JP2021076617A - Terahertz wave measurement device - Google Patents

Abstract

To improve measurement efficiency.SOLUTION: A terahertz wave measurement device (100) comprises: generation means (110) that is irradiated with laser light (LB1) to thereby generate a terahertz wave (THz); detection means (130) that is irradiated with laser light (LB2) to thereby detect the terahertz wave with which a measurement object (10) is irradiated; adjustment means (120) that reflects the laser light to thereby enable an adjustment of an optical path length of the laser light with which the detection means is irradiated; movement means (170) that can move a measurement object; and control means (150) that controls at least one of the adjustment means and movement means so that an adjustment period in which the adjustment means reflects the laser light to thereby adjust the optical path length is synchronized with a movement timing in which the measurement object is located at a desired measurement position.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 with respect to the pump light. The terahertz wave detection element irradiated with probe light (in other words, excitation light) to which a large delay (that is, optical path length difference) is applied is irradiated. As a result, the terahertz wave detection element detects 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.

Here, the optical delay applied to the probe light (or pump light, the same applies hereinafter) causes the probe light to be incident on an optical delayer including a retroreflector capable of retroreflecting the incident light. It is often given by letting it. The term "retroreflection" as used herein refers to a state in which incident light is reflected in a direction parallel to the incident direction of the incident light. As an example of the optical delayer, for example, an optical delayer including a plurality of rotatable retroreflector mirrors (or prisms) can be mentioned.

When the terahertz wave measuring device is equipped with such an optical delayer, the terahertz wave detection element is a period during which the optical delayer actually retroreflects the probe light (that is, an optical delay to the probe light). The terahertz wave is detected during the period during which the light is actually applied.

On the other hand, in order to measure the characteristics of a plurality of points of the measurement target, at least one of the measurement target and the terahertz wave detection element (or the head including the terahertz wave detection element) is a movable stage (or slider, The same shall apply hereinafter). In this case, as the stage moves, the relative positional relationship between the terahertz wave detection element and the object to be measured changes. As a result, the detection position of the terahertz wave in the measurement object moves. Therefore, since the terahertz wave is detected at a plurality of points of the object to be measured, the terahertz wave measuring device can measure the characteristics of the plurality of points of the object to be measured.

Japanese Unexamined Patent Publication No. 2013-174548

In the terahertz wave measuring device described in Patent Document 1 described above, in order to measure the characteristics of a plurality of points of the measurement object, the measurement object is moved so that the terahertz wave is irradiated to a certain measurement point of the measurement object. After that, it is stopped and the terahertz wave irradiated to the measurement point is detected. However, the terahertz wave measuring device described in Patent Document 1 needs to measure the characteristics of the measurement object while repeatedly moving and stopping the measurement object, so that the time required for the measurement becomes relatively long. (That is, the measurement efficiency is relatively deteriorated), which is a technical problem.

Examples of the problems to be solved by the present invention include the above. An object of the present invention is to provide a terahertz wave measuring device capable of improving measurement efficiency.

A terahertz wave measuring device that solves the above problems generates a terahertz wave by irradiating the laser beam, and also emits the generated means for irradiating the generated terahertz wave to the measurement object and the laser beam. The optical path length of the detection means for detecting the terahertz wave applied to the measurement object and the laser light for irradiating at least one of the generating means and the detecting means by reflecting the laser light. The generating means, the detecting means, and the measuring means so that at least one of the irradiation position and the detecting position of the terahertz wave in the measuring object moves along the surface of the measuring object. A moving means capable of moving at least one of the measurement objects, an adjustment period in which the adjusting means adjusts the optical path length by reflecting the laser beam, the generating means, the detecting means, and the measurement. The adjusting means and the control means for controlling at least one of the moving means are provided so that at least one of the objects is synchronized with the moving timing at which the desired measurement position is located.

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. It is a timing chart which shows the waveform of various control signals which a terahertz wave measuring apparatus refers to or generates when the control operation of each driving state of an optical delay mechanism and a scanning mechanism is performed. 6 is a timing chart showing waveforms of various control signals referred to or generated by the terahertz wave measuring device when the time waveform acquisition signal and the image data storage signal are not synchronized.

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

<1>
The terahertz wave measuring device of the present embodiment generates a terahertz wave by irradiating the laser beam, and also by irradiating the generated means for irradiating the measured object with the generated terahertz wave and the laser beam. The optical path length of the detection means for detecting the terahertz wave applied to the measurement object and the optical path length of the laser light irradiated to at least one of the generation means and the detection means by reflecting the laser light. The generating means, the detecting means, and the measuring means so that at least one of the adjustable adjusting means and the irradiation position and the detecting position of the terahertz wave in the measuring object moves along the surface of the measuring object. A moving means capable of moving at least one of the measurement objects, an adjustment period in which the adjusting means adjusts the optical path length by reflecting the laser beam, the generating means, the detecting means, and the measuring target. The adjusting means and the control means for controlling at least one of the moving means are provided so that at least one of the objects is synchronized with the moving timing at which the desired measuring position is located.

According to the terahertz wave measuring device of the present embodiment, the terahertz wave irradiated to the measurement object is detected by the operation of the generating means, the detecting means, the adjusting means, the moving means, and the controlling means. The detected terahertz wave is used to measure the characteristics of the object to be measured. The outline of the terahertz wave detection method will be briefly described below.

The generating means generates a terahertz wave by irradiating the generating means with laser light as excitation light (for example, pump light). The terahertz wave generated by the generating means irradiates the object to be measured.

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

The adjusting means reflects the laser beam and guides the reflected laser beam to at least one of the generating means and the detecting means. Here, the adjusting means can continuously change the state of the laser beam by reflecting the laser beam. Therefore, it can be said that the adjusting means continuously changes the state of the laser beam and guides the continuously changing state of the laser beam to at least one of the generating means and the detecting means. At this time, the adjusting means adjusts the optical path length of the laser beam irradiated to at least one of the generating means and the detecting means. For example, when the adjusting means includes a reflecting mirror that reflects the laser light, the adjusting means may adjust the optical path length of the laser light by physically moving the reflecting mirror. As a result, the 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 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.

The moving means is at least one of the generating means, the detecting means, and the measuring object so that at least one of the terahertz wave irradiation position and the terahertz wave detecting position on the measuring object moves along the surface of the measuring object. Move one. As a result, the detection means can sequentially detect the terahertz wave at a plurality of locations of the measurement target. Alternatively, the generating means can sequentially irradiate a plurality of locations of the measurement target with the terahertz wave. Therefore, the terahertz wave measuring device can measure each of the characteristics of a plurality of places to be measured.

In particular, in the present embodiment, the control means adjusts at least one of the adjusting means and the moving timing so that the adjusting period and the moving timing are synchronized.

The adjustment period is a period during which the adjustment means reflects the laser beam. In other words, it can be said that the adjustment period is a period in which the adjustment means continuously changes the state of the laser beam. That is, the adjustment period is a period in which the adjustment means adjusts a series of optical path lengths. Considering that the terahertz wave waveform is detected due to the adjustment of the optical path length, the terahertz wave waveform detected during the adjustment period is a valid terahertz wave waveform (for example, the characteristic of the object to be measured. It can be said that it is a terahertz wave waveform that is useful for measurement). On the other hand, it can be said that the terahertz wave detected during the non-adjustment period, which is a period other than the adjustment period, is an ineffective terahertz wave waveform (for example, a terahertz wave waveform that is not useful for measuring the characteristics of the object to be measured). In other words, it can be said that the adjustment period is the period during which a valid terahertz wave waveform is detected.

