JP2006308426A - Terahertz measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the transmission and reflection of a specimen efficiently. <P>SOLUTION: A terahertz measuring device comprises optical illumination systems 11, 21, 41, 22, 25, 42 for irradiating the specimen 50 with terahertz light; and detection optical systems 23, 24, 12, 43, 26, 27, 13 for detecting the transmitted and reflected light of the terahertz light generated from the specimen simultaneously. The transmission and reflection can be measured by the measuring device without switching optical paths. Thus, both of the transmitted and reflected light from the specimen 50 can be utilized effectively without waste. Also, even if the state of the specimen 50 changes, transmission measurement data and reflection measurement data can be acquired in the same state. <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. Further, Patent Document 2 discloses a terahertz measurement device that includes an optical system for transmission measurement and an optical system for reflection measurement, and shares most of both.
JP 2004-205360 A JP 2004-191302 A

However, since these measuring apparatuses require switching of the optical path between transmission measurement and reflection measurement, the switching operation takes time and effort. Further, it is difficult to obtain transmission measurement data and reflection measurement data in the same state for the test object whose state changes.
Therefore, an object of the present invention is to provide a terahertz measurement apparatus that can efficiently perform transmission measurement and reflection measurement of an object while avoiding these wastes and inconveniences.

A terahertz measuring device of the present invention includes an illumination optical system that illuminates a test object with terahertz light, and a detection optical system that detects transmitted light and reflected light of the terahertz light generated simultaneously from the test object. It is characterized by that.
The illumination optical system illuminates the test object with terahertz pulse light, and the detection optical system detects the transmitted light and reflected light generated by illumination with the same terahertz pulse light, respectively. Also good.

Further, the detection optical system may detect the transmitted light and the reflected light individually with two detectors.
In addition, the detection optical system detects the transmitted light and the reflected light with the same detector, and an optical path length difference is provided between the optical path of the transmitted light and the optical path of the reflected light. Also good.
The detection optical system may be provided with a mechanism for adjusting the optical path length difference.

Further, shutter means for opening and closing the optical path may be provided on at least one of the transmitted light and the reflected light.
The illumination optical system divides the same terahertz light to illuminate the test object from two types of angles, and the detection optical system generates the small-angle illumination of the two types of angles. The transmitted light and the reflected light generated by illumination at a large angle may be detected.

The small-angle illumination may illuminate the test object from the front.
Further, the illumination optical system may illuminate the test object from one kind of angle.
Moreover, the illumination of the said angle may illuminate the said test object from the front.
In addition, the terahertz measurement device of the present invention may include control means for controlling the timing of the light emission and the detection and detecting the time waveform of the transmitted light and the time waveform of the reflected light, respectively.

  According to the present invention, a terahertz measurement device capable of efficiently performing transmission measurement and reflection measurement of a test object is realized.

[First Embodiment]
A first embodiment of the present invention will be described with reference to FIG. This embodiment is an embodiment of a terahertz spectrometer.
FIG. 1 is a schematic configuration diagram showing a measuring apparatus according to the present embodiment. FIG. 1 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 (the same applies to other figures). .

  As shown in FIG. 1, this measurement apparatus includes a terahertz light generator 11, off-axis parabolic mirrors (collimator mirrors) 21, 22, 23, 24, 25, 26 as an optical system for guiding terahertz light. 27, a beam splitter 41, terahertz photodetectors 12 and 13, and optical path bending mirrors 42 and 43, and a test object 50 such as a semiconductor is disposed at a predetermined position in the optical path. Further, the measuring apparatus includes a laser light source 31, a beam splitter BS, a movable mirror (movable retroreflector) 32, a lens L, a mirror M, an ammeter 33, and the like as an optical system for guiding a control laser. Each unit is controlled by the computer 34.

The laser light source 31 emits laser pulse light having a pulse width of about 10 to 150 fs as a control laser. This laser pulse light is branched by the beam splitter BS.
One of the laser pulse lights branched by the beam splitter BS enters the terahertz light generator 11 through the mirror M and the lens L, and excites the terahertz light generator 11. That is, the laser pulse light serves as pump light.

  The other of the laser pulse beams branched by the beam splitter BS enters the beam splitter BS via the movable mirror 32 and the mirror M, and is further branched. One branched laser pulse light is incident on the terahertz light detector 12 via the mirror M and the lens L, and the other branched laser pulse light is incident on the terahertz light detector 13 via the lens L. . These laser pulse lights serve as probe lights for the terahertz photodetectors 12 and 13.

  The terahertz light generator 11 emits terahertz pulse light having a frequency band of 0.01 THz to 100 THz according to the given pump light. The terahertz pulse light is reflected by an off-axis parabolic mirror 21 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 enters the beam splitter 41 made of a silicon plate or the like and is branched.

