JP2013167477A - Method and device for measuring refractive index - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for measuring a refractive index capable of highly accurately measuring the refractive index of a colloid liquid.SOLUTION: The lower plane of a dielectric transparent flat plate 30 which has a higher refractive index than a colloid liquid 33 and whose upper plane is parallel to the lower plane thereof is brought into contact with the surface of the colloid liquid 33, the lower plane of a Dove prism 32 whose upper plane is parallel to the lower plane thereof is brought into contact with the upper plane of the dielectric transparent flat plate 30 through a matching liquid 38, P-wave light having a narrow spectral width which is suitable for refractive index measurement is made incident on one slope face of the Dove prism 32, an incident angle θis obtained which is minimized in intensity of non-scattered reflection light from the interface between the lower plane of the dielectric transparent flat plate 30 and the surface of the colloid liquid 33, and based on the incident angle θ, a refractive index nof the dielectric transparent flat plate 30, a refractive index nof the Dove prism 32, and a refractive index nof gas in contact with the Dove prism, a refractive index nof the colloid liquid 33 is obtained.

Description

  The present invention relates to a refractive index measuring method and a refractive index measuring apparatus for measuring the refractive index of a colloidal liquid.

  Since the colloidal liquid scatters most of the incident light, the precise refractive index of the colloidal liquid is hardly known. Some of the commercially available refractive index measuring devices are described as being able to measure the refractive index of milk, which is a kind of colloidal liquid, but have a measurement accuracy of about one or two digits after the decimal point.

  As an example of measuring the refractive index of milk, a measurement system combining a Michelson interferometer and a super luminescent diode (SLD) is known (see Non-Patent Document 1). In this measurement system, the outgoing light of the SLD is split by a beam splitter, one light is reflected by a reference light mirror to become reference light, and the other light is incident on the milk surface contained in the container. The light incident on the milk liquid surface is reflected by the milk liquid surface or by a mirror disposed on the bottom surface of the container. When the position of the reference light mirror is adjusted, the reference light interferes with the light reflected by the milk liquid surface, and when the reference light mirror is further moved, the reference light interferes with the light reflected by the mirror at the bottom of the container. If the milk thickness is measured in advance, the refractive index of the milk can be obtained by measuring the scanning distance of the reference light mirror.

Tomohisa Shiraishi, Atsushi Ishida, Toshihiko Imura, Yoshihiro Saida, Yoshinori Nakajima, “Study on Concentration Evaluation of White Suspension”, [online], Saitama Industrial Technology Center Research Report Vol. 6 (2008), [2011 May 30 search], Internet <URL: http: //www.saitec.pref.saitama.lg.jp/research/h19/soushutsu/sou-r/312a.pdf>

  However, since the measurement system measures SLD light propagating in the colloidal liquid, the measurement accuracy greatly depends on the scattering / absorption characteristics of the colloidal liquid. Moreover, although it is necessary to measure the volume, density, and weight of milk and to obtain | require the liquid thickness of milk with high precision, it is difficult to obtain | require the volume change by surface tension precisely. If the liquid thickness is increased, the influence of surface tension can be reduced, but the reference light mirror must be moved using a mechanical movement mechanism, and it is difficult to ensure measurement accuracy. Further, since measurement is performed by exposing milk to air, slight undulations on the milk surface due to air movement reduce measurement accuracy. Further, in measurement by low coherent optical interference, a light source, a vibration isolator, an interferometer, and the like are indispensable, resulting in high costs. Furthermore, there is a problem that a large amount of sample is required for measurement.

  The present invention has been made in view of the above problems, and an object thereof is to provide a refractive index measuring method and a refractive index measuring apparatus capable of measuring the refractive index of a colloidal liquid with high accuracy. It is to provide.

(1) The present invention provides a refractive index measurement method for measuring the refractive index of the colloidal liquid 33.
The lower surface of the dielectric transparent flat plate 30 having a higher refractive index than that of the colloid liquid 33 and parallel to the upper and lower surfaces is brought into contact with the surface of the colloid liquid 33, and the upper surfaces of the dielectric transparent flat plate 30 are parallel to each other. It has an upper plane and a lower plane, and two flat slopes that are not parallel to these planes. The intersection angle (inner angle) between the upper plane and the two slopes is 180 ° -ξ, and the lower plane and the two slopes. And the inner plane ξ is larger than 0 ° and smaller than 90 °, the lower surface of the Dove prism is brought into contact with the matching liquid 38, and
Furthermore, light in which the electric field of the light oscillates in a direction orthogonal to the incident plane including the normal line of the Dove prism and the traveling direction of the incident light is defined as P-wave light, and P-wave light 50 having a narrow spectral width suitable for refractive index measurement is defined. Incident on one slope 35 of the dove prism 32;
An incident angle θ _{1 at} which the intensity of non-scattered reflected light 53 from the interface between the lower flat surface of the dielectric transparent flat plate 30 and the surface of the colloidal liquid 33 is minimized is obtained.
And the incident angle theta _1, wherein a refractive index n _c of the dielectric transparent plate 30, the refractive index and n _p of the Dove prism 32, on the basis of the refractive index n _a of the gas in contact with the Dove prism 32 , and obtains the refractive index n _s of the colloidal liquid 33.

  According to the present invention, the refractive index of the colloidal liquid 33 can be measured with high accuracy.

(2) In the present invention,
When P-wave light 50 having a narrow spectral width suitable for the refractive index measurement is incident on the upper plane of the Dove prism 32, and the rotary stage 12 is adjusted so that the intensity of the reflected light 51 from the upper plane of the Dove prism 32 is minimized. Record the angle θ _a of the rotary stage 12 of
A P-wave light 52 having a narrow spectral width suitable for refractive index measurement is incident on one inclined surface 35 of the Dove prism 32, and the intensity of the non-scattered reflected light 53 from the interface between the dielectric transparent flat plate 30 and the colloidal liquid 33 is minimized. The rotary stage 12 is adjusted so that the angle θ _b of the rotary stage 12 at that time is recorded,
The difference theta _a - [theta] _b of the two angles, using a Brewster angle theta _p refractive index was calculated using the n _a of the gas in contact with the refractive index n _p and Dove prism 32 Dove prism 32, The incident angle θ ₁ on _one inclined surface 35 of the dove prism 32 may be obtained.

