JP6804061B2 - Dielectric spectroscope - Google Patents

Description

The present invention relates to a non-invasive component concentration measuring technique for a living body using dielectric spectroscopy. In particular, the present invention relates to a technique for observing the amplitude and phase of an electromagnetic wave irradiated to a living body in order to measure a component concentration.

As the population ages, dealing with adult diseases is becoming an issue. Whether or not it is an adult disease is determined by examining blood components such as blood glucose levels collected from the patient, but since the blood sampling action itself imposes an excessive psychological burden on the patient, non-invasive blood component concentration measurement technology Is attracting attention.

Currently, there is dielectric spectroscopy as a non-invasive component concentration measuring method. In dielectric spectroscopy, electromagnetic waves are radiated into the patient's skin, and the electromagnetic waves are absorbed into the body by the interaction between glucose molecules that indicate blood sugar levels and water in the body, and the amplitude of the electromagnetic waves that have passed through the patient's body. And, it is a method of measuring the blood component concentration of a patient by observing the phase.

However, the interaction of electromagnetic waves with the target component in the blood is small, and the intensity of electromagnetic waves that can be irradiated is limited in consideration of the effect on the human body, so appropriate measurement results cannot be obtained, and the blood glucose level of the living body. A sufficient effect cannot be obtained in the measurement.

On the other hand, in the field of material analysis using electromagnetic waves such as microwaves, the complex permittivity of a material is evaluated by using various methods such as a resonance method and a coaxial reflection method. At high frequencies such as the terahertz band, the complex permittivity of the sample is measured by the free space method using a pseudo-optical system using a lens or a parabolic mirror. Since the above-mentioned glucose molecules and the like have a correlation with the complex permittivity, it is possible to measure the blood component concentration of the human body as a sample by measuring the amplitude and phase of the electric signal corresponding to the change in the complex permittivity. Is.

As a conventional dielectric spectroscope, there is a dielectric spectroscope that utilizes photoelectric conversion technology in the frequency band from microwave to millimeter wave or higher. The configuration of the dielectric spectroscope disclosed in Patent Document 1 is shown in FIG. FIG. 5 corresponds to FIG. 4 of Patent Document 1.

The dielectric spectroscope shown in FIG. 5 irradiates the measurement sample 100 with a THz beam having a frequency corresponding to the difference frequency between the two continuous wave lights, and transmits and reflects the THz probe beam through the measurement sample 100. A method is adopted in which homodyne detection is performed by a second photomixer 6b to measure the amplitude and phase of an electric signal.

In addition, when homodyne detection of electromagnetic waves, it is necessary that the two optical paths and space propagation lengths at the time of mixing with the second photomixer 6b match, so the propagation length of electromagnetic waves propagating in space and light propagate. The optical fiber length is adjusted. Specifically, the optical fiber length and spatial propagation length from the first coupler 3a to the second photomixer 6b via the first photomixer 6a and the optical fiber length from the second coupler 3b to the second photomixer 6b are set. Matching.

Next, the measurement sample will be described. Moisture and the like are contained in the living body, and when evaluating a liquid sample such as an aqueous solution or oil in a pseudo manner, it is common to enclose the liquid sample in a solution cell or supply the liquid sample by flow for measurement. The size of the sample cell is, for example, several millimeters × several millimeters square or more as the beam size or more, and the window material for fixing the sample includes high resistance Si, Z-cut crystal, high-density polyethylene, polymethylpentene, etc. A material having a high transmittance is used depending on the situation. The sample cell may have a flow cell configuration including an inlet and an outlet.

Further, in the case of the cell for measuring the permittivity, a window material that transmits terahertz waves is provided, but in the continuous wave electromagnetic wave spectroscopy measurement method shown in FIG. 5, multiple reflections of terahertz waves that depend on the thickness of the window material are provided. Is known to occur. Since it is not easy to eliminate the influence of multiple reflections from the thickness, cell thickness, and dielectric constant of the two window materials, for example, a method of reducing the interference ripple on the spectrum by taking a moving average is adopted. There is.

