JP2014228346A - Terahertz wave measurement instrument and optical path length adjustment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of movement of a member like a mirror, which is required for giving the same amount of delay to two laser beams corresponding to pump light and probe light, by adjusting optical path lengths of the two laser beams.SOLUTION: A terahertz wave measurement instrument (100) includes: generation means (110) which generates a terahertz wave (THz) in response to irradiation with a first laser beam (LB1); detection means (120) which detects the terahertz wave emitted to a measurement object from the generation means in response to irradiation with a second laser beam (LB2); and adjustment means (120) which adjusts both of the optical path length of the first laser beam and that of the second laser beam so as to increase the optical path length of one of the first laser beam and the second laser beam and to reduce the optical path length of the other of the first laser beam and the second laser beam.

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.

Japanese Patent No. 4769490 JP-A-5-173075

  The terahertz wave measuring devices disclosed in Patent Documents 1 and 2 are mirrors (reflectors) that give an optical delay only to one of pump light and probe light (typically, probe light). ) Is used.

  The present invention adjusts the optical path lengths of two laser beams corresponding to the pump light and the probe light, thereby moving the amount of movement of a member such as a mirror necessary to give the same delay amount to the laser light. It is an object of the present invention to provide a terahertz wave measuring device and an optical path length adjusting device that make it possible to reduce the frequency.

  In order to solve the above-described problem, the terahertz wave measuring apparatus measures from the generating means by irradiating the first laser beam and generating the terahertz wave by irradiating the first laser beam and the second laser beam. Detecting means for detecting the terahertz wave applied to the object; and an optical path length of one of the first laser beam and the second laser beam is increased, and the first laser beam and the second laser beam are increased. Adjusting means for adjusting the optical path lengths of both the first laser light and the second laser light so that the optical path length of the other laser light of the second laser light is reduced.

  In order to solve the above problems, an optical path length adjusting device is an optical path length adjusting device that adjusts an optical path length difference between an optical path length of a first light beam and an optical path length of a second light beam different from the first light beam. The optical path length of one of the first light beam and the second light beam is increased and the optical path length of the other light beam of the first light beam and the second light beam is decreased. Both the optical path length of the first light beam and the optical path length of the second light beam are adjusted.

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 top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of 1st Example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of 1st Example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of a 1st comparative example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of a 1st comparative example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of the 2nd comparative example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of the 2nd comparative example. It is a block diagram which shows the structure of the terahertz wave measuring device of 2nd Example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of 2nd Example. It is a top view which shows the aspect of adjustment of the optical path length difference in the optical delay device of 2nd Example. It is a block diagram which shows the structure of the terahertz wave measuring device of 3rd Example. It is a block diagram which shows the structure of the terahertz wave measuring device of 4th Example. It is a top view which shows the relationship between the rotation angle of a turntable, and the optical path of pump light and probe light.

  Hereinafter, embodiments of the terahertz wave measuring device and the optical path length adjusting device will be described in order.

(Embodiment of terahertz wave measuring apparatus)
<1>
The terahertz wave measuring apparatus according to the present embodiment is configured to generate a terahertz wave by irradiating the first laser beam and irradiate the second laser beam to the measurement target from the generating unit. Detecting means for detecting the terahertz wave irradiated with the first laser light and the first laser light and the second laser light as an optical path length of one of the first laser light and the second laser light is increased. Adjusting means for adjusting the optical path lengths of both the first laser beam and the second laser beam so that the optical path length of the other laser beam decreases.

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

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

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

  At this time, the adjusting means adjusts the optical path length difference (in other words, the delay amount) that is the difference between the optical path length of the first laser light and the optical path length of the second laser light. In other words, the adjusting means sets the optical path length difference between the optical path length of the first laser light and the optical path length of the second laser light 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.

  In order to adjust the optical path length difference, the adjusting means adjusts the optical path lengths of both the first laser beam and the second laser beam. At this time, it is preferable that the adjusting means simultaneously adjusts the optical path lengths of both the first laser beam and the second laser beam. That is, it is preferable that the adjusting unit performs the adjustment of the optical path length of the first laser beam and the adjustment of the optical path length of the second laser beam in parallel. However, the adjusting means may perform the adjustment of the optical path length of the first laser beam and the adjustment of the optical path length of the second laser beam in succession.

  Particularly in the present embodiment, the adjusting means increases the optical path length of one of the first laser light and the second laser light, and increases the length of the other laser light of the first laser light and the second laser light. The optical path lengths of both the first laser light and the second laser light are adjusted so that the optical path length is reduced. In other words, the adjusting means adjusts the optical path lengths of both the first laser beam and the second laser beam so that when the optical path length of one laser beam increases, the optical path length of the other laser beam decreases. .

  At this time, the adjusting means can adjust the optical path lengths of both the first laser beam and the second laser beam so that the optical path length of one laser beam increases and the optical path length of the other laser beam decreases at the same time. preferable. However, the adjusting means may decrease the optical path length of the other laser beam after the optical path length of the one laser beam is increased, or increase the optical path length of the one laser beam after the optical path length of the other laser beam is decreased. In addition, the optical path lengths of both the first laser beam and the second laser beam may be adjusted.

  As a specific example, for example, the adjusting unit may increase the optical path length of the first laser light and decrease the optical path length of the second laser light while increasing the optical path length of the first laser light. May be adjusted. In this case, if the optical path length of the first laser light is increased by X1 and the optical path length of the second laser light is decreased by X2, the adjustment amount of the optical path length difference between the first laser light and the second laser light. Becomes | X1 + X2 |.

  Similarly, for example, the adjusting unit adjusts the optical path lengths of both the first laser beam and the second laser beam so that the optical path length of the second laser beam increases and the optical path length of the first laser beam decreases. May be. In this case, if the optical path length of the first laser light is reduced by Y1 and the optical path length of the second laser light is reduced by Y2, the adjustment amount of the optical path length difference between the first laser light and the second laser light. Becomes | Y1 + Y2 |.

  Here, the technical effect of the adjusting means of this embodiment will be described with reference to the adjusting means of the first comparative example that adjusts the optical path length difference by adjusting only the optical path length of the second laser light. According to the adjusting means of the first comparative example, if the optical path length of the second laser beam is reduced by X2, the adjustment amount of the optical path length difference between the first laser beam and the second laser beam is | X2 | Become. Therefore, in order for the adjustment amount of the optical path length difference between the first laser beam and the second laser beam to be | X1 + X2 |, the adjustment unit of the first comparative example is compared with the adjustment unit of the present embodiment. It is necessary to further adjust the optical path length of the second laser light. Similarly, in the adjusting means of the first comparative example, if the optical path length of the second laser beam is increased by Y2, the adjustment amount of the optical path length difference between the first laser beam and the second laser beam is | Y2 | Therefore, in order for the adjustment amount of the optical path length difference between the first laser beam and the second laser beam to be | Y1 + Y2 |, the adjustment unit of the first comparative example is compared with the adjustment unit of the present embodiment. It is necessary to further adjust the optical path length of the second laser light. In this case, the adjustment unit of the first comparative example typically needs to move a member such as a mirror that reflects the second laser light more than the adjustment unit of the present embodiment. That is, in the adjustment unit of the first comparative example, the amount of movement of a member such as a mirror necessary for adjusting the optical path length difference by the same amount is larger than that of the adjustment unit of the present embodiment. In other words, the adjustment unit of the present embodiment can reduce the amount of movement of a member such as a mirror necessary for adjusting the optical path length difference by the same amount as compared with the adjustment unit of the first comparative example.

  In the above description, the adjustment means of the first comparative example for adjusting the optical path length difference by adjusting only the optical path length of the second laser light has been described. However, only the optical path length of the first laser light is adjusted. The same applies to the adjusting means of the first comparative example that adjusts the optical path length difference.

  As described above, the adjusting unit of the present embodiment can adjust the optical path length difference by adjusting the optical path lengths of both the first laser beam and the second laser beam. Therefore, the adjustment means of this embodiment is compared with the adjustment means of the comparative example that adjusts the optical path length difference by adjusting only the optical path length of one of the first laser light and the second laser light. Thus, the amount of movement of a member such as a mirror necessary for adjusting the optical path length difference (that is, the delay amount) by the same amount can be reduced.

  As described above, according to the terahertz wave measuring apparatus of the present embodiment, the optical path length difference between the first laser beam and the second laser beam is adjusted by the same amount (that is, the same delay amount is given). The amount of movement of a member such as a mirror necessary for the operation can be reduced.

  In addition, in some cases, the adjustment unit of the present embodiment is compared with the adjustment unit of the second comparative example that propagates the second laser light along an optical path that reciprocates a plurality of times between members such as opposing mirrors. It is possible to reduce the number of times the second laser beam is reflected in order to adjust the optical path length difference by the same amount (that is, to give the same delay amount). For this reason, in the adjustment means of this embodiment, compared with the adjustment means of the second comparative example, there is a possibility that an error in the attachment angle of a member such as a mirror may affect the preferred propagation of the second laser light. Can be smaller. The same applies to the adjusting means of the second comparative example that propagates the first laser light along an optical path that reciprocates a plurality of times between members such as a plurality of opposing mirrors.

<2>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the adjustment unit includes a first reflecting mirror that reflects the first laser light and a second reflecting mirror that reflects the second laser light. The adjusting means adjusts both the optical path length of the first laser light and the optical path length of the second laser light by moving both the first reflecting mirror and the second reflecting mirror.

  According to this aspect, the adjusting means relatively easily adjusts both the optical path length of the first laser light and the optical path length of the second laser light by moving both the first reflecting mirror and the second reflecting mirror. can do. In other words, the adjusting means can increase the optical path length of one laser beam and decrease the optical path length of the other laser beam by moving both the first reflecting mirror and the second reflecting mirror.

