JPH1137937A - Method and apparatus for measuring refractive index distribution using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the temperature of a sample liquid easily by arranging a guide plate oppositely to a container containing a liquid for immersing a cell which holds a specimen in the sample liquid having refractive index substantially identical to that of the specimen. SOLUTION: A specimen A is secured to the lower end of a supporting member 26 in a cell 21 and held rotatably. The cell 21 is filled with a sample liquid having refractive index substantially identical to that of the specimen A. The cell 21 is inserted into a container 31 which is then filled with a liquid C on the outside of the cell 21. The liquid C is circulated by means of a circulator during measurement of refractive index of the specimen A. Furthermore, a guide plate 34 is fixed vertically from the bottom part of the container 31 in front of the outlet 33 of the container 31. The liquid C passed under the cell 21 abuts against the guide plate 34 to ascend vertically and then discharged from the outlet 33 while exchanging heat sufficiently. Since the liquid C touches the cell 21 over a wide range, temperature fluctuation of the sample liquid B is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for three-dimensionally measuring the refractive index distribution of a test object by analyzing interference fringes, and in particular, immersing the test object in a test solution having substantially the same refractive index. The present invention relates to a measuring method and an apparatus for performing the measurement.

[0002]

2. Description of the Related Art In recent years, plastics have been increasingly used as materials for optical lenses used in optical devices such as laser printers and cameras. Compared to a glass polished lens, a plastic molded lens has advantages in that it is superior in cost reduction and manufacturability of an aspherical lens and is inexpensive.

[0003] On the other hand, however, the refractive index distribution is unstable in production as compared with a glass lens, and non-uniformity may occur inside the lens. Non-uniformity inside the lens has a great effect on optical characteristics, leading to deterioration of image quality and blurring. Therefore, it is necessary to measure the refractive index distribution inside the lens with high accuracy and evaluate the homogeneity of the optical lens.

Accordingly, the applicant of the present invention has rotated a specimen around an axis perpendicular to the optical axis while immersing the specimen in a test solution,
Analyze interference fringes at each of a plurality of rotation angle positions, calculate the amount of transmitted wavefront from these interference fringes, perform a first-order Fourier transform, and further perform a two-dimensional inverse Fourier transform to obtain a refractive index distribution. Method developed.

A specific description will be given with reference to FIG. The device shown in the figure has a basic configuration of a Mahachender type interferometer.
A light source 1 for emitting laser light as coherent light, a beam expander 3, and a beam splitter 5 for splitting a light beam
And two reflection mirrors 7 and 9, a beam splitter 11 for superimposing a light beam, an imaging lens 13, an interference fringe detector 15 such as a CCD, and an arithmetic processing device including a high-speed image processing device and a microcomputer. 17 are provided. In the above configuration, the interferometer is configured by the light source 1 to the imaging lens 13.

The laser beam emitted from the light source 1 is expanded in beam diameter by a beam expander 3 and then travels straight through the beam splitter 5 to become a reference beam a. Is divided into another laser beam that becomes the test wave b that passes through the phase object as The reference wave a and the test wave b are set to be approximately 1: 1.

The reflection mirror 7 is supported by an electric-to-displacement conversion element 19 such as a piezo element, and is arranged so that the optical path length of the reference wave a can be changed in the order of wavelength in order to perform interference fringe analysis by the phase shift method. Have been.

The reference wave a is reflected by the reflection mirror 9 and reaches the beam splitter 11, while the other test wave b is the test object A
And reaches the beam splitter 11 and overlaps with the reference wave a, but is adjusted by the electric-displacement conversion element 19 so that the optical path length between the reference wave a and the test wave b has a phase difference of nπ / 2. Is done.

The reference wave a and the test wave b are superimposed, exit from the beam splitter 11, enter the imaging lens 13, and
An interference fringe is imaged on the imaging surface of the interference fringe detector 15. As the interference fringe detector 15, a linear CCD or an array sensor is used.

