JP2021001911A - Terahertz wave measurement device - Google Patents

Abstract

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 the technical field of a terahertz wave measuring device that measures the characteristics of a measurement object using, for example, a terahertz wave.

As a terahertz wave measuring device, a device using terahertz time region spectroscopy (Terahertz Time-Domain Spectroscopy) is known. The terahertz wave measuring device measures the characteristics of the object to be measured by the following procedure. First, the pump light (in other words, the excitation light), which is one laser light obtained by branching the ultrashort pulse laser light (for example, the femtosecond pulse laser light), generates a terahertz wave 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 irradiates the object to be measured. The terahertz wave applied to the object to be measured is another laser light obtained by branching the ultrashort pulse laser light as a reflected terahertz wave or a transmitted terahertz wave from the object to be measured, and is optical to the pump light. The terahertz wave detection element irradiated with the probe light (in other words, the excitation light) to which the delay (that is, the optical path length difference) is applied is irradiated. As a result, the terahertz wave detection element detects a current signal according to the intensity of the terahertz wave reflected or transmitted by the measurement object. By Fourier transforming the detected terahertz wave (that is, the terahertz wave in the time domain and the current signal), the spectrum of the terahertz wave (that is, the frequency response characteristic of the amplitude and the phase) and the like are acquired. As a result, the characteristics of the object to be measured are measured by analyzing the spectrum of the terahertz wave. An example of measuring the characteristics of the object to be measured is described in Patent Document 1, for example.

Here, the optical delay applied to the probe light (or pump light) is the probe light (or pump light) with respect to an optical delayer including a retroreflector capable of retroreflecting the incident light. ) Is often given by incident. The term "retroreflection" as used herein means a state in which the incident light is reflected in a direction parallel to the incident direction of the incident light. As an example of the optical delayer, for example, an optical delayer including a plurality of rotatable retroreflectors (or prisms) can be mentioned (see, for example, Patent Documents 2 to 4).

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

However, when an optical delay is applied to the probe light (or pump light) using a plurality of retroreflectors, an appropriate measurement result cannot be obtained due to the misalignment of the retroreflectors. There is a possibility that a technical problem will occur.

Specifically, for example, Patent Document 2 does not provide a mechanism for adjusting the rotation operation and the detection timing. For this reason, it is not possible to deal 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 the photodiode. In addition, since the position of the retroreflector is always detected during measurement, the unit price and man-hours increase. Further, when a retroreflector is constructed by using two reflectors, only one of the reflectors can be detected by a photodiode. Further, in Patent Document 4, a timing pulse is generated by using the reflected light by the translucent body. Therefore, the optical axis needs to be arranged perpendicular to the translucent body, which increases the man-hours. In addition, the reflected light from the translucent body must be able to withstand use as a timing pulse, and the intensity of the terahertz wave applied to the object to be measured may decrease and the SNR (Signal-Noise Ratio) may deteriorate. The above is an example of the problem to be tried. An object of the present invention is to provide a terahertz wave measuring device capable of obtaining an appropriate measurement result even when the retroreflector is misaligned with a relatively simple configuration.

A terahertz wave measuring device that solves the above problems includes a generating means that generates a terahertz wave by being irradiated with laser light, and (i) a first terahertz wave that is a part of the terahertz wave generated by the generating means. However, while propagating in the first path and not irradiating the measurement object, (ii) the second terahertz wave, which is another part of the terahertz wave generated by the generating means, is a path different from the first path. By irradiating the measurement object with the first adjusting means for adjusting the path of the terahertz wave so as to propagate through the second path having different lengths and irradiate the measurement object, the measurement object is irradiated with the laser light. The first detecting means for detecting the first terahertz wave not irradiated and the second terahertz wave irradiated to the measurement object, and the generating means and the generating means by retroreflecting the laser beam. It includes a second adjusting means for adjusting the optical path length of the laser beam irradiated to at least one of the first detecting means.

It is a block diagram which shows the structure of the terahertz wave measuring apparatus of this Example. It is a top view which shows the structure of the optical delayer of this Example. It is a perspective view which shows the structure of each of the terahertz wave generation element and the terahertz wave detection element. A graph showing the waveform of the terahertz wave when the four retroreflectors of the optical delayer are not misaligned with the period during which each retroreflector is retroreflecting the probe light, and the optical delay. It is a graph which shows the amplitude of the waveform of the terahertz wave (particularly, the second terahertz wave) when the four retroreflectors provided in the instrument are not misaligned. The waveform of the terahertz wave when at least one of the four retroreflectors of the optical delayer is misaligned is shown in association with the period during which each retroreflector retroreflects the probe light. The graph and the graph showing the amplitude of the waveform of the terahertz wave (particularly, the second terahertz wave) when at least one of the four retroreflectors included in the optical delayer is misaligned. .. It is a block diagram which shows the structure of the index signal generation part. It is a graph which shows the time waveform of the 1st terahertz wave. It is a block diagram which shows the modification of the index signal generation part. It is a block diagram which shows the structure of the measurement start signal generation part.

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

<1>
In the terahertz wave measuring device of the present embodiment, a generating means for generating a terahertz wave by being irradiated with laser light and (i) a first terahertz wave which is a part of the terahertz wave generated by the generating means are formed. , While propagating in the first path and not irradiating the object to be measured, (ii) the second terahertz wave, which is another part of the terahertz wave generated by the generating means, has a path length different from that of the first path. Irradiates the measurement object by irradiating the first adjusting means for separating the terahertz wave and the laser light so that the terahertz waves propagate and irradiate the measurement object. The first detection means for detecting the first terahertz wave and the second terahertz wave applied to the measurement object, and the generation means and the first detection by retroreflecting the laser beam. A second adjusting means for adjusting the optical path length of the laser beam irradiated to at least one of the means is provided.

According to the terahertz wave measuring device of the present embodiment, the terahertz irradiated to the measurement object by the operation of the generating means, the first adjusting means, the first detecting means, and the second adjusting means using the terahertz time region spectroscopy. Waves are detected. The detected terahertz wave is used to measure the characteristics of the object to be measured. As the terahertz wave detection method itself using the terahertz time region spectroscopy, an existing detection method may be used. Hereinafter, an outline of a method for detecting a terahertz wave using terahertz time region spectroscopy will be briefly described.

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

The first adjusting means adjusts the path of the terahertz wave generated by the generating means (that is, the path through which the terahertz wave propagates). Specifically, the first adjusting means is the other of the terahertz waves generated by the generating means while the first terahertz wave, which is a part of the terahertz waves generated by the generating means, is not irradiated to the measurement object. The path of the terahertz wave is adjusted so that the second terahertz wave, which is a part of the above, is applied to the object to be measured. Typically, the first adjusting means may adjust the path of the terahertz wave generated by the generating means by separating the terahertz wave generated by the generating means into the first terahertz wave and the second terahertz wave. However, the first adjusting means may adjust the path of the terahertz wave generated by the generating means by using another method.

