JP2002303574A - Terahertz optical device and its adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily adjust alignment of a terahertz optical system. SOLUTION: The terahertz optical system has a terahertz light generator 8, a terahertz light detector 13, and a beam splitter 11 arranged between them, or the like. A rotating mechanism 26 can rotate the beam splitter 11 to a first rotational position (a position shown in Figure 1) of directing probe light to the detector 13 and a second rotational position (a position rotated 90 deg. around an axis perpendicular to the paper surface from the position shown in Figure 1) of directing the probe light to the generator 8. Alignment of a curved mirror 12 and the detector 13 is adjusted so as to converge the probe light on an appropriate position of the detector 13 in the state of the first rotational position. Alignment of a curved mirror 9 and the generator 8 is adjusted so as to converge the probe light on a terahertz pulsed light generating point of the generator 8 in the state of the second rotational position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a terahertz optical device and an adjusting method for adjusting the alignment of the terahertz optical system.

[0002]

2. Description of the Related Art In recent years, the usefulness of terahertz light utilization technology such as terahertz spectroscopy has been recognized in various fields such as measurement, inspection, imaging of materials, and various other fields having terahertz optical systems. Terahertz optical devices have already been provided or are about to be developed.

[0003] Needless to say, terahertz light is invisible to human eyes, and at present, there is no simple observation tool capable of observing terahertz light.

Therefore, conventionally, alignment of a terahertz optical system is adjusted by replacing a terahertz light source such as a dipole antenna with a pinhole and passing visible light or near-infrared light (in many cases, pump light itself) through the pinhole. , While observing the state of the transmitted light. That is, the optical path of the transmitted light through the pinhole is considered to be the same as the optical path of the terahertz light.

[0005] In the case of visible light, the irradiation position and the like can be directly observed with the naked eye. In the case of near-infrared light or the like, a card-type infrared sensor in which a material that emits visible light in response to near-infrared light is applied to a sheet member (for example, “SIRC-
By using a simple observation tool such as “(1)” (trade name), observation can be easily performed.

However, since it is very difficult to accurately replace the terahertz light source at the same position as the pinhole, after adjusting the alignment of the terahertz optical system with reference to the light transmitted through the pinhole, the terahertz light source is moved. The alignment cannot be adjusted exactly by simply replacing

Therefore, in the conventional adjusting method for adjusting the alignment of the terahertz optical system, actually, the alignment is adjusted based on the transmitted light of the pinhole, and then the terahertz light source is replaced with the terahertz light source. The alignment of the terahertz optical system has been optimized by readjusting the intensity of the light detection signal while measuring the intensity of the signal. In this work, it was necessary to repeat trial and error in which the alignment of the terahertz optical system was gradually changed depending on the intensity of the detection signal of the terahertz light.

[0008]

However, in the above-mentioned conventional adjusting method, it is necessary to repeat the above-described trial and error in order to accurately perform alignment of the terahertz optical system. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a terahertz optical device capable of accurately and easily adjusting the alignment of a terahertz optical system.

Another object of the present invention is to provide an adjustment method capable of accurately and easily adjusting the alignment of a terahertz optical system.

[0011]

According to a first aspect of the present invention, there is provided a terahertz optical device.
(A) a generation unit of terahertz light, a detection unit that detects terahertz light that is generated from the generation unit and reaches via a predetermined optical path, and is disposed on an optical path between the generation unit and the detection unit. A terahertz optical system having a beam splitter; and (b) detecting terahertz light by the detection unit,
(C) a first rotation of the beam splitter to direct the probe light from the probe light irradiation unit to the detection unit; And a rotation mechanism capable of rotating the probe light from the probe light irradiation unit to a second rotation position for directing the probe light from the probe light irradiation unit to the generation unit.

The second rotational position can be set, for example, at a position rotated by 90 ° from the first rotational position. This is the same for the second to seventh aspects described later. Further, as the probe light,
For example, visible light or near-infrared light can be used. This is the same for the second to eighth aspects described later.

According to the first aspect, since the rotation mechanism is provided, it is possible to realize, for example, the adjustment methods according to the second to seventh aspects to be described later. The alignment of the system can be adjusted. Then, since the positioning accuracy of the rotation position of the rotation mechanism can be easily increased, after the adjustment of the alignment using the probe light, the repetition of the above-described trial and error, which is necessary in the conventional adjustment method, is significantly increased. Reduced or unnecessary. Therefore, according to the first aspect, the alignment of the terahertz optical system can be adjusted accurately and easily.

The adjusting method according to the second aspect of the present invention comprises:
(A) a generation unit of terahertz light, a detection unit that detects terahertz light that is generated from the generation unit and reaches via a predetermined optical path, and is disposed on an optical path between the generation unit and the detection unit. A terahertz optical system having a beam splitter,
(B) adjusting the alignment of the terahertz optical system of the terahertz optical device including a probe light irradiation unit that irradiates the detection unit with probe light via the beam splitter when the detection unit detects the terahertz light. This is the adjustment method. The adjustment method according to the second aspect includes: (a) the beam splitter includes a first rotation position at which the probe light from the probe light irradiation unit is directed to the detection unit, and the probe light irradiation unit. The state of the probe light in a state where the beam splitter is positioned at the second rotation position by using a rotation mechanism capable of rotating the probe light from a second position to the second rotation position that directs the probe light toward the generation unit. (C) after the first step, adjusting the alignment of the terahertz optical system while observing the position of the beam splitter at the first rotation position using the rotation mechanism. And a second stage to be performed.

In the adjusting method according to a third aspect of the present invention, in the second aspect, the beam splitter is positioned at the first rotation position while observing a state of the probe light. The third step is to adjust the alignment of the terahertz optical system. This third
The temporal relationship between the step and the first and second steps is not limited at all.

