JP2014115189A - Terahertz wave measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an influence arising from a tilt of a retroreflection mirror as to analysis accuracy of characteristics of a measured object employing a terahertz wave.SOLUTION: A terahertz wave measurement device (100) comprises: generation means (110) that is irradiated with first laser light (LB1) to thereby generate a terahertz wave (THz); and retro-reflection means (120) that retro-reflects the first laser light. Detection means has direction dependency in which a tolerance of a position displacement along a first direction (Z1) of an irradiation position of second laser light is larger than a tolerance of a position displacement along a second direction (Y1) of the irradiation position of the second laser light. While a tilt of the retro-reflection means along a third direction (Z2) makes the retro-reflection of the retro-reflection means unperformable, the retro-reflection means has direction dependency in which the retro-reflection is performable even if the tilt of the retro-reflection means along a fourth direction (Y2) is generated, and the first direction (Z1) and the third direction (Z2) are aligned.

Description

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

  As a terahertz wave measuring apparatus, an apparatus using terahertz time-domain spectroscopy (see, for example, Patent Document 1 and Patent Document 2) 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 (particularly the gap portion of the dipole antenna provided in the terahertz wave generating 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 detection element (in particular, the gap portion of the dipole antenna provided in the terahertz wave detection 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.

International Publication No. 2000/079248 Pamphlet JP 2001-21503 A

  Here, the optical delay given to the probe light (or pump light) causes the probe light (or pump light) to be incident on a retroreflector that can retroreflect incident light. It is often given by. Here, “retroreflection” refers to a state in which incident light is reflected in a direction parallel to the incident direction of the incident light. As an example of the retroreflecting mirror, a retro reflector is exemplified. However, in order to manufacture a retro-reflector, it is necessary to arrange three reflecting mirrors whose reflecting surfaces intersect with each other at an angle of 90 degrees with high accuracy. For this reason, it is difficult to manufacture a retroreflector having high deflection angle accuracy (that is, parallelism of reflected light with respect to incident light).

  For this reason, from the viewpoint of ease of manufacture, a retroreflecting mirror composed of two reflecting mirrors each having an angle of 90 degrees is often used. However, a retroreflector composed of two reflectors is different from a retroreflector composed of three reflectors, and when the retroreflector tilts due to vibration or the like, the retroreflector tilts. Depending on the direction, retroreflection may not be possible. For example, even if two reflecting mirrors are tilted along a direction along the plane including the optical path of incident light and the optical path of reflected light when the retroreflecting mirror is retroreflecting, the retroreflecting mirror is Can continue to reflect. On the other hand, if the two reflecting mirrors are tilted in a direction different from the direction along the plane including the optical path of the incident light and the optical path of the reflected light when the retroreflecting mirror is retroreflecting, The reflector cannot be retroreflected. When retroreflection is not possible, there is a possibility that the probe light (or pump light) reflected by the retroreflecting mirror is not appropriately irradiated to the gap portion of the terahertz wave detection element (or terahertz wave generation element). . As a result, the analysis accuracy of the characteristics of the measurement object using terahertz waves may be affected.

  Examples of problems to be solved by the present invention include the above. The present invention reduces the influence on the analysis accuracy of the characteristics of a measurement object using a terahertz wave due to the tilt of a retroreflector that retroreflects a laser beam used to generate or detect the terahertz wave. It is an object of the present invention to provide a terahertz wave measuring apparatus that makes it possible.

  In order to solve the above-described problem, the first terahertz wave measuring apparatus is configured to generate the terahertz wave by irradiating the first laser light, and the generation by irradiating the second laser light. Detecting means for detecting the terahertz wave irradiated to the measurement object from the means, and retroreflecting means for retroreflecting the second laser light and guiding the retroreflected second laser light to the detecting means And the detection means has a second direction in which a tolerance of positional deviation along the first direction of the irradiation position of the second laser light is different from the first direction of the irradiation position of the second laser light. The retroreflective means is not capable of retroreflecting due to the inclination of the retroreflective means along the third direction. , Different from the third direction Even if the inclination of the retroreflector along the fourth direction has a directional dependence that it is possible the retroreflective, the first direction and the third direction are aligned.

  In order to solve the above-described problem, the second terahertz wave measuring apparatus is configured to generate the terahertz wave by irradiating the first laser light, and to generate the terahertz wave by irradiating the second laser light. Detecting means for detecting the terahertz wave irradiated to the measurement object from the means, and retroreflecting means for retroreflecting the first laser light and guiding the retroreflected first laser light to the generating means And the generating means has a second direction in which a tolerance of positional deviation along the first direction of the irradiation position of the first laser light is different from the first direction of the irradiation position of the first laser light. The retroreflective means is not capable of retroreflecting due to the inclination of the retroreflective means along the third direction. , Different from the third direction Even if the inclination of the retroreflector along the fourth direction has a directional dependence that it is possible the retroreflective, the first direction and the third direction are aligned.

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 graph which shows the relationship between the amount of position shift of the irradiation position of the probe light on a terahertz wave detection element, and the current signal output from a terahertz wave detection element. It is a top view which shows the optical path (incident optical path and reflected optical path) of the probe light with respect to the inclination (position shift | offset | difference) of a retroreflection mirror. It is a perspective view which shows the arrangement | positioning aspect of the terahertz wave detection element and retroreflection mirror in 1st Example. It is a top view which shows the other example of a structure of the terahertz wave detection element in 1st Example. It is a top view which shows the other example of a structure of the optical delay device in 1st Example. It is a top view which shows the optical path (incident optical path and reflected optical path) of the probe light with respect to the inclination (position shift | offset | difference) of a retroreflection mirror. It is a perspective view which shows the arrangement | positioning aspect of the terahertz wave detection element and retroreflection mirror in a modification. It is a block diagram which shows the structure of the terahertz wave measuring device of 2nd Example. It is a perspective view which shows the arrangement | positioning aspect of the terahertz wave generation element and retroreflection mirror in 2nd Example.

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

(Terahertz wave measuring apparatus according to the first embodiment)
<1>
The terahertz wave measuring apparatus according to the first embodiment is configured to generate a terahertz wave by irradiating the first laser light and irradiate the second laser light to the measurement object from the generating means. Detecting means for detecting the terahertz wave irradiated on the second laser light, and retroreflecting means for retroreflecting the second laser light and guiding the retroreflected second laser light to the detecting means, The means is that the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light is a positional deviation along the second direction different from the first direction of the irradiation position of the second laser light. The retroreflective means has a direction dependency of greater than the tolerance, and the retroreflective means cannot be retroreflective due to the inclination of the retroreflective means along the third direction. Along a different fourth direction Even if the inclination of the retroreflective means has a directional dependence that it is possible the retroreflective, the first direction and the third direction are aligned.

  According to the terahertz wave measuring apparatus of the first embodiment, the operation of the generation unit, the detection unit, and the retroreflective unit causes the terahertz irradiated to the measurement object using the terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy). A wave is 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).

  In the first embodiment, the retroreflective means retroreflects the second laser light. The retroreflected second laser light is guided to the detection means. As a result, the retroreflective means adjusts the optical path length difference between the optical path of the first laser light and the optical path of the second laser light. In other words, the optical path length difference between the optical path of the first laser light and the optical path of the second laser light is set to a desired value. 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.

  Here, the detection means has direction dependency with respect to the positional deviation of the irradiation position of the second laser light irradiated to the detection means (that is, the irradiation position on the detection means). Specifically, the detection means has a direction dependency that the detection accuracy of the terahertz wave by the detection means varies depending on the direction of displacement of the irradiation position of the second laser light irradiated to the detection means. Have. More specifically, the detection means has a tolerance of positional deviation along the second direction of the irradiation position of the second laser light, and a tolerance of positional deviation along the second direction of the irradiation position of the second laser light. It has a direction dependency of becoming larger. Here, the “tolerance of misalignment” indicates the degree to which the occurrence of misalignment can be tolerated. Specifically, the greater the “tolerance of misalignment”, the greater the effect on the terahertz wave detection accuracy caused by the misalignment (in other words, the effect on the analysis accuracy of the characteristics of the measurement object using such terahertz waves). ) Becomes smaller. Therefore, typically, the detection accuracy of the terahertz wave by the detection unit when the irradiation position of the second laser light is displaced along the first direction is that the irradiation position of the second laser light is along the second direction. It becomes better than the detection accuracy of the terahertz wave by the detection means in the case of displacement. For this reason, typically, the analysis accuracy when the irradiation position of the second laser light is displaced along the first direction is the analysis accuracy when the irradiation position of the second laser light is displaced along the second direction. It becomes better than analysis accuracy.

  In addition, the retroreflective means has a direction dependency on the inclination of the retroreflective means. Specifically, the retroreflective means has a direction dependency that the possibility of retroreflection changes depending on the inclination direction of the retroreflective means. More specifically, the retroreflective means has a direction dependency that the retroreflective becomes impossible by the inclination of the retroreflective means along the third direction. On the other hand, the retroreflective means has a direction dependency that the retroreflective is possible even if the retroreflective means tilts along the fourth direction.

  The first direction and the second direction are preferably orthogonal to each other. However, as long as the first direction and the second direction are different from each other, the first direction and the second direction may be any direction. Similarly, the third direction and the fourth direction are preferably orthogonal to each other. However, as long as the third direction and the fourth direction are different from each other, the third direction and the fourth direction may be any direction.

  In the first embodiment, in particular, the detection unit and the retroreflection unit consider the direction dependency and reduce the influence on the analysis accuracy of the characteristics of the measurement object using the terahertz wave. Are arranged as follows.

