JP2016045099A - Terahertz wave measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an appropriate measurement result using a relatively simple configuration even when the position of a retroreflecting mirror is out of alignment.SOLUTION: A terahertz wave measurement device (100) comprises: generation means (110) for generating a terahertz wave (THz) upon irradiation by a laser beam (LB1); first adjustment means (170) for adjusting the path of the terahertz wave so that, while an object to be measured is not irradiated with a first terahertz wave (THz1) that is one portion of the terahertz wave, the object to be measured is irradiated with a second terahertz wave (THz2) that is the other portion of the terahertz wave; first detection means (130) for detecting the first and second terahertz waves upon irradiation by the laser beam (LB2); and second adjustment means (120) for adjusting the optical path length of the laser beam as the laser beam is retroreflected.SELECTED DRAWING: Figure 1

Description

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

  As a terahertz wave measuring apparatus, an apparatus using terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy) is known. The terahertz wave measuring apparatus measures the characteristics of the measurement object according to the following procedure. First, pump light (in other words, excitation light), which is one laser light obtained by branching ultrashort pulse laser light (for example, femtosecond pulse laser light), generates terahertz waves to which a bias voltage is applied. The element is irradiated. As a result, the terahertz wave generating element generates a terahertz wave. The terahertz wave generated by the terahertz wave generating element is irradiated to the measurement object. The terahertz wave irradiated to the measurement target is another laser beam obtained by branching the ultrashort pulse laser beam as a reflected terahertz wave or a transmitted terahertz wave from the measurement target, and is optically related to the pump light. The terahertz wave detection element to which the probe light (in other words, excitation light) to which a long delay (that is, 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 characteristic of the measurement object is measured by analyzing the spectrum of the terahertz wave. In addition, the example of a measurement of the characteristic of a measurement object is described in patent document 1, for example.

  Here, the optical delay given to the probe light (or pump light) is the probe light (or pump light) with respect to an optical delay device including a retroreflector capable of retroreflecting incident light. ) In many cases. Here, “retroreflection” refers to a state in which incident light is reflected in a direction parallel to the incident direction of the incident light. An example of the optical delay device includes an optical delay device including a plurality of rotatable retroreflecting mirrors (or prisms) (see, for example, Patent Documents 2 to 4).

JP 2007-225349 A JP 2008-515028 A JP 2001-228080 A Japanese Patent No. 3720335

  However, when an optical delay is given to the probe light (or pump light) using a plurality of retroreflecting mirrors, an appropriate measurement result cannot be obtained due to the positional deviation of the retroreflecting mirrors. Technical problems may occur.

Specifically, for example, in Patent Document 2, a mechanism for adjusting the rotation operation and the detection timing is not provided. For this reason, it is not possible to cope with problems caused by misalignment or the like. Further, although Patent Document 3 describes a configuration for generating a timing pulse, it is necessary to separately arrange and adjust a photodiode. In addition, since the position of the retroreflector is always detected during measurement, the unit price and man-hour increase. Further, when a retroreflecting mirror is configured by using two reflecting mirrors, only one of the reflecting mirrors can be detected by a photodiode. Further, in Patent Document 4, the timing pulse is generated using the reflected light from the translucent body. For this reason, it is necessary to arrange | position an optical axis perpendicular | vertical with respect to a translucent body, and a man-hour will increase. In addition, it is necessary that the reflected light from the translucent body can be used as a timing pulse, the intensity of the terahertz wave applied to the object to be measured may decrease, and the SNR (Signal-Noise Ratio) may be deteriorated. Examples of the problem to be attempted include the above. It is an object of the present invention to provide a terahertz wave measuring apparatus that can obtain an appropriate measurement result even when the retroreflecting mirror is misaligned with a relatively simple configuration.

  A terahertz wave measuring apparatus that solves the above-described problem includes a generation unit that generates a terahertz wave when irradiated with laser light, and (i) a first terahertz wave that is a part of the terahertz wave generated by the generation unit. However, (ii) the second terahertz wave, which is another part of the terahertz wave generated by the generating means, is a path that does not irradiate the measurement target and the first target path. A first adjustment unit that adjusts a path of the terahertz wave so that the measurement object is irradiated while propagating through a second path having a different length, and the laser light is applied to the measurement object. First generation means for detecting the first terahertz wave that has not been irradiated and the second terahertz wave that has been irradiated to the measurement object, and the generation by retroreflecting the laser light And a second adjusting means for adjusting the optical path length of the laser beam irradiated in at least one stage and said first detecting means.

It is a block diagram which shows the structure of the terahertz wave measuring device of a present Example. It is a top view which shows the structure of the optical delay device of a present Example. It is a perspective view which shows each structure of a terahertz wave generation element and a terahertz wave detection element. A graph showing the waveform of the terahertz wave in the case where no positional deviation occurs in the four retroreflecting mirrors included in the optical delay device in association with the period in which each retroreflecting mirror retroreflects the probe light, and optical delay 4 is a graph showing the amplitude of a waveform of a terahertz wave (particularly, a second terahertz wave) in a shade when there is no displacement in the four retroreflecting mirrors included in the device. A waveform of a terahertz wave in a case where a positional shift occurs in at least one of the four retroreflecting mirrors included in the optical delay device is shown in association with a period in which each retroreflecting mirror retroreflects the probe light. 6 is a graph showing the amplitude of the waveform of a terahertz wave (particularly, the second terahertz wave) in gray when at least one of four retroreflecting mirrors included in the optical delayer is displaced. . It is a block diagram which shows the structure of an index signal generation part. It is a graph which shows the time waveform of a 1st terahertz wave. It is a block diagram which shows the modification of an index signal generation part. It is a block diagram which shows the structure of a measurement start signal production | generation part.

  Hereinafter, description will be given of embodiments of the terahertz wave of the present invention.

<1>
The terahertz wave measuring apparatus according to the present embodiment includes: a generation unit that generates a terahertz wave when irradiated with laser light; and (i) a first terahertz wave that is a part of the terahertz wave generated by the generation unit. And (ii) the second terahertz wave, which is another part of the terahertz wave generated by the generating means, is a path length from the first path while propagating through the first path and not being irradiated to the measurement target Irradiates the measurement target by irradiating the terahertz wave with the first adjustment means that separates the terahertz wave so that the measurement target is irradiated while propagating through different second paths. First detection means for detecting the first terahertz wave that has not been applied and the second terahertz wave applied to the measurement object; and the generation means by retroreflecting the laser light; and 1 is irradiated on at least one of the detecting means and a second adjusting means for adjusting the optical path length of the laser beam.

  According to the terahertz wave measuring apparatus of this embodiment, the operation of the generating unit, the first adjusting unit, the first detecting unit, and the second adjusting unit uses the terahertz time domain spectroscopy to irradiate the terahertz object to be measured. A wave is detected. The detected terahertz wave is used for measuring 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.

  The generation unit generates a terahertz wave by irradiating the generation unit with laser light as excitation light (for example, pump light).

  The first adjusting unit adjusts the path of the terahertz wave generated by the generating unit (that is, the path through which the terahertz wave propagates). Specifically, the first adjustment unit is configured to prevent the first terahertz wave, which is a part of the terahertz wave generated by the generation unit, from being irradiated to the measurement target, while the other terahertz wave generated by the generation unit The path of the terahertz wave is adjusted so that the second terahertz wave that is a part of the target is irradiated onto the measurement target. Typically, the first adjusting unit may adjust the path of the terahertz wave generated by the generating unit by separating the terahertz wave generated by the generating unit into a first terahertz wave and a second terahertz wave. However, the first adjustment unit may adjust the path of the terahertz wave generated by the generation unit using other methods.

  The first detection unit irradiates the first detection unit with laser light as excitation light (for example, probe light), so that the terahertz wave reflected by the measurement object or transmitted through the measurement object (that is, the first detection unit). 2 terahertz waves) are detected.

  The second adjusting means retroreflects the laser light and guides the retroreflected laser light to at least one of the generating means and the first detecting means. At this time, the second adjusting means adjusts the optical path length of the laser light applied to at least one of the generating means and the first detecting means. For example, when the second adjusting means includes a retroreflecting mirror that retroreflects the laser light, the second adjusting means adjusts the optical path length of the laser light by physically moving the retroreflecting mirror. May be. As a result, the second adjusting means can appropriately adjust the optical path length difference between the optical path of the laser light applied to the generating means and the optical path of the laser light applied to the first detecting means. Such adjustment of the optical path length difference is performed in order to suitably detect a terahertz wave waveform (typically a time waveform, the same applies hereinafter) appearing in the order of sub-picoseconds.

  In particular, in the present embodiment, as described above, the first adjustment unit sets the path of the terahertz wave so that the first terahertz wave is not irradiated on the measurement target while the second terahertz wave is irradiated on the measurement target. adjust. For this reason, a 1st detection means detects not only the 2nd terahertz wave irradiated to the measurement object but the 1st terahertz wave not irradiated to the measurement object.

