JP2006317407A - Terahertz measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terahertz measuring instrument capable of certainly performing both of the measurement of the transmission of an inspection target and the measurement of the reflection thereof separately while using one detector in common. <P>SOLUTION: The terahertz measuring instrument is equipped with illumination optical systems (4 and 3A) for illuminating the inspection target (10) with terahertz light, unifying means (1A, 1B, 71 and 74) for guiding the transmitted light and reflected light of the terahertz light emitted from the inspection target (10) to the same light path and one detector (5) arranged in the same light path, and further equipped with polarizing means (71, 72, 73 and 74) for providing difference in the polarizing azimuths of the transmitted light and the reflected light incident on the detector. The detector 5 is constituted so as to separate the mutually different polarizing components of the incident terahertz light to detect them. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a terahertz measuring apparatus using terahertz light for illumination of a test object (sample to be measured), such as a terahertz imaging apparatus or a terahertz spectrometer.

Terahertz light is an electromagnetic wave having a frequency band of approximately 0.01 THz to 100 THz, and in recent years, its application to identification, analysis, inspection, imaging, etc. of substances has been considered promising. Several terahertz measuring devices using this terahertz light have already been developed and disclosed in Patent Documents 1 and 2.
The terahertz measuring device illuminates a test object with terahertz light emitted from a dedicated generator, and detects terahertz light emitted from the test object with a dedicated detector. There are two types of measurement: reflection measurement that detects reflected light from the test object and transmission measurement that detects transmitted light from the test object, depending on the purpose of the measurement and the type of test object. Can be used properly.

For example, Patent Document 1 discloses a terahertz measurement device in which an optical system for transmission measurement and an optical system for reflection measurement are mounted. Furthermore, Patent Document 2 discloses a terahertz measurement device that shares most of the optical system for transmission measurement and the optical system for reflection measurement.
JP 2004-205360 A JP 2004-191302 A

The present inventor has attempted to further reduce the size of the apparatus by expanding the common part of both. In order to achieve this, we examined the possibility of sharing one detector for transmission and reflection measurements.
Therefore, an object of the present invention is to provide a terahertz measuring apparatus that can perform both transmission measurement and reflection measurement of an object to be reliably separated while sharing one detector.

  The terahertz measurement device of the present invention includes an illumination optical system that illuminates a test object with terahertz light, an integration unit that guides transmitted light and reflected light of the terahertz light generated from the test object to the same optical path, and the same In the terahertz measuring device including one detector disposed in the optical path, the terahertz measuring device further includes polarizing means for providing a difference in polarization azimuth between the transmitted light and the reflected light incident on the detector. The terahertz light is configured to separate and detect different polarization components.

  The detector may include a pair of antennas that individually detect different polarization components of incident terahertz light. Moreover, the terahertz measurement apparatus of the present invention may include a control unit that controls the timing of the illumination and the detection.

  According to the present invention, a terahertz measurement device capable of reliably separating and performing both transmission measurement and reflection measurement of a test object while sharing a single detector is realized.

[Embodiment]
An embodiment of the present invention will be described with reference to FIGS. 1, 2, 3, 4 and 5. This embodiment is an embodiment of a terahertz spectrometer.
FIG. 1 is a block diagram illustrating the principle of this apparatus. As shown in FIG. 1, in this apparatus, the terahertz light generated from the terahertz generator illuminates the test object via the optical system. The transmitted light and reflected light of the terahertz light emitted from the test object are integrated into the same optical path through the optical system for adjusting the polarization direction and the other optical system, and enter the same terahertz light detector. Of these, the optical system that adjusts the polarization azimuth provides a difference between the polarization azimuth of the transmitted light incident on the terahertz light detector and the polarization azimuth of the reflected light, and the detector polarizes the incident terahertz light. This is detected for each component.