  Specifically, a first direction in which the tolerance of the positional deviation of the irradiation position of the second laser light applied to the detection unit is relatively large, and a third direction in which retroreflection in the retroreflection unit is impossible. The detecting means and the retroreflective means are arranged so that the two are aligned (typically coincide). Assuming such an arrangement, assume that the retroreflective means is inclined along the third direction. In this case, as will be described in detail later with reference to the drawings, the retroreflective means gradually reflects the reflected optical path that is not parallel to the incident optical path of the second laser light (typically, along the third direction from the incident optical path). The second laser light is reflected along a reflection optical path that moves away. Therefore, when the retroreflective means is inclined along the third direction, the irradiation position of the second laser light on the detection means is displaced along the third direction. Here, since the third direction and the first direction are aligned, the positional deviation along the third direction of the irradiation position of the second laser light is a position along the first direction of the irradiation position of the second laser light. It is substantially equivalent to the deviation. Then, since the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light is relatively large, the retroreflective means is compared with the case where the first direction and the third direction are not aligned. Is tilted along the third direction (that is, when retroreflection is impossible), the degree of influence of the tilt of the retroreflective means on the terahertz wave detection accuracy in the detection means is reduced. The Therefore, in the first embodiment, the retroreflective means is inclined along the third direction as compared with the case where the first direction and the third direction are not aligned (that is, when retroreflection is impossible). Even so, the influence of the analysis accuracy of the characteristics of the measurement object is reduced.

  For reference, it is assumed that the retroreflective means is inclined along the fourth direction. In this case, as will be described in detail later with reference to the drawings, the retroreflective means reflects the second laser light along a reflected light path parallel to the incident light path of the second laser light. Therefore, even if the retroreflective means is inclined along the fourth direction, the irradiation position of the second laser light on the detection means is hardly or not displaced. Therefore, it goes without saying that even if the retroreflective means is inclined along the fourth direction, the influence on the analysis accuracy of the characteristics of the measurement object using the terahertz wave is reduced.

<2>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the detection unit includes two conductive portions extending so as to sandwich a gap therebetween, and the first direction is an extension of the gap. The second direction is a direction different from the extending direction of the gap.

  According to this aspect, in the detection unit, the tolerance of the positional deviation of the irradiation position of the second laser light along the direction in which the gap extends is different from the direction in which the gap extends (preferably, more preferably intersect). Has a direction dependency that it becomes larger than the tolerance of the positional deviation of the irradiation position of the second laser light along the (perpendicular) direction.

  Here, the detection means detects the terahertz wave by irradiating the second laser light to the gap located between the two conductive portions. Therefore, in order to maintain good detection accuracy of the terahertz wave by the detection means, it is preferable that the second laser light is irradiated to the gap located between the two conductive portions. Considering such characteristics of the detection means, when the irradiation position of the second laser beam is shifted along the direction in which the gap extends, it is different from the direction in which the gap extends (preferably, more Compared to the case where the irradiation position of the second laser beam is preferably shifted along the direction (preferably orthogonal), the possibility that the second laser beam continues to be applied to the gap is higher. Therefore, the tolerance of the positional deviation of the irradiation position of the second laser light along the direction in which the gap extends is such that the positional deviation of the irradiation position of the second laser light along a direction different from the direction in which the gap extends. Presumed to be larger than the tolerance. That is, it is estimated that there is a high possibility that the tolerance of the positional deviation of the irradiation position of the second laser light along the direction in which the gap extends is maximized.

  Therefore, since the first direction, which is the direction in which the gap extends, and the third direction in which retroreflection by the retroreflective means is impossible are aligned, compared with the case where the first direction and the third direction are not aligned. Thus, even when the retroreflective means is inclined along the third direction (that is, when retroreflective is not possible), the influence of the inclination of the retroreflective means on the terahertz wave detection accuracy by the detection means Is relatively reduced. Therefore, the various effects described above are favorably enjoyed.

<3>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the detection unit includes two conductive portions extending so as to sandwich a gap therebetween, and the first direction is an extension of the gap. The second direction is a direction orthogonal to the first direction. The direction is different from each of the direction along the direction and the direction orthogonal to the extending direction of the gap.

  According to this aspect, it is assumed that the tolerance of the positional deviation of the irradiation position of the second laser light along the direction in which the gap extends does not become the maximum. In other words, it may be assumed that the tolerance of displacement of the irradiation position of the second laser light along a direction different from the direction in which the gap extends is maximized. Therefore, according to this aspect, the direction in which the gap extends even when the tolerance of the positional deviation of the irradiation position of the second laser light along the direction different from the direction in which the gap extends is maximized. The first direction, which is different from the first direction, is aligned with the third direction in which retroreflection by the retroreflective means becomes impossible. Therefore, the various effects described above are favorably enjoyed.

<4>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the first direction is a direction in which the tolerance of displacement of the irradiation position of the second laser light is maximized.

  According to this aspect, the first direction, which is the direction in which the tolerance of the displacement of the irradiation position of the second laser light is maximized, and the third direction in which retroreflection by the retroreflective means is impossible are aligned. Therefore, even when the retroreflective means is tilted along the third direction (that is, when retroreflection is impossible) as compared with the case where the first direction and the third direction are not aligned. The degree of influence of the inclination of the retroreflective means on the terahertz wave detection accuracy by the means is relatively reduced. Therefore, the various effects described above are favorably enjoyed.

<5>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the first direction has an amount of deterioration caused by a displacement of the irradiation position of the second laser light in the accuracy of detection of the terahertz wave by the detection unit. This is the smallest direction.

  According to this aspect, the detection accuracy of the terahertz wave by the detection unit is the best (that is, the amount of deterioration in the detection accuracy of the terahertz wave due to the displacement of the irradiation position of the second laser light is minimized). A certain first direction is aligned with a third direction in which retroreflection by the retroreflection means is impossible. Therefore, even when the retroreflective means is tilted along the third direction (that is, when retroreflection is impossible) as compared with the case where the first direction and the third direction are not aligned. The degree of influence of the inclination of the retroreflective means on the terahertz wave detection accuracy by the means is relatively reduced. Therefore, the various effects described above are favorably enjoyed.

<6>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the third laser beam is incident on the retroreflective means in a state where the retroreflective means retroreflects the second laser light in the third direction. A direction different from a direction along a plane including the optical path of the light and the optical path of the second laser light reflected by the retroreflective means, and the fourth direction is the direction in which the retroreflective means reflects the second laser light. The direction is along a plane including the optical path of the second laser light incident on the retroreflective means in a state of retroreflecting and the optical path of the second laser light reflected by the retroreflective means.

  According to this aspect, as will be described in detail later with reference to the drawings, the retroreflective means includes an incident optical path of the second laser light to the retroreflective means and a reflected optical path of the second laser light from the retroreflective means. The inclination of the retroreflective means along a direction different from the direction along the plane (typically, intersecting or orthogonal) (typically the direction along the plane and the incidence of the second laser beam) There is a direction dependency that retroreflection becomes impossible due to the inclination of the retroreflective means having a rotation center in the direction orthogonal to the optical path and the reflected optical path. In addition, the retroreflective means includes an inclination of the retroreflective means along a plane including the incident optical path of the second laser light to the retroreflective means and the reflected optical path of the second laser light from the retroreflective means (typically, There is a direction dependency that retroreflection is possible even if a tilt of the retroreflective means having a rotation center in a direction orthogonal to the plane occurs.

<7>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the retroreflective means includes a first reflecting mirror and a second reflecting surface that intersects the reflecting surface of the first reflecting mirror at an angle of 90 degrees. The third direction is a direction different from the direction in which the reflection surface of the first reflection mirror and the reflection surface of the second reflection mirror face each other, and the fourth direction is the first direction. This is a direction along the direction in which the reflecting surface of the first reflecting mirror faces the reflecting surface of the second reflecting mirror.

  According to this aspect, the retroreflective means can retroreflect the second laser light using two reflecting mirrors (that is, the first reflecting mirror and the second reflecting mirror).

<8>
In another aspect of the terahertz wave measuring apparatus according to the first embodiment, the generating unit has a tolerance of positional deviation along a fifth direction of the irradiation position of the first laser light, the irradiation position of the first laser light. A position dependency along the first direction of the irradiation position of the second laser light has a direction dependency of being larger than a tolerance of a positional deviation along a sixth direction different from the fifth direction. When the tolerance of deviation is larger than the tolerance of deviation of the irradiation position of the first laser light along the fifth direction, (i) the retroreflecting means recursively sends the second laser light. (Ii) the first direction and the third direction are aligned, and the tolerance of positional deviation along the fifth direction of the irradiation position of the first laser light is When the tolerance of positional deviation along the first direction of the irradiation position is larger than Is (i) the retroreflector is retroreflected said first laser beam, and aligned with the third direction and (ii) the fifth direction.

  According to this aspect, the generating means has direction dependency like the detecting means. In other words, the generating means has a direction dependency on the positional deviation of the irradiation position of the first laser light applied to the generating means (that is, the irradiation position on the generating means). Specifically, the generation unit has a characteristic (for example, amplitude) of the terahertz wave generated by the generation unit depending on the direction of displacement of the irradiation position of the first laser light irradiated to the generation unit. It has direction dependency that it fluctuates. Specifically, the generating means is configured such that the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light is greater than the tolerance of the positional deviation along the sixth direction of the irradiation position of the first laser light. It also has a direction dependency that becomes larger. Therefore, typically, the characteristics of the terahertz wave generated by the generating unit when the irradiation position of the first laser light is displaced along the fifth direction is that the irradiation position of the first laser light is along the sixth direction. Therefore, the characteristics of the terahertz wave generated by the generating means when the position is shifted are improved. For this reason, typically, the analysis accuracy when the irradiation position of the first laser beam is displaced along the fifth direction is the analysis accuracy when the irradiation position of the first laser beam is displaced along the sixth direction. It becomes better than analysis accuracy.

  In addition, according to this aspect, the retroreflective means may retroreflect the first laser light in addition to or instead of the second laser light. That is, the retroreflective unit typically retroreflects either one of the first laser beam and the second laser beam, while reflecting the other one of the first laser beam and the second laser beam. There is no need to retroreflect. In this case, based on the magnitude relationship between the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light and the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light. The laser beam retroreflected by the retroreflective means is determined.