Further, since water exhibits extremely strong absorption in the infrared region, it is known that a liquid sample is evaluated using the ATR prism 9 made of high resistance silicon shown in FIG. Conventionally, since the terahertz wave beam between the two lenses 30 is parallel light, the ATR prism 9 is arranged at the center between the two lenses 30 and fixed by the support base 50. The cross-sectional shape of the ATR prism 9 is trapezoidal, and the width and height of the ATR prism 9 are adjusted according to the beam size of the terahertz wave. A permittivity measuring cell is placed on the ATR prism 9, and the transmission signal of the ATR prism 9 reflected by the permittivity measuring cell is received to measure the amplitude and phase.

The dielectric relaxation spectrum is calculated from the amplitude and phase of the electric signal corresponding to the frequency of the radio wave observed as described above. Generally, it is expressed as a linear combination of relaxation curves based on the Core-Cole equation, and the complex permittivity is calculated. In the measurement of biological components, for example, since the complex permittivity has a phase in the amount of blood components such as glucose and cholesterol contained in blood, it is measured as the amplitude and phase of an electric signal corresponding to the change. A calibration model is constructed by measuring the phase between the change in the complex permittivity and the component concentration in advance, and the component concentration is calibrated from the measured change in the dielectric relaxation spectrum.

Japanese Unexamined Patent Publication No. 2013-32933

Jae-Young Kim, 4 outsiders, "Continuous-Wave THz Homodyne Spectroscopy and Imaging System With Electro-Optical Phase Modulation for High Dynamic Range,", IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL.3, NO.2, 2013 March, p.158-p.164 Benjamin S.-Y.Ung, 5 outsiders, "Low-cost ultra-thin broadband terahertz beam-splitter", OPTICS EXPRESS, Vol.20, No.5, February 27, 2012, p.4968-p. 4978

However, in high-band electromagnetic waves such as the terahertz band, in the conventional dielectric spectroscopy device shown in FIG. 5, the SN ratio is lowered due to the influence of noise generated by the photomixer due to the phase noise of the light source. Since these noises cause fluctuations in the amplitude and phase of the observed electrical signal, there is a problem that measurement reproducibility and appropriate measurement accuracy cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce instability due to environmental fluctuations and to perform dielectric spectroscopy measurement in a high frequency band such as a terahertz band with high accuracy.

In order to solve the above problems, the dielectric spectroscopic device according to claim 1 has a propagation path in which an electromagnetic wave having a frequency corresponding to the difference frequency of two lights radiated from the first photomixer to the second photomixer propagates. The ATR prism arranged in the above and the measurement sample is installed, the half mirror arranged in the propagation path of the electromagnetic wave propagating between the first photomixer and the ATR prism, and the half mirror reflected by the half mirror. A third photomixer that receives electromagnetic waves, a splitter that splits the light for homodyne detection input to the second photomixer and inputs it to the third photomixer, and a homodyne in the second photomixer. It includes a correcting unit for correcting the value of the second electrical signal homodyne detection by the value of the first electrical signal a third photo mixer is detected, and the correction unit, the first electrical signal And the second electric signal are detected respectively to detect the amplitude and the phase, respectively, and the amplitude and phase values of the second electric signal are removed from the amplitude and phase values of the first electric signal. It is characterized in that the complex dielectric constant is measured using the amplitude and phase after removal, and the component concentration contained in the measurement sample is measured from the complex dielectric constant .

According to the present invention, instability due to environmental fluctuations can be reduced, and dielectric spectroscopic measurement in a high frequency band such as the terahertz band can be performed with high accuracy.

It is a figure which shows the structure of the dielectric spectroscope which concerns on this embodiment. It is a figure which shows the image of the refraction and reflection of a terahertz wave in an ATR prism. It is a graph which shows the time transition of the amplitude and the phase when the ATR prism is not used. It is a graph which shows the time transition of the amplitude and the phase when using the ATR prism. It is a figure which shows the structure of the conventional dielectric spectroscope. It is a figure which shows the structure of the conventional dielectric spectroscope.