In the adjusting method according to a fourth aspect of the present invention, in the second aspect, the third step is that the state of the probe light emitted from the probe light irradiation section and reaching the vicinity of the detection section And adjusting the alignment of the terahertz optical system while observing.

In the adjusting method according to a fifth aspect of the present invention, in the third or fourth aspect, the third step is that the beam emitted from the probe light irradiation unit is reflected by the detection unit and then reflected by the detection unit. Adjusting the alignment of the terahertz optical system while observing the state of the probe light reaching the vicinity of the generation unit via the splitter.

In the adjustment method according to a sixth aspect of the present invention, in any one of the second to fifth aspects, the first step may include emitting from the probe light irradiating section and reaching near the generating section. While observing the state of the probe light
And adjusting the alignment of the terahertz optical system.

In the adjustment method according to a seventh aspect of the present invention, in any one of the second to sixth aspects, the first step is that the light is emitted from the probe light irradiation unit and reflected by the generation unit. Adjusting the alignment of the terahertz optical system while observing the state of the probe light reaching the vicinity of the detection unit via the beam splitter later.

According to the third to seventh aspects, the alignment of the terahertz optical system can be adjusted using the probe light. Then, since the positioning accuracy of the rotation position of the rotation mechanism can be easily increased, after the adjustment of the alignment using the probe light, the repetition of the above-described trial and error, which is necessary in the conventional adjustment method, is significantly increased. Reduced or unnecessary. Therefore, according to the third to seventh aspects, the alignment of the terahertz optical system can be adjusted accurately and easily.

The adjusting method according to the eighth aspect of the present invention is as follows.
(A) a generation unit of terahertz light, a detection unit that detects terahertz light that is generated from the generation unit and reaches via a predetermined optical path, and is disposed on an optical path between the generation unit and the detection unit. A terahertz optical system having a beam splitter,
(B) adjusting the alignment of the terahertz optical system of the terahertz optical device including a probe light irradiation unit that irradiates the detection unit with probe light via the beam splitter when the detection unit detects the terahertz light. This is the adjustment method. Then, the adjustment method according to the eighth aspect adjusts the alignment of the terahertz optical system while observing the state of the probe light emitted from the probe light irradiation unit and reaching the vicinity of the detection unit. (B) observing the state of the probe light emitted from the probe light irradiation unit and reflected by the detection unit and reaching the vicinity of the generation unit via the beam splitter, while observing the state of the terahertz optical system. Adjusting the alignment.

In the eighth embodiment, while observing the state of the probe light emitted from the probe light irradiation unit and reaching the vicinity of the detection unit, not only the alignment of the terahertz optical system is adjusted, but also the probe light irradiation unit The alignment of the terahertz optical system is adjusted while observing the state of the probe light that is emitted and reflected by the detection unit and reaches the vicinity of the generation unit via the beam splitter. Therefore, according to the eighth aspect, it is possible to adjust the alignment of the terahertz optical system using the probe light without using the rotation mechanism for rotating the beam splitter, and the conventional adjustment method The repetition of the above-described trial and error, which is required in the above, is greatly reduced or becomes unnecessary. Therefore, according to the eighth aspect, the third aspect
As compared with the seventh to seventh aspects, the alignment of the terahertz optical system can be adjusted more accurately and more easily, and the cost of the terahertz optical device can be reduced.

The adjusting method according to the ninth aspect of the present invention includes:
(A) a generation unit of terahertz light, a detection unit that detects terahertz light that is generated from the generation unit and reaches via a predetermined optical path, and is disposed on an optical path between the generation unit and the detection unit. A terahertz optical system having a first beam splitter; and (b) a probe light irradiator for irradiating the detector with probe light via the first beam splitter when the detector detects terahertz light; An adjustment method for adjusting the alignment of the terahertz optical system in the terahertz optical device provided with: Then, in the adjusting method according to the ninth aspect, a second beam splitter is arranged on the optical path of the probe light or the optical path of the terahertz light, and travels to the generation unit via the second beam splitter. In this way, a step of adjusting the alignment of the terahertz optical system while inputting the light for adjustment and observing the state of the light for adjustment is provided. As the adjustment light, for example, visible light or near-infrared light can be used.

In the ninth aspect, the light for adjustment is incident on the optical path of the probe light or the terahertz light via the second beam splitter disposed on the optical path of the terahertz light so as to be directed to the terahertz light generating section. The alignment of the terahertz optical system is adjusted while observing the state of the light for adjustment. Therefore, it is possible to adjust the alignment of the terahertz optical system using the adjustment light introduced from outside without using the rotation mechanism used in the second to seventh aspects. The repetition of the above-described trial and error, which is required in the conventional adjustment method, is greatly reduced or becomes unnecessary. Therefore, according to the ninth aspect, the alignment of the terahertz optical system can be adjusted more accurately and more easily than in the third to seventh aspects, and the cost of the terahertz optical device can be reduced. Can be planned.

The adjusting method according to the tenth aspect of the present invention comprises:
In the ninth aspect, the step includes adjusting an alignment of the terahertz optical system while observing a state of the adjustment light reflected by the generation unit.

When the state of the adjusting light reflected by the terahertz light generating section is observed as in the tenth aspect,
Of the elements of the terahertz optical system, the alignment of the element located on the detection unit side with respect to the second beam splitter can be adjusted based on the adjustment light, which is preferable.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a terahertz optical device and an adjusting method according to the present invention will be described with reference to the drawings.

[First Embodiment]

FIG. 1 is a schematic configuration diagram schematically showing a terahertz optical device according to an embodiment of the present invention.

In the terahertz optical device according to the present embodiment, as shown in FIG. 1, a femtosecond pulse light L1 emitted from a femtosecond pulse light source 1 is split into two pulse lights L2 and L3 by a beam splitter 2. You. In the present embodiment, the femtosecond pulse light source 1 is composed of a laser light source or the like. For example, the femtosecond pulse light L1 has a center wavelength of about 780 to 800 nm in the near infrared region and a pulse width of about 10 to 100 fs. Emits linearly polarized pulsed light.

