JPH09325086A - Method for measuring index of refraction of prism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a prism and measure an index of refraction accurately by arranging a plurality of prisms of the same material having the same vertical angle in parallel to an optical axis of a measurement light to obtain a specific thickness and measuring the index of refraction. SOLUTION: A plurality of prisms of the same material having the same vertical angle are arranged in parallel to an optical axis of a refractive index measurement light to measure a refractive index. That is, a plurality of thin prisms are manufactured under the same conditions and bound. A total breadth (thickness) of the bound prisms is 5-20mm. A bright slit image is obtained if the thickness is at least 5mm or larger. The vertical angles of the prisms are necessary to agree with each other. Since the plurality of prisms bound to a required thickness are arranged to measure the refractive index, a width of a slit is increased and a brightness required for correct measurements is obtained. Accordingly, measurement accuracy necessary for measuring the refractive index of the prism is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the refractive index of a prism.

[0002]

2. Description of the Related Art Conventionally, the refractive index has been measured as a method for evaluating the optical properties of optical materials. Since the refractive index varies depending on the wavelength of light passing through the optical material, it is important to accurately grasp the refractive index of the material in the optical design of the optical device. Generally, it is represented by the refractive index nd with respect to the d-line of the spectrum of helium, but it is natural to perform optical design with the refractive index at the wavelength of light used in the optical equipment.

For example, in an optical material used in a semiconductor manufacturing apparatus, light used is monochromatic light having a narrow wavelength range,
g-line and i-line. Since a high resolution is required for a lens for a semiconductor manufacturing apparatus, the depth of focus is very small. Since the difference in the value of the refractive index used in the optical design stage appears as an error in the imaging position, it is necessary to measure the refractive index of the optical material used for the lens with extremely high accuracy.
The same type of glass has a different refractive index every time the glass is melted, and there may be a variation within ± 0.0005 with respect to the standard value. Therefore, a sample is prepared for each melting and the refractive index is measured.

On the other hand, many plastics have been used as optical materials for lenses and prisms used in 35 mm cameras and video cameras because of their low specific gravity, ease of molding and suitability for mass production. The refractive index of plastic is generally shown as a catalog value of a plastic manufacturer up to three decimal places, and the value below that varies depending on the production lot. Therefore, it is necessary to prepare a sample for each lot of the material purchased from the plastic maker and measure the refractive index.

[0005] As a method of measuring the refractive index, a minimum declination method, an autocollimation method, a V-block method, a Pulfrich method and the like are conventionally known. When measuring the refractive index of an optical material using the above-mentioned method, most of them measure the optical material to be measured as a sample by making a predetermined triangular prism as shown in FIG.

[0006]

However, the conventional measuring method has the following problems. That is, in order to perform accurate measurement, the measurer must accurately match the slit image with the measurement mark, but for this purpose, a bright slit image is required. The present invention
It is an object of the present invention to solve this problem and measure the refractive index with ease and accuracy in forming a prism.

[0007]

In order to solve the above problems, the present invention provides a method for measuring the refractive index of a prism, in which a plurality of prisms made of the same material and having the same apex angle are arranged with respect to the optical axis of the refractive index measurement light. It was decided to measure in parallel. By doing so, a prism having a desired thickness is obtained, and the refractive index is measured by the prism.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the width of the prism must be at least 5 mm or more to obtain a bright slit image. However, it is very difficult to prepare a prism having a thickness of 5 mm or more and having good homogeneity without distortion or sink marks. In view of this, the present inventors obtained a prism as described below and prepared a prism having good homogeneity.

By the way, the prism in the embodiment of the present invention is made of a thermoplastic resin or a thermosetting resin,
It is molded by injection molding, compression molding and casting. Then, the prism obtained by molding has a width of 1 to 3 mm to obtain a prism having no distortion or sink mark. Such a resin prism free from distortion and sink marks can be obtained by molding thinly or compactly. Therefore, the present invention utilizes this fact to obtain a prism free from distortion and sink marks. The width of the prism is the width with respect to the surface on which the light for measuring the refractive index is incident and the surface from which the light is emitted.

A plurality of thin prisms thus obtained were manufactured under the same conditions and bundled as shown in FIG. The total width of the bundled prisms was at least 5 mm to 20 mm. At least 5 mm or more, bright
This is because a lit image can be obtained. In addition, each pre
It is important that the apex angles in
is there.

Since the width of the slit can be widened by arranging a plurality of prisms bundled up to a desired thickness and measuring the refractive index, the brightness required for accurate measurement can be obtained. As a result, the measurement accuracy necessary for measuring the refractive index of the prism can be obtained. It can also be obtained by cutting a prism shape from a small piece or a thin plate of thermoplastic resin or thermosetting resin.