The movement timing is a timing that serves as a reference for the measurement position of the terahertz wave in the measurement object. Considering that at least one of the terahertz wave irradiation position and the detection position in the measurement object moves due to the movement of at least one of the generation means, the detection means, and the measurement object, the movement timing is in the measurement object. It can be said that this is the timing when the terahertz wave detection position is located at the desired measurement position. Alternatively, it can be said that the movement timing is the timing at which the irradiation position of the terahertz wave on the measurement object is located at the desired measurement position. In addition, as will be described in detail later, the detection result of the detection means (that is, the waveform of the terahertz wave) is the desired measurement at the timing when at least one of the irradiation position and the detection position of the terahertz wave is located at the desired measurement position. It is saved in memory or the like in association with the location. Therefore, it can be said that the movement timing is a timing in which the detection result of the detection means is associated with the desired measurement position and then stored in a memory or the like.

As described above, in the present embodiment, the adjustment period and the movement timing are synchronized. Therefore, the time difference between the adjustment period and the movement timing synchronized with the adjustment period hardly or not varies (in other words, fluctuates) every time the measurement position changes. Therefore, the terahertz wave measuring device of the present embodiment uses the terahertz wave waveform detected by the detection means during the adjustment period for each movement timing that arrives at a fixed cycle in synchronization with the adjustment period. It can be acquired (in other words, saved, the same applies hereinafter) as it is associated with the measurement position corresponding to. In other words, the terahertz wave measuring device of the present embodiment obtains the waveform of the terahertz wave detected by the detection means during the adjustment period that arrives at a fixed cycle in synchronization with the movement timing each time the movement timing arrives. It can be acquired by associating it with the measurement position corresponding to the moved movement timing. Therefore, the measurement efficiency by the terahertz wave measuring device is relatively improved.

If the adjustment period and the movement timing are not synchronized, the terahertz wave measuring device does not synchronize the terahertz wave waveform detected by the detection means during the adjustment period with the adjustment period (in other words, during the adjustment period). On the other hand, it is necessary to wait for the arrival of the movement timing (which arrives at a random timing), and then acquire the measurement position in association with the measurement position corresponding to the arrival movement timing. That is, the terahertz wave measuring device needs to wait for the arrival of the movement timing that arrives at a random timing. Due to the waiting time of this movement timing, if the adjustment period and the movement timing are not synchronized, the measurement efficiency by the terahertz wave measuring device may be relatively deteriorated. However, in the present embodiment, since the adjustment period and the movement timing are synchronized, the terahertz wave measuring device synchronizes the waveform of the terahertz wave detected by the detection means during the adjustment period with the adjustment period (in other words). For example, each time a movement timing (which arrives at a fixed timing with respect to the adjustment period) arrives, it can be acquired as it is in association with the measurement position corresponding to the arrival movement timing. Therefore, the measurement efficiency by the terahertz wave measuring device is relatively improved.

If the adjustment period and the movement timing are not synchronized and the terahertz wave measuring device does not wait for the movement timing, the time difference between the adjustment period and the movement timing synchronized with the adjustment period is the measurement position. It may vary each time it changes. As a result, the accuracy of the measurement result obtained from the waveform of the terahertz wave measured at a plurality of locations of the measurement object may deteriorate. This is because the measurement position where the terahertz wave was actually measured during the adjustment period and the position information associated with the detection result when the terahertz wave detection result measured at the measurement position is saved. This is because the amount of deviation between them fluctuates each time measurement is performed. At this time, since the positional relationship of the acquired multidimensional data composed of a plurality of terahertz waves is not a fixed interval, for example, when the image is imaged using the multidimensional data, deterioration such as image distortion occurs. there is a possibility. However, in the present embodiment, the adjustment period and the movement timing are synchronized. Therefore, the time difference between the adjustment period and the movement timing synchronized with the adjustment period hardly or not varies every time the measurement position changes. Therefore, the accuracy of the measurement result obtained from the waveform of the terahertz wave measured at a plurality of locations of the measurement target is hardly or not deteriorated. Therefore, the measurement accuracy by the terahertz wave measuring device is relatively improved.

<2>
In another aspect of the terahertz wave measuring device of the present embodiment, the control means is such that the temporal relationship of the movement timing with respect to the adjustment period is fixed by synchronizing the adjustment period and the movement timing. It controls at least one of the adjusting means and the moving means.

According to this aspect, the time difference between the adjustment period and the movement timing synchronized with the adjustment period hardly or not varies every time the measurement position is changed. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

<3>
In another aspect of the terahertz wave measuring device of the present embodiment, in the control means, the time difference between the reference time and the movement timing during the adjustment period is fixed by synchronizing the adjustment period and the movement timing. At least one of the adjusting means and the moving means is controlled so as to be performed.

According to this aspect, the time difference between the adjustment period and the movement timing synchronized with the adjustment period hardly or not varies every time the measurement position is changed. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

<4>
In another aspect of the terahertz wave measuring device of the present embodiment, the adjusting means includes at least a first reflecting means capable of reflecting the laser light and a second reflecting means capable of reflecting the laser light. The control means generates the means for the first adjustment period in which the adjustment period and the movement timing are synchronized so that the first retroreflection means reflects the laser beam to adjust the optical path length. The optical path length is determined by the temporal relationship of the first movement timing in which at least one of the detection means and the measurement object is located at a desired first measurement position and the second reflection means reflecting the laser beam. The time relationship of the second movement timing at which at least one of the generating means, the detecting means, and the measuring object with respect to the adjusting second adjusting period is located at a desired second measuring position is matched. It controls at least one of the adjusting means and the moving means.

According to this aspect, the time difference between the adjustment period and the movement timing synchronized with the adjustment period hardly or not varies depending on the reflecting means reflecting the laser beam. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

<5>
In another aspect of the terahertz wave measuring device in which the adjusting means includes the first and second reflecting means as described above, the controlling means is the first between the reference time and the first movement timing during the first adjusting period. At least one of the adjusting means and the moving means is controlled so that the one-time difference coincides with the second time difference between the reference time during the second adjusting period and the second moving timing.

According to this aspect, the time difference between the adjustment period and the movement timing synchronized with the adjustment period hardly or not varies depending on the reflecting means reflecting the laser beam. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

<6>
In another aspect of the terahertz wave measuring device of the present embodiment, the adjusting means adjusts the optical path length in an adjusting mode determined based on the first reference signal, and the moving means is determined based on the second reference signal. At least one of the generation means, the detection means, and the measurement object is moved in the movement mode, and the control means moves the first reference signal and the first reference signal so that the adjustment period and the movement timing are synchronized with each other. 2 Generate at least one of the reference signals.

According to this aspect, the terahertz wave measuring device is at least one of the generating means, the detecting means, and the measuring object by the first reference signal and the moving means, which substantially defines the adjusting mode of the optical path length by the adjusting means. By generating at least one of the second reference signals that substantially defines the movement mode, the adjustment period and the movement timing can be synchronized relatively easily.

<7>
In another aspect of the terahertz wave measuring device that generates at least one of the first and second reference signals as described above, the control means are identical to each other so that the adjustment period and the movement timing are synchronized. The first reference signal and the second reference signal are generated.

According to this aspect, the terahertz wave measuring device can relatively easily synchronize the adjustment period and the movement timing by generating the first reference signal and the second reference signal that are the same as each other.

<8>
In another aspect of the terahertz wave measuring device that produces at least one of the first and second reference signals as described above, the control means said that the adjusting means adjusts the optical path length in a desired adjustment mode. 1 The reference signal is generated, and the control means generates the second reference signal based on the first reference signal so that the adjustment period and the movement timing are synchronized.

According to this aspect, the terahertz wave measuring device can generate the second reference signal based on the generated second reference signal after first generating the first reference signal. As a result, the terahertz wave measuring device can relatively easily synchronize the adjustment period with the movement timing.

<9>
In another aspect of the terahertz wave measuring device that generates at least one of the first and second reference signals as described above, the control means is the generating means, the detecting means and the measuring in the movement mode desired by the moving means. The second reference signal is generated so as to move at least one of the objects, and the control means uses the first reference signal based on the second reference signal so that the adjustment period and the movement timing are synchronized. Generate a reference signal.

According to this aspect, the terahertz wave measuring device can generate the first reference signal based on the generated second reference signal after first generating the second reference signal. As a result, the terahertz wave measuring device can synchronize the adjustment period and the movement timing relatively easily.

