JP4996428B2 - Apparatus and method for measuring moisture content in thin section sample - Google Patents

Description

  The present invention relates to an apparatus and a method for measuring the moisture content of a thin slice sample using terahertz light.

  In the present application, an electromagnetic wave having a frequency of approximately 0.1 to 100 THz, that is, far infrared rays and submillimeter waves in this region are referred to as “terahertz waves” and described as “THz waves”.

  For example, Patent Document 1 and Non-Patent Document 2 have already been disclosed as means for generating terahertz waves (THz waves). Non-patent document 1 is a related prior document, and non-patent document 3 is an unpublished document.

Patent Document 1 aims to generate a terahertz wave having an arbitrary frequency at an arbitrary time.
Therefore, according to the present invention, in the apparatus shown in FIG. 11, the KTP crystal 58 receives light from the excitation light source 51 and generates light having the first and second wavelengths according to the arrangement angle. The galvano scanner 52 determines the arrangement angle of the two KTP crystals 58. The galvano scanner control unit 57 controls the drive of the galvano scanner 58 according to the control signal from the main control unit 55 to determine the arrangement angle of the KTP crystal 58. In the storage unit of the main control unit 55, first and second wavelengths for generating a terahertz wave having a desired frequency and a control signal for determining an arrangement angle of the KTP crystal 58 that outputs the wavelength are stored in advance. Remembered. The main control unit 55 refers to the storage unit, acquires each control voltage corresponding to a desired frequency, and outputs the control voltage to the galvano scanner control unit 57. The terahertz wave generating crystal 53 outputs a terahertz wave according to the difference between the first and second wavelengths from the KTP crystal 58.

Non-Patent Document 2 is a THz wave light source using stimulated polariton scattering of LiNbO ₃ crystal in a frequency band of 1 to ₃ THz. This THz wave light source is a light source capable of frequency tuning in a few milliseconds by a ring resonator type terahertz wave parametric oscillator (ring TPO) in terms of rapid frequency change.

  Non-Patent Document 3 is a difference frequency generation method in which laser beams having two different wavelengths are incident on a nonlinear optical crystal and a terahertz wave corresponding to the difference frequency is generated.

Japanese Patent Application Laid-Open No. 2006-215222, “Terahertz Wave Generator and Spectrometer”

J. et al. K. Vij, D.D. R. J. et al. Simpson, O.M. E. Panarina, Far infrared spectroscopy of water at differential temperatures: GHz to THz differential spectroscopy of water, J. MoI. Mol. Liquids, vol. 112, pp. 125-135, 2004. Hiroaki Minamide, Atsushi Sato, Tomofumi Ikari, Hiromasa Ito, "All-in-one THz-wave parametric source driven by a compact LD-pumped Q-switched Nd: YAG laser", CLEO / Pacciffic Rim 2007, Seoul, Korea, August , 2007 Hiromasa Ito, Koji Suizu, Tomoyu Yamashita, Akira Nawahara and Tomohisa Sato, "Random frequency accessible broad tunable terahertz-wave source using phase-matched 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal", JJAP To be published

  The terahertz wave electromagnetic frequency region is an electromagnetic frequency region located at the boundary between light waves and radio waves. As a spectroscopic feature, there are many molecular specific absorption spectra called fingerprint spectra in the THz wave band, and it is expected to play an important role in the field of product inspection technology and medical diagnostic technology development.

  In addition, since THz waves are strongly absorbed by water, handling of moisture is important for applied research. For this reason, in conventional research for medical applications, biological tissues have been dried and used as samples.

Measuring the amount of water in a substance provides useful information for physical property research and product management in industry.
In particular, in the pathological clinical field such as pathological diagnosis in the medical clinical field, the close relationship between the water content and the pathological tissue is suggested, and the water content should be measured easily and quickly without drying the living tissue. Is desired.

  In recent years, therefore, research on water content measurement that actively uses strong absorption of THz wave water has been actively conducted. That is, if the THz wave is used, sufficient attenuation of the transmitted light can be obtained even in a thin sample. Therefore, a report on the activity evaluation of the plant by monitoring the moisture content of the leaf using the THz wave, and the pathology using the reflection optical system. The possibility of diagnosis has been reported.

However, it has been difficult for conventional means to easily and quickly measure the amount of water in a thin slice sample such as a biological sample.
Even when the transmittance of THz waves is used, it is indispensable to adjust the thickness of the sample in order to obtain an appropriate transmittance. In particular, in the case of a living tissue, it takes time and effort to adjust the thickness of the sample.