<Overview>
In the present invention, with respect to the conventional dielectric spectroscopic device shown in FIG. 5, a half mirror that reflects a part of the electromagnetic wave from the first photomixer 6a, a third photomixer that receives the electromagnetic wave reflected by the half mirror, and a third photomixer. The third splitter, which branches the light for homodyne detection from the 2 coupler 3b and inputs it to the second photomixer 6b and the third photomixer, respectively, and the value of the electric signal homodyne detected by the second photomixer 6b are used as the third value. It is further provided with a lock-in amplifier that corrects with the value of an electric signal homodyne-detected by the photomixer of the above, and is characterized in that terahertz spectroscopy is performed by an ATR prism.

By adding these components, it is possible to eliminate the influence of noise generated by the first photomixer 6a and the second photomixer 6b due to the phase noise of the light source. As a result, instability due to environmental fluctuations can be reduced, and dielectric spectroscopy measurement in a high frequency band such as the terahertz band can be performed with high accuracy.

Further, the present invention is characterized in that the condition that the two optical paths / spatial propagation lengths at the time of mixing by the second photomixer 6b and the third photomixer must match is adjusted by using a delay line. And. As a result, homodyne detection can be performed easily and easily.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<Composition>
FIG. 1 is a diagram showing a configuration of a dielectric spectroscope according to the present embodiment. In this embodiment, the free space method using a pseudo optical system is used.

This dielectric reflector includes a first continuous wave light source 1a, a second continuous wave light source 1b, a first splitter 2a, a second splitter 2b, a third splitter 2c, a first coupler 3a, a second coupler 3b, and a first phase modulator. 4a, 2nd phase modulator 4b, light source 5, 1st photomixer 6a, 2nd photomixer 6b, 3rd photomixer 6c, 1st parabolic mirror 7a, 2nd parabolic mirror 7b, 3rd parabolic It includes a surface mirror 7c, a half mirror 8, an ATR prism 9, a delay line 10, a lock-in amplifier 11, and a monitor 12. All these components are connected as shown in FIG. The solid line shown in FIG. 1 is an optical fiber line, the alternate long and short dash line is an electric line, and the broken line is a propagation path of electromagnetic waves.

The first continuous wave light source 1a has a function of outputting a first continuous light wave having a first frequency ω ₁ . The second continuous wave light source 1b has a function of outputting a second continuous light wave having a second frequency ω ₂ (≠ ω ₁ ). A pulse wave from a laser light source may be used instead of the continuous wave of light from the continuous wave light source.

The first splitter 2a splits the optical power of the first continuous light wave into two equal parts, inputs one first continuous light wave to the first coupler 3a, and inputs the other first continuous light wave to the first phase modulator. It has a function to input to 4a. The second splitter 2b splits the optical power of the second continuous light wave into two equal parts, inputs one second continuous light wave to the first coupler 3a, and inputs the other second continuous light wave to the second phase modulator. It has a function to input to 4b.

The first phase modulator 4a has a function of modulating the phase of the first continuous light wave based on the signal from the oscillator 5 and inputting it to the second coupler 3b. The second phase modulator 4b has a function of modulating the phase of the second continuous light wave based on the signal from the oscillator 5 and inputting it to the second coupler 3b.

The first coupler 3a has a function of combining the first continuous light wave and the second continuous light wave and inputting them to the first photomixer 6a. The second coupler 3b combines the phase-modulated first continuous light wave and the second continuous light wave, and inputs them to the second photomixer 6b and the third photomixer 6c via the delay line 10 and the third splitter 2c, respectively. It has a function to do.

The first phase modulator 4a, the second phase modulator 4b, and the second coupler 3b are reference signals (for homodyne detection) used by the second photomixer 6b and the third photomixer 6c to perform homodyne detection, respectively. It constitutes the oscillation source of light).

The first photomixer 6a has a function of radiating a terahertz wave having a frequency corresponding to the difference frequency (| ω ₁ − ω ₂ |) between the first continuous light wave and the second continuous light wave into space. The first photomixer 6a can be realized by, for example, a single traveling carrier photodiode (UTC-PD: Uni-Travelling-Carrier Photodiode).