FIG. 2 is a schematic configuration diagram of the apparatus. FIG. 2 is a schematic diagram mainly showing the optical relationship of each part, and the number of times each optical path is bent and the optical path length may differ from the actual ones.
As shown in FIG. 2, this apparatus includes a terahertz light generator 4, off-axis parabolic mirrors (collimator mirrors) 3A, 3B, polarizers 71, 72, 73, as an optical system for guiding terahertz light. 74, a terahertz photodetector 5, optical path bending mirrors 1A, 1B, and the like, and a test object (sample) 10 such as a semiconductor is disposed at a predetermined position in the optical path. Further, this apparatus supports a laser light source 6, optical path bending mirrors 1a, 1b, 1c, 1d, 1e, 1f, a beam splitter 2, a retro reflector 9, and a retro reflector 9 as an optical system for guiding a control laser. The delay stage 8 and the lens 2 are provided. In addition, a measurement circuit 25 and a computer (not shown) for controlling each unit are also provided.

The laser light source 6 emits laser pulse light having a pulse width of about 10 to 150 fs as a control laser. This laser pulse light enters the beam splitter 2 via the optical path bending mirror 1a and is branched there.
One of the laser pulse beams branched by the beam splitter 2 is incident on the terahertz light generator 4 via the optical path bending mirror 1b and the lens 2, and excites the terahertz light generator 4. That is, the laser pulse light serves as pump light.

The other of the laser pulse beams branched by the beam splitter 2 is incident on the terahertz light detector 5 through the optical path bending mirrors 1 c and 1 d, the retro reflector 9, the optical path bending mirrors 1 f and 1 e, and the lens 2. This laser pulse light serves as probe light for the terahertz light detector 5.
The terahertz light generator 4 emits terahertz pulse light having a frequency band of 0.01 THz to 100 THz in accordance with the supplied pump light. The terahertz pulse light is reflected by the off-axis paraboloidal mirror 3A having a focal point at a position equivalent to the light emission point, and becomes parallel light. The terahertz pulse light that has become parallel light illuminates the measurement region of the test object 10 from the front via the polarizers 71 and 72.

  Of the terahertz pulse light incident on the measurement region of the test object 10, the light transmitted through the measurement region (transmitted pulse light) becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement region, The light enters the polarizer 74 through the optical path bending mirrors 1A and 1B. The terahertz pulse light is transmitted through the polarizer 74, is incident on the off-axis parabolic mirror 3B, receives a condensing action, and has a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 3B. The light enters the photodetector 5.

  Of the terahertz pulse light incident on the measurement region of the test object 10, the light reflected by the measurement region (reflected pulse light) becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement region, The light returns to the polarizer 71 through the polarizer 72 and is reflected there. The terahertz pulse light is incident on the polarizer 74, is reflected there, is integrated into the same optical path as the transmitted pulse light, and enters the terahertz light detector 5 via the off-axis parabolic mirror 3B.

  The terahertz light detector 5 generates an electric current according to the incident terahertz pulse light and the provided probe light. The current value is a value corresponding to the timing at which the probe light is applied in the time-varying waveform (hereinafter simply referred to as “waveform”) of the electric field intensity generated by the terahertz pulse light in the terahertz photodetector 5. Indicates. The current value generated by the terahertz light detector 5 is detected by the measurement circuit 25, and the detection signal is captured by a computer (not shown) and processed. The measurement circuit 25 includes an ammeter, a current / voltage conversion circuit, a lock-in amplifier, an A / D conversion circuit, a constant voltage power supply, a bias voltage application device, a signal modulation device, and the like, and includes the terahertz light detector 5 and the terahertz light. Each generator 4 is operated appropriately.

In the above apparatus, the terahertz light generator 4 → the off-axis parabolic mirror 3A → the polarizer 71 → the polarizer 72 → the test object 10 → the polarizer 73 → the optical path bending mirror 1A → the optical path bending mirror 1B → the polarizer 74. → The off-axis parabolic mirror 3B → the optical path of the terahertz pulse light (transmission pulse light) that passes through the terahertz light detector 5 in this order is the optical path for transmission measurement.
Further, the terahertz light generator 4 → off-axis parabolic mirror 3A → polarizer 71 → polarizer 72 → test object 10 → polarizer 72 → polarizer 71 → polarizer 74 → off-axis parabolic mirror 3B → terahertz The optical path of terahertz pulsed light (reflected pulsed light) that sequentially passes through the photodetector 5 is an optical path for reflection measurement.