The refractive index of the test object A is considerably different from the refractive index of air, and the test wave b transmitted through the test object A is as long as the incident surface and the exit surface of the test object are not parallel. Converges and diverges irregularly. On the other hand, to image interference fringes with an interferometer,
The test wave b must be a substantially parallel light beam. Therefore, the following configuration is adopted because the test wave b transmitted through the test object A becomes almost parallel light beam regardless of the shape of the test object A.

That is, the test object A is set in a container-like cell 21 provided in the optical path of the test wave b. The cell 21 is filled with a test solution B whose refractive index is almost the same as the refractive index of the test object A. The specimen A
Is mounted on a turntable 23, and the turntable 23 is rotatable by an arbitrary angle about an axis orthogonal to the test wave b by a servomotor (not shown) or the like. Both ends of the cell 21, that is, the entrance window 25 and the exit window 27 of the test wave b are parallel to each other, and optical flats 28 and 29 having high surface accuracy are attached to each of them to shield them in a liquid-tight manner. Therefore, the cell 21 filled with the test object A and the test solution B becomes an object having a uniform refractive index as a whole, and
Since the entrance surface and the exit surface are parallel, the test wave b transmitted through the cell 21 is emitted as a substantially parallel light flux.

The interference fringe image is detected by the interference fringe detector 15, photoelectrically converted into an electric image signal, A / D converted by the A / D converter 20, and input to the arithmetic unit 17. . The arithmetic unit 17 includes a transmitted wavefront measuring unit 18 that performs a measurement operation of a transmitted wavefront by analyzing an interference fringe image by a phase shift method or the like.

Next, a description will be given of a method for measuring the refractive index of the test object A using the measuring apparatus having the above-described configuration. First,
In a state where the test object A is not set on the turntable 23, the image signal of the interference fringe image output from the interference fringe detector 15 is taken into the arithmetic processing unit 17 and the transmitted wavefront measuring unit 1 inside the arithmetic processing unit
The interference fringe image is analyzed by 8 to measure the transmitted wavefront in the initial state. Based on the measurement result, an initial process for eliminating a steady error component of the measurement device itself is performed.

Next, the test object A is set on the turntable 23,
The turntable 23 forms an interference fringe on the imaging surface of the interference fringe detector 15 at the position of θ = 0, and the image signal of the interference fringe image output from the interference fringe detector 15 is taken into the arithmetic processing unit 17 to obtain the interference fringe. Perform image analysis.

In the measurement of the transmitted wavefront in which the turntable 23 is at the initial rotation position, the analysis results of the interference fringe image are integrated in the thickness direction (x direction) of the test object A, and a portion having a nonuniform refractive index alone is used. The spatial position of the can not be specified.

Then, the turntable 23 is rotated by a predetermined angle from the initial rotation position, and the test object A on the turntable 23 is changed with respect to the optical axis of the test wave b. Thus, even if the test object A is rotated and displaced, the interference fringe image is formed on the imaging surface of the interference fringe detector 15. In this state, the image signal of the interference fringe image output from the interference fringe detector 15 is taken into the arithmetic processing unit 17 and the transmitted wavefront is measured. Thus, for example, interference fringes are formed a plurality of times from the direction of 180 ° (π) or 360 ° (2π) in increments of 1 °, and the transmitted wavefront is measured. Recompose.
The reconstruction of this image can be performed by using a well-known X-ray CT (Computed Tomog).
raphy) analysis.

FIG. 10 shows the principle of the CT method.
Data p of transmitted wavefront due to test wave incident from angle θ
If (x, θ) is one-dimensionally Fourier-transformed with respect to the variable x, the θ-direction component in the polar coordinate expression of the two-dimensional Fourier transform of the refractive index distribution Δn (x, y) to be obtained can be obtained.

That is, the transmitted wavefront is measured over an angle range of 0 ≦ θ ≦ 2π or 0 ≦ θ ≦ π, the transmitted wavefront data is subjected to one-dimensional Fourier transform, and the polar coordinate data P (x, θ) is converted into orthogonal coordinate data, then two-dimensional inverse Fourier transform, and further converted into a refractive index, whereby the three-dimensional refractive index distribution of the test object A can be reconstructed.

