JP2017075923A - Measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement device that can suppress increase of the size while detecting a terahertz wave applied to a sample efficiently.SOLUTION: A measurement device 1 includes: a single photoconductive element 110, which emits a terahertz wave THz1, polarizing in a first direction, to a sample 10 and detects a terahertz wave THz2, reflected from the sample to polarize in a second direction, to the sample; and a measurement part 150, which measures the characteristics of the sample based on the result of detecting the terahertz wave. The accuracy of detecting the terahertz wave THz2, which polarizes in the second direction, is higher than the accuracy of detecting the terahertz wave THz1, which polarizes in the first direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technical field of a measuring apparatus that measures a characteristic of a sample using an electromagnetic wave such as a terahertz wave.

  A terahertz wave measuring device is known as a measuring device for measuring the characteristics of a sample. The terahertz wave measuring apparatus measures the characteristics of the sample in the following procedure. First, the terahertz wave generating element emits terahertz waves. The terahertz wave emitted from the terahertz wave generating element is irradiated to the sample. The terahertz wave irradiated on the sample is reflected by the sample. The terahertz wave reflected by the sample is detected by the terahertz wave detecting element. The terahertz wave measuring apparatus measures the characteristics of the sample by analyzing the detected terahertz wave (that is, a terahertz wave in the time domain and a current signal).

  The optical path of the terahertz wave irradiated to the sample (hereinafter referred to as “outward path”) may overlap with the optical path of the terahertz wave reflected by the sample (hereinafter referred to as “return path”). For example, when the terahertz wave is irradiated perpendicularly to the surface of the sample, there is a high possibility that the forward path and the backward path overlap. When the forward path and the return path overlap, the terahertz wave emitted from the terahertz wave generating element returns to the terahertz wave generating element instead of the terahertz wave detecting element. For this reason, it is preferable that the terahertz wave measuring apparatus separates the terahertz wave propagating in the forward path and the terahertz wave propagating in the backward path (that is, separating the forward path and the backward path).

  Patent Documents 1 and 2 describe an example of a terahertz wave measuring apparatus that separates a terahertz wave propagating in the forward path and a terahertz wave propagating in the return path.

  In Patent Document 1, a terahertz wave emitted from a terahertz wave generating element is reflected toward a sample, and a half mirror that transmits the terahertz wave reflected by the sample toward the terahertz wave detecting element is used to propagate the forward path. A terahertz wave measuring device that separates a terahertz wave that propagates and a terahertz wave that propagates in the return path is described.

  Patent Document 2 describes a terahertz wave measuring apparatus that separates a terahertz wave propagating in the forward path and a terahertz wave propagating in the return path by using a polarizing beam splitter, a Fresnel ROM prism, and a parabolic mirror. Yes. Specifically, the polarization beam splitter transmits only the P-polarized component of the terahertz wave emitted from the terahertz wave generating element toward the sample. The terahertz wave that has passed through the polarizing beam splitter is reflected by the sample after passing through the Fresnel ROM prism. The terahertz wave reflected by the sample passes through the Fresnel ROM prism again and then reaches the polarizing beam prism. The terahertz wave that reaches the polarizing beam prism is converted into S-polarized light by transmission through the Fresnel ROM prism and reflection from the sample. For this reason, the polarization beam splitter reflects the terahertz wave reflected by the sample toward the terahertz wave detection element.

JP 2014-2024 A JP 2009-300108 A

  In the terahertz wave measuring apparatus described in Patent Document 1, when the terahertz wave emitted from the terahertz wave generating element is reflected toward the sample, the intensity of the terahertz wave is reduced (for example, reduced to about 50%). . Further, when the half mirror transmits the terahertz wave reflected by the sample toward the terahertz wave detecting element, the intensity of the terahertz wave is reduced (for example, reduced to about 50%). For this reason, due to the decrease in the intensity of the terahertz wave that reaches the terahertz wave detection element, the detection efficiency of the terahertz wave by the terahertz wave detection element may deteriorate.

  In the terahertz wave measuring apparatus described in Patent Document 2, the number of optical elements necessary for separating the terahertz wave propagating in the forward path and the terahertz wave propagating in the return path is relatively large. For this reason, the size of the terahertz wave measuring apparatus becomes large.

  Examples of problems to be solved by the present invention include the above. It is an object of the present invention to provide a measuring device that can suppress an increase in size while efficiently detecting a terahertz wave irradiated on a sample.

  The first example of the measuring apparatus of the present invention emits a terahertz wave polarized in a first direction toward a sample, is reflected by the sample, and is polarized in a second direction different from the first direction. A single photoconductive element that detects the terahertz wave, and a measurement unit that measures the characteristics of the sample based on the detection result of the terahertz wave, and is polarized in the second direction by the photoconductive element The detection sensitivity of the terahertz wave is higher than the detection sensitivity of the terahertz wave polarized in the first direction.

FIG. 1 is a block diagram showing the configuration of the terahertz wave measuring apparatus according to the first embodiment. FIG. 2 is a perspective view showing the configuration of the photoconductive element. FIG. 3 is a timing chart showing an example of timing at which the photoconductive element emits terahertz waves and detects terahertz waves. FIG. 4 is a timing chart showing an example of timing at which the photoconductive element emits a terahertz wave and detects the terahertz wave, along with an example of timing at which a bias voltage is applied to the photoconductive element. FIG. 5 is a timing chart showing an example of timing for applying a bias voltage, which is an alternating voltage, to the photoconductive element. FIG. 6 is a block diagram showing the configuration of the terahertz wave measuring apparatus according to the third embodiment. FIG. 7 is a timing chart showing an example of timing at which the photoconductive element emits terahertz waves and detects terahertz waves.

  Hereinafter, an explanation will be given on embodiments of the measuring apparatus.

<1>
The measurement apparatus of the present embodiment emits a terahertz wave polarized in a first direction toward the sample, is reflected by the sample, and is polarized in a second direction different from the first direction. A single photoconductive element that detects the terahertz wave, and a measurement unit that measures the characteristics of the sample based on the detection result of the terahertz wave, and the terahertz wave polarized in the second direction by the photoconductive element The detection sensitivity is higher than the detection sensitivity of the terahertz wave polarized in the first direction.

  According to the measurement apparatus of this embodiment, the photoconductive element that emits the terahertz wave toward the sample and the photoconductive element that detects the terahertz wave reflected by the sample may not be provided separately. For this reason, the measuring apparatus of this embodiment does not need to separate the terahertz wave propagating in the forward path and the terahertz wave propagating in the return path from the first. For this reason, the measuring device of this embodiment can suppress the increase in the size, while efficiently detecting the terahertz wave irradiated to the sample.