The second photomixer 6b receives the terahertz wave from the first photomixer 6a propagating in space via the ATR prism 9 and the measurement sample 100, and receives a reference signal (light for homodyne detection) from the second coupler 3b. ) Is used to perform homodyne detection, and the electric signal is output to the lock-in amplifier 11.

The third photomixer 6c receives the terahertz wave from the first photomixer 6a reflected by the half mirror 8, performs homodyne detection using the reference signal (light for homodyne detection) from the second coupler 3b, and performs homodyne detection thereof. It has a function of outputting an electric signal to the lock-in amplifier 11.

These second photomixers 6b and third photomixers 6c can be realized, for example, by mounting the UTC-PD with an antenna and the optical fiber in the same package. In addition, a photo-conductive antenna (PCA) may be used.

The first parabolic mirror 7a has a function of reflecting the terahertz wave radiated from the first photomixer 6a at an angle of about 90 ° and converting it into parallel light to change the propagation direction of the terahertz wave.

The second parabolic mirror 7b has a function of reflecting the propagation direction of the terahertz wave changed by the first parabolic mirror 7a at an angle of about 90 ° and directing the propagation direction of the terahertz wave toward the second photomixer 6b. Be prepared.

The third parabolic mirror 7c has a function of reflecting the propagation direction of the terahertz wave reflected by the half mirror 8 at an angle of about 90 ° and directing it toward the third photomixer 6c.

The half mirror 8 is arranged in the propagation path of the terahertz wave propagating between the first photomixer 6a and the ATR prism 9, and has a function of transmitting the terahertz wave to the ATR prism 9 and reflecting the terahertz wave.

The ATR prism 9 is an attenuated total reflection prism or a total reflection prism whose cross-sectional shape is trapezoidal and whose width and height are adjusted according to the beam size of the terahertz wave, and is a terahertz emitted from the first photomixer 6a. It is located in the wave propagation path and has a function to perform terahertz spectroscopy.

The third splitter 2c splits the optical power of the reference signal (light for homodyne detection) from the second coupler 3b into two equal parts, inputs one reference signal to the second photomixer 6b, and the other. It has a function of inputting a reference signal to the third photomixer 6c.

The delay line 10 is inserted and connected between the second coupler 3b and the third splitter 2c, and delays the reference signal (light for homodyne detection) input to the second photomixer 6b and the third photomixer 6c. It has a function to make it.

The lock-in amplifier 11 has a function (correction unit) of correcting (removing) the value of the electric signal homodyne-detected by the second photomixer 6b with the value of the electric signal homodyne-detected by the third photomixer 6c, the oscillator 5. It has a function to control the oscillation frequency. The lock-in amplifier 11 may be realized, for example, in a configuration in which signal processing is performed in analog, or an integrated circuit (for example, FPGA (field-programmable gate array)) or ASIC (for example) that performs digital signal processing after A / D conversion. It may be composed of application specific integrated circuit)).

The monitor 12 has a function of displaying the processing result (amplitude, phase, etc. of the electric signal) of the electric signal performed by the lock-in amplifier 11 on the screen.

So far, the functions of the individual components constituting the dielectric spectrometer have been described. The measurement sample 100 for a living body or the like is placed or contact-arranged on the surface of the ATR prism 9 (the surface on the side where the terahertz wave incident from the slope of the ATR prism 9 is refracted).

<Operation>
Next, the operation of the dielectric spectroscope will be described.

(Conventional operation)
First, the operation of the conventional dielectric spectroscope shown in FIG. 5 will be described (Non-Patent Document 1).

A terahertz wave having a frequency corresponding to the difference frequency between the two continuous light waves (or pulse waves) is radiated from the first photomixer 6a, and the terahertz wave transmitted / reflected through the measurement sample 100 is received by the second photomixer 6b.

At the same time, a signal of a single frequency fm is applied to an optical phase modulator 4 using an electro-optical crystal capable of electrically phase modulation by a control signal to perform cellodyne phase modulation, and a frequency shift equivalent to the modulation frequency fm is performed. Is generated in the second continuous light wave, and the combined wave (reference signal (light for homodyne detection)) of the second continuous light wave and the first continuous light wave after the frequency shift is input to the second photomixer 6b.