  In addition, it is preferable that an adjustment means moves both a 1st reflective mirror and a 2nd reflective mirror simultaneously. That is, it is preferable that the adjusting means moves both the first reflecting mirror and the second reflecting mirror in parallel. However, both the first reflecting mirror and the second reflecting mirror may be moved one after the other.

<3>
In another aspect of the terahertz wave measuring apparatus in which the adjusting means includes the first reflecting mirror and the second reflecting mirror as described above, the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror are the first reflecting mirror. The first reflecting mirror and the second reflecting mirror face each other along the moving direction, and the adjusting means moves both the first reflecting mirror and the second reflecting mirror in the same direction. Thus, both the optical path length of the first laser light and the optical path length of the second laser light are adjusted.

  According to this aspect, the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror face opposite sides along the moving direction of the first reflecting mirror and the second reflecting mirror. As a result, the adjusting means moves both the first reflecting mirror and the second reflecting mirror whose reflecting surfaces are opposite to each other along the moving direction of the first reflecting mirror and the second reflecting mirror toward the same direction. By moving, both the optical path length of the first laser beam and the optical path length of the second laser beam can be adjusted relatively easily. In other words, the adjusting means moves both the first reflecting mirror and the second reflecting mirror whose reflecting surfaces are opposite to each other along the moving direction of the first reflecting mirror and the second reflecting mirror toward the same direction. By moving, the optical path length of one laser beam can be increased and the optical path length of the other laser beam can be decreased.

<4>
As described above, another aspect of the terahertz wave measuring apparatus in which the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror are facing opposite to each other along the moving direction of the first reflecting mirror and the second reflecting mirror. Then, the adjusting means moves both the first reflecting mirror and the second reflecting mirror so that the first reflecting mirror and the second reflecting mirror reciprocate on a straight line.

  According to this aspect, the adjusting means reciprocally moves both the first reflecting mirror and the second reflecting mirror on a straight line, thereby causing both the first reflecting mirror and the second reflecting mirror to move in the same direction (for example, a straight line). Direction). As a result, the optical path lengths of both the adjusting means, the first laser beam, and the second laser beam can be adjusted relatively easily.

<5>
As described above, in another aspect of the terahertz wave measuring apparatus in which the adjusting means includes the first reflecting mirror and the second reflecting mirror, the adjusting means is a turntable on which the first reflecting mirror and the second reflecting mirror are installed. Is rotated to move both the first reflecting mirror and the second reflecting mirror.

  According to this aspect, the adjusting means can move both the first reflecting mirror and the second reflecting mirror along the same direction (for example, the rotating direction of the rotating table) by rotating the rotating table. . As a result, the adjusting means can relatively easily adjust both the optical path length of the first laser light and the optical path length of the second laser light.

<6>
As described above, in another aspect of the terahertz wave measuring apparatus in which the adjusting unit includes the first reflecting mirror and the second reflecting mirror, the first reflecting mirror includes a retroreflecting mirror that retroreflects the first laser light. The second reflecting mirror includes a retroreflecting mirror that retroreflects the second laser light.

  According to this aspect, the adjusting means moves the first reflecting mirror and the second reflecting mirror, each of which is a retroreflecting mirror, so that the optical path lengths of both the first laser light and the second laser light are relatively easy. Can be adjusted.

<7>
As described above, in another aspect of the terahertz wave measuring apparatus that rotates the rotating table on which the first reflecting mirror and the second reflecting mirror are installed, the first reflecting mirror has a reflecting surface parallel to the rotating table. Including at least two first rotating reflecting mirrors installed, wherein the second reflecting mirror includes at least two second rotating reflecting mirrors having reflecting surfaces parallel to each other and installed on the rotating table, and the adjusting means. Reflects the one laser beam propagating from at least one of the at least two first rotating reflecting mirrors toward at least one of the at least two first rotating reflecting mirrors, and the turntable A first external reflecting mirror installed outside the at least two second rotating reflecting mirrors and the one laser beam propagating from at least one of the at least two second rotating reflecting mirrors of the at least two second rotating reflecting mirrors And a second external reflecting mirror installed in the reflected and the turntable outside toward one even without.

  According to this aspect, as will be described in detail later with reference to the drawings, the adjusting means includes the first reflecting mirror including at least two first rotating reflecting mirrors and the second reflecting including at least two second rotating reflecting mirrors. By rotating the turntable on which the mirror is installed, the optical path lengths of both the first laser beam and the second laser beam can be adjusted relatively easily.

<8>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the first reflecting mirror reflects the first laser light so that the generation means is irradiated with the first laser light during a first period. Thus, the first laser beam is reflected so that the first laser beam is not irradiated onto the generating means during a second period different from the first period, and the first reflecting mirror is reflected during the second period. And a first light receiving means for receiving the first laser light.

  According to this aspect, the first light receiving means can receive the first laser light without affecting the generation operation of the terahertz wave caused by the irradiation of the first laser light to the generating means. The light reception result of the first laser light by the first light receiving means may be used, for example, for setting the characteristics (for example, power) of the first laser light.

<10>
In another aspect of the terahertz wave measurement device of the present embodiment, the second reflecting mirror reflects the second laser light so that the detection means is irradiated with the second laser light during a third period. The second laser beam is reflected so that the second laser beam is not irradiated on the detection means during a fourth period different from the third period, and the second reflecting mirror reflects during the fourth period. A second light receiving means for receiving the second laser light, and a second setting means for setting the characteristics of the second laser light based on a light reception result of the second light receiving means.

  According to this aspect, the second light receiving means can receive the second laser light without affecting the detection operation of the terahertz wave caused by the irradiation of the second laser light to the detection means. The light reception result of the second laser light by the second light receiving means may be used for setting the characteristics (for example, power) of the second laser light, for example.

(Embodiment of optical path length difference adjusting device)
<11>
The optical path length adjustment device of the present embodiment is an optical path length adjustment device that adjusts an optical path length difference between an optical path length of a first light beam and an optical path length of a second light beam different from the first light beam, The first ray so that the optical path length of one of the first ray and the second ray increases and the optical path length of the other ray of the first ray and the second ray decreases. And the optical path length of the second light beam are adjusted.

  According to the optical path length difference adjusting device of the present embodiment, the same operation as that of the adjusting means provided in the terahertz wave measuring device of the present embodiment described above can be performed. Therefore, according to the optical path length difference adjusting device of the present embodiment, it is possible to suitably enjoy various effects that the adjusting means provided in the terahertz wave measuring device of the present embodiment described above.

  In addition, the optical path length difference adjustment apparatus of this embodiment may be substantially the same as the adjustment means with which the terahertz wave measuring apparatus of this embodiment mentioned above is provided. Moreover, the optical path length difference adjusting device of the present embodiment may also adopt various aspects in response to various aspects that can be adopted by the adjusting means included in the terahertz wave measuring apparatus of the present embodiment described above.

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

  As described above, the terahertz wave measuring apparatus according to the present embodiment includes the generating unit, the detecting unit, and the adjusting unit, and the adjusting unit is one of the first laser beam and the second laser beam. The optical path length of the first laser beam and the optical path length of the second laser beam are both reduced so that the optical path length of the other laser beam of the first laser beam and the second laser beam decreases. adjust. Therefore, the first laser beam is relatively reduced while the possibility that an error in the mounting angle of a member such as a mirror will affect the preferred propagation of at least one of the first laser beam and the second laser beam is relatively reduced. The amount of movement of a member such as a mirror necessary for adjusting the optical path length difference between the first laser beam and the second laser beam by the same amount (that is, providing the same delay amount) can be reduced.

  Similarly, the optical path length difference adjusting device of the present embodiment increases the optical path length of one of the first light beam and the second light beam, and increases the optical path length of the other light beam of the first light beam and the second light beam. To reduce both the optical path length of the first light beam and the optical path length of the second light beam. Therefore, the error of the mounting angle of the member such as the mirror has a relatively small possibility of affecting the suitable propagation of at least one of the first light beam and the second light beam, and the first light beam and the second light beam. It is possible to reduce the amount of movement of a member such as a mirror required to adjust the optical path length difference with the light beam by the same amount (that is, to give the same delay amount).

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

(1) First Example First, a terahertz wave measuring apparatus 100 according to a first example will be described with reference to FIGS. 1 to 8.

(1-1) Configuration of Terahertz Wave Measuring Device of First Example First, the configuration of the terahertz wave measuring device 100 of the first example 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 160, a reflecting mirror 1611, a reflecting mirror 1612, a reflecting mirror 1613, a reflecting mirror 1621, a reflecting mirror 1622, a reflecting mirror 1623, a reflecting mirror 1624, an “adjusting means” and an “optical path”. The optical delay device 120, which is a specific example of “long-difference adjusting device”, the terahertz wave detecting element 130, which is a specific example of “detecting means”, a bias voltage generation unit 141, and IV (current-voltage) conversion Unit 144, lock-in detection unit 145, and arithmetic processing unit 150.

  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 160 via a light guide (not shown) (for example, an optical fiber).

  The beam splitter 160 branches 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 enters the optical delay device 120 through a light guide path and a reflecting mirror 1611 (not shown). On the other hand, the probe light LB2 also enters the optical delay device 120 through a light guide path (not shown), the reflecting mirror 1621, and the reflecting mirror 1622.