  The present invention has been developed to solve such problems. That is, the object of the present invention is to be able to easily and quickly measure the amount of water in a thin slice sample such as a biological sample, and to obtain an appropriate transmittance without precise thickness adjustment of the sample. An object of the present invention is to provide a device and method for measuring the water content of a thin slice sample.

According to the present invention, a terahertz wave generator that generates an arbitrary frequency continuously or discontinuously as a pulse wave or a continuous wave in a predetermined frequency band;
A light wave dividing element for dividing the terahertz wave into incident light and reference light;
A reference light detector for detecting the intensity of the reference light;
An irradiation optical system for condensing and irradiating a part of the thin-section sample with the incident light;
A transmitted light detector for detecting the transmitted light intensity of the terahertz wave transmitted through the thin slice sample;
An arithmetic device for calculating the transmittance and moisture content of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity;
A device for measuring the moisture content of a thin-section sample is provided, comprising: a frequency control device that feeds back the transmittance to control the frequency of generation of terahertz waves.

  According to a preferred embodiment of the present invention, the frequency control device controls the generation frequency of the terahertz wave so that the transmittance is within a predetermined optimum range.

According to the present invention, the terahertz wave is generated in a predetermined frequency band as a pulse wave or a continuous wave, and an arbitrary frequency is generated continuously or discontinuously.
A terahertz wave dividing step for dividing the terahertz wave into incident light and reference light;
A reference light detection step for detecting the intensity of the reference light;
Incident light irradiation step of collecting and irradiating the incident light on a part of the thin slice sample;
A transmitted light detection step of detecting the transmitted light intensity of the terahertz wave transmitted through the thin slice sample;
A calculation step of calculating the transmittance and moisture content of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity,
There is provided a method for measuring the moisture content of a thin slice sample, comprising a frequency control step of controlling the frequency of generation of terahertz waves by feeding back the transmittance.

According to a preferred embodiment of the present invention, in the calculation step,
Obtain the transmittance T of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity,
Using the thickness d of the thin-section sample, the absorption coefficient α of the sample is obtained by the Lambert-Beer law,
From the moisture absorption coefficient α _w , the volume fraction ν _w of moisture contained in the thin slice sample is determined.

  In the frequency control step, the generation frequency of the terahertz wave is controlled so that the transmittance T is T = 0.22 to 0.55.

  The present invention takes advantage of the fact that the proportion of water in the living tissue is large and that the absorption coefficient of water is relatively strong in the THz wave frequency band. The water content is measured using a permeation method.

That is, according to the above-described apparatus and method of the present invention, a terahertz wave is continuously or discontinuously converted into a pulse wave or a continuous wave by a terahertz wave generator in a predetermined frequency band (for example, a frequency range of 1 to 6 THz). Any frequency can be generated.
Further, the incident light intensity can be accurately measured by a light wave splitting element (for example, a half mirror) and a reference light detector (for example, Si bolometer), and an irradiation optical system (for example, a condensing lens) and a transmitted light detector (for example, for example). The transmitted light intensity can be accurately measured by a Si bolometer).
Further, the transmittance T and the water content (volume fraction ν _{w of the} water content) of the irradiated portion of the thin slice sample can be calculated from the incident light intensity and the transmitted light intensity by an arithmetic device (for example, PC).

  Further, since the transmission frequency T is fed back by the frequency control device (for example, PC) to control the generation frequency of the terahertz wave, the transmission T is within a predetermined optimum range (for example, T = 0.22 to 0.55). Thus, the generation frequency of the terahertz wave can be controlled, and high sensitivity close to the maximum sensitivity can be ensured.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is an overall configuration diagram of a moisture content measuring apparatus for thin slice samples according to the present invention.
In this figure, the moisture content measuring apparatus 10 of the present invention includes a terahertz wave generator 12, a light wave dividing element 14, a reference light detector 16, an irradiation optical system 18, a transmitted light detector 20, an arithmetic device 22, and a frequency control device. 24.

The terahertz wave generator 12 generates an arbitrary frequency continuously or discontinuously by using the terahertz wave 2 as a pulse wave or a continuous wave in a predetermined frequency band (for example, a frequency range of 1 to 6 THz).
The light wave dividing element 14 is, for example, a half mirror, and divides the terahertz wave 2 into incident light 3 and reference light 4 at a certain ratio.
The reference light detector 16 is a first terahertz wave detector and detects the intensity of the reference light 4. The reference light detector 16 is, for example, a Si bolometer.
The irradiation optical system 18 is, for example, a condensing lens, and condenses incident light 3 onto a part of the thin slice sample 1 (measurement object). Hereinafter, the thin-section sample 1 is simply referred to as “sample 1”.
The transmitted light detector 20 is a second terahertz wave detector, and detects the transmitted light intensity of the terahertz wave 5 (transmitted light) transmitted through the thin slice sample 1. The transmitted light detector 20 is, for example, a Si bolometer.

