JPH02205756A - Apparatus and method for measuring double refraction - Google Patents

Abstract

PURPOSE:To make it possible to measure double refraction values of a double refraction member at many points in a short time highly accurately by inserting the double refraction member between a first polarizing plate and a second polarizing plate, and inputting a bundle of rays in a condensed pattern into the second polarizing plate from the first polarizing plate. CONSTITUTION:In a measuring apparatus 10, a double refraction member 4 can be inserted between a first polarizing plate 1 and a second polarizing plate 2 which are set in a pattern wherein the polarizing directions are orthogonally intersected. A bundle of rays which is generated in condenser lenses 7 and has the equal distribution of the amounts of light in a condensed pattern is inputted into the second polarizing plate 2 from the first polarizing plate 1 under the state wherein a focal point is positioned at a certain measuring point in the member 4. A plurality of the condenser lenses 7 are continuously arranged in the specified direction along the member 4. The incident light path of a bundle of incident rays 16 is switched to the side of the neighboring lens 7 by the rotation of a rotary mirror 17. The bundle of rays 16 is vertically inputted into the lenses 7 through correcting prisms 18. In this way, the bundle of rays is sequentially moved for every neighboring measuring point of the member 4. The amount of the light which has been transmitted through the polarizing plate 2 is measured for every measuring point with a photoelectric transducer element train 12.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a birefringence measuring device and method.

[Prior Art] Conventionally, for example, in the manufacturing process of magneto-optical disks, it has been necessary to reduce the birefringence value, which is a factor that deteriorates the signal-to-noise ratio (SN ratio), which is an evaluation item of the disk. It is desired to establish a method for measuring this value.

Here, the birefringence value includes an in-plane birefringence value for a light ray that is perpendicularly incident on the surface of the birefringent member, and a thickness direction birefringence value for a light ray that is obliquely incident on the surface of the birefringent member.

The conventional method for measuring in-plane birefringence is called the Senarmont method, and is as follows: First, collimated laser light is transmitted through a polarizing plate to create linearly polarized light in the same direction as the polarizing direction of the polarizing plate. Linearly polarized light is transmitted at 45 degrees to the optical axis of the disk in the 0th order.

At this time, the linearly polarized light becomes elliptically polarized light due to the influence of the birefringence of the disk, but the plane of polarization of the elliptically polarized light does not rotate.However, when this elliptically polarized light is transmitted through a 174-wave plate, the plane of polarization changes. It rotates and becomes linearly polarized light again. This rotation angle changes depending on the magnitude of birefringence; the greater the birefringence, the greater the rotation angle.

Therefore, the in-plane birefringence value can be measured by making a light beam perpendicularly incident on the surface of the birefringent member and measuring the rotation angle with an analyzer.

In addition, the conventional method for measuring birefringence in the thickness direction is to make a light beam that is tilted at a certain angle with respect to the normal to the surface of the birefringent member enter the birefringent material all around, and to measure the maximum and minimum values of the birefringence obtained. The birefringence value in the thickness direction can be measured by substituting the angle of incidence into a complex retardation calculation formula.

[Problems to be Solved by the Invention] However, the conventional method for measuring in-plane birefringence using the Senarmont method has the following problems.

■It is necessary to rotate the analyzer for each measurement point of the birefringent member, which requires complicated equipment and takes a long time to measure.

■Since it amplifies and clarifies the light intensity distribution of linearly polarized light measured by an analyzer, measurement errors are likely to occur.

(2) It is difficult to complete measurements in a short time for a large number of measurement points on a birefringent member.

Further, the method of measuring the birefringence value in the thickness direction using the conventional retardation calculation formula has the following problems (1) and (2).

■A large number of birefringence values at oblique incidence are measured, and more complex calculations are required, and the measurement time is long.

(2) It is difficult to complete measurements in a short time for a large number of measurement points on a birefringent member.

In addition, regardless of the measurement method using the conventional Senarmont method or the measurement method using the retardation calculation formula,
It is not possible to simultaneously measure both the in-plane birefringence value and the thickness direction birefringence value in one measurement operation.

An object of the present invention is to measure the birefringence value of a birefringent member in a short time and with high precision using a simple device.

Another object of the present invention is to simultaneously measure both the in-plane birefringence value and the thickness direction birefringence value by one measurement operation.

Another object of the present invention is to measure birefringence values at multiple points of a birefringent member in a short time.