(3) In the present invention,
A uniaxial crystal is used as the dielectric transparent flat plate 30, and the direction of the optical axis (the direction in which the normal light beam traveling in the crystal and the traveling direction of the extraordinary light coincide) is incident on the inclined surface 35 of the Dove prism. You may arrange | position so that it may orthogonally cross with the vibration direction of the electric field component of P wave light with a narrow spectral width suitable for a rate measurement.

  (4) In the present invention,

It may be obtained refractive index n _s of the colloidal liquid 33 based on.

(5) The present invention relates to a refractive index measurement method for measuring the refractive index of the colloidal liquid 33.
The surface of the colloidal liquid 33 is brought into contact with the lower plane of the Dove prism 34 having a higher refractive index than that of the colloidal liquid 33 and the upper and lower planes are parallel, and the P-wave light 50 having a narrow spectral width suitable for refractive index measurement is obtained. An incident angle θ ₁ is obtained by making it incident on one inclined surface 35 of the Dove prism 34 and minimizing the intensity of the non-scattered reflected light 53 from the interface between the lower plane of the Dove prism 34 and the surface of the colloidal liquid 33,
Wherein the incident angle theta _1, the refractive index and n _p of the Dove prism 34, on the basis of the refractive index n _a of the gas in contact with the Dove prism 34, to obtain the refractive index n _s of the colloidal liquid 33 It is characterized by.

  According to the present invention, the refractive index of the colloidal liquid 33 can be measured with high accuracy.

(6) In the present invention,
When the P-wave light 50 having a narrow spectral width suitable for the refractive index measurement is incident on the upper plane of the Dove prism 34, and the intensity of the reflected light 51 from the upper plane of the Dove prism 34 is minimized by adjusting the rotary stage 12. Record the angle θ _a of the rotary stage 12 of
A P-wave light 52 having a narrow spectral width suitable for refractive index measurement is incident on one inclined surface 35 of the Dove prism 34, and the intensity of the non-scattered reflected light 53 from the interface between the Dove prism 34 and the colloid liquid 33 is minimized. the rotary stage 12 is adjusted so as to record the angle theta _b of the rotary stage 12 at that time,
The difference theta _a - [theta] _b of the two angles, using a Brewster angle theta _p refractive index was calculated using the n _a of the gas in contact with the refractive index n _p and Dove prism 34 of Dove prism 34, The incident angle θ ₁ on the inclined surface 35 of the dove prism 32 may be obtained.

(7) In the present invention,
A uniaxial crystal may be used as the Dove prism 34 so that the direction of the optical axis is orthogonal to the vibration direction of the electric field component of the incident light.

  (8) In the present invention,

It may be obtained refractive index n _s of the colloidal liquid 33 based on.

  (9) In the present invention,

The incident angle θ ₁ may be obtained based on

(10) The present invention provides a refractive index measuring apparatus for measuring the refractive index of the colloidal liquid 33.
A dielectric transparent flat plate 30 that is in contact with the surface of the colloidal liquid 33 and has a higher refractive index than the colloidal liquid 33 and whose upper and lower planes are parallel;
The upper surface of the dielectric transparent flat plate 30 is brought into contact with the upper surface of the dielectric transparent plate 30 via the matching liquid 38 and has an upper surface and a lower surface that are parallel to each other, and two flat slopes that are not parallel to these planes. The intersection angle (inner angle) of both is 180 ° -ξ, the inner angles of the lower plane and the two slopes are both ξ, and the inner angle ξ is larger than 0 ° and smaller than 90 °. 32,
A light irradiator that makes a P-wave light having a narrow spectral width suitable for refractive index measurement incident on one inclined surface 35 of the Dove prism 32;
A light detection unit for detecting the intensity of non-scattered reflected light from the interface between the lower flat surface of the dielectric transparent flat plate 30 and the surface of the colloidal liquid 33;
The incident angle theta ₁ which the intensity of the reflected light of the unscattered is minimized from the interface between the dielectric bottom plane of the transparent plate 30 and the surface of the colloidal liquid 33, the refractive index n _c of the dielectric transparent plate 30 , the refractive index and n _p of the Dove prism 32, on the basis of the refractive index n _a of the gas in contact with the Dove prism 32, a calculation device for performing arithmetic processing for calculating the refractive index n _s of the colloidal liquid 33 40.

  According to the present invention, the refractive index of the colloidal liquid 33 can be measured with high accuracy.

(11) The present invention provides a refractive index measuring apparatus for measuring the refractive index of the colloidal liquid 33.
The upper surface is in contact with the surface of the colloid liquid 33, has a higher refractive index than the colloid liquid 33, and has two upper and lower planes parallel to each other, and two flat slopes non-parallel to these planes. The intersection angle (inner angle) of the two slopes is 180 ° -ξ, the inner angle of the lower plane and the two slopes is both ξ, and the inner angle ξ is greater than 0 ° and less than 90 °. Dove prism 34,
A light irradiating unit that makes a P-wave light having a narrow spectral width suitable for refractive index measurement incident on the inclined surface 35 of the Dove prism 34;
A light detector for detecting the intensity of non-scattered reflected light from the interface between the lower plane of the Dove prism 34 and the surface of the colloidal liquid 33;
The incident angle θ _{1 at} which the intensity of non-scattered reflected light from the interface between the lower plane of the Dove prism 34 and the surface of the colloidal liquid 33 is minimized, the refractive index n _p of the Dove prism 34, and the Dove prism 34 based on the refractive index n _a of the gas in contact with, characterized in that it comprises a processing unit 40 for performing arithmetic processing for calculating the refractive index n _s of the colloidal liquid 33.