One of the pulse lights L2 split by the beam splitter 2 becomes pump light (pulse excitation light) for exciting the terahertz light generator 8 and causing the generator 8 to generate terahertz pulse light. After the pump light L2 is chopped by the chopper 3, the pump light L2 is
Through the terahertz light generator 8. as a result,
The generator 8 is excited to emit the terahertz pulse light L4. In the present embodiment, the generator 8 is used as a point light source of the terahertz pulse light. For example, as such a generator 8, a generator having a dipole antenna formed on a photoconductive film on a substrate such as GaAs, a ZnT
A non-linear optical crystal such as e can be used. When a nonlinear optical crystal is used as the generator 8,
By locally injecting the pump light L2 into the crystal, the crystal can serve as a point light source of terahertz pulse light. When a generator having a dipole antenna is used as the generator 8, a bias voltage is applied.

The terahertz pulse light L generated by the generator 8
4 is approximately 0.1 × 10 ¹² to 100 × 10
Light in the frequency range up to ¹² Hertz is desirable. The terahertz pulse light L4 is converted into parallel light through a curved mirror 9 such as a parabolic mirror, and transmitted through a device under test 10 and a beam splitter 11 described later, and then terahertz by a curved mirror 12 such as a parabolic mirror. The light is locally focused on the photodetector 13, and the detector 13 is used as a point-like detector. In the present embodiment, a nonlinear optical crystal (electro-optical crystal) such as ZnTe is used as the detector 13. Therefore,
When the terahertz pulse light is incident on the detector 13, the electric field causes a birefringence change in the crystal due to an electro-optic effect. As described later, the electric field intensity of the terahertz pulse light is detected by detecting the change in the birefringence using the probe light.

The other pulse light L3 split by the beam splitter 2 becomes probe light for detecting terahertz pulse light. The probe light L3 passes through a movable mirror 14, which is a combination of two or three plane reflecting mirrors, a plane reflecting mirror 15, and a half-wave plate 16, and is detected by a beam splitter 11 when detecting terahertz pulse light. The reflected terahertz pulsed light is guided to travel in the same optical path in the same direction as the terahertz pulse light, and the curved mirror 12
Is locally focused on the same place as in the case of the terahertz pulse light. As the beam splitter 11, for example,
A pellicle or a high-resistance silicon wafer can be used. The high-resistance silicon wafer has high reflectivity for visible light and near-infrared light, and transmits light in the terahertz region well, so that it can be used for this application. When a high-resistance silicon wafer is used as the beam splitter 11, it is preferable to adopt a method for adjusting the alignment of the terahertz optical system as described in a second embodiment of the present invention described later.

The probe light, which is linearly polarized light focused on the detector 13 by the curved mirror 12, passes through the detector 13. The polarization state of the transmitted light changes to elliptically polarized light according to the birefringence change of the detector 13 caused by the terahertz pulse light (that is, the electric field intensity change of the terahertz pulse light). At this time, information on the electric field intensity of the terahertz pulsed light depends on the polarization state of the probe light as a difference from the linearly polarized light. The probe light transmitted through the detector 13 is 1/4
At this time, the information of the electric field intensity of the terahertz pulse light is converted into a difference between the polarization state of the probe light and the circularly polarized light, and is separated into a p-polarized component and an s-polarized component by the polarizing beam splitter 18. These are detected by photodetectors 19 and 20 such as photodiodes, respectively. The signal processing circuit 21 amplifies the difference between the detection signals from the photodetectors 19 and 20. Thus, the 波長 wavelength plate 1
7. Polarizing beam splitter 18 and two photodetectors 1
When the difference between the detection signals from the photodetectors 19 and 20 is calculated using the values 9 and 20, the S
/ N is improved. However, the elements 17, 1
8 and 20 may be removed, an analyzer may be arranged between the detector 13 and the photodetector 19, and the detection signal from the photodetector 19 may be used as the terahertz light detection signal. The half-wave plate 16 is used to set the polarization direction of the linearly polarized light of the probe light when entering the detector 13 in a predetermined relationship according to the crystal orientation of the detector 13 and the polarization direction of the terahertz light. Things. If the pulse light from the femtosecond pulse light source 1 is not linearly polarized light, a polarizer may be used instead of the half-wave plate 16.

As the detector 13, a non-linear optical crystal may be used in which a dipole antenna is formed on a photoconductive film on a substrate such as GaAs. In this case, the elements 17 to 20 in FIG. 1 are removed, an ammeter for detecting a current generated by the detector is used, and the current detection signal is used as a detection signal of the electric field intensity of the terahertz light.

The movable mirror 14 arranged on the optical path of the probe light L3 can be moved in the direction of the arrow X by the moving mechanism 25 under the control of the control / arithmetic processing unit 23. The optical path length of the probe light L3 changes according to the amount of movement of the movable mirror 14, and the time for the probe light L3 to reach the detector 13 is delayed. That is, in the present embodiment, the movable mirror 14 and the moving mechanism 15 constitute a time delay device for the probe light L3.

As described above, the electric field intensity of the terahertz pulse light transmitted through the device under test 10 is detected by the detector 13 as a change in the complex refractive index, and is converted into an electric signal from the signal processing circuit 21.

The repetition period of the femtosecond pulse light L1 emitted from the femtosecond pulse light source 1 is on the order of several KHz to MHz. Therefore, the terahertz pulse light L4 emitted from the generator 8 also has a frequency of several KHz to MHz.
It is emitted in repetition of the order. At present, it is impossible to measure the waveform of the terahertz pulse light instantaneously with its shape.

