pulse laser apparatus 101 during the non-measurement period is smaller than the average light intensity of the pulse laser beam LB output from the pulse laser apparatus 101 during the measurement period. Therefore, the light intensity of the pump light LB1 irradiated to the terahertz wave generation element 110 during the non-measurement period is also smaller than the light intensity of the pump light LB1 irradiated to the terahertz wave generation element 110 during the measurement period. For this reason, the light intensity of the terahertz wave THz emitted from the terahertz wave generation element 110 during the non-measurement period is smaller than the light intensity of the terahertz wave THz emitted from the terahertz wave generation element 110 during the measurement period. For this reason, even if it is the terahertz wave measuring device 300 of 3rd Example, the effect similar to the effect which the terahertz wave measuring device 100 of 1st Example can enjoy can be enjoyed suitably.

(4) Fourth Example Next, a terahertz wave measuring apparatus 400 according to a fourth example will be described with reference to FIGS. 11 to 13. In addition, about the same structure and operation | movement as the terahertz wave measuring apparatus 100 of 1st Example, the detailed description is abbreviate | omitted by attaching | subjecting the same referential mark and step number.

(4-1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 400 of the fourth embodiment will be described with reference to FIG. FIG. 11 is a block diagram illustrating the configuration of the terahertz wave measuring apparatus 400 according to the fourth embodiment.

  As shown in FIG. 11, the terahertz wave measuring apparatus 400 according to the fourth embodiment is different in the arrangement position and operation of the terahertz wave generation control unit 443 from the arrangement position and operation of the terahertz wave generation control unit 143 of the first embodiment. In this respect, it differs from the terahertz wave measuring apparatus 100 of the first embodiment. In addition, the terahertz wave measuring apparatus 400 of the fourth embodiment includes an optical shutter 401 on the optical path between the beam splitter 161 and the terahertz wave generating element 110 (that is, the optical path of the pump light LB1). This is different from the terahertz wave measuring apparatus 100 of the first embodiment. Other configurations of the terahertz wave measurement apparatus 400 of the fourth embodiment may be the same as other configurations of the terahertz wave measurement apparatus 100 of the first embodiment.

  The optical shutter 401 is a shutter capable of adjusting the light amount of the pump light LB1 that is blocked by the optical shutter 401. In other words, the optical shutter 401 is a shutter that can adjust the amount of the pump light LB1 that passes through the optical shutter 401. Examples of such an optical shutter 401 include a mechanical shutter and a liquid crystal shutter.

  In the fourth embodiment, the terahertz wave generation control unit 443 adjusts the cutoff amount of the pump light LB1 by the optical shutter 401 based on the measurement interval signal, so that the light intensity of the terahertz wave THz generated by the terahertz wave generation element 120 is increased. Adjust as appropriate. Further, in the fourth embodiment, the bias voltage generation unit 141 outputs the bias voltage to the terahertz generation element 110 without passing through the terahertz wave generation control unit 343. That is, the bias voltage generated by the bias voltage generation unit 141 is output to the terahertz generation element 110 without being adjusted (in other words, the bias voltage generated by the bias voltage generation unit 141 is used as it is).

  Hereinafter, description will be further made on such an aspect of the adjustment of the light intensity of the terahertz wave THz (in the fourth embodiment, the adjustment of the light intensity of the terahertz wave THz by adjusting the cutoff amount of the pump light LB1).

(4-2) Adjustment of the light intensity of the terahertz wave by the terahertz wave measuring apparatus Subsequently, the adjustment of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 400 of the fourth embodiment will be described with reference to FIGS. The description will proceed with the operation. FIG. 12 is a flowchart showing the flow of the adjustment operation of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 400 of the fourth embodiment. FIG. 13 shows the measurement interval signal and the waveform of the average light intensity of the pump light LB1 observed when the adjustment operation shown in FIG. 12 is performed, the optical path of the pump light LB1 set by the optical delay device 120 and the probe light. It is a graph shown with the optical path length difference between the optical paths of LB2.

  As shown in FIG. 12, also in the fourth embodiment, as in the first embodiment, the measurement section signal generation unit 142 generates a measurement section signal (step S11, step S12, and step S14).