  Specifically, when the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light is larger than the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light. The laser beam retroreflected by the retroreflective means becomes the second laser beam. As a result, the third direction in which retroreflection by the retroreflective means is impossible is aligned with the first direction in which the tolerance of the displacement of the irradiation position of the second laser light that is retroreflected is relatively large. As a result, the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light is larger than the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light. Compared with the case where the direction and the fifth direction are aligned, the degree of the influence of the inclination of the retroreflective means on the analysis accuracy of the characteristics of the measurement object is relatively reduced.

  On the other hand, when the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light is larger than the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light, recursion is performed. The laser beam retroreflected by the reflecting means is the first laser beam. As a result, the third direction in which retroreflection by the retroreflective means becomes impossible is aligned with the fifth direction in which the tolerance of the displacement of the irradiation position of the first laser beam that is retroreflected is relatively large. As a result, the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light is larger than the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light. Compared with the case where the direction and the first direction are aligned, the degree of influence of the inclination of the retroreflective means on the analysis accuracy of the characteristics of the measurement object is relatively reduced.

(Terahertz wave measuring apparatus of the second embodiment)
<9>
The terahertz wave measuring apparatus according to the second embodiment is configured to generate a terahertz wave by irradiating the first laser light, and irradiate the second laser light to the measurement object from the generating means. Detecting means for detecting the terahertz wave irradiated on the first laser light, and retroreflecting means for retroreflecting the first laser light and guiding the retroreflected first laser light to the generating means, The means is that the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light is a positional deviation along the second direction different from the first direction of the irradiation position of the first laser light. The retroreflective means has a direction dependency of greater than the tolerance, and the retroreflective means cannot be retroreflective due to the inclination of the retroreflective means along the third direction. Along a different fourth direction Even if the inclination of the retroreflective means has a directional dependence that it is possible the retroreflective, the first direction and the third direction are aligned.

  According to the terahertz wave measuring apparatus of the second embodiment, similarly to the terahertz wave measuring apparatus of the first embodiment, terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy) is performed by the operations of the generating means, the detecting means, and the retroreflecting means. ) Is used to detect the terahertz wave irradiated to the measurement object.

  In the second embodiment, the retroreflective means retroreflects the first laser light. The first laser beam retroreflected is guided to the generating means. As a result, the retroreflective means adjusts the optical path length difference between the optical path of the first laser light and the optical path of the second laser light. In other words, the optical path length difference between the optical path of the first laser light and the optical path of the second laser light is set to a desired value.

  Here, the generation means has a direction dependency with respect to the positional deviation of the irradiation position of the first laser light irradiated on the generation means (that is, the irradiation position on the generation means). Specifically, the generation unit has a characteristic (for example, amplitude) of the terahertz wave generated by the generation unit depending on the direction of displacement of the irradiation position of the first laser light irradiated to the generation unit. It has direction dependency that it fluctuates. Specifically, the generating means is configured such that the tolerance of positional deviation along the first direction of the irradiation position of the first laser light is greater than the tolerance of positional deviation along the second direction of the irradiation position of the first laser light. It also has a direction dependency that becomes larger. Here, the “tolerance of misalignment” indicates the degree to which the occurrence of misalignment can be tolerated. Specifically, the greater the “tolerance of misalignment”, the greater the effect on the characteristics (eg, amplitude) of the terahertz wave caused by misalignment (in other words, the characteristics of the measurement object using such terahertz waves). Influence on analysis accuracy). Therefore, typically, the characteristics of the terahertz wave generated by the generating means when the irradiation position of the first laser light is displaced along the first direction is that the irradiation position of the first laser light is along the second direction. Therefore, the characteristics of the terahertz wave generated by the generating means when the position is shifted are improved. For this reason, typically, the analysis accuracy when the irradiation position of the first laser beam is displaced along the first direction is the same as the analysis accuracy when the irradiation position of the first laser beam is displaced along the second direction. It becomes better than analysis accuracy.

  In addition, the retroreflective means has a direction dependency on the inclination of the retroreflective means. Note that the direction dependency of the retroreflective means has already been described in the first embodiment, and thus description thereof is omitted here.

  Note that, as in the first embodiment, the first direction and the second direction are preferably orthogonal to each other. However, as long as the first direction and the second direction are different from each other, the first direction and the second direction may be any direction.

  In particular, in the second embodiment, the generation unit and the retroreflective unit reduce the influence on the analysis accuracy of the characteristics of the measurement object using the terahertz wave in consideration of such direction dependency. Are arranged as follows.

  Specifically, a first direction in which the tolerance of the positional deviation of the irradiation position of the first laser light irradiated on the generating unit is relatively large, and a third direction in which retroreflection in the retroreflective unit is impossible. The generating means and the retroreflective means are arranged so that they are aligned (typically coincide). Assuming such an arrangement, assume that the retroreflective means is inclined along the third direction. In this case, as will be described in detail later with reference to the drawings, the retroreflective means gradually reflects the reflected light path that is not parallel to the incident light path of the first laser light (typically, along the third direction from the incident light path). The first laser beam is reflected along a reflection optical path that moves away. Therefore, when the retroreflective means is tilted along the third direction, the irradiation position on the first laser light generating means is displaced along the third direction. Here, since the third direction and the first direction are aligned, the displacement of the irradiation position of the first laser light along the third direction is a position along the first direction of the irradiation position of the first laser light. It is substantially equivalent to the deviation. Then, since the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light is relatively large, the retroreflective means is compared with the case where the first direction and the third direction are not aligned. Even when tilted along the third direction (that is, when retroreflection is impossible), the degree of influence of the tilt of the retroreflective means on the characteristics of the terahertz wave generated by the generating means is reduced. Is done. Therefore, in the second embodiment, the retroreflective means is tilted along the third direction as compared with the case where the first direction and the third direction are not aligned (that is, when retroreflection is impossible). Even so, the influence of the analysis accuracy of the characteristics of the measurement object is reduced.

  For reference, it is assumed that the retroreflective means is inclined along the fourth direction. In this case, as will be described in detail later with reference to the drawings, the retroreflective means reflects the first laser light along a reflected light path parallel to the incident light path of the first laser light. Therefore, even if the retroreflective means is inclined along the fourth direction, the irradiation position on the first laser light generating means is hardly or not displaced. Therefore, it goes without saying that even if the retroreflective means is inclined along the fourth direction, the influence on the analysis accuracy of the characteristics of the measurement object using the terahertz wave is reduced.

<10>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the generating unit includes two conductive portions extending so as to sandwich a gap therebetween, and the first direction is an extension of the gap. The second direction is a direction different from the extending direction of the gap.

  According to this aspect, the generating means has a tolerance of displacement of the irradiation position of the first laser beam along the direction in which the gap extends different from the direction in which the gap extends (preferably, more preferably intersect). Has a direction dependency that it becomes larger than the tolerance of the positional deviation of the irradiation position of the first laser beam along the (perpendicular) direction.

  Here, the generating means generates a terahertz wave by irradiating the first laser beam to the gap located between the two conductive portions. Therefore, in order to maintain the characteristics of the terahertz wave generated by the generating means favorably, it is preferable that the first laser beam is applied to the gap located between the two conductive portions. Considering the characteristics of the generating means, when the irradiation position of the first laser beam is shifted along the direction in which the gap extends, the direction in which the gap extends is different (preferably, more Compared to the case where the irradiation position of the first laser beam is preferably shifted along the (orthogonal) direction, there is a higher possibility that the first laser beam will continue to be applied to the gap. Therefore, the tolerance of the positional deviation of the irradiation position of the first laser light along the direction in which the gap extends is such that the positional deviation of the irradiation position of the first laser light along the direction different from the direction in which the gap extends. Presumed to be larger than the tolerance. That is, it is estimated that there is a high possibility that the tolerance of the positional deviation of the irradiation position of the first laser light along the direction in which the gap extends is maximized.

  Therefore, since the first direction, which is the direction in which the gap extends, and the third direction in which retroreflection by the retroreflective means is impossible are aligned, compared with the case where the first direction and the third direction are not aligned. Thus, even when the retroreflective means is inclined along the third direction (that is, when retroreflective is impossible), the inclination of the retroreflective means is given to the characteristics of the terahertz wave generated by the generating means. The degree of influence is relatively reduced. Therefore, the various effects described above are favorably enjoyed.

<11>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the generating unit includes two conductive portions extending so as to sandwich a gap therebetween, and the first direction is an extension of the gap. The second direction is a direction orthogonal to the first direction. The direction is different from each of the direction along the direction and the direction orthogonal to the extending direction of the gap.

  According to this aspect, it is assumed that the tolerance of the positional deviation of the irradiation position of the first laser light along the direction in which the gap extends does not become the maximum. In other words, it may be assumed that the tolerance of the positional deviation of the irradiation position of the first laser light along the direction different from the direction in which the gap extends is maximized. Therefore, according to this aspect, the direction in which the gap extends even when the tolerance of the positional deviation of the irradiation position of the first laser light along the direction different from the direction in which the gap extends is maximized. The first direction, which is different from the first direction, is aligned with the third direction in which retroreflection by the retroreflective means becomes impossible. Therefore, the various effects described above are favorably enjoyed.

<12>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the first direction is a direction in which the tolerance of displacement of the irradiation position of the first laser light is maximized.

  According to this aspect, the first direction, which is the direction in which the tolerance of the displacement of the irradiation position of the first laser beam is maximized, and the third direction in which retroreflection by the retroreflection means is impossible are aligned. Therefore, it occurs even when the retroreflective means is inclined along the third direction (that is, when retroreflection is impossible) as compared with the case where the first direction and the third direction are not aligned. The degree of the influence of the inclination of the retroreflective means on the characteristics of the terahertz wave generated by the means is relatively reduced. Therefore, the various effects described above are favorably enjoyed.