  The optical delay device 120 includes the optical path length of the pump light LB1 (for example, the optical path length between the beam splitter 160 and the terahertz wave generating element 110) and the optical path length of the probe light LB2 (for example, the beam splitter 160 and the terahertz wave detecting element 130). The difference (hereinafter referred to as “optical path length difference”) is adjusted. Specifically, the optical delay device 120 adjusts the optical path length difference by adjusting the optical path lengths of both the pump light LB1 and the probe light LB2.

  By adjusting the optical path length difference, the timing at which the pump light LB1 enters the terahertz wave generation element 110 (or the timing at which the terahertz wave THz emitted from the terahertz wave generation element 110 enters the terahertz wave detection element 130) The relative deviation amount from the timing at which the probe light LB2 enters the terahertz wave detecting element 130 can be adjusted. For example, when the optical path length difference is changed by 0.3 mm (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 shifted by 1 picosecond (that is, , Early or late). In this case, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is shifted by 1 picosecond (that is, earlier or later). 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 lengths of both the pump light LB1 and the probe light LB2, the optical delay device 120 includes a first retroreflecting mirror 1211 which is a specific example of “first reflecting mirror”, and a “second reflecting mirror”. A second retroreflecting mirror 1212, a feed screw mechanism 122, and a motor 123.

  The first retroreflecting mirror 1211 retroreflects the pump light LB1 incident on the first retroreflecting mirror 1211. That is, the first retroreflecting mirror 1211 reflects the pump light LB1 incident on the first retroreflecting mirror 1211 in a direction parallel to the incident direction of the pump light LB1. In the first embodiment, the first retroreflecting mirror 1211 includes a first reflecting surface 1211a and a second reflecting surface 1211b that intersect at an angle of 90 degrees. The first reflecting surface 1211a reflects the pump light LB1 incident on the first retroreflecting mirror 1211 toward the second reflecting surface 1211b. The second reflecting surface 1211b reflects the pump light LB1 incident on the second reflecting surface 1211b from the first reflecting surface 1211a toward the outside of the optical delay device 120 (for example, the reflecting mirror 1612).

  The first retroreflecting mirror 1211 includes a feed groove that fits into the feed screw mechanism 122. As a result, the first retroreflecting mirror 1211 moves along a predetermined direction in accordance with the rotation of the feed screw mechanism 122 driven by the motor 123. For example, the first retroreflecting mirror 1211 moves along the direction along the optical path of the pump light LB1 at the time of incidence on the first retroreflecting mirror 1211 (that is, the horizontal direction indicated by the arrow in FIG. 1). May be. However, the first retroreflecting mirror 1211 may move along the direction intersecting the optical path of the pump light LB1 at the time of incidence on the first retroreflecting mirror 1211. The movement of the first retroreflecting mirror 1211 adjusts the optical path length of the pump light LB1.

  The second retroreflector 1212 retroreflects the probe light LB2 incident on the second retroreflector 1212. That is, the second retroreflecting mirror 1212 reflects the probe light LB2 incident on the second retroreflecting mirror 1212 in a direction parallel to the incident direction of the probe light LB2. In the first embodiment, the second retroreflecting mirror 1212 includes a first reflecting surface 1212a and a second reflecting surface 1212b that intersect at an angle of 90 degrees. The first reflecting surface 1212a reflects the probe light LB2 incident on the second retroreflecting mirror 1212 toward the second reflecting surface 1212b. The second reflecting surface 1212b reflects the probe light LB2 incident on the second reflecting surface 1212b from the first reflecting surface 1212a toward the outside of the optical delay device 120 (for example, the reflecting mirror 1623).

  The second retroreflecting mirror 1212 includes a feed groove that fits into the feed screw mechanism 122. As a result, the second retroreflecting mirror 1212 moves along a predetermined direction in accordance with the rotation of the feed screw mechanism 122 driven by the motor 123. For example, the second retroreflecting mirror 1212 moves along the direction along the optical path of the probe light LB2 at the time of incidence on the second retroreflecting mirror 1212 (that is, the horizontal direction indicated by the arrow in FIG. 1). It is preferable. However, the second retroreflecting mirror 1212 may move along the direction intersecting the optical path of the probe light LB2 at the time of incidence on the second retroreflecting mirror 1212. The movement of the second retroreflecting mirror 1212 adjusts the optical path length of the probe light LB2.

  In the first embodiment, the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 increase the optical path length of one of the pump light LB1 and the probe light LB2 and at the same time the other of the pump light LB1 and the probe light LB2. Move so that the optical path length decreases. Specifically, the first retroreflector 1211 and the second retroreflector 1212 move so that the optical path length of the probe light LB2 decreases at the same time as the optical path length of the pump light LB1 increases. Similarly, the first retroreflector 1211 and the second retroreflector 1212 move so that the optical path length of the pump light LB1 decreases and at the same time the optical path length of the probe light LB2 increases.

  In order to move so that the optical path length of one of the pump light LB1 and the probe light LB2 increases and at the same time the other optical path length of the pump light LB1 and the probe light LB2 decreases, The two retroreflecting mirrors 1212 are arranged as follows. Specifically, the direction in which the reflecting surfaces of the first retroreflecting mirror 1211 (that is, the first reflecting surface 1211a and the second reflecting surface 1211b) face and the reflecting surface of the second retroreflecting mirror 1212 (that is, the first reflecting surface 1212a). And the direction in which the second reflecting surface 1212b) faces is opposite. More specifically, the reflecting surface of the first retroreflecting mirror 1211 and the reflecting surface of the second retroreflecting mirror 1212 are opposite to each other along the moving direction of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212. Facing. For example, the reflecting surface of the first retroreflecting mirror 1211 faces one side along the moving direction of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212, while the reflecting surface of the second retroreflecting mirror 1212 is The first retroreflector 1211 and the second retroreflector 1212 face the other side (that is, the opposite side of the one side) along the moving direction. In the example shown in FIG. 1, the reflective surface of the first retroreflecting mirror 1211 faces the left side of the paper surface, while the reflective surface of the second retroreflecting mirror 1212 faces the right side of the paper surface.

  FIG. 1 shows an example in which the direction in which the reflecting surface of the first retroreflecting mirror 1211 faces and the direction in which the reflecting surface of the second retroreflecting mirror 1212 faces are approximately 180 °. However, even if the direction in which the reflecting surface of the first retroreflecting mirror 1211 faces and the direction in which the reflecting surface of the second retroreflecting mirror 1212 faces have an obtuse angle (that is, an angle larger than 90 ° and smaller than 180 °). Good. That is, the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 are incident from one side (for example, the left side of the paper) along the moving direction of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212. The pump light LB1 can be retroreflected toward the one side, and is incident from the other side (for example, the right side of the paper surface) along the moving direction of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212. You may arrange | position in the aspect which can retroreflect the probe light LB2 toward the said other side. As long as it is arranged in this manner, the reflecting surface of the first retroreflecting mirror 1211 and the reflecting surface of the second retroreflecting mirror 1212 are in the moving direction of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212. It can be said that they are arranged so as to face each other on the opposite side.

  In addition, since the optical path length of one of the pump light LB1 and the probe light LB2 increases, and the other optical path length of the pump light LB1 and the probe light LB2 moves, the first retroreflecting mirror 1211 and the second retroreflector 1212 move as follows. Specifically, the first retroreflector 1211 and the second retroreflector 1212 move in the same direction. In other words, the first retroreflecting mirror 1211 moves in the same direction as the direction in which the second retroreflecting mirror 1212 moves. In other words, the second retroreflecting mirror 1212 moves in the same direction as the direction in which the first retroreflecting mirror 1211 moves.

  For example, when the first retroreflecting mirror 1211 moves toward the side on which the pump light LB1 enters (left side in FIG. 1), the second retroreflecting mirror 1211 also receives the pump light LB1. Move toward the coming side (left side in FIG. 1). In this case, the optical path length of the pump light LB1 decreases and the optical path length of the probe light LB2 increases. Similarly, for example, when the first retroreflector 1211 moves toward the side on which the probe light LB2 is incident (the right side in FIG. 1), the second retroreflector 1211 also receives the probe light LB2. It moves toward the incident side (right side in FIG. 1). In this case, the optical path length of the pump light LB1 increases and the optical path length of the probe light LB2 decreases.

  In addition, it is preferable that the first retroreflector 1211 and the second retroreflector 1212 move simultaneously. That is, it is preferable that the second retroreflector 1212 also moves simultaneously with the movement of the first retroreflector 1211. However, the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 may move back and forth. In other words, after either one of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 moves, either one of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 moves. Good.

  In consideration of the simultaneous movement of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212, the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 may be integrated. In this case, the optical delay device 120 only needs to include a common feed screw mechanism 122 and a common motor 123 for moving the first retroreflector 1211 and the second retroreflector 1212. However, the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 may not be integrated. In the case where the first retroreflector 1211 and the second retroreflector 1212 are not integrated, the optical delay device 120 includes a feed screw mechanism 122 and a motor 123 for moving the first retroreflector 1211, A feed screw mechanism 122 and a motor 123 for moving the first retroreflecting mirror 1211 may be provided separately and independently. However, even if the first retroreflector 1211 and the second retroreflector 1212 are not integrated, the optical delay device 120 moves the first retroreflector 1211 and the second retroreflector 1212. Therefore, a common feed screw mechanism 122 and a common motor 123 may be provided.

  In addition, it is preferable that the first retroreflector 1211 and the second retroreflector 1212 move by the same amount of movement. That is, it is preferable that the first retroreflector 1211 moves by a predetermined amount of movement and the second retroreflector 1212 also moves by the predetermined amount of movement. However, the moving amount of the first retroreflecting mirror 1211 and the moving amount of the second retroreflecting mirror 1212 may be different.

