JP6483453B2 - Terahertz electric field waveform detector - Google Patents

Description

  The present invention relates to a detection device that detects an electric field waveform of a terahertz wave by terahertz time domain spectroscopy (THz-TDS).

A frequency region of 0.1 to 10 THz (a wave number of 3.3 to 333 cm ⁻¹ ) is called a terahertz region. As a spectral method of the terahertz region waveform, a terahertz pulse wave (THz pulse wave) is incident on the sample, the waveform of the terahertz pulse wave after passing through the sample is time-resolved, and the waveform is Fourier transformed for each frequency. Terahertz time-domain spectroscopy (THz-TDS) is known for detecting the amplitude and phase of the laser. (Patent Documents 1 to 3)

  FIG. 11 is a diagram for explaining the outline of the terahertz time domain spectroscopic device. The optical pulse terahertz generation pump light emitted from the laser and the probe light of the detection system are divided, the pump light is guided to the THz generator 101 to generate a terahertz pulse wave, and the optical path length of the probe light is increased by the time delay device 102. After the change, the terahertz pulse wave is guided to the detection element 103 for detection.

  In the waveform measurement of terahertz pulse waves by the pump-probe method, the electric field waveform of the terahertz pulse wave of the same waveform that repeatedly arrives is sampled while changing the timing at which the probe light reaches the detection element 103 by delaying the probe light. . Since the terahertz pulse wave detection element 103 operates only when the probe light is irradiated, the detector 104 is used to measure only the signal of the terahertz pulse wave that arrives simultaneously with the probe light. The measured time waveform of the terahertz pulse wave is Fourier transformed to obtain the amplitude and phase for each frequency.

JP 2010-127831 A Patent 3799546 Patent No. 3962777

  In the terahertz pulse wave waveform measurement by the above-described pump-probe method, the time waveform and spectrum of the terahertz pulse wave are obtained by time sweeping using the repetitive phenomenon, so that the behavior is different each time, such as phase transfer and destruction phenomenon, It is not suitable for measuring objects such as constantly changing phenomena, moving objects, and phenomena that require a long time for measurement.

  In order to solve this, it has been proposed that time information is mapped to wavelengths using chirp pulses and detection is performed using a spectroscope and a two-dimensional detector, but the detection speed is the detection speed of the two-dimensional detector. There is a problem that it is limited to. In addition, there is a problem with the detection speed, and since the sum frequency light and difference frequency light are detected at the same time, the observed waveform is distorted or converted into a digital signal, so that operations such as waveform multiplication (mixing) are performed. There is a problem that is difficult.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described conventional problems and to detect a terahertz electric field waveform of a single shot (single shot) terahertz wave in a terahertz wave waveform measurement by a pump-probe method.

  Here, the terahertz wave includes a terahertz pulse wave and a continuous terahertz wave. One shot (single shot) terahertz pulse wave means that the measurement target is one pulse signal waveform, and one shot (single shot) continuous terahertz wave is that the measurement target is one continuous signal waveform. Means.

  Further, the present invention provides a single detector (single photodiode) for a terahertz electric field waveform of one shot of terahertz wave in a terahertz wave waveform measurement by a pump-probe method using a terahertz wave and a chirped probe pulse wave. It aims to detect with.

  In the present invention, a portion for detecting a terahertz electric field waveform by writing spectrum information and phase information of a terahertz electric wave waveform of a terahertz wave including a terahertz pulse wave or a continuous terahertz wave into a chirped pulse wave, and information on the terahertz electric field are written By detecting the frequency of the chirp pulse wave in the time direction to reduce the frequency to a frequency that can be detected as an analog signal, it is possible to detect a one-shot terahertz wave with a single detector.

  The terahertz electric field waveform detection apparatus according to the present invention intensity-modulates a chirp pulse wave based on the terahertz electric field waveform of the terahertz pulse wave with the difference frequency light and / or the sum frequency light between the chirp pulse wave and the terahertz wave, and the terahertz wave by this intensity modulation. A chirped wave modulation unit that emits a chirped pulse modulated wave in which spectrum information and phase information of the terahertz electric field are superimposed on the chirped pulse wave from the wave, and waveform expansion that extends the chirped pulse modulated wave obtained by the chirped wave modulating unit in the time direction , A photoelectric conversion unit for converting a chirped pulse modulated extended wave expanded in the time direction by the waveform expansion unit to an analog signal, spectrum information of a terahertz electric field waveform from the analog signal converted by the optical-electric conversion unit, and / or An electric field waveform detection unit for detecting phase information.

  When a chirped pulse wave and a terahertz wave are incident on the electro-optic crystal (EO crystal) in the chirp wave modulation unit, the sum frequency light by the sum frequency process and the difference frequency by the difference frequency process are caused by the second-order nonlinear optical effect of the electro-optic crystal. Light is generated. When light of two different optical frequencies is incident on the electro-optic crystal, a sum frequency light having an optical frequency that is the sum of the two optical frequencies and having a light intensity proportional to the product of the two light intensities is generated. Difference frequency light having an optical frequency that is the difference between the two optical frequencies is generated.

  The sum frequency light and the difference frequency light have wave numbers in different directions with respect to the probe pulse when they are incident non-coaxially. In the known chirp pulse wave and terahertz wave irradiation, the optical axis is coaxially arranged, so that the chirp pulse wave is doubly modulated by the sum frequency process and the difference frequency process, and the resulting chirp modulated wave waveform Is distorted.

  As one configuration for the waveform distortion of the chirp modulation wave, the chirp modulation wave portion of the present invention is configured so that the optical axes of the chirp pulse wave and the terahertz wave are non-coaxial when the chirp pulse wave and the terahertz wave are incident on the electro-optic crystal (EO crystal). Therefore, the chirp pulse modulated wave by the difference frequency process and the chirp pulse modulated wave by the sum frequency process are emitted in different directions with respect to the optical axis direction of the chirp pulse wave.

  As another configuration for the waveform distortion of the chirp modulation wave, the chirp modulation wave portion of the present invention has a configuration of a quarter wavelength plate and a polarization separation element (Wollaston Prism) on the emission side of the electro-optic crystal (EO crystal). By arranging, the chirped pulse modulated wave by the difference frequency process and the chirped pulse modulated wave by the sum frequency process are emitted in different directions with respect to the optical axis direction of the chirped pulse wave.