The calculation device 22 is, for example, a computer (for example, PC), and calculates the transmittance and moisture content of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity.
The frequency control device 24 feeds back the transmittance and controls the generation frequency of the terahertz wave 2. The frequency control device 24 controls the generation frequency of the terahertz wave 2 so that the transmittance T falls within a predetermined optimum range. The predetermined optimum range is, for example, a range of T = 0.22 to 0.55.
In addition, it is preferable to provide a mechanism capable of two-dimensionally scanning the thin slice sample 1 (for example, a biological tissue) to enable measurement of the in-plane distribution of water content.

  FIG. 2 is a diagram showing an embodiment of the terahertz wave generator 12 constituting the present invention. In this figure, the terahertz wave generator 12 includes a two-wavelength light source 32 and a nonlinear optical material 34.

The two-wavelength light source 32 emits light having two different wavelengths.
In this example, the two-wavelength light source 32 is a two-wavelength optical parametric oscillator including two bulk KTP crystals 32a and 32b, mirrors M1, M2 and M3, and a laser oscillator 33, and has two wavelengths λ ₁ and λ ₂ . Laser beams 7 and 8 are emitted. Among these, the wavelength λ ₁ is variable, for example, from 1250 to 1650 nm, and the angle of the two KTP crystals 32a and 32b in the folded arrangement is controlled by a galvano scanner, so that the wavelength of λ ₂ matches the desired terahertz frequency and 1250 It can be varied at 1650 nm.
With this configuration, terahertz frequencies can be generated continuously or in pulses at intervals of 0.01 THz.
The present invention is not limited to this configuration as long as it can emit light 7 and 8 having two different wavelengths.

In FIG. 2, two-wavelength laser beams 7 and 8 of wavelengths λ ₁ and λ ₂ from a two-wavelength light source 32 are perpendicularly incident on the surface of the nonlinear optical material 34 via mirrors M4 and M5 and a lens L. In the present invention, the mirrors M4 and M5 and the lens L are not essential, and they can be omitted.

The nonlinear optical material 34 generates a terahertz wave 2 corresponding to the difference frequency from the light 7 and 8 having two wavelengths λ ₁ and λ ₂ by optical difference frequency generation (DFG).
Non-linear optical material 34 includes DAST crystal (4-N, N-dimethylamino-4-N′-methyl-stylbazolium tosylate), MNA (2-methyl-4-nitroaniline), LiNbO ₃ , KTP, LiIO, GaSe, GaP, GaN, ZnSe, ZnTe, or ZGP is preferable, and a DAST crystal is particularly preferable.

  The DAST crystal can be produced by a recrystallization method in which a saturated ethanol solution of DAST is cooled, and a crystal having a thickness of about 2 cm square and a thickness of 1 mm or more can be produced. This rectangular flat surface has a molecular polarization direction (a-axis). When an a-axis polarized excitation electric field is applied from the outside, a polarization wave is generated, and light having a frequency different from that of the excitation electric field is generated due to a nonlinear optical effect. Therefore, this DAST crystal can be used to generate a broadband terahertz band.

In FIG. 2, reference numeral 31 denotes a control recording device (for example, PC) which controls the two-wavelength light source 32 to record the measured intensity of the terahertz wave 3 and perform necessary analysis. Reference numeral 35 denotes a display device that displays measurement results and analysis results.
Further, the control recording device 31 may have the function of the frequency control device 24 in FIG. 1 and may control the generation frequency of the terahertz wave 2 by feeding back the transmittance.

  The terahertz wave generator 12 is not limited to the configuration shown in FIG. 2, and the terahertz wave 2 is continuously or discontinuously converted into a pulse wave or a continuous wave in a predetermined frequency band (for example, a frequency range of 1 to 6 THz). Other configurations may be used as long as an arbitrary frequency can be generated.