  One of the terahertz pulse beams branched by the beam splitter 41 is reflected by the off-axis parabolic mirror 22 and then illuminates the measurement point of the test object 50 from the front. The terahertz pulse light that has passed through the measurement point (transmission pulse light) becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration at the measurement point, and is off-axis parabolic mirror 23 while diverging. And is reflected there to become parallel light. The terahertz pulse light is reflected by the off-axis parabolic mirror 24 and is incident on the terahertz light detector 12 having a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 24. The arrangement surface of the test object 50 coincides with the focal plane of the off-axis parabolic mirrors 22 and 23.

  The other of the terahertz pulse light branched by the beam splitter 41 is reflected by the off-axis parabolic mirror 25 and then illuminates the measurement point of the test object 50 from the oblique direction via the optical path bending mirror 42. Of the terahertz pulse light, the light reflected from the measurement point (reflected pulse light) becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement point, and diverges through the optical path bending mirror 43. Is incident on the off-axis parabolic mirror 26. The terahertz pulse light is reflected by the off-axis parabolic mirror 26, becomes parallel light, and then reflected by the off-axis parabolic mirror 27. The terahertz pulse light is incident on the terahertz light detector 13 having a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 27. Note that the focal points of the off-axis parabolic mirrors 25 and 26 coincide with the measurement points of the test object 50.

  The terahertz light detectors 12 and 13 generate a detection signal (current) according to the incident terahertz pulse light and the provided probe light. The detection signal indicates a value of a portion corresponding to the timing at which the probe light is given in the time waveform (hereinafter simply referred to as “waveform”) of the electric field intensity generated by the terahertz pulse light in the detector. Detection signals from the terahertz light detectors 12 and 13 are taken into the computer 34 via the ammeter 33 and processed.

  Although not shown in the drawing, this measuring apparatus includes an ammeter as a circuit part for appropriately operating the terahertz light detectors 12 and 13 and the terahertz light generator 11 in addition to the above-described ammeter 33. An I / V conversion circuit that converts the above signal into a voltage value, a lock-in amplifier that amplifies only the necessary detection signal, a bias voltage application device that applies a bias voltage to the terahertz light generator 11, a modulation device that modulates the signal, and the like Provided.

In the above measurement apparatus, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the beam splitter 41 → the off-axis parabolic mirror 22 → the test object 50 → the off-axis parabolic mirror 23 → the off-axis paraboloid. The optical path of the terahertz pulse light sequentially passing through the surface mirror 24 and the terahertz light detector 12 is an optical path for transmission measurement.
Further, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the beam splitter 41 → the off-axis parabolic mirror 25 → the optical path bending mirror 42 → the test object 50 → the optical path bending mirror 43 → the off-axis parabolic mirror 26. → The off-axis parabolic mirror 27 → The optical path of the terahertz pulse light passing through the terahertz light detector 13 in this order is the optical path for reflection measurement.

  The optical path for transmission measurement and the optical path for reflection measurement share one terahertz light generator 11. That is, the test object 50 is illuminated at two different angles with one terahertz pulse light generated by one terahertz light generator 11, and transmitted pulse light is generated with illumination light at a small incident angle (illumination light from the front). The reflected pulse light is generated with illumination light having a large incident angle (illumination light from an oblique direction).

Here, in a state where the movable mirror 32 is arranged at a certain reference position, the sum of the optical path lengths of the optical path of the pump light and the optical path for transmission measurement coincides with the optical path length of the probe light toward the terahertz photodetector 12. And the sum of the optical path lengths of the optical path of the pump light and the optical path for reflection measurement coincides with the optical path length of the probe light toward the terahertz light detector 13.
In this state, the timing at which the transmitted pulsed light reaches the terahertz light detector 12 coincides with the timing at which the probe light enters the terahertz light detector 12, and the reflected pulsed light reaches the terahertz light detector 13. The timing coincides with the timing at which the probe light enters the terahertz light detector 13.

  When the movable mirror 32 is moved from this state, a shift (delay time) occurs in the incident timing of the transmitted pulse light and the probe light with respect to the terahertz light detector 12, and the reflected pulse light and the probe light with respect to the terahertz light detector 13 are generated. A shift (delay time) occurs in the incident timing. However, the delay time related to the terahertz light detector 12 and the delay time related to the terahertz light detector 13 are equal.

  Further, the optical path length of illumination light from the terahertz light generator 11 to the test object 50 in the optical path for transmission measurement, and the optical path length of illumination light from the terahertz light generator 11 to the test object 50 in the optical path for reflection measurement. And are consistent. This is for illuminating the test object 50 simultaneously with the same terahertz pulse light from two different angles. With this configuration, when the test object 50 changes state and detects the change in state, both transmitted pulsed light and reflected pulse light are generated from the test object 50 under the same state. Can do.