  Since the emission directions are different, the sum frequency wave and the difference frequency wave can be selectively detected. Since the terahertz electric field waveforms are written in the sum frequency wave and the difference frequency wave chirp modulated waves without interfering with each other, the terahertz electric field waveforms are interfered with each other by selecting and detecting the chirp modulated wave. Can be measured without any problems.

  The terahertz electric field waveform detection device of the present invention takes out a chirp pulse modulated wave of sum frequency light and a chirp pulse modulated wave of difference frequency light separately according to the difference in emission direction, and sums it with the chirp pulse modulated wave by the extracted difference frequency light. Spectral information and / or phase information of the terahertz electric field waveform is detected using either one or both of the chirped pulse modulated wave by frequency light.

  The waveform stretcher of the present invention stretches the chirped pulse modulated wave in the time direction by using a fiber whose group velocity dispersion is monotonous with respect to the wavelength. The frequency of the chirped pulse modulated wave expanded in the time direction is lowered to the lower frequency side. By reducing the frequency of the chirped pulse modulated wave, the analog signal obtained by opto-electric conversion can be measured with a measuring instrument such as a spectrum analyzer or oscilloscope, eliminating the lengthy measurement time due to sampling. Measurement by one shot becomes possible.

  The photoelectric converter of the present invention can use a single photodetector (single photodiode). The chirped pulse modulated wave is reduced in frequency by the waveform expansion unit, and the analog signal obtained by the opto-electric conversion unit has a frequency that can be measured by a measuring instrument. Therefore, a plurality of sampling data is used with a two-dimensional detector. Instead, it can be converted into an analog signal by a single photodetector (single photodiode).

  The electric field waveform detector of the present invention can detect the terahertz electric field waveform superimposed on the chirped pulse modulated wave in a plurality of forms. The form of the electric field waveform detection unit includes a form using a terahertz pulse wave as a terahertz wave and a form using a continuous terahertz wave. The first and fourth forms shown below are forms by terahertz pulse waves, and the second and third forms are forms by continuous terahertz pulse waves.

(First form of electric field waveform detector)
The first form of the electric field waveform detection unit is a form using a terahertz pulse wave and a chirp pulse wave, and a chirp pulse modulation extension wave obtained by extending the chirp pulse modulation wave by the difference frequency light or the sum frequency light in the time direction. In this configuration, the terahertz electric field waveform superimposed on the chirped pulse modulated extension wave is detected by calculating the integration with the reference signal.

  The electric field waveform detection unit according to the first embodiment performs an optical-electric conversion on a chirped pulse modulated extended wave obtained by extending a chirped pulse modulated wave by a difference frequency light or a chirped pulse modulated wave by a sum frequency light into an analog signal. The reference signal is integrated with the signal by the first integrator. The reference signal can be determined based on the frequency of the chirped pulse wave.

  The frequency component of the terahertz pulse wave is extracted by the integration calculation of the first integrator, and the terahertz electric field waveform is detected.

  In the first embodiment, the reference signal used for the integration calculation is determined based on the frequency of the chirped pulse wave, thereby detecting the terahertz electric field waveform (particularly phase information) of the terahertz pulse wave and measuring one shot of the chirped pulse wave. Do as.

  Further, one shot measurement can be performed a plurality of times by repeating the generation of the chirp pulse wave, and the measurement of one shot is completed within each period, so that interference of one shot measurement can be avoided between adjacent periods. .

(Second form of electric field waveform detection unit)
The second form of the electric field waveform detection unit is a form using a continuous terahertz wave and a chirped pulse wave, and a chirped pulse modulated stretched wave obtained by stretching the chirped pulse modulated wave by the difference frequency light or the sum frequency light with a predetermined period. In this embodiment, the terahertz electric field waveform superimposed on the chirped pulse modulated extension wave is detected by performing an integration operation with the periodic signal.

  The electric field waveform detection unit according to the second embodiment performs an optical-electric conversion on a chirped pulse modulated extended wave obtained by expanding a chirped pulse modulated wave by a difference frequency light or a chirped pulse modulated wave by a sum frequency light into an analog signal, A periodic signal having a frequency that is a constant multiple of the frequency determined by the repetition period of the chirped pulse wave is integrated and calculated by the second integrator.

  The frequency component of the terahertz pulse wave is extracted by the integration calculation of the second integrator, and the terahertz electric field waveform is detected.

  In the first embodiment, the time width of the chirped pulse modulated stretched wave stretched in the time direction by the waveform stretcher is set to be within the time width of the repeated cycle of the chirped pulse wave, and the frequency of the periodic signal of the analog signal used for integration calculation is By making the frequency a constant multiple of the frequency determined by the repetition period of the chirped pulse wave, terahertz electric field waveform detection (particularly phase information) of the terahertz pulse wave is performed using one shot of the chirped pulse wave as the measurement period.

  Further, one shot measurement can be performed a plurality of times by repeating the generation of the chirp pulse wave, and the measurement of one shot is completed within each period, so that interference of one shot measurement can be avoided between adjacent periods. . As a result, the phase change of the terahertz CW laser at each measurement time can be measured, and can be applied to the absolute frequency measurement of the continuous wave terahertz laser.

(Third form of electric field waveform detection unit)
The third form of the electric field waveform detection unit is a form using a continuous terahertz wave and a chirped pulse wave. Similar to the second form, a chirp obtained by expanding a chirped pulse modulated wave by difference frequency light or sum frequency light. This is a form in which the terahertz electric field waveform superimposed on the chirp pulse modulation extension wave is detected by integrating the pulse modulation extension wave and a periodic signal of a predetermined period, and the periodic signal is the time of the chirp pulse modulation extension wave. A width is detected and generated based on the detected time width.

  The electric field waveform detection unit of the third form detects the time width of the analog signal of the photoelectric conversion unit in the time width detector, and sets the time width detected by the time width detector in the periodic signal generator as one cycle. A periodic signal is formed. A chirped pulse modulated extended wave obtained by expanding a chirped pulse modulated wave of difference frequency light or a chirped pulse modulated wave of sum frequency light is photoelectrically converted into an analog signal, and the period of the periodic signal generator is converted to this analog signal. The signal is integrated by a third integrator.

  The frequency component of the terahertz pulse wave is extracted by the integration calculation of the third integrator, and the terahertz electric field waveform is detected.