FIG. 3 is an overall flow diagram of the method for measuring the water content of a thin slice sample according to the present invention.
In this figure, the water content measurement method of the present invention includes a terahertz wave generation step S1, a terahertz wave division step S2, a reference light detection step S3, an incident light irradiation step S4, a transmitted light detection step S5, a calculation step S6, and a frequency. Each step of the control step S7 is included.
In the terahertz wave generation step S1, an arbitrary frequency is generated continuously or discontinuously using the terahertz wave 2 as a pulse wave or a continuous wave in a predetermined frequency band (for example, a frequency range of 1 to 6 THz).
In the terahertz wave dividing step S <b> 2, the terahertz wave 2 is divided into incident light 3 and reference light 4.
In the reference light detection step S3, the intensity of the reference light 3 is detected.
In the incident light irradiation step S4, the incident light 4 is condensed on a part of the thin slice sample 1 and irradiated.
In the transmitted light detection step S5, the transmitted light intensity of the terahertz wave 5 (transmitted light) transmitted through the thin slice sample 1 is detected.

In the calculation step S6, the transmittance and moisture content of the irradiated portion of the thin slice sample 1 are calculated from the incident light intensity and the transmitted light intensity.
In this calculation step S6, the transmittance T of the irradiated portion of the thin slice sample is obtained from the incident light intensity and the transmitted light intensity, and the absorption coefficient α of the sample is determined by the Lambert-Beer law using the thickness d of the thin slice sample. The volume fraction ν _w of water contained in the thin slice sample is obtained from the water absorption coefficient α _w .
The calculation contents in the calculation step S6 will be described later.

In the frequency control step S7, the transmission frequency is fed back to control the generation frequency of the terahertz wave.
In this frequency control step S7, the generation frequency of the terahertz wave is controlled so that the transmittance T is T = 0.22 to 0.55.

According to the apparatus and method of the present invention described above, the terahertz wave generator 12 continuously or discontinuously converts the terahertz wave 2 as a pulse wave or a continuous wave in a predetermined frequency band (for example, a frequency range of 1 to 6 THz). Any frequency can be generated.
Further, the incident light intensity I _in can be accurately measured by the light wave splitting element 14 and the reference light detector 16, and the transmitted light intensity I _out can be accurately measured by the irradiation optical system 18 and the transmitted light detector 20. be able to.
Furthermore, the calculation device 22 can calculate the transmittance T and the amount of moisture contained in the irradiated portion of the thin-section sample from the incident light intensity and the transmitted light intensity (volume fraction ν _{w of} moisture contained in the living tissue).

Further, since the frequency T is fed back by the frequency control device 24 to control the frequency at which the terahertz wave 2 is generated, the transmittance T falls within a predetermined optimum range (for example, T = 0.22 to 0.55). In addition, the generation frequency of the terahertz wave 2 can be controlled.
Hereinafter, the present invention will be described in detail.

1. Measurement Principle First, the measurement principle of the present invention will be described.
FIG. 4 is a measurement principle diagram of the present invention.
In the configuration shown in this figure, when light enters the sample 1, reflection, absorption, and transmission are repeated. In this case, the relationship between the incident intensity and the transmitted intensity with respect to the sample 1 is described by the equation (1) of Formula 1 according to the Lambert-Beer law.
Here, I _in is the incident intensity to the sample 1, I _out is the transmitted intensity from the sample 1, α is the absorption coefficient of the sample, and d is the thickness of the sample. “Light” is not limited to terahertz waves.

Next, assuming that the sample 1 is composed of moisture (indicated by the suffix w) and components other than moisture (indicated by the suffix nw), the absorption coefficient α of the sample 1 is determined by absorption by moisture and absorption by other than moisture. The absorption coefficient α of the sample can be expressed by Equation (2) in Equation 1.
Here, the absorption coefficient of moisture is α _w , and the absorption coefficient of components other than moisture is α _nw . Further, the volume ratio of the moisture in the sample, that is, the volume fraction of the contained water is ν _w, and the volume fraction of the components other than moisture is ν _nw .

The absorption coefficient α _w of moisture in the living tissue is an absorption coefficient at ν _w = 1 (100 [vol%]), and the absorption coefficient α _nw other than moisture is an absorption coefficient at ν _nw = 1 (100 [vol%]). It is. Further, the relationship between the volume fraction ν _w of the contained water and the volume fraction ν _nw of the components other than moisture is given by ν _w + ν _nw = 1 (2a).

Next, considering moisture and other components as components of living tissue, it can be considered that the absorption coefficient α _w due to moisture is sufficiently larger than the other absorption coefficient α _nw. 3) holds.

Moreover, it can be considered that the volume fraction ν _w of the moisture contained in the living tissue is equal to or larger than other volume fractions ν _nw , and Equation (4) of Formula 1 is established.
Therefore, if it is considered that the absorption coefficient α of the sample is mainly due to moisture, the absorption coefficient α of the sample can be approximated as shown in Equation (5).