Therefore, in the present embodiment, taking advantage of the fact that the terahertz pulse light L4 having the same waveform arrives repeatedly from several KHz to the order of MHz, the pump light L2
A so-called pump-probe method of measuring the waveform of the terahertz pulse light by providing a time delay between the light and the probe light L3 is adopted. That is, the electric field intensity of the terahertz pulse light at a time point delayed by τ seconds is measured by delaying the timing of activating the terahertz light detector 13 by τ seconds with respect to the pump light L2 that activates the terahertz light generator 8. it can. In other words, the probe pulse L
Reference numeral 3 indicates that the terahertz photodetector 13 is gated. In addition, moving the movable mirror 9 gradually is nothing but changing the delay time τ gradually.
The electric field strength at each delay time τ of the repeatedly arriving terahertz pulse light is determined by the signal processing circuit 21 while shifting the timing of gate application by the time delay device.
, The time-series waveform E (t) of the electric field intensity of the terahertz pulse light can be measured. The electric signal from the signal processing circuit 23 is A /
A / D conversion is performed by the D converter 22.

In the present embodiment, when measuring the time-series waveform E (t) of the electric field intensity of the terahertz pulse light, the control / arithmetic processing unit 23 gives a control signal to the moving mechanism 25 to set the delay time τ. A / D converter 2 while gradually changing
2 are sequentially stored in a memory (not shown) in the control / arithmetic processing unit 23. As a result, finally, the entire data indicating the time-series waveform E (t) of the electric field intensity of the terahertz pulse light is stored in the memory. Data indicating such a time-series waveform E (t) is obtained for the case where the device under test 10 is arranged at the position shown in FIG.
The control / arithmetic processing unit 23, based on these data,
A desired characteristic of the device under test is determined, and this is displayed on a display unit 24 such as a CRT. For example, the control / arithmetic processing unit 23
Known techniques (Lionel Duvillaret, et al.
Frederic Garet, and Jean-Louis Coutaz) ("A
Reliable Method for Extraction of Material Parame
ters in Terahertz Time-Domain Spectroscopy ", IEEE
Journal of Selected Topics in Quantum Electronics,
According to Vol. 2, No. 3, pp. 739-746 (1996)), the complex refractive index of the device under test 10 is calculated and displayed on the display unit 24.

In the present embodiment, a predetermined area of the device under test 10 is irradiated with parallel terahertz pulsed light and the transmitted light is locally focused on the detector 13. The characteristics such as the average complex refractive index of the terahertz pulse light irradiation range are obtained. In order to obtain local characteristics such as a complex refractive index of the DUT 10, for example, parallel terahertz light is applied between the curved mirror 9 and the DUT 10.
A condensing lens for locally condensing light is provided on the object under test 10.
A collimator lens may be provided between the beam splitter 11 and the beam splitter 11 to convert the light transmitted through the device under test 10 into parallel light again.

As can be seen from the above description, in the present embodiment, the generator 8, the detector 13, and the elements 9, 11, and 12 between them constitute a terahertz optical system. When the condenser lens and the collimator lens are provided as described above, it goes without saying that these are also included in the terahertz optical system.

In order to sufficiently exhibit the above-described operations and functions, it is necessary to accurately align the terahertz optical system. In the present embodiment, a rotation mechanism 26 described below is provided as a mechanism for that purpose.

In this embodiment, the beam splitter 11
Is arranged between the generator 8 and the detector 13 on an optical path where the terahertz pulse light becomes parallel light. In the terahertz optical device according to the present embodiment, the beam splitter 11 moves the probe light transmitted through the half-wave plate 16 to the first rotational position (in the optical path of the parallel light of the terahertz pulse light) to the detector 13. Figure 1 tilted + 45 °
And a position shown in FIG. 2 described later), and a half-wave plate 1
A second rotation position (a position rotated by 90 ° around an axis perpendicular to the paper surface of FIG. 1 with respect to the state shown in FIG. 1) to direct the probe light transmitted through 6 to the generator 9, and the terahertz pulse light (A position tilted by -45 ° with respect to the optical path of the parallel light, and a position shown in FIG. 3 to be described later). In the above description of the operation at the time of terahertz light detection, it has been described that the beam splitter is located at the first rotation position. This rotation mechanism 2
Although various well-known mechanisms can be adopted as 6, the positioning accuracy of the first and second rotational positions can be easily increased.

In the present embodiment, the provision of the rotating mechanism 26 enables, for example, a second embodiment of the present invention to be described later.
In addition, it is possible to adjust the alignment of the terahertz optical system as in the third embodiment.

Prior to the description of these adjustment methods, FIG.
The state of the probe light at each rotation position of the beam splitter 11 will be described with reference to FIG. 2 and 3, the same elements as those in FIG. 1 are denoted by the same reference numerals. 2 and 3, the optical path of the probe light is indicated by a solid line, and the optical path of the terahertz pulse light is indicated by a broken line. 2 and 3 show a state in which the alignment of the terahertz optical system has already been accurately adjusted.

FIG. 2 shows that the beam splitter 11
FIG. 2 is a diagram showing a state of probe light in the terahertz optical system in FIG. FIG. 2A shows a state from when the probe light is incident on the beam splitter 11 to when it is incident on the detector 13.
FIG. 2B shows a state after the light is reflected by the detector 13 and enters the generator 8 after FIG.

When the beam splitter 11 is located at the first rotation position, as shown in FIG.
The beam splitter 11 is transmitted through the half-wave plate 16 in the
Is reflected by the curved mirror 12 on the same optical path as the terahertz pulse light, and is collected at the terahertz pulse light collection point of the detector 13. As shown in FIG. 2B, a certain percentage of the condensed probe light is reflected at this converging point and travels in the opposite optical path when entering the detector 13 in the opposite direction. And beam splitter 1
Return to 1. A certain percentage of the probe light returned to the beam splitter 11 passes through the beam splitter 11 as it is, is reflected by the curved mirror 9, and is condensed on the terahertz pulse light generation point in the generator 8. That is, the probe light reflected by the detector 13 travels on the same optical path as the terahertz pulse light in the opposite direction to the terahertz light as shown in FIG. The light is collected at the point of light generation. Since the amount of the probe light reaching the vicinity of the generator 8 is additionally affected by the reflectance at the detector 13 and the transmittance of the beam splitter 11, the amount of the probe light at the vicinity of the detector 13 It is smaller than the amount of light.