  In the third mode, the time width of the chirped pulse modulated extended wave expanded by the waveform expansion unit is detected by the time width detector, and the frequency of the periodic signal of the analog signal used for the integration calculation is detected by the time width detector. By setting the frequency to be determined by the time width, the terahertz electric field waveform detection of the terahertz pulse wave is performed using one shot of the chirp pulse wave as a measurement cycle.

  Further, one shot measurement can be performed a plurality of times by repeating the generation of the chirp pulse wave, and the measurement of one shot is completed within each period, so that interference of one shot measurement can be avoided between adjacent periods. .

(Fourth form of electric field waveform detector)
A fourth form of the electric field waveform detection unit is a form using a terahertz pulse wave and a chirp pulse wave, and in the first to third forms, any one of the chirp pulse modulated wave by the difference frequency light or the sum frequency light is used. On the other hand, the fourth form of the electric field waveform detection unit uses a chirped pulse modulated stretched wave obtained by stretching the chirped pulse modulated wave by the difference frequency light and the chirped pulse modulated wave by the sum frequency light. In this embodiment, a terahertz electric field waveform superimposed on a chirped pulse modulated extended wave is detected by calculating a difference between the pulse modulated extended wave.

  The electric field waveform detection unit of the fourth embodiment extends the waveform of the chirp pulse modulation wave of the sum frequency light and the analog signal obtained by opto-electric conversion of the chirp pulse modulation expansion wave of the difference frequency light. Only the terahertz pulse wave signal is detected by calculating the difference between the two analog signals by a difference calculator by converting the chirped pulse modulated extension wave into an analog signal.

  Since the difference signal detected by the difference calculator corresponds to the electric field waveform of the terahertz pulse wave, the frequency component of the terahertz pulse wave is extracted therefrom.

  In the fourth embodiment, the difference calculation of the difference calculator is performed in units of one shot of the chirped pulse wave, so that the terahertz electric field waveform detection of the terahertz pulse wave is performed using one shot of the chirped pulse wave as a measurement cycle.

  Further, one shot measurement can be performed a plurality of times by repeating the generation of the chirp pulse wave, and the measurement of one shot is completed within each period, so that interference of one shot measurement can be avoided between adjacent periods. .

  As described above, according to the terahertz electric field waveform detection device of the present invention, in the terahertz wave waveform measurement by the pump-probe method using the terahertz wave and the chirped probe pulse wave, the terahertz electric field of one shot terahertz wave is used. Waveform can be detected.

  Further, the present invention provides a single detector (single photodiode) for a terahertz electric field waveform of one shot of terahertz wave in a terahertz wave waveform measurement by a pump-probe method using a terahertz wave and a chirped probe pulse wave. Can be detected.

It is a figure for demonstrating schematic structure of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the 1st structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the waveform of the 1st structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the 2nd structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the waveform of the 2nd structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the 3rd structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the waveform of the 3rd structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the 4th structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the waveform of the 4th structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the other structural example of the 4th structural example of the terahertz electric field waveform detection apparatus of this invention. It is a figure for demonstrating the outline of a terahertz time-domain spectroscopy apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A schematic configuration of the terahertz electric field waveform detection apparatus according to the present invention will be described with reference to FIG. 1, and a configuration example will be described with reference to FIGS. 2 and 3 are diagrams for explaining a first configuration example of the present invention, FIGS. 4 and 5 are diagrams for explaining a second configuration example, and FIGS. 6 and 7 are third configurations. FIG. 8 is a diagram for explaining an example, and FIGS. 8 to 10 are diagrams for explaining a fourth configuration example.

(Schematic configuration of terahertz electric field waveform detector)
FIG. 1 is a diagram for explaining a schematic configuration of a terahertz electric field waveform detection apparatus according to the present invention. The terahertz electric field waveform detection apparatus 1 includes a chirp wave modulation unit 2 that emits a chirp pulse modulation wave from a chirp pulse wave and a terahertz wave, and a chirp pulse modulation extension wave obtained by expanding the frequency of the chirp pulse modulation wave in the time direction to obtain a frequency. A waveform expansion unit 3 that generates a signal, a photoelectric conversion unit 4 that converts a chirped pulse modulated expansion wave into an analog signal, and an electric field waveform detection unit 5 that detects a terahertz pulse electric field waveform from the analog signal. As the terahertz wave, a terahertz pulse wave or a continuous terahertz wave can be applied. Hereinafter, description will be given with reference to a waveform example (FIG. 3) of the first configuration example.

  The terahertz pulse wave electric field waveform detected by the electric field waveform detector 5 can be displayed on the oscilloscope 6 as well as on the spectrum analyzer 7 by analyzing the spectrum and phase.

A terahertz pulse wave is an electromagnetic wave in a pulse wave frequency region called a terahertz region of 0.1 to 10 THz (a wave number of 3.3 to 333 cm ⁻¹ ), and includes terahertz time-domain spectroscopy (THz−). In TDS, a terahertz pulse wave is incident on a sample, the electric field waveform of the terahertz pulse wave after passing through the sample is time-resolved, and the amplitude and phase of each frequency are measured by Fourier transforming the electric field waveform.

  The optical pulse emitted from the femtosecond taser is divided into pump light for generating a terahertz pulse wave and probe light for detecting the terahertz pulse wave, and the pump light is generated by a terahertz pulse generator (shown in FIG. 1). The terahertz wave (FIG. 3 (a)) is generated by introducing the probe light, and a chirped pulse wave (FIG. 3 (b)) is generated by passing the probe light through the delay time element provided on the optical path. As the terahertz pulse generator, a configuration in which a terahertz pulse wave is generated by irradiating a nonlinear optical crystal with a femtosecond light pulse, or a configuration using a photoconductive antenna can be used.

The chirp wave modulation unit 2 includes an electro-optic crystal (EO crystal), and a chirp pulse wave and a terahertz wave are incident on the electro-optic crystal to emit a chirp pulse modulation wave (FIG. 3C). When light having two different optical frequencies is incident on the electro-optic crystal, sum frequency light and difference frequency light are generated by the second-order nonlinear optical effect of the electro-optic crystal. The optical frequency of the sum frequency light is the sum of the two incident optical frequencies, while the optical frequency of the difference frequency light is the difference between the two incident optical frequencies. The wave number of the difference frequency light is a wave number obtained by subtracting the wave number of the terahertz pulse wave from the wave number of the chirp pulse wave, and the wave number of the sum frequency light is a wave number obtained by adding the wave number of the terahertz pulse wave to the wave number of the chirp pulse wave. The light intensity of the sum frequency light and the difference frequency light is proportional to the product of the two light intensities. As the electro-optic crystal, for example, ZnTe crystal, GaP, LiNbO ₃ or the like can be used.