<13>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the first direction is an amount of decrease in the amplitude of the terahertz wave generated by the generating unit due to a displacement of the irradiation position of the first laser light. Is the direction in which is minimized.

  According to this aspect, the characteristic of the terahertz wave generated by the generating means is the best (that is, the amount of deterioration of the characteristic of the terahertz wave caused by the displacement of the irradiation position of the first laser light (for example, the amount of decrease in amplitude) The first direction, which is the direction in which () is minimized, is aligned with the third direction, in which retroreflection by the retroreflective means is impossible. Therefore, it occurs even when the retroreflective means is inclined along the third direction (that is, when retroreflection is impossible) as compared with the case where the first direction and the third direction are not aligned. The degree of the influence of the inclination of the retroreflective means on the characteristics of the terahertz wave generated by the means is relatively reduced. Therefore, the various effects described above are favorably enjoyed.

<14>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the third laser beam is incident on the retroreflective means in a state where the retroreflective means retroreflects the first laser light in the third direction. The fourth direction is a direction different from a direction along a plane including the optical path of the light and the optical path of the first laser light reflected by the retroreflective means, and the fourth direction is the retroreflective means that reflects the first laser light. This is a direction along a plane including the optical path of the first laser light incident on the retroreflective means in a retroreflected state and the optical path of the first laser light reflected by the retroreflective means.

  According to this aspect, as will be described in detail later with reference to the drawings, the retroreflective means includes an incident optical path of the first laser light to the retroreflective means and a reflected optical path of the first laser light from the retroreflective means. The inclination of the retroreflective means along a direction different from the direction along the plane (typically, intersecting or orthogonal) (typically the direction along the plane and the incidence of the first laser beam) There is a direction dependency that retroreflection becomes impossible due to the inclination of the retroreflective means having a rotation center in the direction orthogonal to the optical path and the reflected optical path. In addition, the retroreflective means includes an inclination of the retroreflective means along a plane including the incident optical path of the first laser light to the retroreflective means and the reflected optical path of the first laser light from the retroreflective means (typically, There is a direction dependency that retroreflection is possible even if a tilt of the retroreflective means having a rotation center in a direction orthogonal to the plane occurs.

<15>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the retroreflective means includes a first reflecting mirror and a reflecting surface that intersects the reflecting surface of the first reflecting mirror at an angle of 90 degrees. The third direction is a direction different from the direction in which the reflection surface of the first reflection mirror and the reflection surface of the second reflection mirror face each other, and the fourth direction is the first direction. This is a direction along the direction in which the reflecting surface of the first reflecting mirror faces the reflecting surface of the second reflecting mirror.

  According to this aspect, the retroreflective means can retroreflect the first laser beam using two reflecting mirrors (that is, the first reflecting mirror and the second reflecting mirror).

<16>
In another aspect of the terahertz wave measuring apparatus according to the second embodiment, the detection means has a tolerance of positional deviation along a fifth direction of the irradiation position of the second laser light, and the irradiation position of the second laser light. A position dependency along the first direction of the irradiation position of the first laser light has a direction dependency of being larger than a tolerance of a positional deviation along a sixth direction different from the fifth direction. When the tolerance of deviation is larger than the tolerance of misalignment along the fifth direction of the irradiation position of the second laser beam, (i) the retroreflecting means recursively sends the first laser beam. (Ii) the first direction and the third direction are aligned, and the tolerance of positional deviation along the fifth direction of the irradiation position of the second laser light is When the tolerance of positional deviation along the first direction of the irradiation position is larger than Is (i) the retroreflector is retroreflected said second laser beam, and aligned with the third direction and (ii) the fifth direction.

  According to this aspect, the detection means has a direction dependency like the generation means. That is, the detection means has a direction dependency with respect to the positional deviation of the irradiation position of the second laser light irradiated to the detection means (that is, the irradiation position on the detection means). Specifically, the detection means has a direction dependency that the detection accuracy of the terahertz wave by the detection means varies depending on the direction of displacement of the irradiation position of the second laser light irradiated to the detection means. Have. More specifically, the detection means has a tolerance of positional deviation along the fifth direction of the irradiation position of the second laser light, and a tolerance of positional deviation along the sixth direction of the irradiation position of the second laser light. It has a direction dependency of becoming larger. Therefore, typically, the detection accuracy of the terahertz wave by the detection means when the irradiation position of the second laser light is displaced along the fifth direction is that the irradiation position of the second laser light is along the sixth direction. It becomes better than the detection accuracy of the terahertz wave by the detection means in the case of displacement. For this reason, typically, the analysis accuracy when the irradiation position of the second laser light is displaced along the fifth direction is the same as the analysis accuracy when the irradiation position of the second laser light is displaced along the sixth direction. It becomes better than analysis accuracy.

  In addition, according to this aspect, the retroreflective means may retroreflect the second laser light in addition to or instead of the first laser light. That is, the retroreflective unit typically retroreflects either one of the first laser beam and the second laser beam, while reflecting the other one of the first laser beam and the second laser beam. There is no need to retroreflect. In this case, based on the magnitude relationship between the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light and the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light. The laser beam retroreflected by the retroreflective means is determined.

  Specifically, when the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light is larger than the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light. The laser light retroreflected by the retroreflective means becomes the first laser light. As a result, the third direction in which retroreflection by the retroreflective means is impossible is aligned with the first direction in which the tolerance of the positional deviation of the irradiation position of the first laser beam that is retroreflected becomes relatively large. As a result, since the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light is larger than the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light, the third Compared with the case where the direction and the fifth direction are aligned, the degree of the influence of the inclination of the retroreflective means on the analysis accuracy of the characteristics of the measurement object is relatively reduced.

  On the other hand, when the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light is larger than the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light, recursion is performed. The laser beam retroreflected by the reflecting means is the second laser beam. As a result, the third direction in which retroreflection by the retroreflective means is impossible is aligned with the fifth direction in which the tolerance of the positional deviation of the irradiation position of the second laser light to be retroreflected is relatively large. As a result, the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light is larger than the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light. Compared with the case where the direction and the first direction are aligned, the degree of influence of the inclination of the retroreflective means on the analysis accuracy of the characteristics of the measurement object is relatively reduced.

  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 first or second embodiment includes the generating unit, the detecting unit, and the retroreflective unit, and allows the displacement of the irradiation position of the first or second laser beam. A first direction in which the degree is relatively large and a third direction in which retroreflection is impossible are aligned. Therefore, it is possible to reduce the influence on the analysis accuracy of the characteristics of the measurement object using the terahertz wave due to the inclination of the retroreflective means that retroreflects the laser light used for generating or detecting the terahertz wave. .

  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 employing such a terahertz time-domain spectroscopy method and a pump-probe method includes a pulse laser apparatus 101 and a terahertz wave generating element which is a specific example of “generating means”. 110, a beam splitter 161, a reflecting mirror 162, a reflecting mirror 163, an optical delay device 120, a terahertz wave detecting element 130 which is a specific example of “detecting means”, a bias voltage generating unit 141, an I− A V (current-voltage) conversion unit 144, a lock-in detection unit 145, 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. It is possible to adjust the relative shift amount between the timing at which the outgoing terahertz wave THz enters the terahertz wave detection element 130 and the timing at which the probe light LB2 enters the terahertz wave detection element 130. 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 wave detection element 130 can indirectly detect the time waveform of the terahertz wave THz.

  In order to adjust the optical path length of the probe light LB2, the optical delay device 120 includes a retroreflector 121, which is a specific example of “retroreflective means”, 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 optical delay device 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 wave 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. Note that the X1, Y1, and Z1 axes in FIG. 2A correspond to three axes that intersect each other at an angle of 90 degrees.

  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 (specifically, the Z1 axis direction in FIG. 2A). The antenna 112 and the antenna 113 are disposed on the substrate 111 so as to be arranged in parallel along the short direction (specifically, the Y1 axis direction in FIG. 2A). A gap (that is, a gap) 114 of about several micrometers is secured between the antenna 112 and the antenna 113. Since the gap 114 is sandwiched between the antenna 112 and the antenna 113 extending in the longitudinal direction, the gap 114 also extends in the longitudinal direction (specifically, the Z1 axis direction in FIG. 2A). ing. 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 and the antenna 113. 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. Note that the X1, Y1, and Z1 axes in FIG. 2B also correspond to three axes that intersect each other at an angle of 90 degrees.

  When the probe light LB2 is irradiated to the gap 134, carriers are generated in the terahertz wave detection element 130 by light excitation by the probe light LB2. When the terahertz wave detecting element 130 is irradiated with the terahertz wave detection element 130 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. To do. 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 lock-in detection unit 145 performs synchronous detection on the voltage signal using the bias voltage generated by the bias voltage generation unit 141 as a reference signal. As a result, the lock-in detection unit 145 detects the sample value of the terahertz wave THz. Thereafter, the lock-in detector 145 detects the time waveform of the terahertz waveform by repeating the same operation 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. can do. However, lock-in detection may not be used when a sufficient signal strength against noise is obtained. Thereafter, 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.

  In such a terahertz wave measuring apparatus 100, in the first embodiment, the terahertz wave detecting element 130 and the retroreflecting mirror 121 are detected by the terahertz wave detecting element 130 with accuracy of detecting the terahertz wave THz (in other words, by the terahertz wave measuring apparatus 100). They are arranged so as to satisfy a predetermined condition determined from the viewpoint of reducing the influence of the tilt (positional deviation) of the retroreflecting mirror 121 on the analysis accuracy of the characteristics of the measurement object. Hereinafter, an arrangement mode of the terahertz wave detecting element 130 and the retroreflecting mirror 121 will be described in detail.

