JP2672718B2 - Refractive index measuring method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractive index measuring method and apparatus capable of accurately and quickly measuring the refractive index of an optical glass or the like in a wide range.

[0002]

2. Description of the Related Art For example, the following methods are known as methods for measuring the refractive index in the field of development research and manufacturing of optical products such as optical glass.

(1) Method using V-block type refractometer (see, for example, Japanese Patent Laid-Open No. 61-169848) As shown in FIG. 2, the outline of this method is as follows. That is, the V-shaped groove 10 of the V-block base 100
1. A V block sample 200 is placed on the V block base 100, and a light source side lateral slit device 3 is provided from one side surface of the V block base 100.
Light emitted from the slit S ₀ of the collimator 30
The parallel light is made incident at 1 and made incident, and the V block base 100
Through. The light passing through the V-block base 100 is made incident on the telescope 400 to form an image of the slit S ₀ . Here, the images of the slit S ₀ formed by the telescope 400 are two images, an image P _{1 formed} by the light passing through the sample 200 and an image P _{2 formed} by the light passing through only the V block base 100. These images P ₁ , P
The distance Δx between the _two depends on the difference Δn between the refractive index n ₁ of the sample 200 and the refractive index n ₀ of the V block base 100. That is, there is a relationship represented by the following equation between them.

Δn = {ntan ⁻¹ (Δx / f)} / 2 (1) where f is the focal length of the telescope 400.

Therefore, the V block base 100 is made of a material having a known refractive index n ₀ , and the two images P ₁ ,
If the distance Δx between P ₂ is obtained, the sample 200
It can be determined refractive index n ₁ of the.

In the V block base 100, a V-shaped groove 101 having a V-shape with an opening angle of 90 degrees is formed on the upper surface side of a glass block which is optically polished so that a pair of opposing side surfaces are parallel to each other. It is a thing. Two orthogonal surfaces of this groove are also optically polished. The sample 200 is V
It is formed into a right-angled triangular prism having a right-angled portion that can be fitted into the groove 101. In this case, the two orthogonal surfaces of the sample 200 come into contact with the two surfaces of the V-shaped groove 101, respectively, but these surfaces may be rough-polished.
Adhesion can be secured by applying index matching oil having the same refractive index as the V block base 100 to these surfaces.

[0007] In this method, it is not necessary to perform precision optical polishing processing on the sample 200, and rough polishing is sufficient. Therefore, sample preparation is easy, and therefore measurement can be performed in a short time (1 piece / minute or less).
In addition, it has excellent reproducibility (reproducibility; Δn = ± 1
× 10 ^-5 ). Therefore, it is used to measure the refractive index of mass-produced products with a large number of inspections by automating the measurement using a computer or the like.

(2) Method Using Rayleigh Interferometer Refractometer As shown in FIG. 3, the outline of this method is as follows. That is, the reference sample 110 of a rectangular parallelepiped shape and the sample of unknown refractive index, both of which have exactly the same length and are optically polished so that both end faces facing each other in the longitudinal direction are precisely parallel to each other. The measurement samples 210 are arranged adjacent to each other so that their longitudinal directions are parallel to each other, and the vertical slit S ₁ of the vertical slit device 310 on the light source side is arranged from one of these end faces.
Light of a single wavelength emitted from the collimator 311 is made into parallel light and made incident, and is passed through the reference sample 110 and the sample to be measured 210. Then, these reference samples 110
Also, the light passing through the sample 210 to be measured is made incident on the double slit device 500 in which the two vertical slits S ₂ and S ₃ are closely arranged in parallel. Then, the vertical slits S ₂ , S
_The light passing through ₃ is condensed by the telescope 410 to form Young's interference fringes Psv on its focal plane. Here, the phase of the interference fringes is determined by the difference Δn between the refractive index n ₀ of the reference sample 110 and the refractive index n ₁ of sample to be measured 210. Therefore, the phase of the interference fringes (interference fringes when the refractive index difference = Δn = 0) obtained by arranging the same sample as the reference sample 110 instead of the sample 110 and the interference fringes obtained by arranging the sample 110 The difference from the phase of (the interference fringes when the refractive index difference = Δn) is Δ
If θ, the following equation holds between them.

Δn = (Δθ · λ) / (2πD) (2) where λ is the wavelength of light used for measurement D is the length of the sample 210.

Therefore, by obtaining Δθ, the refractive index n ₁ of the sample 210 can be obtained by the equation (2).

Observation of interference fringes and measurement of phase difference are
For example, if a computer using a CCD camera and an image processing method are used, the process can be performed quickly and accurately.