In the first detection means, the first detection means is irradiated with laser light as excitation light (for example, probe light), so that the terahertz wave reflected by the measurement target or transmitted through the measurement target (that is, the first detection means) is used. 2 terahertz waves) are detected.

The second adjusting means retroreflects the laser beam and guides the retroreflected laser beam 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 beam irradiated to at least one of the generating means and the first detecting means. For example, when the second adjusting means includes a retroreflector that retroreflects the laser beam, the second adjusting means adjusts the optical path length of the laser beam by physically moving the retroreflector. You may. As a result, the second adjusting means can appropriately adjust the optical path length difference between the optical path of the laser beam irradiated to the generating means and the optical path of the laser beam irradiated to the first detecting means. Such adjustment of the optical path length difference is performed in order to preferably detect a terahertz wave waveform (typically, a time waveform, the same applies hereinafter) that appears in the order of subpicoseconds.

In this embodiment, in particular, as described above, the first adjusting means traverses the path of the terahertz wave so that the first terahertz wave is not irradiated to the measurement object while the second terahertz wave is irradiated to the measurement object. adjust. Therefore, the first detection means detects not only the second terahertz wave irradiated to the measurement object but also the first terahertz wave not irradiated to the measurement object.

In the first adjusting means, the path length of the first terahertz wave path (that is, the path through which the first terahertz wave propagates) is the path of the second terahertz wave path (that is, the path through which the second terahertz wave propagates). Adjust the path of the terahertz wave to be different from the length. Therefore, the first detection means 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 second terahertz wave is applied to the object to be measured, the second terahertz wave detected by the first detection means can be used for the purpose of measuring the characteristics of the object to be measured. On the other hand, since the first terahertz wave is not applied to the object to be measured, the first terahertz wave detected by the first detection means can be used for a purpose different from the measurement of the characteristics of the object to be measured. For example, the first terahertz wave can be used for the purpose of adjusting the timing of measuring the characteristics of the object to be measured.

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 means becomes the first terahertz wave and the other part of the terahertz wave generated by the generating means becomes the second terahertz wave, the first terahertz wave is detected first. The temporal relationship (that is, the time difference) between the timing of reaching the means and the timing of the second terahertz wave reaching the first detecting means is substantially fixed or does not fluctuate. 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 beam by the second adjustment means. The time required to do this is fixed or does not fluctuate. For example, when the first adjusting means adjusts the path of the terahertz wave so as to separate the same terahertz wave into the first and second terahertz waves, the timing and the first when the first terahertz wave reaches the first detecting means. The temporal relationship between the timing at which the 2 terahertz wave reaches the first detection means is substantially fixed or does not fluctuate. 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 waveform of the first terahertz wave appears and the timing at which the waveform of the second terahertz wave appears is substantially fixed. Will or will not fluctuate.

As described above, in the present embodiment, the measurement target is irradiated with the second terahertz wave, which is another part of the terahertz wave generated by the generating means. Therefore, the terahertz wave measuring device can measure the characteristics of the object to be measured based on the detection result of the second terahertz wave.

Further, in the present embodiment, the measurement object is not irradiated with the first terahertz wave, which is a part of the terahertz waves generated by the generating means. Therefore, the terahertz wave measuring device can adjust the timing of measuring the characteristics of the object to be measured based on the detection result of the first terahertz wave. For example, due to the variation in the adjustment accuracy of the optical path length of the laser beam by the second adjusting means (for example, the variation in the adjustment accuracy of the optical path length of the laser beam due to the misalignment of the retroreflector included in the second adjusting means), the first The timing at which the detection means detects the second terahertz wave may vary. In this way, even when the timing at which the first detection means detects the second terahertz wave varies, the terahertz wave measuring device has a variation in the timing at which the first detection means detects the second terahertz wave. The timing for measuring the characteristics of the object to be measured can be adjusted based on the detection result of the first terahertz wave so that the influence on the measurement of the characteristics is eliminated. As a result, the terahertz wave measuring device can measure the characteristics of the object to be measured with relatively high accuracy by using the terahertz wave.

Further, the terahertz wave measuring device 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 device sequentially measures 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 of the first terahertz wave reaching the first detection means and the timing of the second terahertz wave reaching the first detection means is substantially fixed or does not fluctuate. As described above. That is, the second terahertz wave reaches the first detection means after the first terahertz wave reaches the first detection means, regardless of whether or not the adjustment accuracy of the optical path length of the laser beam by the second adjustment means varies. The time required to do this is fixed or does not fluctuate. 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 beam by the second adjustment means. The time required to do this is fixed or does not fluctuate. Therefore, even if the timing of the first detection means for detecting the second terahertz wave varies, the terahertz wave measuring device measures the characteristics of the object to be measured based on the detection result of the second terahertz wave. However, the timing of measuring the characteristics of the object to be measured can be adjusted based on the detection result of the first terahertz wave.

<2>
In another aspect of the terahertz wave measuring device of the present embodiment, the first adjusting means measures the terahertz wave so that the path length difference between the first path and the second path is not fixed or fluctuated. Adjust the route of.

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, regardless of whether or not the adjustment accuracy of the optical path length of the laser beam by the second adjusting means varies. The temporal relationship with the timing of reaching the detection means is fixed or does not fluctuate. Therefore, even if the timing of the first detection means for detecting the second terahertz wave varies, the terahertz wave measuring device measures the characteristics of the object to be measured based on the detection result of the second terahertz wave. However, the timing for measuring the characteristics of the object to be measured can be adjusted based on the detection result of the first terahertz wave.

<3>
In another aspect of the terahertz wave measuring device of the present embodiment, the first adjusting means has a path length difference between the first path and the second path, and the first detecting 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 in an individually identifiable manner.

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

<4>
In another aspect of the terahertz wave measuring device of the present embodiment, the first adjusting means has a path length difference between the first path and the second path, and the first detecting 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 means can detect not only the second terahertz wave irradiated to the measurement object but also the first terahertz wave not irradiated to the measurement object. Therefore, the terahertz wave measuring device measures the characteristics of the measurement object based on the detection result of the second terahertz wave, and adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. be able to.

<5>
In another aspect of the terahertz wave measuring device of the present embodiment, the second adjusting means is irradiated to the detecting means so that the optical path length of the laser beam irradiated to the detecting means becomes shorter with the passage of time. The optical path length of the laser beam is adjusted, and the first adjusting means adjusts 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 device obtains the waveform of the first terahertz wave propagating in the relatively long first path based on the detection results of the first and second terahertz waves by the first detection means. After the detection, the waveform of the second terahertz wave propagating in the relatively short second path can be detected. Therefore, the terahertz wave measuring device measures the characteristics of the measurement object based on the detection result of the second terahertz wave, and adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. be able to.

<6>
In another aspect of the terahertz wave measuring device of the present embodiment, the second adjusting means is irradiated to the detecting means so that the optical path length of the laser beam irradiated to the detecting means becomes longer with the passage of time. The optical path length of the laser beam is adjusted, and the first adjusting means adjusts 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 device obtains the waveform of the first terahertz wave propagating in the relatively short first path based on the detection results of the first and second terahertz waves by the first detection means. After the detection, the waveform of the second terahertz wave propagating in the relatively long second path can be detected. Therefore, the terahertz wave measuring device measures the characteristics of the measurement object based on the detection result of the second terahertz wave, and adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. be able to.

