JP2020020641A - Optical analysis module and optical analyzer - Google Patents

Abstract

To provide an optical analysis module and an optical analyzer with which it is possible to avoid an influence such as an aging fluctuation of the polarization state of probe light and measure the optical parameter of a measurement object easily with high accuracy.SOLUTION: An optical analyzer 1 includes: an optical chopper 11 for cyclically switching the presence and absence of occurrence of a terahertz wave T on the basis of a first frequency signal F1; and a Pockels cell 13 for cyclically switching the polarization state of the terahertz wave T between a first polarization state and a second polarization state on the basis of a second frequency signal F2. A signal generation unit 17 generates a first reference signal R1 the value of which becomes positive in a period when the polarization state of the terahertz wave T is in the first polarization state and becomes negative in a period when no terahertz wave T is generated, and a second reference signal R2 the value of which becomes positive in a period when the polarization state of the terahertz wave T is in the second polarization state and becomes negative in a period when no terahertz wave T is generated.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an optical analysis device and an optical analysis device.

  Non-Patent Documents 1 and 2 are examples of methods for deriving optical parameters of an anisotropic material. Non-Patent Document 1 describes a method of obtaining a time waveform of a terahertz wave for each rotation angle of an anisotropic material, determining the axis orientation, and then deriving a complex refractive index of each axis. Non-Patent Document 2 discloses a method of deriving a birefringence parameter by probing an anisotropic material with a circularly polarized terahertz wave pulse and analyzing the result using a predetermined calculation formula. .

Y. Kim et al., "Investigation of THz birefringence measurement and calculation in Al2O3andLiNbO3", Appl. Opt. 50, 2906, (2011) HS. Katletz et al., "Polarizationsensitive terahertz imaging: detection of birefringence and optical axis", Opt. Express 20, 23025, (2012)

  However, in the method described in Non-Patent Document 1, a time waveform is acquired for each angle while rotating the anisotropic material by a predetermined angle, so that it may take time and effort for measurement. Further, in order to determine the direction of the axis with high resolution, it is necessary to change the angle finely and acquire a time waveform. Further, in the method described in Non-Patent Document 2, due to the nature of the calculation formula used, when the object to be measured has a predetermined thickness, or the refraction between the fast axis and the slow axis of the object to be measured. Measurement is difficult unless the rate difference is sufficiently large. In addition, in this method, it is assumed that the anisotropic material does not have wavelength dispersion of the refractive index, so that it is difficult to measure a material having a distribution such as an absorption peak. Therefore, the methods described in Non-Patent Documents 1 and 2 have a problem to be improved in performing simple measurement.

  Furthermore, the accuracy of the optical analysis using the above method is based on the change over time of the probe light due to fluctuations in the polarization state and the displacement of the pointing, and the change over time of the output of the photodetector due to the drift in sensitivity. May be affected. If the temporal change in the output of the photodetector is greater than the modulation of the probe light by the terahertz wave, the analysis signal may be buried in the temporal fluctuation of the polarization state, and the accuracy of the analysis may be reduced.

  The present disclosure has been made in order to solve the above-described problem, and it is possible to avoid the influence of the temporal fluctuation of the polarization state of the probe light and the like, and to easily and accurately measure an optical parameter of an object to be measured. It is an object of the present invention to provide an optical analysis module and an optical analysis device that can perform the analysis.

  An optical analysis module according to an aspect of the present disclosure includes a terahertz wave generation module that generates a terahertz wave by input of pump light, a terahertz wave detection unit that detects a terahertz wave generated by the terahertz wave generation module, and a terahertz wave detection unit. A light detection unit that detects a probe light modulated by a terahertz wave and outputs an analysis signal, and a signal generation unit that generates a frequency signal used in the terahertz wave generation module and a reference signal used to extract a signal from the analysis signal The terahertz wave generation module periodically switches on / off the input of the pump light based on the first frequency signal from the signal generation unit to periodically determine whether or not the terahertz wave is generated. And a terahertz based on the second frequency signal from the signal generation unit. And a polarization switching unit that periodically switches the polarization state of the terahertz wave between the first polarization state and the second polarization state, and wherein the signal generation unit performs the period in which the polarization state of the terahertz wave is the first polarization state. A first reference signal whose polarity is inverted during a period in which no terahertz wave is generated, and a predetermined value during a period in which the polarization state of the terahertz wave is the second polarization state. And a second reference signal in which the sign is inverted during a period in which is not generated.

  In this optical analysis module, the presence or absence of the generation of the terahertz wave is periodically switched by the input switching unit, and the first reference signal and the second reference signal are inverted such that the value of the period during which the terahertz wave is not generated is inverted. Generate The analytic signal from the light detector indicates that the probe light changes over time due to fluctuations in the polarization state and deviations in pointing during both the period when the terahertz wave is generated and the period when the terahertz wave is not generated. Also, the output of the photodetector due to sensitivity drift may be affected by changes over time. However, the output of the analysis signal is the sum of a certain period of the detection signal obtained by multiplying the reference signal, so that the positive and negative of the first reference signal and the second reference signal are inverted depending on whether or not a terahertz wave is generated. Thus, the signal component based on the temporal fluctuation of the polarization state of the probe light can be canceled. Therefore, with this optical analysis module, it is possible to avoid the influence of the fluctuation of the polarization state of the probe light with time, and to measure the optical parameters of the device under test simply and with high accuracy.

  The terahertz wave detection unit detects the terahertz wave-modulated probe light and outputs a first analysis signal, and the terahertz wave detection unit outputs the first light detection unit and the terahertz wave detection unit. A second light detection unit that detects and outputs a second analysis signal, wherein the optical analysis module further includes a difference detection unit that detects a difference between the first analysis signal and the second analysis signal. You may have. In this case, by detecting the difference between the first analysis signal and the second analysis signal, it is possible to cancel the signal component based on the temporal fluctuation of the intensity of the probe light. Therefore, the measurement accuracy of the optical parameter of the device under test can be further improved.

  The first reference signal is 0 during a period when the polarization state of the terahertz wave is the second polarization state, and the second reference signal is 0 during a period when the polarization state of the terahertz wave is the first polarization state. You may. Thus, the output signal during the period when the polarization state of the terahertz wave is the first polarization state and the output signal during the period when the polarization state of the terahertz wave is the second polarization state can be obtained.

  The switching cycle of the presence or absence of the generation of the terahertz wave may be half the switching cycle of the polarization state of the terahertz wave. This makes it possible to easily form a period in which the terahertz wave is in the first polarization state, a period in which the terahertz wave is in the second polarization state, and a period in which no terahertz wave is generated.

  The switching period of the presence or absence of the terahertz wave may be twice as long as the switching period of the polarization state of the terahertz wave. This makes it possible to easily form a period in which the terahertz wave is in the first polarization state, a period in which the terahertz wave is in the second polarization state, and a period in which no terahertz wave is generated.