<10>
In another aspect of the terahertz wave measuring device that generates at least one of the first and second reference signals as described above, the adjusting means is m (where m is an integer of 1 or more) capable of reflecting the laser beam, respectively. ) The reflecting means and the rotating means for rotationally driving the m reflecting means are provided, and the first reference signal is n (1) while the first pulse having a period of Tr makes one rotation of the rotating means. However, n is a pulse signal that repeatedly appears 10 times (an integer of 1 or more), the second reference signal is a pulse signal in which a second pulse having a period of Ts appears repeatedly, and the first pulse appears during the adjustment period. The reference time in the adjustment period arrives every time n / m appears, the movement timing is the timing that arrives every time k second pulses appear, and the control means is Tr × ( The first reference signal and the above-mentioned first reference signal so that the conditional expression of n / m) = A × Ts × k or Tr × (n / m) = (1 / A) × Ts × k (where A is a natural number) is satisfied. Generates at least one of the second reference signals.

According to this aspect, the terahertz wave measuring device relatively easily synchronizes the adjustment period and the movement timing by generating the first reference signal and the second reference signal so that the above-mentioned conditional expression is satisfied. Can be done.

<11>
In another aspect of the terahertz wave measuring device of the present embodiment, the terahertz wave detection result by the detection means during the adjustment period synchronized with the movement timing is set to the desired measurement position by using the arrival of the movement timing as a trigger. Further provided with a storage means for storing in association with.

According to this aspect, each time the terahertz wave measuring device arrives, the terahertz wave waveform detected by the detection means during the adjustment period which arrives at a fixed cycle in synchronization with the movement timing is arrived. It can be acquired (saved) in association with the measurement position corresponding to the movement timing. In other words, the terahertz wave measuring device responds to the terahertz wave waveform detected by the detection means during the adjustment period each time the movement timing arrives in a fixed cycle in synchronization with the adjustment period. It can be acquired in association with the measurement position. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

<12>
In another aspect of the terahertz wave measuring device including the storage means as described above, the adjusting means includes at least a first reflecting means capable of reflecting the laser light and a second reflecting means capable of reflecting the laser light. The storage means has (i) the first reflection triggered by the arrival of the first movement timing in which at least one of the generation means, the detection means, and the measurement object is located at a desired first measurement position. The detection result of the terahertz wave by the detection means during the first adjustment period in which the means reflects the laser beam to adjust the optical path length is stored in association with the desired first measurement position. ii) The second reflecting means reflects the laser beam triggered by the arrival of a second moving timing in which at least one of the generating means, the detecting means, and the measuring object is located at a desired second measuring position. The detection result of the terahertz wave by the detection means during the second adjustment period in which the optical path length is adjusted is stored in association with the desired second measurement position.

According to this aspect, each time the terahertz wave measuring device arrives, the terahertz wave waveform detected by the detection means during the adjustment period which arrives at a fixed cycle in synchronization with the movement timing is arrived. It can be acquired (saved) in association with the measurement position corresponding to the movement timing. In other words, the terahertz wave measuring device responds to the terahertz wave waveform detected by the detection means during the adjustment period each time the movement timing arrives in a fixed cycle in synchronization with the adjustment period. It can be acquired in association with the measurement position. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

<13>
In another aspect of the terahertz wave measuring device of the present embodiment, the moving means can continuously move at least one of the generating means, the detecting means, and the measuring object, and the controlling means is said. At least one of the adjusting means and the moving means is used so that the adjusting period and the moving timing are synchronized during the period in which at least one of the generating means, the detecting means, and the measurement object is continuously moving. Control.

According to this aspect, the terahertz wave measuring device measures during the adjusting period even if at least one of the generating means, the detecting means and the measuring object is continuously moved and at the same time the laser beam is reflected by the adjusting means. The waveform of the terahertz wave applied to the object can be suitably acquired by associating it with the measurement position corresponding to the movement timing synchronized with the adjustment period. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device are relatively improved.

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 detecting means, an adjusting means, a moving means, and a controlling means. Therefore, the measurement efficiency by the terahertz wave measuring device is relatively improved.

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 measurement object 10 with the terahertz wave THz, and at the same time, the terahertz wave THz transmitted through the measurement object 10 or reflected by the measurement object 10 (that is, the measurement object). The terahertz wave THz) applied to the object 10 is detected. In the example shown in FIG. 1, the terahertz wave measuring device 100 detects the terahertz wave THz reflected by the measurement object 10.

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 measurement object 10 by analyzing the frequency spectrum of the terahertz wave THz applied to the measurement object 10. In the following, for convenience of explanation, the terahertz wave measuring device 100 analyzes the frequency spectrum of the terahertz wave THz irradiated on the measurement object 10 to obtain the measurement object 10 at the position where the terahertz wave THz is irradiated. A cross-sectional image shall be acquired.

In order to acquire the frequency spectrum of the terahertz wave THz applied to the measurement object 10, the terahertz wave measuring device 100 employs terahertz time region spectroscopy (terahertz Time-Domain Spectroscopy). In the terahertz time region spectroscopy, the terahertz wave THz is irradiated to the measurement object 10, and the time waveform of the terahertz wave THz transmitted through the measurement object 10 or reflected from the measurement object 10 is Fourier-transformed to perform the terahertz wave THz. This is a method of acquiring the frequency spectrum of a wave (that is, the 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, beam splitter 161 and reflector 162, reflector 163, half mirror 164, optical delay mechanism 120 which is a specific example of "adjustment means", and terahertz which is a specific example of "detection means". It includes a wave detection element 130, an IV (current-voltage) conversion unit 140, a control unit 150, and a scanning mechanism 170 which is a specific example of the "moving means".

The pulse laser device 101 generates a pulsed laser light LB on the order of subpicoseconds or femtoseconds having a light intensity corresponding to the drive current input to the pulsed 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 optical delay mechanism 120 via a light guide path and a reflector 162 (not shown).

The optical delay mechanism 120 adjusts the difference (that is, the optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Specifically, the optical delay mechanism 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 generating element 110 (or the terahertz wave generating element 110 Adjust the time difference between the timing of generating the terahertz wave THz) and the timing of the probe light LB2 incident on the terahertz wave detection element 130 (or the timing of the terahertz wave detection element 130 detecting the terahertz wave THz) to adjust the terahertz wave THz. (Time waveform, the same applies hereinafter) can be scanned. 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 delay mechanism 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 152, which will be described later, can detect the waveform of the terahertz wave THz based on the detection result of the terahertz wave detection element 130.

Here, the configuration of the optical delay mechanism 120 will be described with reference to FIG. FIG. 2 is a plan view and a cross-sectional view showing the configuration of the optical delay mechanism 120. The optical delay mechanism 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 FIGS. 2 (a) and 2 (b), the optical delay mechanism 120 includes a plurality of (four in FIG. 2) retroreflecting mirrors 121 (four in FIG. 2), each of which is a specific example of the “retroreflection means”. 121a to 121d), a rotating substrate 122, a motor (for example, a direct current (direct current) motor) 123, a rotary encoder 124, a photo interrupter 125, and a photo reflector 126. FIG. 2B is a cross-sectional view taken along the line II-II'of the optical delay mechanism 120 shown in FIG. 2A.

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

The plurality of retroreflective mirrors 121 are arranged at equal intervals on the circumference C centered on the rotation axis 122a of the rotation substrate 122. The rotating shaft 122a of the rotating substrate 122 is connected to the rotating shaft 123a of the motor 123. Therefore, the rotating substrate 122 can be rotated by the operation of the motor 123. As a result, each of the plurality of retroreflecting mirrors 121 orbits on the circumference C as the rotating substrate 122 rotates. By such movement of the retroreflector 121, the optical path length of the probe light LB2 is adjusted.