<7>
In another aspect of the terahertz wave measuring device of the present embodiment, the second adjusting means is irradiated to the generating means so that the optical path length of the laser beam irradiated to the generating means becomes shorter with the passage of time. The optical path length of the laser beam is adjusted, and the first adjusting means adjusts 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 device obtains the waveform of the first terahertz wave propagating in the relatively short first path based on the detection results of the first and second terahertz waves by the first detection means. After the detection, the waveform of the second terahertz wave propagating in the relatively long second path can be detected. Therefore, the terahertz wave measuring device measures the characteristics of the measurement object based on the detection result of the second terahertz wave, and adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. be able to.

<8>
In another aspect of the terahertz wave measuring device of the present embodiment, the second adjusting means is irradiated to the generating means so that the optical path length of the laser beam irradiated to the generating means becomes longer with the passage of time. The optical path length of the laser beam is adjusted, and the first adjusting means adjusts the path of the terahertz wave in which the first path is longer than the second path.

According to this aspect, the terahertz wave measuring device obtains the waveform of the first terahertz wave propagating in the relatively long first path based on the detection results of the first and second terahertz waves by the first detection means. After the detection, the waveform of the second terahertz wave propagating in the relatively short second path can be detected. Therefore, the terahertz wave measuring device measures the characteristics of the measurement object based on the detection result of the second terahertz wave, and adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. be able to.

<9>
In another aspect of the terahertz wave measuring device of the present embodiment, the first adjusting means adjusts the path length difference between the first path and the second path, and the second adjusting means adjusts the optical path length. The path of the terahertz wave is adjusted so that the path length difference is such that the first detecting means can 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 in which 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 device measures the characteristics of the measurement object based on the detection result of the second terahertz wave, and adjusts the timing of measuring the characteristics of the measurement object based on the detection result of the first terahertz wave. be able to.

When the second adjusting means includes a plurality of retroreflectors, the adjusting period corresponds to the period in which each retroreflected light retroreflects the laser beam.

<10>
In another aspect of the terahertz wave measuring device of the present embodiment, the first and second terahertz waves are such that 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. A third adjusting means for adjusting the strength of at least one of the above 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 means 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 of the first detection means (for example, dynamic range). ) Is matched to the intensity of the first terahertz wave and the intensity of the second terahertz wave, whichever is greater. As a result, the first detecting means can suitably detect either one of the first and second terahertz waves having an intensity suitable for the detection sensitivity, but has an intensity not suitable for the detection sensitivity. A technical problem may arise in which one of the first and second terahertz waves may not be suitably detected. However, in this aspect, such technical problems rarely occur.

<11>
In another aspect of the terahertz wave measuring device of the present embodiment, the measuring means for measuring the characteristics of the object to be measured based on the second terahertz wave detected by the second detecting means and the first detecting means. Based on the detection result of the first terahertz wave, the measuring means further includes a fourth adjusting means for adjusting the timing of measuring the characteristics of the measurement object based on the second terahertz wave.

According to this aspect, the terahertz wave measuring device measures the characteristics of the object to be measured based on the detection result of the second terahertz wave, and sets the timing of measuring the characteristics of the object to be measured to the detection result of the first terahertz wave. Can be adjusted based on.

<12>
In another aspect of the terahertz wave measuring device including the fourth adjusting means as described above, the fourth adjusting means is a second detecting means for detecting a feature point of the first terahertz wave detected by the first detecting means. The calculation means for calculating the reference period, which is the period from the reference time to the detection of the feature point, and the measurement means for starting the measurement of the characteristics of the measurement object at a timing determined based on the reference period. It is provided with a control means for controlling the above.

According to this aspect, the second detecting means detects the feature points of the first terahertz wave detected by the first detecting means. The "feature point" of the present embodiment is a point at which fluctuations in the first terahertz wave (for example, fluctuations along the time axis) can be detected with high accuracy. Since the first terahertz wave is not irradiated to the measurement object, the second detection means of the first terahertz wave is performed in parallel with the detection of the second terahertz wave irradiated to the measurement object by the first detection means. Feature points can be detected. That is, the second detection means can detect the feature points of the first terahertz wave in parallel with the measurement of the characteristics of the object to be measured.

When the feature point is detected, the calculation means calculates the reference period, which is the period from the reference time to the detection of the feature point. The "reference time" here 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 means starts measuring the characteristics of the measurement object at a timing corresponding to the reference period (typically, starts analyzing the detection result of the second terahertz wave). 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 target is preferably eliminated.

<13>
In another aspect of the terrahertz wave measuring device comprising the second detecting means, the calculating means and the controlling means as described above, the second adjusting means each includes a plurality of retroreflecting means for recursively reflecting the laser beam. The second detection means separately detects the feature point for each reflection period in which each of the plurality of retroreflection means re-reflects the laser light, and the calculation means separately detects the feature point for each reflection period. The reference period is calculated, and the control means controls the measurement means so as to start measurement of 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 beam irradiated to the generating means and the optical path of the laser beam irradiated to the first detecting means is adjusted by using the plurality of retroreflective means. Specifically, for example, the physical movement of the retroreflective means changes the position of the retroreflective means in the optical axis direction with respect to the laser beam irradiated to at least one of the generating means and the first detecting means. As a result, the optical path length of at least one of the optical paths of the laser light irradiated to at least one of the generating means and the first detecting means changes.

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

Furthermore, feature points are detected separately for each reflection period in which each of the plurality of retroreflection means retroreflects the laser beam (the reflection period is substantially synonymous with the above-mentioned adjustment period). The reference period is calculated separately and the measurement start timing is adjusted. As a result, even when the second adjusting means includes a plurality of retroreflective means, the variation in the timing at which the first detecting means detects the second terahertz wave gives the measurement of the characteristics of the measurement object. The effect is preferably eliminated.

<14>
In another aspect of the terahertz wave measuring device including the second detection means as described above, the feature point is between 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 means can easily and accurately detect the feature points of the first terahertz wave. Therefore, 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 device including the second detection means, the calculation means and the control means as described above, the second detection means detects the feature point a plurality of times, and the calculation means sets the reference period. It is calculated a plurality of times, and the control means controls the measuring means so as 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 points are 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. Then, when the measurement start timing by the measuring means is adjusted, the average value of the reference period detected a plurality of times is used. Since the average value of the reference period is used in this way, it is preferable to unintentionally adjust the timing of starting the measurement of the characteristics of the object to be measured, for example, based on an inappropriate reference period due to erroneous detection of the feature point. Be prevented.

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

As described above, the terahertz wave measuring device of the present embodiment includes a generating means, a first adjusting means, a first detecting means, and a second adjusting means. Therefore, with a relatively simple configuration, it is possible to obtain an appropriate measurement result even when the retroreflector is misaligned.