  The switching cycle of the presence or absence of the generation of the terahertz wave and the switching cycle of the polarization state of the terahertz wave may be equal to each other and the phases may be shifted by １ ／ cycle. This makes it possible to easily form a period in which the terahertz wave is in the first polarization state, a period in which the terahertz wave is in the second polarization state, and a period in which no terahertz wave is generated.

  The duty ratio of the switching cycle for the presence or absence of the generation of the terahertz wave may be twice the duty ratio of the switching cycle of the polarization state of the terahertz wave. This makes it possible to easily form a period in which the terahertz wave is in the first polarization state, a period in which the terahertz wave is in the second polarization state, and a period in which no terahertz wave is generated.

  An optical element for condensing the pump light with respect to the input switching unit may be further provided. In this case, the waveforms of the first analysis signal and the second analysis signal can be sharpened, and the measurement accuracy of the optical parameter of the device under test can be improved.

  The input switching unit may be an optical chopper. In this case, the input switching unit can be realized with a simple configuration.

  The polarization switching unit may be a Pockels cell. In this case, the polarization switching unit can be realized with a simple configuration.

  Further, the optical analysis device according to an aspect of the present disclosure includes the optical analysis module, a first electric field vector of a terahertz wave in a first polarization state, and a second polarization vector based on a detection result of the light detection unit. An electric field vector measuring unit that detects a second electric field vector of the terahertz wave in the state, first analysis data based on spectral data obtained by performing a Fourier transform on a product of the first electric field vector and the rotation matrix, An optical parameter analysis unit for analyzing optical parameters of the device under test based on an intersection of second analysis data based on spectrum data obtained by Fourier transforming a product of the electric field vector and the rotation matrix.

  In this optical analyzer, the input switching unit periodically switches the presence or absence of the generation of the terahertz wave, and the first reference signal and the second reference signal so that the value of the period during which the terahertz wave is not generated is inverted. Generate The analytic signal from the light detector indicates that the probe light changes over time due to fluctuations in the polarization state and deviations in pointing during both the period when the terahertz wave is generated and the period when the terahertz wave is not generated. Also, the output of the photodetector due to sensitivity drift may be affected by changes over time. However, the output of the analysis signal is the sum of a certain period of the detection signal obtained by multiplying the reference signal, so that the positive and negative of the first reference signal and the second reference signal are inverted depending on whether or not a terahertz wave is generated. Thus, the signal component based on the temporal fluctuation of the polarization state of the probe light can be canceled. Therefore, with this optical analyzer, the influence of the fluctuation of the polarization state of the probe light over time can be avoided, and the optical parameters of the measured object can be measured simply and with high accuracy.

  According to the present disclosure, it is possible to avoid the influence of the polarization state of the probe light such as fluctuation over time, and to measure the optical parameters of the device under test simply and with high accuracy.

It is the schematic which shows an example of the optical-analysis apparatus comprised using the optical-analysis module. FIG. 3 is a schematic diagram illustrating an example of a configuration of a terahertz wave generation unit. It is a figure showing the electric field vector of a terahertz wave. It is the schematic which shows the structure of an electric field vector measurement part. 5 is a graph showing first analysis data measured using a terahertz wave T in a first polarization state. It is a graph which shows the 2nd analysis data measured using terahertz wave T of the 2nd polarization state. It is a graph which shows the superposition of the 1st analysis data and the 2nd analysis data. It is the graph which plotted the direction of one optical axis derived | led-out in the frequency band contained in a terahertz wave. FIG. 3 is a diagram illustrating ideal signal processing in the optical analysis device. It is a figure showing realistic signal processing in an optical analysis device. FIG. 3 is a diagram illustrating a first embodiment of signal processing in the optical analysis device. It is a figure showing a 2nd embodiment of signal processing in an optical analysis device. It is a figure showing a 3rd embodiment of signal processing in an optical analysis device. It is a figure showing a 4th embodiment of signal processing in an optical analysis device. It is a figure showing the example of composition of an optical chopper. It is a figure showing the modification of signal processing in an optical analysis device.

Hereinafter, preferred embodiments of an optical analysis module and an optical analysis device according to an aspect of the present disclosure will be described in detail with reference to the drawings.
[Configuration of optical analyzer]

  FIG. 1 is a schematic diagram illustrating an example of an optical analysis device configured using an optical analysis module. The optical analysis device 1 is configured as a device that analyzes optical parameters of the device under test S. The object S is a substance having optical anisotropy such as a birefringent material, and the optical parameters to be analyzed include, for example, the azimuth of the optical axis of the object S, the refractive index, and the extinction coefficient. , Dielectric constant and the like.

  As shown in FIG. 1, the optical analysis apparatus 1 includes a light source 2, a terahertz wave generation module 10, a terahertz wave detection unit 30, a first light detection unit 34A, a second light detection unit 34B, a signal The configuration includes a generation unit 17, an electric field vector measurement unit 40, and an optical parameter analysis unit 50. The electric field vector measurement unit 40 includes a difference detection unit 41 (see FIG. 4). The optical analysis module 20 includes a terahertz wave generation module 10, a terahertz wave detection unit 30, a first light detection unit 34A, a second light detection unit 34B, a signal generation unit 17, And a difference detection unit 41.

  The light source 2 is a device that outputs a laser beam L. In the present embodiment, the light source 2 is a femtosecond laser light source, and outputs a laser beam L having, for example, a wavelength of 800 nm, a pulse width of 100 fs, a repetition frequency of 100 MHz, and an average output of 500 mW. The laser light L output from the light source 2 is split by the beam splitter 3 into pump light La and probe light Lb.

  A delay stage 6 and a mirror 8 are arranged on the optical path of the pump light La branched by the beam splitter 3. The delay stage 6 has a stage 6a that can reciprocate in the optical axis direction of the pump light La branched by the beam splitter 3, and a pair of mirrors 6b and 6c that fold the pump light La. The pump light La is given a predetermined delay with respect to the probe light Lb by the delay stage 6, and is guided to the terahertz wave generation module 10 by the mirror 8. In the present embodiment, the polarization state of the pump light La incident on the terahertz wave generation module 10 is linearly polarized light having the horizontal direction as the reference polarization direction (0 °).

  FIG. 2 is a schematic diagram illustrating an example of the configuration of the terahertz wave generation module 10. As shown in FIG. 1, the terahertz wave generation module 10 includes an optical chopper (input switching unit) 11, a λ / 2 wavelength plate 12, a Pockels cell (polarization switching unit) 13, a λ / 4 wavelength plate 14, The terahertz wave generator 15 and the terahertz wave plate 16 are provided.

  The optical chopper 11 is a member that periodically switches on / off of the pump light La traveling toward the terahertz wave generation unit 15. The optical chopper 11 is a disc-shaped member in which ribs for shielding light are provided radially from the center at a predetermined phase angle (see FIG. 15). The on / off of the pump light La is periodically switched by the rotation of the optical chopper 11, so that the presence or absence of the generation of the terahertz wave T in the terahertz wave generation unit 15 is periodically switched. The rotation drive of the optical chopper 11 is controlled by the first frequency signal F1 generated by the signal generator 17.