If the moisture absorption coefficient α _w is known from the equation (5), the volume fraction ν _{w of the} contained moisture can be obtained from the transmittance T of the THz wave using the relationship between the equations (1) and (5). Here, as a measurement result, the volume fraction of contained water ν _w , that is, the ratio of the volume of moisture in the living tissue is obtained, and therefore the mass m [g / L] of moisture contained in the living tissue unit volume. Is expressed as m = D × ν _w (5a) using the moisture density D [g / L].
That is, in a simple measurement method of irradiating an ecological tissue with a THz wave by approximating the absorption coefficient α _w by the living tissue with the absorption coefficient α _w by water, the region irradiated with the THz wave is measured. Can be measured (measurement of the mass m of water contained per unit volume of living tissue).

2. Estimation of errors caused by approximation In the method of the present invention, it is assumed that the absorption of THz waves in living tissue is due to the contained water. The error caused by this assumption, that is, approximation by the equation (5) will be examined below.

From the measurement principle described above, the volume fraction of the water content to be measured is measured as an apparent volume fraction [nu _^'w. Apparent volume fraction [nu _^'w, the water absorption coefficient alpha _nw and non absorption coefficient alpha _w and moisture, number 2 with the volume fraction [nu _w true water contained in biological tissue formula ( 6).

Therefore, the volume fraction [nu _^'w measured from the equation (6) becomes Expression 2 (7).

Here, since the volume fraction ν _w of the true water is the first term of the equation (7), it can be seen that the component of the second term on the right side of the equation contributes as an error caused by the assumption. Next, in order to quantitatively analyze the error, the relative error E is used as the degree of deviation between the volume fraction ν _w of the true water content and the measured volume fraction ν ^′ _w of the apparent moisture. The relative error E can be expressed as the following equation (8).

From the equation (8), it can be seen that the error E caused by the approximation of the equation (5) depends on the absorption coefficient ratio α _nw / α _w and the volume fraction ratio of the moisture n and the other components. That is, it can be seen that the ratio of the absorption coefficient of moisture to components other than moisture is large, and the relative error is small in the measurement of the volume fraction of high moisture content.

FIG. 5 is a relationship diagram between the moisture volume fraction and the relative error. This figure shows the relative error caused by the assumption of the volume fraction ν _w of the true moisture content and the measured volume fraction ν ^′ _w of the apparent moisture, with the ratio of the absorption coefficient other than moisture and moisture as a parameter. It is calculated.
The hatched area in the figure indicates an area having a volume fraction of water in the living tissue of 0.5 to 0.9 and an absorption coefficient ratio of 0.1 to 0.01. That is, in the measurement under this condition, the error caused by the assumption of Equation (5) is 10% at the maximum, and the measurement can be performed at the minimum of 0.1% or less.

3. Determination of optimal transmittance The measurement of the amount of water by THz waves is based on the transmission measurement method as shown in equation (1). First, the optimum transmittance in the transmission measurement method is examined. The transmittance in the transmission measurement method is closely related to the measurement sensitivity. In order to estimate the sensitivity, it is only necessary to examine the minute change in transmittance with respect to the minute change rate Δα / α of the absorption coefficient α using the equation (1). This change is expressed by the following equation (9) using equation (1).

  Next, the sensitivity s is defined as the ratio between the minute change rate Δα / α of the absorption coefficient α and the transmittance change ΔT caused thereby. The sensitivity s is expressed by Equation (10) in Equation 3.

FIG. 6 is a relationship diagram between transmittance and sensitivity.
Equation (10) is a function that takes a maximum at T = 0.368. FIG. 6 shows the dependency of the sensitivity s on the transmittance. When the transmittance T = 0.368, the maximum value is obtained. At this time, the sensitivity s = 0.368, which is the maximum. Therefore, it is preferable to set the transmittance around 36.8% for the measurement of water content using the transmission measurement method.

Further, assuming that the condition for the transmittance T = 0.368 is determined only by the volume fraction due to the contained water, the relationship of Expression (11) in Equation 3 is established.
In general, the absorption coefficient α _w is a function of frequency and can be rewritten as α _w (f). That is, Expression (11) becomes Expression (12) of Expression 3.

In the measurement of the amount of water contained in the living tissue, the volume fraction ν _w of the contained water is measured as described above, so ν _w is an unknown number. In order to satisfy the equation (12) for the unknown ν _w , at least a method of changing the thickness d or a method of changing the absorption coefficient α _w (f) can be considered.