Since this method uses a paraxial two-beam interferometer using a double slit, it is hardly affected by temperature changes and vibrations, and a high resolution of about ± 1 × 10 ^-6 can be obtained. . Therefore, a minute difference in refractive index can be accurately measured, which is used for precise measurement.

[0013]

However, the above-mentioned conventional method has the following problems.

(1) Method using V-block type refractometer Since it is difficult to measure a refractive index difference of 1 × 10 ^-5 or less by this method, it is necessary to perform a precision measurement requiring a resolution of less than this. It is difficult to use.

That is, when the difference in refractive index is about this,
Since the refraction angle due to the V block becomes extremely small, the distance between the two slit images becomes extremely small, and it becomes difficult to distinguish the two slit images. In order to enable the discrimination of the slit image, it is necessary to lengthen the focal length of a telescope or the like for forming the slit image, or to improve the resolution of the displacement measurement of the slit image. However, if the focal length of the telescope or the like is increased, the influence of the fluctuation of the optical system due to the temperature change is greatly affected, and the measurement error is eventually increased. Further, as a method for improving the resolution of the displacement measurement of the slit image, for example, there is a vibration slit method, etc., but in order to carry out this method, an extremely complicated and expensive detection system is required, and the measurement and analysis Since the work becomes extremely complicated, it is not realistic to apply it to a device used at a manufacturing site or the like.

(2) Method using Rayleigh interference refractometer According to this method, the difference in refractive index on the order of 1 × 10 ⁻⁶ can be measured, but conversely, the difference in refractive index is 1 × 10 ⁻⁵ or more. In some cases, measurement becomes difficult. This is because if the difference in refractive index is more than this level, the phase difference of Young's interference fringes is ± π or more, and it is extremely difficult to compare the images of the interference fringes to obtain these phase differences. . Further, in this method, it is necessary to polish the sample with high precision so that the difference in length from the reference sample is within 20 to 50 nm and the polished surface precision of both end faces of the sample is about λ / 20. Therefore, there is also a problem that the measurement work is complicated.

The present invention has been made under the above-mentioned background, and an object of the present invention is to provide a refractive index measuring method and apparatus capable of accurately and quickly measuring the refractive index of an optical glass or the like in a wide range. It was done.

[0018]

In order to solve the above problems, the present invention provides (1) transmitting light emitted from the same light source through a reference sample of known refractive index and a sample of unknown refractive index, An interference fringe is formed by passing these transmitted lights through two slits provided close to each other, and in the refractive index measurement method for obtaining the refractive index of the sample from the phase information of the interference fringe, the reference sample and The Z axis is parallel to the optical axis of the light passing through the sample, the Y axis is parallel to the longitudinal directions of the two slits provided in close proximity, and the X axis is orthogonal to the Y and Z axes. Respectively, the reference sample and the sample are Z on the same plane parallel to the X and Z planes.
The length in the axial direction is the same, and the length is linearly changed in the Y-axis direction.
A structure in which oblique interference fringes that form a predetermined angle with respect to the Y-axis direction are formed by the light that has passed through the two slits, and the refractive index of the sample is obtained from the phase information of the oblique interference fringes. As an aspect of this configuration 1, (2) in the refractive index measuring method of configuration 1, on the first line when the oblique interference fringes are cut by a first line parallel to the X-axis direction. In the first photodetection intensity distribution curve and the second line on the second line when the interference fringes are cut by a second line parallel to the first line and separated by a predetermined distance in the Y-axis direction. And a refractive index difference between the reference sample and the sample by calculating a phase difference between the first and second light detection intensity distribution curves. , (3) Refractive index measuring method of composition 1 In the above, the reference sample and the sample are held so as to be movable in the Y-axis direction, the reference sample and the sample are fixed at a first position in the Y-axis direction to form the diagonal interference fringes, and the diagonal interference fringes are formed. X stripe
A first photodetection intensity distribution curve on the fixed line obtained by cutting with a fixed line parallel to the axial direction is obtained, and then the reference sample and the sample are moved in the Y-axis direction to obtain a second curve in the Y-axis direction. By fixing at a position to form the oblique interference fringes and obtaining the second photodetection intensity distribution curve on the fixed line when the oblique interference fringes are cut by the fixed line, the first and the second (2) The refractive index difference between the reference sample and the sample is obtained by obtaining the phase difference between the two photodetection intensity distribution curves. The refractive index between the reference sample and the sample is obtained by obtaining the photodetection intensity distribution curve on this line when the interference fringe is cut by a line parallel to the Y axis, and obtaining the phase number between both ends of this photodetection intensity distribution curve. difference (5) In the refractive index measuring method of configuration 1, the reference sample is obtained by obtaining an angle of the oblique interference fringes with respect to the Y axis and a distance in the X axis direction between the interference fringes. And a sample, a difference in refractive index between the sample and the sample is obtained. Further, as a mode of the structure 2 or 3, (6) in the refractive index measuring method of the structure 2 or 3, The second reference sample having the same refractive index as that of the reference sample is used to obtain the phase difference between the two photodetection intensity distribution curves, and then the sample is used instead of the second reference sample. The constitution is characterized in that the phase difference of the detected intensity distribution curve is obtained, and the difference in refractive index between the reference sample and the sample is obtained by obtaining the difference between these phase differences, and other aspects of configurations 1 to 6 As (7) No configuration 1 V in which a V-shaped groove having a V-shape with an opening angle of 90 degrees is formed on the upper surface side of a glass block that is optically polished so that a pair of opposite side surfaces are parallel to each other. Using a block, the reference sample and the sample are formed into a right-angled triangular prism having a right-angled portion so that they can be fitted into the V-shaped groove of the V block, and are fitted and retained in the V-shaped groove. The light is transmitted through the reference sample and the sample by making the light enter from one side surface.

