JPH06241987A - Birefringence measuring device - Google Patents

Abstract

(57) [Summary] [Purpose] In addition to the function of accurately measuring the retardation of a high order with one measuring device, the function of measuring with high resolution regardless of the value of the phase difference and the refraction in the three-axis directions. Be able to perform at least one of the functions that can measure rates. [Structure] A filter 8, a polarizing plate 8 as a polarizer, a phase plate 36, and a sample 2 are arranged in this order from the condenser lens 6 side in the optical path of the measurement light from the light source 2 from the condenser lens 6 to the light receiving element 24.
2. A polarizing plate 18 as an analyzer is arranged. One of the five filters 8 is selected. Polarizing plate 14
And 18 are arranged in a parallel Nicol relationship and rotate integrally. The phase plate 36 is a Babinet-Soleil compensator, and is installed so that it can freely move in and out of the measurement optical path, and its retardation is adjusted. The sample 22 is held by a sample holding device so that the sample 22 can rotate in its plane and can be tilted about a straight line along the surface of the sample 22.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for measuring the retardation of a birefringent material.

[0002]

Stretched plastic sheets generally exhibit birefringence. When the materials are the same, if the sheet has a constant thickness, the degree of stretching can be determined by the degree of birefringence, and conversely, the thickness of a sheet having a constant degree of stretching can be determined. The birefringent sheet is used, for example, in a liquid crystal display device, and in that case also, it is necessary to measure the birefringence characteristic. In addition, the birefringence of a sheet material is measured for various purposes. In some cases, it is necessary to measure the triaxial refractive index of the sheet material.

Birefringence is represented by the refractive index of an ordinary ray and an extraordinary ray, and the difference between the two appears as a phase difference between the ordinary ray and the extraordinary ray transmitted through the sample. This phase difference is called retardation and is determined by the product of the difference between the two refractive indices and the material thickness. By measuring the retardation, the birefringence characteristics of the sheet-shaped sample can be known.

To measure the retardation of a sample,
The sample is placed between two polarizing plates arranged in parallel Nicols or orthogonal Nicols, and the polarizing plate and the sample are relatively rotated. Then, the method of recording the change of light transmitted through the polarizing plate and the sample and calculating the retardation from the result is adopted. Retardation is observed as a phase difference between an ordinary ray and an extraordinary ray that are incident on the sample in the same phase when the sample exits, and the phase difference is generally represented by (2nπ + δ). n is a natural number of 0, 1, 2, ... And is called an order. The thicker the sample, the larger the order n.
The change width of the transmitted light intensity, which is obtained by relatively rotating the polarizing plate and the sample, changes depending on δ. Δ can be directly obtained by measurement
However, there is no method for directly obtaining the order n.

Therefore, conventionally, the phase difference δ corresponding to the retardation is obtained for each of the two lights having different wavelengths. Then, while changing the order n in the order of 1, 2, 3, ...
The order n at which the sample thicknesses calculated for the light of one wavelength best match each other was taken as the correct value.

[0006]

However, in the above method, the difference Δ in the phase difference due to the light of two wavelengths can be obtained only up to 2π, and the difference is 2πm + Δ ′ (m is 1,
The integer m when 2, 3, ..., Δ'is 0 to 2π) cannot be determined. Therefore, the method is actually applicable to the 20th limit of the retardation order n, and it was not possible to measure a thick sample. Moreover, even if the order n of the retardation is 20 or more and the above m is 1, 2, ..., There is a possibility that the order may be determined with m = 0.

Further, when the retardation is in the vicinity of nλ / 2 (λ is the measurement wavelength), the phase difference is in the vicinity of nπ and the resolution is deteriorated, making it difficult to accurately determine the value of the retardation. INDUSTRIAL APPLICABILITY The present invention has a function of accurately measuring a high order retardation with a single measuring device, a function of high resolution measurement regardless of a value of a phase difference, and a function of measuring a refractive index in three axial directions. It is an object of the present invention to provide a composite measuring device capable of performing at least one of the above.