  According to the present invention, the refractive index of the colloidal liquid 33 can be measured with high accuracy.

The figure which shows an example of a structure of the refractive index measuring apparatus in the 1st method of this embodiment. The figure for demonstrating arrangement | positioning of the dielectric transparent flat plate which consists of a uniaxial crystal. The figure which shows an example of a structure of the refractive index measuring apparatus in the 2nd method of this embodiment. The figure which shows an example of the mechanism which crimps | bonds a small cell and a dove prism. The figure which shows the other example of a structure of a light irradiation part. The figure for demonstrating the procedure from the preparation of a sample to the measurement of a refractive index in a 1st method. The figure for demonstrating the measurement of the incident angle of the P wave light of the Dove prism slope in the 1st method. The figure for demonstrating the measurement of the incident angle of the P wave light of the Dove prism slope in the 2nd method The figure which shows the external appearance of a dove prism. The figure which shows the external appearance of a dielectric transparent flat plate. The figure which shows the relationship between the optical detection signal in purified water, and incident angle (theta) ₁ . The figure which shows the relationship between the optical detection signal in medium fat milk, and incident angle (theta) ₁ . The measurement result which shows the relationship between the refractive index of milk and milk fat percentage.

  Hereinafter, this embodiment will be described. In addition, this embodiment demonstrated below does not unduly limit the content of this invention described in the claim. In addition, all the configurations described in the present embodiment are not necessarily essential configuration requirements of the present invention.

1. Measurement Principle and Configuration A measurement principle employed by the refractive index measurement method and the refractive index measurement apparatus according to the present embodiment will be described.

1-1. First Method First, a first method for measuring the refractive index of the colloidal liquid 33 will be described. FIG. 1 is a diagram illustrating an example of the configuration of the refractive index measurement apparatus according to the present embodiment.

  The refractive index measuring apparatus shown in FIG. 1 includes a rotary stage 12 having a light source 10 disposed at the center, a photodetector 20 including a photoelectric sensor (photodetector), and an arithmetic unit 40. As the light source 10, a semiconductor laser, an Ar ion laser that oscillates multiple wavelengths, a He-Ne laser, a dye laser that oscillates continuously at a wide wavelength band position, a titanium sapphire laser, and the like are suitable. Further, incoherent light emitted from a light emitting diode, SLD, Xe lamp, halogen lamp, or the like can be used in place of laser light by selecting a narrow band spectrum by a wavelength filter or a spectroscope.

In the first method of the present embodiment, on the small cell 36 (container) in which the colloidal liquid 33 is stored, the dielectric transparent flat plate 30 having a high refractive index, the upper plane having an internal angle of ξ and 180 ° −ξ, A dove prism 32 having a parallel lower plane is placed, and a P-wave laser beam having a narrow spectral width suitable for the refractive index measurement from the light source 10 (light irradiation unit) is incident on one inclined surface 35 of the dove prism 32. Incident angle θ that irradiates the interface between dielectric transparent flat plate 30 and colloidal liquid 33 and minimizes the intensity of non-scattered reflected light from the interface (reflected light emitted from a slope facing the incident surface of the Dove prism). ₁ is measured.

  The Dove prism is composed of parallel upper and lower planes facing each other, and two flat slopes non-parallel to these planes. The intersection angle (inner angle) between the upper plane and the two slopes is 180 ° −ξ, and the inner angle between the lower plane and the two slopes is both ξ. The inner angle ξ is determined in accordance with the refractive indexes of the Dove prism 32 and the dielectric transparent flat plate 30 within a range larger than 0 ° and smaller than 90 °.

  The lower plane of the dielectric transparent flat plate 30 is in contact with the surface of the colloidal liquid 33, and the upper plane of the dielectric transparent flat plate 30 is in contact with the lower surface of the Dove prism 32 through the matching liquid 38. The upper and lower planes of the dielectric transparent flat plate 30 are optically polished so as to be parallel, and the refractive index thereof is larger than the refractive index of the colloidal liquid 33. Since most of the reflected light from the interface between the dielectric transparent flat plate 30 and the colloidal liquid 33 is scattered, the intensity of the non-scattered reflected light necessary for measuring the refractive index is insufficient. In order to reduce this phenomenon, it is desirable to make the refractive index of the dielectric transparent flat plate 30 much larger than the refractive index of the colloidal liquid 33. If the refractive index of the dielectric transparent flat plate 30 is made sufficiently large, the refractive index can be measured regardless of the magnitude of the refractive index of the colloidal liquid 33.

An optical material suitable for the dielectric transparent flat plate 30 is a trigonal system, point group 3 m LiNbO ₃ crystal and LiTaO ₃ crystal in the visible light to infrared light region. The LiNbO ₃ crystal has a large refractive index of normal refractive index n _o = 2.2868 and extraordinary refractive index n _e = 2.203 at the He—Ne laser light wavelength (λ = 632.8 nm), and is large, transparent and workable. It has the feature that excellent single crystals can be obtained at low cost. Blue light and ultraviolet light have a drawback of being easily damaged by optical damage, but if MgO: LiNbO ₃ crystal doped with several percent of magnesium oxide MgO is used, the damage can be greatly reduced. The LiTaO ₃ crystal has a large refractive index of n _o = 2.1774 and n _e = 2.1818 at λ = 632.8 nm, and is characterized in that a large single crystal having excellent transparency and workability can be obtained at low cost. The optical damage is smaller than that of LiNbO ₃ crystal. In addition, tetragonal, point group 422 TeO ₂ crystals and tetragonal, point group 4 / m PbMoO ₄ crystals are suitable for the dielectric transparent flat plate 30. TeO ₂ crystal is in _{λ = 632.8nm, n o = 2.260} , having a large refractive index of _{n e} = 2.142, PbMoO ₄ crystals in _{λ = 632.8nm, n o = 2.262} , significant that _{n e} = 2.386 Has a refractive index. In both cases, large and high-quality crystals have been put into practical use. Furthermore, in the infrared region, equiaxed crystals and crystals of GaAs, GaP, InP, etc. having a point group of 43 m are also suitable.