  The chirp wave modulation unit 2 uses a difference frequency light between the chirp pulse wave (FIG. 3B) and the terahertz wave (FIG. 3A), a chirp pulse wave based on the terahertz electric field waveform of the terahertz pulse wave by the sum frequency light. The intensity is modulated. This intensity modulation generates a chirped pulse modulated wave (FIG. 3C) in which spectrum information and phase information of the terahertz electric field are superimposed on the chirped pulse wave.

  The chirp wave modulation unit 2 is arranged non-coaxially by shifting the optical axes of the chirp pulse wave and the terahertz pulse wave when the electro-optic crystal is irradiated with the chirp pulse wave and the terahertz pulse wave. With this non-coaxial arrangement, the chirped pulse modulated wave by the difference frequency light and the chirped pulse modulated wave by the sum frequency light are emitted from different directions with respect to the optical axis direction of the chirped pulse wave. In FIG. 1, a terahertz pulse modulated wave of difference frequency light and a terahertz pulse modulated wave of sum frequency light are shown as one terahertz pulse modulated wave.

  The terahertz electric field waveform detection apparatus 1 individually extracts a chirp pulse modulated wave of sum frequency light and a chirp pulse modulated wave of difference frequency light according to the difference in emission direction, and chirp pulse modulated wave and sum frequency light by the extracted difference frequency light. Spectral information and / or phase information of the terahertz electric field waveform is detected using either one or both of the chirped pulse modulated waves.

  The waveform expansion unit 3 generates a chirp pulse modulation expansion wave (FIG. 3D) obtained by extending the chirp pulse modulation wave obtained by the chirp wave modulation unit 2 in the time direction and expanding the waveform to the low frequency side. By reducing the frequency of the chirped pulse modulated stretch wave, the frequency of the detection signal converted into an analog signal can be lowered to a frequency that can be measured by a measuring instrument such as a spectrum analyzer or oscilloscope. Sampling measurement, which is necessary for the measurement, can be made unnecessary, and measurement with one shot can be performed by eliminating the long measurement time. The waveform stretcher 3 can use a fiber whose group velocity dispersion is monotonous with respect to the wavelength.

  The opto-electric conversion unit 4 converts the chirped pulse modulated expansion wave expanded in the time direction by the waveform expansion unit 3 into an analog signal. As the photoelectric conversion unit 4, a single photodetector (single photodiode) can be used.

  Since the chirped pulse modulated stretched wave that has been stretched by the waveform stretcher 3 has a low frequency, a plurality of sampling data can be obtained by a single photodetector (single photodiode) without using a two-dimensional detector. It can be converted into an analog signal having a frequency measurable by a measuring instrument.

  The electric field waveform detection unit 5 detects spectrum information and phase information of the terahertz electric field waveform from the analog signal converted by the photoelectric conversion unit 4.

  The electric field waveform detection unit 5 detects the terahertz electric field waveform superimposed on the chirped pulse modulated extended wave, and performs chirped pulse modulation in which either the difference frequency light or the sum frequency light is expanded in the time direction. In addition to a form in which the extension wave analog signal is integrated with the reference signal, a difference between the chirp pulse modulation extension wave analog signal obtained by extending the chirp pulse modulation wave of the sum frequency light in the time direction can be calculated. . As the reference signal, a signal determined based on the frequency of the chirp pulse signal, a form in which the signal is integrated with a periodic signal of a predetermined period, or an analog signal of a chirp pulse modulation expansion wave obtained by expanding the chirp pulse modulation wave of the difference frequency light is used. Can do.

(First configuration example of terahertz electric field waveform detection apparatus)
2 and 3 are a diagram and a waveform diagram for explaining a first configuration example of the terahertz electric field waveform detection apparatus according to the present invention.

  The first configuration example of the electric field waveform detection unit corresponds to the first embodiment using the terahertz pulse wave and the chirp pulse wave, and converts the chirp pulse modulation wave of either the difference frequency light or the sum frequency light in the time direction. The terahertz electric field waveform superimposed on the chirped pulse modulated stretched wave is detected by performing waveform integration on the obtained signal and integrating the obtained chirped pulse modulated stretched wave with the reference signal.

  As a configuration for generating a chirped pulse wave, a chirped pulse wave forming unit 8A is provided. The chirp pulse wave forming unit 8A includes a sub 10 fs broadband laser 8a and a primary dispersion medium 8b, and a pulse width generated by the sub 10 fs broadband laser 8a of about several hundred THz with a pulse width of 10 fs (femtosecond) or less (FIG. 3 ( By passing b)) through the primary dispersion medium 8b, a chirped pulse wave with a chirp (FIG. 3C) is generated. Here, the frequency of the chirped pulse wave is represented by fo.

  FIG. 3B shows an example in which one pulse of a chirp pulse wave is generated. The detection of the terahertz electric field waveform of the terahertz pulse wave can be performed with one chirp pulse wave generated corresponding to one pulse of the terahertz pulse wave (FIG. 3A).

  A terahertz pulse wave (FIG. 3A) can be generated by guiding a sub 10 fs wave (not shown in FIG. 3) generated by the sub 10 fs broadband laser 8a to a terahertz pulse generator (not shown). As the terahertz pulse generator, a configuration in which a terahertz pulse wave is generated by irradiating a non-linear optical crystal with a femtosecond optical pulse, or a configuration using a photoconductive antenna can be used. Here, the frequency of the terahertz pulse wave is represented by fTHz.

  The chirp wave modulation unit 2A includes an electro-optic crystal (EO element) 2a and a polarizing element 2b. When the electro-optic crystal 2a is irradiated with a terahertz pulse wave (wave number κTHz) as pump light and a chirp pulse wave (frequency fo) as probe light, a chirp pulse modulated wave (frequency (fo + fTHz) of sum frequency light is emitted. ) And a chirp pulse modulated wave (frequency (fo−fTHz)) of the difference frequency light is generated.