FIG. 3 shows that the beam splitter 11
FIG. 2 is a diagram showing a state of probe light in the terahertz optical system in FIG. FIG. 3A shows a state from when the probe light is incident on the beam splitter 11 to when it is incident on the generator 8. FIG. 3B shows a state after the light is reflected by the generator 8 and enters the detector 13 after FIG.

When the beam splitter 11 is located at the second rotation position, as shown in FIG.
The beam splitter 11 is transmitted through the half-wave plate 16 in the
The probe light reflected by the light source travels in the same optical path as the terahertz pulse light in the opposite direction to the terahertz pulse light, is reflected by the curved mirror 9, and is focused on the terahertz pulse light generation point of the generator 8. As shown in FIG. 3B, a certain percentage of the condensed probe light is reflected at this converging point and travels in the same optical path as when entering the generator 8 in the opposite direction. Then, the process returns to the beam splitter 11. A certain percentage of the probe light returned to the beam splitter 11 passes through the beam splitter 11 as it is, and
The light is reflected at 2 and is collected at the terahertz pulse light collection point of the detector 13. The amount of the probe light when reaching the vicinity of the detector 13 is additionally affected by the reflectance of the generator 8 and the transmittance of the beam splitter 11, so that the
It becomes lower than the light amount of the probe light when it reaches the vicinity.

The condition shown in FIG. 2B is based on the premise that the detector 13 has a characteristic of reflecting the probe light at a constant rate (hereinafter referred to as "probe light reflection characteristic" for convenience of explanation). 3 (b), it is assumed that the generator 8 has probe light reflection characteristics, but the detector 13 and the generator 8 usually have probe light reflection characteristics. For example, if the detector 13 and the generator 8 have a nonlinear optical crystal or a dipole antenna as described above, they have a probe light reflection characteristic. FIG.
When the probe light in the situation shown in FIG. 3B or the situation shown in FIG. 3B is used for alignment adjustment, the surfaces of the detector 13 and the generator 8 may be optically polished as necessary.
It is preferable to increase the reflectivity of the probe light. On the other hand, in the situation of FIG. 2A or the situation of FIG. 3A, the presence or absence of the probe light reflection characteristics of the detector 13 and the generator 8 does not matter.

When the intensity of the probe light is increased so as to make the observation of the probe light easier during alignment adjustment, for example, when measuring the electric field intensity of the terahertz pulse light, FIG. It is preferable to reduce the intensity of the probe light with an ND filter or the like so that the reflected light of the probe light shown in (1) does not affect the measurement.

In the first embodiment, since near-infrared light is used as probe light, the probe light is observed by using an observation tool such as the above-described card type infrared sensor. Easy to do. However, in the first embodiment, it is possible to emit visible light from the femtosecond pulse light source 1 and use visible light as probe light. In this case, it is possible to observe the state of the probe light by observing the irradiation position of the probe light on the detector 13 and the generator 8 with the naked eye without using an observation tool.

[Second Embodiment]

Next, an example of a method for adjusting the alignment of the terahertz optical system of the terahertz optical device according to the first embodiment will be described as a second embodiment of the present invention.

In this embodiment, first, when the beam splitter 11 is located at the first rotation position, the state of the probe light reaching the vicinity of the detector 13 is detected by the card type infrared sensor or the like. While observing using the beam splitter (see FIG. 2A), the beam splitter 11 of the terahertz optical system is set so that the probe light is focused on an appropriate position on the detector 13.
The alignment of the element closer to the detector 13, that is, the curved mirror 12 and the detector 13 is adjusted.

Next, the beam splitter 11 is positioned at the second rotation position by the rotation mechanism 26. In this state, the state of the probe light reaching the vicinity of the generator 8 is observed using the card type infrared sensor or the like (FIG. 3).
(A)), elements of the terahertz optical system closer to the generator 8 than the beam splitter 11, that is, the curved mirror 9 and the generator 8 so that the probe light is focused on the terahertz pulse light generation point of the generator 8. Adjust alignment.

Finally, the beam splitter 11 is positioned at the first rotation position by the rotation mechanism 26.

Thus, the terahertz pulse light generated by the terahertz light generator 8 can all reach the terahertz detector 13 effectively.

According to the present embodiment, the alignment of the terahertz optical system can be adjusted using the probe light. Since the positioning accuracy of the rotation position of the rotation mechanism 26 can be easily increased, after the alignment adjustment using the probe light, the repetition of the above-described trial and error, which is necessary in the above-described conventional adjustment method, is greatly increased. Reduced or unnecessary. Therefore, according to the present embodiment, the alignment of the terahertz optical system can be adjusted accurately and easily.

Further, according to the present embodiment, FIG.
Since the probe light in the state shown in FIG. 3A and FIG. 3A is observed, the probe light in a state where the amount of light is relatively large is observed. Generator 8
Even when the detector 13 does not have the probe light reflection characteristic, the alignment of the terahertz optical system can be adjusted.

The order of the alignment adjustment of the curved mirror 12 and the detector 13 at the first rotation position and the alignment adjustment of the curved mirror 9 and the generator 8 at the second rotation position are interchanged. Is also good. That is, (1) First, with the beam splitter 11 positioned at the second rotation position, while observing the state of the probe light reaching the vicinity of the generator 8 (see FIG. 3A), The alignment of the mirror 9 and the generator 8 is adjusted.
6, the beam splitter 11 is positioned at the first rotation position. (3) In this state, while observing the state of the probe light reaching the vicinity of the detector 13 (see FIG. 2A),
The alignment between the curved mirror 12 and the detector 13 may be adjusted. Even in this case, the same advantages as in the present embodiment can be obtained.