[0008]

[Means for Solving the Problem] In order to measure the retardation correctly even if the order becomes high, a phase plate is placed on the sample, and the sample and the phase plate are aligned with respect to light of one wavelength. Phase difference based on retardation is 2
It is set to an integral multiple of π, and in this state, light of another wavelength close to the above wavelength is used, and two polarizing plates (polarizer on the light source side and detector on the detector side are used to keep the polarization direction constant. (Photon) is rotated relative to the sample between them, and the relationship between the maximum value and the minimum value of the transmitted light intensity at that time is applied to the order of the retardation created in advance and this relationship. , Determine the order of retardation of the sample and then get the correct retardation.

In order to measure the retardation with good resolution even when the phase difference between the ordinary ray and the extraordinary ray is near nπ, a plate with known retardation, for example, a 1/4 wavelength plate is used as the optical axis of the refractometer. It is provided so that you can go in and out. In order to automatically increase the resolution when the phase difference is in the vicinity of nπ, a means for detecting that the phase difference is in the vicinity of nπ is provided, and a plate with a known retardation based on the result of the means, for example, The quarter wave plate is automatically inserted on the optical axis of the refractometer. Therefore, the sample is placed between two polarizing plates whose polarization directions are kept constant, the two polarizing plates are rotated relative to the sample, and the two polarizing plates and the three of the samples are transmitted. In the measuring device of the method of determining the retardation of the sample from the maximum value and the minimum value of the intensity of the light, the ratio or difference between the maximum value and the minimum value of the transmitted light intensity is within the predetermined reference range. The detection means for detecting whether or not, and whether or not the ratio or the difference between the maximum value and the minimum value of the transmitted light intensity described above is within a predetermined reference range, the retardation is known like a quarter wave plate. Means for inserting and removing the plate between the above two polarizing plates so as to overlap the sample, means for detecting the azimuth of the sample when giving the maximum value of the transmitted light intensity, that is, the azimuth of the optical principal axis, Test the orientation of the optical principal axis of a known plate. When the ratio or difference between the maximum value and the minimum value of the transmitted light intensity by the means for matching with the azimuth of the optical main axis of the detection means is within the reference range, the retardation known plate is removed from the measurement optical path. Seek retardation at
When the ratio or difference between the maximum value and the minimum value of the transmitted light intensity is not within the reference range, the retardation known plate is overlapped with the sample by aligning the optical principal axis of the plate with the azimuth of the optical principal axis of the sample and transmitting again. A data processing device for detecting the maximum value and the minimum value of the intensity and obtaining the retardation is provided.

In order to measure the refractive index of the sample in the three axial directions, the sample can be rotated in its plane, and means for tilting the sample about a straight line along the surface of the sample is provided. The refractive index is measured while the sample is rotated and tilted by a certain angle.

[0011]

First, the method of measuring retardation will be described. In FIG. 1A, both x and y axes indicate optical principal axes in two orthogonal directions parallel to the sheet surface of the sample, and the direction of arrow C indicates the polarization directions of two polarizing plates arranged in parallel Nicols with the sample in between. ing. The measurement light enters the sample through the upper polarizing plate. The vector indicated by arrow C represents the amplitude vector of the light that enters the sample through the upper polarizing plate. The light represented by the vector C is divided into a y-direction component Y (called an ordinary ray) and an x-direction component X (called an extraordinary ray) and travels in the sample. The components Ax and Ay of the amplitude vectors X and Y in the vector C direction are transmitted through the lower polarizing plate of the sample. At this time, the amplitude vectors Ax and Ay transmitted through the sample
1B, a phase difference δ occurs as shown in FIG. 1B. A composite of two lights of amplitudes Ax and Ay having the phase difference δ (the directions of spatial vectors are the same) is the amplitude of the light transmitted through the lower polarizing plate of the sample, and this is expressed as A, When the light intensity is I, I = A ² = Ax ² + Ay ² + 2Ax Aycosδ (1) δ = 2πR / λ (where R is the retardation and λ is the wavelength of the measurement light in air)