  As described above, in the terahertz wave measuring apparatus 100 according to the first embodiment, the optical delay device 120 increases the optical path length of one of the pump light LB1 and the probe light LB2, and at the same time, among the pump light LB1 and the probe light LB2. The other optical path length can be reduced. The technical effect of the optical delay device 120 that performs such an operation will be described in detail with reference to FIG.

  The first retroreflector 1211 and the second retroreflector 1212 are 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 pump light LB1 emitted from the optical delay device 120 is incident on the terahertz wave generating element 110 through a light guide path (not shown) and the reflecting mirror 1612 and the reflecting mirror 1613. Similarly, the probe light LB2 emitted from the optical delay device 120 is incident on the terahertz wave detecting element 130 via a light guide path (not shown), the reflecting mirror 1623, and the reflecting mirror 1624.

  The reflecting mirror 1611, the reflecting mirror 1612, and the reflecting mirror 1613 are components for propagating the pump light LB1 from the beam splitter 160 to the terahertz wave generating element 110 via the optical delay device 120. Therefore, as long as the pump light LB1 can propagate from the beam splitter 160 to the terahertz wave generation element 110 via the optical delay device 120, the number, arrangement mode, and the like of the reflecting mirror 1611, the reflecting mirror 1612, and the reflecting mirror 1613 are as follows. Is optional. Similarly, the reflecting mirror 1621, the reflecting mirror 1622, the reflecting mirror 1623, and the reflecting mirror 1624 are components for propagating the probe light LB2 from the beam splitter 160 to the terahertz wave detecting element 130 via the optical delay device 120. . Therefore, as long as the probe light LB2 can propagate from the beam splitter 160 to the terahertz wave detecting element 130 via the optical delay device 120, the number of reflecting mirrors 1621, reflecting mirrors 1622, reflecting mirrors 1623, and reflecting mirrors 1624 Arrangement | positioning aspects etc. are arbitrary.

  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.

(1-2) Technical Effect of Optical Delay Device Next, with reference to FIGS. 3 to 8, the optical effect of the optical delay device 120 is adjusted by adjusting only the optical path length of the probe light LB2. Description is made in comparison with the operation of the optical delay device 120b of the second comparative example in which the probe light LB2 is propagated along the optical path reciprocating a plurality of times between the optical delay device 120a of the first comparative example and the reflecting mirror facing each other. To do. FIG. 3 and FIG. 4 are plan views showing how the optical path length difference is adjusted in the optical delay device 120 of the first embodiment. FIG. 5 and FIG. 6 are plan views each showing a mode of adjusting the optical path length difference in the optical delay device 120a of the first comparative example. FIGS. 7 and 8 are plan views showing aspects of adjustment of the optical path length difference in the optical delay device 120b of the second comparative example.

  3 to 8, the state where the optical path length of the pump light LB1 is K1 and the optical path length of the probe light LB2 is K2 is defined as an initial state for convenience.

  As shown in FIG. 3A, in the optical delay device 120 of the first embodiment in the initial state, the first recursion is made toward the side on which the pump light LB1 enters (the left side in FIG. 3A). When the reflecting mirror 1211 moves by a predetermined amount of movement α (where α is a positive real number), the second retroreflecting mirror 1212 also receives the pump light LB1 (in FIG. 3A). (To the left side) by a predetermined movement amount α. In the following description, the amount of movement when the first retroreflector 1211 and the second retroreflector 1212 move toward the side on which the pump light LB1 is incident is “positive”, and the probe light LB2 is incident. The amount of movement when the first retroreflector 1211 and the second retroreflector 1212 move toward the incoming side (the right side in FIG. 3A) is “negative”. Therefore, when the first retroreflector 1211 moves by a predetermined movement amount + α, the second retroreflector 1212 also moves by a predetermined movement amount + α. In this case, the optical path length of the pump light LB1 decreases by 2α, and the optical path length of the probe light LB2 increases by 2α. Therefore, as shown in FIG. 3B, the optical path length of the pump light LB1 is K1-2α, and the optical path length of the probe light LB2 is K2 + 2α. Therefore, as shown in FIG. 3B, the optical path length difference (however, in the following description, the optical path length difference = the optical path length of the probe light LB2−the optical path length of the pump light LB1) is K2−K1 + 4α. Become. Therefore, when the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 move by a predetermined movement amount + α, the optical delay device 120 of the first embodiment has an optical path length difference (= K1−K2) in the initial state. ), The optical path length difference can be increased by 4α.

  Similarly, as shown in FIG. 4A, in the optical delay device 120 of the first embodiment in the initial state, toward the side on which the probe light LB2 is incident (the right side in FIG. 4A). When the first retroreflecting mirror 1211 moves by a predetermined movement amount β (where β is a positive real number), the second retroreflecting mirror 1212 also receives the pump light LB1 (FIG. 4 ( It moves by a predetermined movement amount β toward the right side in a). That is, when the first retroreflector 1211 moves by a predetermined movement amount −β, the second retroreflector 1212 also moves by a predetermined movement amount −β. In this case, the optical path length of the pump light LB1 increases by 2β, and the optical path length of the probe light LB2 decreases by 2β. Therefore, as shown in FIG. 4B, the optical path length of the pump light LB1 is K1 + 2β, and the optical path length of the probe light LB2 is K2-2β. Therefore, as shown in FIG. 4B, the optical path length difference is K2-K1-4β. Therefore, when the first retroreflector 1211 and the second retroreflector 1212 move by a predetermined movement amount −β, the optical delay device 120 of the first embodiment is compared with the optical path length difference in the initial state. The optical path length difference can be shortened by 4β.

  On the other hand, as shown in FIG. 5A, the optical delay device 120a of the first comparative example adjusts the optical path length difference by adjusting only the optical path length of the probe light LB2, so that the pump light LB1 is returned. The first retroreflecting mirror 1211 for reflection may not be provided. Here, as shown in FIG. 5A, the optical delay device 120a of the first comparative example in the initial state is similar to the movement mode in the optical delay device 120 of the first embodiment shown in FIGS. 2, the second retroreflecting mirror 1212 is moved by a predetermined movement amount α toward the side on which the pump light LB1 is incident (the left side in FIG. 5A). That is, it is assumed that the second retroreflector 1212 moves by a predetermined movement amount + α. In this case, the optical path length of the probe light LB2 increases by 2α. Therefore, as shown in FIG. 5B, the optical path length of the probe light LB2 is K2 + 2α. Therefore, as shown in FIG. 5B, the optical path length difference is K2−K1 + 2α. Therefore, when the second retroreflecting mirror 1212 moves by a predetermined movement amount + α, the optical delay device 120a of the first comparative example has an optical path length difference of only 2α compared to the optical path length difference in the initial state. Can't be long. In other words, in the optical delay device 120a of the first comparative example, in order to lengthen the optical path length difference by 4α compared to the optical path length difference in the initial state, the second retroreflecting mirror 1212 has a predetermined movement amount + 2α (that is, In addition, the movement amount of the second retroreflector 1212 in the optical delay device 120 of the first embodiment must also move.

  Similarly, as shown in FIG. 6A, the optical delay device 120a of the first comparative example in the initial state is similar to the movement mode in the optical delay device 120 of the first embodiment shown in FIGS. The second retroreflecting mirror 1212 moves by a predetermined movement amount β toward the side on which the probe light LB2 enters (the right side in FIG. 6A). That is, it is assumed that the second retroreflecting mirror 1212 moves by a predetermined movement amount −β. In this case, the optical path length of the probe light LB2 is decreased by 2β. Accordingly, as shown in FIG. 6B, the optical path length of the probe light LB2 is K2-2β. For this reason, as shown in FIG. 6B, the optical path length difference is K2-K1-2β. Therefore, when the second retroreflecting mirror 1212 moves by a predetermined movement amount + β, the optical delay device 120a of the first comparative example has an optical path length difference of only 2β compared to the optical path length difference in the initial state. It cannot be shortened. In other words, in the optical delay device 120a of the first comparative example, in order to shorten the optical path length difference by 4β compared to the optical path length difference in the initial state, the second retroreflecting mirror 1212 has a predetermined movement amount −2β ( That is, the movement amount twice the movement amount of the second retroreflecting mirror 1212 in the optical delay device 120 of the first embodiment must also move.

  However, unlike the optical delay device 120a of the first comparative example, the optical delay device 120 of the first embodiment increases the optical path length of one of the pump light LB1 and the probe light LB2, and at the same time, the pump light LB1 and the probe light LB1. The other optical path length of the light LB2 can be reduced. Therefore, the optical delay device 120 of the first embodiment is necessary to adjust the optical path length difference by the same amount (that is, to give the same delay amount) as compared with the optical delay device 120a of the first comparative example. The amount of movement of each of the first retroreflecting mirror 1211 and the second retroreflecting mirror 1212 can be reduced. As a result, downsizing of the optical delay device 120 is realized.

  In the above description, the optical delay device 120a of the first comparative example that adjusts the optical path length difference by adjusting only the optical path length of the probe light LB2 has been described. However, the same can be said for the optical delay device 120a of the first comparative example in which the optical path length difference is adjusted by adjusting only the optical path length of the pump light LB1.