[Third Embodiment]

Next, another example of the method for adjusting the alignment of the terahertz optical system of the terahertz optical device according to the first embodiment will be described as a third embodiment of the present invention.

In this embodiment, first, with the beam splitter 11 positioned at the second rotation position, the state of the probe light reaching the vicinity of the generator 8 is determined by the card type infrared sensor or the like. While using and observing (see FIG. 3A), an element of the terahertz optical system closer to the generator 8 than the beam splitter 11, that is, the probe light is focused on the terahertz pulse light generation point of the generator 8, that is, The alignment of the curved mirror 9 and the generator 8 is adjusted.

Next, in a state where the beam splitter 11 is located at the second rotation position, the state of the probe light which is reflected by the generator 8 and reaches the vicinity of the detector 13 is shown by the card type infrared ray. While observing using sensors, etc. (Fig. 3
(B)), an element of the terahertz optical system closer to the detector 13 than the beam splitter 11, that is, the curved mirror 1 so that the probe light is focused at an appropriate position on the detector 13.
2 and the alignment of the detector 13 are adjusted.

Finally, the beam splitter 11 is positioned at the first rotation position by the rotation mechanism 26.

Thus, the terahertz pulse light generated by the terahertz light generator 8 can all reach the terahertz detector 13 effectively.

According to this embodiment, similarly to the second embodiment, the alignment of the terahertz optical system can be adjusted accurately and easily.

[Fourth Embodiment]

Next, still another example of the method for adjusting the alignment of the terahertz optical system of the terahertz optical device according to the first embodiment will be described as a fourth embodiment of the present invention.

In this embodiment, first, with the beam splitter 11 positioned at the first rotation position, the state of the probe light reaching the vicinity of the detector 13 is detected by the card type infrared sensor or the like. While observing using the beam splitter (see FIG. 2A), the beam splitter 11 of the terahertz optical system is set so that the probe light is focused on an appropriate position on the detector 13.
The alignment of the element closer to the detector 13, that is, the curved mirror 12 and the detector 13 is adjusted.

Next, in a state where the beam splitter 11 is located at the first rotation position, the state of the probe light which is reflected by the detector 13 and reaches the vicinity of the generator 8 is shown by the card type infrared ray. While observing using a sensor etc. (Fig. 2
(B)), elements of the terahertz optical system closer to the generator 8 than the beam splitter 11, that is, the curved mirror 9 and the generator 8 so that the probe light is focused on the terahertz pulse light generation point of the generator 8. Adjust alignment.

Thus, all the terahertz pulse light generated by the terahertz light generator 8 can reach the terahertz detector 13 effectively.

According to the present embodiment, similarly to the second embodiment, the alignment of the terahertz optical system can be adjusted accurately and easily. Moreover, according to the present embodiment, it is not necessary to position the beam splitter 11 at the second rotation position, so that the alignment of the terahertz optical system can be more accurately performed as compared with the second and third embodiments. And it can be adjusted more easily.

In the second embodiment, since it is not necessary to position the beam splitter 11 at the second rotation position, the rotation mechanism 26 is removed from the terahertz optical device according to the first embodiment. Is also good. According to the present embodiment, the alignment of the terahertz optical system of the terahertz optical device having no rotating mechanism 26 can also be adjusted.

[Fifth Embodiment]

Next, an alignment adjusting method according to a fifth embodiment of the present invention will be described with reference to an example in which the terahertz optical device to be adjusted is as shown in FIG.

FIG. 4 is a schematic configuration diagram schematically showing another example of the terahertz optical device. 4, elements that are the same as elements in FIG. 1 or that correspond to elements in FIG. 1 are given the same reference numerals, and overlapping descriptions are omitted.

The terahertz light device shown in FIG. 4 is different from the terahertz light device shown in FIG. 1 mainly in the following points.

In the terahertz light device shown in FIG. 4, the probe light is expanded by the beam expander 30 in accordance with the cross section of the terahertz pulse light, passes through the polarizer 31, and then enters the beam splitter 11. Further, the terahertz pulse light transmitted through the beam splitter 11 and the probe light reflected by the beam splitter 11 are removed from the curved mirror 12 in FIG. Light is incident on an optical crystal (electro-optic crystal). Thereby, the detector 1
3 is used as a planar detector. Further, after the probe light transmitted through the detector 13 is analyzed by the analyzer 32, the light intensity distribution is detected by the two-dimensional CCD camera 33. Two-dimensional CCD camera 3 showing the light intensity distribution
The image signal from 3 is subjected to A / D conversion by the A / D converter 22 and then taken into the control / arithmetic processing unit 23. That is, the distribution of the electric field intensity of the terahertz pulse light (the electric field intensity of each part) is collectively taken into the control / arithmetic processing unit 23 as data.

The control / arithmetic processing unit 23 controls the moving mechanism 25 to gradually move the movable mirror 9, and the terahertz pulse light at each delay time (delay time for the terahertz pulse light of the probe light) τ , A time-series waveform E (t) of the electric field intensity of the terahertz pulse light for each part is obtained. Such data indicating the time-series waveform E (t) for each part is obtained for the case where the device under test 10 is arranged at the position shown in FIG. The control / arithmetic processing unit 23 obtains a desired characteristic (that is, a distribution of the desired characteristic) for each part of the DUT based on these data,
It is displayed as an image on a display unit 24 such as an RT.

As can be seen from the above description, in the present embodiment, the generator 8 and the detector 13 and the elements 9 and 11 between them constitute a terahertz optical system.

In the adjusting method according to the present embodiment, the beam splitter 34 is arranged on the optical path of the probe light or the terahertz light, and the beam splitter 34 is adjusted via the beam splitter 34 to the generator 8. Let light in,
The alignment of the terahertz optical system is adjusted while observing the state of the adjustment light.