In the above apparatus, when the laser light source 6 is driven, the test object 10 is illuminated with the terahertz pulse light, and the transmitted pulse light and the reflected pulse light generated from the test object 10 at the same timing are substantially the same. It enters the same terahertz light detector 5 at the timing.
In addition, if the optical path length of the transmitted pulse light and the optical path length of the reflected pulse light are set to be the same, the incident timings can be completely matched. Then, even when the state change of the test object 10 occurs at high speed, transmission measurement and reflection measurement can be performed in the same state. Incidentally, although the optical path lengths of both are slightly different in FIG. 2, if the shorter optical path is routed using an optical path bending mirror, both can be set to the same length.

  Here, in the present apparatus, a 90 ° polarization misalignment is imparted between the transmitted pulsed light and the reflected pulsed light incident on the terahertz light detector 5. For this reason, the polarization direction of the terahertz pulse light first incident on the polarizer 71 and the direction of each transmission axis (reflection axis) of the polarizers 71, 72, 73, and 74 are optimized (details will be described later). Further, the terahertz light detector 5 and the measurement circuit 25 are configured to be able to individually detect the electric field intensities of two polarized components shifted by 90 ° from the incident terahertz pulse light (details will be described later).

  Further, in this apparatus, if the position of the delay stage 8 is shifted in the direction of the arrow in FIG. 2, the delay time from the pump light incident timing to the probe light incident timing changes, so that the waveform by the terahertz light detector 5 is changed. The detection location of is shifted. Therefore, if the delay stage 8 is disposed at each position and the laser light source 6 is driven, the entire waveforms of the transmitted pulsed light and the reflected pulsed light are respectively detected. A computer (not shown) individually performs processing (Fourier transform or the like) on the waveform of the transmitted pulsed light and reflected pulsed light, and extracts spectral data of the transmitted pulsed light and spectral data of the reflected pulsed light, respectively.

Hereinafter, the polarizers 71, 72, 73, and 74 will be described in detail.
FIG. 3 is a diagram for explaining the polarizers 71, 72, 73, and 74 in detail. 3A1 to 3A6 show elements arranged in the optical path for transmission measurement, and FIGS. 3B1 to 3B7 show elements arranged in the optical path for reflection measurement. Note that the X and Y directions in FIG. 3 correspond to the X and Y directions in FIG. That is, the X direction is perpendicular to the plane in which the optical axis exists, and the Y direction is parallel to the plane in which the optical axis exists (this direction notation is the same in other drawings). The white arrow indicates the polarization direction of the terahertz pulse light incident on each element.

First, the polarization direction of the terahertz pulse light that first enters the polarizer 71 is defined as the Y direction. At this time, the transmission axis T71 of the polarizer ₇₁ is set in the Y direction (the reflection axis _R71 is the X direction) (see FIGS. 3A1, 3B1, and 5B). Further, the transmission axis T 72 of the polarizer ₇₂ is set in a direction shifted by 45 ° from the X direction and the Y direction (see FIGS. 3 (A2), (B2), and (B4)). The transmission axis T 73 of the polarizer ₇₃ is set in the Y direction (see FIG. 3 (A4)). The transmission axis T 74 of the polarizer ₇₄ is set in the Y direction (the reflection axis R ₇₄ is the X direction) (see FIGS. 3A5 and 3B6). For each of the polarizers 71, 72, 73, and 74, an element that acts as a polarizer on terahertz pulse light in a frequency band of 0.01 THz to 100 THz, for example, a “wire grid” is used. The operation of each element will be described separately for the optical path for transmission measurement and the optical path for reflection measurement.

(Operation of each element in the optical path for transmission measurement)
As shown in FIG. 3 (A1), the terahertz pulse light to first enters the polarizer 71, because it is polarized in the same direction as the transmission axis T ₇₁ of the polarizer 71, polarization transmitted through the polarizer 71 Head to child 72.
As shown in FIG. 3 (A2), the terahertz pulsed light incident on the polarizer 72, since polarized in the transmission axis T ₇₂ and 45 ° offset direction of the polarizer 72, a polarization component parallel to the transmission axis T ₇₂ Only light passes through the polarizer 72 and illuminates the test object 10 (FIG. 3 (A3)). The vertical polarization component to the transmission axis T ₇₂ reflects the polarizer 72, the unnecessary light. The transmitted pulsed light emitted from the illuminated test object 10 travels to the polarizer 73.