  In the present embodiment, a condenser lens (optical element) 18 and a collimator lens 19 are arranged before and after the optical chopper 11. As a result, the pump light La is condensed at the position of the optical chopper 11 by the condenser lens 18, and after passing through the optical chopper 11, is collimated by the collimator lens 19. The collimated pump light La enters the Pockels cell 13 via the λ / 2 wavelength plate 12.

  The Pockels cell 13 is an element that controls the polarization state of the pump light La by an electro-optic effect. A cell driver (not shown) is electrically connected to the Pockels cell 13, and the polarization state of the pump light La is controlled according to a voltage applied from the cell driver. The direction of the crystal axis of the Pockels cell 13 matches the reference polarization direction of the pump light La. The Pockels cell 13 functions as a λ / 4 wavelength plate during a period when a voltage is applied from the cell driver.

  On the other hand, the Pockels cell 13 does not function as a λ / 4 wavelength plate during a period in which no voltage is applied from the cell driver, and maintains the polarization state of the incident pump light La. Thereby, the polarization state of the terahertz wave T output from the terahertz wave generation module 10 is periodically switched between the first polarization state and the second polarization state. The driving of the cell driver is controlled by the second frequency signal F2 generated by the signal generator 17.

  The terahertz wave generation unit 15 is a part that generates a terahertz wave T by incidence of the pump light La. The terahertz wave generation unit 15 is made of, for example, a nonlinear optical crystal obtained by cutting out a (111) plane of ZnTe which is an optically isotropic medium. The pulse width of the terahertz wave T generated from the crystal is generally about several ps, and includes a frequency component in a band of about 0.1 THz to 3 THz.

  When the crystal axis of the nonlinear optical crystal coincides with the polarization direction of the incident pump light La, the polarization direction of the terahertz wave T generated by the terahertz wave generation unit 15 coincides with the polarization direction of the incident pump light La. . On the other hand, when the crystal axis of the nonlinear optical crystal and the polarization direction of the incident pump light La are shifted by θ, the angle of the polarization direction of the terahertz wave T generated by the terahertz wave generation unit 15 is equal to the incident pump light. Incline by −2θ with respect to the polarization direction of La.

  In the terahertz wave generation module 10 having the above-described configuration, the pump light La, which is linearly polarized light of 0 °, is converted into linearly polarized light of 45 ° by the λ / 2 wave plate 12, and left-handed circularly polarized light by the Pockels cell 13. Or, it is periodically converted to 45 ° linearly polarized light. The λ / 4 wavelength plate 14 converts the pump light La into 0 ° linear polarization when the polarization state of the pump light La is counterclockwise circular polarization, and maintains the polarization state when the pump light La is 45 ° linear polarization. I do.

  In the terahertz wave generation unit 15, when the 0 ° linearly polarized pump light La is incident, a 0 ° linearly polarized terahertz wave T is generated, and when the 45 ° linearly polarized pump light La is incident. Generates a terahertz wave T of -90 [deg.] Linearly polarized light. The terahertz wave plate 16 is a λ / 4 wave plate applicable to the terahertz wave T. When the polarization state of the terahertz wave T is 0 ° linearly polarized light, the clockwise circularly polarized light (first (Polarization state), and if it is -90 ° linearly polarized light, it is converted to counterclockwise circularly polarized light (second polarization state).

  Returning to FIG. 1, on the optical path of the terahertz wave T output from the terahertz wave generation module 10, an arrangement unit 21 in which the device under test S is arranged and a terahertz wave detection unit 30 are arranged. The arrangement unit 21 is configured by a holder or the like, and holds the device under test S such that, for example, the thickness direction of the device under test S matches the propagation direction of the terahertz wave T.

  The terahertz wave detection unit 30 is a part that detects the terahertz wave T. The terahertz wave detector 30 is made of a nonlinear optical crystal obtained by cutting out the (111) plane of ZnTe, which is an optically isotropic medium, similarly to the terahertz wave generator 15. One surface of the terahertz wave detection unit 30 is an incident surface on which the terahertz wave T is incident. The one surface is provided with a reflective coating that transmits the terahertz wave T and reflects the probe light Lb. The other surface of the terahertz wave detection unit 30 is an incident surface on which the probe light Lb is incident. The other surface is provided with an anti-reflection coating for suppressing reflection of the probe light Lb.

FIG. 3 is a diagram illustrating an electric field vector of the terahertz wave T in the terahertz wave detection unit. As shown in the figure, the electric field vector E _T of the terahertz wave T, the amplitude | E T _| and is represented by the orientation theta _T. The azimuth [theta] _T is defined as 0 [deg.] In the <-211> direction on the (111) plane of ZnTe, and the <0-11> direction is defined as the positive direction based on this. When the inclination of the electric field of the terahertz wave T with respect to the <-211> direction is 2θ, birefringence is induced in the −θ direction. The magnitude of the birefringence induced according to the intensity of the terahertz wave T is constant regardless of the direction.

  On the optical path of the probe light Lb branched by the beam splitter 3, a mirror 9 and a polarization adjusting unit 32 are arranged. The polarization adjusting unit 32 is constituted by, for example, a polarizer 36 and a λ / 4 wavelength plate 37. The probe light Lb guided to the polarization adjustment unit 32 via the mirror 9 becomes linearly polarized light in a predetermined direction by the polarizer 36, and is further converted to circularly polarized light by the λ / 4 wavelength plate 37.

  The probe light Lb that has passed through the polarization adjustment unit 32 is split by the non-polarization beam splitter 38 while maintaining the polarization state. One of the probe lights Lb branched by the non-polarization beam splitter 38 enters the terahertz wave detection unit 30 and probes the terahertz wave T. After probing the terahertz wave T, the probe light Lb passes through the non-polarizing beam splitter 38 and enters the rotating analyzer 39. The rotation analyzer 39 is an element in which the analyzer is rotated in a plane by a motor or the like. The rotation analyzer 39 rotates the analyzer at a predetermined frequency of, for example, about 20 Hz to 100 Hz, and modulates the incident probe light Lb. From the rotation analyzer 39, only a specific linearly polarized light component of the probe light Lb is output and enters the first light detection unit 34A.

  The return light generated by the non-polarizing beam splitter 38 is converted into elliptically polarized light close to linearly polarized light by the λ / 4 wavelength plate 37, and most of the light is cut by the polarizer 36. Further, the other probe light Lb branched by the non-polarization beam splitter 38 enters the second light detection unit 34B without passing through the terahertz wave detection unit 30.

  The first light detection unit 34A and the second light detection unit 34B are configured by, for example, photodiodes. The first light detection unit 34A detects the probe light Lb obtained by probing the terahertz wave T in the terahertz wave detection unit 30 and outputs a first analysis signal D1 based on the detection result to the electric field vector measurement unit 40. The first analysis signal D1 includes a signal based on the intensity of the probe light Lb, a signal based on the intensity of the terahertz wave T in the first polarization state, and a signal based on the intensity of the terahertz wave T in the second polarization state. .