  The first adjusting means further has a path length of a path of the first terahertz wave (that is, a path through which the first terahertz wave propagates) and a path of a path of the second terahertz wave (that is, a path through which the second terahertz wave propagates). Adjust the terahertz wave path to be different from the length. For this reason, the first detection unit can detect the first terahertz wave and the second terahertz wave at different timings. That is, the first detection means can continuously detect the first terahertz wave and the second terahertz wave.

  Here, since the measurement object is irradiated with the second terahertz wave, the second terahertz wave detected by the first detection means can be used for the purpose of measuring the characteristic of the measurement object. On the other hand, since the first terahertz wave is not irradiated on the measurement object, the first terahertz wave detected by the first detection unit can be used for a purpose different from the measurement of the characteristics of the measurement object. For example, the first terahertz wave can be used for the purpose of adjusting the timing for measuring the characteristics of the measurement object.

  In particular, the first terahertz wave and the second terahertz wave are substantially generated from the same terahertz wave. Therefore, as long as a part of the terahertz wave generated by the generating unit becomes the first terahertz wave and another part of the terahertz wave generated by the generating unit becomes the second terahertz wave, the first terahertz wave is detected first. The temporal relationship (that is, the time difference) between the timing when the means reaches the timing and the timing when the second terahertz wave reaches the first detection means is substantially fixed or does not vary. Alternatively, the first terahertz wave reaches the first detection means after the second terahertz wave reaches the first detection means without depending on the presence or absence of variation in the adjustment accuracy of the optical path length of the laser light by the second adjustment means. The time required to do this is fixed or does not vary. For example, when the first adjustment unit adjusts the path of the terahertz wave so as to separate the same terahertz wave into the first and second terahertz waves, the timing at which the first terahertz wave reaches the first detection unit and the first time The temporal relationship between the timing at which the 2 terahertz wave reaches the first detection means is substantially fixed or does not vary. As a result, on the terahertz wave waveform indicated by the detection result of the first detection means, the temporal relationship between the timing at which the first terahertz wave waveform appears and the timing at which the second terahertz wave waveform appears is substantially fixed. Or do not fluctuate.

  Thus, in the present embodiment, the second terahertz wave, which is another part of the terahertz wave generated by the generating means, is irradiated to the measurement object. For this reason, the terahertz wave measuring apparatus can measure the characteristics of the measurement object based on the detection result of the second terahertz wave.

  Furthermore, in the present embodiment, the first terahertz wave that is a part of the terahertz waves generated by the generating means is not irradiated to the measurement object. For this reason, the terahertz wave measuring apparatus can adjust the timing for measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. For example, due to variations in the adjustment accuracy of the optical path length of the laser light by the second adjustment means (for example, variations in the adjustment accuracy of the optical path length of the laser light due to the positional deviation of the retroreflector provided in the second adjustment means), There is a possibility that the timing at which the detection means detects the second terahertz wave varies. As described above, even when the timing at which the first detection unit detects the second terahertz wave varies, the terahertz wave measurement apparatus has a variation in timing at which the first detection unit detects the second terahertz wave. The timing for measuring the characteristic of the measurement object can be adjusted based on the detection result of the first terahertz wave so that the influence on the characteristic measurement is eliminated. As a result, the terahertz wave measuring apparatus can measure the characteristics of the measurement object with relatively high accuracy using the terahertz wave.

  Furthermore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. can do. That is, the terahertz wave measuring apparatus sequentially determines the timing for measuring the characteristics of the measurement object based on the detection result of the first terahertz wave in parallel with the measurement of the characteristics of the measurement object based on the detection result of the second terahertz wave. It can be adjusted (in other words, in real time).

  Furthermore, the temporal relationship between the timing at which the first terahertz wave reaches the first detecting means and the timing at which the second terahertz wave reaches the first detecting means is not substantially fixed or fluctuated. As described above. That is, the second terahertz wave reaches the first detection means after the first terahertz wave reaches the first detection means without depending on the presence or absence of variation in the adjustment accuracy of the optical path length of the laser light by the second adjustment means. The time required to do this is fixed or does not vary. Alternatively, the first terahertz wave reaches the first detection means after the second terahertz wave reaches the first detection means without depending on the presence or absence of variation in the adjustment accuracy of the optical path length of the laser light by the second adjustment means. The time required to do this is fixed or does not vary. For this reason, even if the timing at which the first detection means detects the second terahertz wave varies, the terahertz wave measuring apparatus measures the characteristics of the measurement object based on the detection result of the second terahertz wave. However, the timing for measuring the characteristics of the measurement object can be adjusted based on the detection result of the first terahertz wave.

<2>
In another aspect of the terahertz wave measuring apparatus according to the present embodiment, the first adjustment unit is configured so that the difference in path length between the first path and the second path is fixed or does not vary. Adjust the route.

  According to this aspect, the timing at which the first terahertz wave reaches the first detection means and the second terahertz wave are the first and second terahertz waves without depending on the presence or absence of variation in the adjustment accuracy of the optical path length of the laser light by the second adjustment means. The temporal relationship between the timing to reach the detection means is fixed or does not vary. For this reason, even if the timing at which the first detection means detects the second terahertz wave varies, the terahertz wave measuring apparatus measures the characteristics of the measurement object based on the detection result of the second terahertz wave. However, the timing for measuring the characteristics of the measurement object can be adjusted based on the detection result of the first terahertz wave.

<3>
In another aspect of the terahertz wave measuring apparatus according to the present embodiment, the first adjustment means has a path length difference between the first path and the second path, and the first detection means has the first and first paths. The path of the terahertz wave is adjusted such that the path length difference is such that each of the two terahertz waves can be detected in an individually identifiable manner.

  According to this aspect, the first detection unit can detect not only the second terahertz wave irradiated on the measurement object but also the first terahertz wave not irradiated on the measurement object. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

<4>
In another aspect of the terahertz wave measuring apparatus according to the present embodiment, the first adjustment means has a path length difference between the first path and the second path, and the first detection means has the first and first paths. The path of the terahertz wave is adjusted so that the path length difference is such that each of the two terahertz waves can be detected at a timing that does not overlap in time.

  According to this aspect, the first detection unit can detect not only the second terahertz wave irradiated on the measurement object but also the first terahertz wave not irradiated on the measurement object. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

<5>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the second adjustment unit irradiates the detection unit so that an optical path length of the laser light irradiated to the detection unit becomes shorter as time passes. Adjusting the optical path length of the laser beam, and adjusting the path of the terahertz wave so that the first path is longer than the second path.

  According to this aspect, the terahertz wave measuring apparatus calculates the waveform of the first terahertz wave propagating along the relatively long first path based on the detection results of the first and second terahertz waves by the first detection unit. After the detection, the waveform of the second terahertz wave propagating through the relatively short second path can be detected. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

<6>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the second adjustment unit irradiates the detection unit so that the optical path length of the laser light irradiated to the detection unit becomes longer as time elapses. Adjusting the optical path length of the laser beam, and adjusting the path of the terahertz wave so that the first path is shorter than the second path.

  According to this aspect, the terahertz wave measuring apparatus calculates the waveform of the first terahertz wave propagating through the relatively short first path based on the detection results of the first and second terahertz waves by the first detection unit. After detection, the waveform of the second terahertz wave propagating through the relatively long second path can be detected. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

<7>
In another aspect of the terahertz wave measuring apparatus according to the present embodiment, the second adjustment unit irradiates the generation unit so that an optical path length of the laser light irradiated to the generation unit becomes shorter as time elapses. Adjusting the optical path length of the laser beam, and adjusting the path of the terahertz wave so that the first path is shorter than the second path.

  According to this aspect, the terahertz wave measuring apparatus calculates the waveform of the first terahertz wave propagating through the relatively short first path based on the detection results of the first and second terahertz waves by the first detection unit. After detection, the waveform of the second terahertz wave propagating through the relatively long second path can be detected. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

<8>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the second adjustment unit irradiates the generation unit so that an optical path length of the laser light irradiated to the generation unit becomes longer as time elapses. Adjusting the optical path length of the laser beam, and adjusting the path of the terahertz wave so that the first path is longer than the second path.

  According to this aspect, the terahertz wave measuring apparatus calculates the waveform of the first terahertz wave propagating along the relatively long first path based on the detection results of the first and second terahertz waves by the first detection unit. After the detection, the waveform of the second terahertz wave propagating through the relatively short second path can be detected. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

<9>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the first adjustment unit adjusts the path length difference between the first path and the second path, and the second adjustment unit adjusts the optical path length. The terahertz wave path is adjusted such that the first detection means has a path length difference enough to detect both the first and second terahertz waves during the predetermined adjustment period.

  According to this aspect, the first detection means can detect both the first terahertz wave and the second terahertz wave during a certain adjustment period. That is, there is little or no situation where the first detection means can detect only one of the first terahertz wave and the second terahertz wave during a certain adjustment period. Therefore, the terahertz wave measuring apparatus adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave. be able to.

  When the second adjustment means includes a plurality of retroreflecting mirrors, the adjustment period corresponds to a period in which each retroreflected light retroreflects the laser light.

<10>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the first and second terahertz waves are set such that the difference between the intensity of the first terahertz wave and the intensity of the second terahertz wave is a predetermined value or less. 3rd adjustment means to adjust the intensity | strength of at least one of is further provided.