As shown in FIG. 3 (A4), the transmitted pulsed light incident on the polarizer 73 is polarized in a direction deviated from the transmission axis T ₇₃ of the polarizer ₇₃ by 45 °, so that the polarization component parallel to the transmission axis T ₇₃ is obtained. Only passes through the polarizer 73 and travels toward the polarizer 74. The polarized light component perpendicular to the transmission axis T ₇₃ is reflected by the polarizer 73 and becomes unnecessary light.
As shown in FIG. 3 (A5), transmitted pulse light incident on the polarizer 74, because it is polarized in the same direction as the transmission axis T ₇₄ of the polarizer 74, then transmitted through the polarizer 74, the terahertz light detector 5 Head to. Therefore, the polarization direction of the transmitted pulse light incident on the terahertz light detector 5 is the same Y direction as the transmission axis T ₇₄ (FIG. 3 (A6)).

(Effect of each element in the optical path for reflection measurement)
Of the optical path for reflection measurement, the optical path (FIG. 3 (B1), (B2), (B3)) until the object 10 is illuminated is that of the optical path for transmission measurement (FIG. 3 (A1), (A2)). ), (A3)). The reflected pulsed light emitted from the test object 10 returns to the polarizer 72.
As shown in FIG. 3 (B 4), the reflected pulse light returning to the polarizer 72 is polarized in the same direction as the transmission axis T _{72 of} the polarizer 72, so that it passes through the polarizer 72 and returns to the polarizer 71.

As shown in FIG. 3 (B5), the reflected pulse light returning to the polarizer 71, since the polarized reflection axis R ₇₁ and 45 ° offset direction of the polarizer 71, only a polarization component parallel with the reflection axis R ₇₁ Reflects the polarizer 71 and travels toward the polarizer 74. The vertical polarization component and the reflected axis R ₇₁ is transmitted through the polarizer 74, the unnecessary light.
As shown in FIG. 3 (B6), the reflected pulsed light incident on the polarizer 74 is polarized in the same direction as the reflection axis R74 of the polarizer 74. Therefore, the reflected pulsed light is reflected by the polarizer ₇₄ and is detected by the terahertz photodetector. Go to 5. Therefore, the polarization direction of the reflected pulse light incident on the terahertz light detector 5 is the same X direction as the reflection axis R ₇₄ (FIG. 3 (B7)). The polarization azimuth (= X direction) of the reflected pulsed light is 90 ° different from the polarization azimuth (= Y direction) of the transmitted pulsed light.

Hereinafter, the terahertz photodetector 5 will be described in detail.
FIG. 4 is a diagram for explaining the terahertz light detector 5 in detail. As shown in FIG. 4, the terahertz photodetector 5 includes a semiconductor substrate 23, a photoconductive film 22 formed on the semiconductor substrate 23, a metal conductive film 21 formed on the photoconductive film 22, and a hemisphere And a lens 24. Terahertz pulsed light (= transmitted pulsed light and reflected pulsed light) T2 and probe light L3 are incident on the central region C of the photoconductive film 22.

  The pattern of the conductive film 21 is formed by uniformly arranging four L-shaped patterns around the incident region C. These four L-shaped patterns are the same type and the same size, and only their arrangement directions are shifted by 90 °. Among these, two L-shaped patterns shifted from each other by 180 ° form one dipole antenna. Therefore, the entire conductive film 21 becomes a pair of dipole antennas orthogonal to each other in the antenna direction.

More specifically, as shown in FIG. 4B, one dipole antenna 21A has two L-shaped patterns A1 and A2 arranged point-symmetrically with respect to the center of the incident area C. Two patterns facing each other through a gap in C function as an antenna. The direction of the gap (= X direction) is the antenna direction of the dipole antenna 21A.
The other dipole antenna 21B has two L-shaped patterns B1 and B2 arranged point-symmetrically with respect to the center of the incident region C, and two patterns opposed to each other through a gap in the incident region C are provided. , Function as an antenna. The direction of the gap (= Y direction) is the antenna direction of the dipole antenna 21B.