  In such a measuring apparatus, when the laser light source 31 is driven, pump light is given to the terahertz light generator 11, and the same terahertz pulse light illuminates the test object 50 from two different angles at the same timing. . Transmitted pulsed light and reflected pulsed light generated at the same timing from the test object 50 in accordance with the two types of illumination are individually incident on the terahertz light detectors 12 and 13. The delay time related to the terahertz light detector 12 and the delay time related to the terahertz light detector 13 are equal. Therefore, the values at the same location in the waveform of the transmitted pulsed light and the waveform of the reflected pulsed light are respectively detected.

Further, when the position of the movable mirror 32 is shifted in the direction of the arrow in FIG. 1, the delay time related to the terahertz light detector 12 and the delay time related to the terahertz light detector 13 change by the same amount. The detection location of the waveform and the detection location of the waveform by the terahertz light detector 13 are shifted by the same amount.
Therefore, if the movable mirror 32 is arranged at each position and the laser light source 31 is driven, the entire waveform of the transmitted pulsed light and the entire waveform of the reflected pulsed light are detected in the same manner. The computer 34 individually performs processing (Fourier transform or the like) on the waveforms of the transmitted pulsed light and the reflected pulsed light, and extracts the spectral data of the transmitted pulsed light and the spectral data of the reflected pulsed light, respectively.

As described above, since this measurement apparatus detects the transmission pulse light and the reflection pulse light emitted simultaneously from the test object 50, the transmission measurement (here, acquisition of the spectral data of the transmission pulse light) and the reflection measurement (here, the reflection). Both acquisition of spectral data of pulsed light) can be carried out without switching the optical path.
Even if the state of the test object 50 changes, transmission measurement data (here, spectral data of transmitted pulsed light) and reflection measurement data (here, spectral data of reflected pulsed light) in the same state are acquired. can do.

In addition, in this measurement apparatus, the delay time related to the terahertz light detector 12 and the delay time related to the terahertz light detector 13 always coincide with each other, so that the waveform of the transmitted pulse light and the waveform of the reflected pulse light are detected in parallel. be able to.
Therefore, the total movement amount of the movable mirror 32 is suppressed to only one pulse (that is, the minimum), and the measurement time is also suppressed to the minimum.

In this measurement apparatus, the optical path lengths of the two types of illumination light are made to coincide with each other. However, when the state change of the test object 50 can be ignored or when the state change of the test object 50 occurs, As long as it is sufficiently slower than the above, there may be a difference in the optical path lengths of the two types of illumination light.
In the present measurement apparatus, in particular, the total length of the optical path for transmission measurement (from the terahertz light generator 11 to the terahertz light detector 12) and the total length of the optical path for reflection measurement (from the terahertz light generator 11 to the terahertz light detector). 13), the detection timing of the transmitted pulse light and the detection timing of the reflected pulse light can be matched, which is more efficient.

  However, even if the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement coincide with each other, the detection timing of the transmitted pulse light and the detection timing of the reflected pulse light are shifted depending on the thickness and material of the test object 50. In this case, an appropriate optical path length difference may be provided between the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement. Further, the optical path length difference may be adjusted according to the thickness or material of the test object 50.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIG. This embodiment is also an embodiment of a terahertz spectrometer. Here, differences from the first embodiment (FIG. 1) will be mainly described.
FIG. 2 is a schematic configuration diagram showing the measurement apparatus of the present embodiment. FIG. 2 shows only the optical system that guides the terahertz light. As shown in FIG. 2, the difference from the first embodiment is that the optical path bending mirrors 42 and 43 are omitted.

The terahertz light generator 11 emits terahertz pulse light according to the pump light. The terahertz pulse light is reflected by an off-axis parabolic mirror 21 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 enters the beam splitter 41 made of a silicon plate or the like and is branched.
One of the terahertz pulse lights branched by the beam splitter 41 is reflected by the off-axis parabolic mirror 22 and then illuminates the measurement point of the test object 50 from the front. The terahertz pulse light transmitted through the measurement point becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement point, and is incident on the off-axis parabolic mirror 23 while diverging and is reflected there. It becomes parallel light. The terahertz pulse light is reflected by the off-axis parabolic mirror 24 and is incident on the terahertz light detector 12 having a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 24. The arrangement surface of the test object 50 coincides with the focal plane of the off-axis parabolic mirrors 22 and 23.

  The other of the terahertz pulse light branched by the beam splitter 41 is reflected by the off-axis parabolic mirror 25 and then illuminates the measurement point of the test object 50 from an oblique direction. The terahertz pulse light reflected at the measurement point becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration at the measurement point, and enters the off-axis parabolic mirror 26 while diverging. The terahertz pulse light is reflected by the off-axis parabolic mirror 26, becomes parallel light, and then reflected by the off-axis parabolic mirror 27. The terahertz pulse light is incident on the terahertz light detector 13 having a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 27. Note that the focal points of the off-axis parabolic mirrors 25 and 26 coincide with the measurement points of the test object 50.