[Means for Solving the Problems] The birefringence measurement device of the present invention according to claim 1 includes a birefringence member installed between a first polarizing plate and a second polarizing plate whose polarization directions are set to be perpendicular to each other. A bundle of light rays with an equal light intensity distribution in a condensing shape is directed from the first polarizing plate to the second (i! and an optical system capable of measuring the amount of light rays making up the condensed ray bundle after passing through the second polarizing plate for each incident angle with respect to the measurement point of the birefringent member. It is designed to be configured.

According to the second aspect of the present invention, a birefringent member can be inserted between the first polarizing plate and the second Ii light plate whose polarization directions are set to be orthogonal to each other, and the beam bundle is condensed and has an equal light quantity distribution. The above-mentioned birefringent member causes the light rays forming the condensed ray bundle to enter the birefringent member from the first polarizing plate toward the second polarizing plate in a state where the focal point is set to be located at a certain measurement point within the birefringent member. constitute an optical system capable of measuring the amount of light after passing through the second polarizing plate of the light rays for each incident angle with respect to the measurement point, and the measured value of the light amount and the birefringence value for each of the incident angles in the optical system. The above-mentioned correlation is determined in advance, and the above-mentioned light amount measurement value and the above-mentioned correlation at each above-mentioned incident angle at a certain measurement point of the birefringent member measured with the above-mentioned optical system in which the birefringent member as the measurement target is installed this time. The birefringence value for the measurement point of the birefringent member is determined from the above.

The present invention according to claim 3 provides that the correlation between the light quantity measurement value and the birefringence value for each predetermined incident angle in the optical system is determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, and this time The value of the birefringent member can be determined from the above-mentioned light intensity measurement value for each incident angle and the above-mentioned correlation at a certain measurement point of the birefringent member measured by the above-mentioned optical system in which the birefringent member as the measurement object is inserted. The in-plane birefringence value and the thickness-direction birefringence value for a measurement point are determined.

The present invention as set forth in claim 4 provides a method for relatively moving the condensed light beam in a specific direction along the birefringent member, and for each of the incident angles of the light rays constituting the condensed light beam. The amount of light after the light beam passes through the second polarizing plate is measured at each measuring point of the birefringent member.

According to a fifth aspect of the present invention, both the condensed light beam and the birefringent member are moved together, and their moving directions are perpendicular to each other.

[Action] According to the present invention as set forth in claim 1.2, there are the following effects (1) and (2).

■Using an optical system that includes a light source, a condensing means, first and second polarizing plates, and a light receiving device, a condensed bundle of light rays enters from the first polarizing plate and forms this bundle of rays. For each angle of incidence of the rays on a certain measurement point of the birefringent member, the second
The birefringence value of the birefringent member can be measured by a simple operation of measuring the amount of light after passing through the polarizing plate. Therefore, birefringence values can be measured in a short time using a simple device.

■Since the birefringence value is determined by measuring the amount of light,
Birefringence values can be measured with higher accuracy than the Senarmont method, which measures light intensity distribution.

According to the present invention as set forth in claim 3, there is the following effect (2).

■Since the correlation between the measured light intensity value and the birefringence value for each incident angle was determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, the measured light intensity distribution for each incident angle, which is the measurement result this time, is suitable. By searching for different parameters, both the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously in one measurement operation.

According to the present invention as set forth in claim 4, there is the following effect (2).

■Measure the birefringence value, in-plane birefringence value, and thickness direction birefringence value at each measurement point of the birefringent member into which the condensed light beam is incident, by performing multiple measurements along the movement path of the light beam. The birefringence value, in-plane birefringence value, and thickness direction birefringence value of each point of the birefringent member (for example, each point in the radial direction of a magneto-optical disk) can be measured in a short time by moving the points sequentially.

According to the present invention as set forth in claim 5, there is the following effect (2).

■Measurement of the birefringence value, in-plane birefringence value, and thickness direction birefringence value for each measurement point of the birefringent member into which the condensed light beam is incident is carried out along the movement path of the light beam that is orthogonal to each other. and a plurality of measurement points determined on both the movement path of the birefringent member, and the birefringence value or In-plane birefringence value and thickness direction birefringence value can be measured in a short time.

[Example] Fig. 1 is a schematic diagram showing an example of the present invention, Fig. 2 is a schematic diagram showing the principle of the present invention, and Fig. 3 is a diagram showing the relationship between the measured light amount and the birefringence value in the present invention. It is a line diagram.

First, regarding the principle behind the establishment of the present invention, Figures 2 (A) and (B)
, (C).