  Furthermore, since the polarization direction of the terahertz wave emitted from the photoconductive element (that is, the vibration direction of the electric field constituting the terahertz wave) and the polarization direction of the terahertz wave detected by the photoconductive element are different, a single photoconductive element is used. Can detect the terahertz wave while emitting the terahertz wave.

  Furthermore, the detection sensitivity of the terahertz wave polarized in the second direction is higher than the detection sensitivity of the terahertz wave polarized in the first direction. Therefore, the terahertz wave polarized in the first direction, which is not reflected by the sample yet emitted from the photoconductive element, is converted into the terahertz wave polarized in the second direction reflected by the sample. The possibility of erroneous detection is relatively reduced. For this reason, the photoconductive element can detect the terahertz wave while emitting the terahertz wave.

<2>
In another aspect of the photoconductive element of the present embodiment, the photoconductive element emits the terahertz wave polarized in the first direction and has a pair of first electrodes with a gap secured therebetween, A terahertz wave polarized in the second direction, and a pair of second electrode portions in which the gap secured between the pair of first electrodes is secured.

  According to this aspect, the photoconductive element emits the terahertz wave polarized in the first direction using the pair of first electrodes and is polarized in the second direction using the pair of second electrodes. Terahertz waves can be detected.

<3>
As described above, in another aspect of the measuring device in which the photoconductive element includes a pair of first electrodes and a pair of second electrodes, each of the pair of first electrodes extends along a third direction corresponding to the first direction. Each of the pair of second electrodes has a longitudinal shape that is different from the third direction and extends in a fourth direction corresponding to the second direction.

  According to this aspect, the detection sensitivity of the terahertz wave polarized in the second direction is higher than the detection sensitivity of the terahertz wave polarized in the first direction.

<4>
As described above, in another aspect of the measurement apparatus in which the photoconductive element includes the pair of first electrodes and the pair of second electrodes, the first optical element that branches the predetermined excitation light into the first excitation light and the second excitation light. And the second optical element that adjusts the optical path length of the second excitation light, and the first excitation light and the second excitation light that is adjusted in the optical path length propagate in the same optical path. A third optical element that guides the first excitation light and the second excitation light with the adjusted optical path length to the photoconductive element; and the first excitation light and the second excitation guided by the third optical element. Each of the lights is applied to the gap.

  According to this aspect, even when the gap between the pair of first electrodes is also used as the gap between the pair of second electrodes, the photoconductive element emits a terahertz wave polarized in the first direction. In addition, the terahertz wave polarized in the second direction can be detected.

<5>
As described above, in another aspect of the measuring apparatus in which the photoconductive element includes a pair of first electrodes and a pair of second electrodes, the photoconductive element includes: (i) a first excitation light irradiated to the gap; The terahertz wave polarized in the first direction is emitted during one period, and (ii) the second excitation light is polarized in the second direction during the second period when the gap is irradiated to the gap. The terahertz wave is detected, and a bias voltage for emitting the terahertz wave is applied to the pair of first electrodes during the first period, while the pair of first terahertz waves is applied during the second period. An application unit that does not apply the bias voltage to one electrode is further provided.

  According to this aspect, since the bias voltage is applied to the pair of first electrodes during the first period in which the terahertz wave is to be emitted, the photoconductive element is polarized in the first direction during the first period. Terahertz waves can be emitted. Since the bias voltage is not applied to the pair of first electrodes during the second period in which the terahertz wave is to be detected (that is, the second period in which it is preferable not to emit the terahertz wave), the photoconductive element is in the second period. In addition, no terahertz wave polarized in the first direction is emitted. Therefore, the photoconductive element can detect the terahertz wave polarized in the second direction while emitting the terahertz wave polarized in the first direction.

<6>
In another aspect of the measurement apparatus of the present embodiment, the photoconductive element emits the terahertz wave that is the first linearly polarized light that is polarized in the first direction, and is polarized in the second direction. Detecting the terahertz wave being the second linearly polarized light, converting the terahertz wave being the first linearly polarized light propagating from the photoconductive element toward the sample into the circularly polarized terahertz wave, A fourth optical element that converts the circularly polarized terahertz wave propagating from the light toward the photoconductive element into the terahertz wave that is the second linearly polarized light that is polarized in the second direction.

  According to this aspect, the terahertz wave that is the first linearly polarized light emitted from the photoconductive element passes through the fourth optical element and is reflected by the sample, whereby the photoconductive element is converted into the terahertz wave that is the second linearly polarized light. Come back to. Therefore, the photoconductive element can detect the terahertz wave polarized in the second direction while emitting the terahertz wave polarized in the first direction.

  The operation and other gains of the measurement apparatus according to the present embodiment will be described in more detail in the following examples.

  As described above, the measuring apparatus according to the present embodiment emits a terahertz wave polarized in the first direction and detects a single photoconductive element that detects the terahertz wave polarized in the second direction. Is provided. Therefore, a measuring apparatus capable of suppressing an increase in size while efficiently detecting a terahertz wave irradiated on a sample is provided.

  Hereinafter, embodiments of the measuring apparatus will be described with reference to the drawings. In particular, the following description will be given using the terahertz wave measuring apparatus 1 which is a specific example of “measuring apparatus”.

(1) Terahertz wave measuring apparatus 1 of the first embodiment
First, the terahertz wave measuring apparatus 1 according to the first embodiment will be described with reference to FIGS. 1 to 3.

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

  As shown in FIG. 1, the terahertz wave measuring apparatus 1 irradiates the sample 10 with the terahertz wave THz, and transmits the sample 10 or reflects the terahertz wave THz reflected by the sample 10 (that is, the terahertz wave irradiated on the sample 10). THz) is detected. In the example shown in FIG. 1, the terahertz wave measuring apparatus 1 detects the terahertz wave THz reflected by the sample 10.

The terahertz wave THz is an electromagnetic wave including an electromagnetic wave component belonging to a frequency region (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). The terahertz region is a frequency region that combines light straightness and electromagnetic wave transparency. The terahertz region is a frequency region in which various substances have unique absorption spectra. Therefore, the terahertz wave measuring apparatus 1 can measure the characteristics of the sample 10 by analyzing the terahertz wave THz irradiated on the sample 10.

  Here, since the period of the terahertz wave THz is a period of the order of sub-picoseconds, it is technically difficult to directly detect the waveform of the terahertz wave THz. Therefore, the terahertz wave measuring apparatus 1 indirectly detects the waveform of the terahertz wave THz by employing a pump-probe method based on time delay scanning. Hereinafter, the terahertz wave measuring apparatus 1 that employs such a pump-probe method will be described more specifically.