  In the above measurement apparatus, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the beam splitter 41 → the off-axis parabolic mirror 22 → the test object 50 → the off-axis parabolic mirror 23 → the off-axis paraboloid. The optical path of the terahertz pulse light sequentially passing through the surface mirror 24 and the terahertz light detector 12 is an optical path for transmission measurement. Further, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the beam splitter 41 → the off-axis parabolic mirror 25 → the test object 50 → the off-axis parabolic mirror 26 → the off-axis parabolic mirror 27 → the terahertz The optical path of the terahertz pulse light that sequentially passes through the photodetector 13 is an optical path for reflection measurement.

  Also in this measurement apparatus, each optical path is set so that the delay time related to the terahertz light detector 12 and the delay time related to the terahertz light detector 13 are equal to each other as in the measurement apparatus of the first embodiment. Further, each optical path is set so that the test object 50 is simultaneously illuminated with the same terahertz pulse light from two kinds of angles. Therefore, according to this measuring apparatus, it is possible to perform the same measurement as the measuring apparatus of the first embodiment.

  Moreover, in the present measuring apparatus, unlike the measuring apparatus of the first embodiment, since the optical path bending mirrors 42 and 43 are omitted, the number of parts can be reduced. In order to omit the optical path bending mirrors 42 and 43, the optical path for transmission measurement and the optical path for reflection measurement are partially crossed. However, since the terahertz light passing through both optical paths is pulsed light, it is a cross portion. But they do not interfere with each other.

Also in this measurement apparatus, when the state change of the test object 50 can be ignored or as long as the state change of the test object 50 is sufficiently slower than the deviation amount of the illumination timing, the optical paths of the two types of illumination light There may be differences in length.
Also in this measurement apparatus, the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement may be matched to match the detection timing of the transmitted pulse light and the detection timing of the reflected pulse light.

  However, even if the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement coincide with each other, the detection timing of the transmitted pulse light and the detection timing of the reflected pulse light are shifted depending on the thickness and material of the test object 50. In this case, an appropriate optical path length difference may be provided between the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement. Further, the optical path length difference may be adjusted according to the thickness or material of the test object 50.

[Third Embodiment]
A third embodiment of the present invention will be described with reference to FIG. This embodiment is also an embodiment of a terahertz spectrometer. Here, differences from the first embodiment (FIG. 1) will be mainly described.
FIG. 3 is a schematic configuration diagram showing the measurement apparatus of the present embodiment. FIG. 3 shows only the optical system that guides the terahertz light. As shown in FIG. 3, the difference from the first embodiment is that the illumination light path is made into one system without being separated into two systems.

  The terahertz light generator 11 emits terahertz pulse light according to the pump light. The terahertz pulse light is reflected by an off-axis parabolic mirror 21 having a focal point at a position equivalent to the light emission point, and becomes parallel light. The terahertz pulse light is reflected by the off-axis parabolic mirror 22 and then illuminates the measurement point of the test object 50 from the front through the half mirror 61 made of a silicon plate or the like.

  Of the terahertz pulse light that illuminates the test object 50, the light transmitted through the measurement point (transmission pulse light) becomes light containing information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement point, and diverges. The light enters the off-axis parabolic mirror 23 and is reflected there to become parallel light. The terahertz pulse light is reflected by the off-axis parabolic mirror 24 and is incident on the terahertz light detector 12 having a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 24.

  Of the terahertz pulse light that illuminates the test object 50, the light reflected from the measurement point (reflected pulse light) becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement point, and diverges. Returning to the half mirror 61, the optical path is bent by the half mirror 61. The terahertz pulse light is reflected by the off-axis parabolic mirror 25, becomes parallel light, and then reflected by the off-axis parabolic mirror 26. The terahertz pulse light is incident on the terahertz light detector 13 having a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 26. The arrangement surface of the test object 50 coincides with the focal plane of the off-axis parabolic mirrors 22, 23, and 25.

  In the above measuring apparatus, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the off-axis parabolic mirror 22 → the half mirror 61 → the test object 50 → the off-axis parabolic mirror 23 → the off-axis paraboloid. The optical path of the terahertz pulse light sequentially passing through the surface mirror 24 and the terahertz light detector 12 is an optical path for transmission measurement. Further, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the off-axis parabolic mirror 22 → the half mirror 61 → the test object 50 → the half mirror 61 → the off-axis parabolic mirror 25 → the off-axis parabolic surface. The optical path of the terahertz pulse light sequentially passing through the mirror 26 → the terahertz light detector 13 is an optical path for reflection measurement.

  Also in this measurement apparatus, each optical path is set so that the delay time related to the terahertz light detector 12 and the delay time related to the terahertz light detector 13 are equal to each other as in the measurement apparatus of the first embodiment. Further, in this measurement apparatus, transmitted pulsed light and reflected pulsed light that are simultaneously emitted from the test object 50 are detected. Therefore, according to this measuring apparatus, it is possible to perform the same measurement as the measuring apparatus of the first embodiment.