Further, as Io incident light intensity on the sample, the azimuth angle of the amplitude vector ^{φ, Ax = Xsinφ = Csin 2} φ Ay = Ycosφ = Ccos 2 φ which (1) Taking into equation, C = Io Therefore, I = Io {sin ⁴ φ + cos ⁴ φ + ² sin ² φcos ² φcos δ}. When this equation is arranged, I / Io = 1-sin ² 2φ (1-cosδ) / 2 (2) Equation (2) has a maximum of I = Io when sin2φ = 0.
Becomes Further, the expression (2) becomes minimum when sin2φ = 1, and at this time, I / Io = (1 + cosδ) / 2. That is, the sample is relatively rotated between two polarizing plates arranged in parallel Nicols, the transmitted light intensity pattern as shown in FIG. 2 is measured, and the maximum transmitted light intensity is Io and the minimum transmitted light intensity is measured. Is Im, cos δ = 2Im / Io−1 (3), and the cos of the phase difference δ is obtained.

Next, a method of determining the order n will be described.
From the equation (3), Im = Io (1 + cosδ) / 2, and when the order n is introduced into this, Im = Io (1 + cos (2nπ + δ)) / 2 (4), and the value of Im is 0. It is a value that changes with Io. When the variation of Im is illustrated by taking the retardation R on the horizontal axis, a sine waveform A as shown in FIG. 3 is obtained. The order n increases by 1 for each cycle of this waveform. When the wavelength of the measuring light of the waveform A in air is λ _1, and a similar curve is drawn for the measuring light having a slightly different wavelength (wavelength λ _{2 in} air), the sine waveform B in FIG. 3 is obtained. The waveforms A and B have slightly different periods. Here, the phase plates are overlapped and the wavelength λ
The light of ₁ is moved so that the apparent phase difference based on the retardation is 0, that is, to the position of Im = Io in FIG. And the wavelength λ with slightly different wavelength
Im is calculated for the light of ₂ . This is the waveform A in FIG.
Is to obtain Im by the light of wavelength λ ₂ when the maximum value is obtained. That is, in FIG. 3, the values of a, b, c ... Are calculated. When the values of Im in a, b, c, ... Of waveform B are connected, a curve indicated by C is obtained, and the order is n.
Becomes larger and decreases monotonically. The waveforms A and B become 0 in the order in which they are exactly opposite in phase, and thereafter, they start to increase monotonically.

Since the measured value of Im varies depending on the measurement conditions such as the intensity of the light source, in practice Im /
It is better to use Io or (Io-Im) / Io. Im
The value of / Io is a function of the order n, and the order at which Im / Io becomes 0 is determined by the wavelengths of the two measurement lights.
If the relationship between (or (Io-Im) / Io) and n is obtained, n can be determined from the measured value of Im / Io (or (Io-Im) / Io).

The order n can be determined as follows. Let cos δ be C ₁ when the phase plates are overlapped so that the apparent phase difference based on the retardation is 0 for the light of wavelength λ ₁ . Next, in place of the measuring light of wavelength λ ₂ , the polarizing plates 14 and 18 are rotated to measure the transmitted light intensity, and the ratio Im / Io of the maximum value Io and the minimum value Im of the pattern of FIG. And call it C ₂ . C
Substituting ₂ and C ₁ into the following relational expression obtained from FIG. 3,
The order candidate n (even number) is determined. C ₂ = C ₁ · sin (π / 2− (n / 2) (λ ₂ −λ ₁ ) 2π / λ ₂ ) (5) Also, using the measurement light of wavelength λ _{1 and} the measurement light of wavelength λ _2. Even if a graph showing the relationship between the order n and Im / Io is obtained in advance and the ratio Im / Io at the measurement light of the wavelength λ ₂ is applied to the graph, the order n can be obtained on the diagram. Good. It suffices to obtain a plurality of values for the order candidates while sequentially changing the measurement wavelengths, and to determine one n from them, for example, by a majority vote.

Once the order n has been determined, when the retardation increment r of the phase plate which makes the apparent phase difference based on the retardation 0 for the light of wavelength λ ₁ is known, The required retardation can be calculated as nλ ₁ −r. If the retardation increment r of the phase plate is not known, the polarizing plate is rotated once relative to the sample with the phase plate removed from the measurement optical path, and measurement light of wavelength λ ₁ is used. When the transmitted light is measured, the retardation R of the sample can be obtained in the range of 0 to 2π, and thus the retardation of the sample can be obtained as (n-1) λ ₁ + R using the determined order n. . Also, for each measurement wavelength, create a matrix that shows the correspondence between the order candidates and the retardation, and use the order in which the retardations match between the measurement wavelengths as the true order, and also the retardation at that time. You may do it.