  Thereafter, the terahertz wave generation control unit 143 to which the high-level measurement interval signal is input sets the cutoff amount of the optical shutter 401 to E (step S43). On the other hand, the terahertz wave generation control unit 143 to which the low-level measurement interval signal is input sets the cutoff amount of the optical shutter 401 to F (where F is a cutoff amount greater than E) (step S45). That is, in the fourth embodiment, the light amount of the pump light LB1 blocked by the optical shutter 401 during the non-measurement period is larger than the light amount of the pump light LB1 blocked by the optical shutter 401 during the measurement period. In other words, in the fourth embodiment, the light amount of the pump light LB1 blocked by the optical shutter 401 during the non-measurement period is increased as compared with the light amount of the pump light LB1 blocked by the optical shutter 401 during the measurement period. ing.

  The above operation is repeated until the terahertz wave THz detection operation by the terahertz wave measuring apparatus 100 is completed (step S16).

  Here, the average light intensity of the pump light LB1 will be described in more detail with reference to FIG.

  For the pump light LB1 having the light intensity shown in the fourth graph of FIG. 13 (that is, having a constant light intensity before being cut off), the cut-off amount during the measurement period is 0% and the non-measurement period Assume that an adjustment operation is performed in which the amount of interruption is 50%. That is, it is assumed that an adjustment operation is performed in which the pump light LB1 is not blocked during the measurement period, while half of the light amount of the pump light LB1 is blocked during the non-measurement period. In this case, as shown in the fifth graph in FIG. 13, the terahertz wave generating element 110 is relatively large (that is, more than the light intensity of the pump light LB1 irradiated in the non-measurement period during the measurement period. Pump light LB1 having a large light intensity is irradiated. On the other hand, as shown in the fifth graph of FIG. 13, the terahertz wave generating element 110 is relatively small in the non-measurement period (that is, the light intensity of the pump light LB1 irradiated in the measurement period). The pump light LB1 having a smaller light intensity is irradiated.

  Alternatively, with respect to the pump light LB1 having the light intensity shown in the fourth graph of FIG. 13 (that is, having a constant light intensity before being blocked), the cutoff amount during the measurement period is 0% and non- Assume that an adjustment operation in which the cutoff amount during the measurement period is 100% is performed. That is, it is assumed that an adjustment operation is performed in which the pump light LB1 is not blocked during the measurement period, but all the light amount of the pump light LB1 is blocked during the non-measurement period. In this case, as shown in the sixth graph in FIG. 13, the terahertz wave generating element 110 is irradiated with the pump light LB1 branched by the beam splitter 161 as it is during the measurement period. On the other hand, as shown in the sixth graph in FIG. 13, the terahertz wave generating element 110 is not irradiated with the pump light LB1 during the non-measurement period.

  As described above, in the terahertz wave measuring apparatus 400 according to the fourth embodiment, the light amount of the pump light LB1 blocked by the optical shutter 401 during the non-measurement period is the light amount of the pump light LB1 blocked by the optical shutter 401 during the non-measurement period. More than that. Therefore, the light intensity of the pump light LB1 irradiated to the terahertz wave generation element 110 during the non-measurement period is smaller than the light intensity of the pump light LB1 irradiated to the terahertz wave generation element 110 during the measurement period. For this reason, the light intensity of the terahertz wave THz emitted from the terahertz wave generation element 110 during the non-measurement period is smaller than the light intensity of the terahertz wave THz emitted from the terahertz wave generation element 110 during the measurement period. For this reason, even if it is the terahertz wave measuring device 400 of 4th Example, the effect similar to the effect which the terahertz wave measuring device 100 of 1st Example can enjoy can be enjoyed suitably.

(5) Fifth Embodiment Next, a terahertz wave measuring apparatus 500 according to a fifth embodiment will be described with reference to FIGS. In addition, about the same structure and operation | movement as the terahertz wave measuring apparatus 100 of 1st Example, the detailed description is abbreviate | omitted by attaching | subjecting the same referential mark and step number.

(5-1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 500 of the fifth embodiment will be described with reference to FIG. FIG. 14 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 500 according to the fifth embodiment.