As shown in FIG. 2(A), a pair of first and second polarizing plates 1
．． 2 polarization directions IA and 2A are set to be perpendicular to each other,
The collimated light beam is passed from the first polarizing plate 1 to the second polarizing plate 2.
Make the light incident perpendicularly to the target. At this time, the first polarizing plate 1
The incident light oscillates in multiple directions like natural light, and is polarized by the first polarizing plate 1 to produce linearly polarized light 3, but this linearly polarized light 3 does not pass through the second polarizing plate 2.

However, as shown in FIG. 2(B), the first polarizing plate 1 and the second polarizing plate
When a birefringent member 4 is inserted between the polarizing plates 2, linearly polarized light 3 polarized by the first polarizing plate 1 passes through the birefringent member 4 and becomes elliptically polarized light 5, and a part of the elliptically polarized light 5 becomes second polarized light. The light passes through the plate 2 and becomes leaked light 6. The amount of this leaked light 6 changes depending on the magnitude of the birefringence value of the birefringent member 4, and increases as the birefringence value increases.

Furthermore, when the incident light on the surface of the birefringent member 4 is incident obliquely than from the perpendicular direction, the amount of leaked light 6 and the birefringence value of the birefringent member 4 become larger, and the larger the incident angle Amount of leaked light 6 and birefringent member 4
The birefringence value increases (see FIG. 2(C)). The change in birefringence value due to the difference in incidence angle is determined by the in-plane birefringence value and the thickness direction birefringence value.

In other words, a condensing lens 7 as shown in FIG. 2(C) is used to condense a bundle of rays with an equal light quantity distribution so that the focal point is located at a certain measuring point of the birefringent member 4. By making the angles of incidence of each of the light rays constituting the condensed light beam on the birefringent member 4 different from each other and reading the change in the amount of leaked light 6 corresponding to each of the light rays, the This means that the refraction value, as well as the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously.

That is, as in the present invention as set forth in claim 2, (1) the correlation between the measured light amount of the leaked light 6 and the birefringence value for each incident angle in the optical system consisting of the polarizing plate 1'4.2; If , is determined in advance, the birefringent member 4 measured by the above-mentioned optical system in which the birefringent member 4 to be measured this time is inserted.
The birefringence value of the birefringent member 4 for each incident angle at the measurement point can be determined from the light intensity measurement value for each incident angle at a certain measurement point and the above correlation.

In addition, as in the present invention as set forth in claim 3, (2) the correlation between the light quantity measurement value and the birefringence value at each predetermined incident angle in the optical system is determined by the in-plane birefringence value and the thickness direction birefringence value. is determined as a parameter, and the birefringence can be calculated from the above-mentioned light intensity measurement value for each incident angle and the above-mentioned correlation at a certain measurement point of the birefringent member 4 measured with the above-mentioned optical system in which the birefringent member 4 is installed this time. The in-plane birefringence value and the thickness direction birefringence value for the measurement point of the member 4 can be determined.

Next, an embodiment of the present invention will be described with reference to FIGS. 1(A) and 1(B).

In FIG. 1, 10 is a birefringence side determining device, 1 is a first polarizing plate, 2 is a second polarizing plate, 4 is a birefringent member such as an optical disk, 7 is a condenser lens, and 12 is a light receiving device. 13 is a rotating shaft, 14 is a chuck, 15 is a motor, 16 is an incident light beam, 17 is a rotating mirror, and 18 is a correction prism.

The birefringence measurement device 10 can insert a birefringence member 4 between a first polarizing plate 1 and a second polarizing plate 2 whose polarization directions are set to be orthogonal, and collect light generated by a condensing lens 7. The first polarizing plate 1 is set so that the focal point is located at a certain measuring point in the birefringent member 4, and the beam flux is uniform in light intensity distribution.
After the light rays constituting the condensed ray bundle are transmitted through the second polarizing plate 2 at each incident angle with respect to the measurement point of the birefringent member 4, The amount of light can be measured by the photoelectric conversion element array 12.

At this time, in the birefringence measuring device 10, the polarizing plate 1
．． 2. The correlation between the measured light amount and the birefringence value for each angle of incidence in the optical system composed of the condenser lens 7 and the photoelectric conversion element array 12 is determined in advance, for example, as shown in FIG. 3. Furthermore, this correlation is determined as a parameter for the in-plane birefringence value and the thickness direction birefringence value. The correlation shown in Figure 3 is that the in-plane birefringence value Δn, , = 12 nm
, the thickness direction birefringence value Δns=405n@ is used as a parameter.