  According to this aspect, since the difference between the intensity of the first terahertz wave and the intensity of the second terahertz wave is equal to or less than a predetermined value, the first detection unit preferably uses both the first and second terahertz waves. Can be detected.

  If the difference between the intensity of the first terahertz wave and the intensity of the second terahertz wave is larger than a predetermined value (for example, excessively large), the detection sensitivity (for example, dynamic range) of the first detection unit is used. ) Is matched to the larger one of the intensity of the first terahertz wave and the intensity of the second terahertz wave. As a result, the first detection means can suitably detect one of the first and second terahertz waves having an intensity suitable for detection sensitivity, while the first detection means has an intensity not suitable for detection sensitivity. There may arise a technical problem that there is a possibility that either one of the first and second terahertz waves cannot be suitably detected. However, in this embodiment, such a technical problem hardly occurs.

<11>
In another aspect of the terahertz wave measuring apparatus of the present embodiment, the measurement unit that measures the characteristics of the measurement object based on the second terahertz wave detected by the second detection unit, and the first detection unit Based on the detection result of the first terahertz wave, the measurement unit further includes a fourth adjustment unit that adjusts the timing at which the characteristic of the measurement object is measured based on the second terahertz wave.

  According to this aspect, the terahertz wave measuring apparatus measures the characteristic of the measurement target based on the detection result of the second terahertz wave, and sets the timing for measuring the characteristic of the measurement target as the detection result of the first terahertz wave. Can be adjusted based on.

<12>
As described above, in another aspect of the terahertz wave measuring apparatus including the fourth adjustment unit, the fourth adjustment unit detects a feature point of the first terahertz wave detected by the first detection unit. Calculating means for calculating a reference period, which is a period from the reference time to detection of the feature point, and the measurement means so as to start measuring the characteristics of the measurement object at a timing determined based on the reference period. And control means for controlling.

  According to this aspect, the second detection unit detects the feature point of the first terahertz wave detected by the first detection unit. Note that the “feature point” in the present embodiment is a point at which the fluctuation of the first terahertz wave (for example, fluctuation along the time axis) can be detected with high accuracy. In addition, since the first terahertz wave is not irradiated to the measurement object, the second detection unit performs the first terahertz wave in parallel with the detection by the first detection unit of the second terahertz wave irradiated to the measurement object. Feature points can be detected. That is, the second detection means can detect the feature point of the first terahertz wave in parallel with the measurement of the characteristic of the measurement object.

  When the feature point is detected, the calculation means calculates a reference period that is a period from the reference time to detection of the feature point. Here, the “reference time” is a reference time for calculating the reference period, and is determined by a predetermined reference signal or the like. It can be said that the reference period calculated in this way is a value indicating the time position of the feature point with respect to the reference time.

  When the reference period is calculated, the control unit starts measurement of the characteristics of the measurement object at a timing according to the reference period (typically, the analysis of the detection result of the second terahertz wave is started). Control the measuring means. As a result, the influence of the variation in the timing at which the first detection means detects the second terahertz wave on the measurement of the characteristics of the measurement object is suitably eliminated.

<13>
In another aspect of the terahertz wave measuring apparatus including the second detection unit, the calculation unit, and the control unit as described above, the second adjustment unit includes a plurality of retroreflection units each re-reflecting the laser beam, The second detection means detects the feature point separately for each reflection period during which each of the plurality of retroreflective means re-reflects the laser light, and the calculation means separately detects the feature point for each reflection period. A reference period is calculated, and the control means controls the measurement means so as to start measuring the characteristics of the measurement object at a timing determined according to the reference time corresponding to the reflection period for each reflection period. To do.

  According to this aspect, the optical path length difference between the optical path of the laser light applied to the generating means and the optical path of the laser light applied to the first detecting means is adjusted using a plurality of retroreflective means. Specifically, for example, when the retroreflective unit physically moves, the position of the retroreflective unit in the optical axis direction with respect to the laser beam irradiated on at least one of the generating unit and the first detecting unit changes. As a result, the optical path length of at least one of the optical paths of the laser light applied to at least one of the generating means and the first detecting means changes.

  The second adjusting unit may further include a rotating unit that moves the plurality of recurring reflecting units so as to rotate on the circumference. In this case, for example, the position of the retroreflective means in the optical axis direction with respect to the laser light applied to at least one of the generating means and the first detecting means is rotated by rotating the rotating substrate on which the plurality of retroreflective means are arranged. Change. As a result, the optical path length of at least one of the optical paths of the laser light applied to at least one of the generating means and the first detecting means changes.

  Furthermore, a feature point is detected separately for each reflection period in which each of the plurality of retroreflection means retroreflects the laser light (note that the reflection period is substantially the same as the adjustment period described above), The reference period is calculated separately, and the measurement start timing is adjusted. As a result, even when the second adjustment unit includes a plurality of retroreflective units, the timing variation at which the first detection unit detects the second terahertz wave is given to the measurement of the characteristics of the measurement object. The influence is preferably eliminated.

<14>
In another aspect of the terahertz wave measuring apparatus including the second detection unit as described above, the feature points are the maximum value, the minimum value, and the maximum value and the minimum value of the waveform of the first terahertz wave. At least one of the zero cross points.

  According to this aspect, the second detection unit can easily and accurately detect the feature point of the first terahertz wave. For this reason, the calculation means can calculate a more appropriate reference period. Therefore, the control means can control the first detection means so that a more appropriate timing determined based on such a reference period becomes a timing for measuring the characteristics of the measurement object.

<15>
In another aspect of the terahertz wave measuring apparatus including the second detection unit, the calculation unit, and the control unit as described above, the second detection unit detects the feature point a plurality of times, and the calculation unit calculates the reference period. The control means calculates a plurality of times, and the control means controls the measurement means to start measurement of the characteristics of the measurement object at a timing determined according to the average value of the reference period calculated a plurality of times.

  According to this aspect, the feature point is detected a plurality of times, and the reference period is calculated a plurality of times based on each of the detected plurality of feature points. And when the measurement start timing by a measurement means is adjusted, the average value of the reference period detected in multiple times is used. Since the average value of the reference period is used in this way, unintentional adjustment based on an inappropriate reference period caused by erroneous detection of feature points, for example, at the timing of starting measurement of the characteristics of the measurement object is suitable. Is prevented.

  The operation and other gains of the terahertz wave measuring apparatus according to this embodiment will be described in more detail in the following examples.

  As described above, the terahertz wave measuring apparatus according to the present embodiment includes the generating unit, the first adjusting unit, the first detecting unit, and the second adjusting unit. Therefore, an appropriate measurement result can be obtained with a relatively simple configuration even when the retroreflector is misaligned.

  Hereinafter, with reference to the drawings, description will be given of embodiments of the terahertz wave measuring apparatus according to the present invention.

(1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 100 of the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 100 according to the present 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 the measurement target or reflected from the measurement target (that is, irradiated to the measurement target). Detected terahertz wave THz). In the example illustrated in FIG. 1, the terahertz wave measuring apparatus 100 detects the terahertz wave THz reflected from the measurement object.

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 measure 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 sub-picoseconds, it is a technique to directly detect the waveform of the terahertz wave THz (typically, a time waveform, and the same applies hereinafter). Is difficult. Therefore, the terahertz wave measuring apparatus 100 indirectly detects the waveform of the terahertz wave THz, which employs a pump-probe method based on time delay scanning.

  As shown in FIG. 1, a terahertz wave measuring apparatus 100 employing such a terahertz time-domain spectroscopy method and a pump-probe method includes a pulse laser apparatus 101 and a terahertz wave generating element which is a specific example of “generating means”. 110, a beam splitter 161, a reflecting mirror 162, a reflecting mirror 163, an optical path adjuster 170 which is a specific example of “first adjusting means”, and an optical delay which is a specific example of “second adjusting means”. 120, a terahertz wave detecting element 130 which is a specific example of “first detecting means”, a bias voltage generating unit 141, an IV (current-voltage) converting unit 144, a lock-in detecting unit 145, An arithmetic processing unit 150, which is a specific example of “measuring means”, a reference signal generation unit 181, an index signal generation unit 182 which is a specific example of “second detection means”, and a “fourth adjustment means” And a measurement start signal generation unit 183 is a body example.

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

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

  The optical delay device 120 adjusts the difference (that is, the optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Specifically, the optical delay device 120 adjusts the optical path length between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 by adjusting the optical path length of the probe light LB2. The timing at which the pump light LB1 enters the terahertz wave generating element 110 (or the terahertz wave generating element 110 is adjusted) is adjusted by adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Relative timing between the timing at which the terahertz wave THz is generated) and the timing at which the probe light LB2 is incident on the terahertz wave detecting element 130 (or the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz). Can be adjusted. For example, when the optical path of the probe light LB2 is increased by 0.3 millimeters (however, the optical path length in the air) by the optical delay device 120, the timing at which the probe light LB2 enters the terahertz wave detection element 130 is delayed by 1 picosecond. Become. In this case, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is delayed by 1 picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the terahertz wave detecting element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is gradually shifted. Thus, the terahertz wave detection element 130 can indirectly detect the waveform of the terahertz wave THz. That is, the lock-in detection unit 145 described later can detect the waveform of the terahertz wave THz based on the detection result of the terahertz wave detection element 130.