As a mode of the apparatus for carrying out the methods of the constitutions 1 to 7, (8) a light source for emitting light of a single wavelength, and a light source side slit device for converting the light emitted from this light source into linear divergent light When,
A collimator for collimating the linearly divergent light emitted from the light source side slitting device and a glass block which is arranged in the optical path of the parallel light and is optically polished so that a pair of opposite side surfaces are parallel to each other. A V block having a V-shaped groove having an opening angle of 90 degrees and having a V shape, and having a right-angled triangular prism having a right-angled portion that can be fitted into the V-shaped groove of the V block. A sample and a V block that is fitted and held adjacent to the V-shaped groove to hold the sample, and two adjacent blocks that pass the reference sample and the light that has passed through the sample held in the V block are provided in close proximity to each other. A double slit device having a slit, a telescope device that forms interference fringes by entering light that has passed through the double slit device, an imaging device that detects an image of the interference fringe, and By analyzing the image information of the interference fringes sent from the unit is obtained by a structure in which an image processing apparatus for obtaining the phase information of the interference fringes.

[0020]

According to the above configuration 1, since the phase information of the interference fringe includes the information of the refractive index difference between the reference sample and the sample, by analyzing this phase information, the refractive index between the reference sample and the sample is analyzed. The difference is determined, which allows the refractive index of the sample to be determined.

That is, light emitted from the same light source is transmitted through a reference sample having a known refractive index and a sample having an unknown refractive index, and these transmitted lights are passed through two slits provided close to each other. It is known that an image of interference fringes can be obtained by forming an image with a telescope or the like.

Here, the light transmitted through the reference sample and the light transmitted through the sample are out of phase with each other in accordance with the difference in the optical distance obtained by adding the difference in the refractive index to the difference in the geometric distance of the transmission.
Therefore, an interference fringe corresponding to this phase shift is formed. In this case, the phase of the interference fringe is determined depending on the optical path difference between the two, and when the optical path difference changes, the phase of the interference fringe shifts accordingly. The conventional method using the Rayleigh interferometer simply compares the phase of the interference fringes of the reference sample and the phase of the interference fringes of the reference sample and the sample, and measures the phase shift amount between the two. However, with this conventional method, the interference fringes perpendicular to the Y-axis are aligned in parallel at a constant interval, so when the phases of the two deviate by ± π or more, which fringe is used as a reference. It becomes impossible to determine whether to measure the deviation amount. On the other hand, according to the method of Configuration 1, when attention is paid to one interference fringe in the diagonal interference fringes, the deviation itself in the X-axis direction of the one continuous diagonal interference fringe is the difference between the reference sample and the sample. Represents the phase shift corresponding to the optical path difference of. Even if the deviation is ± π or more, it can be easily discriminated because of one continuous stripe. This is the basic difference between the present invention and the conventional Rayleigh interferometer method. As a result, it is possible to perform measurement over a wide measurement region, which is not possible with the method using the Rayleigh interferometer, while ensuring the advantage of the method using the Rayleigh interferometer, that is, the advantage that high-precision measurement can be performed.