(1-2) Arrangement Mode of Terahertz Wave Detection Element and Retroreflecting Mirror Subsequently, an arrangement mode of the terahertz wave detection element 130 and the retroreflecting mirror 121 will be described with reference to FIGS. FIG. 3 is a graph showing the relationship between the amount of positional deviation of the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 and the current signal output from the terahertz wave detecting element 130. FIG. 4 is a plan view showing the optical path (incident optical path and reflected optical path) of the probe light LB2 with respect to the inclination (positional deviation) of the retroreflecting mirror 121. FIG. FIG. 5 is a perspective view showing an arrangement mode of the terahertz wave detecting element 130 and the retroreflecting mirror 121 in the first embodiment.

  First, the terahertz wave detecting element 130 depends on the direction in which the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 is shifted, and the terahertz wave detecting element 130 detects the terahertz wave THz (specifically, terahertz wave THz). The direction dependency is that the fluctuation amount of the current signal output from the wave detection element 130 fluctuates. Specifically, as described above, the terahertz wave detection element 130 outputs a current signal when the gap 134 is irradiated with the terahertz wave THz while the probe light LB2 is irradiated onto the gap 134. Here, the gap 134 extends along the Z1 axis direction, which is a specific example of the “third direction”. Considering the extending direction of the gap 134, even if the irradiation position of the probe light LB2 is shifted along the extending direction of the gap 134 (that is, the Z1 axis direction in FIG. 2B), the probe light LB2 is still more likely to continue being irradiated to the gap 134. On the other hand, the irradiation position of the probe light LB2 is a direction orthogonal to the extending direction of the gap 134, and a direction orthogonal to both the direction of the optical path of the probe light LB (that is, the X1 axis direction in FIG. 2B). If it deviates along (that is, the Y1 axis direction in FIG. 2B), the possibility that the probe beam LB2 is not irradiated to the gap 134 becomes relatively high.

  Then, as shown in FIG. 3, when the irradiation position of the probe light LB2 is shifted along the extending direction (Z1 axis direction) of the gap 134, the fluctuation amount of the current signal output from the terahertz wave detection element 130 (specifically, Specifically, the decrease amount) is a current signal output from the terahertz wave detection element 130 when the irradiation position of the probe light LB2 is shifted along the direction orthogonal to the extending direction of the gap 134 (Y1-axis direction). It becomes smaller than the fluctuation amount (specifically, the reduction amount). Specifically, as shown in FIG. 3, when the irradiation position of the probe light LB2 is shifted along the extending direction (Z1-axis direction) of the gap 134, and the direction orthogonal to the extending direction (Y1-axis direction). In any case, the current signal output from the terahertz wave detecting element 130 decreases as the amount of deviation increases (for the sake of simplicity of explanation, the current signal in FIG. ). However, as shown in FIG. 3, the decrease amount of the current signal output from the terahertz wave detection element 130 when the irradiation position of the probe light LB2 is shifted by a predetermined amount along the extending direction (Z1-axis direction) of the gap 134. Is smaller than the decrease amount of the current signal output from the terahertz wave detection element 130 when the irradiation position of the probe light LB2 is shifted by the same amount along the direction orthogonal to the extending direction of the gap 134 (Y1-axis direction). It has become. Typically, when the irradiation position of the probe light LB2 is shifted along the extending direction of the gap 134 (Z1-axis direction), the irradiation position of the probe light LB2 is the extending direction of the gap 134 (Z1-axis direction). In many cases, the amount of decrease in the current signal output from the terahertz wave detection element 130 is minimized as compared with a case where the current signal is shifted along a different direction. That is, when the irradiation position of the probe light LB2 is shifted along the extending direction (Z1-axis direction) of the gap 134, the irradiation position of the probe light LB2 is orthogonal to the extending direction of the gap 134 (Y1-axis direction). It can be said that the influence on the detection accuracy of the terahertz wave THz by the terahertz wave detection element 130 (in other words, the analysis accuracy of the characteristics of the measurement object by the terahertz wave measurement device 100) is small. Typically, when the irradiation position of the probe light LB2 is shifted along the extending direction of the gap 134 (Z1-axis direction), the irradiation position of the probe light LB2 is the extending direction of the gap 134 (Z1-axis direction). Compared to the case where the terahertz wave detection element 130 is shifted along a different direction, the influence on the detection accuracy of the terahertz wave THz by the terahertz wave detection element 130 (in other words, the analysis accuracy of the characteristics of the measurement object by the terahertz wave measurement device 100) is minimal. Often becomes. In other words, from the viewpoint of reducing the influence on the detection accuracy of the terahertz wave THz by the terahertz wave detection element 130 (in other words, the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring device 100), the extension of the gap 134 is achieved. The positional deviation of the irradiation position of the probe light LB2 along the existing direction (Z1-axis direction) is more than the positional deviation of the irradiation position of the probe light LB2 along the direction orthogonal to the extending direction of the gap 134 (Y1-axis direction). Easy to be tolerated.

  As described above, in the terahertz wave detection element 130, the tolerance for the displacement of the irradiation position of the probe light LB2 along the extending direction (Z1-axis direction) of the gap 134 is orthogonal to the extending direction of the gap 134 ( It has a direction dependency of being larger than the tolerance for the positional deviation of the irradiation position of the probe light LB2 along the Y1-axis direction). The “Z1 axis direction” and the “Y1 axis direction” are specific examples of the “first direction” and the “second direction”, respectively.

  On the other hand, the retroreflecting mirror 121 also has direction dependency that whether or not the probe light LB2 can be appropriately retroreflected depends on the inclination direction of the retroreflecting mirror 121. .

  Specifically, as shown in FIGS. 4A and 4B, each of the two reflecting surfaces 121a and 121b is in a plane defined by two orthogonal axes, the X2 axis and the Y2 axis. The orthogonal retroreflection mirror 121 will be described as an example.

  Here, as shown in FIG. 4A, the retroreflecting mirror 121 receives the incident light path of the probe light LB2 incident on the retroreflecting mirror 121 and the probe light LB2 emitted from the retroreflecting mirror 121. The direction along the plane including the reflected optical path (X2-Y2 plane in FIG. 4A) and orthogonal to the incident optical path and the reflected optical path of the probe light LB2 (specifically, FIG. A case is assumed in which it is tilted along the Y2 axis direction of a). In other words, the case where the retroreflecting mirror 121 is tilted with the direction perpendicular to the plane including the incident optical path and the reflected optical path of the probe light LB2 (specifically, the Z2 axis direction in FIG. 4A) as the rotation center. Suppose. In other words, the retroreflection 121 is reflected along the yaw direction (specifically, the Y2 axis direction in FIG. 4A) with respect to the incident optical path of the probe light LB2 incident on the retroreflector 121. Assume a tilted case.

  In this case, as shown in the lower drawing of FIG. 4A, the retroreflecting mirror 121 can retroreflect the probe light LB2. Therefore, the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 is hardly displaced along the inclination direction of the retroreflecting mirror 121 (Y2-axis direction, yaw direction). That is, the retroreflective mirror 121 has a relatively high deviation angle accuracy in the yaw direction with respect to the incident optical path of the probe light LB2 incident on the retroreflective mirror 121.

  On the other hand, as shown in FIG. 4 (b), the retroreflecting mirror 121 receives the incident light path of the probe light LB 2 incident on the retroreflecting mirror 121 and the probe light LB 2 emitted from the retroreflecting mirror 121. A case is assumed in which it is tilted along a direction (specifically, the Z2 axis direction in FIG. 4B) perpendicular to the plane including the reflected light path (X2-Y2 plane in FIG. 4B). In other words, the retroreflecting mirror 121 is in a direction along a plane including the incident optical path and the reflected optical path of the probe light LB2 and is orthogonal to each of the incident optical path and the reflected optical path of the probe light LB2 (specifically, A case is assumed in which tilting is performed with the Y2 axis direction in FIG. In other words, the retroreflective mirror 121 moves along the pitch direction (specifically, the Z2 axis direction in FIG. 4B) with respect to the incident optical path of the probe light LB2 incident on the retroreflective mirror 121. Assume a tilted case.

  In this case, as shown in the lower drawing of FIG. 4B, the retroreflecting mirror 121 cannot retroreflect the probe light LB2. Specifically, the reflected light path of the probe light LB2 emitted from the retroreflecting mirror 121 is the direction of the inclination of the retroreflecting mirror 121 with respect to the incident light path of the probe light LB2 incident on the retroreflecting mirror 121 ( It is gradually shifted along the Z2 axis direction (pitch direction). Accordingly, the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 is also displaced along the inclination direction of the retroreflecting mirror 121 (Z2-axis direction, pitch direction). That is, the retroreflective mirror 121 has relatively low declination accuracy in the pitch direction with respect to the incident optical path of the probe light LB2 incident on the retroreflective mirror 121.

  Thus, the retroreflecting mirror 121 cannot retroreflect the probe light LB2 due to the inclination of the retroreflecting mirror 121 along the pitch direction with respect to the incident optical path of the probe light LB2, while the probe light LB2 Even if the retroreflector 121 is tilted along the yaw direction with respect to the incident optical path, the probe light LB2 can continue to be retroreflected even if it is tilted. The “Z2 axis direction (pitch direction)” and “Y2 axis direction (yaw direction)” are specific examples of “third direction” and “fourth direction”, respectively.

  Considering the direction dependency of the terahertz wave detection element 130 and the direction dependency of the retroreflector 121, in the first embodiment, the probe light LB2 cannot be retroreflected as shown in FIG. The direction of the retroreflecting mirror 121 (that is, the Z2 axis direction and the pitch direction) and the direction of the terahertz wave detection element 130 (that is, preferably the maximum) with a relatively large tolerance (that is, the maximum). , The Z1 axis direction) are aligned (typically coincide) with each other, the terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged. In other words, the detection accuracy of the terahertz wave THz caused by the tilt direction of the retroreflector 121 (that is, the Z2 axis direction and the pitch direction) that makes it impossible to retroreflect the probe light LB2 and the tilt of the retroreflector 121. Of the terahertz wave detecting element 130 (that is, the direction in which the current signal decreases) is typically relatively small (preferably minimized) (that is, in the Z1 axis direction). The terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged so as to match. That is, the gap 134 provided in the terahertz wave detecting element 130 indicates the direction of displacement of the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction). The terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged so as to be aligned with the extending direction of.