  Moreover, in the present measuring apparatus, unlike the measuring apparatus of the first embodiment, the number of parts can be reduced because there is only one illumination optical path. In addition, since the illumination direction of the transmission measurement and the illumination direction of the reflection measurement are the same, there is an advantage that the algorithm for processing the waveform of the transmitted pulsed light and the algorithm for processing the waveform of the reflected pulsed light can be shared. is there. Further, since the illumination direction is front, there is an advantage that the algorithm can be simplified.

In this measurement apparatus, in particular, the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement are matched, and the detection timing of the transmitted pulse light and the detection timing of the reflected pulse light are matched. Good.
However, even if the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement coincide with each other, the detection timing of the transmitted pulse light and the detection timing of the reflected pulse light are shifted depending on the thickness and material of the test object 50. In this case, an appropriate optical path length difference may be provided between the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement. Further, the optical path length difference may be adjusted according to the thickness or material of the test object 50.

[Fourth Embodiment]
A fourth embodiment of the present invention will be described with reference to FIG. This embodiment is also an embodiment of a terahertz spectrometer. Here, differences from the first embodiment (FIG. 1) will be mainly described.
FIG. 4A is a schematic configuration diagram illustrating the measurement apparatus of the present embodiment. Elements in FIG. 4 (A) that are the same as those in FIG. As shown in FIG. 4A, the difference from the first embodiment is that one terahertz photodetector 12 is shared for detection of transmitted pulsed light and detection of reflected pulsed light. Correspondingly, the optical system for guiding the control laser is also simplified (the optical path of the laser light toward the terahertz light detector 13 is omitted).

The illumination optical path of this measurement apparatus is the same as that of the measurement apparatus of the first embodiment, and illuminates the measurement point of the test object 50 from two directions.
The terahertz pulsed light (transmitted pulsed light) transmitted through the measurement point of the test object 50 becomes light including information on the complex dielectric constant, electrical characteristics, impurity concentration, etc. of the measurement point, and is off-axis parabolic mirror while diverging , And is reflected there to become parallel light. The terahertz pulse light is reflected by an off-axis parabolic mirror 24 via a composite mirror 44 made of a silicon plate or the like, and has a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 24. The light enters the photodetector 12. The arrangement surface of the test object 50 coincides with the focal plane of the off-axis parabolic mirrors 22 and 23.

  The terahertz pulse light (reflected pulse light) reflected at the measurement point of the test object 50 becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration at the measurement point, and passes through the optical path bending mirror 43 while diverging. Is incident on the off-axis parabolic mirror 26. The terahertz pulse light is reflected by the off-axis parabolic mirror 26 toward the synthesis mirror 44 and enters the synthesis mirror 44 in the state of parallel light. The terahertz pulse light follows the same optical path as the transmitted pulse light, and enters the terahertz light detector 12 through the off-axis parabolic mirror 24. Note that the focal points of the off-axis parabolic mirrors 25 and 26 coincide with the measurement points of the test object 50.

  In the above measuring apparatus, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the beam splitter 41 → the off-axis parabolic mirror 22 → the test object 50 → the off-axis parabolic mirror 23 → the synthetic mirror 44 → The optical path of the terahertz pulse light that sequentially passes through the off-axis parabolic mirror 24 and the terahertz light detector 12 is an optical path for transmission measurement. Further, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the beam splitter 41 → the off-axis parabolic mirror 25 → the optical path bending mirror 42 → the test object 50 → the optical path bending mirror 43 → the off-axis parabolic mirror 26. The optical path of the terahertz pulse light that passes through the synthesis mirror 44, the off-axis parabolic mirror 24, and the terahertz light detector 12 in this order is an optical path for reflection measurement.

Here, in this measurement apparatus, an optical path length difference of one pulse or more is provided between the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement. This is because the transmitted pulsed light and the reflected pulsed light are incident on the terahertz light detector 12 at different timings.
FIG. 4B is a diagram illustrating a waveform of terahertz light that reaches the terahertz light detector 12 (time change in electric field intensity). This waveform has two large peaks, one of which is the waveform of the transmitted pulsed light and the other is the waveform of the reflected pulsed light. FIG. 4B shows an example in which the optical path length for transmission measurement is shorter than the optical path length for reflection measurement, and the transmitted pulsed light reaches first. The optical path length difference is ensured so that these transmitted pulsed light and reflected pulsed light are completely separated in time. However, the optical path length difference is desirably set to an appropriate value so that the arrival timing deviation amount ΔT is minimized.

In the above measurement apparatus, when the laser light source 31 is driven, the pump light is given to the terahertz light generator 11 and the terahertz pulse light is applied to the object 50 at the same timing as in the measurement apparatus of the first embodiment. Illuminate from two different angles.
However, in this measurement apparatus, the transmitted pulsed light and the reflected pulsed light generated from the test object 50 at the same timing reach the terahertz light detector 12 with the arrival timing shift amount ΔT. The waveform of the incident light with respect to the terahertz light detector 12 is as shown in FIG. The terahertz light detector 12 detects a value at a certain position of the waveform at the timing when the probe light is given.