FIG. 5 is a diagram illustrating the measurement circuit 25 (particularly around the ammeter). FIG. 5 also shows the antenna portion of the terahertz photodetector 5 in order to show the connection relationship.
As shown in FIG. 5, the measurement circuit 25 includes a pair of ammeters 25a and 25b. One ammeter 25a is connected to two L-shaped patterns A1 and A2 (L-shaped transmission line) of a dipole antenna 21A, and the other ammeter 25b is connected to two L-shaped patterns of a dipole antenna 21B. Mold patterns B1 and B2 (L-shaped transmission lines) are connected.

The antenna unit 31a of the dipole antenna 21A generates a current according to the electric field strength of a component polarized in the antenna direction (= X direction) of the terahertz pulse light incident on the incident region C. The current value is detected by the ammeter 25a.
The antenna unit 31b of the dipole antenna 21B generates a current according to the electric field strength of a component polarized in the antenna direction (= Y direction) of the terahertz pulse light incident on the incident region C. The current value is detected by the ammeter 25b.

  That is, the measuring device 25 uses the pair of ammeters 25a and 25b to generate a detection signal indicating the electric field intensity of the transmitted pulsed light (polarization direction = Y direction) and the electric field intensity of the reflected pulsed light (polarization direction = X direction). The detection signals shown are generated individually. These two types of detection signals pass through a current / voltage conversion circuit, a lock-in amplifier, an A / D conversion circuit, etc. (not shown), and then are recognized and processed individually by a computer (not shown).

Here, a size example of each part of the dipole antennas 21A and 21B is shown below.
・ Gap length of antenna portions 31a and 31b: 5 μm,
-Pattern width of the conductive film 21 ... 4 μm,
-Pattern length d until bending from antenna parts 31a, 31b ... 10-20 m,
In general, the gap lengths of the antenna portions 31a and 31b and the pattern width of the conductive film 21 are set slightly narrower than the diameter of the incident region C, and the pattern length d is a value corresponding to the frequency band to be detected by the terahertz pulse light. Set to Moreover, if the gap length of the antenna part 31a and the gap length of the antenna part 31b are made equal, the transmitted pulsed light and the reflected pulsed light can be detected under the same conditions.

  As described above, in the present apparatus, the transmitted pulsed light and the reflected pulsed light generated from the test object 10 are incident on one terahertz light detector 5. Further, the transmitted pulse light and the reflected pulse light incident on the terahertz light detector 5 are given a 90 ° polarization misalignment by the polarizers 71, 72, 73 and 74. Further, the terahertz photodetector 5 is provided with a pair of antennas that are shifted by 90 ° in the antenna direction.

Therefore, although this apparatus is provided with only one terahertz light detector 5, it can detect the transmitted pulsed light and the reflected pulsed light separately.
Moreover, since this apparatus shares one terahertz photodetector 5 for transmission measurement and reflection measurement, the number of parts is reduced. Therefore, cost reduction and space saving can be achieved.
Further, in this apparatus, since two systems of the optical path for transmission measurement and the optical path for reflection measurement are formed at the same time, the transmitted pulse light and the reflected pulse light can be detected simultaneously. Therefore, there is no need to switch the optical path in order to detect both transmitted pulsed light and reflected pulsed light.

Further, the total measurement time for transmission measurement and reflection measurement can be reduced. Even when the state of the test object 10 changes, both transmission measurement and reflection measurement can be performed in the same state.
Further, in this apparatus, since the optical path length of the transmitted pulse light and the optical path length of the reflected pulse light are completely matched, the transmitted pulse light and the reflected pulse light are completely detected simultaneously. Therefore, the detection of both waveforms and the acquisition of the spectral data of both are performed in the shortest time.

[Modification of Measurement Circuit 25]
FIG. 6 is a diagram illustrating a modification of the measurement circuit 25 (particularly in the vicinity of the ammeter). FIG. 6 also shows the antenna portion of the terahertz photodetector 5 in order to show the connection relationship.
As shown in FIG. 6, the measurement circuit 25 of this modification includes a changeover switch 26 and one ammeter 27. The terminals Ta1 and Ta2 of the changeover switch 26 are respectively connected to the two L-shaped patterns A2 and A1 of the dipole antenna 21A, and the terminals Tb1 and Tb2 of the changeover switch 26 are the two L-shaped patterns of the dipole antenna 21B. Connected to B2 and B1, respectively. The terminals Tc1 and Tc2 of the changeover switch 26 are connected to the ammeter 27.