Hereinafter, examples of the terahertz wave measuring device of the present invention will be described with reference to the drawings.

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

As shown in FIG. 1, the terahertz wave measuring device 100 irradiates the terahertz wave THz on the measurement object, and also irradiates the terahertz wave THz that has passed through or reflected from the measurement object (that is, the measurement object is irradiated). The terahertz wave THz) is detected. In the example shown in FIG. 1, the terahertz wave measuring device 100 detects the terahertz wave THz reflected from the object to be measured.

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 has both the straightness of light and the transmission of electromagnetic waves. The terahertz region is the frequency domain in which various substances have their own absorption spectra. Therefore, the terahertz wave measuring device 100 can measure the characteristics of the object to be measured by analyzing the frequency spectrum of the terahertz wave THz applied to the object to be measured.

In order to acquire the frequency spectrum of the terahertz wave THz irradiated on the object to be measured, the terahertz wave measuring device 100 employs terahertz time region spectroscopy (terahertz Time-Domain Spectroscopy). In the terahertz time region spectroscopy, the frequency of the terahertz wave is irradiated by irradiating the object to be measured with the terahertz wave THz, and the time waveform of the terahertz wave THz transmitted through the object to be measured or reflected from the object is Fourier transformed. This is a method of acquiring a spectrum (that is, amplitude and phase for each frequency).

Here, since the period of the terahertz wave THz is a period on the order of subpicoseconds, it is a technique to directly detect the waveform of the terahertz wave THz (typically, it is a time waveform, and the same applies hereinafter). Is difficult. Therefore, the terahertz wave measuring device 100 indirectly detects the waveform of the terahertz wave THz, which employs a pump-probe method based on time-delayed scanning.

As shown in FIG. 1, the terahertz wave measuring device 100 that employs such a terahertz time region spectroscopy and a pump-probe method includes a pulse laser device 101 and a terahertz wave generating element that is a specific example of the “generation means”. 110, a beam splitter 161 and a reflector 162, a reflector 163, an optical path adjuster 170 which is a specific example of the "first adjusting means", and a light delay which is a specific example of the "second adjusting means". A device 120, a terahertz wave detection element 130 which is a specific example of the "first detection means", a bias voltage generation unit 141, an IV (current-voltage) conversion unit 144, a lock-in detection unit 145, and the like. One of the arithmetic processing unit 150, the reference signal generation unit 181 which is a specific example of the "measurement means", the index signal generation unit 182 which is a specific example of the "second detection means", and the "fourth adjustment means". A measurement start signal generation unit 183, which is a specific example, is provided.

The pulse laser device 101 generates a pulse laser light LB on the order of subpicoseconds or femtoseconds having a light intensity corresponding to the drive current input to the pulse laser device 101. The pulsed laser light LB generated by the pulsed laser device 101 is incident on the beam splitter 161 via a light guide path (for example, an optical fiber or the like) (not shown).

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

The optical delayer 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 delayer 120 adjusts 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 by adjusting the optical path length of the probe light LB2. By adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2, the timing at which the pump light LB1 is incident on the terahertz wave generation element 110 (or the terahertz wave generation element 110 The relative amount of deviation 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 detection element 130 (or the timing at which the terahertz wave detection element 130 detects the terahertz wave THz). Can be adjusted. For example, if the optical path of the probe light LB2 is lengthened by 0.3 mm (however, the optical path length in air) by the optical delayer 120, the timing at which the probe light LB2 is incident on the terahertz wave detection element 130 is delayed by 1 picosecond. Become. In this case, the timing at which the terahertz wave detection element 130 detects the terahertz wave THz is delayed by one picosecond. Considering that terahertz wave THz having the same waveform is repeatedly incident on the terahertz wave detection element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detection element 130 detects the terahertz wave THz is gradually shifted. As a result, the terahertz wave detection element 130 can indirectly detect the waveform of the terahertz wave THz. That is, the lock-in detection unit 145, which will be described later, can detect the terahertz wave THz waveform based on the detection result of the terahertz wave detection element 130.

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

As shown in FIG. 2, the optical delayer 120 includes a plurality of retroreflectors 121 (four in FIG. 2) (four in FIG. 2), each of which is a specific example of the “retroreflector means”, and a rotating substrate 122. And have.

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

The plurality of retroreflectors 121 are arranged at equal intervals on the circumference C centered on the rotation axis of the rotating substrate 122. The rotating substrate 122 can be rotated by the operation of a motor or the like (not shown). Therefore, each of the plurality of retroreflectors 121 orbits on the circumference C as the rotating substrate 122 rotates. By moving the retroreflector 121 in this way, the optical path length of the probe light LB2 is adjusted.

In the example shown in FIG. 2, each retroreflector 121 moves so as to approach the incident direction of the probe light LB2. As a result, each retroreflector 121 moves so that the optical path of the probe light LB2 becomes shorter with the passage of time (that is, with the movement of each retroreflector 121).

The movement of the retroreflector 121 is performed under the control of the arithmetic processing unit 150. That is, the arithmetic processing unit 150 controls the rotational 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.

Again, in FIG. 1, the probe light LB2 emitted from the optical delayer 120 enters the terahertz wave detection element 130 via a light guide path (not shown) and a reflector 163.

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 configurations of the terahertz wave generating element 110 and the terahertz wave detecting element 130, respectively. The configurations of the terahertz wave generating element 110 and the terahertz wave detecting element 130 shown in FIG. 3 are merely examples, and a light conduction antenna or a photoconducting switch having a configuration different from the configuration shown in FIG. 3 is the terahertz wave generating element 110. And may be used as a terahertz wave detection element 130.

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, for example, 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 to each other along the lateral 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 form 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 light LB1 is applied to the gap 114 while an effective bias voltage (for example, a bias voltage other than 0V) is applied to the gap 114, the terahertz wave generating element 110 is subjected to carrier by photoexcitation by the pump light LB1. appear. As a result, the terahertz wave generating element 110 generates a pulsed current signal on the order of subpicoseconds or femtoseconds according to the generated carrier. As a result, the terahertz wave THz generated by the pulsed current signal is generated in the terahertz wave generating element 110.

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 detection 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 configurations 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 photoexcitation by the probe light LB2. When the terahertz detection element 130 is irradiated with the terahertz wave THz while the probe light LB2 is irradiated to 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.

Again, in FIG. 1, the terahertz wave THz emitted from the terahertz wave generating element 110 is incident on the optical path adjuster 170. The optical path adjuster 170 separates the terahertz wave THz into a first terahertz wave THz1 and a second terahertz wave THz2. Further, the optical path adjuster 170 guides both the separated first terahertz wave THz1 and second terahertz wave THz2 to the terahertz wave detection element 130.

In order to perform such an operation, the optical path adjuster 170 includes a beam splitter 171 and a reflector 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 is incident on the reflector 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 object to be measured as the second terahertz wave THz2.