  On the other hand, as shown in FIG. 7A, the optical delay device 120b of the second comparative example adjusts the optical path length difference by adjusting only the optical path length of the probe light LB2. The first retroreflecting mirror 1211 for reflection may not be provided. Further, the optical delay device 120b of the second comparative example propagates the probe light LB2 along an optical path that reciprocates a plurality of times (two times in the example shown in FIG. 7A) between the opposing reflecting mirrors. In order to adjust the optical path length difference, two second retroreflecting mirrors 1212 (that is, the second retroreflecting mirror 1212b-1 and the second retroreflecting mirror 1212b-2), and the reflecting mirrors 1625b and 1626b are further provided. Yes. The second retroreflecting mirror 1212b-1 retroreflects the probe light LB2 incident on the second retroreflecting mirror 1212b-1 toward the reflecting mirror 1625b. The reflecting mirror 1625b reflects the probe light LB2 incident on the reflecting mirror 1625b toward the reflecting mirror 1626b. The reflecting mirror 1626b reflects the probe light LB2 incident on the reflecting mirror 1626b toward the second retroreflecting mirror 1212b-2. The second retroreflecting mirror 1212b-2 retroreflects the probe light LB2 incident on the second retroreflecting mirror 1212b-2 toward the reflecting mirror 1623.

  Here, as shown in FIG. 7A, the optical delay device 120b of the second comparative example in the initial state is similar to the movement mode in the optical delay device 120 of the first embodiment shown in FIGS. , The second retroreflector 1212b-1 and the second retroreflector 1212b-2 move by a predetermined movement amount α toward the side on which the pump light LB1 is incident (the left side in FIG. 7A). It shall be. That is, the second retroreflector 1212b-1 and the second retroreflector 1212b-2 are moved by a predetermined movement amount + α. In this case, the optical path length of the probe light LB2 increases by 4α. Therefore, as shown in FIG. 7B, the optical path length of the probe light LB2 is K2 + 4α. Therefore, as shown in FIG. 7B, the optical path length difference is K2−K1 + 4α. Therefore, when the second retroreflector 1212b-1 and the second retroreflector 1212b-2 move by a predetermined movement amount + α, the optical delay device 120b of the second comparative example has an optical path length difference in the initial state. In comparison, the optical path length difference can be increased by 4α. However, in the optical delay device 120b of the second comparative example, the number of reflections of the probe light LB2 (particularly, the number of reflections of the probe light LB2 via the optical delay device 120b) compared to the optical delay device 120 of the first embodiment. Will become relatively large.

  Similarly, as shown in FIG. 8A, the optical delay device 120b of the second comparative example in the initial state is similar to the movement mode in the optical delay device 120 of the first embodiment shown in FIGS. , The second retroreflector 1212b-1 and the second retroreflector 1212b-2 move by a predetermined movement amount β toward the side on which the probe light LB2 is incident (the right side in FIG. 8A). It shall be. That is, it is assumed that the second retroreflector 1212b-1 and the second retroreflector 1212b-2 move by a predetermined movement amount -β. In this case, the optical path length of the probe light LB2 is decreased by 4β. Therefore, as shown in FIG. 8B, the optical path length of the probe light LB2 is K2-4β. Therefore, as shown in FIG. 8B, the optical path length difference is K2−K1−4β. Therefore, when the second retroreflector 1212b-1 and the second retroreflector 1212b-2 move by a predetermined movement amount -β, the optical delay device 120b of the second comparative example has an optical path length difference in the initial state. As compared with the above, the optical path length difference can be shortened by 4β. However, in the optical delay device 120b of the second comparative example, the number of reflections of the probe light LB2 (particularly, the number of reflections of the probe light LB2 via the optical delay device 120b) compared to the optical delay device 120 of the first embodiment. Will become relatively large.

  As described above, the optical delay device 120 of the first embodiment adjusts the optical path length difference by the same amount (that is, gives the same delay amount), similarly to the optical delay device 120b of the second comparative example. The required amount of movement of each of the first retroreflector 1211 and the second retroreflector 1212 can be reduced. Nevertheless, the optical delay device 120 of the first embodiment can reduce the number of reflections of the probe light LB2 as compared with the optical delay device 120b of the second comparative example. Therefore, in the optical delay device 120 of the first embodiment, the error in the mounting angle of the second retroreflecting mirror 1212 has an influence on the preferred propagation of the probe light LB2, as compared with the optical delay device 120b of the second comparative example. The possibility of giving is reduced. For example, the optical delay device 120 of the first embodiment is different from the optical delay device 120b of the second comparative example in the amount of displacement of the irradiation position of the probe light LB2 due to the error in the mounting angle of the second retroreflecting mirror 1212. Can be made relatively small.

  In the above description, the optical delay device 120b of the second comparative example that adjusts the optical path length difference by adjusting only the optical path length of the probe light LB2 has been described. However, the same applies to the optical delay device 120b of the second comparative example that adjusts the optical path length difference by adjusting only the optical path length of the pump light LB1. In this case, the optical delay device 120 of the first embodiment has an error in the mounting angle of the first retroreflecting mirror 1211 with respect to the preferable propagation of the pump light LB1 as compared with the optical delay device 120b of the second comparative example. The possibility of influencing can be reduced. For example, the optical delay device 120 of the first embodiment is different from the optical delay device 120b of the second comparative example in the amount of displacement of the irradiation position of the pump light LB1 due to the error in the mounting angle of the first retroreflecting mirror 1211. Can be made relatively small.

  The optical delay device 120b of the second comparative example is used for the purpose of explaining that the optical delay device 120 of the first embodiment can reduce the number of reflections of the probe light LB2. Therefore, in the optical delay device 120b of the second comparative example, the optical delay device 120 of the first embodiment has the same configuration as the optical delay device 120b of the second comparative example (that is, reciprocates a plurality of times between opposing reflecting mirrors). This does not prevent the adoption of the configuration in which the probe light LB2 is propagated along the optical path. That is, the optical delay device 120 according to the first embodiment may adopt a configuration in which at least one of the pump light LB1 and the probe light LB2 is propagated along an optical path that reciprocates a plurality of times between opposing reflecting mirrors. .

  In the above description, an example in which the optical delay device 120 is used in the terahertz wave measuring apparatus 100 is described. However, the optical delay device 120 is used for any device other than the terahertz wave measuring device 100 (for example, a device that performs some processing or operation by adjusting the optical path length difference between two laser beams or two light beams). May be. As an example of such an apparatus, for example, an apparatus using optical coherence tomography, an apparatus using pump / probe spectroscopy, and the like can be given.

(2) Second Example Next, a terahertz wave measuring apparatus 200 according to a second example will be described with reference to FIGS. 9 to 11. In addition, about the component same as the component with which the terahertz wave measuring apparatus 100 of 1st Example is provided, the detailed description is irradiated by attaching | subjecting the same referential mark.

(2-1) Configuration of Terahertz Wave Measuring Device of Second Example First, the configuration of the terahertz wave measuring device 200 of the second example will be described with reference to FIG. FIG. 9 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 200 according to the second embodiment.

  As shown in FIG. 9, the terahertz wave measuring apparatus 200 according to the second embodiment is similar to the terahertz wave measuring apparatus 100 according to the first embodiment, in that the pulse laser apparatus 101, the terahertz wave generating element 110, the beam splitter 160, The terahertz wave detecting element 130, the bias voltage generating unit 141, the IV (current-voltage) converting unit 144, the lock-in detecting unit 145, and the arithmetic processing unit 150 are provided.

  The terahertz wave measuring apparatus 200 according to the second embodiment further includes a polarizing beam splitter 2601, a polarizing beam splitter 2602, a reflecting mirror 2611, a reflecting mirror 2621, a reflecting mirror 2622, a reflecting mirror 2623, and a half-wave plate. 231, ½ wavelength plate 232, ½ wavelength plate 233, ¼ wavelength plate 241, ¼ wavelength plate 242, and optical delay device 220.

  In the second embodiment, the pulse laser beam LB generated by the pulse laser apparatus 101 is transmitted through the half-wave plate 231 and then enters the beam splitter 160. The half-wave plate 231 adjusts the ratio (substantially the branching ratio) between the pump light LB1 and the probe light LB2. The beam splitter 160 branches the pulse laser beam LB into the pump beam LB1 and the probe beam LB2 as in the first embodiment.

  The pump light LB1 branched in the beam splitter 160 passes through the half-wave plate 232, the polarization beam splitter 2601 and the quarter-wave plate 241 and then enters the optical delay device 220. On the other hand, the probe light LB2 branched in the beam splitter 160 is reflected by the reflecting mirror 2621 and then passes through the half-wave plate 233. The probe light LB2 that has passed through the half-wave plate 233 is reflected by the polarization beam splitter 2602 and then passes through the quarter-wave plate 242. The probe light LB2 that has passed through the quarter-wave plate 242 enters the optical delay device 220.

  Note that the half-wave plate 232 is such that the pump light LB1 transmitted through the half-wave plate 232 (that is, the pump light LB1 propagating from the pulse laser device 101 toward the polarization beam splitter 2601) passes through the polarization beam splitter 2601. The polarization direction of the pump light LB1 is adjusted so that it is transmitted. Similarly, in the half-wave plate 233, the probe light LB2 transmitted through the half-wave plate 233 (that is, the probe light LB2 propagating from the pulse laser device 101 toward the polarization beam splitter 2602) is the polarization beam splitter 2602. The polarization direction of the probe light LB2 is adjusted so as to be reflected by. The quarter-wave plate 241 adjusts the polarization state of the pump light LB1 so that the pump light LB1 returning from the optical delayer 220 to the polarization beam splitter 2601 is reflected by the polarization beam splitter 2601. Similarly, the quarter wavelength plate 242 adjusts the polarization state of the probe light LB2 so that the probe light LB2 returning from the optical delayer 220 to the polarization beam splitter 2602 passes through the polarization beam splitter 2602.

  Similar to the optical delay device 120 of the first embodiment, the optical delay device 220 adjusts an optical path length difference that is a difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Similarly to the optical delay device 120 of the first embodiment, the optical delay device 220 adjusts the optical path length difference by adjusting the optical path lengths of both the pump light LB1 and the probe light LB2.