The rotary encoder 124 is an annular member connected to the rotating substrate 122. Therefore, the rotary encoder 124 rotates in accordance with the rotation of the rotating substrate 122. The rotary encoder 124 includes a plurality of slits 124a arranged at equal intervals and in an annular shape along the outer edge of the rotating substrate 122. Each slit 124a is assigned an identification number unique to each slit 124a. The numbers shown in the slits 124a in FIG. 2A indicate the identification numbers of the slits 124a.

The photo interrupter 125 includes a light emitting element 125a and a light receiving element 125b. A rotating rotary encoder 124 is arranged between the light emitting element 125a and the light receiving element 125b. The laser beam emitted by the light emitting element 125a is received by the light receiving element 125b at the timing when the slit 124a is located between the light emitting element 125a and the light receiving element 125b. On the other hand, the laser light emitted by the light emitting element 125a is not received by the light receiving element 125b at a timing when the slit 124a is not located between the light emitting element 125a and the light receiving element 125b. Therefore, the control unit 150 monitors the light receiving result of the light receiving element 125b (specifically, the pulse-shaped rotation cycle detection signal output from the light receiving element 125b), thereby rotating the rotating substrate 122 (that is, rotating). Speed) can be detected.

Further, a marker 122b indicating a reference position of the rotation phase (that is, the rotation angle) of the rotation substrate 122 is installed on a part of the side surface of the rotation substrate 122. Therefore, the marker 122b is installed at one location on the side surface of the rotating substrate 122. In the example shown in FIG. 2A, it is assumed that the reference position indicated by the marker 122b is the position where the slit 124a # 0 having the identification number 0 is formed.

The photo reflector 126 irradiates the side surface of the rotating substrate 122 on which the marker 122b is installed with a laser beam. The laser beam emitted by the photo reflector 126 is reflected by the side surface of the rotating substrate 122. The laser beam reflected by the side surface of the rotating substrate 122 is detected by the photoreflector 126. Here, the intensity of the laser light reflected by the portion of the side surface of the rotating substrate 122 where the marker 122b is installed is the intensity of the laser light reflected by the portion of the side surface of the rotating substrate 122 where the marker 122b is not installed. Different from strength. Therefore, the light receiving result of the photo reflector 126 is a pulse signal in which one pulse appears for each rotation of the rotating substrate 122. Therefore, the control unit 150 monitors the light receiving result of the photoreflector 126 (specifically, the pulsed rotation phase detection signal output from the photoreflector 126) to rotate the rotary encoder 124 (that is, rotate). The reference position of the rotation phase of the substrate 122) can be detected.

The control unit 150 can detect the rotation phase of the rotation substrate 122 based on the rotation cycle signal indicating the rotation cycle of the rotation substrate 122 and the rotation phase signal indicating the rotation phase. That is, the control unit 150 can detect which pulse of the pulse-shaped rotation cycle detection signal corresponds to which slit 124a. Here, considering that the rotation phase of the rotation substrate 122 is related to the state of retroreflection of the probe light LB2 by the retroreflection mirror 121, the control unit 150 is based on the rotation cycle signal and the rotation phase signal. It is possible to detect which retroreflector 121 is retroreflecting the probe light LB2. For example, during the period in which the pulse corresponding to the slit 124a having the identification numbers 22 to 23 and 0 to 2 is detected as the rotation cycle detection signal, the control unit 150 retroreflects the probe light LB2 by the retroreflection 121a. It can be detected that it is. For example, during the period in which the pulse corresponding to the slit 124a having the identification number 4 to 8 is detected as the rotation cycle detection signal, the control unit 150 states that the retroreflection 121b retroreflects the probe light LB2. Can be detected. For example, during the period in which the pulse corresponding to the slit 124a having the identification number 10 to 14 is detected as the rotation period detection signal, the control unit 150 states that the retroreflection 121c retroreflects the probe light LB2. Can be detected. For example, during the period in which the pulse corresponding to the slit 124a having the identification number 16 to 20 is detected as the rotation cycle detection signal, the control unit 150 states that the retroreflection 121d retroreflects the probe light LB2. Can be detected.

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

Here, the terahertz wave generating element 110 irradiated with the pump light LB1 and the terahertz detecting element 130 irradiated with the probe light LB2 will be described in more detail with reference to FIG. FIG. 3 is a perspective view showing the 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 151 included in the control unit 150 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 140 via the antenna 132 and the antenna 133.

Again, in FIG. 1, the terahertz wave THz emitted from the terahertz wave generating element 110 passes through the half mirror 164. The terahertz wave THz transmitted through the half mirror 164 is applied to the measurement object 10. The terahertz wave THz applied to the measurement object 10 is reflected by the measurement object 10. The terahertz wave THz reflected by the measurement object 10 is reflected by the half mirror 164. The terahertz wave THz reflected by the half mirror 164 is incident on the terahertz wave detection element 130.

As a result, the terahertz wave detection element 130 detects the terahertz wave THz. That is, the terahertz wave detection element 130 outputs a current signal having a signal intensity corresponding to the intensity of the terahertz wave THz.

In parallel with the irradiation and detection of the terahertz wave THz, the scanning mechanism 170 moves the measurement object 10. For example, the scanning mechanism 170 may move the measurement object 10 along an in-plane orthogonal to the direction in which the terahertz wave THz is incident on the measurement object 10 (the left-right direction in FIG. 1). Therefore, the measurement position by the terahertz wave THz (that is, the position where the measurement is performed) moves along the surface of the measurement object 10. As a result, the control unit 150 can measure the characteristics of the measurement object 10 in a so-called three-dimensional manner. That is, the control unit 150 can acquire a cross-sectional image of the measurement object 10 in a so-called three-dimensional manner.

In order to move the measurement object 10, the scanning mechanism 170 may include, for example, a stage and a servomotor for moving the stage. The measurement object 10 is mounted on the stage. The servomotor is driven in a mode defined by a scanning mechanism drive signal described later. As a result, the servomotor can move the stage (that is, the measurement object mounted on the stage) in a desired movement mode.

However, the scanning mechanism 170 may move at least one of the terahertz wave generating element 110 and the terahertz wave detecting element 130 in addition to or instead of moving the measurement object 10. Even in this case, the measurement position by the terahertz wave THz moves along the surface of the measurement object 10.

The current signal output from the terahertz wave detection element 130 is converted into a voltage signal by the IV conversion unit 140.

The control unit 150 analyzes the detection result of the terahertz wave detection element 130 (that is, the voltage signal output by the IV conversion unit 140). In order to analyze the detection result of the terahertz wave detection element 130, the control unit 150 includes a lock-in detector 152 and a data processing unit 153.

The lock-in detection unit 152 performs synchronous detection of the voltage signal using the bias voltage generated by the bias voltage generation unit 151 as a reference signal. As a result, the lock-in detection unit 152 detects the sample value of the terahertz wave THz. After that, the same operation is repeated while appropriately adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2, so that the lock-in detection unit 152 has a terahertz wave THz waveform (time). Waveform) can be detected.

The data processing unit 153 can acquire a waveform signal indicating a terahertz wave THz waveform by taking the detection result of the lock-in detection unit 152 into a buffer. At this time, the data processing unit 153 captures the detection result of the lock-in detection unit 152 into the buffer during the period in which the time waveform acquisition signal described in detail later becomes active. Further, the data processing unit 153 associates the acquired waveform signal with the position information indicating the scanning position of the measurement object 10, and the waveform signal associated with the position information is image data (for example, a cross-sectional image of the measurement object 10). (Image data indicating) is stored in a memory that employs a FIFO (First In First Out) method or the like. At this time, the data processing unit 153 indicates the scanning position of the measurement object 10 at the timing when the image data storage signal, which will be described in detail later, becomes active, and the acquired waveform signal at the time when the image data storage signal becomes active. Along with associating with the position information, the waveform signal associated with the position information is saved in the memory. Further, the data processing unit 153 acquires the frequency spectrum (that is, the amplitude and phase for each frequency) of the terahertz wave THz by Fourier transforming the waveform signal stored in the memory. Further, the data processing unit 153 measures the characteristics of the measurement object 10 by analyzing the frequency spectrum of the terahertz wave THz.