Structures 2 to 6 are specific modes of the method of Structure 1 for obtaining a phase difference based on an optical path difference from oblique interference fringes. Here, according to the configuration 2, the phase difference is immediately obtained by one observation. Further, according to the configuration 3, the process for obtaining the phase difference is made relatively easy. The configuration 4 is particularly effective when the phase difference is large. further,
According to the configuration 6, it is possible to cancel an error due to a device factor and perform more accurate measurement. According to the configuration 7, it is possible to make a quick measurement by taking advantage of the V-block method. Then, according to the configuration 8, it is possible to obtain an apparatus capable of implementing the method of the configurations 1 to 7.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Refractive Index Measuring Method of One Embodiment FIG. 1 is an explanatory view of a refractive index measuring method according to one embodiment of the present invention, FIG. 4 is an explanatory view of an optical path based on a V block of FIG. 1, and FIG.
Is an explanatory diagram of interference fringes, and FIG. 6 is a diagram showing intensity distributions on the A and B lines of the interference fringes of FIG. Hereinafter, a method according to an embodiment of the present invention will be described with reference to these drawings.

In these figures, reference numeral 1 is a V block base, reference numeral 11 is a reference sample, reference numeral 21 is a sample to be measured,
Reference numeral 3 is a light source side vertical slit device, reference numeral 4 is a telescope, and reference numeral 5 is a double slit device.

The outline of the method of this embodiment is as follows. That is, the V-block reference sample 11 and the V-block sample 21 are placed close to each other in the V-shaped groove 1a of the V-block base 1, and the light source side vertical slit device 3 is provided from one side surface of the V-block base 1. The single-wavelength light L emitted from the vertical slit S ₁ is collimated into parallel light by the collimator 31 and is incident on the collimator 31 to pass through the V block base 1. The light passing through the V-block base 1 has two vertical slits S ₂ ,
Double slit device 5 in which S ₃ is provided in close proximity and in parallel
Incident on In this case, the light passing through the sample 21 passes through the slit S ₂ and the light passing through the reference sample 11 passes through the slit S _3.
To pass through. Then, the vertical slits S ₂ , S ₃
The light that has passed through is condensed by the telescope 4 and Young's interference fringes Pso are formed on the focal plane thereof. Here, this Young's interference fringe Pso has the optical axis direction of the measuring light L as the Z axis, the direction orthogonal to this Z axis, and the direction parallel to the longitudinal direction of the vertical slits S ₂ , S ₃ as the Y axis, and Y , Z is an oblique interference fringe in the X and Y planes that forms an angle with the Y axis direction when the axis orthogonal to the Z axis is defined as the X axis. In the method of one embodiment, the oblique interference fringes Pso are observed, and the refractive index of the sample is obtained from the information contained in the interference fringes. Next, the principle of obtaining the refractive index of the sample from this oblique interference fringe Pso will be described.

In FIG. 4, A and B are two planes parallel to the X and Z planes and having a distance h from each other. The light that has passed through the sample 21 and the reference sample 11 on the plane A and passed through the vertical slits S ₂ and S ₃ of the double slit 5 forms interference fringes. Similarly, light that has passed through the sample 21 and the reference sample 11 on the plane B and passed through the vertical slits S ₂ and S ₃ of the double slit 5 also forms interference fringes.

Here, the V-shaped groove 1a of the V-block base 1
When the opening angle of is 90 degrees, the light traveling on the plane A is
Sample 21 and standard sample 1 rather than light traveling on plane B
The distances (geometrical distances) passing 1 are both long by 2h. Therefore, in contrast to the interference fringes due to the light traveling on the plane A, the interference fringes due to the light traveling on the plane B are caused by the difference in the passing distance (geometrical distance). ), The phase is shifted by a value corresponding to. That is, if the amount of this phase shift is Δθ, Δθ depends on this optical path difference. This optical path difference depends on the difference in geometrical distance and the difference in refractive index, and of these, the difference in geometrical distance (2h) can be known by setting,
By measuring Δθ, the refractive index n ₀ of the reference sample 11 is measured.
And the refractive index n ₁ of the sample 21 can be calculated by the following equation.

Δn = (Δθ · λ) / (4π · h) (3) where λ is the wavelength of the light ray L.

FIG. 5 shows the interference fringes Pso actually formed on the focal plane of the telescope 4, and the interference fringes are formed between the planes A and B and outside the range, and these interference fringes are formed. Since the phase gradually shifts as it moves in the Y-axis direction, each interference fringe eventually becomes a continuous diagonal fringe. The intersections of the straight lines A and B and the interference fringes in FIG. 5 correspond to the interference fringes due to the light passing on the planes A and B in FIG. 4, respectively.

In order to actually measure this phase difference Δθ, for example, an image of the interference fringe Pso is photographed by a CCD camera or the like, and the interference fringe Pso is cut by a computer image processing method as shown in FIG. It is sufficient to set the lines A and B, draw the detection intensity curves A and B on these lines as shown in FIG. 6, and obtain the deviation amount Δθ between these curves A and B.

Modification of Method of One Embodiment Next, a modification of the method of the above-described one embodiment will be described.