Then, using the reference signal, homodyne detection with the received terahertz wave is performed by the second photomixer 6b. Since the second photomixer 6b outputs an electric signal having a frequency of fm by homodyne detection, the electric signal is synchronously detected to detect the amplitude and phase.

(Operation of the present embodiment)
Next, the operation of the dielectric spectroscope according to the present embodiment will be described with reference to FIG.

A terahertz wave having a frequency corresponding to the difference frequency between two continuous light waves (or pulse waves) is radiated from the first photomixer 6a, and the first parabolic mirror 7a, the half mirror 8, the ATR prism 9, the measurement sample 100, and The terahertz wave propagated through the second parabolic mirror 7b is received by the second photomixer 6b.

Further, the terahertz wave is received by the second photomixer 6b, and the terahertz wave before it is incident on the ATR prism 9, to be exact, the first parabolic mirror 7a, the half mirror 8, and the third parabolic mirror 7c. The terahertz wave propagated through the third photomixer 6c is received.

Along with them, a single frequency fm signal from the oscillator 5 is applied to the first phase modulator 4a and the second phase modulator 4b using an electro-optical crystal capable of electrically phase modulation by a control signal, and the cellodyne phase is applied. Modulation is performed to generate a frequency shift equivalent to the modulation frequency fm in the first continuous light wave and the second continuous light wave, respectively, and the combined wave of the first continuous light wave and the second continuous light wave after the frequency shift (reference signal (for homodyne detection)). Light)) is input to the second photomixer 6b and the third photomixer 6c, respectively.

Then, using the reference signal, homodyne detection with the terahertz wave including the amount of change in the ATR prism 9 and the measurement sample 100 is performed by the second photomixer 6b, and the amount of change in the ATR prism 9 and the measurement sample 100 is included. Homodyne detection with no terahertz wave is performed with the third photomixer 6c.

After that, since each electric signal having a frequency fm by homodyne detection is output from the second photomixer 6b and the third photomixer 6c, each electric signal is synchronously detected and the amplitude and phase are detected by the lock-in amplifier 11. Then, the amplitude and phase values of the third photomixer 6c are removed from the amplitude and phase values of the second photomixer 6b.

Finally, the complex permittivity is measured using the amplitude and phase after removal with the lock-in amplifier 11 or a dedicated device (not shown), and the component concentration contained in the measurement sample 100 is measured from the complex permittivity.

According to the present embodiment, the half mirror 8 is arranged between the first photomixer 6a and the ATR prism 9, and the third photomixer 6c uses the terahertz wave reflected by the half mirror 8 before the ATR prism is incident. Since homodyne detection is performed and the value of the electric signal homodyne detected by the third photomixer 6c is removed from the value of the electric signal homodyne detected by the second photomixer 6b, the first continuous wave light source 1a and the second continuous wave are removed. It is possible to eliminate the influence of noise generated by the first photomixer 6a and the second photomixer 6b due to the phase noise of the light source 1b. As a result, instability due to environmental fluctuations can be reduced, and dielectric spectroscopy measurements in the terahertz band can be performed with high accuracy.

<How to adjust the optical path / spatial propagation length between the coupler and the photomixer>
Next, a method of adjusting the optical path / spatial propagation length between the coupler and the photomixer will be described. When detecting electromagnetic waves in homodyne, it is necessary that the two optical paths and spatial propagation lengths at the time of mixing by the second photomixer 6b match, as described in the background art. The same applies when mixing is performed with the third photomixer 6c.

Regarding this condition, in the conventional dielectric spectrometer shown in FIG. 5, the optical fiber length and the spatial propagation length from the first coupler 3a to the second photomixer 6b via the first photomixer 6a and the second coupler 3b to the second The length of the optical fiber up to 2 photomixers 6b was matched.