  The optical delay device 220 includes a first reflecting mirror 2211 and a first reflecting mirror 2212 that are specific examples of a “first rotating reflecting mirror”, and a first reflecting mirror 2213 that is a specific example of a “first external reflecting mirror”. A second reflecting mirror 2221 and a second reflecting mirror 2222 that are specific examples of the “second rotating reflecting mirror”, a first reflecting mirror 2223 that is a specific example of the “second external reflecting mirror”, and a turntable. 223.

  The first reflecting mirror 2211, the first reflecting mirror 2212, the second reflecting mirror 2221, and the second reflecting mirror 2222 are on a turntable 223 that can rotate in a predetermined direction (for example, a clockwise direction in FIG. 9). is set up. In particular, the first reflecting mirror 2211, the first reflecting mirror 2212, the second reflecting mirror 2221, and the second reflecting mirror 2222 are installed on a circumference located at a predetermined radius from the rotation center of the turntable 223. preferable. As the turntable 223 rotates, the positions of the first reflecting mirror 2211 and the first reflecting mirror 2212 with respect to the pump light LB1 and the positions of the second reflecting mirror 2221 and the second reflecting mirror 2222 with respect to the probe light LB2 are changed. As a result, the optical path lengths of both the pump light LB1 and the probe light LB2 are adjusted.

  Depending on the rotation angle of the turntable 223, the pump light LB1 incident on the optical delay device 220 can be incident on the first reflecting mirror 2211. In this case, the first reflecting mirror 2211 reflects the pump light LB1 incident on the first reflecting mirror 2211 from the outside of the optical delay device 220 to the first reflecting mirror 2212. The first reflecting mirror 2212 reflects the pump light LB1 incident on the first reflecting mirror 2212 from the first reflecting mirror 2211 to the first reflecting mirror 2213. The first reflecting mirror 2213 reflects the pump light LB1 incident on the first reflecting mirror 2213 from the first reflecting mirror 2212 to the first reflecting mirror 2212. The first reflecting mirror 2212 reflects the pump light LB1 incident on the first reflecting mirror 2212 from the first reflecting mirror 2213 to the first reflecting mirror 2211. The first reflecting mirror 2211 converts the pump light LB1 incident on the first reflecting mirror 2211 from the first reflecting mirror 2212 to the outside of the optical delay device 220 (specifically, a polarization beam splitter via the quarter wavelength plate 241). 2601).

  Alternatively, the pump light LB1 incident on the optical delay device 220 can be incident on the first reflecting mirror 2212 according to the rotation angle of the turntable 223. In this case, the first reflecting mirror 2212 reflects the pump light LB1 incident on the first reflecting mirror 2212 from the outside of the optical delay device 220 to the first reflecting mirror 2211. The first reflecting mirror 2211 reflects the pump light LB1 incident on the first reflecting mirror 2211 from the first reflecting mirror 2212 to the first reflecting mirror 2213. The first reflecting mirror 2213 reflects the pump light LB1 incident on the first reflecting mirror 2213 from the first reflecting mirror 2211 to the first reflecting mirror 2211. The first reflecting mirror 2211 reflects the pump light LB1 incident on the first reflecting mirror 2211 from the first reflecting mirror 2213 to the first reflecting mirror 2212. The first reflecting mirror 2212 converts the pump light LB1 incident on the first reflecting mirror 2212 from the first reflecting mirror 2211 to the outside of the optical delay device 220 (specifically, a polarization beam splitter via the quarter-wave plate 241). 2601).

  On the other hand, the probe light LB <b> 2 incident on the optical delay device 220 can be incident on the second reflecting mirror 2221 depending on the rotation angle of the turntable 223. In this case, the second reflecting mirror 2221 reflects the probe light LB2 incident on the second reflecting mirror 2221 from the outside of the optical delay device 220 to the second reflecting mirror 2222. The second reflecting mirror 2222 reflects the probe light LB2 incident on the second reflecting mirror 2222 from the second reflecting mirror 2221 to the second reflecting mirror 2223. The second reflecting mirror 2223 reflects the probe light LB2 incident on the second reflecting mirror 2223 from the second reflecting mirror 2222 to the second reflecting mirror 2222. The second reflecting mirror 2222 reflects the probe light LB2 incident on the second reflecting mirror 2222 from the second reflecting mirror 2223 to the second reflecting mirror 2221. The second reflecting mirror 2221 transmits the light incident on the second reflecting mirror 2221 from the second reflecting mirror 2222 to the outside of the optical delay device 220 (specifically, the polarization beam splitter 2602 via the quarter-wave plate 242). Reflect to the back.

  Alternatively, the probe light LB2 incident on the optical delay device 220 can be incident on the second reflecting mirror 2222 according to the rotation angle of the turntable 223. In this case, the second reflecting mirror 2222 reflects the probe light LB 2 incident on the second reflecting mirror 2222 from the outside of the optical delay device 220 to the second reflecting mirror 2221. The second reflecting mirror 2221 reflects the probe light LB2 incident on the second reflecting mirror 2221 from the second reflecting mirror 2222 to the second reflecting mirror 2223. The second reflecting mirror 2223 reflects the probe light LB2 incident on the second reflecting mirror 2223 from the second reflecting mirror 2221 to the second reflecting mirror 2221. The second reflecting mirror 2221 reflects the probe light LB2 incident on the second reflecting mirror 2221 from the second reflecting mirror 2223 to the second reflecting mirror 2222. The second reflecting mirror 2222 converts the light incident on the second reflecting mirror 2222 from the second reflecting mirror 2221 to the outside of the optical delay device 220 (specifically, the polarization beam splitter 2602 via the quarter-wave plate 242). Reflect to the back.

  The rotation of the turntable 223 is performed under the control of the arithmetic processing unit 150. That is, the arithmetic processing unit 150 controls the operation of the motor by outputting to the motor a control signal that specifies the drive amount of the motor (not shown) for rotating the turntable 223.

  In the second embodiment, similarly to the optical delay device 120 of the first embodiment, the optical delay device 220 increases the optical path length of one of the pump light LB1 and the probe light LB2 and simultaneously the pump light LB1 and the probe light LB2. The optical path lengths of both the pump light LB1 and the probe light LB2 are adjusted so that the other of the optical path lengths decreases. For example, in the optical delay device 220 of the second embodiment, the first reflecting mirror 2211 and the first reflecting mirror 2212 and the second reflecting mirror 2221 and the second reflecting mirror 2222 are either one of the pump light LB1 and the probe light LB2. The optical path length is increased so that the other optical path length of the pump light LB1 and the probe light LB2 decreases at the same time. Specifically, the direction in which the reflecting surfaces of the first reflecting mirror 2211 and the first reflecting mirror 2212 face and the direction in which the reflecting surfaces of the second reflecting mirror 2221 and the second reflecting mirror 2222 face are opposite to each other. . More specifically, the reflecting surfaces of the first reflecting mirror 2211 and the first reflecting mirror 2212 and the reflecting surfaces of the second reflecting mirror 2221 and the second reflecting mirror 2222 are in the rotation direction of the turntable 223 (that is, , The first reflecting mirror 2211 and the first reflecting mirror 2212 and the second reflecting mirror 2221 and the second reflecting mirror 2222 move in the opposite direction. For example, the respective reflecting surfaces of the first reflecting mirror 2211 and the first reflecting mirror 2212 face one side along the rotation direction of the turntable 223, while the second reflecting mirror 2221 and the second reflecting mirror 2222, respectively. Is directed to the other side (that is, the opposite side of the one side) along the rotation direction of the turntable 223. In the example shown in FIG. 9, the respective reflecting surfaces of the first reflecting mirror 2211 and the first reflecting mirror 2212 face the rear side with respect to the rotation direction of the turntable 223, while the second reflecting mirror 2221 and the second reflecting mirror 2221. In the example, each reflecting surface of the reflecting mirror 2222 faces the front side with respect to the rotation direction of the turntable 223.

  In the example shown in FIG. 9, the reflecting surface of the first reflecting mirror 2211 and the reflecting surface of the first reflecting mirror 2212 are parallel. Further, the reflecting surface of the second reflecting mirror 2221 and the reflecting surface of the second reflecting mirror 2222 are parallel. In the example shown in FIG. 9, the reflecting surface of the first reflecting mirror 2211 intersects with a line segment connecting the center of the turntable 223 and the installation position of the first reflecting mirror 2211 at an angle of 45 °. Similarly, the reflecting surface of the first reflecting mirror 2212 intersects at a 45 ° angle with respect to a line segment connecting the center of the turntable 223 and the installation position of the first reflecting mirror 2212. Similarly, the reflecting surface of the second reflecting mirror 2221 intersects at a 45 ° angle with respect to a line segment connecting the center of the turntable 223 and the installation position of the second reflecting mirror 2221. Similarly, the reflecting surface of the second reflecting mirror 2222 intersects with a line segment connecting the center of the turntable 223 and the installation position of the second reflecting mirror 2222 at an angle of 45 °. In addition, in the example illustrated in FIG. 9, the first reflecting mirror 2211 and the first reflecting mirror 2212 are installed on a line segment passing through the rotation center of the turntable 223. Similarly, the second reflecting mirror 2221 and the second reflecting mirror 2222 are installed on a line segment passing through the rotation center of the turntable 223.

  In addition, the installation aspect of the 1st reflective mirror 2211 and the 1st reflective mirror 2212 which were mentioned above, the 2nd reflective mirror 2221, and the 2nd reflective mirror 2222 is an example to the last. Accordingly, the first reflecting mirror 2211, the first reflecting mirror 2212, the second reflecting mirror 2221, and the second reflecting mirror 2222 have the optical path length of one of the pump light LB1 and the probe light LB2 increased, and at the same time, the pump light LB1 and the probe light LB1. As long as the other optical path length of the light LB2 decreases, it may be installed in any manner.