  Here, the configuration of the optical delay device 120 will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration of the optical delay device 120. The optical delay device 120 shown in FIG. 2 is merely an example, and an optical delay device having a configuration different from the configuration shown in FIG. 2 may be used.

  As shown in FIG. 2, the optical delay device 120 includes a plurality of (four in FIG. 2) retroreflecting mirrors 121 (121a to 121d), each of which is a specific example of “retroreflecting means”, and a rotating substrate 122. And.

  Each retroreflecting mirror 121 retroreflects the probe light LB2 incident on each retroreflecting mirror 121. That is, each retroreflecting mirror 121 reflects the probe light LB2 incident on each retroreflecting mirror 121 in a direction parallel to the incident direction of the probe light LB2. Each retroreflecting mirror 121 reflects the probe light LB2 incident on each retroreflecting mirror 121 toward the outside of the optical delay device 120 (for example, the reflecting mirror 163).

  The plurality of retroreflecting mirrors 121 are arranged at equal intervals on a circumference C around the rotation axis of the rotating substrate 122. The rotating substrate 122 can be rotated by an operation of a motor (not shown) or the like. Accordingly, each of the plurality of retroreflecting mirrors 121 circulates on the circumference C as the rotating substrate 122 rotates. By such a movement of the retroreflecting mirror 121, the optical path length of the probe light LB2 is adjusted.

  In the example illustrated in FIG. 2, each retroreflecting mirror 121 moves so as to approach the incident direction of the probe light LB <b> 2. As a result, each retroreflecting mirror 121 moves so that the optical path of the probe light LB2 becomes shorter as time passes (that is, as each retroreflecting mirror 121 moves).

  The retroreflecting mirror 121 is moved under the control of the arithmetic processing unit 150. That is, the arithmetic processing unit 150 controls the rotation operation of the rotating substrate 122 by outputting a control signal that specifies the driving amount of the motor that drives the rotating substrate 122.

  In FIG. 1 again, the probe light LB2 emitted from the optical delay device 120 enters the terahertz wave detection element 130 via a light guide path and a reflecting mirror 163 (not shown).

  Here, the terahertz wave generating element 110 irradiated with the pump light LB1 and the terahertz detecting element 130 irradiated with the probe light LB2 will be described in more detail with reference to FIG. FIG. 3 is a perspective view showing the configuration of each of the terahertz wave generating element 110 and the terahertz wave detecting element 130. The configurations of the terahertz wave generation element 110 and the terahertz wave detection element 130 illustrated in FIG. 3 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. 3A, the terahertz wave generating element 110 includes a substrate 111, an antenna (in other words, a transmission line) 112, and an antenna (in other words, a transmission line) 113.

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

  A bias voltage output from the bias voltage generation unit 141 is applied to the gap 114 via the antenna 112 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. 3B, 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 a substrate 131, an antenna (in other words, a transmission line) 132, and an antenna (in other words, a transmission line) 133. The substrate 131, the antenna 132, and the antenna 133 have the same configuration as the substrate 111, the antenna 112, and the antenna 113, respectively.

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

  In FIG. 1 again, the terahertz wave THz emitted from the terahertz wave generating element 110 enters the optical path adjuster 170. The optical path adjuster 170 separates the terahertz wave THz into the first terahertz wave THz1 and the second terahertz wave THz2. Furthermore, the optical path adjuster 170 guides both the separated first terahertz wave THz1 and second terahertz wave THz2 to the terahertz wave detecting element 130.

  In order to perform such an operation, the optical path adjuster 170 includes a beam splitter 171 and a reflecting mirror 172.

  The terahertz wave THz generated by the terahertz wave generating element 110 is incident on the beam splitter 171. The beam splitter 171 reflects a part of the terahertz wave THz incident on the beam splitter 171 and transmits a part of the terahertz wave THz. A part of the terahertz wave THz reflected by the beam splitter 171 enters the reflecting mirror 172 as the first terahertz wave THz1. On the other hand, the other part of the terahertz wave THz transmitted through the beam splitter 171 is irradiated to the measurement object as the second terahertz wave THz2.

  The first terahertz wave THz 1 incident on the reflecting mirror 172 is reflected by the reflecting mirror 172. The first terahertz wave THz1 reflected by the reflecting mirror 172 is incident on the beam splitter 171 again. On the other hand, the second terahertz wave THz2 applied to the measurement object 172 is reflected by the measurement object. The second terahertz wave THz2 reflected by the measurement object is incident on the beam splitter 171 again.

  A distance d1 between the beam splitter 171 and the reflecting mirror 172 (typically an optical distance, the same applies hereinafter) is different from a distance d2 between the beam splitter 171 and the measurement object. That is, the length 2d1 of the propagation path of the first terahertz wave THz1 returning from the beam splitter 171 to the beam splitter 171 through the reflecting mirror 172 (typically an optical length, the same applies hereinafter) is The second terahertz wave THz2 returning from the beam 171 to the beam splitter 171 through the measurement object is different from the propagation path length 2d2. Furthermore, while the terahertz wave measuring apparatus 100 analyzes the characteristics of the measurement object, the distance d1 and the distance d2 are fixed or do not vary. That is, while the terahertz wave measuring apparatus 100 analyzes the characteristics of the measurement object, the difference between the distance d1 and the distance d2 is fixed or does not vary. Therefore, the beam splitter 171 and the reflecting mirror 172 are disposed at appropriate positions that can satisfy the above-described conditions in consideration of the position where the measurement object is disposed.

  In the present embodiment, as described above, each retroreflecting mirror 121 moves so that the optical path of the probe light LB2 becomes shorter as time passes (that is, as each retroreflecting mirror 121 moves). In this case, the distance d1 is preferably larger than the distance d2.

  The reflecting mirror 172 has a reflectance such that the difference between the intensity of the first terahertz wave THz1 reflected by the reflecting mirror 172 and the intensity of the second terahertz wave THz reflected by the measurement object is equal to or less than a predetermined value. It is preferable to reflect the first terahertz wave THz. For example, considering that there is a high possibility that the reflectance of the measurement object with respect to the second terahertz wave THz2 is generally less than 100%, the reflecting mirror 172 has a reflectance with respect to the first terahertz wave THz1 of less than 100%. A reflective surface may be provided.

  The beam splitter 171 transmits the first terahertz wave THz1 reflected by the reflecting mirror 172. The first terahertz wave THz1 transmitted through the beam splitter 171 enters the terahertz wave detection element 130. On the other hand, the beam splitter 171 reflects the second terahertz wave THz2 reflected by the measurement object. Similarly to the first terahertz wave THz1, the second terahertz wave THz2 reflected by the beam splitter 171 also enters the terahertz wave detecting element 130. That is, the beam splitter 171 substantially combines the first terahertz wave THz1 and the second terahertz wave THz2 and then combines the combined first terahertz wave THz1 and second terahertz wave THz2 to the terahertz wave detection element 130. It can be said that it is incident. Hereinafter, for convenience of description, the first terahertz wave THz1 and the second terahertz wave THz2 synthesized by the beam splitter 171 are referred to as a terahertz wave THz0.

  As a result, the terahertz wave detecting element 130 detects the terahertz wave THz0 (that is, the first terahertz wave THz1 and the second terahertz wave THz2). That is, the terahertz wave detection element 130 outputs a current signal having a signal intensity corresponding to the intensity of the terahertz wave THz0 (that is, the first terahertz wave THz1 and the second terahertz wave THz2).

  Here, as described above, the distance d1 between the beam splitter 171 and the reflecting mirror 172 is different from the distance d2 between the beam splitter 171 and the measurement object. For this reason, the terahertz wave detection element 130 detects the first terahertz wave THz1 and the second terahertz wave THz2 at substantially different timings. In the present embodiment, the terahertz wave detecting element 130 detects the first terahertz wave THz1 and the second terahertz wave THz2 in a manner that can be distinguished along the time axis, or the distance d1 and the distance d2 (or the distance d1 and the distance It is preferable that a difference from d2 is set. That is, a current signal having a signal intensity corresponding to the intensity of the first terahertz wave THz1 and a current signal having a signal intensity corresponding to the intensity of the second terahertz wave THz2 can be distinguished from each other along the time axis. It is preferable that the distance d1 and the distance d2 (or the difference between the distance d1 and the distance d2) are set so as to be output in such a manner.

  In addition, in the present embodiment, the terahertz wave detecting element 130 detects both the first terahertz wave THz1 and the second terahertz wave THz2 during the reflection period in which each retroreflecting mirror 121 retroreflects the probe light LB2. It is preferable that the distance d1 and the distance d2 (or the difference between the distance d1 and the distance d2) are set so that That is, the retroreflector 121a retroreflects the probe light LB2, the first reflection period, the retroreflector 121b retroreflects the probe light LB2, the retroreflector 121c retroreflects the probe light LB2. The terahertz wave detecting element 130 detects both the first terahertz wave THz1 and the second terahertz wave THz2 in each of the third reflecting period and the fourth reflecting period in which the retroreflecting mirror 121d retroreflects the probe light LB2. It is preferable that the distance d1 and the distance d2 (or the difference between the distance d1 and the distance d2) are set so that they can be detected.