  As shown in FIG. 1, the terahertz wave measuring apparatus 1 includes a pulse laser apparatus 1, a photoconductive element 110, a half-wave plate 161, and a polarization beam splitter 162 that is a specific example of “first optical element”. A polarization beam splitter 163 that is a specific example of “third optical element”, a right-angle prism 170 that is a specific example of “fourth optical element”, and an optical that is a specific example of “second optical element”. The delay mechanism 120 includes a bias voltage generation unit 141, which is a specific example of the “application unit”, an IV (current-voltage) conversion unit 142, and a control unit 150.

  The pulse laser device 1 generates pulse laser light LB in the order of subpicosecond or femtosecond having a light intensity corresponding to the drive current input to the pulse laser device 1. The pulse laser beam LB generated by the pulse laser device 1 is incident on the polarization beam splitter 162 via a light guide (not shown) (for example, an optical fiber) and a half-wave plate 161. The pulse laser beam LB is a specific example of “predetermined excitation light”.

  The polarization beam splitter 162 branches the pulsed laser light LB into pump light LB1 which is a specific example of “first excitation light” and probe light LB2 which is a specific example of “second excitation light”. Specifically, the polarization beam splitter 162 transmits the first polarization component (for example, the polarization component having an electric field component oscillating along the third direction) of the pulsed laser light LB as the pump light LB1. On the other hand, the polarization beam splitter 162 uses the second polarization component (for example, a polarization component having an electric field component oscillating along a fourth direction different from the third direction) in the pulsed laser light LB as the probe light LB2. reflect. The pump light LB1 is incident on the polarization beam splitter 163. On the other hand, the probe light LB2 is incident on the polarization beam splitter 163 via a light guide path and an optical delay mechanism 120 (not shown).

  The ratio between the intensity of the pump light LB1 and the intensity of the probe light LB2 is determined depending on the half-wave plate 161 described above. More specifically, the ratio between the intensity of the pump light LB1 and the intensity of the probe light LB2 is determined by the azimuth angle of the polarization plane of the pulse laser light LB (that is, the vibration direction of the electric field constituting the pulse laser light LB) 1 / It depends on the amount of deviation of the two-wave plate 161 from the high-speed axis.

  Similar to the polarization beam splitter 162, the polarization beam splitter 163 transmits the pump light LB1 that is the first polarization component. Similarly to the polarization beam splitter 162, the polarization beam splitter 163 reflects the probe light LB2 that is the second polarization component. In particular, the polarization beam splitter 163 reflects the probe light LB2 so that the pump light LB1 and the probe light LB2 propagate on the same optical path. Each of the pump light LB1 transmitted by the polarization beam splitter 163 and the probe light LB2 reflected by the polarization beam splitter 163 propagates the same light and then enters the photoconductive element 110.

  The photoconductive element 110 emits a terahertz wave THz (hereinafter, the terahertz wave THz emitted from the photoconductive element 110 is referred to as “terahertz wave THz1”) by using the pump light LB1 as excitation light. At this time, as will be described in detail later, the photoconductive element 110 generates a terahertz wave THz1, which is linearly polarized light having an electric field component that vibrates along the first direction.

  The terahertz wave THz1 emitted from the photoconductive element 110 enters the right-angle prism 170. The right-angle prism 170 includes a first surface 171, a second surface 172, and a third surface 173. The first surface 171 is an optical surface on which the terahertz wave THz1 emitted from the photoconductive element 110 is incident. The second surface 172 is an optical surface that reflects the terahertz wave THz1 that has propagated into the right-angle prism 170 via the first surface 171. The third surface 173 is an optical surface that intersects the first surface 171 at an angle of 90 ° and emits the terahertz wave THz1 reflected by the second surface 172.

  The terahertz wave THz1 emitted from the photoconductive element 110 is reflected (typically total reflection) by the second surface 172 of the right-angle prism 170 and propagates toward the sample 10. Due to the reflection of the terahertz wave THz1 on the second surface 172, the phase of the terahertz wave THz1 reflected by the second surface 172 is compared with the phase of the terahertz wave THz1 not reflected by the second surface 172, Shift by π / 2. Therefore, the terahertz wave THz1 is incident on the second surface 172 at an incident angle at which the phase of the terahertz wave THz1 is shifted by π / 2 due to the reflection of the terahertz wave THz1 on the second surface 172. For example, when the right-angle prism 170 is made of silicon having a refractive index of 3.4, the terahertz wave THz1 is incident on the second surface 172 at an incident angle of 41.9 degrees. As a result, due to the reflection of the terahertz wave THz1 on the second surface 172, the terahertz wave THz1 that is linearly polarized light is converted into the terahertz wave THz1 that is circularly polarized light (for example, clockwise circularly polarized light). That is, the right-angle prism 170 functions as a quarter wavelength plate with respect to the terahertz wave THz1. The terahertz wave THz1 reflected by the second surface 172 propagates toward the outside of the right-angle prism 170 via the third surface 173. As a result, the terahertz wave THz1 reflected by the second surface 172 is applied to the sample 10.

  The terahertz wave THz1 irradiated on the sample 10 is reflected by the sample 10. Hereinafter, the terahertz wave THz propagating from the sample 10 toward the photoconductive element 110 is distinguished from the terahertz wave THz1 emitted from the photoconductive element 110 (that is, the terahertz wave THz propagating from the photoconductive element 110 toward the sample). Therefore, it is referred to as “terahertz wave THz2”.

  The terahertz wave THz2 reflected by the sample 10 is circularly polarized light. However, due to the reflection of the terahertz wave THz1 on the sample 10, the rotation direction of the polarization plane of the terahertz wave THz2 is opposite to the rotation direction of the polarization plane of the terahertz wave THz1.

  The terahertz wave THz2 reflected by the sample 10 is incident on the right-angle prism 170 (particularly, the third surface 173) again. The terahertz wave THz 2 incident on the third surface 173 is reflected by the second surface 172. Due to the reflection of the terahertz wave THz2 on the second surface 172, the phase of the terahertz wave THz2 reflected by the second surface 172 is compared with the phase of the terahertz wave THz2 not reflected by the second surface 172, Shift by π / 2. As a result, due to the reflection of the terahertz wave THz2 on the second surface 172, the terahertz wave THz1 that was circularly polarized light is linearly polarized light having an electric field component that vibrates along a second direction orthogonal to the first direction. It is converted into a certain terahertz wave THz2. That is, the right-angle prism 170 functions as a quarter-wave plate for the terahertz wave THz2. The terahertz wave THz2 reflected by the second surface 172 propagates toward the outside of the right-angle prism 170 via the first surface 171. As a result, the terahertz wave THz <b> 2 reflected by the second surface 172 enters the photoconductive element 110.