The first terahertz wave THz1 incident on the reflector 172 is reflected by the reflector 172. The first terahertz wave THz1 reflected by the reflector 172 is incident on the beam splitter 171 again. On the other hand, the second terahertz wave THz2 irradiated on the measurement target 172 is reflected by the measurement target. The second terahertz wave THz2 reflected by the measurement object is incident on the beam splitter 171 again.

The distance d1 between the beam splitter 171 and the reflector 172 (typically an optical distance, the same applies hereinafter) is different from the distance d2 between the beam splitter 171 and the object to be measured. That is, the length 2d1 (typically, the optical length, the same applies hereinafter) of the propagation path of the first terahertz wave THz1 returning from the beam splitter 171 to the beam splitter 171 via the reflecting mirror 172 is the beam splitter. The second terahertz wave THz2 returning from 171 to the beam splitter 171 via the object to be measured is different from the length of the propagation path 2d2. Further, while the terahertz wave measuring device 100 is analyzing the characteristics of the object to be measured, the distance d1 and the distance d2 are fixed or do not fluctuate. That is, while the terahertz wave measuring device 100 is analyzing the characteristics of the object to be measured, the difference between the distance d1 and the distance d2 is fixed or does not fluctuate. Therefore, the beam splitter 171 and the reflector 172 are arranged at appropriate positions capable of satisfying the above-mentioned conditions in consideration of the positions where the measurement objects are arranged.

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

The reflector 172 has a reflectance such that the difference between the intensity of the first terahertz wave THz1 reflected by the reflector 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 the reflectance of the object to be measured with respect to the second terahertz wave THz2 is likely to be less than 100%, the reflector 172 has a reflectance of less than 100% with respect to the first terahertz wave THz1. It may have a reflective surface.

The beam splitter 171 transmits the first terahertz wave THz1 reflected by the reflector 172. The first terahertz wave THz1 transmitted through the beam splitter 171 is incident on the terahertz wave detection element 130. On the other hand, the beam splitter 171 reflects the second terahertz wave THz2 reflected by the object to be measured. The second terahertz wave THz2 reflected by the beam splitter 171 also enters the terahertz wave detection element 130 in the same manner as the first terahertz wave THz1. That is, the beam splitter 171 substantially combines the first terahertz wave THz1 and the second terahertz wave THz2, and then transfers the combined first terahertz wave THz1 and second terahertz wave THz2 to the terahertz wave detection element 130. It can be said that they are incident. Hereinafter, for convenience of explanation, the first terahertz wave THz1 and the second terahertz wave THz2 synthesized by the beam splitter 171 will be referred to as terahertz wave THz0.

As a result, the terahertz wave detection 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 reflector 172 is different from the distance d2 between the beam splitter 171 and the object to be measured. Therefore, the terahertz wave detection element 130 detects the first terahertz wave THz1 and the second terahertz wave THz2 at substantially different timings. In this embodiment, the distance d1 and the distance d2 (or the distance d1 and the distance) are such that the terahertz wave detection element 130 detects the first terahertz wave THz1 and the second terahertz wave THz2 in a mode that can be identified along the time axis. Difference from d2) is preferably set. That is, from the terahertz wave detection element 130, 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 that the output can be performed in any manner.

In addition, in this embodiment, the terahertz wave detection element 130 detects both the first terahertz wave THz1 and the second terahertz wave THz2 during the reflection period in which each retroreflector 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 the distance d1 and the distance d2 can be set. That is, the retroreflective mirror 121a retroreflects the probe light LB2 in the first reflection period, the retroreflective mirror 121b retroreflects the probe light LB2 in the second reflection period, and the retroreflective mirror 121c retroreflects the probe light LB2. The terahertz wave detection element 130 performs both the first terahertz wave THz1 and the second terahertz wave THz2 in each of the third reflection period in which the light is reflected and the fourth reflection period in which the retroreflector 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 the light can be detected.

The object to be measured may move in parallel with irradiation of the second terahertz wave THz2. For example, the measurement target may move in a plane orthogonal to the direction in which the second terahertz wave THz2 is incident on the measurement target (horizontal 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 in a so-called three-dimensional manner.

The current signal output from the terahertz wave detection element 130 is converted into a voltage signal by the IV conversion unit 144. After that, 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 sample values of the terahertz wave THz0 (that is, the first terahertz wave THz1 and the second terahertz wave THz2). After that, 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 the waveform signal indicating the waveform of the terahertz wave THz0 by acquiring the detection result of the lock-in detection unit 145. At the same time, the arithmetic processing unit 150 Fourier transforms the waveform signal indicating the waveform of the terahertz wave THz0 detected by the lock-in detection unit 145 to Fourier transform the frequency spectrum of the terahertz wave THz0 (that is, the amplitude and phase for each frequency). To get. Further, the arithmetic processing unit 150 measures the characteristics of the object to be measured by analyzing the frequency spectrum of the terahertz wave THz0.

The reference signal generation unit 181 generates a reference signal synchronized with the rotation of each retroreflector 121. The reference signal is, for example, a signal in which one pulse appears for each rotation of the rotating substrate 122 on which the retroreflector 121 is mounted. Such a reference signal is a signal for defining a reference time as a reference when measuring the characteristics of the object to be measured by the arithmetic processing unit 150. The reference signal is generated by using, for example, a drive control pulse from the optical delayer 120 or the arithmetic processing unit 150.

The index signal generation unit 182 detects the feature points 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 time position of the detected feature point is output to the measurement start signal generation unit 183 as an index signal.

The measurement start signal generation unit 183 measures during each reflection period in which each retroreflector 121 included in the optical delayer 120 retroreflects the probe light LB2 according to the index signal input from the index signal generation unit 182. Generate a measurement start signal to adjust the start timing. As for the measurement start timing, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object 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's time to do it. 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 the timing corresponding to the measurement start signal.

(2) Technical Problems Due to Misalignment of the Retroreflector 121 Next, with reference to FIGS. 4 and 5, technical problems that occur due to the misalignment of the retroreflector 121 will be described. FIG. 4A shows a waveform of a terahertz wave THz0 when the four retroreflectors 121 included in the optical delayer 120 are not displaced, and each retroreflector 121 retroreflects the probe light LB2. It is a graph which shows in association with the period. FIG. 4B is a graph showing the amplitude of the waveform of the terahertz wave THz0 (particularly, the second terahertz wave THz2) when the four retroreflectors 121 included in the optical delayer 120 are not displaced. is there. FIG. 5A shows a waveform of a terahertz wave THz0 when at least one of the four retroreflectors 121 included in the optical delayer 120 is displaced, and each retroreflector 121 recurses the probe light LB2. It is a graph which shows in association with the period of reflection. FIG. 5B shows the amplitude of the waveform of the terahertz wave THz0 (particularly, the second terahertz wave THz2) when at least one of the four retroreflectors 121 included in the optical delayer 120 is displaced. 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 retroreflector 121 retroreflects the probe light LB2 as shown in FIG. 4A. Acquired as a waveform signal. For example, if the rotation angle of the rotating substrate 122 at the time when the retroreflecting mirror 121a starts to retroreflect the probe light LB2 is defined as 0 °, the rotation angle of the rotating substrate 122 of the retroreflecting mirror 121a is from 0 ° to X1 ° ( However, the probe light LB2 is retroreflected during the first reflection period when 0 ° <X1 <90 °). Similarly, the retroreflector 121b retroreflects the probe light LB2 during the second reflection period when the rotation angle of the rotating substrate 122 is 90 ° to X2 ° (however, 90 ° <X2 <180 °). Similarly, the retroreflector 121c retroreflects the probe light LB2 during the third reflection period when the rotation angle of the rotating substrate 122 is 180 ° to X3 ° (however, 180 ° <X3 <270 °). Similarly, the retroreflector 121d retroreflects the probe light LB2 during the fourth reflection period when the rotation angle of the rotating substrate 122 is from 270 ° to X4 ° (however, 270 ° <X4 <360 °). After that, the same operation is repeated.