  The second light detection unit 34B is a detection unit used for monitoring the power fluctuation of the probe light Lb, detects the probe light Lb that is not directed to the terahertz wave detection unit 30, and obtains a second analysis signal D2 based on the detection result. Is output to the electric field vector measurement unit 40. The second analysis signal D2 includes only a signal based on the intensity of the probe light Lb.

  The signal generation unit 17 is a unit that generates a frequency signal used in the terahertz wave generation module 10 and a reference signal used in the electric field vector measurement unit 40. Specifically, the signal generation unit 17 generates a first frequency signal F1 to be output to the optical chopper 11 and a second frequency signal F2 to be output to the driver of the Pockels cell 13. In addition, the signal generation unit 17 generates a first reference signal R1 output to the first lock-in detection unit 45A and a second reference signal R2 output to the first lock-in detection unit 45B. Details of these signals will be described later.

  The electric field vector measurement unit 40 is a part that measures the electric field vector of the terahertz wave T. As shown in FIG. 4, the electric field vector measurement unit 40 includes a difference detection unit 41, a first lock-in detection unit 45A, 45B at the front stage, a second lock-in detection unit 46A, 46B at the rear stage, and a signal processing unit. A part 47 is provided.

  The difference detection unit 41 is a part that detects a difference between the first analysis signal D1 output from the first light detection unit 34A and the second analysis signal D2 output from the second light detection unit 34B. is there. The difference detector 41 outputs a difference signal E based on the difference between the first analysis signal D1 and the second analysis signal D2 to the first lock-in detectors 45A and 45B, respectively. By performing the difference detection, the intensity fluctuation component of the probe light Lb is removed. In performing the difference detection, the sensitivity adjustment of the first light detection unit 34A and the second light detection unit 34B is performed so that the intensity of the difference signal E of the difference detection unit 41 becomes zero when the terahertz wave T is not incident. Is preferably performed.

  The first lock-in detectors 45A and 45B are sections that perform lock-in detection of the preceding stage for the difference signal E. The first lock-in detection unit 45A refers to the first reference signal R1 generated by the signal generation unit 17, and detects the intensity of the terahertz wave T in the first polarization state among the signals included in the difference signal E. Only the signal based on the lock-in is detected, and the first detection signal K1 based on the detection result is output to the second lock-in detector 46A. The first lock-in detection unit 45B refers to the second reference signal R2 generated by the signal generation unit 17, and detects the intensity of the terahertz wave T in the second polarization state among the signals included in the difference signal E. Only the signal based on the lock-in is detected, and the second detection signal K2 based on the detection result is output to the second lock-in detector 46B.

  The second lock-in detectors 46A and 46B are sections that perform lock-in detection of the differential signal E at a subsequent stage. The second lock-in detectors 46A and 46B are, for example, two-phase lock-in detectors, and have a function of simultaneously detecting the amplitude and phase of a signal that changes in synchronization with the frequency of the reference signal. The second lock-in detection unit 46A performs lock-in detection on the first detection signal K1 output from the first lock-in detection unit 45A, using a frequency twice the rotation frequency of the rotation analyzer 39 as a reference signal. . The second lock-in detection unit 46A outputs the first detection signal K1 after lock-in detection to the signal processing unit 47. The second lock-in detector 46B uses the frequency twice as high as the rotation frequency of the rotation analyzer 39 as a reference signal, and locks in the second detection signal K2 output from the second lock-in detector 46B. To detect. The second lock-in detection unit 46B outputs the second detection signal K2 after lock-in detection to the signal processing unit 47.

  Note that the first lock-in detectors 45A and 45B and the second lock-in detectors 46A and 46B may be configured by independent lock-in detectors, for example, an FPGA (field-programmable gate array). ), Or may be configured by a program as software on a computer.

  The signal processing unit 47 converts the electric field vector of the terahertz wave T based on the first detection signal K1 from the second lock-in detection unit 46A and the second detection signal K2 from the second lock-in detection unit 46B. This is the part to be detected. The signal processing unit 47 is physically configured by a computer system including a CPU, a memory, a communication interface, and the like. A method for detecting the electric field vector in the signal processing unit 47 will be described below.

The amplitude A _L and the phase phi _L included in the detection signal K1, K2, the amplitude of the electric field vector of the terahertz wave T | E T _| Between and orientation theta _T, holds the following relationship. A _C in the following equation, non-linear optical constant and thickness of the electro-optical crystal used as the terahertz wave detecting unit 30, which is a constant determined on the basis of such a wavelength of the probe light Lb. The electric field vector of the terahertz wave T can be uniquely determined based on the detection results from the second lock-in detectors 46A and 46B by using the following equation.

In addition, when the amplitude of the electric field vector of the terahertz wave T is sufficiently small, the following equation is established. In this case, the amplitude A _L included in the detection signal amplitude of the electric field vector of the intact terahertz wave T | is regarded _| E T.

The two phase lock-in detector in accordance with the phase of the reference signal and the _A L cos [phi _L and _A L sin [phi _L can be outputted respectively. When the amplitude of the electric field vector of the terahertz wave T is sufficiently small, the following equation is established between these outputs and the components of the electric field vector of the terahertz wave T in two axial directions orthogonal to each other. Therefore, based on the two outputs from the second lock-in detectors 46A and 46B, signals E _Tx and E _Ty proportional to two mutually orthogonal axial components in the electric field vector of the terahertz wave T are obtained. Becomes In the present embodiment, for example, _ETx has a horizontal direction as an axial direction, and _ETy has a vertical direction as an axial direction.

  The optical parameter analysis unit 50 is a part that analyzes the optical parameters of the device under test S based on the detected electric field vector. The optical parameter analysis unit 50 is physically configured by a computer system including a CPU, a memory, a communication interface, and the like. The optical parameter analysis unit 50 may be configured by the same computer system as the electric field vector measurement unit 40. The optical parameter analysis unit 50 may execute the analysis of the optical parameters subsequent to the detection of the electric field vector, may temporarily store the data of the detected electric field vector in a memory or the like, and may execute the data at an arbitrary timing. .

  The optical parameter analysis unit 50 obtains first analysis data based on spectrum data obtained by performing a Fourier transform on a product of the first electric field vector of the terahertz wave T in the first polarization state and a rotation matrix. Further, the optical parameter analysis unit 50 acquires the second analysis data based on the spectrum data obtained by Fourier transforming the product of the rotation vector and the second electric field vector of the terahertz wave T in the second polarization state. . Then, the optical parameter analysis unit 50 determines the optical parameters of the device under test S based on the intersection between the first analysis data and the second analysis data.

As described above, the electric field vector measurement unit 40 obtains signals E _Tx and E _{Ty that} are proportional to two axial components orthogonal to each other in the electric field vector of the terahertz wave T. That is, the electric field vector E is represented by the following equation.