  In parallel with the irradiation of the second terahertz wave THz2, the measurement object may move. For example, the measurement object may move in a plane orthogonal to the direction in which the second terahertz wave THz2 is incident on the measurement object (the left-right direction in FIG. 1). Such movement of the measurement object may be realized by a stage on which the measurement object is mounted. As a result, the arithmetic processing unit 150 can measure the characteristics of the measurement object three-dimensionally.

  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 as a reference signal. As a result, the lock-in detection unit 145 detects the sample value of the terahertz wave THz0 (that is, the first terahertz wave THz1 and the second terahertz wave THz2). Thereafter, the lock-in detection unit 145 detects the waveform of the terahertz wave THz0 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. As a result, the arithmetic processing unit 150 can acquire a waveform signal indicating the waveform of the terahertz wave THz0 by acquiring the detection result of the lock-in detection unit 145. In addition, the arithmetic processing unit 150 performs Fourier transform on the waveform signal indicating the waveform of the terahertz wave THz0 detected by the lock-in detection unit 145, so that the frequency spectrum of the terahertz wave THz0 (that is, the amplitude and phase for each frequency). To get. Furthermore, the arithmetic processing unit 150 analyzes the frequency spectrum of the terahertz wave THz0, thereby measuring the characteristics of the measurement object.

  The reference signal generation unit 181 generates a reference signal synchronized with the rotation of each retroreflector 121. For example, the reference signal is a signal in which one pulse appears every time the rotating substrate 122 on which the retroreflecting mirror 121 is mounted makes one rotation. Such a reference signal is a signal for defining a reference time serving as a reference when the characteristic of the measurement object is measured by the arithmetic processing unit 150. The reference signal is generated using, for example, a drive control pulse from the optical delay device 120 or the arithmetic processing unit 150.

  The index signal generation unit 182 detects a feature point of the first terahertz wave THz1 detected by the terahertz wave detection element 130. The index signal generation unit 182 calculates the time position of the feature point with respect to the reference time defined by the reference signal. The detected time position of the feature point is output to the measurement start signal generation unit 183 as an index signal.

  The measurement start signal generation unit 183 performs measurement during each reflection period in which each retroreflector 121 included in the optical delay device 120 retroreflects the probe light LB2 according to the index signal input from the index signal generation unit 182. A measurement start signal for adjusting the start timing is generated. Note that the measurement processing is started by the arithmetic processing unit 150 using the waveform signal indicating the waveform of the terahertz wave THz0 (particularly, the second terahertz wave THz2) detected by the lock-in detection unit 145. It is time to do. The measurement start signal generated by the measurement start signal generation unit 183 is output to the arithmetic processing unit 150. As a result, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object at a timing according to the measurement start signal.

(2) Technical problems due to the positional deviation of the retroreflecting mirror 121 Next, the technical problems caused by the positional deviation of the retroreflecting mirror 121 will be described with reference to FIGS. 4 and 5. FIG. 4A shows the waveform of the terahertz wave THz0 when the four retroreflecting mirrors 121 included in the optical delay device 120 are not displaced, and each retroreflecting mirror 121 retroreflects the probe light LB2. It is a graph shown in association with a period. FIG. 4B is a graph showing the amplitude of the waveform of the terahertz wave THz0 (particularly, the second terahertz wave THz2) in gray when the four retroreflecting mirrors 121 included in the optical delay device 120 are not displaced. is there. FIG. 5A shows the waveform of the terahertz wave THz0 when the positional deviation occurs in at least one of the four retroreflecting mirrors 121 included in the optical delay device 120, and each retroreflecting mirror 121 returns the probe light LB2. It is a graph shown in association with a reflecting period. FIG. 5B shows the amplitude of the waveform of the terahertz wave THz0 (particularly, the second terahertz wave THz2) in the case where the positional deviation occurs in at least one of the four retroreflecting mirrors 121 included in the optical delay device 120. It is a graph shown by.

  As shown in FIG. 4A, the arithmetic processing unit 150 shows the terahertz wave THz0 detected during the reflection period in which each retroreflecting mirror 121 retroreflects the probe light LB2, as shown in FIG. As a simple waveform signal. For example, if the rotation angle of the rotating substrate 122 when the retroreflecting mirror 121a starts retroreflecting the probe light LB2 is defined as 0 °, the retroreflecting mirror 121a has a rotating angle of the rotating substrate 122 from 0 ° to X1 ° ( However, the probe light LB2 is retroreflected during the first reflection period in which 0 ° <X1 <90 °. Similarly, the retroreflecting mirror 121b retroreflects the probe light LB2 during the second reflection period in which the rotation angle of the rotating substrate 122 is 90 ° to X2 ° (where 90 ° <X2 <180 °). Similarly, the retroreflecting mirror 121c retroreflects the probe light LB2 during the third reflection period in which the rotation angle of the rotating substrate 122 is 180 ° to X3 ° (where 180 ° <X3 <270 °). Similarly, the retroreflecting mirror 121d retroreflects the probe light LB2 during the fourth reflection period in which the rotation angle of the rotating substrate 122 is 270 ° to X4 ° (where 270 ° <X4 <360 °). Thereafter, the same operation is repeated.

  As a result, the arithmetic processing unit 150 acquires a waveform signal indicating the waveform of the terahertz wave THz0 including the waveform of the first terahertz wave THz1 and the waveform of the second terahertz wave THz2 during the first reflection period. The same applies to the second reflection period to the fourth reflection period.

  Here, as described above, in the present embodiment, each retroreflecting mirror 121 moves so that the optical path of the probe light LB2 becomes shorter as time passes (that is, as each retroreflecting mirror 121 moves), and A distance d1 between the beam splitter 171 and the reflecting mirror 172 is larger than a distance d2 between the beam splitter 171 and the measurement object. In this case, the arithmetic processing unit 150 acquires the detection result of the lock-in detection unit 145, thereby acquiring the waveform signal indicating the waveform of the first terahertz THz1 and the second terahertz wave THz2 in this order during each reflection period. . The time interval between the waveform of the first terahertz THz1 and the waveform of the second terahertz THz2 is a fixed value that is determined according to the difference between the distance d1 and the distance d2.

  Such a waveform (waveform signal) of the second terahertz wave THz2 is used, for example, for measuring characteristics of the measurement object (for example, obtaining a tomographic image of the measurement object). For this reason, the peak positions of the waveform signals of the second terahertz wave THz2 during each reflection period are aligned with each other (for example, the rotating substrate 122 at the time when each of the re-reflecting mirrors 121 that are not displaced starts to retroreflect. The relative positions from the time positions corresponding to the rotation angles of 0 °, 90 °, 180 ° and 270 ° are preferably aligned. In the example shown in FIG. 4A, the four retroreflecting mirrors 121 are not misaligned. For this reason, the peak positions of the waveform signals of the second terahertz wave THz2 during each reflection period are aligned with each other. That is, the relative peak position of the waveform signal of the second terahertz wave THz2 during the first reflection period from the time position corresponding to 0 °, the second terahertz during the second reflection period from the time position corresponding to 90 °. The relative peak position of the waveform signal of the wave THz2, the relative peak position of the waveform signal of the second terahertz wave THz2 during the third reflection period from the time position corresponding to 180 °, and the time corresponding to 270 ° The relative peak positions of the waveform signals of the second terahertz wave THz2 during the fourth reflection period from the position are aligned with each other. Accordingly, the second terahertz wave THz2 as shown in FIG. 4B obtained by arranging the waveform signals of the second terahertz wave THz2 shown in FIG. The tomographic image acquired based on the waveform signal is an XZ tomographic image without a step (where the Z direction is the incident direction of the second terahertz wave THz2 with respect to the measurement object, and the X direction is the measurement object) It can be seen that this is a direction along a plane perpendicular to the incident direction of the second terahertz wave THz2.

  On the other hand, FIG. 5A illustrates a case where the retroreflecting mirrors 121b and 121c out of the four retroreflecting mirrors 121 (the retroreflecting mirror 121a to the retroreflecting mirror 121d) included in the optical delay device 120 are displaced. The waveform of the terahertz wave THz0 is shown. Specifically, the retroreflective mirror 121b has a rotation angle of 70 ° to Y2 ° (70 ° <Y2 <190 °) due to the positional deviation occurring in the retroreflective mirror 121b. During the second reflection period, the probe light LB2 is retroreflected. Similarly, the retroreflective mirror 121c recursively transmits the probe light LB2 during the third reflection period in which the rotation angle of the rotary substrate 122 is changed from 190 ° to X3 ° due to the positional deviation generated in the retroreflective mirror 121c. Reflected.