  In the terahertz wave measuring apparatus 100 in which the terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged in such a manner, it is assumed that the retroreflecting mirror 121 is tilted along the Z2 axis direction (pitch direction). In this case, due to the tilt of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction), the irradiation position of the probe light LB2 on the terahertz wave detection element 130 is the tilt direction of the retroreflecting mirror 121 (that is, The position is shifted along the Z2 axis direction (pitch direction) (see the dashed line arrow in FIG. 5). Therefore, if there is no contrivance in the arrangement mode of the terahertz wave detecting element 130 and the retroreflecting mirror 121 (specifically, unless arranged with a positional relationship as shown in FIG. 5), the probe light LB2 The gap 134 may not be irradiated. However, in the first embodiment, the direction of displacement of the irradiation position of the probe light LB2 caused by the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction) is the gap 134 provided in the terahertz wave detection element 130. It is aligned with the extending direction. Therefore, even if the irradiation position of the probe light LB2 is displaced due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction), the probe light LB2 may still be irradiated to the gap 134. Becomes higher. As a result, the influence of the tilt of the retroreflector 121 along the Z2 axis direction (pitch direction) on the detection accuracy of the terahertz wave THz by the terahertz wave detecting element 130 is reduced. In other words, deterioration of the detection accuracy of the terahertz wave THz by the terahertz wave detecting element 130 due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction) can be minimized. For this reason, the influence of the tilt of the retroreflector 121 along the Z2 axis direction (pitch direction) on the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 is reduced. In other words, the degradation of the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 due to the inclination of the retroreflector 121 along the Z2 axis direction (pitch direction) can be minimized.

  For reference, it is assumed that the retroreflector 121 is tilted along the Y2 axis direction (yaw direction). In this case, the retroreflective mirror 121 is a probe regardless of the presence / absence of the arrangement of the terahertz wave detection element 130 and the retroreflector 121 (specifically, the arrangement having a positional relationship as shown in FIG. 5). The light LB2 can be retroreflected. Therefore, the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 is hardly displaced along the inclination direction of the retroreflecting mirror 121 (Y2-axis direction, yaw direction). For this reason, even if the retroreflector 121 is tilted along the Y2 axis direction (yaw direction), there is a high possibility that the probe beam LB2 is still applied to the gap 134. Therefore, the retroreflector along the Y2 axis direction (pitch direction) with respect to the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 (in other words, the detection accuracy of the terahertz wave THz by the terahertz wave detection element 130). Needless to say, the influence of the inclination of 121 is small.

  Note that the above-described terahertz wave detecting element 130 is merely an example, and a terahertz wave detecting element 130 different from the terahertz wave detecting element 130 illustrated in FIG. 2B may be used. For example, as shown in FIG. 6A, a terahertz wave detecting element 130a including a striped antenna 132a and an antenna 133a may be used. Alternatively, for example, as shown in FIG. 6B, a terahertz wave detecting element 130b including a bow-tie antenna 132b and an antenna 133b may be used. Alternatively, for example, as shown in FIG. 6C, a terahertz wave detecting element 130c including a spiral antenna 132c and an antenna 133c may be used. Regardless of the terahertz wave detecting element 130, the terahertz wave THz detection accuracy (specifically, the terahertz wave detecting element 130 is dependent on the direction in which the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 is shifted). Has a direction dependency that the fluctuation amount of the current signal output from the terahertz wave detection element 130 fluctuates. Furthermore, not only the terahertz wave detection element 130 illustrated in FIGS. 6A to 6C but also the terahertz wave depending on the direction in which the irradiation position of the probe light LB2 on the terahertz wave detection element 130 is shifted. As long as the detection accuracy of the terahertz wave THz by the detection element 130 (specifically, the fluctuation amount of the current signal output from the terahertz wave detection element 130) varies, any terahertz wave may be used. A detection element 130 may be used.

  Even in the case where the terahertz wave detecting element 130c is used from each of the terahertz detecting elements 130a, the direction of the retroreflecting mirror 121 that cannot retroreflect the probe light LB2 (that is, the Z2 axis direction and the pitch) The terahertz wave detecting element 130 and the direction of the terahertz wave detecting element 130 (that is, the Z1 axis direction) in which the tolerance of displacement is relatively large (typically coincide). A retroreflector 121 is preferably disposed. As a result, the various effects described above are favorably enjoyed.

  The terahertz wave generating element 110 is also different from the terahertz wave generating element 110 illustrated in FIG. 2A as in the terahertz wave detecting element 130 (for example, FIG. 6A to FIG. 6 (c)) may be used.

  The optical delay device 120 described above is merely an example, and an optical delay device 120 different from the optical delay device 120 illustrated in FIG. 1 may be used. For example, as shown in FIG. 7, an optical delay device 120a including a rotating substrate 122a that can be rotated by the operation of a motor 123 (not shown) and a plurality of (four in FIG. 7) retroreflecting mirrors 121 is used. May be. In such an optical delay device 120a, the plurality of retroreflecting mirrors 121 are preferably arranged at equal intervals on a circle C centered on the rotation axis of the rotating substrate 122a. Accordingly, each of the plurality of retroreflecting mirrors 121 circulates on the circle C as the rotating substrate 122a rotates.

  Even in such an optical delay device 120a, each retroreflecting mirror 121 determines whether or not the probe light LB2 can be appropriately retroreflected depending on the inclination direction of the retroreflecting mirror 121. It has direction dependency.

  Specifically, as shown in FIG. 8A, the description will be focused on a certain reflecting mirror 121. The retroreflecting mirror 121 includes a plane including the incident optical path of the probe light LB2 incident on the retroreflecting mirror 121 and the reflected optical path of the probe light LB2 exiting from the retroreflecting mirror 121 (in FIG. 8A). A case is assumed in which it is tilted along a direction (specifically, the Z2 axis direction in FIG. 8A) perpendicular to the (X2-Y2 plane). Specifically, as shown in the upper drawing of FIG. 8A, as an initial state, the retroreflecting mirror 121 is inclined so as to have an angle of α degrees with respect to the Z2 axis direction. Further, as shown in the lower drawing of FIG. 8A, as an initial state, a line connecting the center of the rotating substrate 122a and the retroreflecting mirror 121 is assumed to coincide with the Y2 axis direction.

  In this case, as shown in the upper drawing of FIG. 8A, the retroreflecting mirror 121 cannot retroreflect the probe light LB2. Specifically, the reflected light path of the probe light LB2 emitted from the retroreflecting mirror 121 has an angle of 2α degrees with respect to the incident light path of the probe light LB2 incident on the retroreflecting mirror 121. .

  Based on such an initial state, a state is assumed in which the rotating substrate 122a is rotated by θ degrees as shown in FIG. 8B. That is, it is assumed that a line connecting the center of the rotating substrate 122a and the retroreflecting mirror 121 intersects at an angle of θ degrees with respect to the Y2 axis direction.

  In this case, as shown in the upper drawing of FIG. 8B, the retroreflective mirror 121 is inclined so as to have an angle of β degrees with respect to the Z2 axis direction as the rotating substrate 122a rotates. . This angle β is expressed by a mathematical formula: β = arctan (tan α × cos θ). That is, it can be seen that the angle β varies depending on the rotation angle θ of the rotating substrate 122a. Therefore, the irradiation position of the probe light LB2 on the terahertz wave detecting element 130 is also shifted along the inclination direction of the retroreflecting mirror 121 (Z2-axis direction and pitch direction) and depending on the rotation angle of the rotating substrate 122a. It will be displaced by the amount.

  Even when such an optical delay device 120a is used, the inclination direction of the retroreflector 121 (that is, the Z2 axis direction and the pitch direction) and the position where the probe light LB2 cannot be retroreflected, and the position The terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged so that the direction of the terahertz wave detecting element 130 (that is, the Z1 axis direction) in which the tolerance of displacement is relatively large is aligned (typically coincides). Preferably they are arranged. As a result, the various effects described above are favorably enjoyed.

(1-3) Modified Example of Arrangement Mode of Terahertz Wave Detection Element and Retroreflecting Mirror Next, a modified example of the arrangement mode of the terahertz wave detecting element 130 and the retroreflecting mirror 121 will be described with reference to FIG. FIG. 9 is a perspective view showing an arrangement mode of the terahertz wave detecting element 130 and the retroreflecting mirror 121 in a modified example.

  In the above description, the description has been made by using an example in which the direction of the inclination of the retroreflecting mirror 121 in which the probe light LB2 cannot be retroreflected is aligned with the extending direction of the gap 134 of the terahertz wave detecting element 130. . This is because, in the above description, the tolerance of the positional deviation of the irradiation position of the probe light LB2 along the extending direction of the gap 134 of the terahertz wave detecting element 130 is maximized (that is, the terahertz wave by the terahertz wave detecting element 130). This is because it is estimated that the detection accuracy of the wave THz is maximized (substantially, the decrease amount of the current signal is minimized).

  However, depending on the characteristics of the terahertz wave measuring apparatus 100 (for example, the shape of the gap 134 of the terahertz wave detecting element 130 and the specification of the retroreflecting mirror 121), the extending direction of the gap 134 of the terahertz wave detecting element 130 There may be a case where the tolerance of displacement of the irradiation position of the probe light LB2 does not become maximum. For example, along a direction (a direction along a dashed line arrow in FIG. 9) that is different from the extending direction of the gap 134 of the terahertz wave detection element 130 (for example, intersects at an angle larger than 0 degree and smaller than 90 degrees). In addition, the tolerance of displacement of the irradiation position of the probe light LB2 may be maximized. In this case, as shown in FIG. 9, the direction of the inclination of the retroreflector 121 where the probe light LB2 cannot be retroreflected is the direction in which the tolerance of the displacement of the irradiation position of the probe light LB2 is maximized. It is preferable that the terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged so as to be aligned with (for example, the direction along the one-dot chain line arrow in FIG. 9).