The relationship between Im / Io and the order n is as follows. Now, the wavelengths of the two measurement lights are λ ₁ and λ _2, and the refractive indices of the two optical principal axes of the sample are ν ₁ and ν ₂ . Although the refractive index has wavelength dependency, in this case, since the wavelengths λ ₁ and λ ₂ are close to each other, the change in the refractive index at both wavelengths can be ignored. And measured at a wavelength lambda ₁ of the light, and the thickness of the first time in FIG. 2 pattern thickness of the sample was gradually increased from 0 becomes a circle and _{S, R = S (ν 1} -ν 2) = Λ ₁ (6) At this time, the phase difference δ in the measurement with the light of the wavelength λ ₂ is δ = 2πS (ν ₁ −ν ₂ ) / λ ₂ = 2π + e. When the thickness of the sample is an integer n times S, the phase difference based on the retardation for light of wavelength λ ₁ is apparently 0.
And the order is n. At this time, the phase difference based on the retardation with respect to the light of the wavelength λ ₂ is nδ = 2πn + ne, but the apparent phase difference is ne. This ne becomes 2π when the curve C in FIG. 3 draws one cycle. If n at this time is n ₀ , then 2πn ₀ S (ν ₁ −ν ₂ ) / λ ₂ = 2πn ₀ + n ₀ e = 2π (n ₀ +1). Therefore, using the equation (6), n ₀ λ ₁ / λ ₂ = n ₀ +1. Therefore, n ₀ = λ ₂ / (λ ₁ −λ ₂ ) ... (6), and n ₀ is determined only by the wavelength. n ₀ when λ ₁ and λ ₂ are close
Becomes a large order, and Im /
The order n can be determined from the measured value of Io. Order n
Is determined, the true retardation of the sample can be obtained from the apparent retardation R and nλ obtained from the actual measurement with the measurement light having the wavelength λ.

As can be seen from FIG. 3, cos δ is ± 1,
That is, when the phase difference δ is an integral multiple of π, the rate of change of cos δ with respect to the change of δ, that is, the rate of change of Im is small, so it is difficult to accurately obtain δ (and thus the retardation R). Conversely, in the vicinity of cos δ = 0, δ and Im change in proportion to each other, so that the measurement sensitivity of δ is good, and δ can be accurately determined. Therefore, when cos δ is in the vicinity of ± 1, cos δ is almost 0 when retardation is known, preferably when sheets having a phase difference δ of π / 2 are stacked so that the total phase difference is an odd multiple of π / 2. Therefore, the total retardation can be easily and precisely measured, and thus the retardation of the sample can be accurately obtained.

In a preferred embodiment of the present invention, whether or not to use a sheet of known retardation is set to a constant value D such that 0 <D <1, and when | cosδ |> D, the retardation is known. Use sheets. In the above description, it is assumed that neither the polarizing plate nor the sample absorbs light. However, since light is actually absorbed, Io in the formula (3) is not the incident light intensity but the transmitted light intensity. It is preferable to use the maximum value.

[0020]

EXAMPLE FIG. 4 shows a first example. White light source 2
The measurement light from is guided by the optical fiber 4 and is emitted as a parallel light flux by the condenser lens 6. In the optical path of the measurement light from the condenser lens 6 to the light receiving element 24, the filter 8, the polarizing plate 14 serving as a polarizer, the phase plate 36, in order from the condenser lens 6 side.
A sample 22 and a polarizing plate 18 as an analyzer are arranged. In the filter 8, five filters F1 to F5 having different transmitted light characteristics are arranged along the circumferential direction of the filter holding plate 10. A stepping motor 12 that rotates the filter holding plate 10 selects one of the filters and inserts it into the optical path of the measurement light. Of these filters 8, the filter F1 is a bandpass filter that allows light of a wavelength for retardation measurement to pass, and filters F2 to F2
Reference numeral 5 is a filter selected such that the transmission wavelength difference from the filter F1 increases in order from F2 to F5. The wavelength may be selected at any position on the optical path from the light source 2 to the light receiving element 24. Therefore, the position where the filter 8 is arranged is not limited to the position shown in FIG.