  As shown in FIG. 14, in the terahertz wave measuring apparatus 500 of the fifth embodiment, the terahertz wave generation control unit 543 adjusts the bias voltage output to the terahertz wave generating element 110 based on the measurement interval signal. Thus, it differs from the terahertz wave measuring apparatus 100 of the first embodiment in that the drive current output to the pulse laser beam element 101 is adjusted based on the measurement interval signal. That is, the terahertz wave measuring apparatus 500 of the fifth embodiment has a configuration in which the terahertz wave measuring apparatus 100 of the first embodiment and the terahertz wave measuring apparatus 300 of the third embodiment are combined. Other configurations of the terahertz wave measuring apparatus 500 of the fifth embodiment may be the same as other configurations of the terahertz wave measuring apparatus 100 of the first embodiment and the terahertz wave measuring apparatus 300 of the third embodiment.

(5-2) Adjustment of the light intensity of the terahertz wave by the terahertz wave measurement apparatus Subsequently, the adjustment of the light intensity of the terahertz wave THz by the terahertz wave measurement apparatus 500 of the fifth embodiment will be described with reference to FIGS. The description will proceed with the operation. FIG. 15 is a flowchart showing the flow of the operation of adjusting the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 500 of the fifth embodiment. FIG. 16 shows a pump in which the measurement interval signal, the bias voltage, the drive current, and the average light intensity waveform of the pulsed laser beam LB observed when the adjustment operation shown in FIG. It is a graph shown with the optical path length difference between the optical path of light LB1, and the optical path of probe light LB2.

  As shown in FIG. 15, in the fifth embodiment, as in the first embodiment, the measurement section signal generation unit 142 generates a measurement section signal (Step S11, Step S12, and Step S14).

  Thereafter, the terahertz wave generation control unit 543 to which the high-level measurement interval signal is input multiplies the reference voltage output from the bias voltage generation unit 141 by a predetermined coefficient A (where A is a real number of 1 or more). The voltage obtained by doing so is output to the terahertz wave generating element 110 as a bias voltage (step S13). Further, the terahertz wave generation control unit 143 to which the high-level measurement interval signal is input drives the current obtained by multiplying the reference current by a predetermined coefficient C (where C is a real number of 1 or more). It outputs to the pulse laser apparatus 101 as an electric current (step S33).

  On the other hand, the terahertz wave generation control unit 143 to which the low level measurement interval signal is input has a predetermined coefficient B (provided that B is equal to or greater than 0) with respect to the reference voltage output from the bias voltage generation unit 141. A voltage obtained by multiplying by a real number less than 1 is output to the terahertz wave generation element 110 as a bias voltage (step S15). Further, the terahertz wave generation control unit 143 to which the low-level measurement interval signal is input multiplies the reference current by a predetermined coefficient D (where D is a real number less than 1 and greater than 0). The obtained current is output to the pulse laser apparatus 101 as a drive current (step S35).

  The above operation is repeated until the terahertz wave THz detection operation by the terahertz wave measuring apparatus 100 is completed (step S16).

  Note that, when the terahertz wave THz light intensity adjustment operation is performed by the terahertz wave measuring apparatus 500 according to the fifth embodiment, the bias voltage is adjusted in the manner shown in the fifth graph of FIG. 16 ( However, the graph in the fifth row in FIG. 16 shows an example in which the predetermined coefficient A = 1 and the predetermined coefficient B = 0. Note that the mode of adjusting the bias voltage shown in FIG. 16 is the same as the mode of adjusting the bias voltage in the first embodiment shown in the sixth graph in FIG. In addition, the drive current is adjusted in the manner shown in the sixth graph of FIG. 16 (however, the sixth graph of FIG. 16 has a predetermined coefficient C = 1 and a predetermined coefficient D = 0. Here is an example: As a result, the average light intensity of the pulsed laser beam LB generated by the pulsed laser apparatus 101 is adjusted in the manner shown in the seventh graph of FIG. Note that the mode of adjustment of the drive current and the average light intensity of the pulse laser beam LB shown in FIG. 16 is the same as the drive current and pulse laser beam LB in the third embodiment shown in the seventh and eighth graphs of FIG. This is the same as the adjustment of the average light intensity.

  Even in the terahertz wave measuring apparatus 500 of the fifth embodiment, the same effects as those that can be enjoyed by the terahertz wave measuring apparatus 100 of the first embodiment and the terahertz wave measuring apparatus 300 of the third embodiment. Can be enjoyed suitably.