Since the LiNbO ₃ crystal, LiNbO ₃ crystal, TeO ₂ crystal, and PbMoO ₄ crystal are uniaxial crystals, the light incident on the crystal is separated into an ordinary ray and an extraordinary ray by birefringence. In order to prevent this phenomenon from appearing, as shown in FIG. 2, the direction of the optical axis of the uniaxial crystal (the direction in which the normal ray propagating in the crystal and the traveling direction of the extraordinary ray coincide) is the electric field of the incident light of the P wave. It arrange | positions so that it may orthogonally cross with the vibration direction of a component. On the other hand, since GaAs crystal, GaP crystal, and InP crystal are equiaxed crystals, they can be arranged freely regardless of the vibration direction of P-wave light.

Hereinafter, the measurement principle for obtaining the refractive index of the colloidal liquid 33 based on the incident angle θ ₁ in the first method will be described.

The incident angles at which the intensity of non-scattered reflected light from the interface between the dielectric transparent flat plate 30 and the colloid liquid 33 is minimized, with the refractive indexes of the dielectric transparent flat plate 30 and the colloid liquid 33 being n _c and n _s , respectively. When the theta ₄ (incidence angle of the P wave light incident on the interface between the dielectric transparent flat plate 30 and the colloid solution 33), the refractive index n _s of the colloidal liquid 33, from the law of Brewster, tables as follows Is done.

  On the incident surface of the Dove prism 32, the following Snell's law is established.

Here, n _a is the refractive index of air (gas) in contact with the entrance surface of the Dove prism 32, n _p is the refractive index of the dove prism 32. Θ ₁ is a spectrum suitable for measuring the refractive index incident on the incident surface of the Dove prism 32 when the intensity of the non-scattered reflected light from the interface between the dielectric transparent flat plate 30 and the colloid liquid 33 is minimized. It is an incident angle of narrow P-wave light, and θ ₂ is a refraction angle. A matching liquid 38 having a refractive index close to the refractive index of the Dove prism 32 exists between the Dove prism 32 and the dielectric transparent flat plate 30. If the upper plane and the lower plane of the matching liquid 38 are parallel, the refractive index of this layer does not affect the refractive index of the colloid liquid 33, and therefore the description of the matching liquid 38 is omitted in the following description.

  At the interface between the dove prism 32 and the dielectric transparent flat plate 30, the following Snell's law is established.

Here, θ ₃ is an incident angle of the P wave light incident on the interface between the Dove prism 32 and the dielectric transparent flat plate 30.

In FIG. 1, the internal angle formed by the incident surface and the lower plane of the Dove prism 32 is ξ, so the following relational expression is established between θ ₂ and θ ₃ .

Equation (1) to equation (4), the refractive index _{n s} of the colloidal liquid 33 may be obtained by the following equation.

That is, by changing the incident angle of the P-wave light having a narrow spectral width suitable for the refractive index measurement incident on one inclined surface 35 of the Dove prism 32, the interface between the dielectric transparent flat plate 30 and the colloid liquid 33 (the colloid liquid 33 If the incident angle θ _{1 at} which the intensity of the non-scattered reflected light from the surface) is minimized, the refractive index n _s of the colloidal liquid 33 can be obtained from the equation (5).

  The photodetector 20 in FIG. 1 photoelectrically converts the non-scattered reflected light reflected from the surface of the colloid liquid 33 and outputs the light intensity information (light detection signal) to the arithmetic unit 40.

  Since scattered light is generated at the reflection point G (intersection of incident light and reflected light) on the surface of the colloidal liquid 33, it is preferable to use the photodetector 20 having a small light receiving area and high sensitivity. Here, the scattered light is uniformly scattered in all directions, the non-scattered light is specularly reflected without spreading, the light receiving area of the photodetector 20 is equal to the cross-sectional area of the incident light, the incident light amount is large, and the photodetector Assuming that the thermal noise of 20 is ignored, the signal-to-noise ratio (SNR) of the detection signal is expressed by the following equation.

Here, α is the non-scattered light amount, β is the total scattered light amount, d is the distance from the reflection point G on the surface of the colloidal liquid 33 to the photodetector 20, and S is the light receiving area of the photodetector 20. It is. For example, assuming that S = 0.5 mm ² and d = 150 mm, even if α / β = 0.01, the SN ratio (SNR) of the detection signal is

Thus, the intensity of non-scattered light can be measured with a sufficient S / N ratio.

  As shown in FIG. 1, when the incident angle of the P-wave light incident on the incident surface of the Dove prism 32 changes, the reflection angle of the non-scattered reflected light emitted from the exit side slope of the Dove prism 32 also changes. Therefore, in the present embodiment, the incident angle of the P wave light is changed by the rotary stage 12, and the photodetector 20 is rotated by a rotating mechanism (not shown) according to the change of the incident angle, whereby the Dove prism 32 is changed. Non-scattered reflected light (non-scattered reflected light reflected from the surface of the colloidal liquid 33) emitted from the exit-side slope is configured to enter the photodetector 20.

The arithmetic device 40 shown in FIG. 1 includes an arithmetic processing unit 42 and a storage unit 44. Arithmetic processing unit 42, the incident angle theta ₁ which the intensity of the reflected light of the non-scattering from the surface of the colloidal liquid 33 is minimized, and the refractive index n _c of the dielectric transparent plate 30, the refractive index n _p of the Dove prism 32 If, on the basis of the refractive index n _a of the gas, it performs arithmetic processing for calculating the refractive index n _s of the colloidal liquid 33 by equation (5). Further, the arithmetic processing unit 42 may obtain the incident angle θ ₁ based on the intensity information of the reflected light detected every time the incident angle of the P wave light is changed.

  The storage unit 44 has a function of temporarily storing various data. For example, the light intensity information output from the photodetector 20 may be stored in association with the incident angle of the P wave light.

1-2. Second Method Next, a second method for measuring the refractive index of the colloidal liquid 33 will be described with reference to FIG.