  When the terahertz wave THz2 is incident on the photoconductive element 110, the photoconductive element 110 detects the terahertz wave THz2 by using the probe light LB2 as excitation light. In particular, as described above, the vibration direction of the electric field component of the terahertz wave THz2 that is linearly polarized light is orthogonal to the vibration direction of the electric field component of the terahertz wave THz1 that is linearly polarized light. Therefore, the photoconductive element 110 detects the terahertz wave THz2, which is linearly polarized light having an electric field component that vibrates along the second direction. As a result, the photoconductive element 110 outputs a current signal having a signal intensity corresponding to the intensity of the terahertz wave THz2.

  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 by adjusting the optical path length of the probe light LB2. When the optical path length difference is adjusted, the timing at which the pump light LB1 enters the photoconductive element 110 (or the timing at which the photoconductive element 110 generates the terahertz wave THz1), and the probe light LB2 enters the photoconductive element 110. The time difference from the timing (or the timing at which the photoconductive element 110 detects the terahertz wave THz2) is adjusted. The terahertz wave measuring apparatus 1 indirectly detects the waveform of the terahertz wave THz2 by adjusting this time difference. For example, when the optical path of the probe light LB2 is increased by 0.3 millimeter (however, the optical path length in the air) by the optical delay mechanism 120, the timing at which the probe light LB2 enters the photoconductive element 110 is delayed by 1 picosecond. . In this case, the timing at which the photoconductive element 110 detects the terahertz wave THz is delayed by 1 picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the photoconductive element 110 at intervals of about several tens of MHz, the timing at which the photoconductive element 110 detects the terahertz wave THz is gradually shifted. The photoconductive element 110 can indirectly detect the waveform of the terahertz wave THz. That is, the lock-in detector 151 described later can detect the waveform of the terahertz wave THz based on the detection result of the photoconductive element 110.

  The current signal output from the photoconductive element 110 is converted into a voltage signal by the IV conversion unit 142.

  The control unit 150 measures the characteristics of the sample 10 based on the detection result of the photoconductive element 110 (that is, the voltage signal output from the IV conversion unit 142). In order to measure the characteristics of the sample 10, the control unit 150 includes a lock-in detection unit 151 and a signal processing unit 152.

  The lock-in detection unit 151 performs synchronous detection on the voltage signal output from the IV conversion unit 142 using the bias voltage generated by the bias voltage generation unit 141 as a reference signal. As a result, the lock-in detection unit 151 detects the sample value of the terahertz wave THz2. Thereafter, the same operation is repeated while appropriately adjusting 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. The waveform (time waveform) of the terahertz wave THz2 detected by the element 110 can be detected. The lock-in detection unit 151 outputs a waveform signal indicating the waveform of the terahertz wave THz2 detected by the photoconductive element 110.

  The signal processing unit 152 measures the characteristics of the sample 10 based on the waveform signal output from the lock-in detection unit 151. For example, the signal processing unit 152 acquires the frequency spectrum of the terahertz wave THz2 using terahertz time domain spectroscopy, and measures the characteristics of the sample 10 based on the frequency spectrum.

(1-2) Configuration of Photoconductive Element 110 Next, the configuration of the photoconductive element 110 will be described with reference to FIG. FIG. 2 is a perspective view showing the configuration of the photoconductive element 110. In FIG. 2, the photoconductive element 110 will be described using a three-dimensional coordinate space defined by an X axis, a Y axis, and a Z axis orthogonal to each other.

  As shown in FIG. 2, the photoconductive element 110 includes a substrate 111, an antenna (in other words, a transmission line or an electrode, which is the same hereinafter) 112 as a specific example of “first electrode”, and a “first electrode”. An antenna 113 which is a specific example, an antenna 114 which is a specific example of “second electrode”, and an antenna 115 which is a specific example of “second electrode” are provided.

  The substrate 111 is, for example, a semiconductor substrate parallel to the XY plane. The substrate 111 may be an InP (indium phosphide) substrate, a GaAs (gallium arsenide) substrate, a Si (silicon) substrate, or the like. The shape of the substrate 111 is a plate shape, but may be other shapes.

  The antenna 112 includes a first antenna portion 112-1 and a second antenna portion 112-2 that are physically integrated or electrically connected. The first antenna portion 112-1 has a longitudinal shape extending along the Y-axis direction. The second antenna portion 112-2 has a longitudinal shape extending along the X-axis direction. The first antenna portion 112-1 extends in the −Y-axis direction from the end on the + X-axis side of the second antenna portion 112-2 as a starting point. The second antenna portion 112-2 extends in the −X-axis direction starting from the end on the + Y-axis side of the first antenna portion 112-1. A bias voltage is applied to the end of the second antenna portion 112-2 on the −X axis side.

  The antenna 113 includes a first antenna portion 113-1 and a second antenna portion 113-2 that are physically integrated or electrically connected. The first antenna portion 113-1 has a longitudinal shape extending along the Y-axis direction. The second antenna portion 113-2 has a longitudinal shape extending along the X-axis direction. The first antenna portion 113-1 extends in the + Y-axis direction starting from the end portion on the −X-axis side of the second antenna portion 113-2. The second antenna portion 113-2 extends in the + X-axis direction starting from the end portion on the −Y-axis side of the first antenna portion 113-1. A bias voltage is applied to the end of the second antenna portion 113-2 on the + X axis side.

  The antenna 114 includes a first antenna portion 114-1 and a second antenna portion 114-2 that are physically integrated or electrically connected. The first antenna portion 114-1 has a longitudinal shape extending along the X-axis direction. The second antenna portion 114-2 has a longitudinal shape extending along the Y-axis direction. The first antenna portion 114-1 extends in the + X-axis direction starting from the end on the + Y-axis side of the second antenna portion 114-2. The second antenna portion 114-2 extends in the −Y-axis direction starting from the −X-axis side end of the first antenna portion 114-1.

  The antenna 115 includes a first antenna portion 115-1 and a second antenna portion 115-2 that are physically integrated or electrically connected. The first antenna portion 115-1 has a longitudinal shape extending along the X-axis direction. The second antenna portion 115-2 has a longitudinal shape extending along the Y-axis direction. The first antenna portion 115-1 extends in the −X-axis direction starting from the end portion on the −Y-axis side of the second antenna portion 115-2. The second antenna portion 115-2 extends in the + Y-axis direction starting from the end on the + X-axis side of the first antenna portion 115-1.

  The first antenna portions 112-1 and 113-1 are arranged along the Y-axis direction. A gap (that is, a gap) 116 of about several micrometers is formed between the −Y-axis side end of the first antenna portion 112-1 and the + Y-axis side end of the first antenna portion 113-1. Secured. The first antenna portions 112-1 and 113-1 constitute a pair of antennas.