When a biological tissue is used as the sample 1, the method of changing the thickness d complicates the operation and cannot be said to be a simple method. On the other hand, focusing on the fact that the absorption coefficient is given as a function α _w (f) of the frequency, even if the thickness d is not changed, only the frequency to be measured is changed, and ν _w is unknown under the condition of unknown (12) It can be seen that

  Here, in the measurement accompanied by the variation of the transmittance T, it is necessary to give a certain tolerance to the transmittance. That is, it is assumed that the sensitivity s is allowed to some extent with respect to the condition of Expression (12). For example, assuming that the range in which the sensitivity is reduced by about 10% is an allowable range of transmittance, the range of the transmittance in which the sensitivity is reduced by 10% is T = 0.22 to 0.55 from FIG. In other words, the relationship between the absorption coefficient, the thickness, and the volume fraction is expressed by Equation (13) in Equation 3.

4). Determination of the thickness of the sample The thickness of the sample used for the measurement of the volume fraction ν _w of the water content will be discussed. First, in this measurement, the absorption coefficient of the THz wave band of water becomes important. FIG. 7 shows the water absorption coefficient calculated based on Non-Patent Document 1. In 1～6THz, in the range of absorption coefficient 1400 cm ^-1 from 200 cm ^-1, it can be seen that monotonically increases with increasing frequency.

8, when the volume fraction [nu _w of moisture content as a parameter indicating the relationship between the absorption coefficient becomes T = 0.368 alpha _w and thickness d. Here, the parameter is a volume fraction, and the calculation result with ν _w = 0.2 to ν _w = 0.9 is shown by a solid line in the figure. In addition, the shaded area in the figure is a thickness range that satisfies Equation (13) with respect to ν _w = 0.2 and ν _w = 0.9.

It can be seen from FIG. 8 that at a certain volume fraction, as the absorption coefficient increases, the thickness of the sample that satisfies the expression (13) decreases. From FIG. 7, the absorption coefficient of the THz wave varies from about 200 to 1400 cm ⁻¹ at ¹ to 6 THz, so that the equation (13) is obtained for a sample whose volume fraction is between 0.2 and 0.9. In order to measure while satisfying the above, the thickness range is in the range of 10 to 250 μm.

  On the other hand, in the medical / biological field, a thin slice sample prepared by a freezing microtome is widely used, and its thickness is about 2 μm to 200 μm. A region indicated by a double-pointed arrow in FIG. 8 is a typical thickness range that can be produced by a microtome.

  It almost coincides with the thickness range of the sample that can be measured by the absorption coefficient of the THz wave. Therefore, it is possible to measure the water content in a biological tissue section produced by a frozen microtome by using a THz wave. Therefore, the present invention has an advantage that it can be combined with a conventional sample preparation technique, and is considered to be applicable to a wider field.

The relationship between the thickness of the sample, the THz frequency, and the measurable volume fraction in the measurement of the water content in the thin slice sample will be discussed. The water absorption coefficient varies depending on the frequency f as shown in FIG. Therefore, the relationship between the absorption coefficient _αw and the thickness d can be the relationship between the frequency f and the thickness d as shown in FIG. From FIG. 9, d where T = 0.368 differs depending on the frequency band. For example, 1 to 3 THz corresponds to a sample thickness of about 50 to 100 μm. On the high frequency side, it corresponds to a relatively thin sample.

5. Determination of Optimal Frequency Next, FIG. 10 shows the relationship between the frequency f and the volume fraction ν _w of the contained water when the thickness d is a parameter. In the frequency range of 1 to 6 THz, the widest range of ν _w is obtained when d = 40 μm, and at this time, measurement of ν _w = 0.2 or more is possible.

In other words, if the thickness of the sample can be freely prepared, it can be performed over a wide range of ν _w if a sample having a thickness of about 40 μm is used. In the measurement of ν _w , first, the frequency f is measured while changing the transmittance while monitoring the transmittance to determine the frequency f so that the transmittance is near T = 0.368, and the moisture content is measured. It will be. Therefore, in this measurement method, a broadband and frequency variable THz wave light source is a key device.

6). Apparatus Configuration In the present invention, the moisture content of a sample is measured using a terahertz wave having a single frequency (for example, a frequency variation of 0.01 to 0.1 THz). The frequency must be changed according to Furthermore, considering practicality, it is necessary to be able to measure quickly. Therefore, as a THz wave light source used for measurement, a THz wave light source capable of changing the frequency quickly and having a monochromatic broadband frequency variable is suitable.
The inventors of the present invention have so far developed and filed a THz wave light source using a nonlinear optical effect.