In the second method of this embodiment, instead of placing the high refractive index dielectric transparent flat plate 30 on the small cell 36 in which the colloid liquid 33 is stored, the high refractive index Dove prism is placed on the small cell 36. 34 (a dove prism having an inner angle of ξ and 180 ° −ξ and whose upper and lower planes are parallel). The upper and lower planes of the Dove prism 34 are optically polished so that they are parallel, and the lower plane of the Dove prism 34 is in contact with the surface of the colloidal liquid 33. The only difference between the Dove prism 32 and the Dove prism 34 is the refractive index. The rest of the configuration excluding the dielectric transparent flat plate is the same as the configuration in the first method shown in FIG. Then, a P-wave laser beam having a narrow spectral width suitable for the refractive index measurement from the light source 10 (light irradiation unit) is incident on the inclined surface 35 of the Dove prism 34, and enters the interface between the Dove prism 34 and the colloid liquid 33. Irradiation is performed, and the incident angle θ _{1 at} which the intensity of the non-scattered reflected light from the interface (reflected light emitted from the outgoing side slope facing the slope 35) is minimized is measured.

The refractive index of the dove prism 34 is larger than the refractive index of the colloidal liquid 33. Since most of the reflected light from the interface between the Dove prism 34 and the colloid liquid 33 is scattered, the intensity of the non-scattered light necessary for measuring the refractive index is insufficient. In order to reduce this phenomenon, it is desirable to make the refractive index of the Dove prism 34 much larger than the refractive index of the colloidal liquid 33. If the refractive index of the dove prism 34 is sufficiently increased, the refractive index can be measured regardless of the refractive index of the colloidal liquid 33. As the optical material of the dove prism 34, a dielectric material similar to that of the dielectric transparent flat plate 30 in FIG. 1 may be used. When a uniaxial crystal such as a LiNbO ₃ crystal, a LiNbO ₃ crystal, a TeO ₂ crystal, or a PbMoO ₄ crystal is used as the optical material of the Dove prism 34, the direction in which the electric field of the incident light of the P wave vibrates and the crystal The dove prism 34 is arranged so that the optical axes thereof are orthogonal to each other.

Hereinafter, the measurement principle for obtaining the refractive index of the colloidal liquid 33 based on the incident angle θ ₁ in the second method will be described.

The refractive angles of the Dove prism 34 and the colloid liquid 33 are n _p and n _s , respectively, and the incident angle at which the intensity of the non-scattered reflected light from the interface between the Dove prism 34 and the colloid liquid 33 is minimized (the Dove prism 34). If the incident angle of the P-wave light incident on the interface between the liquid and the colloid liquid 33 is θ ₅ , the refractive index n _s of the colloid liquid 33 is expressed by the following equation from Brewster's law.

  On the incident surface of the dove prism 34, the following Snell's law is established.

In FIG. 3, since the inner angle formed by the slope 35 and the lower plane of the Dove prism 34 is ξ, the following relational expression is established between θ ₂ and θ ₅ .

Equation (8) to equation (10), the refractive index _{n s} of the colloidal liquid 33 may be obtained by the following equation.

That is, the incident angle of the P-wave light having a narrow spectral width suitable for the refractive index measurement incident on the inclined surface 35 of the Dove prism 34 is changed to change from the interface between the Dove prism 34 and the colloid liquid 33 (the surface of the colloid liquid 33). If the incident angle θ _{1 at} which the intensity of the non-scattered reflected light is minimized is measured, the refractive index n _s of the colloidal liquid 33 can be obtained from the equation (11).

  FIG. 4 is a view showing an example of a mechanism for pressure-bonding the small cell 36 storing the colloidal liquid 33 and the dove prism 34 placed thereon. As shown in FIG. 4, the small cell 36 storing the colloidal liquid 33 and the dove prism 34 are arranged between the pedestal and the block, and the small cell 36 and the dove prism 34 are integrated using screws and springs. Retained. By this mechanism, the small cell 36 and the dove prism 34 are pressure-bonded so that the lower surface of the dove prism 34 and the surface of the colloidal liquid 33 are in complete contact. In the configuration of FIG. 1 as well, the same mechanism is used to hold the small cell 36, the dielectric transparent flat plate 30 and the dove prism 32 as one body, and the small cell 36 and the dielectric transparent flat plate 30 are pressure-bonded to form a dielectric transparent flat plate. The lower surface of 30 and the surface of the colloidal liquid 33 are brought into full contact.

  FIG. 5 is a diagram illustrating another example of the configuration of the light irradiation unit. In the example shown in FIGS. 1 and 3, the case where the light source 10 is arranged at the center of the rotary stage 12 to configure the light irradiation unit has been described. However, as shown in FIG. 5, the optical fiber connected to the light source 10. 14, an optical system 16 that converts light emitted from the optical fiber 14 into parallel light, and a polarizing plate 18 that transmits P-wave light may be disposed on the rotary stage 12 to constitute a light irradiation unit. Here, the exit of the optical fiber 14 is fixed to the center O (rotary axis) of the rotary stage 12. In addition, at least a part between the exit port and the exit port of the optical fiber 14 is in an unfixed state so that the rotational movement force of the rotary stage 12 is not applied to the entrance / exit port of the optical fiber 14.

  Further, in place of the configuration in which the light source 10 or the optical fiber 14 is disposed on the rotary stage 12, a mechanism for pressure-bonding the small cell 36 storing the colloid liquid 33 and the dove prism 34 (or the small cell 36 storing the colloid liquid 33, A mechanism for pressing the dielectric transparent flat plate 30 and the dove prism 34) may be arranged on the rotary stage 12. In this case, the colloid liquid 33 is arranged so that the surface of the colloid liquid 33 is located on a straight line passing through the center O of the rotary stage 12. In this way, while the light source 10 is fixed, the colloidal liquid 33 can be horizontally rotated to change the incident angle of the P wave light, and the measurement system can be easily constructed.