In order to satisfy the same conditions, in the present embodiment, the first optical path length from the first coupler 3a to the second photomixer 6b via the first photomixer 6a and the second coupler 3b to the third splitter 2c are used. The second optical path length to the second photomixer 6b is made equal to the third optical path length from the second coupler 3b to the third photomixer 6c via the third splitter 2c. That is, the delay lengths of the first optical path length, the second optical path length, and the third optical path length are made equal.

At this time, for example, light is emitted between the first coupler 3a and the first photomixer 6a, between the third splitter 2c and the second photomixer 6b, and between the third splitter 2c and the third photomixer 6c, respectively. Although they are connected by fibers, the actual length of the optical fiber between them is often different. Therefore, in order to satisfy the condition that the optical path lengths are equivalent, the delay line 10 is inserted. For example, the optical fiber length between the first coupler 3a and the first photomixer 6a is the optical fiber length between the third splitter 2c and the second photomixer 6b, or the third splitter 2c and the third photomixer 6c. If it is longer than the optical fiber length between them, a delay line 10 is inserted on the optical fiber between the second coupler 3b and the third splitter 2c, as shown in FIG.

As described above, in the present embodiment, the conditions for equalizing the optical path lengths can be satisfied only by adjusting the delay amount of the delay line 10, so that homodyne detection can be performed reliably and easily. Instead of inserting the delay line 10 into the optical fiber between the second coupler 3b and the third splitter 2c, the delay line may be inserted into another optical fiber. For example, the optical fiber length between the third splitter 2c and the second photomixer 6b or the optical fiber length between the third splitter 2c and the third photomixer 6c is different from that of the first coupler 3a and the first photomixer 6a. If it is longer than the optical fiber length between, a delay line is inserted into the optical fiber between the first coupler 3a and the first photomixer 6a.

<Characteristics of ATR prism>
Next, the characteristics of the ATR prism 9 will be described. Since the ATR prism 9 is made of silicon and has a temperature characteristic of a refractive index, the optical path length changes due to temperature fluctuations, and the phase to be measured changes.

Therefore, as shown in FIG. 2, the temperature control element 13 is installed at the bottom of the ATR prism 9. It may be installed on the side surface in addition to the bottom surface of the ATR prism 9. Further, in order to perform stable measurement, the ATR prism 9 and the temperature control element 13 are fixed on the support base 50.

In the present embodiment, since the temperature control element 13 and the support base 50 are used for the ATR prism 9, the dielectric spectroscopic measurement in the terahertz band can be performed with higher accuracy.

<Characteristics of half mirror and parabolic mirror>
Next, the characteristics of the half mirror 8 and the first parabolic mirror 7a will be described.

The terahertz wave shown by the broken line in FIG. 2 is irradiated with a plane wave at a predetermined position on one slope of the Dove type ATR prism 9, reflected by the measurement sample 100 on the upper surface, and then emitted from the other slope. When incident and emitted, it is reflected by about 30% at the interface between silicon, which is the material of the ATR prism 9, and air.

Further, as shown in FIG. 1, in the present embodiment, the half mirror 8 is installed between the first photomixer 6a and the ATR prism 9, and instead of adjusting the propagation path of the terahertz wave with a lens. A parabolic mirror is used. A part of the terahertz wave paralleled by the first parabolic mirror 7a is reflected by the half mirror 8 of the propagation path at an angle of about 90 °, reaches the third parabolic mirror 7c, and reaches the third photomixer. It is incident on 6c. After passing through the half mirror 8, the other terahertz waves enter the ATR prism 9, reach the second parabolic mirror 7b via the measurement sample 100, and enter the second photomixer 6b. Such a half mirror 8 can be realized by adjusting the thickness of the thin layer of the metal layer (Non-Patent Document 2). The reflectance of the half mirror may be adjusted so as to be divided into equal parts.

In the present embodiment, since a parabolic mirror is used instead of the lens, it is possible to eliminate the multiple reflection of the terahertz wave generated by the lens. As a result, the complex permittivity can be measured stably, and the dielectric spectroscopic measurement can be performed with higher accuracy.