  In irradiating the electro-optic crystal (EO element) 2a, the optical axis for irradiating the terahertz pulse wave (frequency fTHz) is shifted from the optical axis for irradiating the chirped pulse wave (frequency fo) so as to be non-coaxial. By arranging the terahertz pulse wave and the chirp pulse wave non-coaxially, the chirp pulse modulation wave of the sum frequency light and the chirp pulse modulation wave of the difference frequency light have different wave numbers from the chirp pulse wave. The waves are emitted in different directions with respect to the optical axis direction of the chirped pulse wave.

  The polarizing element 2b receives either a chirped pulse modulated wave of sum frequency light or a chirped pulse modulated wave of difference frequency light emitted from the electro-optic crystal 2a, and changes the polarization state from linearly polarized light to circularly polarized light. Convert to polarized light. FIG. 2 shows an example of selecting a chirped pulse modulated wave (frequency (fκo−fTHz)) (FIG. 3C) of difference frequency light.

  The waveform stretching unit 3A includes a fiber 3a whose group velocity dispersion is monotonous with respect to the wavelength. The chirped pulse modulated stretched wave (FIG. 3D) is generated. By extending the waveform, the frequency of the chirped pulse modulated extended wave is reduced to fTHz / m.

  Here, m represents the rate of expansion in the time direction by the fiber 3a, and depends on the optical characteristics and length of the fiber 3a.

  The photoelectric conversion unit 4A includes a single photodetector (single photodiode), and converts the chirped pulse modulated stretch wave into an analog signal (FIG. 3 (e)). The analog signal can be displayed on the oscilloscope 6A.

  The electric field waveform detection unit 5A includes a first integrator 5a. The first integrator 5a performs an integration operation on the analog signal (FIG. 3 (e)) obtained by converting the chirped pulse modulated extension wave and the reference signal. The frequency of the reference signal is determined based on the frequency fo of the chirp pulse in order to remove the frequency component of the chirp pulse wave included in the analog signal by integration with the analog signal of the chirped pulse modulated extension wave.

  Here, an outline of the integration calculation is shown in the case where the frequency of the analog signal obtained by converting the chirped pulse modulated extension wave of the difference frequency light is expressed by fTHz / m. The magnitude of m is set so that the frequency of the analog signal is a response speed that can be supported by a measuring device such as an oscilloscope.

The multiplication operation in the mixer of the signal F (frequency fTHz / m) and the signal G (frequency fref) is expressed by Expression (1).
F × G = sin (2π (fTHz) t / m + φ) × sin (2πn × fref) (1)

Here, assuming that fTHz / m and fref are substantially equal, Expression (1) is expressed by Expression (2) below.
F × G =
1/2 [cos (2πt (fTHz / m−fref) + φ) −cos (2πt (fTHz / m + fref + φ))]
... (2)

  Since fref is known from the equation (2), the output of the first integrator 5a includes information on the frequencies of (fref−fTHz / m) and (fref + fTHz / m). If the phase of fref is known from the equation (2), the value of φ can also be determined. FIG. 3F shows a signal waveform obtained by integration calculation.

  Therefore, the amplitude component and the phase component of the terahertz electric field waveform can be detected by the spectrum analyzer based on the calculation result calculated by the first integrator 5a. In the above description, the difference frequency light is used. However, a sum frequency light may be used.

(Second configuration example of terahertz electric field waveform detection apparatus)
4 and 5 are a diagram and a waveform diagram for explaining a second configuration example of the terahertz electric field waveform detection apparatus according to the present invention.

  The second configuration example of the electric field waveform detection unit is a configuration corresponding to the second form using a continuous terahertz wave and a chirp pulse wave, and either a chirp pulse modulated wave of either difference frequency light or sum frequency light. Is expanded in the time direction, and the obtained chirped pulse modulated stretched wave is integrated with a periodic signal having a predetermined period to detect a terahertz electric field waveform superimposed on the chirped pulse modulated stretched wave.

  A chirp pulse wave forming unit 8B is provided as a configuration for generating a chirp pulse wave. The chirp pulse wave forming unit 8B includes a sub 10 fs broadband laser 8a and a primary dispersion medium 8b, and a pulse wave of about several hundred THz with a pulse width generated by the sub 10 fs broadband laser 8a of 10 fs (femtosecond) or less (FIG. 5 ( By passing a)) through the primary dispersion medium 8b, a chirped pulse wave (FIG. 5C) with a chirp is generated. Here, the wave number of the chirped pulse wave is represented by κo.

  FIG. 5C shows an example in which the chirped pulse wave shown is repeatedly generated with a period of 1 / frep. Since the terahertz electric field waveform can be detected with one chirped pulse wave generated within one period, the terahertz electric field waveform at different measurement points is detected by repeatedly generating the chirped pulse wave.

  The continuous terahertz wave (FIG. 5B) can be generated by guiding the sub 10 fs wave (FIG. 5A) generated by the sub 10 fs broadband laser 8a to a terahertz pulse generator (not shown). As the terahertz pulse generator, a configuration in which a terahertz pulse wave is generated by irradiating a non-linear optical crystal with a femtosecond optical pulse, or a configuration using a photoconductive antenna can be used. Here, the frequency of the terahertz pulse wave is represented by fTHz.

  The chirp wave modulating unit 2B includes an electro-optic crystal (EO element) 2a and a polarizing element 2b. When the electro-optic crystal 2a is irradiated with a terahertz pulse wave (frequency fTHz) as pump light and a chirp pulse wave (frequency fo) as probe light, a chirp pulse modulated wave (frequency (fo + fTHz) of sum frequency light is emitted. ) And a chirp pulse modulated wave (frequency (fo−fTHz)) of the difference frequency light is generated.

  In irradiating the electro-optic crystal (EO element) 2a, the optical axis for irradiating the terahertz pulse wave is shifted from the optical axis for irradiating the chirped pulse wave so as to be non-coaxial. By arranging the terahertz pulse wave and the chirp pulse wave non-coaxially, the chirp pulse modulation wave of the sum frequency light and the chirp pulse modulation wave of the difference frequency light have different wave numbers from the chirp pulse wave. The waves are emitted in different directions with respect to the optical axis direction of the chirped pulse wave.