Non-Patent Document 2 is a THz wave light source using stimulated polariton scattering of LiNbO ₃ crystal in a frequency band of 1 to ₃ THz, and Non-Patent Document 3 is a difference frequency generation THz wave light source using organic nonlinear crystal DAST. Yes, an ultra-wideband frequency variable light source at 2-60 THz has been realized. In terms of rapid frequency change, in the former, a ring resonator type terahertz wave parametric oscillator (ring TPO) is a light source that can be tuned in a few milliseconds, and in the latter, the angle of the KTP crystal is adjusted by galvano scanner control. As a result, a THz wave light source having a mechanism capable of instantaneously changing the two-wavelength excitation light is realized.

  FIG. 1 described above is a schematic diagram of a moisture content measurement system according to the present invention using a wide-band frequency variable THz wave generator. The THz wave 2 from the terahertz wave generator 12 is divided into two light waves 3 and 4, and one THz wave 3 is collected by the objective lens 18 and irradiated to the living tissue 1 and transmitted through the transmitted THz wave 5. Is detected. The other light wave is detected by the reference light detector 16 as the reference light 4. The transmittance T is calculated from the detected intensity through measurement / data processing and calculation. Here, as already described, since the sensitivity is good in the vicinity of the transmittance T = 0.368, the frequency control device 24 of the THz wave light source is important as a feedback mechanism for adjusting the transmittance. In addition, if a mechanism capable of two-dimensionally scanning a living tissue is provided, it is possible to measure the in-plane distribution of moisture content.

7). Relationship between THz wave light source and measurement concentration range Ring TPO has an oscillation THz frequency of 1 to 3 THz wave. From FIG. 9, in the frequency range of 1 to 3 THz, when a sample having a thickness of 40 μm is used, measurement can be performed while satisfying Expression (12) in the range of ν _w = 0.41 to 1.0. In addition, a THz wave source using a DAST crystal can measure ν _w = 0.19 to 1.0.

  As described above, the present invention has proposed a method for measuring the amount of water in a thin slice sample using THz waves. According to the present invention, it is assumed that the proportion of water in the living tissue is large and that the absorption coefficient of water in the THz wave frequency band is larger than the absorption by other components, and the absorption of THz waves in the living tissue. If water is due to moisture, the moisture content can be measured by a simple method using a permeation measurement method. Furthermore, the error caused by the assumption that the absorption of THz waves in the living tissue is due to moisture is determined by the ratio of the absorption coefficient of the THz wave band of water and other components and the ratio of their volume fractions. It became clear.

Next, regarding the measurement sensitivity, it was found that the sensitivity defined by the change in transmittance with respect to a minute change in volume fraction was maximized when the transmittance was 36.8%. In order to achieve this, it has been found that the transmittance needs to be adjusted.
In the adjustment of the transmittance, an appropriate transmittance can be obtained by changing the measurement frequency by paying attention to the fact that the absorption coefficient is a function of frequency and the frequency dependence of the absorption coefficient of water in the THz wave band is monotonically increasing. It was proposed that
In addition, when considering the absorption coefficient of 1 to 6 THz wave as the thickness of the sample, it became clear that the volume fraction of the high water content can be measured in the widest range at 40 μm.

  According to the above-described apparatus and method of the present invention, for example, by the two-wavelength light source 32 and the organic nonlinear optical material 34, the difference between the two different wavelengths of light 7 and 8 is generated by optical difference frequency generation (DFG). Therefore, the terahertz wave 2 having a desired frequency can be easily generated by making the two wavelengths 7 and 8 variable.

Further, the calculation device 22 can calculate the transmittance T and the amount of moisture contained in the irradiated portion of the thin slice sample (volume fraction ν _{w of the} moisture contained in the thin slice sample) from the incident light intensity and the transmitted light intensity.

  Further, since the frequency control device 24 feeds back the transmittance to control the frequency at which the terahertz wave 2 is generated, the transmittance T falls within a predetermined optimum range (for example, T = 0.22 to 0.55). The generation frequency of the terahertz wave can be controlled, and high sensitivity close to the maximum sensitivity can be ensured.

  In addition, the adjustment of the transmittance in concentration measurement by the transmission method is generally performed by changing the thickness of the sample. In the present invention, in order to obtain the simplicity and speed of measurement, the absorption coefficient is a function of frequency. And a method for adjusting the transmittance using the fact that the frequency dispersion of the absorption coefficient of water in the THz wave band monotonously changes. This makes it possible to perform simple and rapid measurement under measurement conditions that require labor for adjusting the thickness of the sample, such as a biological tissue.