The polarizing plates 14 and 18 are arranged so that their polarization directions are parallel to each other, and are held by holding discs 16 and 20, respectively. The holding discs 16 and 20 are pulleys 28, which are fixed on a shaft 32 via belts 25 and 26, respectively.
30 and the shaft 32 is rotated by a stepping motor 34 so that both polarizing plates 1
4, 18 are rotated integrally. A mark of a reflector is provided on one side surface of the holding disk 16 on which the polarizing plate 14 is mounted, and the initial position of rotation of the polarizing plates 14 and 18 is detected by detecting this reflector with a photoelectric detector. To be detected. The measuring light of the wavelength selected by any of the filters F1 to F5 is transmitted through the polarizing plate 14 and is incident on the sample 22 installed between the polarizing plates 14 and 18, and the measuring light transmitted through the sample 22 is polarized. The light is incident on the light receiving element 24 through the plate 18 and is measured.

A phase plate 36 is provided between the polarizing plate 14 and the sample 22.
Is installed by a stepping motor 48 so that it can freely move in and out. As the phase plate 36, a Babinet-Soleil compensating plate is used so that its retardation is variable. A stepping motor 38 changes the retardation of the compensator 36. The azimuth of the phase plate 36 needs to be determined so that its optical principal axis is parallel to or orthogonal to the optical principal axis of the sample 22. for that reason,
The phase plate 36 is attached to a rotary table 40, the rotary table 40 is rotatably supported by a support table 42, and the phase plate 36 can be rotated by a stepping motor 46 via a belt 44.

An amplifier circuit is provided to amplify the detection output of the light receiving element 24, and an A / D converter is provided to convert the amplified output into a digital signal. 5
Reference numeral 0 represents the amplifier circuit and the A / D converter together. The output converted into a digital signal is taken into a computer 52 that also performs data processing and operation control of the measuring device, and the result of data processing is displayed on a CRT display device 54. The computer 52 processes the measurement data and sends a pulse to each motor 12, 34, 38, 46, 48 to control the rotation of each motor.

A method of determining the order n and measuring the retardation by the apparatus of FIG. 4 will be described. With the phase plate 36 inserted in the measurement optical path, first, the filter F1 (transmission wavelength λ ₁ ) that selects the light of the measurement reference wavelength is positioned on the measurement optical path. The azimuth of the phase plate 36 is set by driving the motor 46 so that the optical main axis of the phase plate 36 matches the optical main axis of the sample 22. When the sample 22 is, for example, a stretched sheet material, the optical principal axis of the sample 22 coincides with the stretching direction. Therefore, the optical principal axis of the phase plate 36 may coincide with the longitudinal direction of the sample 22. If the direction of the optical principal axis of a general sample is not known in advance, for example, if the sample is a semi-finished product that has already been punched from a sheet material into a predetermined shape,
First, with the phase plate 36 removed from the measurement optical path, the polarizing plate 1
The outputs of the light receiving element 24 with respect to the rotation angles of the polarizing plates 14 and 18 are obtained by rotating the lenses 4 and 18. The computer 52 takes in the output of the light receiving element 24 from the time when the reflector on the side surface of the holding disk 16 of the polarizing plate 14 is detected by the photoelectric detector, and rotates the polarizing plates 14 and 18 once. This result is as shown in FIG. 2 when displayed in song coordinates. From this output, the polarizing plate 14,
22.5 ° before and after each rotation angle of 18, that is, the difference between the outputs at two angular positions separated by 45 ° is calculated for each rotation angle of the polarizing plates 14 and 18,
There are eight corners where this difference becomes 0 (positions where positive and negative are inverted) during one rotation of, and there are four corners where the output of the light receiving element becomes maximum in the middle. These four angular positions are 90 ° apart from each other, and this direction is the optical principal axis of the sample 22 or a direction orthogonal to it.