  The polarizing element 2b receives either a chirped pulse modulated wave of sum frequency light or a chirped pulse modulated wave of difference frequency light emitted from the electro-optic crystal 2a, and changes the polarization state from linearly polarized light to circularly polarized light. Convert to polarized light. FIG. 5 shows an example of selecting a chirp pulse modulated wave (frequency (fo−fTHz)) (FIG. 5D) of difference frequency light.

  The waveform stretching unit 3B includes a fiber 3a whose group velocity dispersion is monotonous with respect to the wavelength. The chirped pulse modulated wave (FIG. 5 (d)) of the chirp wave modulating unit 2 is stretched in the time direction to expand the waveform toward the low frequency side. The chirped pulse modulated stretched wave (FIG. 5E) is generated. By extending the waveform, the frequency of the chirped pulse modulated extended wave is reduced to fTHz / m.

  Here, m represents the rate of expansion in the time direction by the fiber 3a, and depends on the optical characteristics and length of the fiber 3a. The time width of the chirped pulse modulated stretched wave that expands in the time direction by waveform stretching and the time width of the cycle of repeating the chirped pulse wave (1 / frep) are the chirped pulse modulated stretch generated at the cycle of one chirped pulse wave. The wave is set so that it does not overlap with the chirped pulse modulated stretched wave generated at the next chirped pulse wave period.

  For example, when the period (1 / frep) of the chirp pulse wave is predetermined, the degree m of the waveform expansion of the chirp pulse wave is adjusted, and when the degree m of the waveform expansion of the chirp pulse wave is the default, the chirp is adjusted. Adjust the period (1 / frep) of the pulse wave.

  The photoelectric conversion unit 4B includes a single photodetector (single photodiode), and converts the chirped pulse modulated extension wave into an analog signal (FIG. 5 (f)). The analog signal can be displayed on the oscilloscope 6B.

  The electric field waveform detection unit 5B includes a first integrator 5a and a frequency converter 5b. The frequency converter 5b multiplies the repetitive wave frep (FIG. 5 (g)) generated in synchronization with the sub 10fs wave (FIG. 5 (a)) of the sub 10fs broadband laser 8a by n times to obtain an n × frep A frequency signal (FIG. 5 (h)) is generated.

  The integrator 5a integrates and calculates the analog signal (FIG. 5 (f)) obtained by converting the chirped pulse modulated extension wave and the signal having the frequency of n × frep (FIG. 5 (h)). The periodic signal for performing the integration calculation is a frequency (n × frep) obtained by multiplying the frequency frep determined by the repetition period of the chirp pulse wave by a constant (n times) by the frequency converter 5b.

  Here, an outline of the integration calculation is shown in the case where the frequency of the analog signal obtained by converting the chirped pulse modulated extension wave of the difference frequency light is expressed by fTHz / m.

A multiplication operation in a mixer (integrator) of the signal F (frequency fTHz / m) and the signal G (frequency n × frep) is expressed by Expression (3).
F × G = sin (2π (fTHz) t / m + φ) × sin (2πn × frep t) (3)

Here, since fo / m and n × frep are substantially equal, Expression (3) is expressed by the following Expression (4).
F × G =
1/2 [cos (2πt (fTHz / m × n × fren) + φ) −cos (2πt (fTHz / m + n × frep + φ))]
... (4)

  Expression (4) indicates that (n × frep) is known, and therefore the output of the integrator 5a includes information related to the frequency of (n × frep−fTHz / m).

  Further, if the phase of (n × frep) is known from the equation (4), the value of φ can also be determined.

  Therefore, the amplitude component and the phase component of the terahertz electric field waveform can be detected by the spectrum analyzer 7B based on the calculation result obtained by the integration calculation by the integrator 5a. FIG. 5 (i) represents the phase signal.

  The time width of the chirp pulse modulation expansion wave expanded in the time direction by the waveform expansion unit 3B is set to be within the time width of the repetition cycle of the chirp pulse wave, and the frequency of the periodic signal of the analog signal used for integration calculation is By setting the frequency to a constant multiple (n times) of the frequency determined by the repetition period, terahertz electric field waveform detection of the terahertz pulse wave is performed using one shot of the chirp pulse wave as the measurement period. Further, one shot measurement can be performed a plurality of times by repeating the generation of the chirp pulse wave, and the measurement of one shot is completed within each period, so that interference of one shot measurement can be avoided between adjacent periods. . In the above description, the difference frequency light is used. However, a sum frequency light may be used.

(Third configuration example of terahertz electric field waveform detection apparatus)
6 and 7 are a diagram and a waveform diagram for explaining a third configuration example of the terahertz electric field waveform detection apparatus according to the present invention.

  The third configuration example of the electric field waveform detection unit is a configuration corresponding to the third form using a continuous terahertz wave and a chirp pulse wave, and the waveform of the chirp pulse modulation wave by the difference frequency light or the sum frequency light is expanded. This is a configuration that detects the terahertz electric field waveform superimposed on the chirped pulse modulated stretched wave by multiplying the chirped pulse modulated stretched wave with a periodic signal of a predetermined cycle. A signal generated based on the repetition time width of the pulse modulation stretch wave is used.

  The terahertz electric field waveform detection device 1C of the third configuration example is similar to the terahertz electric field waveform detection devices 1A and 1B of the first and second configuration examples, with a chirp wave modulation unit 2C, a waveform expansion unit 3C, and an optical-electric conversion unit. 4C and an electric field waveform detector 5C. Among these configurations, the chirp wave modulation unit 2C, the waveform expansion unit 3C, and the photoelectric conversion unit 4C are the same as the configurations included in the terahertz electric field waveform detection device 1B of the second configuration example. The description in is omitted, and only the electric field waveform detection unit 5C will be described.

  The electric field waveform detector 5C includes a time width detector 5f, a periodic signal generator 5g, and a third integrator 5d.

  The time width detector 5f detects the time width T of the analog signal of the photoelectric conversion unit 4C. The time width T is detected by generating a pulse wave as a pilot signal (FIG. 7 (g)) from the sub 10 fs broadband laser 8a of the chirp pulse wave forming unit 8C, and the time width detector 5f receives the pulse wave of the pilot signal. Start measuring the time span. The time width detector 5f monitors the analog signal (FIG. 7 (h)) of the photoelectric conversion unit 4C, ends the measurement of the time width when the analog signal ends, and outputs the time width output T (FIG. 7 ( i)) is output.