[0019]

According to the above-described method for measuring the refractive index, the test solution B immersed in the phase object as the test object A is affected by the air around the apparatus or the heat generated by the laser. Its temperature gradually rises. When the temperature changes, the refractive index of the test solution B also changes. At this time,
If the temperature change is small, the change in the refractive index is small, and the measurement of interference fringes can be subsequently performed. However, when the temperature change is large, the change in the refractive index is large, the parallelism of the test wave b transmitted through the test object is disturbed, and it becomes difficult to form interference fringes.

Therefore, it is important to control the temperature change of the test solution B during measurement within a certain range so that the difference between the refractive index of the test solution and the refractive index of the test object can be kept small. If possible, we want to keep the temperature of the reagent solution during measurement constant. However, the above-mentioned heat source is also indispensable to the apparatus, and maintaining a change in the temperature of the test solution within a certain range is in a trade-off relationship. The present invention has been conceived from the above facts, and has as its object to provide a refractive index measuring method and a measuring apparatus that can easily control the temperature of a test solution.

[0021]

In order to achieve the above object, an apparatus according to the present invention divides coherent light from the same light source into a reference wave and a test wave, and superimposes these to form interference fringes. Interferometer, a cell having an entrance window and an exit window which are parallel to each other while holding the specimen in a test solution having a refractive index substantially equal to the specimen, and a cell provided outside the cell. A container containing a liquid to be entirely immersed; a liquid inlet formed above one side of the container; an outlet formed below the other side of the container; and a position facing the outlet in the container. And a guide plate provided so that the liquid in the container flows over the surface of the cell over a wide range by the guide plate.

The distance from the guide plate to the cell, the distance from the guide plate to the inner wall of the container on the outlet side, and the distance from the upper end of the guide plate to the liquid surface are substantially equal. It is desirable.

A baffle is provided at a position facing the entrance,
The liquid coming from the inlet is prevented from directly hitting the cell, the container is provided with a monitoring window that can be opened and closed, or the cell is provided with a cylinder communicating the inside and outside of the cell, and the cylinder is a container. The cell may be provided with an openable / closable lid for injecting the test solution into the cell. The measuring method of the present invention is characterized in that one of the above measuring devices is used, the transmitted wavefront is measured one after another while rotating the test object, and the refractive index distribution of the test object is measured using CT analysis. I have.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing a main part of a first embodiment of the present invention. FIG. 9 shows a refractive index measuring apparatus according to the present invention.
Only the configuration around the test object A in the conventional refractive index measuring device described in FIG.

The test object A of the present invention is fixed to the lower end of the support member 26 in the cell 21 and held rotatably about an axis c orthogonal to the test wave b. The support member 26 has a structure that can move up and down and can freely adjust the height of the test object A. The cell 21 is filled with a test solution B having a refractive index substantially equal to that of the test object A. In the present invention, this cell 21
Is inserted into the container 31, and the container 31 outside the cell 21 is filled with the liquid C. As the liquid C, water is used. The container 31 has a liquid inlet 32 and a liquid outlet 33, and is connected to circulators such as pumps provided separately by hoses so that the liquid C can circulate.

The entrance window and the exit window of the cell 21 are
And the optical flats 28 and 29 are fitted therein. With such a configuration, the liquid C disappears from the optical path of the test wave b, and the influence of the flow of the liquid C on the test wave b can be eliminated.

During the measurement of the refractive index of the test object A, the liquid C is circulated by a circulator (not shown). The liquid C has a larger heat capacity than a gas such as air, and can be set to an arbitrary temperature by an appropriate heating / cooling means, so that the test liquid B can be maintained within a desired temperature range in a short time. If water is used as the liquid C, it is inexpensive and easily available.

In the present invention, as shown in FIG.
A guide plate 34 is attached vertically from the bottom of the container just before the outlet 33 (drain outlet) of the liquid C in the container. Guide plate 3
Numeral 4 is almost the same length as the container from the entrance window side to the exit window side, and the height is considerably lower than the liquid level.