(Modification 1) In this modification, when the phase difference Δθ is actually measured by the computer image processing method in the above-described embodiment, as shown in FIG. 5, interference occurs in the X-axis direction. Instead of setting two lines A and B that cut the stripe Pso, one setting line is used, and instead, the V block base 1 is moved by a predetermined distance (h) in the Y-axis direction. The difference Δθ between the detected intensity curve on the setting line in Fig. 6 and the detected intensity curve after movement (corresponding to curves A and B in Fig. 6) is obtained, and Δn is obtained from this Δθ and the movement distance h by the equation (3). Is.

(Modification 2) This modification is an effective method especially when the refractive index difference Δn is large and the phase difference Δθ is large.

First, as shown in FIG. 7, as the double slit device 5, a device having long lengths H ₀ of the vertical slits S ₂ and S ₃ , for example, the dimension H of the sample 21 and the reference sample 11 in the Y-axis direction is used. Use a longer one. When such a double slit device 5 is used, the interference fringes formed on the focal plane of the telescope 4 are as shown in FIG. Here, in FIG. 8, the interference fringes are cut along the Y-axis to obtain a detection intensity distribution curve on the Y-axis. At this time, the interference fringes are cut in the Y-axis direction due to the dimension H of the sample in the Y-axis direction. Count the phase number α of the interference fringes in this cut range,
Δn is calculated from the following equation.

Δn = (α · λ) / (2 · H) (4) (Modification 3) In FIG. 8, the angle φ formed by the Y-axis and the interference fringes
Depends on the refractive index difference Δn. Therefore, in this modified example, Δn is obtained from the angle φ and the distance u between the interference fringes in the X-axis direction by the following equation.

Δn = C · {(tan φ) · λ} / (2u) (5) where C is the dimensional ratio of the object plane and the image plane in the Y-axis direction.

The method for obtaining each φ can be performed by an image processing method.
In front of the CCD camera, a slit image is formed on the image pickup surface of the camera, and a rotary slit device that can freely rotate the slit image with respect to the Y-axis direction and can read the rotation angle is provided. A method may be used in which the slit image formed is first matched with the Y axis and then with the interference fringes, and the rotation angle at that time is read.

(Modification 4) This modification is a method capable of canceling a measurement error due to a device factor such as a deviation of the surface accuracy of the V block base 1 and an inclination or distortion of the double slit device 5 with respect to the optical axis.

First, as shown in FIG. 9 or FIG.
As the double slit device 5, a set of vertical slits S ₂ ,
Below the S _3, use those provided with the longitudinal slits S _4, S ₅ another set of the same configuration as the slits. here,
In the double slit device 5 of FIG. 9, the slits S ₂ and S ₃ transmit the light transmitted through the sample 21 and the reference sample 11, and the other set of vertical slits S ₄ and S ₅ is the V block base 1
The arrangement relationship is such that only the light transmitted through is transmitted. In addition, the double slit device 5 of FIG. 10 has slits S ₂ , S _{3 and} another pair of vertical slits S ₄ , S.
_In both cases, the arrangement relationship is such that the light transmitted through the sample 21 and the reference sample 11 is transmitted. The method is
Any of these may be used. The straight lines A and B in FIGS. 9 and 10 indicate the positions on the slit of the lines corresponding to the lines A and B that cut the interference fringes in the above-described embodiment.

In this method, first, as shown in FIG. 11 (a), the reference sample 11a exactly the same as the reference sample 11 is placed on the portion of the V block base 1 on which the sample is placed, and the interference fringes are placed. Is formed, the detected intensity distribution curves on the lines A and B are drawn, and the phase difference between these curves is obtained. The phase difference caused by this is due to device factors.

Next, as shown in FIG. 11B,
A sample 21 is placed instead of the reference sample 11a, interference fringes are formed in the same manner, detection intensity distribution curves on the lines A and B are drawn, the phase difference between these curves is calculated, and from the phase difference calculated here, The true phase difference Δθ is obtained by subtracting the phase difference due to the device factor obtained above.

Apparatus for Implementing Method of One Embodiment FIG. 12 is a diagram showing a configuration of an apparatus for implementing the method of one embodiment. It should be noted that this device is an example of a device that performs the method of the first modification of the method of the above-described one embodiment. In addition,
The basic configuration is the same as in the case of the method of the above-described embodiment shown in FIG. 1, so common parts are assigned the same reference numerals and duplicate explanations are omitted.

Now, in this apparatus, as the light source 33, Na
A bright line lamp (wavelength: 589.29 nm) was used. Further, the light emitted from the light source 33 is condensed by the condenser lens 32 so as to be incident on the light source side vertical slit 3. This light source side vertical slit device 3 has a slit width of 50 μm along the Y axis.
The vertical slit S ₁ is formed.