Among these, in a state where the terminal Ta1 and the terminal Tc1 are connected and the terminal Ta2 and the terminal Tc2 are connected, only the antenna portion 31a is effective. On the other hand, in a state where the terminal Tb1 and the terminal Tc1 are connected and the terminal Tb2 and the terminal Tc2 are connected, only the antenna portion 31b is effective.
Therefore, the measurement circuit 25 of the present modification can detect both the transmitted pulsed light and the reflected pulsed light even though the measuring circuit 25 includes only one ammeter 27. However, unlike the measurement apparatus 25 of the above-described embodiment, switching of terminal connection is required, and transmitted pulsed light and reflected pulsed light are detected non-simultaneously.

[Modification of Terahertz Photodetector 5]
In addition, as the pair of antennas of the terahertz photodetector 5, an antenna of a different type from that described above may be used. Further, although the positions of the pair of antennas described above overlap, the positions of the pair of antennas may be separated.
For example, a pair of antennas 121A and 121B having an H-shaped pattern as shown in FIG. 7 may be independently arranged at different positions on the conductive film 122. In FIG. 7, the portion indicated by reference numeral 131a functions as an antenna that detects a polarization component in the X direction, and the portion indicated by reference numeral 131B functions as an antenna that detects a polarization component in the Y direction. Also in this case, the incident regions of the terahertz pulse light and the probe light cover the antenna portions 131a and 131b of both the antennas 121A and 121B.

[First Variation of Polarizer Arrangement Method]
Further, the arrangement method of the polarizer is not limited to the above-described one, and may be modified as shown in FIG. 8, for example.
FIG. 8 is a diagram for explaining a method of arranging the polarizers of this modification. In FIG. 8, only the optical system that guides the terahertz light is illustrated in a simplified manner. In FIG. 8, reference numerals 1A ′ and 1B ′ are half mirrors (silicon plates and the like) for branching and integrating terahertz pulse light, and reference numerals 81 and 82 are polarizers (wire grids and the like). The half mirrors 1A ′ and 1B ′ reflect a part of the incident terahertz pulse light regardless of the polarization direction and transmit the other part regardless of the polarization direction.

As shown in FIG. 8, the optical path for transmission measurement of this modification is the terahertz light generator 4 → half mirror 1A ′ → test object 10 → polarizer 81 → polarizer 82 → optical path bending mirror 1A → optical path bending mirror. 1B → the half mirror 1B ′ → the optical path passing through the terahertz light detector 5 in order. Two polarizers 81 and 82 are arranged in the optical path for transmission measurement.
On the other hand, the optical path for reflection measurement of this modification is an optical path that passes through the terahertz light generator 4 → the half mirror 1A ′ → the test object 10 → the half mirror 1A ′ → the half mirror 1B ′ → the terahertz light detector 5. is there. A polarizer is not disposed in the optical path for reflection measurement.

FIG. 9 is a diagram illustrating the polarizers 81 and 82 in detail. Note that the notation in FIG. 9 is the same as that in FIG. Further, it is assumed that the polarization direction of the terahertz pulse light first incident on the half mirror 1A ′ is the Y direction.
First, as shown in FIG. 9 (A1), the transmission axis T81 of the polarizer ₈₁ is set in a direction shifted by 45 ° from the X direction and the Y direction. As shown in FIG. The transmission axis _T82 is set in the X direction.

At this time, the polarization direction of the transmitted pulsed light passing through the optical path for transmission measurement is as shown in FIG. 9 (A1), FIG. 9 (A2), and FIG. 9 (A3) by the action of the two polarizers 81 and 82. When it changes and enters the terahertz light detector 5, it becomes the X direction.
On the other hand, the polarization direction of the reflected pulsed light passing through the optical path for reflection measurement does not change at all, and remains in the Y direction when entering the terahertz light detector 5 as shown in FIG. 9 (B1). .