If the guide plate 34 is not provided, the container 31
The liquid C sent from the upper left inlet 32 of the cell 2
1 directly through the lower right outlet 33 to the container 31
As a result, sufficient heat exchange was not performed on the upper right side of the cell 21. On the other hand, the guide plate 34
Is provided, the liquid C that has passed below the cell 21 hits the guide plate 34 and rises vertically upward, sufficiently exchanges heat with the upper right side of the cell and passes over the guide plate 34, and exits 33 at the lower right of the container. Come out of. By providing the guide plate 34 in this manner, the liquid C can contact the outside of the cell 21 over a wide range, and the efficiency of heat exchange is improved. That is, the temperature unevenness of the test solution B can be reduced.

FIG. 2 shows a second embodiment of the present invention. In the embodiment of this figure, the three distances of the distance from the guide plate 34 to the cell 21, the distance from the inner wall of the container 31 on the outlet 33 side, and the distance from the upper end of the guide plate to the water surface of the liquid C are substantially equal. a. Thereby, the flow path of the liquid C which rises against the guide plate 34 and goes over the guide plate 34 toward the outlet has no neck, so that the pressure loss when the fluid C flows through the container can be reduced, and the test solution B Can be further reduced.

FIG. 3 shows a third embodiment of the present invention. In the embodiment of this figure, a baffle plate 35 is attached at a position facing the entrance 32 of the container 31. The liquid C entering from the inlet 32 directly hits the cell 21 due to the pressure, and the heat exchange was locally promoted, so that the temperature unevenness was easily generated. 21 can be prevented, and the occurrence of local temperature unevenness can be prevented.

Further, the liquid C hitting the baffle plate 35 is
Circulates along the baffle plate 35 toward the lower side of the container. Thereby, it is possible to prevent the vibration due to the water absorption from being transmitted to the cell 21. Therefore, it is possible to reduce the adverse effect of the vibration due to the collision with the liquid C on the light of the interferometer. In addition, the circulation of water is improved, and the temperature can be controlled evenly.

FIG. 4 shows a fourth embodiment of the present invention. In this embodiment, upper lids 36, 36 are provided on the left and right of the upper surface of the container 31, and can be opened and closed by hinges 37, 37, respectively.
Further, a handle 36a may be provided on the upper lid to facilitate opening and closing. When the upper lid 36 is opened, the inside of the container 31 can be seen, and in particular, the state of circulation of the liquid C can be visually confirmed. In addition, to prevent dust and the like from entering the liquid C, so that the room temperature does not affect the liquid C,
Normally, the upper cover 36 is closed. In addition, a hole 38 for inserting the test object A into the cell 21 may be formed substantially at the center of the upper surface of the container 31.

FIGS. 5 and 6 show a fifth embodiment of the present invention. In this embodiment, the cylindrical body 22 is attached to the side surface of the cell 21, the tip of the cylindrical body 22 is opened on the upper surface of the container 31, and the thermometer 23 can be inserted therefrom. With such a configuration, the temperature of the test solution B in the cell 21 can be measured at any time. FIG. 7 is a view showing a sixth embodiment of the present invention, and FIG. 8 is a perspective view thereof.
In this embodiment, a lid 24 is provided at the upper opening of the cell 21. When the measurement device is not used, plugging the cell 21 can prevent dust and the like from entering the cell.

[0035]

According to the present invention as described above,
A container that immerses almost the entire cell in a liquid outside the cell, an inlet for the liquid formed in the container, an outlet, and a guide plate disposed at a position facing the outlet, the liquid being supplied by the guide plate. Since the liquid flows over the surface of the cell over a wide area, the liquid flowing under the cell is prevented from flowing directly to the drain, and the liquid is circulated along the guide plate to the upper side of the container before draining. Head to mouth. For this reason, the liquid
It can be circulated better in the container. Thereby,
The temperature control of the test object can be performed more quickly without unevenness, and more accurate interference measurement can be performed. In addition, it is possible to avoid the influence of vibration due to the discharge of the liquid from being directly transmitted to the container containing the refraction liquid, reducing the adverse effect on the measurement of the test object, and achieving more accurate interference measurement. It becomes possible.