  The first antenna portions 114-1 and 115-1 are arranged along the X-axis direction. A gap 116 is secured between the end on the + X-axis side of the first antenna portion 114-1 and the end on the −X-axis side of the first antenna portion 115-1. That is, the gap 116 between the first antenna portion 112-1 and the first antenna portion 113-1 is also used as the gap 116 between the first antenna portion 114-1 and the first antenna portion 115-1. . The first antenna portions 114-1 and 115-1 constitute a pair of antennas.

  The photoconductive element 110 mainly uses the antennas 112 and 113 to emit the terahertz wave THz1. In this case, the photoconductive element 110 uses the antennas 112 and 113 (particularly, the first antenna portions 112-1 and 113-1) as one dipole antenna in order to emit the terahertz wave THz1. Specifically, a bias voltage output from the bias voltage generation unit 141 is applied to the gap 116 via the antennas 112 and 113. When the pump light LB1 is irradiated to the gap 116 in a state where an effective bias voltage (for example, a bias voltage other than 0 V) is applied to the gap 116, carriers are generated in the photoconductive element 110 by light excitation by the pump light LB1. To do. As a result, the photoconductive element 110 generates a pulsed current signal in the order of subpicoseconds or in the order of femtoseconds corresponding to the generated carriers. As a result, the terahertz wave THz1 resulting from the pulsed current signal is generated in the photoconductive element 110.

  In particular, since the first antenna portions 112-1 and 113-1 are used as dipole antennas extending along the Y-axis direction, the photoconductive element 110 has a first direction corresponding to the Y-axis direction (typically, A terahertz wave THz1 which is linearly polarized light having an electric field component oscillating along the Y-axis direction is emitted. On the other hand, the photoconductive element 110 is a terahertz wave THz1 that is linearly polarized light having an electric field component that vibrates along a second direction (typically, the X-axis direction) corresponding to the X-axis direction orthogonal to the Y-axis direction. Little or no light. Alternatively, the proportion of the terahertz wave THz1 that is linearly polarized light having an electric field component oscillating along the second direction (typically the X-axis direction) is relative to the terahertz wave THz1 emitted from the photoconductive element 110. Or very small.

  On the other hand, the photoconductive element 110 mainly uses the antennas 114 and 115 to detect the terahertz wave THz2. In this case, the photoconductive element 110 uses the antennas 114 and 115 (particularly, the first antenna portions 114-1 and 115-1) as one dipole antenna in order to detect the terahertz wave THz2. Specifically, when the probe light LB2 is irradiated to the gap 116, carriers are generated in the photoconductive element 110 by light excitation by the probe light LB2. As a result, a current signal corresponding to the carrier flows through the antennas 114 and 115 (particularly, the first antenna portions 114-1 and 115-1). When the photoconductive element 110 is irradiated with the terahertz wave THz2 while the probe light LB2 is irradiated to the gap 116, the signal intensity of the current signal flowing through the antennas 114 and 115 changes according to the light intensity of the terahertz wave THz2. To do. A current signal whose signal intensity changes according to the light intensity of the terahertz wave THz2 is output to the IV conversion unit 142 via the antennas 114 and 115 (particularly, the second antenna portions 114-2 and 115-2). The

  In particular, since the first antenna portions 114-1 and 115-1 are used as dipole antennas extending along the X-axis direction, the photoconductive element 110 has a second direction corresponding to the X-axis direction (typically, A terahertz wave THz2 which is linearly polarized light having an electric field component oscillating along the (X-axis direction) is detected. On the other hand, the photoconductive element 110 is a terahertz wave THz1 that is linearly polarized light having an electric field component that vibrates along a first direction (typically, the Y-axis direction) corresponding to the Y-axis direction orthogonal to the X-axis direction. Is detected little or no. Therefore, the detection sensitivity of the terahertz wave THz2 by the photoconductive element 110 is higher than the detection sensitivity of the terahertz wave THz1 by the photoconductive element 110.

  The photoconductive element 111 shown in FIG. 2 is an example. Therefore, the terahertz wave detection device 1 has a structure that emits the terahertz wave THz1 and can detect the terahertz wave THz2 instead of the photoconductive element 111, and has another structure that is different from the structure shown in FIG. A conductive element may be provided. For example, the terahertz wave detection device 1 generates a pair of first antennas that can emit a terahertz wave THz1 having an electric field component that oscillates along a first direction and a terahertz wave THz2 that has an electric field component that oscillates along a second direction. Another photoconductive element including a pair of detectable second antennas may be provided.

  In another photoconductive element, the gap between the pair of first antennas and the gap between the pair of second antennas may be ensured separately and independently. In this case, the pump light LB1 and the probe light LB2 are applied to other gaps so that the gap between the pair of first antennas is irradiated with the pump light LB1 and the gap between the pair of second antennas is irradiated with the probe light LB2. It is preferable to adjust the optical system leading to the photoconductive element.

(1-3) Timing Chart Regarding Terahertz Wave THz Emission and Detection Subsequently, an example of timing at which the photoconductive element 110 emits the terahertz wave THz1 and detects the terahertz wave THz2 will be described with reference to FIG. FIG. 3 is a timing chart showing an example of timing at which the photoconductive element 110 emits the terahertz wave THz1 and detects the terahertz wave THz2.

  As shown in FIG. 3, it is assumed that the pulse laser device 1 emits the laser beam LB at time t31. In this case, the gap 116 of the photoconductive element 110 is irradiated with the pump light LB1 at time t32 later than time t31. As a result, the photoconductive element 110 emits the terahertz wave THz1 at time t32.

  On the other hand, the gap 116 of the photoconductive element 110 is irradiated with the probe light LB2 at time t33 later than time t31. As a result, the photoconductive element 110 detects the terahertz wave THz2 at time t33.

  However, the first timing at which the terahertz wave THz1 emitted from the photoconductive element 110 returns to the photoconductive element 110 as the terahertz wave THz2, and the second timing at which the probe light LB2 is applied to the gap 116 of the photoconductive element 110. Does not match or overlap, the photoconductive element 110 cannot detect the terahertz wave THz2 at time t33. For this reason, the measuring device 1 adjusts the time t33 in order to make the first timing coincide with or overlap the second timing. Here, the time difference between time t33 and time t32 is proportional to the optical path length difference adjusted by the optical delay mechanism 120. That is, the time t33 is substantially adjusted by the optical delay mechanism 120. For this reason, the first timing and the second timing coincide with each other when the optical path length difference adjusted by the optical delay mechanism 120 reaches a specific optical path length difference. Thereafter, the photoconductive element 110 repeatedly detects the terahertz wave THz2 while the optical delay mechanism 120 adjusts the optical path length difference around a specific optical path length difference. As a result, the photoconductive element 110 can indirectly acquire the waveform of the terahertz wave THz2 using the pump-probe method.