  Note that the terahertz wave measuring apparatus 500 of the fifth embodiment corresponds to a combination of the terahertz wave measuring apparatus 100 of the first embodiment and the terahertz wave measuring apparatus 300 of the third embodiment. On the other hand, even the terahertz wave measuring apparatus corresponding to the combination of the terahertz wave measuring apparatus 100 of the first embodiment and the terahertz wave measuring apparatus 400 of the fourth embodiment, Effects similar to those that can be enjoyed by the terahertz wave measuring apparatus 400 of the fourth embodiment can be suitably enjoyed. Alternatively, even the terahertz wave measuring apparatus corresponding to the combination of the terahertz wave measuring apparatus 100 according to the third embodiment and the terahertz wave measuring apparatus 400 according to the fourth embodiment may be the terahertz wave measuring apparatus 300 according to the third embodiment or the fourth embodiment. The same effect as that which can be enjoyed by the terahertz wave measuring apparatus 400 of the embodiment can be suitably enjoyed.

(6) Sixth Example Next, a terahertz wave measuring apparatus 600 according to a sixth example will be described with reference to FIGS. In addition, about the same structure and operation | movement as the terahertz wave measuring apparatus 100 of 1st Example, the detailed description is abbreviate | omitted by attaching | subjecting the same referential mark and step number.

(6-1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 600 of the sixth embodiment will be described with reference to FIG. FIG. 17 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 600 according to the sixth embodiment.

  As shown in FIG. 17, the terahertz wave measuring apparatus 600 of the sixth embodiment includes the chopper 601 between the terahertz wave generating element 110 and the measurement object, and the terahertz wave measurement of the first embodiment. Different from the device 100. Other configurations of the terahertz wave measuring apparatus 300 of the third embodiment may be the same as other configurations of the terahertz wave measuring apparatus 100 of the first embodiment.

  The chopper 601 alternately and repeatedly transmits and blocks the terahertz wave THz emitted from the terahertz wave generating element 110 in accordance with the chopper control signal output from the arithmetic processing unit 150.

  In the sixth embodiment, since the terahertz wave THz is modulated by the chopper 601, the bias voltage output to the terahertz wave generating element 110 may be a DC voltage (in other words, not an AC voltage). Good). Furthermore, in the sixth embodiment, when the arithmetic processing unit 150 performs synchronous detection, in addition to or instead of using a signal corresponding to the bias voltage as a reference signal, a chopper control signal (or the chopper control signal) It is preferable to use a signal synchronized with the reference signal as a reference signal.

(6-2) Adjusting operation of light intensity of terahertz wave by terahertz wave measuring apparatus Subsequently , adjusting the light intensity of terahertz wave THz by the terahertz wave measuring apparatus 600 of the sixth embodiment with reference to FIGS. The description will proceed with the operation. FIG. 18 is a flowchart showing the flow of the operation of adjusting the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 600 of the sixth embodiment. FIG. 19 shows the waveform of the measurement interval signal and the bias voltage observed when the adjustment operation shown in FIG. 18 is performed, between the optical path of the pump light LB1 and the optical path of the probe light LB2 set by the optical delay device 120. It is a graph shown with the optical path length difference between.

  As shown in FIG. 18, in the sixth embodiment, the light intensity adjustment operation of the terahertz wave THz is performed in the same manner as the first embodiment (step S11 to step S16). Therefore, the description of the adjustment operation of the light intensity of the terahertz wave THz by the terahertz wave measuring apparatus 600 of the sixth embodiment is omitted.

  Further, as shown in FIG. 19, the bias voltage is also adjusted in the same manner as in the first embodiment (see the example shown in FIG. 5 where the bias voltage is a DC voltage). In addition, the waveform of the terahertz wave THz after being modulated by the chopper 601 is shown in the seventh graph in FIG.

  Even with the terahertz wave measuring apparatus 600 of the sixth embodiment, it is possible to suitably enjoy the same effects as the effects that the terahertz wave measuring apparatus 100 of the first embodiment can enjoy.

  In the second to fifth embodiments described above, the chopper 601 described in the sixth embodiment may be used.

  Further, the present invention can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and a terahertz wave measuring apparatus and method involving such a change are also included in the present invention. Included in technical thought.