The control unit 150 further controls the driving state of the optical delay mechanism 120 (particularly, the rotating state of the rotating substrate 122) and the driving state of the scanning mechanism 170. In order to control the driving states of the optical delay mechanism 120 and the scanning mechanism 170, the control unit 150 further scans the timing generation unit 154, which is a specific example of the "control means", the optical delay mechanism driving unit 155, and the scanning mechanism. It includes a mechanism drive unit 156.

Hereinafter, the control operations of the drive states of the optical delay mechanism 120 and the scanning mechanism 170, which are mainly performed by the timing generation unit 154, the optical delay mechanism driving unit 155, and the scanning mechanism driving unit 156, will be further described.

(2) Control operation of driving state of optical delay mechanism 120 and scanning mechanism 170 Subsequently, referring to FIG. 4, optical delay mainly performed by the timing generation unit 154, the optical delay mechanism driving unit 155, and the scanning mechanism driving unit 156. The control operation of the drive state of each of the mechanism 120 and the scanning mechanism 170 will be described. FIG. 4 is a timing chart showing waveforms of various control signals referred to or generated by the terahertz wave measuring device when the control operations of the driving states of the optical delay mechanism 120 and the scanning mechanism 170 are performed.

As shown in FIG. 4, the timing signal generation unit 154 generates a rotation cycle reference signal for defining the driving state of the rotation substrate 122. The rotation cycle reference signal is a pulse signal in which a plurality of pulses repeatedly appear in the cycle Tr. The timing signal generation unit 154 outputs the generated rotation cycle reference signal to the optical delay mechanism drive unit 155. The rotation cycle reference signal is a specific example of the "first reference signal".

The optical delay mechanism driving unit 155 acquires a rotation period detection signal which is a detection result of the photo interrupter 125. As shown in FIG. 4, the rotation cycle detection signal has, for example, (i) the signal level becomes high at the timing when the slit 124a is located between the light emitting element 125a and the light receiving element 125b, and (ii) the light emitting element 125a. This is a pulsed signal whose signal level becomes low at the timing when the slit 124a is not positioned between the light receiving element 125b and the light receiving element 125b. In addition, assuming that the number of slits 124a provided in the rotary encoder 124 is n, the rotation cycle detection signal is a pulse-like signal in which a pulse appears every time the rotation substrate 122 rotates by 360 ° / n. In the example shown in FIG. 2A, since n = 24, the rotation cycle detection signal is a pulse-like signal in which a pulse appears every time the rotating substrate 122 rotates by 360 ° / 24 = 15 °.

The optical delay mechanism drive unit 155 controls the operating state of the optical delay mechanism 120 so that the rotation cycle reference signal and the rotation cycle detection signal are synchronized. As a result, the rotating substrate 122 is driven in the driving mode defined by the rotation cycle reference signal. That is, the rotating substrate 122 rotates in the rotation mode defined by the rotation cycle reference signal.

In the state of "the rotation cycle reference signal and the rotation cycle detection signal are synchronized" referred to here, the frequency of the rotation cycle detection signal matches the frequency of the rotation cycle reference signal and the phase of the rotation cycle detection signal is the rotation cycle reference. It means a state that matches the phase of the signal. Therefore, the optical delay mechanism drive unit 155 detects the frequency error by comparing the frequency of the rotation cycle detection signal with the frequency of the rotation cycle reference signal. Further, the optical delay mechanism driving unit 155 detects the phase error by comparing the phase of the rotation cycle detection signal with the phase of the rotation cycle reference signal. After that, the optical delay mechanism drive unit 155 feedback-controls the motor 123 based on the frequency error so as to compensate for the rotation frequency. Further, the optical delay mechanism drive unit 155 feedback-controls the motor 123 based on the phase error so as to compensate for the rotation phase.

However, in the state of "the rotation cycle reference signal and the rotation cycle detection signal are synchronized" referred to here, the frequency of the rotation cycle detection signal matches the frequency of the rotation cycle reference signal, but the phase of the rotation cycle detection signal is the same. It may mean a state in which the phase of the rotation period reference signal is deviated by a predetermined amount that does not fluctuate with the passage of time. Alternatively, in the state of "the rotation cycle reference signal and the rotation cycle detection signal are synchronized" referred to here, the frequency of the rotation cycle detection signal is A ₁ times or 1 / A ₁ times the frequency of the rotation cycle reference signal (however, A). ₁ may mean a state in which it becomes a natural number).

The optical delay mechanism drive unit 155 acquires a rotation phase detection signal, which is a detection result of the photoreflector 126, in addition to the rotation cycle detection signal. The optical delay mechanism drive unit 155 outputs the acquired rotation cycle detection signal and rotation phase detection signal to the data processing unit 153.

The data processing unit 153 detects the rotation phase of the rotation substrate 122 based on the rotation cycle detection signal and the rotation phase detection signal. Specifically, the data processing unit 153 counts the count value for detecting the rotation phase each time a pulse of the rotation cycle detection signal appears (that is, each time the rotation cycle detection signal transitions from a low level to a high level). Up. Further, in the data processing unit 153, the rotation phase detection signal pulse appears at the timing when the rotation cycle detection signal pulse appears (that is, the rotation phase detection signal is high at the timing when the rotation cycle detection signal transitions from low level to high level. If it becomes a level), the count value is reset to zero. The count value counted in this way corresponds to an identification number (that is, rotation phase) for identifying the slit 124a. As a result, the data processing unit 153 can specify the association between each pulse included in the rotation cycle detection signal and each of the plurality of slits 124a to which the identification numbers from 0 to 23 are assigned. The numbers given to each pulse of the rotation cycle detection signal in FIG. 4 indicate the identification number (that is, the count value) of the slit 124a corresponding to each pulse. Considering that the identification number of the slit 124a substantially corresponds to the rotation phase of the rotating substrate 122, the data processing unit 153 can detect the rotation phase of the rotating substrate 122.

When the rotation phase of the rotating substrate 122 is detected, the data processing unit 153 detects the detection result of the lock-in detection unit 152 (that is, the terahertz wave THz detected by the lock-in detection unit 152) based on the rotation phase of the rotating substrate 122. Waveform) is generated by the data processing unit 153 for a time waveform capture signal that defines a period for capturing the data in the buffer. Specifically, as described above, the terahertz wave measuring device 100 detects the waveform of the terahertz wave THz by using the pump-probe method. Therefore, the lock-in detection unit 152 can suitably detect the waveform of the terahertz wave THz during the period in which the optical path length of the probe light LB2 is adjusted. Conversely, the lock-in detection unit 152 cannot suitably detect the terahertz wave THz waveform during the period when the optical path length of the probe light LB2 is not adjusted. The period during which the optical path length of the probe light LB2 is adjusted coincides with the period during which the retroreflective mirror 121 retroreflects the probe light LB2. Therefore, the data processing unit 153 may obtain the detection result of the lock-in detection unit 152 during the period in which the retroreflector 121 retroreflects the probe light LB2 in order to suitably acquire the waveform signal indicating the waveform of the terahertz wave THz. Is preferably taken into the buffer. Therefore, the data processing unit 153 generates a time waveform acquisition signal that becomes active during the period in which the retroreflective mirror 121 retroreflects the probe light LB2. The period during which the time waveform capture signal is at a high level is a specific example of the “adjustment period”. Further, in the following, as an example of the "signal active" state, the description will proceed using "the signal level of the signal becomes high level".