Therefore, also in the present modification, as in the above-described embodiment, a 90 ° polarization misalignment is imparted to the transmitted pulsed light and the reflected pulsed light incident on the terahertz light detector 5.
[Second Modification of Polarizer Arrangement Method]
Further, the arrangement method of the polarizer may be modified as shown in FIG. 10, for example.
FIG. 10 is a diagram for explaining a method of arranging the polarizers according to this modification. In addition, the notation method of FIG. 10 is the same as that of FIG.

  As shown in FIG. 10, the number of polarizers provided in the modification is one (only the polarizer 81). The optical path for transmission measurement is an optical path that passes through the terahertz light generator 4 → the half mirror 1A ′ → the test object 10 → the optical path bending mirror 1A → the optical path bending mirror 1B → the polarizer 81 → the terahertz light detector 5. On the other hand, the optical path for reflection measurement is an optical path that passes through the terahertz light generator 4 → the half mirror 1A ′ → the test object 10 → the half mirror 1A ′ → the polarizer 81 → the terahertz light detector 5.

In this modification, when the polarization direction of the terahertz pulse light incident on the half mirror 1A ′ is the Y direction, the transmission axis of the polarizer 81 is set to a direction shifted by 45 ° from the Y direction.
At this time, the polarization direction of the terahertz pulse light that illuminates the test object 10, the transmitted pulse light immediately after being emitted from the test object 10, and the reflected pulse light immediately after being emitted from the test object 10 is Y. Direction.

When the transmitted pulse light passing through the optical path for transmission measurement is transmitted through the polarizer 81, the polarization direction thereof is limited only to the direction of the transmission axis of the polarizer 81. On the other hand, when the reflected pulse light passing through the optical path for reflection measurement is reflected by the polarizer 81, the polarization direction thereof is limited only to the direction of the reflection axis of the polarizer 81 (which forms an angle of 90 ° with the transmission axis). .
Therefore, a 90 ° polarization misalignment is imparted to the transmitted pulsed light and the reflected pulsed light when entering the terahertz light detector 5.

That is, this modification can also obtain the same effects as the above-described embodiment and modification. In addition, since one polarizer 81 is used for both the adjustment of the polarization direction and the optical path integration, the number of parts is reduced.
In addition to the above-described methods for arranging the polarizers, for example, there is a method in which one polarizer is arranged for each of the single optical path for transmission measurement and the single optical path for reflection measurement. In that case, the angle formed by the transmission axes of the two polarizers may be 90 °, and the transmission axis of each polarizer may be set to be 45 ° with the polarization direction of the incident terahertz pulse light.

[First modification of illumination type]
Further, the illumination type is not limited to those described above, and may be modified as shown in FIG. 11, for example.
FIG. 11 is a diagram for explaining the illumination type of this modification. In FIG. 11, only the optical system that guides the terahertz light is illustrated.

As shown in FIG. 11, there are two illumination optical paths in this modification, one of which is an illumination optical path for transmission measurement, and the other is an illumination optical path for reflected illumination. Further, the light beam that illuminates the test object 10 is not a parallel light beam but a condensed light beam.
The optical path for transmission measurement is: terahertz light generator 4 → off-axis parabolic mirror 3A → half mirror 1A ′ → off-axis parabolic mirror 3B → test object 10 → off-axis parabolic mirror 3C → polarizer 81 → Off-axis parabolic mirror 3D → optical path passing through the terahertz light detector 5 in order. According to the optical path for transmission measurement, the test object 10 is illuminated from the front.

  The optical path for reflection measurement is: terahertz light generator 4 → off-axis parabolic mirror 3A → half mirror 1A ′ → off-axis parabolic mirror 3E → optical path bending mirror 1A → test object 10 → optical path bending mirror 1B → axis This is an optical path that passes through the parabolic mirror 3F, the polarizer 81, the off-axis parabolic mirror 3D, and the terahertz photodetector 5 in this order. According to the optical path for reflection measurement, the test object 10 is illuminated from an oblique direction.