Although it is possible to directly determine the maximum angular position of the light receiving element output, the change in the light receiving element output is small in the vicinity of the maximum light receiving element output, and the angular position cannot be accurately determined. It is better to obtain it from the angular position where is reversed. However, the method of detecting the optical principal axis of the sample is not limited to this.

After setting the optical principal axis of the phase plate 36 to coincide with the optical principal axis of the sample 22 and installing the phase plate 36 in the measurement optical path, the polarizing plates 14 and 18 are rotated to change the intensity of the sample transmitted light. The measurement is performed, and the relational data between the rotation angles of the polarizing plates 14 and 18 and the transmitted light intensity are captured. This relationship generally has a flower shape as shown in FIG.

Next, the polarization directions of the polarization plates 14 and 18 are shifted by 45 ° from the optical principal axis of the sample.
Rotate 8 to stop. While outputting a trigger to the A / D converter 50 and taking in, for example, 12-bit data, the phase plate 36 of the phase plate 36 is adjusted so that the value becomes substantially the same as the maximum value of the relationship between the rotation angle and the transmitted light intensity measured previously. Change the retardation. The transmitted light intensity reaches its maximum when the total retardation of the sample 22 and the phase plate 36 becomes an integral multiple of the wavelength of the measurement light transmitted through the filter F1. At this time, it means that the pattern of FIG. 2 becomes a circle.

With the phase plate 36 in that state, the polarizing plate 1
4, 18 are returned to the measurement start position, and the pattern showing the relationship between the rotation angle and the transmitted light intensity is measured again. If the pattern is not a perfect circle (Im / Io = 1), the motor 3
8 slightly change the retardation of the phase plate 36,
Repeat until the pattern is as close to a perfect circle as possible. Let cos δ at this time be C ₁ .

Next, the filter is changed to F2 (transmission wavelength λ ₂ ) and the polarization plates 14 and 18 are rotated to measure the transmitted light intensity. The maximum value Io of the pattern of FIG. 2 obtained at this time
And the minimum value Im. The ratio Im / Io to co
Find sδ and call it C ₂ . The order candidate n (even number) is determined from the relationship between C ₂ and C ₁ and the equation (5). By performing the same measurement while sequentially changing the filter 8 to F3, F4, and F5, four values can be obtained for the order candidate n. For example, one n is determined by a majority vote. If the order n is determined, the retardation of the sample can be obtained. In this measurement, the accuracy when the apparent phase difference of the sample 22 and the phase plate 36 at the reference wavelength by the filter F1 is set to 0 is related to the measurement accuracy. Therefore, 1 for separate reference wavelength lambda ₁ of the light from the phase plate 36
Prepare a half-wave plate. Sample 22 and phase plate 36 and 1
Retardation when combined with a / 2 wave plate is π,
That is, after adjusting the phase plate 36 so that the transmitted light intensity when the polarizing plates 14 and 18 are rotated changes between 0 and the maximum, the 1/2 wavelength plate is removed from the measurement optical path. At this time, the apparent retardation of the sample 22 and the phase plate 36 is 0. This method can adjust the phase plate 36 with higher sensitivity than adjusting the phase plate 36 so that the pattern of transmitted light intensity shown in FIG. 2 becomes a circle.

When the order of retardation increases, the ordinary ray is affected by the spread of the wavelength of the monochromatic light used,
The interference of extraordinary rays becomes blurred, and the change in transmitted light intensity when the polarizing plates 14 and 18 are rotated becomes small, so that the retardation apparently becomes small. Therefore, it is desirable that the light source used has high monochromaticity. As a light source, it is better to use a discharge tube and select some bright line light with a filter than to select light with a continuous spectrum light source with a filter. For example, the bright line 450 of a xenon discharge tube.
1nm, 462.4nm, 467.1nm,
When the 467.1 nm emission line is used with the 2.4 nm emission line as the reference wavelength, n _{0 in the} equation (6) becomes about 100,
It is possible to measure up to the 50th order.

A Babinet-Soleil compensator is used as the phase plate 36, but this is expensive, so the retardation is known as the phase plate 36 for determining the order, and the values are slightly different from each other. A plurality of plates may be provided so as to be replaceable in a turret type like the filters F1 to F5. In the relationship between the rotation angle of the polarizing plate and the detection output of the light receiving element (FIG. 2), when the difference between the maximum value Io and the minimum value Im is small, the detection accuracy decreases, so the absolute value of cos δ has a certain value D ( It is possible to determine whether it is larger than 0 <D <1), and when it is larger than D, the phase plate 36 can be automatically inserted into the measurement optical path to enhance the detection sensitivity.