  Even if it arrange | positions in this way, the various effects mentioned above are enjoyed suitably. In addition, particularly when a plurality of retroreflecting mirrors 121 are arranged on the rotating substrate 122a as shown in FIG. 7, even if the retroreflecting mirror 121 is inclined along the Z2 axis direction, The irradiation position of the probe light LB2 may be shifted not only along the Z2 axis direction but also along the Y2 axis direction. Even in this case, the inclination direction of the retroreflecting mirror 121 where the probe light LB2 cannot be retroreflected is the direction in which the tolerance of displacement of the irradiation position of the probe light LB2 is maximized (that is, the terahertz wave). The terahertz wave detecting element 130 and the retroreflecting mirror 121 are aligned in a direction in which the detection accuracy of the terahertz wave THz by the detecting element 130 is maximized and substantially the direction in which the amount of decrease in the current signal is minimized. Has been placed. For this reason, the deterioration of the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 due to the inclination of the retroreflecting mirror 121 remains unchanged.

(2) Second Example Next, a terahertz wave measuring apparatus 200 according to a second example will be described with reference to FIGS. FIG. 10 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 200 according to the second embodiment. FIG. 11 is a perspective view showing an arrangement mode of the terahertz wave generating element 110 and the retroreflecting mirror 121 in the second embodiment. 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.

  As shown in FIG. 10, the terahertz wave measuring apparatus 200 of the second embodiment is different from that of the first embodiment in that the arrangement position of the optical delay device 120 is different from the arrangement position of the optical delay device 120 of the first embodiment. Different from the terahertz wave measuring apparatus 100. That is, the terahertz wave measuring apparatus 200 according to the second embodiment is the first embodiment in which the optical delay 120 is arranged in the optical path of the probe light LB2 in that the optical delay 120 is arranged in the optical path of the pump light LB1. Different from the terahertz wave measuring apparatus 100 of FIG. Other configurations of the terahertz wave measuring apparatus 200 of the second embodiment may be the same as other configurations of the terahertz wave measuring apparatus 100 of the first embodiment.

  Here, similarly to the terahertz wave detection element 130, the terahertz wave generation element 110 also generates the terahertz wave generation element 110 depending on the direction in which the irradiation position of the pump light LB1 on the terahertz wave generation element 110 is shifted. It has direction dependency that the characteristic (for example, amplitude) of the terahertz wave THz varies. Specifically, as described above, the terahertz wave generation element 110 generates the terahertz wave THz when a bias voltage is applied to the gap 114 while the pump light LB1 is irradiated on the gap 114. Here, the gap 114 extends along the Z1 axis direction (see FIG. 2A). Considering the extending direction of the gap 114, even if the irradiation position of the pump light LB1 is shifted along the extending direction of the gap 114 (that is, the Z1 axis direction in FIG. 2A), the pump light There is a relatively high possibility that LB1 is still irradiated to the gap 114. On the other hand, if the irradiation position of the pump light LB1 is shifted along the direction orthogonal to the extending direction of the gap 114 (that is, the Y1 axis direction in FIG. 2A), the pump light LB1 is irradiated to the gap 114. The possibility of disappearing is relatively high.

  Then, when the irradiation position of the pump light LB1 is shifted along the extending direction (Z1-axis direction) of the gap 114, the amount of fluctuation (specifically, the amount of fluctuation of the terahertz wave THz generated by the terahertz wave generating element 110) The amount of fluctuation in the amplitude of the terahertz wave THz generated by the terahertz wave generation element 110 when the irradiation position of the pump light LB1 is shifted along the direction in which the gap 114 extends (Y1 axis direction). Actually, it becomes smaller than the decrease amount). Typically, when the irradiation position of the pump light LB1 is shifted along the extending direction (Z1 axis direction) of the gap 114, the amount of decrease in the amplitude of the terahertz wave THz generated by the terahertz wave generating element 110 is minimized. Often becomes. That is, when the irradiation position of the pump light LB1 is shifted along the extending direction (Z1-axis direction) of the gap 114, the irradiation position of the pump light LB1 is orthogonal to the extending direction of the gap 114 (Y1-axis direction). ), The influence on the characteristics of the terahertz wave THz generated by the terahertz wave generating element 110 (in other words, the accuracy of analysis of the characteristics of the measurement object by the terahertz wave measuring apparatus 100) is small. . Typically, when the irradiation position of the pump light LB1 is shifted along the extending direction (Z1-axis direction) of the gap 114, the characteristics of the terahertz wave THz generated by the terahertz wave generating element 110 (in other words, terahertz) In many cases, the influence on the analysis accuracy of the characteristics of the measurement object by the wave measuring device 100 is minimized. In other words, from the viewpoint of reducing the influence on the characteristics of the terahertz wave THz generated by the terahertz wave generation element 110 (in other words, the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100), The positional deviation of the irradiation position of the pump light LB1 along the extending direction (Z1-axis direction) is more than the positional deviation of the irradiation position of the pump light LB1 along the direction orthogonal to the extending direction of the gap 114 (Y1-axis direction). Even easier to accept.

  As described above, in the terahertz wave generating element 110, the tolerance for the displacement of the irradiation position of the pump light LB1 along the extending direction (Z1-axis direction) of the gap 114 is perpendicular to the extending direction of the gap 114 ( It has a direction dependency of being larger than the tolerance for the positional deviation of the irradiation position of the pump light LB1 along the Y1-axis direction).

  Therefore, in the second embodiment, as in the first embodiment, as shown in FIG. 11, the tilt direction of the retroreflector 121 that makes it impossible to retroreflect the pump light LB1 (that is, the Z2 axis direction). , The pitch direction) and the direction of the terahertz wave generating element 110 (that is, the Z1 axis direction) in which the tolerance of displacement is relatively large (preferably maximized) are aligned (typically coincident). ), The terahertz wave generating element 110 and the retroreflecting mirror 121 are arranged. In other words, the tilt direction of the retroreflector 121 (that is, the Z2-axis direction and the pitch direction) that makes it impossible to retroreflect the pump light LB1 and the amplitude of the terahertz wave THz due to the tilt of the retroreflector 121 are shown. The terahertz wave generating element 110 is arranged so that the direction of the terahertz wave generating element 110 (that is, preferably, the amount of decrease) is relatively small (preferably, the Z1 axis direction) is aligned (typically coincides). In addition, a retroreflector 121 is disposed. That is, the gap 114 provided in the terahertz wave generating element 110 indicates the direction of displacement of the irradiation position of the pump light LB1 on the terahertz wave generating element 110 due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction). The terahertz wave generating element 110 and the retroreflecting mirror 121 are arranged so as to be aligned with the extending direction of.

  In the terahertz wave measuring apparatus 100 in which the terahertz wave generating element 110 and the retroreflecting mirror 121 are arranged in such a manner, it is assumed that the retroreflecting mirror 121 is tilted along the Z2 axis direction (pitch direction). In this case, due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction), the irradiation position of the pump light LB1 on the terahertz wave generating element 110 is the inclination direction of the retroreflecting mirror 121 (that is, The position is shifted along the Z2 axis direction (pitch direction) (see the dashed line arrow in FIG. 11). Therefore, if there is no contrivance in the arrangement mode of the terahertz wave generating element 110 and the retroreflecting mirror 121 (specifically, unless arranged with a positional relationship as shown in FIG. 11), the pump light LB1 The gap 114 may not be irradiated. However, in the second embodiment, the direction of displacement of the irradiation position of the pump light LB21 due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction) is the gap 114 included in the terahertz wave generating element 110. It is aligned with the extending direction. Therefore, even if the irradiation position of the pump light LB1 due to the tilt of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction) is displaced, the pump light LB1 may still be irradiated to the gap 114. Get higher. As a result, the influence of the tilt of the retroreflector 121 along the Z2 axis direction (pitch direction) on the characteristics of the terahertz wave THz generated by the terahertz wave generating element 110 is reduced. In other words, the deterioration of the characteristics of the terahertz wave THz generated by the terahertz wave generating element 110 due to the inclination of the retroreflecting mirror 121 along the Z2 axis direction (pitch direction) can be minimized. For this reason, the influence of the tilt of the retroreflector 121 along the Z2 axis direction (pitch direction) on the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 is reduced. In other words, the degradation of the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 due to the inclination of the retroreflector 121 along the Z2 axis direction (pitch direction) can be minimized.

  For reference, it is assumed that the retroreflector 121 is tilted along the Y2 axis direction (yaw direction). In this case, the retroreflective mirror 121 is a pump regardless of the arrangement of the terahertz wave generating element 110 and the retroreflective mirror 121 (specifically, the arrangement having a positional relationship as shown in FIG. 11). The light LB1 can be retroreflected. Therefore, the irradiation position of the pump light LB1 on the terahertz wave generating element 110 is hardly displaced along the inclination direction of the retroreflecting mirror 121 (Y2-axis direction, yaw direction). For this reason, even if the retroreflector 121 is tilted along the Y2 axis direction (yaw direction), there is a high possibility that the pump light LB1 is still applied to the gap 114. Therefore, retroreflective along the Y2 axis direction (pitch direction) with respect to the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 (in other words, the characteristics of the terahertz wave THz generated by the terahertz wave generating element 110). Needless to say, the influence of the tilt of the mirror 121 is small.

  Needless to say, the various configurations described in the first embodiment may be applied as appropriate in the second embodiment.