  In this case, the peak positions of the waveform signal of the second terahertz wave THz2 during each reflection period are not aligned with each other due to the positional deviation of the retroreflecting mirrors 121b and 121c. That is, the relative peak position of the waveform signal of the second terahertz wave THz2 during the first reflection period from the time position corresponding to 0 ° and the second terahertz during the fourth reflection period from the time position corresponding to 270 °. The relative peak position of the waveform signal of the wave THz2 is the relative peak position of the waveform signal of the second terahertz wave THz2 during the second reflection period from the time position corresponding to 90 ° and the time position corresponding to 180 °. This is different from the relative peak position of the waveform signal of the second terahertz wave THz2 during the third reflection period from. Accordingly, the second terahertz wave THz2 as shown in FIG. 5B obtained by arranging the waveform signals of the second terahertz wave THz2 shown in FIG. It can be seen that the tomographic image acquired based on the waveform signal is an XZ tomographic image having a step.

  On the other hand, in order to acquire an XZ tomographic image without a step based on the waveform signal of the second terahertz wave THz2 shown in FIG. 5A, the arithmetic processing unit 150 uses the waveform signal of the second terahertz wave THz2. The waveform signal of the second terahertz wave THz2 may be handled so that the state shown in FIG. 4A is in the state shown in FIG. For example, the arithmetic processing unit 150 temporally shifts the waveform signals of the second reflection period and the third reflection period in the waveform signal of the second terahertz wave THz2 illustrated in FIG. The waveform signal of the second terahertz wave THz2 can be handled such that the state of the waveform signal of the second terahertz wave THz2 shown in FIG. That is, the arithmetic processing unit 150 temporally shifts at least a part of the waveform signal of the second terahertz wave THz2 obtained when the retroreflecting mirror 121 has a positional shift, so that the retroreflecting mirror 121 The waveform signal of the second terahertz wave THz2 acquired when there is a positional shift can be handled as the waveform signal of the second terahertz wave THz2 acquired when there is no positional shift in the retroreflector 121. .

  Therefore, in this embodiment, the arithmetic processing unit 150 uses a part of the waveform signal of the second terahertz wave THz2 to measure, in order to temporally shift at least part of the waveform signal of the second terahertz wave THz2. The timing for measuring the characteristics of the object (that is, the measurement start timing described above) is adjusted. In other words, the arithmetic processing unit 150 indirectly realizes a state in which at least a part of the waveform signal of the second terahertz wave THz2 is temporally shifted by adjusting the measurement start timing. However, the arithmetic processing unit 150 may temporally shift at least a part of the waveform signal of the second terahertz wave THz2 in addition to or instead of adjusting the measurement start timing. In other words, in addition to or instead of adjusting the measurement start timing, the arithmetic processing unit 150 shifts at least a part of the waveform signal of the second terahertz wave THz2 in time, so that the waveform of the second terahertz wave THz2 A state in which at least a part of the signal is shifted in time may be directly realized.

  In the present embodiment, as described above, the distance d1 and the distance d2 are fixed or do not vary while the terahertz wave measuring apparatus 100 analyzes the characteristics of the measurement target. For this reason, even if a positional deviation occurs in the retroreflecting mirrors 121b and 121c, the waveform between the first terahertz THz1 waveform and the second terahertz THz2 waveform detected during the second and third reflection periods is not obtained. Is the difference between the distance d1 and the distance d2 in the same manner as the time interval between the first terahertz THz1 waveform and the second terahertz THz2 waveform detected during the first and fourth reflection periods. It becomes a fixed value determined according to. In other words, regardless of whether or not the retroreflecting mirror 121 is misaligned, the waveform signal from the first terahertz THz1 is acquired until the waveform signal from the second terahertz THz2 is acquired in all reflection periods. The period is a fixed value determined according to the difference between the distance d1 and the distance d2.

  Therefore, the terahertz measurement apparatus 100 according to the present embodiment adjusts the measurement start timing using the first terahertz wave THz1 in which the temporal relationship with the second terahertz wave THz2 is always fixed. Specifically, the arithmetic processing unit 150 generates a waveform signal of the second terahertz wave THz2 acquired during the first reflection period based on the waveform signal of the first terahertz wave THz1 acquired during the first reflection period. The measurement start timing for starting the measurement of the characteristics of the measurement object is adjusted. Similarly, the arithmetic processing unit 150 uses the waveform signal of the second terahertz wave THz2 acquired during the second reflection period based on the waveform signal of the first terahertz wave THz1 acquired during the second reflection period. The measurement start timing for starting the measurement of the characteristics of the measurement object is adjusted. In the third and fourth reflection periods, the arithmetic processing unit 150 performs the same operation. As a result, the arithmetic processing unit 150 obtains the second terahertz wave THz2 that is acquired when the retroreflector 121 is misaligned even when the misalignment occurs in the at least one retroreflector 121. Can be handled as the waveform signal of the second terahertz wave THz2 acquired when the retroreflecting mirror 121 is not misaligned. Hereinafter, the operation for adjusting the measurement start timing will be further described.

(3) Operation for Adjusting Measurement Start Timing As described above, the measurement start timing mainly includes the reference signal generation unit 181 that generates the reference signal, the index signal generation unit 182 that generates the index signal, and the measurement indicating the measurement start timing. Adjustment is performed by a measurement start signal generation unit 183 that generates a start signal. Here, as described above, the reference signal generation unit 181 generates a reference signal in which one pulse appears each time the rotating substrate 122 rotates once. Therefore, hereinafter, the index signal generation operation by the index signal generation unit 182 and the measurement start signal generation operation by the measurement start signal generation unit 183 will be further described, so that the description of the operation for adjusting the measurement start timing will proceed. .

  The reference signal generator 181, index signal generator 182, and measurement start signal generator 183 may be hardware circuits. Alternatively, the reference signal generation unit 181, the index signal generation unit 182 and the measurement start signal generation unit 183 may be logical processing blocks realized by software.

(3-1) Index Signal Generation Operation by Index Signal Generation Unit 182 First, the index signal generation operation by the index signal generation unit 182 will be described with reference to FIGS. FIG. 6 is a block diagram showing the configuration of the index signal generation unit 182. As shown in FIG. FIG. 7 is a graph showing a waveform of the first terahertz wave THz1. FIG. 8 is a block diagram illustrating a modified example of the index signal generation unit 182.

  As illustrated in FIG. 6, the index signal generation unit 182 is a specific example of the low-pass filter 1821, a feature point detection unit 1822 that is a specific example of “second detection unit”, and a “calculation unit”. A time position extraction unit 1823 and a selector 1824 are provided.

  The low-pass filter 1821 extracts a predetermined frequency band component by performing a filtering process on the waveform signal of the first terahertz wave THz1. For example, the low-pass filter 1821 can convert the waveform signal shown in FIG. 7A to a relatively smooth waveform signal shown in FIG.

  The feature point detector 1822 detects feature points from the waveform signal of the first terahertz wave THz. The feature point detection unit 1822 may include, for example, a maximum value detection unit 1822a, a zero cross detection unit 1822b, and a minimum value detection unit 1822c. The maximum value detection unit 1822a detects “a point where the instantaneous value of the first terahertz wave THz1 is maximum (maximum point)” indicated by a point A in FIG. 7B as a feature point. The minimum value detector 1822c detects “a point (minimum value) at which the instantaneous value of the first terahertz wave THz1 is minimum” as indicated by a point C in FIG. 7B as a feature point. The zero-cross detection unit 1822b uses the maximum point detected by the maximum value detection unit 1822a and the minimum point detected by the minimum value detection unit 1822c to generate a “zero cross point (that is, as indicated by a point B in FIG. , The point at which the instantaneous value of the first terahertz wave THz1 becomes zero) ”is detected as a feature point.

  The time position extraction unit 1823 calculates the time position of the feature point detected by the feature point detection unit 1822. The time position extraction unit 1823 includes a first time position extraction unit 1823a corresponding to the maximum value detection unit 1822a, a second time position extraction unit 1823b corresponding to the zero cross detection unit 1822b, and a third value corresponding to the minimum value detection unit 1822c. A time position extraction unit 1823c. The first time position extraction unit 1823a calculates the time position of the maximum point. The second time position extraction unit 1823b calculates the time position of the zero cross point. The third time position extraction unit 1823c calculates the time position of the minimum point. The time position extraction unit 1823 calculates the time position of the feature point as a period from the reference time indicated by the reference signal until the feature point is detected.

  The selector 1823 selects any one time position from the time positions calculated by the first time position extraction unit 1823a, the second time position extraction unit 1823b, and the third time position extraction unit 1823c. The selector 1823 outputs an index signal indicating the selected time position.

  As described above, the index signal generation unit 182 detects a feature point from the input waveform signal of the first terahertz wave THz1, and outputs an index signal indicating the time position of the feature point.

  As shown in FIG. 8, the terahertz wave measuring apparatus 100 may include a plurality of index signal generation units 182 each corresponding to one reflection period. For example, in this embodiment, considering that the optical delay device 120 includes four retroreflecting mirrors 121, the terahertz wave measuring apparatus 100 includes four index signal generation units (index signal generation unit 182 in FIG. 8). -1, an index signal generator 182-2, an index signal generator 182-3, and an index signal generator 182-4). The index signal generation unit 182-1 outputs an index signal during the first reflection period in which the retroreflecting mirror 121a retroreflects the probe light LB2. The index signal generator 182-2 outputs an index signal during the second reflection period in which the retroreflecting mirror 121b retroreflects the probe light LB2. The index signal generation unit 182-3 outputs an index signal during the third reflection period in which the retroreflecting mirror 121c retroreflects the probe light LB2. The index signal generation unit 182-4 outputs an index signal during the fourth reflection period in which the retroreflecting mirror 121d retroreflects the probe light LB2.