<Operation of lock-in amplifier>
Next, the operation of the lock-in amplifier 11 will be described. As described above, the lock-in amplifier 11 removes the value of the electric signal homodyne-detected by the third photomixer 6c from the value of the electric signal homodyne-detected by the second photomixer 6b.

Here, ignoring wave atmospheric absorption of the space propagation path, received power S ₂ of each terahertz wave reaching each second photo mixer 6b and third photo mixer _6c, S 3 _(dB), respectively formula (1 ) And equation (2).

S ₂ = P _1- L _ATR- L _S- L _HM -2L _PM ... (1)
S ₃ = P _1- L _HM -2L _PM ... (2)
P ₁ is the signal loss due to the first photo mixer 6a terahertz wave transmission power emitted _{from, L ATR} signal loss due to ATR prism 9, _{L S} is the signal loss due to sample _{100, L HM} the half mirror _{8, L PM} Is the signal loss due to the first parabolic mirror 7a, the second parabolic mirror 7b, or the third parabolic mirror 7c. When determining the difference between the two reception power _S 2, _{S 3} becomes Equation (3).

L _ATR + L _S = S _3- S ₂ ... (3)
From equation (3), by taking the difference or ratio of the received power S _2, S ₃ of the terahertz wave reaching the second photo mixer 6b and third photo mixer 6c, noise generated by the first photo-mixer 6a etc. It is excluded, and the signal loss due to only the ATR prism 9 and the measurement sample 100 can be obtained. Since the lock-in amplifier 11 performs arithmetic processing corresponding to the equation (3), the dielectric spectroscopic measurement can be performed with high accuracy.

Further, the lock-in amplifier 11 further removes the _LATR by using the reception powers S ₂₁ and S ₃₁ when the measurement sample 100 is not present and the reception powers S ₂₂ and S ₃₂ when the measurement sample 100 is present. Do.

Specifically, the reception powers S ₂₁ and S ₂₂ of the second photomixer 6b can be described as equations (4) and (5), respectively.

S ₂₁ = P _1- L _ATR- L _HM -2L _PM ... Equation (4)
S ₂₂ = P _1- L _ATR- L _S- L _HM -2L _PM ... Equation (5)
The reception powers S ₃₁ and S ₃₂ of the third photomixer 6c are the same as those on the right side of the equation (2) regardless of the presence or absence of the measurement sample 100. Similar to the formula (3), the difference between the received powers S ₂₁ and S ₃₁ when the measurement sample 100 is not obtained is the formula (6), and the difference between the received powers S ₂₂ and S ₃₂ when the measurement sample 100 is present is obtained. When calculated, it becomes equation (7).

L _ATR = S _31- S ₂₁ ... Equation (6)
L _ATR + L _S = S _32- S ₂₂ ... Equation (7)
The difference between the equation (6) and the equation (7) is obtained by the equation (8).

L _S = (S _32- S ₂₂ )-(S _31- S ₂₁ ) ... Equation (8)
Since the equation (8) does not include the _LATR , the signal loss due to the measurement sample 100 alone can be obtained. Since the lock-in amplifier 11 also performs arithmetic processing corresponding to the equation (8), the dielectric spectroscopic measurement can be performed with higher accuracy.

FIG. 3 is a diagram showing measurement results when the ATR prism 9 is not installed in the atmosphere. (A) and (b) of FIG. 3 show the time transition of the amplitude and the phase, respectively. Amp1 and Pha1 indicate the amplitude and phase of the electric signal output from the second photomixer 6b to the lock-in amplifier 11, respectively, and Amp2 and Pha2 indicate the amplitude and phase of the electric signal output from the third photomixer 6c to the lock-in amplifier 11, respectively. Shows the amplitude and phase of the signal. Since _{L ATR} and _{L S} in equation (3) can be ignored, atmospheric absorption and second photo mixer 6b, the residual by the reception characteristics of the third photo-mixer 6c ΔA (= Amp1-Amp2) , Δφ (= Pha1 -Pha2).