100, 200, 300, 400, 500, 600 Terahertz wave measuring device 101 Pulse laser device 110 Terahertz wave generating element 120, 220 Optical delay device 121 Retroreflector 122 Feed screw mechanism 123 Motor 130 Terahertz wave detecting element 141 Bias voltage generating unit 142 Measurement section signal generation unit 143, 343, 443, 543 Terahertz wave generation control unit 144 IV conversion unit 150 arithmetic processing unit 161 beam splitter 162, 163 reflector 401 optical shutter 601 chopper LB pulse laser beam LB1 pump beam LB2 probe Light THz terahertz wave

Claims (12)

Generating means for generating a terahertz wave by being irradiated with the first laser beam;
Detecting means for detecting the terahertz wave irradiated to the measurement object from the generating means by being irradiated with the second laser beam;
Adjusting means for adjusting the optical path length difference between the optical path length of the first laser light and the optical path length of the second laser light;
Compared with the light intensity of the terahertz wave generated by the generating means in a detection period in which the detecting means detects the terahertz wave and is determined according to the optical path length difference adjusted by the adjusting means, A terahertz wave measuring device comprising: a control unit that reduces the light intensity of the terahertz wave generated by the generating unit during a non-detection period that is a period other than the detection period.   The terahertz wave measuring apparatus according to claim 1, wherein the control unit does not cause the generation unit to generate the terahertz wave during the non-detection period. The generating means includes two conductive portions to which a bias voltage is applied while sandwiching a gap portion therebetween,
2. The terahertz wave measuring apparatus according to claim 1, wherein the control unit decreases the bias voltage applied in the non-detection period as compared with the bias voltage applied in the detection period.   The control means compares the light intensity of the first laser light applied to the generating means during the non-detection period as compared with the light intensity of the first laser light applied to the generating means during the detection period. The terahertz wave measuring apparatus according to claim 1, wherein the terahertz wave measuring apparatus is decreased. Light source means for generating the first laser light in response to a drive current;
The terahertz wave measuring apparatus according to claim 4, wherein the control unit reduces the drive current in the non-detection period as compared to the drive current in the detection period. And further comprising a blocking unit that is disposed on an optical path of the first laser beam toward the generating unit and blocks a part or all of the propagation of the first laser beam,
The control unit increases the blocking amount of the first laser beam by the blocking unit in the non-detection period as compared to the blocking amount of the first laser beam by the blocking unit in the detection period. The terahertz wave measuring device according to claim 4 or 5. The generating means includes two conductive portions to which a bias voltage is applied while sandwiching a gap portion therebetween,
The terahertz wave measuring apparatus according to claim 2, wherein the control unit sets the bias voltage applied during the non-detection period to zero.   The terahertz wave measuring apparatus according to claim 2, wherein the control unit sets the light intensity of the first laser light applied to the generation unit to zero during the non-detection period. Light source means for generating the first laser light in response to a drive current;
The terahertz wave measuring apparatus according to claim 8, wherein the control unit sets the drive current to zero during the non-detection period. And further comprising a blocking unit that is disposed on an optical path of the first laser beam toward the generating unit and blocks a part or all of the propagation of the first laser beam,
10. The terahertz wave measuring apparatus according to claim 8, wherein the control unit causes the blocking unit to block all propagation of the first laser light during the non-detection period.   11. The detection period according to claim 1, wherein the detection period is a period including a period in which the adjustment unit adjusts the optical path length so that a variation rate of the optical path length difference changes linearly. The terahertz wave measuring device according to one item. Generating means for generating a terahertz wave by being irradiated with the first laser beam;
Detecting means for detecting the terahertz wave irradiated to the measurement object from the generating means by being irradiated with the second laser beam;
A terahertz wave measuring method in a terahertz wave measuring apparatus, comprising: an adjusting unit that adjusts an optical path length difference between the optical path length of the first laser light and the optical path length of the second laser light,
A setting step of setting a non-detection period that is a detection period in which the detection unit detects the terahertz wave and is a period other than the detection period determined according to the optical path length difference adjusted by the adjustment unit;
And a control step of reducing the light intensity of the terahertz wave generated by the generating means during the non-detection period as compared with the light intensity of the terahertz wave generated by the generating means during the detection period. Terahertz wave measurement method.

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