The collimator 31 converts the divergent light L emitted from the vertical slit device 3 into parallel light and has a focal length f.
= 90 mm, diameter φ = 50 mm convex lens.

FIG. 13 is a perspective view of the V block base 1. The V block base 1 itself is a known one.
In this example, glass having a refractive index of 1.61999 was used. V
The opening angle of the character groove 1a is 90 degrees. The light entrance / exit surfaces 1A and 1B and the surfaces 1C and 1D of the V-shaped groove 1a are both optically polished.

FIG. 14 is a perspective view of the reference sample 11. As the reference sample 11, glass having the same refractive index (n ₀ = 1.61999) as that of the V block base 1 was formed into a rectangular prism shape. Light entrance / exit surface 11A,
11B has been subjected to optical polishing. When this reference sample 11 is fitted in the V-shaped groove 1a of the V-block base 1, index matching oil with a refractive index of 1.620 is applied to the contact surfaces (surfaces 11A and 11B) to improve the adhesion of the contact surfaces. .

FIG. 15 is a perspective view of the sample 21. The sample 21 is formed into a right-angle prism shape having the same shape as the reference sample 11 by using a glass material to be measured. The accuracy of the right angle part is about 90 degrees ± 3 minutes. Moreover, the light entrance / exit surface does not need to be optically polished, and the mesh 8
No. 00 is good for rough printing. When this sample is fitted in the V-shaped groove of the V block base 1, index matching oil having a refractive index of 1.620 is applied to the contact surface as in the case of the reference sample 11 to improve the adhesion of the contact surface.

FIG. 16 is a front view of the double slit device 5. The double slit device 5 has two slits S ₂ and S ₃ formed in close proximity to each other along the Y-axis direction. Both of these two slits S ₂ and S ₃ have a slit width of 0.5 mm and a length in the Y-axis direction of 2.5 m.
m, the distance between them is 5 mm. As shown in FIG. 17, the double slit device 5 has two slits S ₂ and S ₂ when viewed from the collimator 31 side along the Z-axis direction.
It is arranged so that the boundary line between the reference sample 11 and the sample 21 is located in the center between the _three . And these two slits S
₂ , the relative position of the S block ₃ and the V block 1 in the Y-axis direction can be precisely changed by the upper / lower moving stage 6.

FIG. 18 is a perspective view of the up / down moving device 6. The upper / lower moving stage 6 is a micrometer 63.
By rotating, the up / down moving mechanism 62 operates to move the fixed base 61 up / down with high accuracy according to the rotation angle of the micrometer. Moreover, the distance of the up / down movement can be accurately obtained from the rotation angle of the micrometer.

The light that has passed through the double slit device 5 is incident on the telescope objective lens 41 to form interference fringes, which are formed on the image pickup surface of the CCD camera 7 through the telescope eyepiece lens 42. To be imaged. The telescope objective lens 41 has a focal length f = 600 m
The telescope eyepiece lens 42 is a cylindrical lens having a focal length of 30 mm.

The image of the interference fringes obtained by the CCD camera 7 is recorded by the frame memory 8 and then converted into numerical values to be taken into the computer 9.

This computer 9 has a frame memory 8
The interference fringes recorded in 1) are cut along one line along the X-axis direction, a detection intensity distribution curve is created by taking in the detection intensity information on that line, and a fast Fourier transform (F
FT) processing is performed to calculate and store the frequency and the initial phase. Next, the upper / lower moving stage 6 is driven to lower the V block base by 10.00 mm, and at that position, the interference fringes are cut on the same line as in the above case in the same manner as described above. Taking in the detected intensity information, the frequency and the initial phase at this time are calculated in the same manner. Then, when the difference Δθ between the initially obtained initial phase and the subsequently obtained initial phase is obtained, this Δθ corresponds to Δθ in the equation (3), and the descending distance h = 10 of the up / down moving stage 6 is obtained. ．
00 mm corresponds to h in the expression (3). Therefore, these values, the wavelength λ of the light source 33 = 589.29 nm, and the value of the refractive index n ₀ = 1.61999 of the reference sample are added to the equation (3) and Δ
Find n.

The results of actually measuring the refractive index using the above apparatus are shown below. Since the following measurement example is for confirming the accuracy of the device, the sample 21 having a known refractive index is also used.