Ideally, long-term drift is reduced and it is desirable to be constant at 100% amplitude or constant at phase 0. When comparing the drift amounts of Amp1 and ΔA, ΔA is closer to the ideal value, and when comparing the drift amounts of Pha1 and Δφ, Δφ is closer to the ideal value, so that the effect according to the present invention is recognized. For example, it can be understood that one hour after the start of measurement, the amplitude is suppressed to a drift of about 1% and the phase is suppressed to a drift of about 3 °. When the standard deviation was obtained, the standard deviation of the amplitude was 0.25% when the differential calculation according to the equation (3) was not performed, but it could be reduced to 0.07% by performing the differential calculation. As for the phase, the standard deviation could be reduced from 0.8 ° to 0.2 °.

FIG. 4 is a diagram showing measurement results when the ATR prism 9 is installed in the atmosphere. Time transitions of amplitude and phase are also shown in FIGS. 4A and 4B, respectively. The measurement sample 100 is not arranged. Since the signal loss due to L _S in equation (3) can be ignored, shows a residual Δ by atmospheric absorption and second photo mixer 6b, reception characteristics of the third photo-mixer 6c. From FIG. 4, it can be understood that the same effect can be obtained even if the ATR prism 9 is installed. For example, one hour after the start of measurement, it can be understood that the amplitude is suppressed to the drift within the ± 1% range and the phase is reduced to the drift within the ± 1.8 ° range.

<Effect>
From the above, according to the present embodiment, the half mirror 8 is arranged between the first photomixer 6a and the ATR prism 9, and the third photo using the terahertz wave before the ATR prism is incident reflected by the half mirror 8. Since homodyne detection is performed by the mixer 6c and the value of the electric signal homodyne detected by the third photomixer 6c is removed from the value of the electric signal homodyne detected by the second photomixer 6b, the amplitude of the signal via the ATR prism 9 is removed. And when measuring the phase, it is possible to suppress a decrease in the SN ratio due to the influence of the noise of the transmission power of the terahertz wave generated by the first photomixer 6a and the second photomixer 6b due to the phase noise of the light source. As a result, fluctuations in signal amplitude and phase can be suppressed, and measurement reproducibility and measurement accuracy can be improved. The dielectric spectroscope described in the present embodiment can be applied to a non-invasive component concentration measuring technique for solution components forming humans or animals.

1a ... 1st continuous wave light source 1b ... 2nd continuous wave light source 2a ... 1st splitter 2b ... 2nd splitter 2c ... 3rd splitter 3a ... 1st coupler 3b ... 2nd coupler 4 ... Optical phase modulator 4a ... 1st phase Modulator 4b ... Second phase modulator 5 ... Oscillator 6a ... First photomixer 6b ... Second photomixer 6c ... Third photomixer 7a ... First parabolic mirror 7b ... Second parabolic mirror 7c ... Third Parabolic mirror 8 ... Half mirror 9 ... ATR prism 10 ... Delay line 11 ... Lock-in amplifier 12 ... Monitor 13 ... Temperature control element 30 ... Lens 50 ... Support stand 100 ... Measurement sample

Claims (1)

An ATR prism placed in a propagation path where electromagnetic waves with a frequency corresponding to the difference frequency of two lights radiated from the first photomixer to the second photomixer propagate , and a measurement sample is installed .
A half mirror arranged in the propagation path of the electromagnetic wave propagating between the first photomixer and the ATR prism, and
A third photomixer that receives the electromagnetic wave reflected by the half mirror, and
A splitter that branches the light for homodyne detection input to the second photomixer and inputs it to the third photomixer.
And a correcting unit for correcting the value of the second electrical signal homodyne detection in the second first the value of the electrical signal of the third photo-mixer which is homodyne detection in photomixer,
The correction unit
The first electric signal and the second electric signal are detected respectively to detect the amplitude and phase, respectively, and the amplitude and phase of the second electric signal are obtained from the amplitude and phase values of the first electric signal. A dielectric spectroscopic apparatus characterized in that the value of is removed, the complex dielectric constant is measured using the amplitude and phase after removal, and the concentration of components contained in the measurement sample is measured from the complex dielectric constant .

Images