  As described above, when the terahertz measurement apparatus 100 includes the plurality of index signal generation units 182, an index signal is generated separately for each reflection period in which each retroreflecting mirror 121 retroreflects the probe light LB <b> 2. Therefore, an increase in the processing load on the index signal generation unit 182 due to the single index signal generation unit 182 outputting an index signal over all reflection periods is suppressed. That is, complication of the configuration of the index signal generation unit 182 is suppressed.

  As shown in FIG. 8, an average value calculation unit 185 that calculates an average value of the index signals may be arranged at the subsequent stage of each index signal generation unit 182. As a result, it is suitably prevented that the time position indicated by the index signal becomes an unintended value due to erroneous measurement or the like. The average value calculation unit 185 is arranged not only when the terahertz measurement apparatus 100 includes a plurality of index signal generation units 182 but also when the terahertz measurement apparatus 100 includes a single index signal generation unit 182. Also good.

(3-2) Measurement Start Signal Generation Operation by Measurement Start Signal Generation Unit 183 Subsequently, the configuration of the measurement start signal generation unit 183 will be described with reference to FIG. FIG. 9 is a block diagram illustrating a configuration of the measurement start signal generation unit.

  As illustrated in FIG. 9A, the measurement start signal generation unit 183 includes a storage circuit 1831a, an RW_CTL unit 1832a, an offset unit 1833a, and a measurement start unit 1834a.

  The storage circuit 1831a stores the index signal input from the index signal generation unit 182. The storage circuit 1831a temporarily buffers the index signal input from the index signal generation unit 182.

  The RW_CTL unit 1832a performs read control on the storage circuit 1831a according to the mirror number assigned to each retroreflector 121. For example, when the current time is included in the first reflection period in which the retroreflecting mirror 121a retroreflects the probe light LB2, the RW-CTL unit 1832a has an index signal corresponding to the mirror number assigned to the retroreflecting mirror 121a. Is read. That is, the RW-CTL unit 1832a reads the index signal generated by the index signal generation unit 182 during the first reflection period. For example, when the current time is included in the second reflection period in which the retroreflecting mirror 121b retroreflects the probe light LB2, the RW-CTL unit 1832a generates an index signal corresponding to the mirror number assigned to the retroreflecting mirror 121b. Is read. That is, the RW-CTL unit 1832a reads the index signal generated by the index signal generation unit 182 during the second reflection period. The same operation is performed from the third reflection period to the fourth reflection period.

  The offset unit 1833a subtracts a constant value from the index signal read from the storage circuit 1831a. The index signal from which the constant value is subtracted is output to the measurement start unit 1834a as a signal indicating the adjustment amount of the measurement start timing.

  As an example, the constant value may be an index signal that is detected when there is no displacement in each retroreflecting mirror 121. Such a constant value may be stored in advance in, for example, a memory provided in the terahertz measurement apparatus 100 as an operation parameter. In this case, the offset unit 1833a detects the index signal when the retroreflecting mirror 121a is not displaced from the index signal read during the first reflection period in which the retroreflecting mirror 121a retroreflects the probe light LB2. A constant value corresponding to is subtracted. When there is no position shift in the retroreflecting mirror 121a, the adjustment amount of the measurement start timing corresponding to the index signal obtained by subtracting a certain value is zero. Therefore, in this case, the default measurement start timing is used as the measurement start timing. When there is a positional shift in the retroreflecting mirror 121a, the measurement start timing adjustment amount corresponding to the index signal from which a certain value is subtracted is a desired amount different from zero. This adjustment amount corresponds to a temporal shift amount of the second terahertz wave THz2 due to the positional shift of the retroreflector 121a (see FIGS. 5A and 5B). Therefore, in this case, the measurement start timing obtained by performing adjustment based on the adjustment amount with respect to the default measurement start timing is used as the measurement start timing.

  Not only the index signal during the first reflection period but also the offset unit 1833a performs the same processing for the index signal during the second reflection period to the fourth reflection period. That is, the offset unit 1833a subtracts a constant value corresponding to the index signal detected when there is no positional deviation in the retroreflecting mirror 121b from the index signal read during the second reflection period. The offset unit 1833a subtracts a constant value corresponding to the index signal detected when the retroreflecting mirror 121c is not displaced from the index signal read during the third reflection period. The offset unit 1833a subtracts a constant value corresponding to the index signal detected when the retroreflecting mirror 121d is not displaced from the index signal read during the fourth reflection period.

  The measurement start unit 1834a adjusts the measurement start timing during the reflection period in which the corresponding retroreflective means 121 retroreflects the probe light LB2 based on the adjustment amount output from the offset unit 1833a and the reference signal. For example, the measurement start unit 1834a adjusts the measurement start timing during the first reflection period based on the adjustment amount and the reference signal output by the offset unit 1833a during the first reflection period. For example, the measurement start unit 1834a adjusts the measurement start timing during the second reflection period based on the adjustment amount and the reference signal output by the offset unit 1833a during the second reflection period. The same operation is performed in the third reflection period and the fourth reflection period.

  The measurement start unit 1834a outputs a measurement start signal that defines the adjusted measurement start timing to the arithmetic processing unit 150. As a result, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object based on the waveform signal of the second terahertz THz2 in synchronization with the measurement start timing defined by the measurement start signal output from the measurement start unit 1834a. . For example, during the first reflection period, the arithmetic processing unit 150 synchronizes with the measurement start timing defined by the measurement start signal output from the measurement start unit 1834a during the first reflection period, and the waveform of the second terahertz THz2 The measurement of the characteristics of the measurement object based on the signal is started. The same operation is performed in the second reflection period to the fourth reflection period.

  Here, as shown in FIG. 5A, the measurement start timing in the case where a positional deviation has occurred in the retroreflecting mirrors 121b and 121c will be described.

  First, since there is no position shift in the retroreflecting mirror 121a, the adjustment amount of the measurement start timing calculated based on the waveform signal of the first terahertz wave detected during the first reflection period is zero. Therefore, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object based on the waveform signal of the second terahertz THz2 at the default measurement start timing during the first reflection period. Note that the same operation is performed in the fourth reflection period.

  On the other hand, since the position of the retroreflecting mirror 121b is displaced, the adjustment amount of the measurement start timing calculated based on the waveform signal of the first terahertz wave detected during the second reflection period is different from zero. The desired amount. Therefore, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object based on the waveform signal of the second terahertz THz2 at the adjusted measurement start timing during the second reflection period. Note that the same operation is performed in the third reflection period.

  Here, even if a positional deviation occurs in the retroreflecting mirror 121b, the time interval between the waveform of the first terahertz THz1 and the waveform of the second terahertz THz2 detected during the second reflection period is as follows. Fixed value. For this reason, the temporal shift amount of the waveform of the first terahertz wave THz1 due to the positional shift in the retroreflector 121b is the temporal shift of the waveform of the second terahertz wave THz2 due to the positional shift in the retroreflector 121b. Equal to the amount. Therefore, the adjustment amount of the measurement start timing calculated based on the waveform signal of the first terahertz wave detected during the second reflection period is acquired when the position of the retroreflecting mirror 121b is displaced. The measurement start timing at which the waveform signal of the terahertz wave THz2 can be handled as the waveform signal of the second terahertz wave THz2 acquired when there is no positional deviation in the retroreflecting mirror 121b is substantially shown. That is, the adjustment amount of the measurement start timing calculated based on the waveform signal of the first terahertz wave detected during the second reflection period is obtained when the retroreflecting mirror 121b is misaligned. Start of measurement capable of substantially converting the waveform signal of the terahertz wave THz2 into a waveform signal of the second terahertz wave THz2 obtained when the retroreflecting mirror 121b is not misaligned by temporally shifting the waveform signal. Timing is substantially shown. Therefore, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object at the measurement start timing adjusted based on such an adjustment amount, thereby eliminating the influence of the positional deviation of the retroreflecting mirror 121b. The characteristics of the measurement object can be measured.

  As shown in FIG. 9B, the measurement start signal generation unit 183 may further include an addition unit 1835b and a division unit 1836b. In this case, the adding unit 1835b adds the past n index signals. The past n index signals added by the adder 1835b are divided by n by the divider 1836b. Thereby, the average value of the past n index signals is calculated. Therefore, a measurement start signal that defines the measurement start timing is output using the average value of the index signals. When the average value of the index signals is used in this way, an inappropriate measurement start signal is prevented from being generated due to erroneous measurement or the like.

  As shown in FIG. 9C, the measurement start signal generation unit 183 may include m (that is, the same number as the retroreflecting mirrors 121) low-pass filters 1837c. In this case, since the index processing is performed on the index signal by the m low-pass filters 1837c, the measurement start signal is generated while suppressing the influence of noise.