  Note that a gap 116 between the first antenna portion 112-1 and the first antenna portion 113-1 used for emitting the terahertz wave THz1 is a first antenna portion 114 used for detecting the terahertz wave THz2. -1 and the first antenna portion 115-1 are also used as the gap 116 as described above. In this case, if the gap 116 is irradiated with the probe light LB2, the photoconductive element 110 may emit the terahertz wave THz1 at the same time as detecting the terahertz wave THz2. When the photoconductive element 110 detects the terahertz wave THz2 and emits the terahertz wave THz1 at the same time, the photoconductive element 110 outputs the terahertz wave THz1 that has been emitted from the photoconductive element 110 but has not yet been reflected by the sample 10. It is assumed that it may be erroneously detected as the terahertz wave THz2 reflected by 10. However, as described above, the first antenna portions 112-1 and 113-1 used for emitting the terahertz wave THz1 extend in the Y-axis direction, while the first antenna used for detecting the terahertz wave THz2. The portions 114-1 and 115-1 extend in the X-axis direction. That is, the detection sensitivity of the terahertz wave THz2 by the photoconductive element 110 is higher than the detection sensitivity of the terahertz wave THz1 by the photoconductive element 110. Therefore, the possibility that the photoconductive element 110 erroneously detects the terahertz wave THz1 as the terahertz wave THz2 is relatively reduced. For this reason, the photoconductive element 110 can suitably detect the terahertz wave TH2 while emitting the terahertz wave THz1.

  As described above, the terahertz wave measuring apparatus 1 according to the first embodiment includes the single photoconductive element 110 that emits the terahertz wave THz1 and detects the terahertz wave THz2. That is, the terahertz wave measuring apparatus 1 according to the first embodiment may not include the photoconductive element that emits the terahertz wave THz1 and the photoconductive element that detects the terahertz wave THz2 separately. For this reason, the terahertz wave measuring apparatus 1 according to the first embodiment does not need to separate the terahertz wave THz1 from the photoconductive element 110 toward the sample 10 and the terahertz wave THz2 from the sample 10 toward the photoconductive element 110 in the first place. Therefore, in comparison with the terahertz wave measuring apparatus of the first comparative example that separates the terahertz wave THz1 and the terahertz wave THz2 by arranging a half mirror or a polarizing beam splitter in at least one optical path of the terahertz waves THz1 and THz2. The intensity of the terahertz wave THz detected by the photoconductive element 110 is increased. As a result, the terahertz wave measuring apparatus 1 according to the first embodiment can efficiently detect the terahertz wave THz2 reflected by the sample 10. Furthermore, the terahertz wave measuring apparatus of the first embodiment is compared with the terahertz wave measuring apparatus of the second comparative example that is provided with a photoconductive element that emits the terahertz wave THz1 and a photoconductive element that detects the terahertz wave THz2 separately. The increase in the size of 1 is suppressed.

  Further, in the terahertz wave measuring apparatus 1 according to the first embodiment, the polarization direction of the terahertz wave THz emitted from the photoconductive element 110 (that is, the vibration direction of the electric field constituting the terahertz wave THz1) and the terahertz detected by the photoconductive element 110 are detected. The polarization direction of the wave THz2 is different. For this reason, the terahertz wave THz2 can be detected while the single photoconductive element 110 emits the terahertz wave THz1.

(2) Terahertz wave measuring apparatus 2 of the second embodiment
Next, the terahertz wave measuring apparatus 2 according to the second embodiment will be described. The terahertz wave measuring apparatus 2 according to the second embodiment is different from the terahertz wave measuring apparatus 1 according to the first embodiment in that the timing at which the bias voltage is applied to the photoconductive element 110 is different. Other configuration requirements and operations of the terahertz wave measurement apparatus 2 of the second embodiment may be the same as other configuration requirements and operations of the terahertz wave measurement apparatus 1 of the first embodiment. Therefore, in the following, the timing at which the terahertz wave measuring apparatus 2 according to the second embodiment applies a bias voltage to the photoconductive element 110 will be described with reference to FIGS. 4 and 5. FIG. 4 is a timing chart showing an example of the timing at which the photoconductive element 110 emits the terahertz wave THz1 and detects the terahertz wave THz2, together with an example of the timing at which the bias voltage is applied to the photoconductive element 110. FIG. 5 is a timing chart showing an example of timing for applying a bias voltage, which is an AC voltage, to the photoconductive element 110.

  As shown in FIG. 4, in the second embodiment, an effective bias voltage is applied to the antennas 112 and 113 during the first period in which the pump light LB1 is irradiated to the gap 116 of the photoconductive element 110. On the other hand, an effective bias voltage is not applied to the antennas 112 and 113 during the second period in which the probe light LB2 is applied to the gap 116 of the photoconductive element 110. For reference, in the first embodiment, the effective bias voltage is not only during the first period in which the pump light LB1 is applied to the gap 116 of the photoconductive element 110, but also when the probe light LB2 is applied to the photoconductive element 110. It is also applied to the antennas 112 and 113 during the second period during which the gap 116 is irradiated.

  In order to perform the bias switching control in which the bias voltage is applied in the first period and the bias voltage is not applied in the second period, the terahertz wave measuring apparatus 2 includes at least one of the bias voltage generation unit 141 and the antennas 112 and 113. There may be provided a control mechanism (typically a switch) for controlling the electrical connection between the two. In this case, when the bias voltage generator 141 and at least one of the antennas 112 and 113 are electrically connected by the control mechanism, the bias voltage is applied to the antennas 112 and 113. On the other hand, if the bias voltage generator 141 and at least one of the antennas 112 and 113 are electrically disconnected (insulated) by the control mechanism, the bias voltage is not applied to the antennas 112 and 113.

  Alternatively, the bias voltage generation unit 141 itself may perform bias switching control. That is, the bias voltage generation unit 141 does not need to generate an effective bias voltage during the second period while generating an effective bias voltage during the first period.

  According to the terahertz wave measuring apparatus 2 of the second embodiment, it is possible to preferably enjoy the same effects as those received by the terahertz wave measuring apparatus 1 of the first embodiment. Further, in the second embodiment, during the second period in which the gap 116 is irradiated with the probe light LB2, the photoconductive element 110 detects the terahertz wave THz2, but does not emit the terahertz wave THz1. Therefore, the possibility that the photoconductive element 110 erroneously detects the terahertz wave THz1 as the terahertz wave THz2 is further reduced or eliminated. For this reason, the photoconductive element 110 can suitably detect the terahertz wave TH2 while emitting the terahertz wave THz1.

  Note that the bias voltage is used as a reference signal for the lock-in detection unit 151 as described above. For this reason, as shown in the third graph in FIG. 5, the bias voltage is often an alternating voltage whose voltage value changes in a sine wave shape. Thus, even when the bias voltage is an AC voltage, the terahertz wave measuring apparatus 2 preferably performs bias switching control.