This correlation is based on birefringence for which the birefringence value for each incident angle, in-plane birefringence value, and thickness direction birefringence value are known using a conventional birefringence measurement method such as the Senarmont method. The member is inserted between the first polarizing plate 1 and the second polarizing plate 2, and at that time, the amount of leaked light 6 (see Fig. 2) transmitted through the second polarizing plate 2 at each incident angle is measured by a photoelectric conversion element. It is determined by measuring column 12. At this time, the photoelectric conversion element array 12 photoelectrically converts the amount of received light and displays it as a voltage. The larger the output voltage of the photoelectric conversion element array 12, the larger the birefringence value.

Therefore, when the birefringent member 4 to be measured this time is inserted into the optical system of the birefringence measuring device 10, the amount of leakage light 6 transmitted through the second polarizing plate 2 at each incident angle at a certain measurement point. From the correlation between this light amount measurement value and the above-mentioned FIG. You can find the value.

Furthermore, the birefringence measuring device 10 includes a plurality of condensing lenses 7 arranged in succession in a specific direction along the birefringent member 4 (for example, in the same radial direction of the magneto-optical disk), and a rotating mirror 17.
The incident light beam 16 whose incident optical path has been switched to the side of the adjacent condensing lens 7 by the rotation of The generated condensed light beam is passed through a birefringent member,
4 in the above-mentioned specific direction, and the birefringent member 4, which is a bundle of light rays, is sequentially moved for each adjacent measurement point. At this time, the photoelectric conversion elements constituting the photoelectric conversion element array 12 are arranged in a line corresponding to each of the consecutively arranged total condensing lenses 7, and the light rays constituting the condensed beam bundle are For each incident angle, the amount of light after passing through the second polarizing plate 2 is measured by the photoelectric conversion element array 12 at each measurement point of the birefringent member 4.

Thereby, for example, the birefringence value, in-plane birefringence value, and thickness direction birefringence value at each point in the radial direction of the optical axis disk can be continuously measured.

The birefringence measurement device 10 also uses a chuck 14 to hold the birefringence member 4 (for example, the center of a magneto-optical disk) on the rotating shaft 1.
3, and by rotating this rotating shaft 13 with a motor 15, the birefringent member 4 is also moved in a direction perpendicular to the continuous arrangement direction of the condensing lens 7 (for example, in the circumferential direction of the magneto-optical disk). At the same time, the light intensity measurement by the photoelectric conversion element array 12 is repeated at each point in the moving direction, and at this time, the incident light beam 16 is switched to move in the continuous arrangement direction of the condenser lens 7 by rotation of the rotating mirror 17. The speed is set to be considerably higher than the rotational speed of the rotating shaft 13. Thereby, for example, the birefringence value, in-plane birefringence value, and thickness direction birefringence value at each point in the circumferential direction of the magneto-optical disk can be continuously measured.

The birefringence measuring device 10 uses the data of the light intensity measurement value obtained for each measurement point of the birefringence member 4 as the position of the measurement point (for example, the radial and circumferential position of the magneto-optical disk).
The above-mentioned birefringence value, as well as the in-plane birefringence value and the thickness direction birefringence value can be determined by data processing by a microcomputer. Thereby, for example, the birefringence value, in-plane birefringence value, and thickness direction birefringence value of the entire surface of the magneto-optical disk can be measured in a short time, and abnormal points can be easily found.

Next, the operation of the above embodiment will be explained.

■Using an optical system consisting of a light source, a condensing lens 7, first and second polarizing plates 1.2, and a photoelectric conversion element array 12, a condensed beam of light is incident from the first polarizing plate 1. However, the birefringence can be determined by a simple operation of measuring the amount of light after the light rays that make up this light beam have passed through the second polarizing plate 2 for each incident angle with respect to a measurement point of the birefringence member 4. The birefringence value of the member 4 can be measured. Therefore, birefringence values can be measured in a short time using a simple device.

■Since the birefringence value is determined by measuring the amount of light,
Birefringence values can be measured with higher accuracy than the Senarmont method, which measures light intensity distribution.

■Since the correlation between the measured light amount and birefringence value for each incident angle was determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, the measured light amount distribution for each incident angle, which is the measurement result, is compatible. By searching for the parameters,
Both the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously by one measurement operation.