  As described above, the terahertz wave measuring apparatus 100 according to the present embodiment irradiates the measurement target with the second terahertz wave THz. For this reason, the terahertz wave measuring apparatus 100 can measure the characteristics of the measurement object based on the detection result of the second terahertz wave THz.

  Furthermore, the terahertz measurement apparatus 100 does not irradiate the measurement target with the first terahertz wave THz1. For this reason, the terahertz wave measuring apparatus 100 can adjust the measurement start timing for starting the measurement of the characteristics of the measurement object based on the detection result of the second terahertz wave THz, based on the detection result of the first terahertz wave THz1. it can. For example, as described above, the timing at which the terahertz detecting element 130 detects the second terahertz wave THz2 varies due to the displacement of the retroreflecting mirror 121 (see FIGS. 5A and 5B). ). Thus, even when the timing at which the terahertz detection element 130 detects the second terahertz wave THz2 varies, the terahertz wave measuring apparatus 100 measures variations in timing at which the terahertz detection element 130 detects the second terahertz wave THz2. The measurement start timing can be adjusted based on the detection result of the first terahertz wave THz1 so that the influence on the measurement of the characteristics of the object is eliminated. As a result, the terahertz wave measuring apparatus 100 can measure the characteristics of the measurement object with relatively high accuracy by using the terahertz wave THz.

  Furthermore, the terahertz wave measuring apparatus 100 can adjust the measurement start timing based on the detection result of the first terahertz wave THz1, while measuring the characteristics of the measurement object based on the detection result of the second terahertz wave THz2. it can. That is, the terahertz wave measuring apparatus 100 sequentially measures the measurement start timing based on the detection result of the first terahertz wave in parallel with the measurement of the characteristics of the measurement object based on the detection result of the second terahertz wave THz2 (in other words, Can be adjusted in real time).

  Further, each retroreflecting mirror 121 moves so that the optical path of the probe light LB2 is shortened with time (that is, with the movement of each retroreflecting mirror 121), and between the beam splitter 171 and the reflecting mirror 172. The distance d1 is larger than the distance d2 between the beam splitter 171 and the measurement object. For this reason, the arithmetic processing unit 150 acquires the detection result of the lock-in detection unit 145, thereby acquiring the waveform signal indicating the waveform of the first terahertz THz1 and the second terahertz wave THz2 in this order during each reflection period. . Therefore, the terahertz measurement apparatus 100 adjusts the measurement start timing based on the detection result of the first terahertz wave during a certain reflection period, and then adjusts the second terahertz wave THz2 at the adjusted measurement start timing during the certain reflection period. Measurement of the characteristics of the measurement object based on the detection result can be started.

  In addition, when each retroreflecting mirror 121 moves so that the optical path of the probe light LB2 becomes longer with time, the distance d1 is preferably smaller than the distance d2. Alternatively, when each retroreflecting mirror 121 retroreflects the pump light LB1 instead of the probe light LB2, and when each retroreflecting mirror 121 moves so that the optical path of the pump light LB1 becomes shorter as time passes. The distance d1 is preferably smaller than the distance d2. Alternatively, when each retroreflecting mirror 121 retroreflects the pump light LB1 instead of the probe light LB2, and when each retroreflecting mirror 121 moves so that the optical path of the pump light LB1 becomes longer as time passes. The distance d1 is preferably larger than the distance d2. As a result, the arithmetic processing unit 150 acquires the detection result of the lock-in detection unit 145, thereby acquiring the waveform signal indicating the waveform of the first terahertz THz1 and the second terahertz wave THz2 in this order during each reflection period. be able to.

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

DESCRIPTION OF SYMBOLS 100 Terahertz wave measuring device 101 Pulse laser apparatus 110 Terahertz wave generating element 121 Retroreflecting mirror 130 Terahertz wave detecting element 150 Arithmetic processing part 170 Optical path adjuster 171 Beam splitter 172 Reflecting mirror 181 Reference signal generating part 182 Index signal generating part 183 Measurement start Signal generator LB1 Pump light LB2 Probe light THz Terahertz wave THz1 First terahertz wave THz2 Second terahertz wave

Claims (15)

Generating means for generating terahertz waves by being irradiated with laser light;
(I) The first terahertz wave, which is a part of the terahertz wave generated by the generating unit, propagates through the first path and is not irradiated to the measurement target, while (ii) the terahertz generated by the generating unit The path of the terahertz wave is adjusted so that the second terahertz wave, which is another part of the wave, propagates through the second path having a path length different from that of the first path and is applied to the measurement object. First adjusting means;
First detection means for detecting the first terahertz wave that has not been irradiated to the measurement object and the second terahertz wave that has been irradiated to the measurement object by being irradiated with the laser light; ,
A terahertz wave measuring apparatus, comprising: a second adjusting unit that adjusts an optical path length of the laser beam that is applied to at least one of the generating unit and the first detecting unit by retroreflecting the laser beam. . The said 1st adjustment means adjusts the path | route of the said terahertz wave so that the path length difference between the said 1st path | route and the said 2nd path | route may be fixed, or may not change. The terahertz wave measuring device described. The first adjusting means detects a difference in path length between the first path and the second path in such a manner that the first detecting means can individually identify each of the first and second terahertz waves. The terahertz wave measuring apparatus according to claim 1, wherein the terahertz wave path is adjusted so as to have a path length difference that can be performed. The first adjusting means detects a difference in path length between the first path and the second path at a timing at which the first detecting means does not overlap each of the first and second terahertz waves in time. The terahertz wave measuring apparatus according to any one of claims 1 to 3, wherein the terahertz wave path is adjusted so as to have a path length difference that can be performed. The second adjusting means adjusts the optical path length of the laser light irradiated to the detecting means so that the optical path length of the laser light irradiated to the detecting means becomes shorter as time passes,
5. The terahertz wave according to claim 1, wherein the first adjustment unit adjusts the path of the terahertz wave so that the first path is longer than the second path. Measuring device. The second adjusting means adjusts the optical path length of the laser light irradiated to the detecting means so that the optical path length of the laser light irradiated to the detecting means becomes longer as time passes,
The terahertz wave measurement according to any one of claims 1 to 4, wherein the first adjustment unit adjusts the path of the terahertz wave so that the first path is shorter than the second path. apparatus. The second adjusting means adjusts the optical path length of the laser light irradiated to the generating means so that the optical path length of the laser light irradiated to the generating means becomes shorter as time passes,
The terahertz wave measurement according to any one of claims 1 to 4, wherein the first adjustment unit adjusts the path of the terahertz wave so that the first path is shorter than the second path. apparatus. The second adjusting means adjusts the optical path length of the laser light irradiated to the generating means so that the optical path length of the laser light irradiated to the generating means becomes longer as time passes,
5. The terahertz wave measuring apparatus according to claim 1, wherein the first adjusting unit adjusts the terahertz wave path such that the first path is longer than the second path. The first adjustment means is configured such that a difference in path length between the first path and the second path is determined by the first detection means during a predetermined adjustment period in which the second adjustment means adjusts the optical path length. 9. The path of the terahertz wave is adjusted so that the path length difference is such that both the first and second terahertz waves can be detected. 9. Terahertz wave measuring device. Third adjusting means for adjusting the intensity of at least one of the first and second terahertz waves so that a difference between the intensity of the first terahertz wave and the intensity of the second terahertz wave is a predetermined value or less. The terahertz wave measuring apparatus according to any one of claims 1 to 9, wherein the terahertz wave measuring apparatus is provided. Measurement means for measuring characteristics of the measurement object based on the second terahertz wave detected by the second detection means;
And a fourth adjusting unit that adjusts a timing at which the measurement unit measures a characteristic of the measurement object based on the second terahertz wave based on a detection result of the first terahertz wave by the first detection unit. The terahertz wave measuring apparatus according to claim 1, comprising: a terahertz wave measuring apparatus according to claim 1. The fourth adjusting means is
Second detection means for detecting a feature point of the first terahertz wave detected by the first detection means;
Calculating means for calculating a reference period that is a period from a reference time to detection of the feature point;
The terahertz wave measuring apparatus according to claim 11, further comprising: a control unit that controls the measurement unit so as to start measurement of characteristics of the measurement object at a timing determined based on the reference period. The second adjusting means includes a plurality of retroreflective means each re-reflecting the laser beam,
The second detection means detects the feature point separately for each reflection period in which each of the plurality of retroreflective means re-reflects the laser light,
The calculation means calculates the reference period separately for each reflection period,
The control means controls the measurement means so as to start measurement of characteristics of the measurement object at a timing determined according to the reference time corresponding to the reflection period for each reflection period. The terahertz wave measuring device according to claim 12. The feature point is at least one of a maximum value, a minimum value, and a zero cross point between the maximum value and the minimum value of the waveform of the first terahertz wave. The terahertz wave measuring device described. The second detection means detects the feature point a plurality of times,
The calculation means calculates the reference period a plurality of times,
The control means controls the measurement means so as to start measurement of characteristics of the measurement object at a timing determined according to an average value of the reference period calculated a plurality of times. The terahertz wave measuring device according to claim 14.