  Here, when the bias switching control is performed using the control mechanism that controls the electrical connection between the bias voltage generation unit 141 and at least one of the antennas 112 and 113, the bias voltage generation unit 141 Alternatively, an alternating voltage whose voltage value changes in a sine wave shape shown in the third graph of FIG. 5 may be generated as a bias voltage. In this case, the lock-in detection unit 151 can use the bias voltage generated by the bias voltage generation unit 141 as a reference signal. Furthermore, the bias voltage actually applied to the photoconductive element 110 by the operation of the control mechanism has an effective voltage value during the first period as shown in the fourth graph of FIG. The pulse voltage does not have a valid voltage value during the period. Furthermore, the line connecting the voltage values of the pulse voltage during the first period changes in a sine wave shape.

  On the other hand, when the bias voltage generation unit 141 itself performs bias switching control, the bias voltage generation unit 141 is effective as the bias voltage during the first period as shown in the fourth graph of FIG. A pulse voltage that has a voltage value but does not have an effective voltage value during the second period and in which a line connecting the voltage values of the pulse voltage during the first period changes in a sine wave form is generated. Is preferred. When such a pulse voltage is generated as a bias voltage, the lock-in detection unit 151 can use the bias voltage generated by the bias voltage generation unit 141 as a reference signal.

(3) Terahertz wave measuring apparatus 3 of the third embodiment
Next, the terahertz wave measuring apparatus 3 according to the third embodiment will be described. In addition, the terahertz wave measuring apparatus 2 of the second embodiment is compared with the terahertz wave measuring apparatus 1 of the first embodiment, in addition to the terahertz wave THz2 reflected by the sample 10, the terahertz wave THz ( Hereinafter, “Terahertz wave THz3”) is also detected. Other configuration requirements and operations of the terahertz wave measurement apparatus 3 of the third embodiment may be the same as other configuration requirements and operations of the terahertz wave measurement apparatus 1 of the first embodiment. Therefore, in the following, with reference to FIG. 6, description will be given on the components for detecting the terahertz wave THz3 among the components constituting the terahertz wave measuring apparatus 3 of the third embodiment. FIG. 6 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 3 according to the third embodiment.

  As shown in FIG. 6, the terahertz wave measuring device 3 includes, as components for detecting the terahertz wave THz3, as compared with the terahertz wave measuring device 1, a half-wave plate 361, an optical delay mechanism 320, The difference is that it further includes a reflecting mirror 362, a right-angle prism 370, and a photoconductive element 310.

  The terahertz wave THz3 transmitted through the sample 10 enters the right-angle prism 370. The right-angle prism 370 includes a first surface 371, a second surface 372, and a third surface 373. The first surface 371 is an optical surface on which the terahertz wave THz3 transmitted through the sample 10 is incident. The second surface 372 is an optical surface that reflects the terahertz wave THz3 that has propagated into the right-angle prism 370 through the first surface 271. The third surface 373 is an optical surface that intersects the first surface 371 at an angle of 90 ° and emits the terahertz wave THz3 reflected by the second surface 372.

  The terahertz wave THz3 transmitted through the sample 10 is reflected by the second surface 372 of the right-angle prism 370 and propagates toward the photoconductive element 310. The structure of the photoconductive element 310 is the same as that of the photoconductive element 110. However, the photoconductive element 310 may not emit the terahertz wave THz1. For this reason, the photoconductive element 310 may not include the antenna 112 and the antenna 113.

  In order for the photoconductive element 310 to detect the terahertz wave THz3, the photoconductive element 310 is irradiated with the probe light LB2. Specifically, in the third embodiment, the probe light LB2 whose optical path length is adjusted by the optical delay mechanism 120 enters the polarization beam splitter 163 via the half-wave plate 361. The polarization beam splitter 163 reflects a first polarization component (for example, a polarization component having an electric field component oscillating along the fifth direction) in the probe light LB2 as the probe light LB2 incident on the photoconductive element 110. On the other hand, the polarization beam splitter 163 receives the second polarization component (for example, a polarization component having an electric field component oscillating along the sixth direction) of the probe light LB2 and enters the photoconductive element 310 with the probe light LB2 ( Thereafter, the probe light LB2 incident on the photoconductive element 310 is transmitted as “probe light LB3” in order to distinguish it from the probe light LB2 incident on the photoconductive element 110). The probe light LB2 is applied to the gap 116 of the photoconductive element 110. On the other hand, the probe light LB3 is irradiated to the gap 116 of the photoconductive element 310 via a light guide path (not shown), the optical delay mechanism 320, and the reflecting mirror 362.

  The ratio of the intensity of the probe light LB2 incident on the photoconductive element 110 and the intensity of the probe light LB3 incident on the photoconductive element 310 is determined depending on the half-wave plate 361 described above. More specifically, the ratio between the intensity of the probe light LB2 incident on the photoconductive element 110 and the intensity of the probe light LB3 incident on the photoconductive element 310 is the polarization of the probe light LB2 incident on the half-wave plate 361. It is determined depending on the amount of deviation between the azimuth angle of the surface (that is, the vibration direction of the electric field constituting the probe light LB2) and the high speed axis of the half-wave plate 361.

  Here, in order for the terahertz wave measuring apparatus 3 to indirectly detect the waveform of the terahertz wave THz3 using the pump-probe method, the difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB3 ( That is, the optical path length difference) needs to be adjusted. On the other hand, considering that the probe light LB3 is a part of the probe light LB2 that has passed through the optical delay mechanism 120, it can be said that the optical path length of the probe light LB3 has already been adjusted by the optical delay mechanism 120. . Therefore, in the third embodiment, the optical delay mechanism 320 adjusts the optical path length of the probe light LB3 in order to adjust the difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB3 (that is, the optical path length difference). It is not necessary to adjust the length.

  However, in the third embodiment, the optical delay mechanism 320 is configured such that the terahertz wave THz1 emitted from the photoconductive element 110 returns to the photoconductive element 310 as the terahertz wave THz3, and the probe light LB3 is the photoconductive element. The optical path length of the probe light LB3 is adjusted so that the fourth timing irradiated to the gap 116 of 310 matches or overlaps. The optical delay mechanism 320 does not need to adjust the optical path length of the probe light LB3 after the third timing and the fourth timing once match or overlap. That is, the optical delay mechanism 320 may fix the optical path length of the probe light LB3 after the third timing and the fourth timing are once matched.

  Thereafter, the photoconductive element 310 repeatedly detects the terahertz wave THz3 while adjusting the difference (optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB3 by the optical delay mechanism 120. As a result, the photoconductive element 310 can indirectly acquire the waveform of the terahertz wave THz3 using the pump-probe method.