The optical parameter analysis unit 50 obtains an electric field vector E ′ on an axis inclined by an arbitrary analysis angle θ from the original reference axis by multiplying the electric field vector E by a rotation matrix as shown in the following equation. In the present embodiment, the analysis angle θ is set in the range of 0 ° to 180 °, and the electric field vector E ′ is obtained at arbitrary angle steps within the range. In the electric field vector E ′, the component of the electric field vector E on an axis inclined by an angle θ from the axis of the signal E _Tx is obtained as E _{Tx ′} , and the component of the electric field vector E on an axis inclined by an angle θ from the axis of the signal E _{Ty Is} obtained as E _{Ty ′} .

  Next, at each analysis angle θ at which the electric field vector E ′ has been acquired, the optical parameter analysis unit 50 performs transmission measurement analysis on the object S to derive desired optical parameters. In the transmission measurement, an electric field vector measured in a state where the object S is not arranged in the arrangement unit 21 is used as a reference measurement result, and an electric field vector measured in a state where the object S is arranged in the arrangement unit 21 is calculated. Let it be a sample measurement result.

For example, when obtaining the real part of the refractive index, the spectrum data is obtained by Fourier transforming the _{ETx '} component of the electric field vector E' obtained from the reference measurement result and the sample measurement result. Then, based on the difference between the sample measurement result and the reference measurement result in the phase component of the spectrum data and the thickness of the DUT S, analysis data indicating the relationship between each analysis angle θ and the real part of the refractive index is obtained. I do. The analysis data includes first analysis data based on the terahertz wave T in the first polarization state and second analysis data based on the terahertz wave T in the second polarization state. Note that when it is desired to acquire only the difference (for example, the refractive index difference) between two orthogonal axes (slow axis and fast axis) of the DUT S, the reference measurement is unnecessary. In this case, only the sample measurement needs to be performed.

5 and 6 are diagrams illustrating an example of analysis data in the optical parameter analysis unit. In this example, analysis data is shown when an object to be measured S arranged with the optical axis inclined by 20 ° from the axis of the electric field vector E measured by the electric field vector measuring unit 40 is measured. That is, the device under test S has a slow axis at a position of 20 ° and a fast axis at a position of 110 °, with the axis from which the reference signal _ETx is obtained being 0 °. The value of the refractive index real part of the slow axis is n _{o =} 2.4, the value of the real part of the refractive index in the fast axis has a n _{e =} 2.0.

  FIG. 5 is a graph showing first analysis data measured using the terahertz wave T in the first polarization state. FIG. 6 is a graph showing second analysis data measured using the terahertz wave T in the second polarization state. More specifically, FIG. 5 shows analysis data obtained by using a clockwise circularly polarized terahertz wave T, and FIG. 6 shows analysis data obtained by using a counterclockwise circularly polarized terahertz wave T. In each graph, the horizontal axis is the analysis angle θ, and the vertical axis is the calculated value of the real part of the refractive index.

  FIG. 7 is a graph in which a graph showing the first analysis data and a graph showing the second analysis data are superimposed. As shown in FIG. 7, the two graphs intersect at two positions where the analysis angle θ is 20 ° and 110 °. The optical parameter analysis unit 50 specifies an intersection between the graph indicating the first analysis data and the graph indicating the second analysis data, and derives the optical parameters. That is, in the above example, the optical parameter analysis unit 50 derives the azimuths 20 ° and 110 ° at the intersection as the positions of the slow axis and the fast axis. The optical parameter analysis unit 50 calculates the value of the real part of the refractive index at the intersection of 20 ° as 2.4 and the value of the real part of the refractive index at the other intersection of 110 ° as the value of the real part of the refractive index. 2.0 is derived.

In the present embodiment, the terahertz wave T incident on the device under test S includes at least a frequency component in a band of 1 to 2 THz. Therefore, the optical parameter analysis unit 50 may derive the first analysis data and the second analysis data for different frequency components, respectively. In this case, the optical parameter analysis unit 50 can derive an optical parameter for each frequency component. FIG. 8 is a graph in which the azimuth of one optical axis derived in the frequency band of 1 THz to 2 THz is plotted. The optical parameter analysis unit 50 can determine the value of the azimuth of the optical axis by calculating the average value of the azimuth obtained for each frequency component.
[First Embodiment of Signal Processing]

  Next, the signal processing in the optical analysis device 1 described above will be described in more detail.

FIG. 9 is a diagram showing ideal signal processing in the optical analysis device 1. FIG. 9A shows a first analysis signal D1 at the first light detection unit 34A and a second analysis signal D2 at the second light detection unit 34B. The first analysis signals D1, because it contains the probe results Ruth wave T to Terra, the signal component S _A according to the terahertz wave T clockwise circularly polarized light, the signal component due to the terahertz wave T of the left-handed circularly polarized light and the S _B appear alternately. The second analysis signal D2, because it does not contain the probe results in the terahertz wave T, includes only the signal component S ₀ based on intensity of the probe light Lb. Signal component S _A value obtained by subtracting the signal component S ₀ from A, and the signal component S value B obtained by subtracting the signal component S ₀ from _B the ideal signal components to be used in the electric field vector measuring unit 40.

FIG. 9B shows a difference signal E between the first analysis signal D1 and the second analysis signal D2. The difference signal E, a difference signal component of the signal component S ₀ from the signal component S _A, and a signal component obtained by subtracting the signal component S ₀ from the signal component S _B appear alternately. FIG. 9C shows a first reference signal R1 and a second reference signal R2 used for lock-in detection. The first reference signal R1 and the second reference signal R2 are signals in which 1 and 0 are mutually inverted in the same cycle. FIG. 9D shows the first detection signal K1 and the second detection signal K2 after lock-in detection. By performing lock-in detection of the difference signal E by the first reference signal R1, the first detection signal K1, the signal component S _A value A obtained by subtracting the signal component S ₀ from periodically emerge. Further, by performing lock-in detection of the difference signal E by the second reference signal R2, the second detection signal K2, the signal component S value B obtained by subtracting the signal component S ₀ from _B to periodically appearing .

On the other hand, FIG. 10 is a diagram showing realistic signal processing in the optical analysis device 1. In the optical analysis apparatus 1, the first light detection unit 34A and the second light detection unit 34B change over time of the probe light Lb due to fluctuations in the polarization state, deviations in pointing, and the like, and drifts in sensitivity. 10 (a), the signal component based on the intensity of the probe light Lb as shown in FIG. 10 (a). S ₀ is considered that fluctuates over time, the signal component S _c. When the variation value of the signal component S _c for the signal component S ₀ is C, Figure 10 the difference signal E (b), the signal component S _A signal component obtained by adding a variation value C of the signal component S ₀ to S _A and 'a, the signal component S _B to the signal component S ₀ signal component S _B in consideration of the change value C _of' appear alternately. When lock-in detection of the difference signal E is performed using a first reference signal R1 and a second reference signal R2 (both are the same as in FIG. 9C) shown in FIG. The signal component caused by the fluctuation of the intensity of the probe light Lb can be canceled, but the signal component caused by the change over time of the polarization state of the probe light Lb is not canceled. Therefore, as shown in FIG. 10 (d), the first detection signal K1, the signal component S _{A 'is} the period in consideration of the variation value C from the signal component S _A signal components S ₀ to the difference value A to appear, to the second detection signal K2, so that the signal component S _B signal components in consideration of the variation value C signal component S ₀ to the difference value B from S _{B 'are} periodically appearing.