2. Measurement Method Taking the first method of the present embodiment as an example, the procedure from sample preparation to refractive index measurement will be described.

  First, as shown in FIGS. 6A and 6B, the colloidal liquid 33 is put into the small cell 36 just before overflowing from the small cell 36. Next, as shown in FIG. 6C, the lower plane of the dielectric transparent flat plate 30 is brought into close contact with the small cell 36, and the colloidal liquid 33 overflows from the small cell 36. In order to avoid multiple reflection interference on the dielectric transparent flat plate 30, the thickness of the dielectric transparent flat plate 30 is sufficiently thicker than the beam diameter of incident light. Next, as shown in FIG. 6D, the matching liquid 38 is applied to the upper plane of the dielectric transparent flat plate 30. Next, as shown in FIG. 6E, the lower plane of the dove prism 32 is brought into close contact with the upper plane of the dielectric transparent flat plate 30, and is crimped using the mechanism shown in FIG. 4 (not shown).

In this state, as shown in FIG. 6E, the P-wave laser light 50 is incident on the upper plane of the Dove prism 32 from the semiconductor laser 10 installed at the center of the rotary stage 12, and the intensity of the reflected light 51 is minimized. and so that, by adjusting the rotary stage 12, to record the angle theta _a at that time. Next, P-wave laser light 52 is incident on the inclined surface 35 of the dove prism 32, and the rotary stage 12 is set so that the intensity of the non-scattered reflected light 53 from the interface between the dielectric transparent flat plate 30 and the colloidal liquid 33 is minimized. And record the angle θ _b at that time.

From these two angle measurements, the incident angle θ ₁ of the laser beam 52 incident on the inclined surface 35 of the Dove prism 32 can be obtained. The process of deriving the incident angle θ ₁ will be described with reference to FIG. 7 in which a part of FIG. A point O in FIG. 7 is the rotation center of the rotary stage 12 and coincides with the position of the light emitting portion of the semiconductor laser 10. Since the upper and lower planes of the dove prism 32 and the upper and lower planes of the dielectric transparent flat plate 30 are all parallel, the straight line HK is a normal line common to these four surfaces. The normal line HK is selected so as to pass through the intersection A between the incident light beam 50 and the upper plane of the dove prism 32. When ∠OAH = θ _p , θ _p is a Brewster angle and is given by the following equation.

Refractive index n _a of the air, because they sought detail, be previously accurately measure the refractive index n _p of the Dove prism 32, the equation (12) can be obtained theta _p.

  Next, the intersection of the P-wave laser beam 52 and the inclined surface 35 of the dove prism 32 is defined as O ′, the intersection of the normal of the inclined surface 35 passing through the intersection O ′ and the laser beam 50 is defined as B, and the normal line BO ′. Let C be the intersection of the normals HK. Since the angle between the normal line BC and the normal line HK is ∠BCH = ξ,

It becomes. From the equations (13) to (15),

Get.

In summary, the rotary stage when the P-wave laser beam 50 is incident on the upper plane of the Dove prism 32 and the intensity of the reflected light 51 from the upper plane of the Dove prism 32 is adjusted by adjusting the rotary stage 12. record the 12 angle theta _a, then the incident laser beam 52 of the P-wave on the slope 35 of the Dove prism 32, and the intensity of the reflected light 53 from the interface between the dielectric transparent flat plate 30 and the colloidal liquid 33 minimum The rotary stage 12 is adjusted so that the angle θ _b of the rotary stage 12 at that time is recorded, the difference between the two angles θ _a -θ _b , the refractive index n _p of the Dove prism 32 and the Dove prism 32 the equation (16) using the Brewster angle theta _p calculated by using the refractive index n _a of the gas that you are, it is possible to obtain the incident angle theta ₁ at slope 35 of the dove prism 32. When calculating the refractive index n _s of the colloidal liquid 33 may be substituted equation (16) into equation (5).

  The wave plate 21 shown in FIG. 6F is used for alignment of the photodetector 20 that measures the reflected light intensity. As the incident angle approaches the Brewster angle, the intensity of the P-wave non-scattered reflected light approaches zero, making it difficult to align the photodetector 20. Therefore, a part or most of the P-wave incident light is converted into S-wave light by the wave plate 21, the pinhole 22 and the photodetector 20 are aligned, the wave plate 21 is removed, and the non-P wave is removed. Measure the intensity of scattered reflected light.

In the case of the second method of the present embodiment shown in FIG. 3, as shown in FIG. 8, a P-wave laser beam 50 is incident on the upper plane of the Dove prism 34, and the rotary stage 12 is adjusted to adjust the Dove prism. non-scattering intensity of the reflected light 51 from the upper surface 34 to record the angle theta _a rotary stage 12 when the minimum, then the incident laser beam 52 of the P-wave on the slope 35 of the dove prism 34, double The rotary stage 12 is adjusted so that the intensity of the non-scattered reflected light 53 from the interface between the prism 34 and the colloid liquid 33 is minimized, and the angle θ _b of the rotary stage 12 at that time is recorded, and the two angles are recorded. the difference θ _a -θ _b, the equation (16) using the Brewster angle theta _p calculated by using the refractive index n _a of the gas in contact with the refractive index n _p and Dove prism 34 of Dove prism 34 On the slope 35 of the dove prism 34 It is possible to obtain the incident angle theta _1. When calculating the refractive index _{n s} of the colloidal liquid 33 may be substituted equation (16) into equation (11).

3. Measurement Result Using the measurement system of FIG. 1, the refractive index of purified water and the refractive index of milk which is a kind of colloidal liquid 33 were measured.

  As the light source 10, an InGaAlP semiconductor laser (wavelength: 670.0 nm, output: 3 mW) was used. The semiconductor laser was fixed to the center of the electric rotary stage 12 whose rotation angle can be remotely controlled in increments of 4/1000 °, and a polarizing film for selecting P wave light was attached to the exit port.