  Here, an example of the timing at which the photoconductive element 110 emits the terahertz wave THz1 and detects the terahertz wave THz2 and the timing at which the photoconductive element 310 detects the terahertz wave THz3 will be described with reference to FIG. FIG. 7 is a timing chart showing an example of the timing at which the photoconductive element 110 emits the terahertz wave THz1 and detects the terahertz wave THz2, and the timing at which the photoconductive element 310 detects the terahertz wave THz3.

  As shown in FIG. 7, it is assumed that the pulse laser device 1 emits the laser beam LB at time t71. In this case, the gap 116 of the photoconductive element 110 is irradiated with the pump light LB1 at time t72 later than time t71. As a result, the photoconductive element 110 emits the terahertz wave THz1 at time t72.

  On the other hand, the gap 116 of the photoconductive element 110 is irradiated with the probe light LB2 at time t73 later than time t71. As a result, the photoconductive element 110 detects the terahertz wave THz2 at time t73. However, in the third embodiment, as in the first embodiment, the first timing when the terahertz wave THz1 emitted from the photoconductive element 110 returns to the photoconductive element 110 as the terahertz wave THz2 and the probe light LB2 are light. The time t73 is adjusted by the optical delay mechanism 120 in order to match or overlap with the second timing irradiated to the gap 116 of the conductive element 110. For this reason, the first timing and the second timing coincide with each other when the optical path length difference between the pump light LB1 and the probe light LB2 adjusted by the optical delay mechanism 120 reaches a specific first optical path length difference. Thereafter, the photoconductive element 110 repeatedly detects the terahertz wave THz2 while the optical path length difference between the pump light LB1 and the probe light LB2 is adjusted by the optical delay mechanism 120 around the specific first optical path length difference. As a result, the photoconductive element 110 can indirectly acquire the waveform of the terahertz wave THz2 using the pump-probe method.

  On the other hand, the gap 116 of the photoconductive element 310 is irradiated with the probe light LB3 at time t74 which is later than time t71. As a result, the photoconductive element 310 detects the terahertz wave THz3 at time t74. However, as described above, the third timing when the terahertz wave THz1 emitted from the photoconductive element 110 returns to the photoconductive element 310 as the terahertz wave THz3 and the probe light LB3 are irradiated to the gap 116 of the photoconductive element 310. The time t74 is adjusted by the optical delay mechanism 320 in order to match or overlap the fourth timing. Specifically, the optical delay mechanism 320 adjusts the optical path length of the probe light LB3 in order to adjust the time t74. When the optical path length of the probe light LB3 adjusted by the optical delay mechanism 320 reaches a certain second optical path length, the third timing matches the fourth timing. Thereafter, the optical delay mechanism 320 does not adjust the optical path length of the probe light LB3. On the other hand, when the optical path length difference between the pump light LB1 and the probe light LB2 is adjusted by the optical delay mechanism 120, the optical path length difference between the pump light LB1 and the probe light LB3 is also adjusted. Accordingly, the photoconductive element 310 repeatedly detects the terahertz wave THz3 while the optical path length difference between the pump light LB1 and the probe light LB3 is adjusted by the optical delay mechanism 120. As a result, the photoconductive element 310 can indirectly acquire the waveform of the terahertz wave THz3 using the pump-probe method.

  According to the terahertz wave measuring apparatus 3 of the third embodiment, it is possible to suitably enjoy the same effects as those received by the terahertz wave measuring apparatus 1 of the first embodiment. Furthermore, in the third embodiment, not only the terahertz wave THz2 reflected by the sample 10 but also the terahertz wave THz3 transmitted through the sample 10 is detected. Therefore, the terahertz wave measuring apparatus 3 can measure the characteristics of the sample 10 with higher accuracy.

  The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. Moreover, it is included in the technical scope of the present invention.

1, 2, 3 Terahertz wave measuring device 10 Sample 101 Pulse laser device 110 Photoconductive element 111 Substrate 112, 113, 114, 115 Antenna 116 Gap 120 Optical delay mechanism 150 Control unit 151 Lock-in detection unit 152 Signal processing unit 162, 163 Beam splitter 170 Right angle prism 310 Photoconductive element 320 Optical delay mechanism 361 Half wave plate 362 Reflector 370 Right angle prism LB1 Pump light LB2 Probe light LB3 Probe light THz, THz1, THz2, THz3 Terahertz wave

Claims (6)

A single photoconductive device that emits a terahertz wave polarized in a first direction toward the sample and detects the terahertz wave reflected by the sample and polarized in a second direction different from the first direction. Elements,
A measurement unit that measures the characteristics of the sample based on the detection result of the terahertz wave,
The measurement apparatus according to claim 1, wherein the photoconductive element has higher detection sensitivity of the terahertz wave polarized in the second direction than detection sensitivity of the terahertz wave polarized in the first direction. The photoconductive element is:
A pair of first electrodes for emitting the terahertz wave polarized in the first direction and having a gap therebetween;
A pair of second electrodes that detect the terahertz wave polarized in the second direction and that have the gap secured between the pair of first electrodes. The measuring device according to claim 1. Each of the pair of first electrodes has a longitudinal shape extending along a third direction corresponding to the first direction,
3. The pair of second electrodes each have a longitudinal shape that is different from the third direction and extends along a fourth direction corresponding to the second direction. 4. Measuring device. A first optical element for branching predetermined excitation light into first excitation light and second excitation light;
A second optical element for adjusting an optical path length of the second excitation light;
The first excitation light and the second excitation light having the adjusted optical path length are transmitted so that the first excitation light and the second excitation light having the adjusted optical path length propagate through the same optical path. A third optical element that leads to the photoconductive element;
4. The measurement apparatus according to claim 2, wherein each of the first excitation light and the second excitation light guided by the third optical element is applied to the gap. 5. The photoconductive element (i) emits the terahertz wave polarized in the first direction during a first period in which the first excitation light is applied to the gap, and (ii) second excitation light. Detecting the terahertz wave polarized in the second direction during a second period during which the gap is irradiated to the gap,
During the first period, a bias voltage for emitting the terahertz wave is applied to the pair of first electrodes, while the bias voltage is applied to the pair of first electrodes during the second period. The measuring device according to claim 2, further comprising an application unit that does not. The photoconductive element emits the terahertz wave that is the first linear polarization polarized in the first direction and detects the terahertz wave that is the second linear polarization polarized in the second direction. And
The terahertz wave, which is the first linearly polarized wave propagating from the photoconductive element toward the sample, is converted into the circularly polarized terahertz wave, and the circularly polarized wave propagating from the sample toward the photoconductive element 6. The optical system according to claim 1, further comprising: a fourth optical element that converts the terahertz wave into the terahertz wave that is the second linearly polarized light that is polarized in the second direction. Measuring device.

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