  The pump light LB1 emitted from the optical delay device 220 is reflected by the polarization beam splitter 2601 after passing through the quarter-wave plate 241. The pump light LB1 reflected by the polarization beam splitter 2601 passes through the reflecting mirror 2611 and then enters the terahertz wave generating element 110. Similarly, the probe light LB2 emitted from the optical delay device 220 is reflected by the reflecting mirror 2622 and the reflecting mirror 2623 after passing through the quarter-wave plate 242 and the polarization beam splitter 2602. The probe light LB2 reflected by the reflecting mirror 2623 is incident on the terahertz wave detecting element 130.

  Incidentally, the arrangement mode of the reflection mirror 2611, the reflection mirror 2621, the reflection mirror 2622, and the reflection mirror 2623 (further, the arrangement mode of the polarization beam splitter 2601 and the polarization beam splitter 2602, the half-wave plate 231 and the half-wave plate It is the same as in the first embodiment that the arrangement mode of the 232 and the half-wave plate 233 and the arrangement mode of the quarter-wave plate 241 and the quarter-wave plate 242 are arbitrary.

(2-2) Technical Effect of Optical Delay Device Next, the technical effect of the optical delay device 220 will be described with reference to FIGS. 10 to 11. FIGS. 10 and 11 are plan views showing aspects of adjustment of the optical path length difference in the optical delay device 220 of the second embodiment.

  In the description using FIGS. 10 to 11, the state where the optical path length of the pump light LB1 is K1 and the optical path length of the probe light LB2 is K2 is defined as an initial state for convenience. In the initial state, the pump light LB1 is incident on the reflecting surfaces of the first reflecting mirror 2611 and the first reflecting mirror 2612 at an incident angle of 45 °, and the probe light LB2 is incident on the second reflecting mirror 2621 and the second reflecting mirror 2621. It is assumed that the light enters the reflection surface of the reflecting mirror 2622 at an incident angle of 45 ° (see the state of the optical delay device 220 in FIG. 9). Further, the rotation angle of the turntable 223 in the initial state is defined as 0 ° for convenience.

  As shown in FIG. 10A, it is assumed that the rotation angle of the turntable 223 is + δ1 ° (where δ1 is a positive real number). In the following description, the rotation angle toward the clockwise direction with respect to the rotation angle of 0 ° is “positive”, and the rotation angle toward the clockwise direction with reference to the rotation angle of 0 ° is “negative”. To do. In this case, the optical path length of the pump light LB1 increases by γ, and the optical path length of the probe light LB2 decreases by γ. Therefore, as shown in FIG. 10B, the optical path length of the pump light LB1 is K1 + γ, and the optical path length of the probe light LB2 is K2-γ. For this reason, as shown in FIG. 10B, the optical path length difference is K2−K1-2γ. Therefore, when the rotation angle of the turntable 223 is + δ1 °, the optical delay device 220 of the second embodiment compares the optical path length difference 2γ with the optical path length difference (= K1−K2) in the initial state. Can only be shortened.

  Similarly, as shown in FIG. 11A, it is assumed that the rotation angle of the turntable 223 is −δ2 ° (where δ2 is a positive real number). In this case, the optical path length of the pump light LB1 decreases by ε, and the optical path length of the probe light LB2 increases by ε. Therefore, as shown in FIG. 11B, the optical path length of the pump light LB1 is K1-ε, and the optical path length of the probe light LB2 is K2 + ε. For this reason, as shown in FIG. 11B, the optical path length difference is K2−K1 + 2ε. Therefore, when the rotation angle of the turntable 223 is −δ2 °, the optical delay device 220 of the second embodiment can increase the optical path length difference by 2ε compared to the optical path length difference in the initial state. it can.

  On the other hand, although not shown, an optical delay device of a third comparative example that adjusts the optical path length difference by adjusting only the optical path length of the probe light LB2 (for example, the first reflecting mirror 2211 and the first reflecting mirror shown in FIG. 9). Consider an optical delay device that does not include the mirror 2212. In the optical delay device of the third comparative example, when the rotation angle of the turntable 223 is + δ1 °, the optical path length of the probe light LB2 decreases by γ. Therefore, when the rotation angle of the turntable 223 is + δ1 °, the optical delay device of the third comparative example can shorten the optical path length difference only by γ as compared with the optical path length difference in the initial state. .

  As described above, the optical delay device 220 of the second embodiment increases the optical path length of one of the pump light LB1 and the probe light LB2 at the same time as the optical delay device 120 of the first embodiment. And the other optical path length of the probe light LB2 can be reduced. Therefore, the optical delay device 220 of the second embodiment can enjoy various effects that can be enjoyed by the optical delay device 120 of the first embodiment, preferably or appropriately. For example, the optical delay device 220 of the second embodiment has the same amount of optical path length difference as the optical delay device of the third comparative example that adjusts the optical path length difference by adjusting only the optical path length of the probe light LB2. Therefore, the amount of rotation of the turntable 223 required for adjustment only (that is, to give the same delay amount) can be reduced.

(3) Third Example Next, a terahertz wave measuring apparatus 300 according to a third example will be described with reference to FIG. FIG. 12 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 300 according to the third embodiment. In addition, about the component same as the component with which the terahertz wave measuring apparatus 200 of 2nd Example is provided, the detailed description is irradiated by attaching | subjecting the same referential mark.

  As shown in FIG. 12, the terahertz wave measuring apparatus 300 according to the third embodiment is different from the terahertz wave measuring apparatus 200 according to the second embodiment in that the configuration of the optical delay device 320 is different. . Other components of the terahertz wave measuring apparatus 300 of the third embodiment may be the same as other components of the terahertz wave measuring apparatus 200 of the second embodiment.

  In the optical delay device 320 of the third embodiment, compared to the optical delay device 220 of the second embodiment, the first reflecting mirror 2211 and the first reflecting mirror 2212 are respectively the first retroreflecting mirror 3211 and the first retroreflecting mirror. The difference is that the mirror 3212 is replaced. Similarly, in the optical delay device 320 of the third embodiment, compared to the optical delay device 220 of the second embodiment, the second reflecting mirror 2221 and the second reflecting mirror 2222 are respectively the second retroreflecting mirror 3221 and the second reflecting mirror 3221. The difference is that two retroreflecting mirrors 3222 are replaced. In addition, the optical delay device 320 of the third embodiment is different from the optical delay device 220 of the second embodiment in that the first reflecting mirror 2213 and the second reflecting mirror 2223 are not provided.

  Also in the third embodiment, as in the second embodiment, the optical delay device 220 increases the optical path length of one of the pump light LB1 and the probe light LB2 and at the same time the other of the pump light LB1 and the probe light LB2. The optical path lengths of both the pump light LB1 and the probe light LB2 are adjusted so as to reduce the optical path length of the light beam. For example, in the optical delay device 320 of the third embodiment, the first retroreflector 3211, the first retroreflector 3212, the second retroreflector 3221 and the second antiretroreflector 3222 are provided with the pump light LB1 and the probe light LB2. The optical path length of one of the light beams is increased so that the optical path length of the other of the pump light beam LB1 and the probe light beam LB2 decreases. Specifically, the direction in which the respective reflecting surfaces of the first retroreflecting mirror 3211 and the first retroreflecting mirror 3212 face and the direction in which the respective reflecting surfaces of the second retroreflecting mirror 3221 and the second retroreflecting mirror 3222 are directed. Reverse. More specifically, the respective reflecting surfaces of the first retroreflecting mirror 3211 and the first retroreflecting mirror 3212 and the reflecting surfaces of the second retroreflecting mirror 3221 and the second antiretroreflecting mirror 3222 are the turntable 223. Of the first retroreflector 3211, the first retroreflector 3212, the second retroreflector 3221, and the second antiretroreflector 3222 toward each other. For example, while the reflecting surfaces of the first retroreflecting mirror 3211 and the first retroreflecting mirror 3212 face one side along the rotation direction of the turntable 223, the second retroreflecting mirror 3221 and the second antirecursive mirror Each reflecting surface of the projector 3222 faces the other side (that is, the opposite side of the one side) along the rotation direction of the turntable 223. In the example shown in FIG. 12, each of the first retroreflecting mirror 3211 and the first retroreflecting mirror 3212 has a reflecting surface facing rearward with respect to the rotation direction of the turntable 223, while the second retroreflecting mirror 3221. And the example which each reflective surface of the 2nd antirecursive reflector 3222 faces the front side with respect to the rotation direction of the turntable 223 is shown.

  In the example shown in FIG. 12, the first retroreflecting mirror 3211 and the first retroreflecting mirror 3212 are installed on a line segment passing through the rotation center of the turntable 223. Similarly, the second retroreflecting mirror 3221 and the second retroreflecting mirror 3222 are installed on a line segment passing through the rotation center of the turntable 223.

  In addition, the installation aspect of the 1st retroreflective mirror 3211 and the 1st retroreflective mirror 3212 which were mentioned above, the 2nd retroreflective mirror 3221, and the 2nd antirecursive mirror 3222 is an example to the last. Accordingly, the first retroreflector 3211, the first retroreflector 3212, the second retroreflector 3221, and the second antiretroreflector 3222 increase the optical path length of one of the pump light LB1 and the probe light LB2. As long as the optical path length of the other of the pump light LB1 and the probe light LB2 decreases, it may be installed in any manner.