  Further, when the position of the movable mirror 32 is shifted in the direction of the arrow in FIG. 4, the delay time from the pump light incident timing to the probe light incident timing changes, and the detected position of the waveform is shifted. Therefore, if the movable mirror 32 is disposed at each position and the laser light source 31 is driven, the entire waveform is detected. The first half of the detected waveform is the transmitted pulsed light waveform, and the second half is the waveform of the reflected pulsed light. The computer 34 individually performs processing (Fourier transform or the like) on both waveforms, and acquires spectral data of transmitted pulsed light and spectral data of reflected pulsed light, respectively.

As described above, since the measurement apparatus detects the transmission pulse light and the reflection pulse light simultaneously emitted from the test object 50, transmission measurement is performed without switching the optical path (here, acquisition of spectral data of the transmission pulse light). And reflection measurement (here, acquisition of spectral data of reflected pulsed light) can be performed.
Moreover, even if the state of the test object 50 changes, transmission measurement data and reflection measurement data in the same state can be acquired.

In addition, in the present measuring apparatus, since one terahertz light detector 12 is shared for detecting transmitted pulsed light and reflected pulsed light, the number of parts can be suppressed.
In this measurement apparatus, instead of sharing one terahertz light detector 12, the arrival timings of the transmitted pulsed light and the reflected pulsed light are shifted, so the waveform of the transmitted pulsed light and the waveform of the reflected pulsed light are: Detected in series rather than in parallel. For this reason, the total movement amount and measurement time of the movable mirror 32 are longer than those of the first embodiment. However, since the arrival timing shift amount ΔT is minimized, the total movement amount and the total measurement time of the movable mirror 32 are minimized.

  Here, in the present measuring apparatus, the arrival timing deviation amount ΔT (see FIG. 4B) varies depending on the thickness and refractive index of the test object 50. For this reason, depending on the thickness and material (refractive index, etc.) of the test object 50, a part of the transmitted pulsed light and a part of the reflected pulsed light may overlap, making it impossible to separate the waveforms of both. The inability to separate is the same as the inability to perform both transmission and reflection measurements.

Therefore, as shown by a dotted line in FIG. 4A, a shutter 71 may be provided in the single optical path of the reflected pulse light. If this shutter 71 is used, at least transmission measurement can be reliably performed regardless of the thickness and refractive index of the test object 50.
Instead of being arranged in the optical path of the reflected pulsed light, a shutter may be arranged in the single optical path of the transmitted pulsed light. In that case, at least the reflection measurement can be reliably performed regardless of the thickness and refractive index of the test object 50.

Alternatively, a shutter may be disposed in each of the single optical path of the transmitted pulse light and the single optical path of the reflected pulse light. In that case, the transmission measurement and the reflection measurement can be reliably performed regardless of the thickness and refractive index of the test object 50.
[Fifth Embodiment]
A fifth embodiment of the present invention will be described with reference to FIG. This embodiment is a modification of the fourth embodiment (FIG. 4). Here, only differences from the fourth embodiment will be described.

FIG. 5A is a schematic configuration diagram showing the measurement apparatus of the present embodiment. In FIG. 5A, only the optical system that guides the terahertz light is shown in a simplified manner. The difference from the fourth embodiment is that the optical path length difference between the optical path for transmission measurement and the optical path for reflection measurement is made variable instead of arranging the shutter.
Specifically, in this measuring apparatus, an optical path bending mirror M, a movable mirror (movable retroreflector) 72, and an optical path bending mirror M are inserted in the single optical path of the reflected pulsed light. When the movable mirror 72 is moved in the direction of the arrow in FIG. 5A, the optical path length of the reflected pulse light can be adjusted.

FIG. 5B is a diagram illustrating a waveform of terahertz light (time change in electric field intensity) reaching the terahertz light detector 12. When the optical path length of the reflected pulse light is adjusted, the arrival timing of the reflected pulse light is shifted as indicated by an arrow in FIG.
Therefore, if the position of the movable mirror 72 is adjusted according to the thickness and material (refractive index, etc.) of the test object 50, it is possible to prevent the transmitted pulsed light waveform and the reflected pulsed light waveform from overlapping. Also, the amount of deviation ΔT between the arrival timings of both can be kept to a minimum.

Therefore, according to the present measuring apparatus, it is possible to reliably carry out both the transmission measurement and the reflection measurement without depending on the thickness and the refractive index of the test object 50, and to suppress the measurement time to the minimum necessary. Can do.
In addition, although this measuring apparatus enables adjustment of the optical path length of the reflected pulse light, the optical path length of the transmitted pulse light may be adjustable instead of making the optical path length of the reflected pulse light adjustable. Further, the optical path lengths of both may be adjustable.