In the embodiment of FIG. 4, an operation for increasing such detection sensitivity will be described with reference to the flowchart of FIG. The phase plate 36 is set so as to act as a quarter wavelength plate with respect to the measurement wavelength. The phase plate 36 is initially removed from the measurement optical path. The sample 22 is set in the device and the measurement operation is started. The computer 52 measures the transmitted light intensity at every angle of 1 ° while rotating the polarizing plates 14 and 18, and stores the value in the memory together with the data of the rotation angles of the polarizing plates 14 and 18. Next, the maximum value Io and the minimum value Im of the transmitted light intensity are searched from the acquired data. The relationship between the transmitted light intensity and the rotation angles of the polarizing plates 14 and 18 has a flower shape as shown in FIG. 2 when illustrated by the curved coordinates, and when the phase difference δ is 2π, the flower shape becomes a circle and the maximum value. The difference between the minimum value and the minimum value becomes small, and the retardation cannot be obtained accurately. Therefore, cosδ
It is determined whether the absolute value of is larger than a preset constant D.

When cos δ is D or less, the phase difference δ is calculated from the obtained Im and Io by the equation (3) and the operation is finished. On the other hand, when the absolute value of cos δ is larger than D, first the direction of the optical principal axis of the sample is searched. Therefore, as an example, as described above, from the data obtained by rotating the polarizing plates 14 and 18 once, the angular positions of the polarizing plates 14 and 18 are 4
The pair of transmitted light intensities separated by 5 degrees are sequentially obtained, and the azimuth of the optical principal axis of the sample 22 is obtained as the intermediate direction of the angular positions separated by 45 degrees when the sign of the difference is reversed. When this azimuth is obtained, the motor 46 is driven to match the azimuth of the optical principal axis of the phase plate 36 with it, and the motor 48 is driven to move the phase plate 36 onto the measurement optical path. Then, the polarizing plates 14 and 18 are rotated to perform the measurement. By inserting the phase plate 36 in the measurement optical path, the absolute value of cos δ becomes D or less, and the retardation when the phase plates 36 are stacked is obtained.

In the next step, it is checked whether or not it is the measurement after the phase plate 36 is inserted in the measurement optical path (second measurement). If so, the phase plate 36 is used. Π / 2 is subtracted from the obtained δ, the retardation of the sample is calculated from the value, and the measurement operation is completed. In this operation, even when the retardation of the sample is around nλ / 2 and it is difficult to accurately determine, the situation is automatically judged and the phase plate 36 is automatically inserted into the measurement optical path for measurement. Since the measurement is performed, the person who performs the measurement can easily and accurately measure the retardation without spending extraordinary judgment power.

FIG. 6 shows an embodiment in which a means for measuring the refractive index of light transmitted through the sample at various angles is added to the embodiment of FIG. In FIG. 6, in order to measure the refractive index of the sample 22 in the three axial directions, the sample 22 can be rotated in its plane, and the sample can be tilted about a straight line along the surface of the sample 22. In order to do so, the sample 22 is held by the sample holding device.

Details of the sample holding device are shown in FIG. A hole 72 is provided in the center of the sample holder 70, a back surface is hollowed out in a ring shape to form a concave portion, and a holding plate 74 for holding and holding the sample is provided at two positions on the upper surface. A rotating table 78 having a ring-shaped convex portion 76 that fits into a concave portion on the back surface of the sample holding table 70 is attached to the substrate 80, and holds the sample holding table 70 rotatably around an axis perpendicular to the sample surface. There is. A belt 86 is mounted between the side surface of the sample holder 70 fitted into the rotary table 78 and the pulley 84 attached to the rotary shaft of the stepping motor 82, and the sample holder 70 is rotated by the motor 82. The motor 82 is also the substrate 8
No. 0 attached to the pulley 84 and the sample holder 70.
Motor 82 and the turntable 7 so that they are arranged in one plane.
8 mounting surfaces are configured. Shafts 88 and 90 are attached to a pair of side surfaces of the substrate 80, and are arranged so that the central axes of the shafts 88 and 90 come to the surface of the sample holder 70. These axes 80 and 90 are supported by the birefringence meter body. The pulley 62 is attached to one of the shafts 88,
A belt 64 is written between a pulley 66 of a stepping motor 68 provided on the birefringence meter main body side and the pulley 62, and a substrate 80 is tilted by the motor 68. Computer 52 also controls the operation of motors 68 and 82.