(A) Example of measurement when the difference in refractive index is large (when the difference in refractive index is on the order of 10 ⁻⁴ ) As the reference sample 11, glass having a refractive index n ₀ = 1.61999 is used, and as the sample 21, a refractive index n ₁ is used. = 1.61959 glass was used. This sample 21 has a known refractive index difference from the reference sample 11 in the order of 10 ⁻⁵ (Δn = −40.0 × 10).
^-5 ) has no known difference in refractive index on the order of 10 ^-6 . Three samples 21 (samples 1, 2 and 3) were prepared and the refractive index with the reference sample on the order of 1 × 10 ⁻⁶ was measured. Sample No Phase difference (degree) Δn (× 10 ^-6 ) Sample 1 -4859 -397.7 Sample 2 -4883 -399.7 Sample 3 -4938 -404.2 (B) Measurement example when the difference in refractive index is small (refractive index difference is 10
^-6 order) Two of the three samples used as the sample in the measurement example (A) were combined to form the sample 21 and the reference sample 11, respectively, and the refractive index on the order of 1 × 10 ^-6 The difference was measured.

Combination Reference Sample Sample Refractive Index Difference Δn (× 10 ⁻⁶ ) Sample 1 Sample 2 -2.4 Sample 1 Sample 3 -6.9 Sample 2 Sample 1 2.5 Sample 2 Sample 3 -2.5 Sample 3 Sample 1 5.0 Sample 3 Sample 2 2.5 As described in detail above, according to the above-described embodiment, the measurement accuracy is equivalent to that of the conventional Rayleigh interferometer in a very wide range of the case where the refractive index difference is in the order of 10 ⁻⁴ to 10 ^−6. Can be measured with extremely high accuracy. Therefore, in the past, one device can serve as a device that requires two or more types of measuring devices depending on the measurement range. Further, the time and effort required for the preparation and setting of the sample are the same as those of the conventional V block method, which is extremely simple and enables quick measurement. Moreover, the structure of the device for performing the measurement is relatively simple, and the parts used can be the same as the ones that have been conventionally used and are easily available and have high reliability. Make it possible to get.

The embodiment described in detail above has an example using V blocks, but the present invention is not necessarily limited to this, and X, Z instead of V blocks are used.
A reference sample and a sample that are formed so that the length in the Z-axis direction is the same on the same plane parallel to the plane and that this length changes linearly in the Y-axis direction can be held in a precise positional relationship. Any means may be used.

[0058]

As described above in detail, according to the present invention, light emitted from the same light source is transmitted through a reference sample having a known refractive index and a sample having an unknown refractive index, and these transmitted lights are brought close to each other. In the refractive index measuring method in which interference fringes are formed by passing through two slits provided in the reference sample, and the refractive index of the sample is obtained from the phase information of the interference fringes, the optical axis of the light passing through the reference sample and the sample. When the Z axis is taken in the direction parallel to the Y axis, the Y axis is taken in the direction parallel to the longitudinal direction of the two slits provided in close proximity, and the X axis is taken in the direction orthogonal to these Y and Z axes, The sample and the sample are formed such that the lengths in the Z-axis direction on the same plane parallel to the X and Z planes are the same and the lengths change linearly in the Y-axis direction. Passed through two slits It is characterized by forming an oblique interference fringe at a predetermined angle with respect to the Y-axis direction and obtaining the refractive index of the sample from the phase information of this oblique interference fringe. It enables measurement in the area.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a refractive index measuring method according to an example.

FIG. 2 is an explanatory diagram of a conventional V-block refractometer.

FIG. 3 is an explanatory diagram of a conventional Rayleigh interference refractometer.

FIG. 4 is an explanatory diagram of an optical path based on a V block in FIG.

FIG. 5 is an explanatory diagram of interference fringes.

6 is a diagram showing the intensity distribution on the A and B lines of the interference fringes of FIG.

FIG. 7 is a diagram showing a double slit device used in Modification 2;

FIG. 8 is an explanatory diagram of interference fringes according to Modification 2.

FIG. 9 is an explanatory diagram of a double slit device used in Modification 4;

FIG. 10 is an explanatory diagram of a double slit device used in Modification 4;

FIG. 11 is an explanatory diagram of a method of Modified Example 4;

FIG. 12 is a diagram showing an overall configuration of a refractive index measuring device of an example.

FIG. 13 is a perspective view of a V block base.

FIG. 14 is a perspective view of a reference sample.

FIG. 15 is a perspective view of a sample to be measured.

FIG. 16 is a front view of a double slit device.

FIG. 17 is a diagram showing a positional relationship of a double slit device.

FIG. 18 is a perspective view of an upper / lower moving stage.

[Explanation of symbols]

1 ... V block base, 3 ... Light source side slit, 4 ... Telescope, 5 ... Double slit device, 6 ... Up / down moving stage, 7 ... CCD camera, 8 ... Frame memory, 9 ...
Computer, 11 ... Reference sample, 21 ... Sample.