[Sixth Embodiment]
A sixth embodiment of the present invention will be described with reference to FIG. This embodiment is also an embodiment of a terahertz spectrometer. Here, differences from the fourth embodiment (FIG. 4) will be mainly described.
FIG. 6 is a schematic configuration diagram showing the measurement apparatus of the present embodiment. FIG. 6 shows only an optical system that guides terahertz light. As shown in FIG. 6, the difference from the fourth embodiment is that the illumination optical path is not divided into two systems but one system (illuminated from an oblique direction).

The terahertz light generator 11 emits terahertz pulse light according to the pump light. The terahertz pulse light is reflected by an off-axis parabolic mirror 21 having a focal point at a position equivalent to the light emission point, and becomes parallel light. The terahertz pulse light is reflected by the off-axis parabolic mirror 25 and then illuminates the measurement point of the test object 50 from the oblique direction via the optical path bending mirror 42.
Of the terahertz pulse light that illuminates the test object 50, the light transmitted through the measurement point (transmission pulse light) becomes light containing information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement point, and diverges. The light enters the off-axis parabolic mirror 23 and is reflected there to become parallel light. The terahertz pulse light is reflected by an off-axis parabolic mirror 24 via a composite mirror 44 made of a silicon plate or the like, and has a detection center at a position equivalent to the focal point of the off-axis parabolic mirror 24. The light enters the photodetector 12.

  Of the terahertz pulse light that illuminates the test object 50, the light reflected from the measurement point (reflected pulse light) becomes light including information such as the complex dielectric constant, electrical characteristics, and impurity concentration of the measurement point, and diverges. The light enters the optical path bending mirror 43, where the optical path is bent and then reflected off the off-axis parabolic mirror 26, becomes parallel light, and then enters the combining mirror 44. The terahertz pulse light follows the same optical path as the transmitted pulse light, and enters the terahertz light detector 12 through the off-axis parabolic mirror 24.

  In the above measuring apparatus, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the off-axis parabolic mirror 25 → the optical path bending mirror 42 → the test object 50 → the off-axis parabolic mirror 23 → the synthetic mirror 44. → The off-axis parabolic mirror 24 → The optical path of the terahertz pulse light passing through the terahertz photodetector 12 in this order is the optical path for transmission measurement. Further, the terahertz light generator 11 → the off-axis parabolic mirror 21 → the off-axis parabolic mirror 25 → the optical path bending mirror 42 → the test object 50 → the optical path bending mirror 43 → the off-axis parabolic mirror 26 → the synthetic mirror 44. → The off-axis parabolic mirror 24 → The optical path of the terahertz pulse light passing through the terahertz photodetector 12 in this order is the optical path for reflection measurement.

Also in this measurement apparatus, an appropriate optical path length difference is provided between the total length of the optical path for transmission measurement and the total length of the optical path for reflection measurement, as in the measurement apparatus of the fourth embodiment. Therefore, this measurement apparatus can also perform the same measurement as the measurement apparatus of the fourth embodiment.
Moreover, in the present measuring apparatus, unlike the measuring apparatus of the fourth embodiment, the number of parts is reduced because there is only one illumination optical path. In addition, since the illumination direction of the transmission measurement and the illumination direction of the reflection measurement are the same (in this case, the oblique direction), an algorithm for processing the waveform of the transmitted pulsed light and an algorithm for processing the waveform of the reflected pulsed light are There is also an advantage that it can be shared.

In this measuring apparatus, the shutter 71 may be provided in at least one of the single optical path of the reflected pulse light and the single optical path of the transmitted pulse light. Also, this measurement apparatus can be modified in the same manner as in the fifth embodiment (the optical path length difference between the optical path for transmission measurement and the optical path for reflection measurement can be made variable).
[Seventh Embodiment]
A seventh embodiment of the present invention will be described with reference to FIG. This embodiment is a modification of the third embodiment (FIG. 3). Here, only differences from the third embodiment will be described.

  FIG. 7 is a schematic configuration diagram showing the measuring apparatus of the present embodiment. FIG. 7 shows only an optical system that guides terahertz light. As shown in FIG. 7, the difference from the third embodiment is that, instead of the off-axis paraboloidal mirrors 21 and 22, one elliptical mirror 31 having the same action is used, and the off-axis parabolic Instead of the object mirrors 25 and 26, a point using one elliptical mirror 33 that performs the same function as those, and instead of the off-axis paraboloidal mirrors 23 and 24, one elliptical mirror that performs the same function as them. 32.

  The ellipsoidal mirror 31 has one focus at a position equivalent to the emission point of the terahertz light generator 11, and the ellipsoidal mirror 32 has one focus at a position equivalent to the detection center of the terahertz light detector 12. The ellipsoidal mirror 33 has one focal point at a position equivalent to the detection center of the terahertz photodetector 13. The arrangement surface of the test object 50 coincides with a focal plane formed by the other focal points of the ellipsoidal mirrors 31, 32, and 33.