For example, as shown in FIG. 4, a beam splitter 34 is arranged between the analyzer 32 and the CCD camera 33 on the optical path of the probe light to adjust visible light or near-infrared light. Is irradiated from the adjustment light irradiation unit 35 to the beam splitter 34, and travels on the same optical path as the probe light via the beam splitter 34 in the opposite direction to the probe light (that is, toward the generator 8). .

Assuming that the alignment of the terahertz optical system has already been accurately adjusted, the light for this adjustment is
After passing through the analyzer 32, the detector 13, and the beam splitter 11, the light is reflected by the curved mirror 9, condensed at the terahertz pulse light generation point of the generator 8, and reflected there. The reflected light travels on the same optical path as the terahertz pulse light and reaches the detector 13, passes through the detector 13, the analyzer 32 and the beam splitter 34, and reaches the CCD camera 33.

Therefore, the adjusting light is made incident from the adjusting light irradiating section 35 through the beam splitter 34 as described above, and for example, the adjustment light is observed while observing the state of the adjusting light near the CCD camera 33. Light for CCD camera 3
If the alignment of the terahertz optical system is adjusted so as to appropriately irradiate 3, the alignment can be adjusted accurately. At this time, the state of the light for adjustment may be observed by operating the CCD camera 33 to display an image obtained from the CCD camera on the display unit 24 and viewing the image. This may be performed using an infrared sensor or the like. In addition, while observing the state of the probe light reaching the vicinity of the generator 8 using the card type infrared sensor or the like, the adjustment light is focused on the terahertz pulse light generation point of the generator 8. The alignment of the curved mirror 9 and the generator 8 may be adjusted.

After the alignment adjustment is completed, it is preferable that the adjustment light irradiation section 35 and the beam splitter 34 be removed from the terahertz optical device.

The position at which the beam splitter 34 is inserted is not limited to the position between the analyzer 32 and the CCD camera 33. For example, the camera 33 and the curved mirror 9 may be inserted.
And any position between them.

According to the present embodiment, the alignment of the terahertz optical system can be adjusted by using the adjustment light introduced from the outside without using the rotation mechanism corresponding to the rotation mechanism 26 in FIG. In addition, the repetition of the above-described trial and error, which is required in the conventional adjustment method, is significantly reduced or becomes unnecessary. For this reason, according to the present embodiment, the alignment of the terahertz optical system can be adjusted more accurately and more easily than in the second and third embodiments, and the cost of the terahertz optical device can be reduced. Can be achieved.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

For example, in the fifth embodiment, the terahertz optical device shown in FIG. 4 is modified as shown in FIG. 5, and the terahertz optical device shown in FIG. 4 is modified as shown in FIG. The present invention can also be applied to the adjustment of the alignment of the terahertz optical system of the terahertz optical device described above.

FIG. 5 and FIG. 6 are schematic configuration diagrams schematically showing main parts of each example of the terahertz optical device. FIG.
6 and FIG. 6, the same or corresponding elements as those in FIG. 4 are denoted by the same reference numerals.

The terahertz light device shown in FIG. 5 is different from the terahertz light device shown in FIG. 4 in that the curved mirror 9 is removed and the terahertz light generator 8 is a planar generator (for example, a nonlinear optical crystal or a Budiort optical device). , Margolies,
Jeongu, Son and Boco (E. Budiarto, J. Margolie
s, S. Jeong, J. Son and J. Bokor) ("High-Inten
sity Terahertz Pulses at 1-kHz Repetition Rate ", I
EEE Journal of Quantum Electronics, Vol. 32, No. 10,
pp1839-1846 (1996)), a large-diameter optical switch element is used), and the pump light is incident on the generator 8 after being expanded by the beam expander 40. Only points. Since the terahertz pulse light generated from the generator 8 is not completely parallel light, a convex lens may be disposed immediately after the generator 8 with an interval from the generator 8 as necessary. The interval is a focal length of the convex lens. Even in this case, the adjustment method of the fifth embodiment can be applied.

The terahertz light device shown in FIG. 6 is different from the terahertz light device shown in FIG. 4 in that the curved mirror 9 is removed and the terahertz light generator 8 is a semiconductor such as InAs which is a reflection type planar generator. Is used, and after the pump light is expanded by the beam expander 41, the light is incident on the generator 8, and the silicon wafer 4 that functions as a filter that shields the pump light and selectively transmits the terahertz pulse light.
The only difference is that 2 is added.

The fifth embodiment can also be applied to the alignment adjustment of the terahertz optical system of the terahertz optical device shown in FIG. Further, in the second and third embodiments, if the rotation mechanism 26 is provided in the terahertz optical devices shown in FIGS. 4 to 6, respectively, the alignment of the terahertz optical system of these terahertz optical devices can be adjusted. Can be applied. The fourth embodiment can be applied to the alignment adjustment of the terahertz optical system of the terahertz optical device shown in each of FIGS. 4 to 6 without adding a rotation mechanism.

As can be seen from the above description, the second
The adjustment method according to the fifth to fifth embodiments is applicable to the terahertz light detector irrespective of whether the terahertz light generator is a point-like generator or a planar generator, and the terahertz light detector is a point-like detector. The present invention can be applied to adjustment of alignment of various terahertz optical systems regardless of whether the detector is a planar detector or a planar detector.

The terahertz optical system of the terahertz optical device to which the adjustment method according to the present invention is applied does not include (1) a transmission element (for example, a transmission lens) through which terahertz light passes (that is, a terahertz light generation). Reflection elements that reflect terahertz light (eg, mirrors such as plane mirrors and curved mirrors) other than the detector and the terahertz light detector
Only)) or
(2) In the case where a transmissive element that transmits terahertz light is included, the transmissive element has a material (TPX (which has a refractive index substantially equal to that of terahertz light and probe light (or light for adjustment)) having substantially the same refractive index. The refractive index is preferably substantially the same for terahertz light and visible / infrared light.