Specifically, a pulse having a count value of 22 to 23 and 0 to 2 (that is, a pulse corresponding to a slit 124a having an identification number of 22 to 23 and 0 to 2) is detected as a rotation cycle detection signal. During the period, the data processing unit 153 can detect that the retroreflection 121a is retroreflecting the probe light LB2. Therefore, the data processing unit 153 generates a time waveform acquisition signal having a high level during the period in which the pulse having the count values of 22 to 23 and 0 to 2 is detected as the rotation period detection signal. For example, during a period in which a pulse having a count value of 4 to 8 (that is, a pulse corresponding to a slit 124a having an identification number of 4 to 8) is detected as a rotation cycle detection signal, the data processing unit 153 may perform the data processing unit 153. It can be detected that the retroreflection 121b is retroreflecting the probe light LB2. Therefore, the data processing unit 153 generates a time waveform acquisition signal having a high level during the period in which the pulse having a count value of 4 to 8 is detected as the rotation period detection signal. For example, during a period in which a pulse having a count value of 10 to 14 (that is, a pulse corresponding to a slit 124a having an identification number of 10 to 14) is detected as a rotation cycle detection signal, the data processing unit 153 may perform the data processing unit 153. It can be detected that the retroreflection 121c is retroreflecting the probe light LB2. Therefore, the data processing unit 153 generates a time waveform acquisition signal having a high level during the period in which the pulse having a count value of 10 to 14 is detected as the rotation period detection signal. For example, during a period in which a pulse having a count value of 16 to 20 (that is, a pulse corresponding to a slit 124a having an identification number of 16 to 20) is detected as a rotation cycle detection signal, the data processing unit 153 may perform the data processing unit 153. It can be detected that the retroreflection 121d is retroreflecting the probe light LB2. Therefore, the data processing unit 153 generates a time waveform acquisition signal having a high level during the period in which the pulse having a count value of 16 to 20 is detected as the rotation period detection signal.

The time waveform capture signal generated in this way is a rectangular wave-like signal in which a plurality of rectangular waves repeatedly appear in a period Tw. Here, the number of slits 124a provided in the rotary encoder 124 (that is, the number of pulses included in the rotation cycle detection signal detected during one rotation of the rotating substrate 122) is set to n, and the rotary encoder 124 is installed on the rotating substrate 122. Assuming that the number of retroreflectors 121 is m, Tw = Tr × (n / n /) between the period Tw of the square wave included in the time waveform capture signal and the period Tr of the pulse included in the rotation period reference signal. The relationship m) is established. In the example shown in FIG. 2A, since n = 24 and m = 4, the relationship of Tw = Tr × (24/4) = 6 × Tr is established. However, the relationship of Tw = Tr × (n / m) is established when the state in which the rotation cycle reference signal and the rotation cycle detection signal are synchronized is the frequency of the rotation cycle detection signal and the frequency of the rotation cycle reference signal. This is the case when it means a state that matches with. On the other hand, the state in which the rotation cycle reference signal and the rotation cycle detection signal are synchronized is A ₁ times or 1 / A ₁ times the frequency of the rotation cycle detection signal and the frequency of the rotation cycle reference signal (however, A ₁ is When it means a state of (natural number), _{the relationship of Tw = (Tr / A 1} ) × (n / m) or Tw = (Tr × A ₁ ) × (n / m) is established.

The data processing unit 153 captures the detection result of the lock-in detection unit 152 into the buffer during the period when the time waveform acquisition signal is at a high level. On the other hand, the data processing unit 153 does not have to capture the detection result of the lock-in detection unit 152 into the buffer during the period when the time waveform acquisition signal is at a low level.

On the other hand, the timing signal generation unit 154 further generates a scanning mechanism reference signal for defining the driving state of the scanning mechanism 170. The scanning mechanism reference signal is a pulse signal in which a plurality of pulses repeatedly appear in a period Ts. The timing signal generation unit 154 outputs the generated scanning mechanism reference signal to the scanning mechanism driving unit 156. The scanning mechanism reference signal is a specific example of the “second reference signal”.

The scanning mechanism driving unit 156 generates a scanning mechanism driving signal obtained by extracting a predetermined number of pulses from the scanning mechanism reference signal. Therefore, the scanning mechanism drive signal is a pulse signal in which a predetermined number of pulses repeatedly appear in the period Ts. Here, as described above, the scanning mechanism 170 includes a stage on which the measurement object 10 is mounted and a servomotor that moves the stage. The servomotor drives the stage to move by a certain reference step amount each time a pulse is input. Therefore, by appropriately adjusting the number of pulses included in the scanning mechanism drive signal and the appearance timing of the pulses, the servomotor can be driven so as to move the stage at a desired timing and by a desired amount. Therefore, the scanning mechanism driving unit 156 generates a scanning mechanism driving signal capable of moving the stage (that is, the measurement object 10) along a desired movement path.

Here, as described above, the data processing unit 153 corresponds to the position information of the detection result (that is, the waveform signal) of the lock-in detection unit 152 captured in the buffer during the period when the time waveform capture signal becomes high level. The waveform signal associated with the position information is saved in the memory. In this embodiment, the data processing unit 153 associates the waveform signal captured in the buffer with the position information and saves the waveform signal associated with the position information in the memory each time the measurement object 10 moves by a predetermined amount. To do.

The association between the waveform signal and the position information and the timing of storing the waveform signal associated with the position information in the memory are defined by the image data storage signal. Therefore, the data processing unit 153 generates an image data storage signal that becomes active each time the measurement object 10 moves by a predetermined amount, based on the scanning mechanism drive signal generated by the scanning mechanism drive unit 156. Specifically, as shown in FIG. 4, the data processing unit 153 generates an image data storage signal in which one pulse appears each time k (where k is a natural number) pulses included in the scanning mechanism drive signal appear. To do. In the example shown in FIG. 4, the data processing unit 153 generates an image data storage signal in which one pulse appears every time six pulses included in the scanning mechanism drive signal appear. Therefore, the period Td of the pulse included in the image data storage signal satisfies the relationship of Td = Ts × k.

Each time a pulse appears in the image data storage signal, the data processing unit 153 associates the waveform signal captured in the buffer with the position information, and stores the waveform signal associated with the position information in the memory. Specifically, when a pulse appears in the image data storage signal, the data processing unit 153 is the latest waveform signal that has been taken into the buffer by the time the pulse appears, and is associated with the position information. Corresponds the incomplete waveform signal with the position information. At this time, the position information associated with the waveform signal is the position information indicating the scanning position of the measurement object 10 at the time when the pulse appears in the image data storage signal. After that, the data processing unit 153 stores the waveform signal associated with the position information in the memory.

Here, the scanning mechanism drive unit 156 counts the number of pulses included in the scanning mechanism drive signal to scan the scanning position of the measurement object 10 (in other words, the current position of the measurement object 10 or the measurement object 10 above. The measurement position by the terahertz wave THz in the above) can be detected. Therefore, it is preferable that the scanning mechanism driving unit 156 appropriately detects the scanning position of the measurement object 10 and outputs the position information indicating the scanning position of the detected measurement object 10 to the data processing unit 153. As a result, the data processing unit 153 can suitably acquire the position information to be associated with the waveform signal.

More specifically, as shown in FIG. 4, since the time waveform capture signal becomes a high level during the period from time t11 to time t12, the data processing unit 153 performs the time t11 to time t12. The waveform signal # 1 which is the detection result of the lock-in detection unit 152 during the period is taken into the buffer. The uptake of the waveform signal # 1 into the buffer is completed at time t12. On the other hand, at time t12, pulse P # 1 appears in the image data storage signal. Therefore, the data processing unit 153 sets the latest waveform signal # 1, which has been taken into the buffer by the time the pulse P # 1 appears, of the measurement object 10 at the time t12 when the pulse P # 1 appears. Corresponds to the position information indicating the scanning position. After that, the data processing unit 10 stores the waveform signal # 1 associated with the position information in the memory.

After that, during the period from time t21 to time t22, the time waveform acquisition signal becomes high level again, so that the data processing unit 153 detects the lock-in detection unit 152 during the period from time t21 to time t22. The resulting waveform signal # 2 is taken into the buffer. The uptake of the waveform signal # 2 into the buffer is completed at time t22. On the other hand, at time t22, pulse P # 2 appears in the image data storage signal. Therefore, the data processing unit 153 transfers the latest waveform signal # 2, which has been taken into the buffer by the time the pulse P # 2 appears, to the measurement object 10 at the time t22 when the pulse P # 2 appears. Corresponds to the position information indicating the scanning position. After that, the data processing unit 10 stores the waveform signal # 2 associated with the position information in the memory.