Further, a dove prism 32 with ξ = 45 ± 0.05 ° was made using BK7 glass, and a dielectric transparent flat plate 30 was made using LiTaO ₃ (LT crystal). The appearance of the dove prism 32 is shown in FIG. 9, and the appearance of the dielectric transparent flat plate 30 is shown in FIG.

  As shown in FIG. 9, the AA'B'B surface and CC'D'D surface of the Dove prism are parallel, the ABDC surface and A'B'D'C 'surface are parallel, and ∠ACD = ∠A 'C'D' = ∠BDC = ∠B'D'C '= 45 ° ± 0.05 °, and ∠CAB = ∠C'A'B' = ∠ABD = ∠A'B'D '= 135 ° ± 0.05 °. Further, the four surfaces of the AA'C'C surface, the BB'D'D surface, the AA'B'B surface, and the CC'D'D surface are optically polished.

  As shown in FIG. 10, the LT crystal used for the dielectric transparent flat plate 30 has a rectangular parallelepiped shape processed along the main axis of the crystal, and has two normal planes parallel to the Z axis (optical axis). The surface is optically polished.

The P wave light of the InGaAlP semiconductor laser is incident on the AA'B'B surface, which is the upper plane of the Dove prism, and the optically polished plane of the LT crystal (dielectric transparent flat plate), the Brewster angle is measured, and each refraction is measured. The rate was determined. The refractive index n _p of the Dove prism was 1.51370, and the normal refractive index of the LT crystal was n _c = 2.17236.

  The small cell 36 into which the colloid liquid 33 is placed is a circular glass cell having an outer diameter of 10 mm, an inner diameter of 8 mm, and a height of 10 mm. The colloidal liquid 33 stored in the small cell 36 is about 1 ml.

First, in order to check the measurement accuracy, the refractive index of purified water was measured. FIG. 11 shows the relationship between the light detection signal (output signal of the light detector obtained by photoelectrically converting the reflected light) and the incident angle θ ₁ when purified water is measured at a measurement temperature of 18 ° C. The incident angle θ _{1 at} which the light detection signal is minimized is 50.380 °, and the refractive index of water is 1.33050 from the equation (5). The measurement result was in good agreement with the published value (Science Chronology, 1.36704 at a wavelength of 670 nm and a temperature of 18 °), and it was confirmed that the refractive index of water can be accurately measured with the measurement system of this embodiment.

  Next, the milk fat percentage is 0.1% (no fat), 1.8% (low fat), 2.3% (medium fat), 3.0% (medium fat), 3.7% (high), respectively. The refractive index of five types of milk (fat) was measured in an environment of 18 ° C.

FIG. 12 shows the relationship between the light detection signal and the incident angle θ ₁ when measuring medium fat milk of 2.3% milk fat. Table 1 shows the refractive index obtained based on the incident angle θ ₁ at which the light detection signal measured for each of the five types of milk is minimized.

  FIG. 13 is a measurement result showing the relationship between the milk fat percentage and the refractive index of milk. The measurement results in FIG. 13 indicate that the refractive index measurement device and the refractive index measurement method of this embodiment can accurately measure the refractive index of milk, which is a kind of colloidal liquid 33. Further, according to the method of the present embodiment, since the intensity of the reflected light from the surface of the colloidal liquid 33 is measured, the colloidal liquid 33 having a large absorption rate can also be measured. Further, if a dielectric material having a large refractive index is used as the dielectric transparent flat plate 30 (see FIG. 1) or the dove prism 32 (see FIG. 3) serving as a lid for the colloid liquid 33, the refractive indexes of all the colloid liquids 33 are used. Can be measured.

  The technical scope of the present invention is not limited to the above-described embodiment, and appropriate modifications can be made without departing from the spirit of the present invention.

10 light source, 12 rotating stage, 14 optical fiber, 16 optical system, 18 polarizing plate, 20 photodetector, 21 wave plate, 22 pinhole, 30 dielectric transparent flat plate, 32 dove prism, 33 colloidal liquid, 34 dove prism, 35 slopes, 36 small cells, 38 matching liquids, 40 arithmetic units, 42 arithmetic processing units, 44 storage units

Claims (11)

In a refractive index measurement method for measuring the refractive index of a colloidal liquid,
The lower surface of the dielectric transparent plate having a refractive index higher than that of the colloid solution and parallel to the upper and lower surfaces is brought into contact with the surface of the colloid solution, and upper surfaces parallel to each other are formed on the upper surface of the dielectric transparent plate. It has a lower plane and two flat slopes that are not parallel to these planes. The intersection angle (inner angle) between the upper plane and the two slopes is 180 ° -ξ, and the inner angle between the lower plane and the two slopes is , Both of which are ξ and the inner angle ξ is larger than 0 ° and smaller than 90 °, the lower surface of the Dove prism is brought into contact with the matching liquid, and includes the normal line of the Dove prism and the traveling direction of the incident light. Light whose electric field of light oscillates in a direction perpendicular to the incident surface is defined as P-wave light, and P-wave light having a narrow spectral width suitable for refractive index measurement is incident on one inclined surface of the Dove prism,
Obtaining an incident angle θ _{1 at} which the intensity of non-scattered reflected light from the interface between the lower flat surface of the dielectric transparent plate and the surface of the colloidal liquid is minimized;
Wherein the incident angle theta _1, the refractive index n _c of the dielectric transparent plate, a refractive index and n _p of the Dove prism, on the basis of the refractive index n _a of the gas in contact with the Dove prism, the colloidal A refractive index measurement method for obtaining a refractive index _ns of a liquid. In claim 1,
The P-wave light with a narrow spectral width suitable for the refractive index measurement is incident on the upper plane of the Dove prism, and the intensity of the reflected light from the upper plane of the Dove prism is adjusted by adjusting the rotation stage for changing the incident angle of the P-wave light. There was recorded the angle theta _a rotary stage when the minimum, a narrow P-wave optical spectral width suitable to the refractive index measurement is incident on one of the slopes of Dove prism then, a dielectric transparent flat plate and the colloidal liquid The rotation stage is adjusted so that the intensity of the non-scattered reflected light from the interface of the substrate is minimized, the angle θ _b of the rotation stage at that time is recorded, the difference between the two angles θ _a -θ _b, and the Dove prism using Brewster angle theta _p calculated by using the refractive index n _a of the gas in contact with the refractive index n _p and Dove prism of obtaining the incident angle theta ₁ at one slope Dove prism, the refractive index Measuring method. In claim 1 or 2,
The dielectric transparent flat plate is a uniaxial crystal, and the direction of the optical axis (the direction in which the normal ray and the extraordinary ray propagating in the crystal coincide with each other) has a narrow spectral width suitable for refractive index measurement. The refractive index measurement method arrange | positions so that it may orthogonally cross with the vibration direction of the electric field component of incident light. In any one of Claims 1 thru | or 3,