[0099]

As described above, according to the present invention,
The alignment of the terahertz optical system can be adjusted accurately and easily.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram schematically showing a terahertz optical device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a state of probe light in the terahertz optical system in FIG. 1 when the beam splitter is located at a first rotation position.

FIG. 3 is a diagram illustrating a state of probe light in the terahertz optical system in FIG. 1 when the beam splitter is located at a second rotation position.

FIG. 4 is a schematic configuration diagram schematically illustrating another example of the terahertz optical device.

FIG. 5 is a schematic configuration diagram schematically illustrating a main part of still another example of the terahertz optical device.

FIG. 6 is a schematic configuration diagram schematically illustrating a main part of still another example of the terahertz optical device.

[Explanation of symbols]

 Reference Signs List 8 terahertz light generator (generator) 9, 12 curved mirror 10 device under test 11 beam splitter 13 terahertz light detector (detector) 26 rotation mechanism 35 adjustment light irradiation unit 34 beam splitter

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2G020 AA03 BA17 BA20 CB27 CB42 CB54 2G059 AA01 AA05 EE01 EE05 GG01 GG04 GG08 HH01 HH06 JJ13 JJ14 JJ15 JJ19 JJ20 JJ22 JJ24 KK01 KK10 MM04 AB03 AB16 AB23 BA09 BB14 BB24 BB32 BB33 BB44 BB48 BC13 BC15 BC22 BC28 BC33 BC35 BD03 DA05 DA15 2H043 AA04 AA09 AA17 AA19 AA24 2K002 AA04 AB18 BA02 BA03 CA13 DA04 HA13

Claims (10)

[Claims] 1. A terahertz light generating section, a detecting section for detecting terahertz light generated from the generating section and arriving via a predetermined optical path, and disposed on an optical path between the generating section and the detecting section A beam splitter, and a terahertz optical system having a terahertz optical system, a probe light irradiator that irradiates the detector with probe light via the beam splitter when the detector detects terahertz light, and the beam splitter, Rotating the probe light from a probe light irradiating section to a first rotational position for directing the probe light to the detecting section, and a second rotating position for directing the probe light from the probe light irradiating section to the generating section; A terahertz optical device, comprising: 2. A terahertz light generator, a detector for detecting terahertz light generated from the generator and arriving via a predetermined optical path, and disposed on an optical path between the generator and the detector. A terahertz optical system having a beam splitter, and a probe light irradiator that irradiates the detector with probe light via the beam splitter when the detector detects terahertz light. An adjustment method for adjusting the alignment of the terahertz optical system, wherein the beam splitter is configured to direct the probe light from the probe light irradiation unit to the detection unit, and the probe light irradiation. The beam splitter to a second rotation position that directs the probe light from the unit to the generation unit, using a rotation mechanism that can rotate the beam splitter. A first stage of adjusting the alignment of the terahertz optical system while observing a state of the probe light in a state where the probe light is located at a second rotation position; and using the rotation mechanism after the first stage. A second position for positioning the beam splitter at the first rotation position.
And an adjustment method, comprising: 3. The method according to claim 1, further comprising a third step of adjusting an alignment of the terahertz optical system while observing a state of the probe light with the beam splitter positioned at the first rotation position. 3. The adjustment method according to claim 2, wherein: 4. The step of adjusting the alignment of the terahertz optical system while observing a state of the probe light emitted from the probe light irradiation unit and reaching the vicinity of the detection unit. 4. The adjustment method according to claim 3, wherein: 5. The third step is to observe a state of the probe light emitted from the probe light irradiation unit, reflected by the detection unit, and reaching the vicinity of the generation unit via the beam splitter. The method according to claim 3, further comprising adjusting alignment of the terahertz optical system. 6. The step of adjusting the alignment of the terahertz optical system while observing a state of the probe light emitted from the probe light irradiation unit and reaching the vicinity of the generation unit. The adjustment method according to claim 2, wherein: 7. The first step is to observe a state of the probe light emitted from the probe light irradiation unit, reflected by the generation unit, and then reached near the detection unit via the beam splitter. 7. The adjustment method according to claim 2, further comprising adjusting the alignment of the terahertz optical system. 8. A terahertz light generating section, a detecting section detecting terahertz light generated from the generating section and arriving via a predetermined optical path, and disposed on an optical path between the generating section and the detecting section. A terahertz optical system having a beam splitter, and a probe light irradiator that irradiates the detector with probe light via the beam splitter when the detector detects terahertz light. An adjustment method for adjusting the alignment of the terahertz optical system, wherein the alignment of the terahertz optical system is adjusted while observing a state of the probe light emitted from the probe light irradiation unit and reaching the vicinity of the detection unit. And after being emitted from the probe light irradiation unit and reflected by the detection unit, near the generation unit via the beam splitter. Wherein while observing the state of the probe light, adjustment method characterized by comprising a, and adjusting the alignment of the terahertz optical system reach. 9. A terahertz light generating unit, a detecting unit for detecting terahertz light generated from the generating unit and arriving via a predetermined optical path, and disposed on an optical path between the generating unit and the detecting unit A terahertz optical system having a first beam splitter, and a probe light irradiator that irradiates the detector with probe light via the first beam splitter when the detector detects terahertz light. An adjustment method for adjusting alignment of the terahertz optical system of the provided terahertz optical device, wherein a second beam splitter is arranged on an optical path of the probe light or an optical path of the terahertz light, and the second Adjustment light is incident on the generation unit via the beam splitter, and alignment of the terahertz optical system is performed while observing the state of the adjustment light. An adjustment method, comprising the step of: 10. The method according to claim 11, wherein the step includes adjusting an alignment of the terahertz optical system while observing a state of the adjustment light reflected by the generation unit. Adjustment method.