  Further, the tolerance for the displacement of the irradiation position of the pump light LB1 along the extending direction (Z1-axis direction) of the gap 114 of the terahertz wave generating element 110 and the extending direction of the gap 134 of the terahertz wave detecting element 130 (Z1). The laser light that should be retroreflected by the retroreflecting mirror 121 is the pump light LB1 and the probe light LB2 according to the magnitude relationship between the tolerance for the positional deviation of the irradiation position of the probe light LB2 along the axial direction). Either of them may be determined.

  For example, the tolerance for the displacement of the irradiation position of the pump light LB1 along the extending direction (Z1-axis direction) of the gap 114 of the terahertz wave generating element 110 is the extending direction of the gap 134 of the terahertz wave detecting element 130 (Z1). When the tolerance for the positional deviation of the irradiation position of the probe light LB2 along the axial direction is larger than the tolerance, the retroreflecting mirror 121 may retroreflect the pump light LB1. That is, the retroreflecting mirror 121 may be installed in the optical path of the pump light LB1. In other words, the retroreflecting mirror 121 may not be installed in the optical path of the probe light LB2. In this case, the terahertz wave generating element in which the tilt direction (that is, the Z2 axis direction and the pitch direction) of the retroreflecting mirror 121 in which the pump light LB1 cannot be retroreflected and the tolerance of displacement is relatively large. It is preferable that the terahertz wave generating element 110 and the retroreflector 121 are arranged so that the direction of 110 (that is, the direction of the Z1 axis and the extending direction of the gap 114) is aligned. In other words, even if the terahertz wave detecting element 130 is arranged without considering the tilt direction of the retroreflector 121 that cannot retroreflect the probe light LB2 (that is, the Z2 axis direction and the pitch direction). Good.

  Alternatively, for example, the tolerance for the displacement of the irradiation position of the probe light LB2 along the extending direction (Z1-axis direction) of the gap 134 of the terahertz wave detecting element 130 is the extending direction of the gap 114 of the terahertz wave generating element 110. When the tolerance for the displacement of the irradiation position of the pump light LB1 along (Z1 axis direction) is larger than the tolerance, the retroreflecting mirror 121 may retroreflect the probe light LB2. That is, the retroreflecting mirror 121 may be installed in the optical path of the probe light LB2. In other words, the retroreflecting mirror 121 may not be installed in the optical path of the pump light LB1. In this case, the tilt direction of the retroreflective mirror 121 that cannot retroreflect the probe light LB2 (that is, the Z2 axis direction and the pitch direction) and the terahertz wave detection element in which the tolerance for positional deviation is relatively large. It is preferable that the terahertz wave detecting element 130 and the retroreflecting mirror 121 are arranged so as to align with the direction 130 (that is, the Z1 axis direction and the extending direction of the gap 134). In other words, even if the terahertz wave generating element 110 is arranged without considering the inclination direction of the retroreflector 121 that cannot retroreflect the pump light LB1 (that is, the Z2 axis direction and the pitch direction). Good.

  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 with such a change is also a technical concept of the present invention. include.

100, 200 Terahertz wave measuring device 101 Pulse laser device 110 Terahertz wave generating element 111 Substrate 112, 113 Antenna 114 Gap 120, 220 Optical delay device 121 Retroreflector 122 Feed screw mechanism 123 Motor 130 Terahertz wave detecting element 131 Substrate 132, 133 Antenna 134 Gap 141 Bias voltage generator 144 I-V converter 145 Lock-in detector 150 Arithmetic processor 161 Beam splitter 162, 163 Reflector LB Pulse laser light LB1 Pump light LB2 Probe light THz Terahertz wave

Claims (16)

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;
Retroreflective means for retroreflecting the second laser light and retroreflecting the second laser light retroreflected to the detection means,
The detection means has a position along a second direction in which a tolerance of positional deviation along the first direction of the irradiation position of the second laser light is different from the first direction of the irradiation position of the second laser light. It has a direction dependency of becoming larger than the tolerance of deviation,
While the retroreflective means makes the retroreflective impossible due to the inclination of the retroreflective means along the third direction, the retroreflective means may be inclined along a fourth direction different from the third direction. It has a direction dependency that the retroreflection is possible,
The first direction and the third direction are aligned. A terahertz wave measuring device, wherein: The detection means includes two conductive portions extending so as to sandwich a gap therebetween,
The first direction is a direction along the extending direction of the gap,
The terahertz wave measuring apparatus according to claim 1, wherein the second direction is a direction different from an extending direction of the gap. The detection means includes two conductive portions extending so as to sandwich a gap therebetween,
The first direction is a direction different from a direction along the extending direction of the gap and a direction perpendicular to the extending direction of the gap,
The terahertz wave measuring apparatus according to claim 1, wherein the second direction is a direction orthogonal to the first direction.   4. The terahertz wave measuring apparatus according to claim 1, wherein the first direction is a direction in which a tolerance of displacement of the irradiation position of the second laser light is maximized. 5.   The first direction is a direction in which the amount of deterioration due to the positional deviation of the irradiation position of the second laser light of the detection accuracy of the terahertz wave by the detection unit is minimized. 5. The terahertz wave measuring device according to any one of 4. In the third direction, the second laser beam reflected by the retroreflective means and the optical path of the second laser light incident on the retroreflective means in a state where the retroreflective means retroreflects the second laser light. The direction is different from the direction along the plane including the optical path of the laser beam,
In the fourth direction, the optical path of the second laser light incident on the retroreflective means in a state where the retroreflective means retroreflects the second laser light and the second reflected by the retroreflective means. The terahertz wave measuring device according to any one of claims 1 to 5, wherein the terahertz wave measuring device is in a direction along a plane including an optical path of laser light. The retroreflective means includes a first reflecting mirror and a second reflecting mirror having a reflecting surface that intersects the reflecting surface of the first reflecting mirror at an angle of 90 degrees.
The third direction is a direction different from the direction in which the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror face each other.
The said 4th direction is a direction along the direction where the reflective surface of a said 1st reflective mirror and the reflective surface of a said 2nd reflective mirror oppose. The claim 1 characterized by the above-mentioned. The terahertz wave measuring device described. The generating means has a position along a sixth direction in which a tolerance of positional deviation along the fifth direction of the irradiation position of the first laser light is different from the fifth direction of the irradiation position of the first laser light. It has a direction dependency of becoming larger than the tolerance of deviation,
When the tolerance of the positional deviation along the first direction of the irradiation position of the second laser light is larger than the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light (I) The retroreflective means retroreflects the second laser beam, and (ii) the first direction and the third direction are aligned,
When the tolerance of the positional deviation along the fifth direction of the irradiation position of the first laser light is larger than the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light. (I) The retroreflective means retroreflects the first laser beam, and (ii) the fifth direction and the third direction are aligned. 8. 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;
Retroreflective means for retroreflecting the first laser light, and retroreflecting means for guiding the retroreflected first laser light to the generating means,
The generating means has a position along a second direction in which a tolerance of positional deviation along the first direction of the irradiation position of the first laser light is different from the first direction of the irradiation position of the first laser light. It has a direction dependency of becoming larger than the tolerance of deviation,
While the retroreflective means makes the retroreflective impossible due to the inclination of the retroreflective means along the third direction, the retroreflective means may be inclined along a fourth direction different from the third direction. It has a direction dependency that the retroreflection is possible,
The first direction and the third direction are aligned. A terahertz wave measuring device, wherein: The generating means includes two conductive portions extending so as to sandwich a gap therebetween,
The first direction is a direction along the extending direction of the gap,
The terahertz wave measuring apparatus according to claim 9, wherein the second direction is a direction different from an extending direction of the gap. The generating means includes two conductive portions extending so as to sandwich a gap therebetween,
The first direction is a direction different from a direction along the extending direction of the gap and a direction perpendicular to the extending direction of the gap,
The terahertz wave measuring apparatus according to claim 9, wherein the second direction is a direction orthogonal to the first direction.   The terahertz wave measuring apparatus according to any one of claims 9 to 11, wherein the first direction is a direction in which a tolerance of a positional deviation of the irradiation position of the first laser light is maximized.   The first direction is a direction in which an amount of decrease in amplitude of the terahertz wave generated by the generating unit due to a displacement of an irradiation position of the first laser light is minimized. The terahertz wave measuring device according to any one of 1 to 12. In the third direction, the optical path of the first laser light incident on the retroreflective means in a state where the retroreflective means retroreflects the first laser light and the first reflected by the retroreflective means. The direction is different from the direction along the plane including the optical path of the laser beam,
In the fourth direction, the optical path of the second laser light incident on the retroreflective means in a state where the retroreflective means retroreflects the first laser light and the first reflected by the retroreflective means. The terahertz wave measuring device according to any one of claims 9 to 13, wherein the terahertz wave measuring device is in a direction along a plane including an optical path of laser light. The retroreflective means includes a first reflecting mirror and a second reflecting mirror having a reflecting surface that intersects the reflecting surface of the first reflecting mirror at an angle of 90 degrees.
The third direction is a direction different from the direction in which the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror face each other.
The said 4th direction is a direction along the direction where the reflective surface of a said 1st reflective mirror and the reflective surface of a said 2nd reflective mirror oppose. The any one of Claim 9 to 14 characterized by the above-mentioned. The terahertz wave measuring device described. The detecting means has a position along a sixth direction in which a tolerance of positional deviation along the fifth direction of the irradiation position of the second laser light is different from the fifth direction of the irradiation position of the second laser light. It has a direction dependency of becoming larger than the tolerance of deviation,
When the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light is larger than the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light (I) The retroreflective means retroreflects the first laser beam, and (ii) the first direction and the third direction are aligned,
When the tolerance of the positional deviation along the fifth direction of the irradiation position of the second laser light is larger than the tolerance of the positional deviation along the first direction of the irradiation position of the first laser light (I) The retroreflective means retroreflects the second laser beam, and (ii) the fifth direction and the third direction are aligned. The terahertz wave measuring device according to one item.

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