  On the other hand, in the optical analysis device 1, the signal generation unit 17 generates the first frequency signal F1, the second frequency signal F2, the first reference signal R1, and the second reference signal R2 as follows. I do. FIG. 11 is a diagram illustrating a first embodiment of signal processing in the optical analysis device 1. FIG. 11A shows a switching cycle of the presence or absence of the generation of the terahertz wave T by the first frequency signal F1 and a switching cycle of the polarization state of the terahertz wave T by the second frequency signal F2.

  When the optical chopper 11 driven based on the first frequency signal F1 passes the pump light La, a terahertz wave T is generated by the pump light La, and when the pump light La is cut off by the optical chopper 11, No terahertz wave T is generated. When the second frequency signal F2 is on, a terahertz wave T whose polarization state is clockwise circularly polarized light is generated, and when the second frequency signal F2 is off, the polarization state is counterclockwise. A Terahertz wave T, which is circularly polarized light, is generated.

In the present embodiment, the switching period of the presence or absence of the generation of the terahertz wave T is half the switching period of the polarization state of the terahertz wave T. Therefore, in one cycle of the difference signal E output from the difference detection section 41, there are four periods T1 to T4 having the same length as shown in FIG. 11B. The period T1 is a period in which the polarization state of the terahertz wave T is the first polarization state, and the period T2 is a period in which the terahertz wave T is not generated. Further, the period T3 is a period in which the polarization state of the terahertz wave T is the second polarization state, and the period T4 is a period in which the terahertz wave T is not generated. In the difference signal E, the signal component based on the intensity of the probe light Lb is canceled. Therefore, in the period T1, a signal component in which the signal component S _C is added to the signal component S _A appears, and in the period T3, a signal component in which the signal component S _B is added to the signal component S _C appears. Further, in the period T2, T4, only the signal component caused by the signal component _{S C} appears.

  FIG. 11C shows the first reference signal R1 and the second reference signal R2. The first reference signal R1 becomes 1 (positive value) during a period T1 in which the polarization state of the terahertz wave T is the first polarization state, and -1 (negative value) in a period T2 in which no terahertz wave is generated. Becomes Further, the first reference signal R1 becomes 0 in a period T3 in which the polarization state of the terahertz wave T is the second polarization state and in a period T4 in which the terahertz wave T is not generated. On the other hand, the second reference signal R2 becomes 0 in a period T1 in which the polarization state of the terahertz wave T is the first polarization state and in a period T2 in which no terahertz wave is generated. Further, the second reference signal R2 becomes 1 (positive value) in a period T3 in which the polarization state of the terahertz wave T is the second polarization state, and -1 (negative value) in a period T4 in which the terahertz wave T is not generated. ).

FIG. 11D shows the first detection signal K1 and the second detection signal K2. First reference signal R1 The results of the lock-in detection using, in a first detection signal K1, the period T1, the signal components obtained by adding the signal component S _C to the signal component S _A appeared, the period T2 the signal components -S _C multiplied by -1 in signal component _{S C} appears. The final output of the first detection signal K1 is the sum of a certain period. Therefore, the signal output to the signal processing section 47, the periods T1 and T2 equal in length, and the signal component S _C in the period T1, and a signal component -S _C in the period T2 is canceled.

Each of the signal component S _C and the signal component −S _C is a signal component based on a fluctuation value C due to a temporal change in the polarization state of the probe light Lb, but generally, the first reference signal R 1 and the second reference signal R 2. for reference signal R2 frequency (lock-in frequency) is sufficiently large with respect to temporal change of the polarization state of the probe light Lb, the fluctuation value C included in the signal component S _C and signal components -S _C are equal to each other Can be considered. Therefore, in canceling the signal component S _C and the signal component −S _C , it is possible to cancel the fluctuation value C due to a change over time in the polarization state of the probe light Lb.

The same applies to the second detection signal K2. The period T3 in the second detection signal K2, the signal component _{S B} signal components in consideration of the signal component _{S C} appeared to, the period T4, the signal components multiplied by -1 in signal component _{S C} -S _C Appears. The final output of the second detection signal K2 is the sum of a certain period. Therefore, the signal output to the signal processing unit 47, in the period T3 and the period T4 equal in length, and the signal component S _C in the period T3, and a signal component -S _C in the period T4 is canceled.

  As described above, in the optical analysis apparatus 1, the polarity of the probe light Lb over time is inverted by inverting the sign of the first reference signal R1 and the sign of the second reference signal R2 depending on whether or not the terahertz wave T is generated. Signal components based on various changes and the like can be canceled. Therefore, the optical analyzer 1 can avoid the influence of the change in the polarization state of the probe light Lb over time, and can easily and accurately measure the optical parameters of the DUT S.

  In the optical analysis apparatus 1, the terahertz wave detection unit 30 detects the probe light Lb modulated by the terahertz wave T and outputs a first analysis signal D1. A second light detection unit 34B that detects the probe light Lb that does not pass through and outputs a second analysis signal D2, and a difference detection that detects a difference between the first analysis signal D1 and the second analysis signal D2. A part 41 is provided. By detecting the difference between the first analysis signal D1 and the second analysis signal D2, it is possible to cancel the signal component based on the temporal fluctuation of the intensity of the probe light Lb. Therefore, the measurement accuracy of the optical parameters of the object S can be further improved.

  Further, in the optical analysis device 1, the first reference signal R1 becomes 0 during a period when the polarization state of the terahertz wave T is the second polarization state, and the second reference signal R2 has the polarization state of the terahertz wave T. It becomes 0 during the period of the first polarization state. Thereby, the output signal in the period T1 in which the polarization state of the terahertz wave T is the first polarization state and the output signal in the period T3 in which the polarization state of the terahertz wave T is the second polarization state can be obtained. .

  In addition, in the optical analysis device 1, the switching cycle of the presence or absence of the generation of the terahertz wave T is half the switching cycle of the polarization state of the terahertz wave T. Accordingly, a period T1 in which the polarization state of the terahertz wave T is the first polarization state, a period T3 in which the polarization state of the terahertz wave T is the second polarization state, and periods T2 and T4 in which no terahertz wave is generated. It can be easily formed.