After that, the same operation is repeated.

In this embodiment, the timing generation unit 154 uses the time waveform acquisition signal that defines the period during which the data processing unit 153 captures the waveform signal that is the detection result of the lock-in detection unit 152 into the buffer, and the waveform signal that is captured in the buffer. The rotation cycle reference signal and the scanning mechanism reference signal are generated so as to synchronize with the image data storage signal indicating the timing of storing the waveform signal associated with the position information and the position information in the memory.

The state in which the time waveform acquisition signal and the image data storage signal are synchronized in this embodiment means a state in which the period of the time waveform acquisition signal coincides with the period of the image data storage signal. However, in the state where the time waveform acquisition signal and the image data storage signal are synchronized, the period of the time waveform acquisition signal is A ₂ times or 1 / A ₂ times the period of the image data storage signal (however, A _2). May mean a state in which (is a natural number).

Here, as described above, the period Tw of the rectangular wave included in the time waveform capture signal is expressed by the mathematical formula Tw = Tr × (n / m). Further, as described above, the pulse period Td included in the image data storage signal is expressed by the mathematical formula Td = Ts × k. Therefore, the timing generation unit 154 generates the rotation cycle reference signal and the scanning mechanism reference signal so that the relationship of Tw = Td is established. That is, the timing generation unit 154 generates the rotation cycle reference signal and the scanning mechanism reference signal so that the relationship Tr × (n / m) = Ts × k is established.

In the example shown in FIG. 4, since n = 24, m = 4, and k = 6, the timing generator 154 holds the mathematical formula Tr × (24/4) = Ts × 6. , Rotation cycle reference signal and scanning mechanism reference signal are generated. That is, the timing generation unit 154 generates the rotation cycle reference signal and the scanning mechanism reference signal so that the mathematical formula Tr = Ts holds. That is, the timing generation unit 154 generates a rotation cycle reference signal and a scanning mechanism reference signal in which pulses appear in the same cycle.

In the example shown in FIG. 4, the timing generation unit 154 generates a rotation cycle reference signal and a scanning mechanism reference signal in which the pulses appear in the same cycle and the pulses are in phase. That is, the timing generation unit 154 generates a rotation cycle reference signal and a scanning mechanism reference signal that are the same as each other. However, the timing generation unit 154 may generate a rotation cycle reference signal and a scanning mechanism reference signal in which the pulses appear in the same cycle but the pulses are out of phase by a predetermined amount. Even in this case, as long as the above-mentioned relationship of Tw = Td is established, a state in which the time waveform capture signal and the image data storage signal are synchronized is realized.

The timing generation unit 154 first creates a rotation cycle reference signal, and then uses the pulse cycle Tr included in the generated rotation cycle reference signal to perform the above-mentioned Tr × (n / m) = Ts × k. A scanning mechanism reference signal satisfying the above relationship may be generated. That is, the timing generation unit 154 first creates a rotation cycle reference signal in which a plurality of pulses repeatedly appear in a cycle Tr, and then a scanning mechanism reference in which a plurality of pulses appear in a cycle Ts = Tr × (n / m) / k. A signal may be generated.

Alternatively, the timing generation unit 154 first creates a scanning mechanism reference signal, and then uses the pulse period Ts included in the generated scanning mechanism reference signal to perform Tr × (n / m) = Ts × k described above. A rotation cycle reference signal satisfying the above relationship may be generated. That is, the timing generation unit 154 first creates a scanning mechanism reference signal in which a plurality of pulses repeatedly appear in a period Ts, and then a rotation cycle reference in which a plurality of pulses appear in a period Tr = Ts × k / (n / m). A signal may be generated.

As described above, the terahertz wave measuring device 100 of this embodiment generates a rotation period reference signal and a scanning mechanism reference signal so that the time waveform acquisition signal and the image data storage signal are synchronized. As a result, the timing at which the acquisition of the waveform signal, which is the detection result of the lock-in detection unit 152, is completed, and the timing at which the data processing unit 153 associates the position information with the waveform signal and saves the waveform signal associated with the position information. Synchronize. That is, the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal is fixed regardless of the passage of time.

In the example shown in FIG. 4, the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal is zero regardless of the passage of time. When the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal becomes zero regardless of the passage of time, the following technical effects can be obtained. Specifically, the data processing unit 153 can associate the waveform signal acquired immediately after the acquisition of the waveform signal is completed with the position information and store the waveform signal associated with the position information. Therefore, the data processing unit 153 does not have to wait for the timing of associating the captured waveform signal with the position information after the acquisition of the waveform signal is completed. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device 100 are relatively improved.

Furthermore, if the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal is fixed regardless of the passage of time, the following technical effects can be obtained. Specifically, the data processing unit 153 associates the captured waveform signal with the position information and the waveform signal associated with the position information at the timing when a fixed fixed time elapses after the acquisition of the waveform signal is completed. Can be saved. Therefore, the measurement efficiency and measurement accuracy of the terahertz wave measuring device 100 are relatively improved.

For reference, as shown in FIG. 5, when the time waveform acquisition signal and the image data storage signal are not synchronized, the timing at which the waveform signal acquisition is completed and the position information are associated with the waveform signal. The amount of deviation from the timing may fluctuate over time.

Specifically, since the time waveform capture signal becomes a high level during the period from time t11'to time t12', the data processing unit 153 locks during the period from time t11' to time t12'. The waveform signal # 1 which is the detection result of the in-detection unit 152 is taken into the buffer. The uptake of the waveform signal # 1 into the buffer is completed at time t12'. On the other hand, pulse P # 1 appears in the image data storage signal at time t12'. Therefore, the data processing unit 153 measures the latest waveform signal # 1, which has been taken into the buffer by the time the pulse P # 1 appears, at the time t12'when the pulse P # 1 appears. Corresponds to the position information indicating the scanning position of. In this case, the amount of deviation between the timing at which the acquisition of the waveform signal # 1 is completed and the timing at which the position information is associated with the waveform signal # 1 is zero.

After that, during the period from time t21'to time t22', the time waveform capture signal becomes high level, so that the data processing unit 153 is the lock-in detection unit during the period from time t21'to time t22'. The waveform signal # 2 which is the detection result of 152 is taken into the buffer. The uptake of the waveform signal # 2 into the buffer is completed at time t22'. On the other hand, the pulse P # 2 appears in the image data storage signal at a time t22 ″ earlier than the time t22 ″. However, at the time t22 ″, the uptake of the waveform signal # 2 into the buffer is not completed, and the association with the position information of the waveform signal # 1 is completed. Therefore, the data processing unit 153 cannot associate the waveform signal with the position information even when the pulse P # 2 appears. On the other hand, the pulse P # 3 appears in the image data storage signal at a time t32 ″ later than the time t22 ″. Therefore, the data processing unit 153 measures the latest waveform signal # 2, which has been taken into the buffer by the time the pulse P # 3 appears, at the time t32'' when the pulse P # 3 appears. Corresponds to the position information indicating the scanning position of 10. In this case, the amount of deviation between the timing at which the acquisition of the waveform signal # 2 is completed and the timing at which the position information is associated with the waveform signal # 2 is the amount of deviation # 2 (= time t32''-time t22'≠ 0. ).

After that, during the period from time t31'to time t32', the time waveform capture signal becomes high level, so that the data processing unit 153 is the lock-in detection unit during the period from time t31'to time t32'. The waveform signal # 3, which is the detection result of 152, is taken into the buffer. The uptake of the waveform signal # 3 into the buffer is completed at time t32'. On the other hand, the pulse P # 4 appears in the image data storage signal at the time t42 ″, which is later than the time t32 ″. Therefore, the data processing unit 153 measures the latest waveform signal # 3, which has been taken into the buffer by the time the pulse P # 4 appears, at the time t42'' when the pulse P # 4 appears. Corresponds to the position information indicating the scanning position of 10. In this case, the amount of deviation between the timing at which the acquisition of the waveform signal # 3 is completed and the timing at which the position information is associated with the waveform signal # 3 is the amount of deviation # 3 (= time t42''-time t32'≠ 0. ≠ deviation amount # 2).