Therefore, this measuring apparatus is optically equivalent to the measuring apparatus of the third embodiment, but only the number of parts is greatly reduced.
Although this embodiment is a modification of the third embodiment, other embodiments can be similarly modified. That is, the two parabolic mirrors arranged in series in the measurement apparatus of each embodiment can be replaced with one elliptical mirror.

[Others]
In the measurement apparatus of each embodiment described above, silicon plates are used for the beam splitter 41, the combining mirror 44, and the half mirror 61. However, a part of the incident terahertz light is reflected and the other part is transmitted. However, an optical member other than a silicon plate may be used as long as it has such a property (however, at least in the terahertz region, it is desirable that the reflection / transmittance does not have wavelength characteristics). For example, a wire grid that reflects a specific polarization component of incident terahertz light and transmits another specific polarization component can be used.

Moreover, in the measuring apparatus of each embodiment mentioned above, it is desirable that the atmosphere of the optical system that guides the terahertz light is kept in a vacuum state. This is because terahertz light has a feature of absorbing water, and it is necessary to eliminate the influence of moisture in the atmosphere.
Moreover, in the measuring apparatus of each embodiment mentioned above, you may add the mechanism to which the test object 50 is moved. If the test object 50 is moved along the arrangement plane, the test object 50 can be two-dimensionally scanned at the measurement point, so that an imaging function can be provided.

  In addition to the terahertz spectroscopic device, the present invention can be applied to a non-scanning terahertz spectroscopic imaging device, a terahertz imaging device not equipped with a spectroscopic function, and the like. 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 schematic block diagram which shows the measuring apparatus of 1st Embodiment. It is a schematic block diagram which shows the measuring apparatus of 2nd Embodiment. It is a schematic block diagram which shows the measuring apparatus of 3rd Embodiment. (A) is a schematic block diagram which shows the measuring apparatus of 4th Embodiment, (B) is a figure which shows the waveform (temporal change of an electric field strength) of the terahertz light which reaches | attains the terahertz photodetector 12. FIG. (A) is a schematic block diagram which shows the measuring apparatus of 5th Embodiment, (B) is a figure which shows the waveform (time change of an electric field strength) of the terahertz light which reaches | attains the terahertz photodetector 12. FIG. It is a schematic block diagram which shows the measuring apparatus of 6th Embodiment. It is a schematic block diagram which shows the measuring apparatus of 7th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Terahertz light generator, 12, 13 ... Terahertz light detector, 41 ... Beam splitter, 42, 43 ... Optical path bending mirror, 44 ... Synthetic mirror, 21, 22, 23, 24, 25, 26, 27 ... off-axis parabolic mirrors, 31 ... laser light source, 32 ... movable mirror, 34 ... computer, 33 ... ammeter, 50 ... test object

Claims (11)

An illumination optical system that illuminates the test object with terahertz light;
A terahertz measuring device comprising: a detection optical system that detects transmitted light and reflected light of the terahertz light simultaneously generated from the test object. The terahertz measurement device according to claim 1,
The illumination optical system includes:
Illuminate the specimen with terahertz pulse light,
The detection optical system includes:
A terahertz measuring device, wherein the transmitted light and reflected light generated by illumination with the same terahertz pulsed light are respectively detected. In the terahertz measuring device according to claim 1 or 2,
The detection optical system includes:
The transmitted light and the reflected light are individually detected by two detectors. The terahertz measurement device according to claim 2,
The detection optical system includes:
The transmitted light and reflected light are detected by the same detector,
Between the optical path of the transmitted light and the optical path of the reflected light,
A terahertz measuring device, characterized in that an optical path length difference is provided. In the terahertz measuring device according to claim 4,
In the detection optical system,
A terahertz measurement device comprising a mechanism for adjusting the optical path length difference. In the terahertz measuring device according to claim 4 or 5,
In at least one optical path of the transmitted light and the reflected light,
A shutter means for opening and closing an optical path is provided. In the terahertz measuring device according to any one of claims 1 to 6,
The illumination optical system includes:
Divide the same terahertz light to illuminate the test object from two angles,
The detection optical system includes:
The terahertz measuring device, wherein the transmitted light generated by illumination at a small angle of the two kinds of angles and the reflected light generated by illumination at a large angle are detected. The terahertz measurement device according to claim 7,
The small angle illumination is
The terahertz measuring device, wherein the test object is illuminated from the front. In the terahertz measuring device according to any one of claims 1 to 6,
The illumination optical system includes:
A terahertz measuring device illuminating the test object from one kind of angle. The terahertz measurement device according to claim 9,
The illumination at the angle is
The terahertz measuring device, wherein the test object is illuminated from the front. In the terahertz measuring device according to any one of claims 1 to 10,
A terahertz measurement device comprising control means for controlling the timing of the light emission and the detection and detecting the time waveform of the transmitted light and the time waveform of the reflected light, respectively.

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