  The periodic signal generator 5g forms a periodic signal Frep (FIG. 7 (j)) having the time width T detected by the time width detector 5f as one period.

  The third integrator 5d photoelectrically converts the chirped pulse modulated wave obtained by expanding the chirped pulse modulated wave or the chirped pulse modulated wave of the sum frequency light into the difference frequency light, and converts it into an analog signal (FIG. 7 (f)). And the periodic signal Frep of the periodic signal former 5g are integrated. The third integrator 5d extracts the frequency component of the terahertz pulse wave by the integration calculation and detects the terahertz electric field waveform.

  In the third configuration, the time width T of the chirped pulse modulated expanded wave expanded by the waveform expansion unit 3C is detected by the time width detector 5f, and the frequency Frep of the periodic signal of the analog signal used for integration calculation is used as the time. By using the frequency determined by the time width T detected by the width detector 5f, terahertz electric field waveform detection of the terahertz pulse wave is performed using one shot of the chirp pulse wave as a measurement cycle.

  Similarly to the first configuration, one shot measurement can be performed a plurality of times by repeating generation of the chirp pulse wave, and one shot measurement is completed within each period. Measurement interference can be avoided.

(Fourth configuration example of terahertz electric field waveform detection apparatus)
8 and 9 are a diagram and a waveform diagram for explaining a fourth configuration example of the terahertz electric field waveform detection apparatus according to the present invention.

  The fourth configuration example of the electric field waveform detection unit corresponds to the fourth configuration using the terahertz pulse wave and the chirp pulse wave, and chirp pulse modulation by the chirp pulse modulated wave light by the difference frequency light and the sum frequency light. This configuration detects the terahertz electric field waveform superimposed on the chirped pulse-modulated stretched wave by using the chirped-pulse modulated stretched wave obtained by stretching each wave in the time direction and performing the differential operation of both the chirped-pulse modulated stretched wave. .

  The terahertz electric field waveform detection device 1D of the fourth configuration example is similar to the terahertz electric field waveform detection devices 1A to 1C of the first to third configuration examples, as described above, a chirp wave modulation unit 2D, a waveform expansion unit 3D, and an optical-electric conversion unit. 4D and the electric field waveform detection part 5D are provided.

  The chirp wave modulation unit 2D includes an electro-optic crystal (EO element) 2a and two polarizing elements 2b and 2c. When the electro-optic crystal 2a is irradiated with a terahertz pulse wave (frequency fTHz) as pump light and a chirp pulse wave (frequency fo) as probe light, a chirp pulse modulated wave (frequency (fo + fTHz) of sum frequency light is emitted. ) And a chirped pulse modulated wave (frequency (fo−fTHz)) of the difference frequency light is generated.

  The polarization elements 2b and 2c each receive one of a chirp pulse modulated wave of sum frequency light or a chirp pulse modulated wave of difference frequency light emitted from the electro-optic crystal 2a, and convert the polarization state from linearly polarized light to elliptically polarized light. . In FIG. 8, the chirp pulse modulated wave (frequency (fo−fTHz)) of the difference frequency light is selected and emitted from the polarizing element 2b, and the chirp pulse modulated wave (frequency (fo + fTHz)) of the sum frequency light is output from the polarizing element 2c. An example of sorting and emitting is shown. FIG. 9 shows an example in which a chirped pulse modulated wave (frequency (fo−fTHz)) (FIG. 9D) of difference frequency light is selected.

  The waveform stretching unit 3D includes fibers 3a and 3b whose group velocity dispersion is monotonous with respect to the wavelength. The fiber 3a includes a chirped pulse modulated wave (frequency (fo−fTHz)) of a difference frequency light obtained by extending the chirped pulse modulated wave (FIG. 9D) of the chirped wave modulation unit 2D in the time direction (FIG. 9E). Produces

  The fiber 3b is a chirped pulse modulated extended wave (FIG. 9 (h)) obtained by extending the chirped pulse modulated wave (frequency (fo + fTHz)) (FIG. 9 (g)) of the sum frequency light of the chirped wave modulation unit 2D in the time direction. Generate. By extending the waveform, the frequency of the chirped pulse modulated extended wave of the difference frequency light and the sum frequency light is reduced to fTHz / m.

  The photoelectric conversion unit 4D includes a single photodetector (single photodiode) 4a and 4b, and the photodetector 4a converts a chirped pulse modulated stretch wave of difference frequency light into an analog signal (FIG. 9 (f)). Then, the photodetector 4b converts the chirped pulse modulated extended wave of the sum frequency light into an analog signal (FIG. 9 (i)). Each analog signal can be displayed on the oscilloscope 6D.

  The electric field waveform detection unit 5D includes a difference calculator 5h, a fiber 5i, a single photodetector (single photodiode) 5j, a frequency converter 5i, and a divider 5k.

  The difference calculator 5h calculates the difference between the analog signal I1 of the chirped pulse modulation extension wave and the analog signal I2 of the chirped pulse modulation extension wave of the sum frequency light, and obtains a difference signal (I1-I2) (FIG. 9 (j)). Is output. The difference signal (I1-I2) can be obtained as a terahertz electric field waveform by referring to the waveform of the chirped pulse wave without the terahertz electric field waveform.

  The fiber 5i generates a chirped pulse modulated stretched wave (frequency fo / m) obtained by stretching the chirped pulse wave (frequency fo) that has passed through the primary dispersion medium 8b in the time direction. The single photodetector (single photodiode) 5j photoelectrically converts the chirped pulse modulated extension wave (frequency fo / m) and outputs an analog signal Iref having the frequency (fo / m). The divider 5k divides the difference signal (I1-I2) using the analog signal Iref as a reference signal. The obtained (I1-I2) / Iref represents a terahertz electric field waveform and can be displayed on the oscilloscope 6D.

  In the fourth configuration example, the difference calculation of the difference calculator is performed in units of one shot of the chirped pulse wave, so that the terahertz electric field waveform detection of the terahertz pulse wave is performed using one shot of the chirped pulse wave as the measurement cycle. Can do. Further, one shot measurement can be performed a plurality of times by repeating the generation of the chirp pulse wave, and the measurement of one shot is completed within each period, so that interference of one shot measurement can be avoided between adjacent periods. .