■Measurement of the birefringence value, in-plane birefringence value, and thickness direction birefringence value at each measurement point of the birefringent member 4 into which the condensed light beam is incident is carried out at multiple points along the movement path of the light beam. By proceeding sequentially through the measurement points, the birefringence values, in-plane birefringence values, and thickness direction birefringence values at multiple points on the birefringent member 4 (for example, multiple points in the radial direction of the magneto-optical disk) can be measured in a short time.

■Measurement of the birefringence value, in-plane birefringence value, and thickness direction birefringence value for each measurement point of the birefringent member 4 into which a condensed beam of light is incident is performed by moving the beam of light orthogonally to each other. A plurality of measurement points determined both on the path and the path along which the birefringent member 4 moves are sequentially measured, and the measurement is performed at multiple points in the plane of the birefringent member 4 (for example, multiple points in the radial direction and circumferential direction of the magneto-optical disk). The refraction value, in-plane birefringence value, and thickness direction birefringence value can be measured in a short time.

In carrying out the present invention, a light source having a single wavelength, an equal output distribution, and a collimated light source is used.

Also, when generating a condensed bundle of rays with a condensing lens, the f value of the ray is! 3/2, the maximum incident angle is preferably 30 degrees, and the difference in birefringence experienced by incident light with an incident angle of 30 degrees is significant. On the other hand, if the angle of incidence is 30 degrees or more, the birefringence value becomes excessive, making measurement difficult, and reflection within the birefringent member makes it impossible to obtain proper transmitted light, which is not appropriate.

[Effects of the Invention] As described above, according to the present invention, the birefringence value of a birefringent member can be measured in a short time and with high precision using a simple device.

Further, according to the present invention, both the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously by one measurement operation.

Further, according to the present invention, birefringence values at multiple points of a birefringent member can be measured in a short time.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a schematic diagram showing the principle of the invention, and Fig. 3 is a diagram showing the relationship between the measured light amount and the birefringence value in the present invention. . DESCRIPTION OF SYMBOLS 1... 1st polarizing plate, 2... 2nd@light plate, 4... Birefringent member, 7... Condensing lens, 12... Photoelectric conversion element row, 13... Rotation axis, 17... Rotating mirror 18... Correction prism. Patent applicant: Sekisui Chemical Co., Ltd. Representative Hiroshi 1) Kaoru Figure 1 (A) Old Figure 1) Figure 2 (A) Old Figure 2)

Claims (5)

[Claims] (1) A first polarizing plate and a second polarizing plate whose polarization directions are orthogonal to each other.
A birefringent member can be inserted between the first polarizing plate and the first polarizing plate, with the focus set to be located at a certain measurement point within the birefringent member. from the second
For each incident angle of the light rays that are incident toward the polarizing plate and that constitute the condensed light beam with respect to the measurement point of the birefringent member,
A birefringence measuring device comprising an optical system capable of measuring the amount of light after the light rays pass through a second polarizing plate. (2) A first polarizing plate and a second polarizing plate whose polarization directions are orthogonal to each other.
A birefringent member can be inserted between the first polarizing plate and the first polarizing plate, with the focus set to be located at a certain measurement point within the birefringent member. from the second
For each incident angle of the light rays that are incident toward the polarizing plate and that constitute the condensed light beam with respect to the measurement point of the birefringent member,
An optical system that can measure the amount of light after passing through the second polarizing plate is configured, and the correlation between the measured value of the amount of light and the birefringence value for each angle of incidence in the optical system is determined in advance, and the object to be measured this time is The measurement point of the birefringent member can be determined from the above-mentioned light amount measurement value for each incident angle and the above-mentioned correlation about the measurement point of the birefringence member measured with the above-mentioned optical system in which the birefringence member is installed. Birefringence measurement method to find the birefringence value for. (3) The correlation between the light quantity measurement value and the birefringence value for each predetermined incident angle in the optical system is determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, and the birefringent member as the measurement target this time The in-plane birefringence at the measuring point of the birefringent member is calculated from the above-mentioned light intensity measurement value for each incident angle and the above correlation at a certain measuring point of the birefringent member, which is measured by the optical system equipped with the birefringent member. 3. The method for measuring birefringence according to claim 2, wherein a refraction value and a thickness direction birefringence value are determined. (4) relatively moving the condensed light beam in a specific direction along the birefringent member, and applying a second polarizing plate for each of the incident angles of the light rays constituting the condensed light beam; Claim 2: The amount of light after passing through is measured at each measurement point of the birefringent member.
Or the birefringence measurement method described in 3. (5) The birefringence measurement method according to claim 4, wherein both the condensed light beam and the birefringence member are moved, and the directions of movement thereof are perpendicular to each other.