Further, in the optical analysis device 1, a condensing lens 18 that condenses the pump light La on the optical chopper 11 is provided. Accordingly, the waveforms of the first analysis signal D1 and the second analysis signal D2 can be sharpened, and the measurement accuracy of the optical parameters of the device S can be increased. Furthermore, in the optical analysis device 1, the input switching unit is configured by the optical chopper 11, so that the input switching unit can be realized with a simple configuration. The polarization switching unit is configured by the Pockels cell 13, thereby simplifying the configuration. Thus, a polarization switching unit can be realized.
[Second embodiment of signal processing]

  FIG. 12 is a diagram illustrating a second embodiment of the signal processing in the optical analysis device 1. This embodiment differs from the first embodiment in that, as shown in FIG. 12A, the switching period of the presence or absence of the terahertz wave T is the switching period of the polarization state of the terahertz wave T. ing.

  As shown in FIG. 12B, the difference signal E includes a period T1 in which the polarization state of the terahertz wave T is the first polarization state, a period T2 in which the polarization state of the terahertz wave T is the second polarization state, and a terahertz wave. There is a period T3 during which no wave T is generated, and a period T4 during which no terahertz wave T is generated. The first reference signal R1 becomes 1 (positive value) during the period T1 and becomes 0 during the period T2, as shown in FIG. Further, the first reference signal R1 becomes −1 (negative value) in the period T3 and becomes 0 in the period T4. The second reference signal R2 becomes 0 during the period T1, and becomes 1 (positive value) during the period T2. Further, the second reference signal becomes 0 in the period T3 and becomes −1 (negative value) in the period T4.

In the first detection signal K1, as shown in FIG. 12 (d), the signal components obtained by adding the signal component _{S C} to the signal component _{S A} appeared in the period T1, a -1 signal component _{S C} in the period T3 multiplied signal components -S _C appears. In the second detection signal K2, the signal components obtained by adding the signal component _{S C} to the signal component _{S B} appeared in the period T2, the signal components -S _C multiplied by -1 in signal component _{S C} in the period T4 Appear.

Also in such a mode, as in the first embodiment, the polarity of the probe light Lb is inverted by inverting the sign of the first reference signal R1 and the second reference signal R2 depending on whether or not the terahertz wave T is generated. It is possible to cancel a signal component based on a temporal change or the like. Therefore, it is possible to avoid the influence of the change in the polarization state of the probe light Lb over time and the like, and it is possible to easily and accurately measure the optical parameters of the DUT S.
[Third Embodiment of Signal Processing]

  FIG. 13 is a diagram illustrating a third embodiment of signal processing in the optical analysis device 1. In this embodiment, as shown in FIG. 13A, the switching period of the presence or absence of the terahertz wave T and the switching period of the polarization state of the terahertz wave T are equal to each other and the phases are shifted by １ ／ period. This is different from the first embodiment.

  As shown in FIG. 13 (b), the difference signal E includes a period T1 in which the polarization state of the terahertz wave T is the first polarization state, a period T2 in which the terahertz wave T does not occur, and a period T3 in which the terahertz wave T does not occur And the period T4 in which the polarization state of the terahertz wave T is the second polarization state. As shown in FIG. 13C, the first reference signal R1 becomes 1 (positive value) in the period T1, and becomes -1 (negative value) in the period T2. Further, the first reference signal R1 becomes 0 in the periods T3 and T4. The second reference signal R2 becomes 0 during the periods T1 and T2. Further, the second reference signal R2 becomes -1 (negative value) in the period T3 and becomes 1 (positive value) in the period T4.

In the first detection signal K1, as shown in FIG. 13 (d), the signal components obtained by adding the signal component _{S C} to the signal component _{S A} appeared in the period T1, a -1 signal component _{S C} in the period T2 multiplied signal components -S _C appears. In the second detection signal K2, the signal component _S signal components -S _C multiplied by -1 to _C appeared in the period T3, the signal components in consideration of the signal component _{S C} to the signal component _{S B} in the period T4 Appear.

Also in such a mode, as in the first embodiment, the polarity of the probe light Lb is inverted by inverting the sign of the first reference signal R1 and the second reference signal R2 depending on whether or not the terahertz wave T is generated. It is possible to cancel a signal component based on a temporal change or the like. Therefore, it is possible to avoid the influence of the change in the polarization state of the probe light Lb over time and the like, and it is possible to easily and accurately measure the optical parameters of the DUT S.
[Fourth Embodiment of Signal Processing]

  FIG. 14 is a diagram illustrating a fourth embodiment of the signal processing in the optical analysis device 1. In this embodiment, as shown in FIG. 14A, the duty ratio of the switching period of the presence or absence of the terahertz wave T is twice the duty ratio of the switching period of the polarization state of the terahertz wave T. This is different from the first embodiment. In the example shown in the drawing, the duty ratio of the switching cycle of the presence or absence of the generation of the terahertz wave T is about 0.66, and the duty ratio of the switching cycle of the polarization state of the terahertz wave T is about 0.33. The duty ratio of the switching period for the presence or absence of the terahertz wave T is the ratio of the ON period in the entire period, and the duty ratio of the switching period of the polarization state of the terahertz wave T is the first polarization state in the entire period. Is the ratio of the period.

  As shown in FIG. 14B, the difference signal E includes a period T1 in which the polarization state of the terahertz wave T is the first polarization state, a period T2 in which the polarization state of the terahertz wave T is the second polarization state, and a terahertz wave. There is a period T3 during which no wave T occurs. As shown in FIG. 14C, the first reference signal R1 becomes 1 (positive value) in the period T1, becomes 0 in the period T2, and becomes -1 (negative value) in the period T3. The second reference signal R2 becomes 0 during the period T1, becomes 1 (positive value) during the period T2, and becomes -1 (negative value) during the period T3.

In the first detection signal K1, as shown in FIG. 14 (d), the signal components obtained by adding the signal component _{S C} to the signal component _{S A} appeared in the period T1, a -1 signal component _{S C} in the period T3 multiplied signal components -S _C appears. In the second detection signal K2, the signal components obtained by adding the signal component _{S C} to the signal component _{S B} appeared in the period T2, the signal components -S _C multiplied by -1 in signal component _{S C} in the period T3 Appear.

  Also in such a mode, as in the first embodiment, the polarity of the probe light Lb is inverted by inverting the sign of the first reference signal R1 and the second reference signal R2 depending on whether or not the terahertz wave T is generated. It is possible to cancel a signal component based on a temporal change or the like. Therefore, it is possible to avoid the influence of the change in the polarization state of the probe light Lb over time and the like, and it is possible to easily and accurately measure the optical parameters of the DUT S.

As in the first to third embodiments, when the duty ratio of the switching period of the presence or absence of the generation of the terahertz wave T is 0.5, for example, as shown in FIG. In the chopper 11, the width W1 of the rib 51 for shielding light may be equal to the interval W2 between the ribs 51,51. On the other hand, when the switching cycle of the presence or absence of the generation of the terahertz wave T is 0.66 as in the fourth embodiment, for example, as shown in FIG. In contrast, the interval W2 between the ribs 51, 51 may be doubled.
[Other Modifications]

  The present disclosure is not limited to the above embodiment. For example, in the optical analysis apparatus 1, the arrangement unit 21 may be configured to be able to scan the position of the DUT S on a plane perpendicular to the traveling direction of the terahertz wave T. In this case, the scanning of the arrangement unit 21 can be configured by, for example, an XY stage. For example, by outputting the position information of the object S on the XY stage to the optical parameter analysis unit 50, it becomes possible to map the optical parameters at each position of the object S based on the position information.