As a result, the arithmetic processing unit 150 acquires a waveform signal showing 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 this embodiment, each retroreflector 121 moves with the passage of time (that is, with the movement of each retroreflector 121) so that the optical path of the probe light LB2 becomes shorter, and The distance d1 between the beam splitter 171 and the reflector 172 is larger than the distance d2 between the beam splitter 171 and the object to be measured. In this case, the arithmetic processing unit 150 acquires the detection result of the lock-in detection unit 145, thereby acquiring the waveform signal showing the waveform of the first terahertz THz1 and the second terahertz wave THz2 in this order during each reflection period. .. Further, the time interval between the waveform of the first terahertz THz1 and the waveform of the second terahertz THz2 is a fixed value 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 the characteristics of the measurement target (for example, acquiring a tomographic image of the measurement target). Therefore, 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 retroreflector 121 without misalignment begins to retroreflect. It is preferable that the relative positions from the time positions corresponding to the rotation angles of 0 °, 90 °, 180 ° and 270 ° are aligned with each other). In the example shown in FIG. 4A, the four retroreflectors 121 are not misaligned. Therefore, 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 °, and the second terahertz during the second reflection period from the time position corresponding to 90 °. Relative peak position of the waveform signal of the wave THz2, 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 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. Therefore, as shown in FIG. 4B obtained by arranging the waveform signals of the second terahertz wave THz2 shown in FIG. 4A on the vertical axis and adding shades according to the amplitude, the second terahertz wave THz2 The tomographic image acquired based on the waveform signal of is an XZ tomographic image without steps (however, 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. The direction is along the plane orthogonal to the incident direction of the second terahertz wave THz2).

On the other hand, FIG. 5A shows a case where the retroreflectors 121b and 121c of the four retroreflectors 121 (from the retroreflector 121a to the retroreflector 121d) included in the optical delayer 120 are displaced. , Terahertz wave THz0 waveform is shown. Specifically, in the retroreflector 121b, the rotation angle of the rotating substrate 122 is changed from 70 ° to Y2 ° (however, 70 ° <Y2 <190 °) due to the positional deviation caused in the retroreflector 121b. During the second reflection period, the probe light LB2 is retroreflected. Similarly, the retroreflector 121c recurses the probe light LB2 during the third reflection period when the rotation angle of the rotating substrate 122 changes from 190 ° to X3 ° due to the misalignment occurring in the retroreflector 121c. It is reflecting.

In this case, the peak positions of the waveform signals of the second terahertz wave THz2 during each reflection period are not aligned with each other due to the misalignment of the retroreflectors 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 °. It is different from the relative peak position of the waveform signal of the second terahertz wave THz2 during the third reflection period from. Therefore, as shown in FIG. 5 (b) obtained by arranging the waveform signals of the second terahertz wave THz2 shown in FIG. 5 (a) on the vertical axis and adding shades according to the amplitude, the second terahertz wave THz2 It can be seen that the tomographic image acquired based on the waveform signal of is an XZ tomographic image with steps.

On the other hand, in order to acquire an XZ tomographic image without steps based on the waveform signal of the second terahertz wave THz2 shown in FIG. 5A, the arithmetic processing unit 150 performs the waveform signal of the second terahertz wave THz2. As shown in FIG. 4A, the waveform signal of the second terahertz wave THz2 may be handled. For example, the arithmetic processing unit 150 temporally shifts the waveform signals of the second reflection period and the third reflection period among the waveform signals of the second terahertz wave THz2 shown in FIG. 5 (a), thereby showing FIG. 5 (a). The waveform signal of the second terahertz wave THz2 can be handled so that the state of the waveform signal of the second terahertz wave THz2 is as shown in FIG. 4 (a). That is, the arithmetic processing unit 150 shifts at least a part of the waveform signal of the second terahertz wave THz2 acquired when the retroreflector 121 is displaced in time to the retroreflector 121. The waveform signal of the second terahertz wave THz2 acquired when the misalignment occurs can be handled as the waveform signal of the second terahertz wave THz2 acquired when the retroreflector 121 does not have the misalignment. ..

Therefore, in the present embodiment, the arithmetic processing unit 150 uses a part of the waveform signal of the second terahertz wave THz2 to measure in order to shift at least a part of the waveform signal of the second terahertz wave THz2 in time. Adjust the timing to measure the characteristics of the object (that is, the measurement start timing described above). 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 time-shifted by adjusting the measurement start timing. However, the arithmetic processing unit 150 may, in addition to or instead of adjusting the measurement start timing, shift at least a part of the waveform signal of the second terahertz wave THz2 in time. That is, the arithmetic processing unit 150 shifts 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, 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.

By the way, in this embodiment, the distance d1 and the distance d2 are fixed or do not fluctuate while the terahertz wave measuring device 100 is analyzing the characteristics of the object to be measured, as described above. Therefore, even if the retroreflectors 121b and 121c are misaligned, between the first terahertz THz1 waveform and the second terahertz THz2 waveform detected during the second and third reflection periods. The time interval is the difference between the distance d1 and the distance d2, similar to the time interval between the first terahertz THz1 waveform and the second terahertz THz2 waveform detected during the first and fourth reflection periods. It is a fixed value that is determined according to. That is, regardless of whether or not the retroreflector 121 is misaligned, the waveform signal of the first terahertz THz1 is acquired until the waveform signal of the second terahertz THz2 is acquired during the entire reflection period. The period is a fixed value determined according to the difference between the distance d1 and the distance d2.

Therefore, the terahertz measuring device 100 of this 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 obtains the 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. Use to adjust the measurement start timing to start measuring the characteristics of the object to be measured. 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. Adjust the measurement start timing to start measuring the characteristics of the object to be measured. In the third and fourth reflection periods, the arithmetic processing unit 150 performs the same operation. As a result, the arithmetic processing unit 150 acquires the second terahertz wave THz2 when the retroreflector 121 is misaligned even if at least one retroreflector 121 is misaligned. Can be treated as a waveform signal of the second terahertz wave THz2 acquired when the retroreflector 121 is not displaced. Hereinafter, the operation of adjusting the measurement start timing will be further described.