  Further, as shown in FIG. 1, the device under test 1 is fixed on the two-dimensional stage 11, and the device under test 1 is scanned to change the portion irradiated with the THz wave, or the THz wave beam is scanned. It is possible to measure the spatial distribution of the moisture content of the DUT 1 by changing the irradiation position. In other words, substances can be differentiated by the difference in water content. In addition, if the measurement result of the moisture content is stored in a storage device in the computer at each time, the time variation of the moisture content can be monitored. In other words, it is possible to measure changes in moisture content over time.

  In addition, this invention is not limited to the Example and embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a whole block diagram of the moisture content measuring apparatus of the thin section sample by this invention. It is a figure which shows one Embodiment of the terahertz wave generator 12 which comprises this invention. It is a whole flowchart of the moisture content measuring method of the thin section sample by this invention. It is a measurement principle figure of this invention. It is a related figure of a moisture volume fraction and a relative error. It is a relationship diagram of transmittance and sensitivity. The water absorption coefficient α _w (f) is calculated based on Non-Patent Document 1. It is a figure which shows the relationship between the absorption coefficient (alpha) _{w used as} T = 0.368, and thickness d when the volume fraction (nu) _w of a water content is made into a parameter. It is a relationship figure of the frequency f and the thickness d of a sample. It is a figure which shows the relationship between the frequency f when thickness d is made into a parameter, and the volume fraction (nu) _w of a containing water. It is a schematic diagram of the apparatus of patent document 1. FIG.

Explanation of symbols

1 Thin slice sample (object to be measured), 2 terahertz wave, 3 incident light,
4 reference light, 5 terahertz wave (transmitted light), 7, 8 laser light,
10 moisture content measuring device, 11 two-dimensional stage,
12 terahertz wave generator,
14 light wave splitting element (half mirror), 16 reference light detector (Si bolometer),
18 irradiation optical system, 20 transmitted light detector (Si bolometer),
22 arithmetic units, 24 frequency control units,
31 Control recording device (PC), 32 2 wavelength light source,
32a, 32b Bulk KTP crystal,
34 Nonlinear optical material (DAST crystal),
35 display devices

Claims (5)

A terahertz wave generator that generates an arbitrary frequency continuously or discontinuously as a pulse wave or a continuous wave in a predetermined frequency band;
A light wave dividing element for dividing the terahertz wave into incident light and reference light;
A reference light detector for detecting the intensity of the reference light;
An irradiation optical system for condensing and irradiating a part of the thin-section sample with the incident light;
A transmitted light detector for detecting the transmitted light intensity of the terahertz wave transmitted through the thin slice sample;
An arithmetic device for calculating the transmittance and moisture content of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity;
A device for measuring the moisture content of a thin-section sample, comprising: a frequency control device that feeds back the transmittance to control the frequency of generation of terahertz waves.   The apparatus for measuring a moisture content in a thin-section sample according to claim 1, wherein the frequency control device controls the generation frequency of the terahertz wave so that the transmittance falls within a predetermined optimum range. A terahertz wave generation step of generating an arbitrary frequency continuously or discontinuously as a pulse wave or a continuous wave in a predetermined frequency band; and
A terahertz wave dividing step for dividing the terahertz wave into incident light and reference light;
A reference light detection step for detecting the intensity of the reference light;
Incident light irradiation step of collecting and irradiating the incident light on a part of the thin slice sample;
A transmitted light detection step of detecting the transmitted light intensity of the terahertz wave transmitted through the thin slice sample;
A calculation step of calculating the transmittance and moisture content of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity,
And a frequency control step of controlling the generation frequency of the terahertz wave by feeding back the transmittance, and measuring the moisture content of the thin-section sample. In the calculation step,
Obtain the transmittance T of the irradiated portion of the thin slice sample from the incident light intensity and the transmitted light intensity,
Using the thickness d of the thin-section sample, the absorption coefficient α of the sample is obtained by the Lambert-Beer law,
The method for measuring the moisture content of a thin slice sample according to claim 3, wherein the volume fraction ν _w of the moisture content of the thin slice sample is obtained from the moisture absorption coefficient α _w .   4. The moisture content of the thin-section sample according to claim 3, wherein in the frequency control step, the frequency at which the terahertz wave is generated is controlled so that the transmittance T is T = 0.22 to 0.55. Quantity measuring method.

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