Thus, even when the illumination light path is made into two systems, the same effects as those of the above-described devices can be obtained as long as the polarizer 81 is appropriately arranged. In this modification shown in FIG. 11, as in the apparatus shown in FIG. 10, one polarizer 81 is used for both adjustment of the polarization direction and optical path integration.
[Second modification of illumination type]
FIG. 12 is a diagram for explaining the illumination type of the present modification. In FIG. 12, only an optical system that guides terahertz light is illustrated.

As shown in FIG. 12, the illumination optical path of this modification is one system, and the light beam that illuminates the test object 10 is a condensed light beam.
The optical path for transmission measurement is: terahertz light generator 4 → off-axis parabolic mirror 3A → off-axis parabolic mirror 3B → optical path bending mirror 1A → test object 10 → off-axis parabolic mirror 3C → polarizer 81 → Off-axis parabolic mirror 3D → optical path passing through the terahertz light detector 5 in order.

The optical path for reflection measurement is: terahertz light generator 4 → off-axis parabolic mirror 3A → off-axis parabolic mirror 3B → optical path bending mirror 1A → test object 10 → optical path bending mirror 1B → off-axis parabolic mirror. 3E → polarizer 81 → off-axis parabolic mirror 3D → the optical path passing through the terahertz photodetector 5 in this order.
Also in this case, if the polarizer 81 is appropriately arranged, the same effects as the above-described devices can be obtained. In this modification shown in FIG. 12, as in the apparatus shown in FIG. 10, one polarizer 81 is used for both adjustment of the polarization direction and optical path integration.

[Other variations]
In each of the above-described apparatuses, it is desirable that the atmosphere of the optical system that guides the terahertz light is kept in a vacuum state. This is because water vapor has a characteristic of absorbing terahertz light and it is necessary to eliminate the influence of water vapor in the atmosphere.
In each of the above-described devices, a mechanism for moving the test object 10 may be added. If the test object 10 is moved along the arrangement surface, the measurement region moves on the test object 10, so that an imaging function can be provided.

  In addition, each of the above-described devices is an application of the present invention to a terahertz spectroscopic device, but the present invention is not equipped with a non-scanning terahertz spectroscopic imaging device or a spectroscopic function other than the terahertz spectroscopic device. The present invention can be similarly applied to a terahertz imaging apparatus. Incidentally, the non-scanning spectroscopic imaging apparatus includes an imaging optical system that forms an image of terahertz pulse light emitted from a test object, an electro-optic crystal that detects the electric field intensity distribution on the imaging surface, and polarization A board etc. are provided.

It is a block diagram explaining the principle of the apparatus of this embodiment. It is a schematic block diagram of the apparatus of this embodiment. It is a figure explaining polarizer 71,72,73,74 in detail. It is a figure explaining the terahertz photodetector 5 in detail. 3 is an explanatory diagram of a measurement circuit 25. FIG. FIG. 10 is a diagram for explaining a modification of the measurement circuit 25. It is a figure explaining the modification of the terahertz photodetector. It is a figure explaining the 1st modification of the arrangement | positioning method of a polarizer. It is a figure explaining the polarizers 81 and 82 in detail. It is a figure explaining the 2nd modification of the arrangement | positioning method of a polarizer. It is a figure explaining the 1st modification of an illumination type. It is a figure explaining the 2nd modification of an illumination type.

Explanation of symbols

  4 ... terahertz light generator, 3A, 3B ... off-axis parabolic mirror (collimator mirror), 71, 72, 73, 74 ... polarizer, 6 ... laser light source, 9 ... Retroreflector, 8 ... Delay stage, 25 ... Measuring circuit

Claims (3)

An illumination optical system that illuminates the test object with terahertz light;
Integration means for guiding the transmitted light and reflected light of the terahertz light generated from the test object to the same optical path;
A terahertz measuring device comprising one detector arranged in the same optical path,
Further comprising polarization means for providing a difference in the polarization direction of the transmitted light and the reflected light incident on the detector,
The detector is configured to separate and detect different polarization components of incident terahertz light. The terahertz measurement device according to claim 1,
The detector includes
A terahertz measuring device comprising a pair of antennas for individually detecting different polarization components of incident terahertz light. In the terahertz measuring device according to claim 1 or 2,
The terahertz measuring device further comprising control means for controlling the timing of the illumination and the detection.

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