  In addition, FIG. 12 shows an example in which the optical delay device 320 includes a first retroreflector 3211, a first retroreflector 3212, a second retroreflector 3221, and a second antiretroreflector 3222. . However, the optical delayer 320 may include the first retroreflecting mirror 3211 and the second retroreflecting mirror 3221, while not including the first retroreflecting mirror 3212 and the second antiretroreflecting mirror 3222.

  Such a terahertz wave measuring apparatus 300 according to the third embodiment can enjoy various effects that can be enjoyed by the terahertz wave measuring apparatus 200 according to the second embodiment, preferably or appropriately.

(4) Fourth Example Next, a terahertz wave measuring apparatus 400 according to a fourth example will be described with reference to FIGS. 13 and 14. FIG. 13 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 400 according to the fourth embodiment. FIG. 14 is a plan view showing the relationship between the rotation angle of the turntable 223 and the optical paths of the pump light LB1 and the probe light LB2. In addition, about the component same as the component with which the terahertz wave measuring apparatus 200 of 2nd Example is provided, the detailed description is irradiated by attaching | subjecting the same referential mark.

  As illustrated in FIG. 13, the terahertz wave measuring apparatus 400 according to the fourth embodiment further includes a first light receiving element 421 and a second light receiving element 422 as compared with the terahertz wave measuring apparatus 200 according to the second embodiment. Is different. Other components of the terahertz wave measuring apparatus 400 of the fourth embodiment may be the same as other components of the terahertz wave measuring apparatus 200 of the second embodiment.

  The first light receiving element 421 is a photodetector that receives the pump light LB1 during a period in which the optical delay device 220 does not reflect the pump light LB1 toward the polarization beam splitter 2601. In other words, the first light receiving element 421 receives the pump light LB1 during a period in which the optical delay device 220 does not appropriately reflect the pump light LB1 so that the pump light LB1 reaches the terahertz wave generating element 110.

  Similarly, the second light receiving element 422 is a photodetector that receives the probe light LB2 during a period in which the optical delay device 220 does not reflect the probe light LB2 toward the polarization beam splitter 2602. In other words, the second light receiving element 422 receives the probe light LB2 during a period in which the optical delay device 220 does not appropriately reflect the probe light LB2 so that the probe light LB2 reaches the terahertz wave detecting element 130.

  Specifically, as shown in FIG. 14A, when the rotation angle of the turntable 223 is within a predetermined first range, the optical delay device 220 causes the pump light LB1 to reach the terahertz wave generating element 110. In addition, the pump light LB1 and the probe light LB2 can be appropriately reflected so that the probe light LB2 reaches the terahertz wave detection element 130. In this case, the pump light LB1 does not reach the first light receiving element 421. Similarly, the probe light LB2 does not reach the second light receiving element 422.

  On the other hand, as shown in FIG. 14B, when the rotation angle of the turntable 223 is in the predetermined second range, the optical delay device 220 causes the pump light LB1 to reach the terahertz wave generation element 110 and The pump light LB1 and the probe light LB2 cannot be appropriately reflected so that the probe light LB2 reaches the terahertz wave detection element 130. In this case, the pump light LB1 reaches the first light receiving element 421. In other words, the first light receiving element 421 is arranged at a position where the pump light LB1 arrives at this timing. Similarly, the probe light LB2 reaches the second light receiving element 422. In other words, the second light receiving element 422 is disposed at a position where the probe light LB2 arrives at this timing.

  The first light receiving element 421 may measure the light intensity (in other words, power) of the pump light LB1 by receiving the pump light LB1. Similarly, the second light receiving element 422 may measure the light intensity (in other words, power) of the probe light LB2 by receiving the probe light LB2. In this case, the arithmetic processing unit 150 determines the characteristics (for example, light intensity, etc.) of the pulsed laser light LB generated by the pulsed laser device 101 based on at least one of the light intensity of the pump light LB1 and the light intensity of the probe light LB2. ) May be set.

  In the above description, the terahertz wave generation device 400 outputs the pump light LB1 during a period in which the optical delay device 220 does not appropriately reflect the pump light LB1 so that the pump light LB1 reaches the terahertz wave generation element 110. The first light receiving element 421 that receives light and the second light receiving element that receives the probe light LB2 during a period in which the optical delay device 220 does not appropriately reflect the probe light LB2 so that the probe light LB2 reaches the terahertz wave detecting element 130. Both 422 are provided. However, the terahertz wave measuring apparatus 400 receives the pump light LB1 during a period in which the optical delay device 220 does not appropriately reflect the pump light LB1 so that the pump light LB1 reaches the terahertz wave generating element 110, and the probe A single light receiving element that receives the probe light LB2 during a period in which the optical delay device 220 does not appropriately reflect the probe light LB2 so that the light LB2 reaches the terahertz wave detecting element 130 may be provided.

  The terahertz wave measuring apparatus 400 according to the fourth embodiment can enjoy various effects that can be enjoyed by the terahertz wave measuring apparatus 200 according to the second embodiment, preferably or appropriately. In addition, the terahertz wave measuring apparatus 400 according to the fourth embodiment preferably uses the respective light intensities of the pump light LB1 and the probe light LB2 without affecting the analysis operation of the characteristics of the measurement object using the terahertz wave THz. Can be measured.

  Various components described in the first to fourth embodiments may be appropriately combined.

  Further, the present invention can be appropriately changed without departing from the gist or concept of the present invention which can be read from the claims and the entire specification, and a terahertz wave measuring apparatus and an optical path length difference adjusting apparatus accompanying such a change are also included. It is also included in the technical idea of the present invention.

DESCRIPTION OF SYMBOLS 100 Terahertz wave measuring device 101 Pulse laser apparatus 110 Terahertz wave generating element 120 Optical delay device 1211 1st retroreflecting mirror 1212 2nd retroreflecting mirror 130 Terahertz wave detecting device 150 Arithmetic processing part 200 Terahertz wave measuring device 220 Optical delay device 2211 2212, 2213 First reflecting mirror 2221, 2222, 2223 Second reflecting mirror 300 Terahertz wave measuring device 320 Optical delay device 3211, 3212 First retroreflecting mirror 3221, 3222 Second retroreflecting mirror 400 Terahertz wave measuring device 421 First light receiving Element 422 Second light receiving element LB1 Pump light LB2 Probe light THz Terahertz wave

Claims (10)

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;
The optical path length of one of the first laser light and the second laser light is increased, and the optical path length of the other laser light of the first laser light and the second laser light is decreased. The terahertz wave measuring device further comprising: adjusting means for adjusting optical path lengths of both the first laser beam and the second laser beam. The adjusting means includes a first reflecting mirror that reflects the first laser light and a second reflecting mirror that reflects the second laser light,
The adjusting means adjusts both the optical path length of the first laser light and the optical path length of the second laser light by moving both the first reflecting mirror and the second reflecting mirror. The terahertz wave measuring device according to claim 1. The reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror are facing opposite to each other along the moving direction of the first reflecting mirror and the second reflecting mirror,
The adjusting means moves both the first reflecting mirror and the second reflecting mirror in the same direction, thereby reducing both the optical path length of the first laser light and the optical path length of the second laser light. The terahertz wave measuring device according to claim 2, wherein the terahertz wave measuring device is adjusted. The adjustment means moves both the first reflecting mirror and the second reflecting mirror so that the first reflecting mirror and the second reflecting mirror reciprocate on a straight line. Or the terahertz wave measuring device of 3. The adjusting means moves both the first reflecting mirror and the second reflecting mirror by rotating a turntable on which the first reflecting mirror and the second reflecting mirror are installed. Item 5. The terahertz wave measuring device according to any one of Items 2 to 4. The first reflecting mirror includes a retroreflecting mirror that retroreflects the first laser beam,
The terahertz wave measuring apparatus according to any one of claims 2 to 5, wherein the second reflecting mirror includes a retroreflecting mirror that retroreflects the second laser light. The first reflecting mirror includes at least two first rotating reflecting mirrors having reflecting surfaces parallel to each other and installed on the turntable,
The second reflecting mirror includes at least two second rotating reflecting mirrors having reflecting surfaces parallel to each other and installed on the turntable,
The adjusting means reflects the one laser beam propagating from at least one of the at least two first rotating reflecting mirrors toward at least one of the at least two first rotating reflecting mirrors; A first external reflecting mirror installed outside the rotating table and the one laser beam propagating from at least one of the at least two second rotating reflecting mirrors, the at least two second rotating reflecting mirrors. The terahertz wave measuring device according to claim 5, further comprising: a second external reflecting mirror that reflects toward at least one of the rotating table and is installed outside the rotating table. The first reflecting mirror reflects the first laser beam so that the first laser beam is applied to the generating unit during the first period, while the second reflecting mirror is in a second period different from the first period. Reflecting the first laser beam so that the first laser beam is not irradiated onto the generating means;
The terahertz wave measurement according to any one of claims 1 to 7, further comprising first light receiving means for receiving the first laser light reflected by the first reflecting mirror during the second period. apparatus. The second reflecting mirror reflects the second laser beam so that the second laser beam is applied to the detection means during a third period, while the fourth reflector is in a fourth period different from the third period. Reflecting the second laser beam so that the second laser beam is not irradiated on the detection means;
The terahertz wave measurement according to any one of claims 1 to 8, further comprising second light receiving means for receiving the second laser light reflected by the second reflecting mirror during the fourth period. apparatus. An optical path length adjusting device for adjusting an optical path length difference between an optical path length of a first light beam and an optical path length of a second light beam different from the first light beam,
The first ray so that the optical path length of one of the first ray and the second ray increases and the optical path length of the other ray of the first ray and the second ray decreases. The optical path length adjusting device is configured to adjust both the optical path length of the second light beam and the optical path length of the second light beam.

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