  In the optical analysis device 1, for example, when the dynamic range of lock-in detection is sufficiently large, the detection of the difference signal E by the difference detection unit 41 does not necessarily have to be performed. In this case, for example, the arrangement of the second light detection unit 34B and the difference detection unit 41 may be omitted, and the analysis signal from the first light detection unit 34A may be directly input to the first lock-in detection units 45A and 45B. .

FIG. 16 is a diagram illustrating a modified example of the signal processing in the configuration. The switching period of the presence or absence of the terahertz wave T shown in FIG. 16A and the switching period of the polarization state of the terahertz wave T are the same as those in the first embodiment shown in FIG. Further, the first reference signal R1 and the second reference signal shown in FIG. 16B are the same as those in the first embodiment shown in FIG. In the first detection signal K1, as shown in FIG. 16 (c), the signal component S ₀ to the signal component S _{A 'signal} components in consideration of the advent, the signal component S ₀ in the period _T3' during the period T1 in - A signal component −S ₀ ′ multiplied by 1 appears. In the second detection signal K2, _'considering the signal component appears a signal component S ₀ in the period _T4' signal component S ₀ to the signal component S _B in the period T2 signal components -S multiplied by -1 ₀ 'appears. Since the difference detection is not performed in this configuration, the signal component S ₀ ′ includes the signal component S ₀ based on the intensity of the probe light Lb and the signal component S _c due to a temporal change in the polarization state of the probe light Lb. And may be included.

  Also in such a mode, as in the first embodiment, the polarity of the probe light Lb is inverted by inverting the sign of the first reference signal R1 and the second reference signal R2 depending on whether or not the terahertz wave T is generated. A signal component based on a temporal change or the like can be canceled together with a signal component based on the intensity of the probe light Lb. Therefore, it is possible to avoid the influence of the change in the polarization state of the probe light Lb over time and the like, and it is possible to easily and accurately measure the optical parameters of the DUT S. Note that a mode in which the difference detection unit 41 does not detect the difference signal E can be applied to the above-described second to fourth embodiments.

  In the above embodiment, the reference signal is set to 1 (positive value) during a period in which the polarization state of the terahertz wave T is the first polarization state or the second polarization state, and -1 during a period in which the terahertz wave is not generated. (Negative value), but is not limited to this. For example, the reference signal is set to −1 (negative value) during the period when the polarization state of the terahertz wave T is the first polarization state or the second polarization state, and is set to 1 (positive value) during the period when the terahertz wave T is not generated. ). The positive and negative values of the reference signal are not limited to 1 as long as they are absolute values that are equal to each other, and any value can be used.

  DESCRIPTION OF SYMBOLS 1 ... Optical analysis apparatus, 10 ... Terahertz wave generation module, 11 ... Optical chopper (input switching part), 13 ... Pockels cell (polarization switching part), 17 ... Signal generation part, 18 ... Condensing lens (optical element), 20 ... Optical analysis module, 30 ... Terahertz wave detection unit, 34A ... First light detection unit (light detection unit), 34B ... Second light detection unit (light detection unit), 40 ... Electric field vector measurement unit, 41 ... Difference Detection unit, 50: optical parameter analysis unit, D1: first analysis signal, D2: second analysis signal, R1: first reference signal, R2: second reference signal, La: pump light, Lb: probe Light, T ... Terahertz wave.

Claims (11)

A terahertz wave generation module that generates a terahertz wave by input of pump light,
A terahertz wave detection unit that detects the terahertz wave generated by the terahertz wave generation module,
A light detection unit that detects a probe light modulated by the terahertz wave in the terahertz wave detection unit and outputs an analysis signal;
A signal generation unit that generates a frequency signal used in the terahertz wave generation module, and a reference signal used for signal extraction from the analysis signal,
The terahertz wave generation module,
An input switching unit that periodically switches on / off of the input of the pump light based on a first frequency signal from the signal generation unit, thereby periodically switching presence or absence of the terahertz wave;
A polarization switching unit that periodically switches a polarization state of the terahertz wave between a first polarization state and a second polarization state based on a second frequency signal from the signal generation unit,
The signal generator,
A first reference signal having a positive or negative predetermined value during a period in which the polarization state of the terahertz wave is the first polarization state, and a positive or negative inversion during a period in which the terahertz wave is not generated;
An optical analysis module that generates a second reference signal that has the predetermined value during a period in which the polarization state of the terahertz wave is the second polarization state and that reverses sign during a period in which the terahertz wave is not generated. A first light detection unit that detects a probe light modulated by the terahertz wave in the terahertz wave detection unit and outputs a first analysis signal; and a probe that does not pass through the terahertz wave detection unit. A second light detection unit that detects light and outputs a second analysis signal,
The optical analysis module according to claim 1, further comprising a difference detection unit that detects a difference between the first analysis signal and the second analysis signal. The first reference signal becomes 0 during a period in which the polarization state of the terahertz wave is the second polarization state,
The optical analysis module according to claim 1, wherein the second reference signal is 0 during a period in which the polarization state of the terahertz wave is the first polarization state.   The optical analysis module according to any one of claims 1 to 3, wherein a switching cycle of the presence or absence of the generation of the terahertz wave is half of a switching cycle of the polarization state of the terahertz wave.   The optical analysis module according to any one of claims 1 to 3, wherein a switching period of the presence or absence of the terahertz wave is twice as long as a switching period of the polarization state of the terahertz wave.   The optical analysis module according to any one of claims 1 to 3, wherein a switching cycle of the presence / absence of the terahertz wave and a switching cycle of the polarization state of the terahertz wave are equal to each other and the phases are shifted by 1/4 cycle.   The optical analysis module according to any one of claims 1 to 3, wherein a duty cycle of a switching cycle of the presence or absence of the terahertz wave is twice as large as a duty cycle of a switching cycle of the polarization state of the terahertz wave.   The optical analysis module according to claim 1, further comprising an optical element that collects the pump light with respect to the input switching unit.   The optical analysis module according to claim 1, wherein the input switching unit is an optical chopper.   The optical analysis module according to claim 1, wherein the polarization switching unit is a Pockels cell. An optical analysis module according to any one of claims 1 to 10,
An electric field for detecting a first electric field vector of the terahertz wave in the first polarization state and a second electric field vector of the terahertz wave in the second polarization state based on a detection result by the light detection unit. Vector measurement unit,
A spectrum obtained by performing a Fourier transform on a first analysis data based on spectral data obtained by performing a Fourier transform on a product of the first electric field vector and a rotation matrix, and a spectrum obtained by performing a Fourier transform on a product of the second electric field vector and a rotation matrix An optical parameter analysis unit that analyzes an optical parameter of the device under test based on an intersection with second analysis data based on the data.

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