The method of bundling a plurality of thin prisms is as follows when the refractive index of the prism is measured by the well-known V block method. A V block excavated into a V shape by a desired thickness is used, and the manufactured prism is put in the groove of the excavated V block.
At this time, it is possible to bring the respective prisms into close contact with each other by inserting thin prisms into the groove of the V block until the number of insertable prisms reaches a maximum. Further, when the prism is inserted into the V block, the prism is inserted while supplying the immersion liquid to the V block. This is because the contact surface between the V block and the prism can be brought into optical contact by supplying the immersion liquid to the V block.

In addition, the bundled prism can be used as a vise.
Therefore, you can bundle them . However, at this time
Must be bundled with a force that does not cause distortion in the prism itself.
Must. By the way, in these prisms,
The surface where the rhythm and the prism come into contact is preferably smooth.
Good. If the surface where the prisms contact each other is rough,
The transmission of light in that part cannot be expected. After all, that
Since the part does not function as an optical path, a sufficient amount of light can be obtained.
It's gone.

In this way, each thin prism is
By bundling and measuring the optical properties, the bending of the substance
The folding rate can be accurately measured.

[0015]

EXAMPLES Next, an example of the embodiment of the present invention will be described. In one embodiment of the present invention, a case where the refractive index is measured by the V block method will be described. FIG. 3 is a schematic configuration diagram of a refractive index measuring device using the V block method. Light source 1, filter 2, slit 3,
The collimator 4 and a glass V block (hereinafter referred to as a V prism) 5 having a known refractive index with respect to the wavelength of the light source 1.
And a telescope 6 having an objective lens, a focusing plate having a marked line on the focal plane of the objective lens, and an eyepiece lens capable of magnifying and observing an image formed on the focusing plate. The portion of the V prism 5 on which the sample 7 is placed is 90 degrees.
Therefore, if one corner of the triangular prism to be sample 7 is
It is necessary to mold it to 0 degrees ± 1 minute. Sample 7 is sample 7
It is placed on the V prism 5 through the contact liquid whose refractive index is adjusted to the same level as the above. Even the sample 7 divided into several pieces can be stably placed due to the surface tension of the contact liquid. The difference in refractive index between the sample 7 and the contact liquid may be within 0.02.

The triangular prism to be the sample 7 is molded by a dedicated die. The shape of the triangular prism is a triangular prism having an angle of 90 degrees and two isosceles triangles each having two sides forming the angle of 20 mm on opposite surfaces and a width of 3 mm. As the sample 7, an array of three triangular prisms is used. The situation is shown in FIG. In the measurement, the three triangular prisms are arranged in parallel on the V prism in the incident direction of the measurement light.

A spectrum lamp is used as the light source 1, and a filter 2 extracts light having a wavelength required for measurement. Since the slit 3 is at the front focus position of the collimator 4, the light passing through the slit 3 becomes a parallel light flux and enters the V prism 5. The light transmitted through the V prism 5, the sample 7, and the V prism 5 is refracted by passing through the V prism 5 and the sample 7, and is emitted at an angle inclined by γ degrees from the emission surface. The observer looks into the eyepiece of the telescope 6 and looks at the V prism 5
The telescope 6 is moved until the slit image of the further emitted light and the marked line of the telescope 6 match. The angle γ at the time of coincidence is read.

The refractive index nλ of the sample 7 at the wavelength λ is obtained from the refractive index Nλ of the V prism 5 and the angle γ read by the measurement by the following formula.

[0019]

[Equation 1]

Table 1 shows an example of the measurement result of the refractive index of the plastic measured by this method. Measurement wavelength is d line 58
It is 7.6 nm.

[0021]

[Table 1]

Although only the V-block method has been described in this embodiment, the present invention is not limited to this.
Other measurement methods using a prism as a sample, such as the minimum deviation method and the autocollimation method, are similarly effective.

[0023]

According to the refractive index measuring method of the present invention, since it is possible to measure with a thin prism, it is possible to easily form a good prism without distortion and sink marks, and to obtain a bright slit image by arranging a plurality of prisms. , Accurate measurement is possible. Also, if the prism is thin, it adapts quickly to the measurement environment, so there is an advantage that measurement can be performed immediately after bringing it into the measurement room.

Furthermore, according to the present invention, it is possible to measure even a small sample which could not be measured in the past.

[Brief description of drawings]

FIG. 1 is a diagram showing a state during measurement of a prism in an example of the present invention.

FIG. 2 is a diagram showing a configuration of a refractive index measuring device.

FIG. 3 is a diagram showing an example of the shape of a prism in a conventional measuring method.

[Explanation of symbols]

 1 ... Light source 2 ... Filter 3 ... Slit 4 ... Collimator 5 ... V prism 6 ... Telescope 7 ... Sample

Claims (3)

[Claims] 1. A method of measuring a refractive index of a prism, wherein a plurality of prisms having the same apex angle and made of the same material are arranged in parallel to the optical axis of the refractive index measuring light in measuring the refractive index of the prism. 2. The individual thickness of the plurality of prisms is 3
The method for measuring the refractive index of a prism according to claim 1, wherein the method is less than or equal to millimeters. 3. The method for measuring the refractive index of a prism according to claim 1, wherein the total thickness of the prisms after being arranged is 5 mm or more.