  In the fourth configuration example, the terahertz electric field waveform is obtained by the difference between the difference frequency and the sum frequency. In addition to the configuration in which the terahertz pulse wave and the chirp pulse wave are incident non-coaxially with respect to the potential optical crystal, The present invention can also be applied to an incident configuration. An application example of the non-coaxial arrangement of the fourth configuration example will be described with reference to FIG. Here, in the terahertz electric field waveform detection apparatus 1E, only the chirp wave modulation unit 2E and the waveform expansion unit 3E will be described.

  The chirp wave modulation unit 2E generates a chirped pulse wave fo with a chirp by passing the pulse wave generated by the sub 10 fs broadband laser 8a through the primary dispersion medium 8b, and also generates a terahertz pulse fTHz.

  The waveform stretching unit 3E includes an electro-optic crystal 2a, a quarter-wave plate 2d, and a polarization separation element 2e. The polarization separating element 2e can use Wollaston Prism. By arranging this configuration, the chirped pulse modulated wave by the difference frequency process and the chirped pulse modulated wave by the sum frequency process are polarized by the quarter wavelength plate and then separated by the polarization separation element 2e, and the chirped pulse wave light is separated. The light is emitted in different directions with respect to the axial direction.

  The terahertz electric field waveform detection apparatus of the present invention can be applied to material analysis for non-destructive inspection of various materials such as semiconductors and resins, monitoring on a production line, spectrum imaging, and the like.

1, 1A, 1B, 1C, 1D, 1E Terahertz electric field waveform detector 2, 2A, 2B, 2C, 2D, 2E Chirp wave modulator 2a Electro-optic crystal 2b, 2c Polarizing element 2d 1/4 wavelength plate 2e Polarization separating element 3, 3A, 3B, 3C, 3D, 3E Waveform expansion unit 3a, 3b, 3c Fiber 4, 4A, 4B, 4C, 4D Photo-electric conversion unit 4a, 4b Photodetector 5, 5A, 5B, 5C, 5D Electric field Waveform detector 5a Accumulator 5b Frequency converter 5c Accumulator 5d Time width detector 5e Periodic signal generator 5f Accumulator 5g Fiber 5i Frequency converter 5j Subtractor 6, 6A, 6B, 6C, 6D Oscilloscope 7, 7A, 7B , 7C Spectrum analyzer 8A, 8B, 8C, 8D, 8E Chirped pulse wave forming unit 8a Sub 10 fs broadband laser 8b Primary dispersion medium 01 generator 102 hours delay unit 103 detecting elements 104 two-dimensional detector

Claims (7)

The chirp pulse wave based on the terahertz electric field waveform of the terahertz wave is intensity-modulated by the difference frequency light and / or the sum frequency light of the chirp pulse wave and the terahertz wave, and the spectrum information and phase information of the terahertz electric wave waveform from the terahertz wave by the intensity modulation A chirped wave modulator that emits a chirped pulse modulated wave that is superimposed on the chirped pulse wave;
A waveform expansion unit that expands the chirp pulse modulation wave of the chirp wave modulation unit in the time direction and shifts the wave number to the low wave number side; and
An opto-electric converter that converts the chirped pulse modulated stretched wave stretched in the time direction by the waveform stretcher into an analog signal;
An electric field waveform detection unit for detecting spectrum information and / or phase information of the terahertz electric field waveform from the analog signal converted by the photoelectric conversion unit ,
The chirp wave modulator is
The optical axes of the chirped pulse wave and the terahertz wave are arranged non-coaxial with respect to an electro-optic crystal (EO crystal), and the chirped pulse modulated wave by the difference frequency light and the chirped pulse modulated wave by the sum frequency light are converted into the chirped pulse wave. The terahertz electric field waveform detection apparatus emits light from different directions with respect to the optical axis direction .   The terahertz electric field waveform detection apparatus according to claim 1, wherein the waveform stretching unit is a fiber whose group velocity dispersion is monotonous with respect to a wavelength.   The terahertz electric field waveform detection apparatus according to claim 1, wherein the photoelectric conversion unit is a single photodetector (single photodiode). The terahertz wave is a terahertz pulse wave,
The electric field waveform detection unit is an analog signal obtained by opto-electric conversion of a chirped pulse modulated wave by the difference frequency light or a chirped pulse modulated wave obtained by extending the chirped pulse modulated wave by the sum frequency light in the time direction, and
The terahertz electric field waveform detection apparatus according to claim 1, further comprising a first integrator that detects a terahertz electric field waveform by an integration calculation with a reference signal. The terahertz wave is a continuous terahertz wave;
The electric field waveform detection unit includes an analog signal obtained by opto-electric conversion of a chirped pulse modulated wave generated by the difference frequency light or a chirped pulse modulated wave obtained by extending the chirped pulse modulated wave generated by the sum frequency light in a time direction. A second integrator for detecting a terahertz electric field waveform by an integration operation with a periodic signal having a frequency that is a constant multiple of the frequency determined by the repetition period of the chirped pulse wave,
2. The terahertz electric field waveform detection apparatus according to claim 1, wherein a time width of the chirped pulse modulation stretched wave that is waveform-stretched by the waveform stretching unit is equal to or less than a time width of a repetition period of the chirped pulse wave. The terahertz wave is a continuous terahertz wave;
The electric field waveform detector includes a time width detector that detects a time width (T) of an analog signal of the photoelectric conversion unit,
A periodic signal former for forming a periodic signal having the time width as one period;
An analog signal obtained by opto-electric conversion of a chirped pulse modulated wave obtained by expanding the chirped pulse modulated wave of the difference frequency light or the chirped pulse modulated wave of the sum frequency light in the time direction; and a periodic signal of the periodic signal former; The terahertz electric field waveform detection apparatus according to claim 1, further comprising a third integrator that detects a phase of the terahertz electric field waveform by the integration calculation. The terahertz wave is a terahertz pulse wave,
The electric field waveform detection unit is configured to extend an analog signal obtained by opto-electric conversion of a chirped pulse modulated extended wave obtained by extending the chirped pulse modulated wave of the difference frequency light and a chirped pulse modulated wave of the sum frequency light in the time direction. 2. A terahertz electric field waveform detection according to claim 1, further comprising: a difference calculator that obtains a differential signal between the chirp pulse wave and the terahertz pulse wave by an analog signal obtained by opto-electrically converting the chirped pulse modulated extension wave. apparatus.