When the time waveform acquisition signal and the image data storage signal are not synchronized in this way, the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal is large. , Will fluctuate over time. In this case, the data processing unit 153 associates the captured waveform signal with the position information and saves the waveform signal associated with the position information. You have to wait. Alternatively, the data processing unit 153 has reached the timing of associating the waveform signal with the position information, but the acquisition of the waveform signal to which the position information should be associated has not been completed at that timing, so that the measurement object 10 It becomes necessary to temporarily stop the movement of. As a result, when the time waveform acquisition signal and the image data storage signal are not synchronized, the measurement efficiency by the terahertz wave measuring device 100 may be relatively deteriorated.

However, in this embodiment, the time waveform acquisition signal and the image data storage signal are synchronized. Therefore, the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal hardly or completely fluctuates with the passage of time. Therefore, deterioration of measurement efficiency by the terahertz wave measuring device 100, which may occur when the time waveform acquisition signal and the image data storage signal are not synchronized, is preferably prevented. Typically, the terahertz wave measuring device 100 captures the waveform signal, associates the waveform signal with the position information, and stores the waveform signal associated with the position information while the measurement object 10 keeps moving. It can be carried out. Therefore, the measurement efficiency by the terahertz wave measuring device 100 is relatively improved.

Further, if the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal is fixed regardless of the passage of time, the following technical effects can be further obtained. .. Specifically, when the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal fluctuates with the passage of time, measurements are taken at a plurality of locations of the measurement target 10. The accuracy of the measurement result obtained from the terahertz wave THz waveform may deteriorate. This is because when the measurement position where the terahertz wave THz is measured during the period when the time waveform acquisition signal is active and the waveform signal which is the detection result of the terahertz wave measured at the measurement position are saved in the memory. This is because the amount of deviation from the scanning position indicated by the position information associated with the waveform signal may fluctuate each time measurement is performed. However, in this embodiment, the amount of deviation between the timing at which the acquisition of the waveform signal is completed and the timing at which the position information is associated with the waveform signal is fixed regardless of the passage of time. Therefore, when the measurement position where the terahertz wave THz is measured during the period when the time waveform acquisition signal is active and the waveform signal which is the detection result of the terahertz wave measured at the measurement position are saved in the memory, the corresponding The amount of deviation from the scanning position indicated by the position information associated with the waveform signal hardly or not fluctuates each time measurement is performed. As a result, the accuracy of the measurement result obtained from the waveform of the terahertz wave THz irradiated to a plurality of places of the measurement object 10 is hardly or not deteriorated. Typically, the terahertz wave measuring device 100 can acquire a three-dimensional cross-sectional image of the measurement object 10 with high accuracy.

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.

10 Object to be measured 100 Terahertz wave measuring device 101 Pulse laser device 110 Terahertz wave generating element 121 Retroreflector 122 Rotating board 124 Rotary encoder 124a Slit 130 Terahertz wave detecting element 150 Control unit 152 Lock-in detection unit 153 Data processing unit 154 Timing generation 155 Optical delay mechanism drive 156 Scanning mechanism drive LB1 Pump light LB2 Probe light THz terahertz wave

Claims (9)

A terahertz wave is generated by irradiating the laser beam, and a generating means for irradiating the generated terahertz wave to the measurement object,
A detection means for detecting the terahertz wave irradiated to the measurement object by irradiating the laser beam, and
An adjusting means capable of adjusting the optical path length of the laser light irradiated to at least one of the generating means and the detecting means by reflecting the laser light.
At least one of the generating means, the detecting means, and the measuring object so that at least one of the terahertz wave irradiation position and the detecting position of the measuring object moves along the surface of the measuring object. A means of transportation that allows you to move one
The adjustment timing in which the optical path length is adjusted to a predetermined length during the adjustment period in which the adjustment means reflects the laser beam to adjust the optical path length, and the moving means is the generating means, the detecting means, and the detection means. Control to control at least one of the adjusting means and the moving means so as to synchronize with the moving timing of moving at least one of the measurement objects to the current measurement position separated by a certain amount from the previous measurement position. Means and
A terahertz wave measuring device characterized by being equipped with. The adjusting means includes at least a first reflecting means capable of reflecting the laser light and a second reflecting means capable of reflecting the laser light.
The control means has the optical path length during the first adjustment period in which the adjustment timing and the movement timing are synchronized so that the first reflecting means reflects the laser beam to adjust the optical path length. The first adjustment timing in which is adjusted to the predetermined length, and the first measurement position in which the moving means separates at least one of the generation means, the detection means, and the measurement object from the previous measurement position by the fixed amount. The optical path length is adjusted to the predetermined length during the second adjustment period in which the optical path length is adjusted by reflecting the laser beam by the time difference from the first movement timing to be moved to. The time difference between the second adjustment timing and the second movement timing for moving at least one of the generating means, the detecting means, and the measurement object to the second measurement position separated from the first measurement position by the fixed amount. The terahertz wave measuring apparatus according to claim 1, wherein at least one of the adjusting means and the moving means is controlled so as to match the above. The adjusting means adjusts the optical path length in an adjusting mode determined based on the first reference signal.
The moving means moves at least one of the generating means, the detecting means, and the measuring object in a moving mode determined based on the second reference signal.
Claim 1 or the control means is characterized in that at least one of the first reference signal and the second reference signal is generated so that the adjustment timing and the movement timing during the adjustment period are synchronized with each other. 2. The terahertz wave measuring device according to 2. 3. The control means is characterized in that the first reference signal and the second reference signal that are identical to each other are generated so that the adjustment timing and the movement timing during the adjustment period are synchronized with each other. The terahertz wave measuring device described in. The control means generates the first reference signal so that the adjusting means adjusts the optical path length in a desired adjustment mode.
3. The control means according to claim 3, wherein the control means generates the second reference signal based on the first reference signal so that the adjustment timing and the movement timing during the adjustment period are synchronized with each other. Terahertz wave measuring device. The control means generates the second reference signal so that the moving means moves at least one of the generating means, the detecting means, and the measuring object in a desired moving mode.
The third aspect of claim 3, wherein the control means generates the first reference signal based on the second reference signal so that the adjustment timing and the movement timing during the adjustment period are synchronized with each other. Terahertz wave measuring device. The adjusting means includes m (where m is an integer of 1 or more) reflecting means capable of reflecting the laser beam, and rotating means for rotationally driving the m reflecting means.
The first reference signal is a pulse signal in which a first pulse having a period of Tr appears repeatedly n times (where n is an integer of 1 or more) during one rotation of the rotating means.
The second reference signal is a pulse signal in which a second pulse having a period of Ts appears repeatedly.
The adjustment period is a period in which the adjustment timing during the adjustment period arrives every time n / m of the first pulse appears.
The movement timing is a timing that arrives every time k of the second pulses appear.
The control means satisfies the conditional expression Tr × (n / m) = A × Ts × k or Tr × (n / m) = (1 / A) × Ts × k (where A is a natural number). The terahertz wave measuring apparatus according to any one of claims 3 to 6, wherein at least one of the first reference signal and the second reference signal is generated. With the arrival of the movement timing as a trigger, the detection result of the terahertz wave by the detection means during the adjustment period, which arrives at a constant cycle in synchronization with the movement timing, is set as the measurement position corresponding to the arrival movement timing. The terahertz wave measuring apparatus according to any one of claims 1 to 7, further comprising a storage means for storing in association with each other. The moving means can continuously move at least one of the generating means, the detecting means, and the measuring object.
The control means synchronizes the adjustment timing and the movement timing during the adjustment period during a period in which at least one of the generation means, the detection means, and the measurement object is continuously moving. The terahertz wave measuring apparatus according to any one of claims 1 to 8, wherein at least one of the adjusting means and the moving means is controlled.

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