If the three distances, namely, the distance from the guide plate to the cell, the distance from the inner wall of the container on the outlet side, and the distance from the upper end of the guide plate to the liquid surface are almost equal, the pressure loss due to the circulation of the liquid is obtained. Can be reduced, so that temperature control with less temperature unevenness can be performed.

A baffle plate is provided at a position facing the inlet so that the liquid entering from the inlet does not directly hit the cell, so that the pressure of the liquid entering the container is reduced by the pressure of the container containing the refraction liquid. , Temperature unevenness can be reduced, and the influence of vibration can be eliminated.

If a monitoring window which can be opened and closed is provided in the container, the monitoring window can be opened only when necessary to check the operation status of the apparatus. Further, when unnecessary, it can be closed so that dust and the like do not enter. If the cell is provided with a cylinder that communicates with the inside and outside of the cell, and if the cylinder opens to the outside of the container, a thermometer is inserted from here to observe the temperature of the sample solution at any time while operating the machine. Becomes possible. Thereby, it can be confirmed that the machine is operating properly.
In addition, it is possible to immediately and correctly confirm that the refraction liquid has reached a desired temperature.

By using this lid when the temperature control device is not operating, it is possible to prevent dust or the like from entering the liquid having a refractive index substantially equal to that of the test object. This enables more accurate interference measurement.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a main configuration of an apparatus for measuring a refractive index distribution according to the present invention, wherein FIG. 1A is a longitudinal sectional view, and FIG.

FIG. 2 is a sectional view showing a configuration of a main part of a second embodiment of the present invention.

FIG. 3 is a sectional view showing a configuration of a main part of a third embodiment of the present invention.

FIG. 4 is a top view showing a configuration of a main part of a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a configuration of a main part of a fifth embodiment of the present invention.

FIG. 6 is a top view showing a configuration of a main part of a fifth embodiment of the present invention.

FIG. 7 is a sectional view showing a configuration of a main part of a sixth embodiment of the present invention.

FIG. 8 is a perspective view showing a configuration of a main part of a sixth embodiment of the present invention.

FIG. 9 is a plan view showing a configuration of an apparatus for measuring a refractive index distribution.

FIG. 10 is a diagram illustrating the principle of CT analysis.

[Explanation of symbols]

 A test object B reagent solution C liquid a reference wave b test wave 1 light source 21 cell 25 entrance window 27 emission window 31 container

Claims (7)

[Claims] 1. An interferometer that divides coherent light from the same light source into a reference wave and a test wave, and superimposes them on each other to form an interference fringe. A cell having an entrance window and an exit window which are held in the same sample solution and are parallel to each other, a container which is provided outside the cell and contains a liquid which immerses almost the entire cell, and a container provided above one side of the container. It has an inlet for the formed liquid, an outlet formed below the other side of the container, and a guide plate disposed at a position facing the outlet in the container, and the liquid in the container is arranged by the guide plate. An apparatus for measuring a refractive index distribution, characterized in that it flows over the surface of the cell over a wide range. 2. The method according to claim 1, wherein the distance from the guide plate to the cell, the distance from the guide plate to the inner wall of the container on the outlet side, and the distance from the upper end of the guide plate to the liquid surface are substantially equal. The apparatus for measuring a refractive index distribution according to claim 1. 3. The refractive index distribution according to claim 1, wherein a baffle plate is provided at a position facing the inlet so that liquid entering from the inlet does not directly hit the cell. measuring device. 4. The apparatus for measuring a refractive index distribution according to claim 1, wherein a monitoring window that can be opened and closed is provided in the container. 5. The refractor according to claim 1, wherein the cell is provided with a cylindrical body communicating between the inside and the outside of the cell, and the cylindrical body is opened to the outside of the container. Measurement device for rate distribution. 6. The apparatus for measuring a refractive index distribution according to claim 1, wherein an openable / closable lid for injecting the reagent is provided in the cell. 7. The refractive index distribution according to claim 1, wherein the transmitted wavefront is measured successively while rotating the object, and the refractive index distribution of the object is measured using CT analysis. Of measuring the refractive index distribution using the measuring device of the present invention.