(3) Operation for Adjusting Measurement Start Timing As described above, the measurement start timing mainly indicates the reference signal generation unit 181 for generating the reference signal, the index signal generation unit 182 for generating the index signal, and the measurement indicating the measurement start timing. It is adjusted by the measurement start signal generation unit 183 that generates the start signal. Here, as described above, the reference signal generation unit 181 generates a reference signal in which one pulse appears for each rotation of the rotating substrate 122. Therefore, in the following, the operation of adjusting the measurement start timing will be described by further explaining 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. ..

The reference signal generation unit 181 and the index signal generation unit 182 and the measurement start signal generation unit 183 may be hardware circuits. Alternatively, the reference signal generation unit 181 and 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, an index signal generation operation by the index signal generation unit 182 will be described with reference to FIGS. 6 to 8. FIG. 6 is a block diagram showing the configuration of the index signal generation unit 182. FIG. 7 is a graph showing a waveform of the first terahertz wave THz1. FIG. 8 is a block diagram showing a modified example of the index signal generation unit 182.

As shown in FIG. 6, the index signal generation unit 182 is a low-pass filter 1821, a feature point detection unit 1822 which is a specific example of the “second detection means”, and a specific example of the “calculation means”. It is configured to include a time position extraction unit 1823 and a selector 1824.

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

The feature point detection unit 1822 detects the feature point 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 the "point at which the instantaneous value of the first terahertz wave THz1 is maximized (maximum point)" indicated by the point A in FIG. 7B as a feature point. The minimum value detection unit 1822c detects a "point at which the instantaneous value of the first terahertz wave THz1 is minimized (minimum value)" as shown by point C in FIG. 7B as a feature point. The zero cross detection unit 1822b utilizes the maximum point detected by the maximum value detection unit 1822a and the minimum point detected by the minimum value detection unit 1822c to obtain a “zero cross point (that is, that is) as shown by point B in FIG. 7 (b). , 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 time position extraction unit 1823b corresponding to the minimum value detection unit 1822c. It is provided with 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 to the detection of the feature point.

The selector 1823 selects any one of the time positions 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. Selector 1823 outputs an index signal indicating the selected time position.

As described above, the index signal generation unit 182 detects the 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 device 100 may include a plurality of index signal generation units 182, each of which corresponds to one reflection period. For example, considering that the optical delayer 120 includes four retroreflectors 121 in this embodiment, the terahertz wave measuring device 100 has four index signal generation units (index signal generation unit 182 in FIG. 8). -1, index signal generation unit 182-2, index signal generation unit 182-3, and index signal generation unit 182-4) may be provided. The index signal generation unit 182-1 outputs an index signal during the first reflection period in which the retroreflector 121a retroreflects the probe light LB2. The index signal generation unit 182-2 outputs an index signal during the second reflection period in which the retroreflector 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 retroreflector 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 retroreflector 121d retroreflects the probe light LB2.

As described above, when the terahertz measuring device 100 includes a plurality of index signal generation units 182, an index signal is generated separately for each reflection period in which each retroreflector 121 retroreflects the probe light LB2. Therefore, the increase in the processing load of the index signal generation unit 182 due to the single index signal generation unit 182 outputting the index signal over the entire reflection period is suppressed. That is, the complexity of the configuration of the index signal generation unit 182 is suppressed.

Further, as shown in FIG. 8, an average value calculation unit 185 for calculating the average value of the index signals may be arranged after each index signal generation unit 182. As a result, it is preferably 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 measuring device 100 includes a plurality of index signal generation units 182 but also when the terahertz measuring device 100 includes a single index signal generation unit 182. May be good.

(3-2) Operation of Generating Measurement Start Signal 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. 9. FIG. 9 is a block diagram showing a configuration of a measurement start signal generation unit.

As shown in FIG. 9A, the measurement start signal generation unit 183 includes a storage circuit 1831a, a 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-out control for 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 retroreflector 121a retroreflects the probe light LB2, the RW-CTL unit 1832a is an index signal corresponding to the mirror number assigned to the retroreflector 121a. Is read. That is, the RW-CTL unit 1832a reads out 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 retroreflector 121b retroreflects the probe light LB2, the RW-CTL unit 1832a is an index signal corresponding to the mirror number assigned to the retroreflector 121b. Is read. That is, the RW-CTL unit 1832a reads out the index signal generated by the index signal generation unit 182 during the second reflection period. The same operation is performed during 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 a constant value has been 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 detected when each retroreflector 121 is not misaligned. Such a constant value may be stored in advance in a memory or the like included in the terahertz measuring device 100 as an operation parameter, for example. In this case, the offset portion 1833a is an index signal detected when the retroreflector 121a is not displaced from the index signal read during the first reflection period in which the retroreflector 121a retroreflects the probe light LB2. Subtract a constant value corresponding to. When the retroreflector 121a is not displaced, the adjustment amount of the measurement start timing corresponding to the index signal to which a constant value is subtracted becomes zero. Therefore, in this case, the default measurement start timing is used as the measurement start timing. When the retroreflector 121a is misaligned, the adjustment amount of the measurement start timing corresponding to the index signal from which a constant value is subtracted is a desired amount different from zero. This adjustment amount corresponds to the temporal shift amount of the second terahertz wave THz2 due to the misalignment of the retroreflector 121a (see FIGS. 5 (a) and 5 (b)). Therefore, in this case, as the measurement start timing, the measurement start timing in which the default measurement start timing is adjusted based on the adjustment amount is used.

The offset unit 1833a performs the same processing not only on the index signal during the first reflection period but also on 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 the retroreflector 121b is not displaced 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 retroreflector 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 retroreflector 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 and the reference signal output by the offset unit 1833a. 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 THz 2 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. Start measuring the characteristics of the measurement object based on the signal. The same operation is performed during the second reflection period to the fourth reflection period.

Here, as shown in FIG. 5A, the measurement start timing when the retroreflectors 121b and 121c are misaligned will be described.

First, since the retroreflector 121a is not displaced, 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, during the first reflection period, 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. The same operation is performed during the fourth reflection period.

On the other hand, since the retroreflector 121b is misaligned, 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. It becomes 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 THz 2 at the adjusted measurement start timing during the second reflection period. The same operation is performed during the third reflection period.

Here, even when the retroreflector 121b is misaligned, 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 It is a fixed value. Therefore, the amount of temporal deviation of the waveform of the first terahertz wave THz1 due to the misalignment of the retroreflector 121b is the temporal deviation of the waveform of the second terahertz wave THz2 due to the misalignment of the retroreflector 121b. Equal to the quantity. 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 retroreflective mirror 121b is misaligned. It substantially shows the measurement start timing at which the waveform signal of the terahertz wave THz2 can be treated as the waveform signal of the second terahertz wave THz2 acquired when the retroreflector 121b is not displaced. 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 acquired when the retroreflective mirror 121b is misaligned. Measurement start that can be substantially converted into the waveform signal of the second terahertz wave THz2 acquired when the retroreflector 121b is not displaced by shifting the waveform signal of the terahertz wave THz2 in time. It effectively shows the timing. Therefore, the arithmetic processing unit 150 starts measuring the characteristics of the measurement object at the adjusted measurement start timing based on such an adjustment amount, thereby eliminating the influence of the positional deviation of the retroreflector 121b. The characteristics of the object to be measured 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 addition unit 1835b adds the past n index signals. The past n index signals added by the addition unit 1835b are divided by n by the division unit 1836b. As a result, the average value of the past n index signals is calculated. Therefore, the 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, it is possible to prevent an inappropriate measurement start signal from being generated due to erroneous measurement or the like.