Claims (8)

(57) [Claims] 1. Lights emitted from the same light source are transmitted through a reference sample having a known refractive index and a sample having an unknown refractive index, and these transmitted lights are passed through two slits provided in close proximity to each other. In the refractive index measuring method for forming an interference fringe and obtaining the refractive index of the sample from the phase information of the interference fringe, in the direction parallel to the optical axis of the light passing through the reference sample and the sample, the Z axis is close to The Y-axis in the direction parallel to the longitudinal direction of the two slits
When the X axis is taken in the direction orthogonal to the axis, the reference sample and the sample have the same length in the Z axis direction on the same plane parallel to the X and Z planes, and this length is Y.
It is formed so as to change linearly in the axial direction, so that the light passing through the two slits forms oblique interference fringes forming a predetermined angle with respect to the Y-axis direction. Refractive index measuring method, characterized in that the refractive index of the sample is obtained from the phase information of. 2. The refractive index measuring method according to claim 1, wherein when the oblique interference fringe is cut by a first line parallel to the X-axis direction, the first line on the first line is cut.
Of the light detection intensity distribution curve of Y and parallel to this first line
A second photodetection intensity distribution curve on the second line obtained by cutting the interference fringes by the second line that is separated by a predetermined distance in the axial direction is obtained, and then the first and second photodetections are detected. A refractive index measuring method, characterized in that a refractive index difference between the reference sample and the sample is obtained by obtaining a phase difference between intensity distribution curves. 3. The refractive index measuring method according to claim 1, wherein the reference sample and the sample are held so as to be movable in the Y-axis direction, and the reference sample and the sample are fixed at a first position in the Y-axis direction. Then, the oblique interference fringes are formed, and when the oblique interference fringes are cut by a fixed line parallel to the X-axis direction, a first photodetection intensity distribution curve on the fixed line is obtained, and then the reference On the fixed line when the sample and the sample are moved in the Y-axis direction and fixed at the second position in the Y-axis direction to form the oblique interference fringes, and the oblique interference fringes are cut by the fixed line. 2nd light detection intensity distribution curve in
The refractive index measuring method is characterized in that the refractive index difference between the reference sample and the sample is obtained by obtaining the phase difference between the photodetection intensity distribution curves. 4. The refractive index measuring method according to claim 1, wherein when the oblique interference fringes are cut along a line parallel to the Y axis, a photodetection intensity distribution curve on this line is obtained, and the photodetection intensity distribution is obtained. A refractive index measuring method, characterized in that a refractive index difference between the reference sample and the sample is obtained by obtaining a phase number between both ends of a curve. 5. The refraction index between the reference sample and the sample according to claim 1, wherein the angle of the oblique interference fringes with respect to the Y axis and the distance between the interference fringes in the X axis direction are obtained. A refractive index measuring method characterized by obtaining a difference in refractive index. 6. The refractive index measuring method according to claim 2, wherein first, instead of the sample, a second reference sample having the same refractive index as the reference sample is used to detect the two light rays. The phase difference between the intensity distribution curves is obtained, then the phase difference between the two photodetection intensity distribution curves is obtained using a sample instead of the second reference sample, and the difference between these phase differences is obtained to obtain the reference. A refractive index measuring method characterized by obtaining a refractive index difference between samples. 7. The refractive index measuring method according to claim 1, wherein a glass block optically polished such that a pair of opposed side surfaces are parallel to each other is V-shaped with an opening angle of 90 degrees on the upper surface side of the glass block. V-shaped groove having a V-shaped groove having a V-shaped groove is formed, and the reference sample and the sample are formed into a right-angled triangular prism having a right-angled portion into which the V-shaped groove of the V-block can be fitted. A refraction index measuring method characterized in that the light is transmitted through the reference sample and the sample by allowing the light to enter from one side surface of the V block and holding the same. 8. A light source that emits light of a single wavelength, a light source side slit device that converts the light emitted from this light source into linear divergent light, and a linear divergent light emitted from this light source side slit device into parallel light. And a collimator that is placed in the optical path of the parallel light and is optically polished so that a pair of opposing side surfaces are parallel to each other.
A V block in which a V-shaped groove having a V shape is formed, and a reference sample and a sample which are formed in the shape of a right-angled triangular prism having a right-angled portion that can be fitted into the V-shaped groove of the V block are V-shaped grooves. A V-block adapted to be fitted and held adjacent to the V-block, and a double-slit device having two slits provided in close proximity to each other for passing the reference sample and the light transmitted through the sample held in the V-block, respectively. , A telescope device that forms interference fringes by entering light that has passed through this double slit device, an imaging device that detects the image of this interference fringe, and image information of the interference fringes that is sent from this imaging device And an information processing device for obtaining the phase information of the interference fringes.