Determining the refractive index n _s of the colloidal solution on the basis of the refractive index measurement method. In a refractive index measurement method for measuring the refractive index of a colloidal liquid,
The surface of the colloid liquid has a higher refractive index than that of the colloid liquid, and has an upper plane and a lower plane that are parallel to each other, and two flat slopes that are not parallel to these planes. An intersection angle (inner angle) is 180 ° -ξ, an inner angle between the lower plane and the two slopes is ξ, and the inner angle ξ is larger than 0 ° and smaller than 90 °. Light whose electric field oscillates in a direction perpendicular to the incident surface including the normal line of the Dove prism and the incident light traveling direction is defined as P-wave light with a lower plane in contact, and has a narrow spectral width suitable for refractive index measurement. P-wave light is incident on one slope of the Dove prism,
Obtaining an incident angle θ _{1 at} which the intensity of non-scattered reflected light from the interface between the lower plane of the Dove prism and the colloidal liquid surface is minimized;
And the incident angle theta _1, the refractive index and n _p of the Dove prism, on the basis of the refractive index n _a of the gas in contact with the Dove prism, determining the refractive index n _s of the colloidal solution, the refractive index measurement Method. In claim 5,
The P-wave light with a narrow spectral width suitable for the refractive index measurement is incident on the upper plane of the Dove prism, and the intensity of the reflected light from the upper plane of the Dove prism is adjusted by adjusting the rotation stage for changing the incident angle of the P-wave light. interface but to record the angle theta _a rotary stage when the minimum, then the narrow P-wave optical spectral width suitable to the refractive index measurement is incident on one of the slopes of Dove prism, the Dove prism and colloidal liquid The rotary stage is adjusted so that the intensity of the non-scattered reflected light from the light is minimized, the angle θ _b of the rotary stage at that time is recorded, the difference between the two angles θ _a -θ _b and the refraction of the Dove prism Refractive index measurement method for obtaining an incident angle θ ₁ on _one inclined surface of a Dove prism using a Brewster angle θ _p calculated using _a refractive index n _p and a refractive index na of _a gas in contact with the Dove prism . In claim 5 or 6,
The dove prism is a uniaxial crystal, and is arranged so that the direction of its optical axis is orthogonal to the vibration direction of the electric field component of incident light. In any of claims 5 to 7,

Determining the refractive index n _s of the colloidal solution on the basis of the refractive index measurement method. In claim 2 or 6,

The refractive index measurement method for obtaining the incident angle θ ₁ based on In a refractive index measuring device that measures the refractive index of a colloidal liquid,
A dielectric transparent flat plate that is in contact with the surface of the colloidal liquid and has a higher refractive index than the colloidal liquid and whose upper and lower planes are parallel;
The upper surface of the dielectric transparent flat plate is contacted via a matching liquid, has an upper surface and a lower surface that are parallel to each other, and two flat slopes that are not parallel to these planes. An angle (inner angle) is 180 ° -ξ, an inner angle between the lower plane and the two slopes is ξ, and the inner angle ξ is greater than 0 ° and less than 90 °,
Light whose electric field of light oscillates in a direction orthogonal to the incident plane including the normal of the Dove prism and the incident light traveling direction is defined as P-wave light, and P-wave light having a narrow spectral width suitable for refractive index measurement is defined as the Dove prism. A light irradiator that is incident on the slope of
A light detection unit for detecting the intensity of non-scattered reflected light from the interface between the lower flat surface of the dielectric transparent plate and the colloidal liquid surface;
Wherein the incident angle theta ₁ which the intensity of the reflected light of the unscattered is minimized from the interface between the lower plane of the dielectric transparent plate and said colloidal liquid surface, and the refractive index n _c of the dielectric transparent plate, the Dove prism including refractive index and n _p of, based on the refractive index n _a of the gas in contact with the Dove prism, and a processing unit for performing arithmetic processing for calculating the refractive index n _s of the colloidal solution, the refractive index measuring device. In a refractive index measuring device that measures the refractive index of a colloidal liquid,
Contact with the surface of the colloidal liquid, have a higher refractive index than the colloidal liquid, and have an upper plane and a lower plane that are parallel to each other, and two flat slopes that are not parallel to these planes. A dub characterized in that the angle of intersection (inner angle) of the slope is 180 ° -ξ, the inner angle of the lower plane and the two slopes are both ξ, and the inner angle ξ is greater than 0 ° and less than 90 °. Prism,
Light whose electric field of light oscillates in a direction orthogonal to the incident plane including the normal of the Dove prism and the incident light traveling direction is defined as P-wave light, and P-wave light having a narrow spectral width suitable for refractive index measurement is defined as the Dove prism. A light irradiator that is incident on the slope of
A light detector for detecting the intensity of non-scattered reflected light from the interface between the lower surface of the Dove prism and the colloidal liquid surface;
The incident angle θ _{1 at} which the intensity of the non-scattered reflected light from the interface between the lower plane of the Dove prism and the colloidal liquid surface is minimized, the refractive index n _p of the Dove prism, and the Dove prism in contact with each other. And a calculation processing unit that performs a calculation process for calculating the refractive index n _s of the colloidal liquid based on the refractive index n _{a of the} gas.

Images