Further, as shown in FIG. 9C, the measurement start signal generation unit 183 may include m (that is, the same number as the retroreflector 121) low-pass filters 1837c. In this case, since the index signal is filtered 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 device 100 of this embodiment irradiates the measurement object with the second terahertz wave THz. Therefore, the terahertz wave measuring device 100 can measure the characteristics of the object to be measured based on the detection result of the second terahertz wave THz.

Further, the terahertz measuring device 100 does not irradiate the measurement object with the first terahertz wave THz1. Therefore, the terahertz wave measuring device 100 can adjust the measurement start timing to start measuring 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 detection element 130 detects the second terahertz wave THz2 varies due to the misalignment of the retroreflector 121 (see FIGS. 5 (a) and 5 (b)). ). Even when the timing at which the terahertz detection element 130 detects the second terahertz wave THz2 varies in this way, the terahertz wave measuring device 100 measures the variation in the 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 device 100 can measure the characteristics of the object to be measured with relatively high accuracy by using the terahertz wave THz.

Further, the terahertz wave measuring device 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, in parallel with the measurement of the characteristics of the measurement object based on the detection result of the second terahertz wave THz2, the terahertz wave measuring device 100 sequentially sets the measurement start timing based on the detection result of the first terahertz wave (in other words, in other words. Can be adjusted (in real time).

Further, each retroreflector 121 moves with the passage of time (that is, with the movement of each retroreflector 121) so that the optical path of the probe light LB2 becomes shorter, and between the beam splitter 171 and the reflector 172. The distance d1 is larger than the distance d2 between the beam splitter 171 and the object to be measured. Therefore, by acquiring the detection result of the lock-in detection unit 145, the arithmetic processing unit 150 acquires the waveform signal showing the waveform of the first terahertz THz1 and the second terahertz wave THz2 in this order during each reflection period. .. Therefore, the terahertz measuring device 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 measurement start timing of the second terahertz wave THz2 during the certain reflection period. Measurement of the characteristics of the measurement object based on the detection result can be started.

When each retroreflector 121 moves so that the optical path of the probe light LB2 becomes longer with the passage of time, the distance d1 is preferably smaller than the distance d2. Alternatively, when each retroreflector 121 retroreflects the pump light LB1 instead of the probe light LB2 and each retroreflector 121 moves so that the optical path of the pump light LB1 becomes shorter with the passage of time. It is preferable that the distance d1 is smaller than the distance d2. Alternatively, when each retroreflector 121 retroreflects the pump light LB1 instead of the probe light LB2 and each retroreflector 121 moves so that the optical path of the pump light LB1 becomes longer with the passage of time. It is preferable that the distance d1 is larger than the distance d2. As a result, the arithmetic processing unit 150 acquires the detection result of the lock-in detection unit 145, and acquires the waveform signal showing 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 modified within the scope of claims and within a range not contrary to the gist or idea of the invention that can be read from the entire specification, and terahertz wave measurement accompanied by such modification. The device is also included in the technical scope of the present invention.

100 Terahertz wave measuring device 101 Pulse laser device 110 Terahertz wave generating element 121 Retroreflector 130 Terahertz wave detecting element 150 Arithmetic processing unit 170 Optical path regulator 171 Beam splitter 172 Reflector 181 Reference signal generator 182 Index signal generator 183 Measurement start Signal generator LB1 Pump light LB2 Probe light THz terahertz wave THz1 1st terahertz wave THz2 2nd terahertz wave

Claims (5)

A means of generating a terahertz wave when irradiated with laser light,
(I) The first terahertz wave, which is a part of the terahertz wave generated by the generating means, propagates in the first path and is not irradiated to the measurement target, while (ii) the terahertz generated by the generating means. Separation means for separating the terahertz wave so that the second terahertz wave, which is another part of the wave, propagates in the second path having a path length different from that of the first path and irradiates the measurement object. When,
With the first detection means for detecting the first terahertz wave that is not irradiated to the measurement object and the second terahertz wave that is irradiated to the measurement object by being irradiated with the laser beam. ,
An optical path length adjusting means for adjusting the optical path length of the laser beam irradiated to at least one of the generating means and the first detecting means by retroreflecting the laser beam.
A measuring means for measuring the characteristics of the measurement object based on the second terahertz wave detected by the first detecting means, and a measuring means.
A timing adjusting means for adjusting the timing at which the measuring means measures the characteristics of the measurement object based on the detection result of the first terahertz wave by the first detecting means is provided .
The timing adjusting means
A second detection means for detecting a feature point of the first terahertz wave detected by the first detection means, and a second detection means.
A calculation means for calculating the reference period, which is the period from the reference time to the detection of the feature point, and
A control means for controlling the measurement means so as to start measurement of the characteristics of the measurement object at a timing determined based on the reference period.
The terahertz wave measuring apparatus according to claim Rukoto equipped with. Each of the optical path length adjusting means includes a plurality of retroreflecting means for re-reflecting the laser beam.
The second detecting means separately detects the feature point for each reflection period in which each of the plurality of retroreflective means re-reflects the laser beam.
The calculation means separately calculates the reference period for each reflection period.
The control means controls the measurement means so as to start measurement of the 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 1 . According to claim 1 or 2 , 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 and
The calculation means calculates the reference period a plurality of times.
The control means of claims 1, wherein the controller controls the measurement unit so as to start measuring the characteristics of the measurement object at the timing determined according to the average value of the reference period which has been calculated more than once The terahertz wave measuring apparatus according to any one of 3 . The means of generating electromagnetic waves and
Separation means for separating the electromagnetic wave generated by the generating means into a first electromagnetic wave propagating in a first path that is not irradiated to the measurement object and a second electromagnetic wave that propagates in a second path that is irradiated to the measurement object. When,
The first detection that detects the first and second electromagnetic waves by incident the first electromagnetic wave propagating in the first path and the second electromagnetic wave propagating in the second path and irradiating with light. Means and
An optical path length adjusting means for adjusting the optical path length of the light irradiated to the first detecting means, and an optical path length adjusting means.
A measuring means for measuring the characteristics of the measurement object based on the second electromagnetic wave detected by the first detecting means, and a measuring means.
A second detecting means for detecting a feature point of the first electromagnetic wave detected by the first detecting means, and
A control means that controls the measurement means so as to start measurement of the characteristics of the measurement object at a timing determined based on the reference period, which is the period from the reference time to the detection of the feature point.
A terahertz wave measuring device characterized by being equipped with.