The birefringence of a sample is measured by the apparatus of the embodiment shown in FIG. 6 as follows. The sample 22 is attached to the sample holder 70, and the retardation R of the sample is calculated and stored by the same operation as in the embodiment of FIG. When one measurement is completed, the motor 82 is driven and the sample holder 70 is rotated by a fixed angle, for example, 10 degrees, and the same operation as above is performed again. In this way, the retardation is obtained while changing the orientation of the sample.

Further, the retardation is obtained by repeating the above measurement operation while driving the motor 68 and inclining the sample holder 70 by a constant angle, for example, 5 °, while changing the inclination angle of the sample. In the computer 52, the rotation angle of the sample holder 70 is read by the drive pulse of the motor 82, and the tilt angle of the sample holder 70 is read by the drive pulse of the motor 68.

According to the embodiment shown in FIG. 6, the birefringence of the sheet-shaped sample can be measured while automatically adjusting the tilt angle and the rotation angle of the sample, and the birefringence in the triaxial directions can be measured. The measurement can be automatically performed with high accuracy. In the embodiment of FIG. 6 as well, the phase plate 36 is used as a phase plate when determining the order of retardation using a plurality of wavelengths, and when the difference between the maximum value Io and the maximum value Im of the light receiving element output is small. It can also function as a phase plate for moving the retardation of the sample by 1/4 wavelength. The sample holding mechanism 60 can rotate and tilt the sample 22. as a result,
In the measuring apparatus of FIG. 6, the order and retardation can be accurately obtained, and the refractive index in the three axial directions can be measured with high accuracy while changing the rotation angle and the tilt angle of the sample.

[0040]

According to the present invention, not only the order n can be determined and the retardation can be measured, but also the maximum value I
When the difference between o and the minimum value Im is small, the detection accuracy can be improved. By further adding a mechanism capable of adjusting the tilt angle and the rotation angle of the sample, it becomes possible to accurately obtain the order and retardation while changing the rotation angle and the tilt angle of the sample.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of retardation measurement, where (A) shows the relationship between the optical principal axis of a sample and the polarization direction of a polarizing plate, and (B) shows the positions of ordinary and extraordinary rays transmitted through the sample. It is a figure which shows a phase difference.

FIG. 2 is a diagram showing an intensity distribution of a light receiving element detection output with respect to a rotation angle of a polarizing plate.

FIG. 3 is a diagram showing an order determining operation in the present invention.

FIG. 4 is a schematic perspective view showing a first embodiment.

5 is a flow chart diagram showing an example of the operation of the embodiment of FIG.

FIG. 6 is a schematic perspective view showing a second embodiment.

7 is an exploded perspective view showing a sample holding device in the embodiment of FIG.

[Explanation of symbols]

2 light source 8 filter 12, 34, 38, 46, 48 stepping motor 14, 18 polarizing plate 22 sample 24 light receiving element 36 phase plate 52 computer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kyoji Imagawa 4-3-1 Jōkoji, Amagasaki City, Hyogo Prefecture Kanzaki Paper Co., Ltd. Kanzaki Mill

Claims (6)

[Claims] 1. A light source section for supplying measuring light to a measuring optical path, a filter section for selecting a wavelength of the measuring light, and two polarizing plates arranged on the measuring optical path and keeping polarization directions in a constant relationship. A polarizing / analyzing unit that rotates relative to the sample disposed between them; a retardation variable phase plate disposed on the measurement optical path between the light source side polarizing plate and the sample; A moving mechanism that moves the phase plate between a position on the measurement optical path and a position deviated from the measurement optical path, so that the direction of the optical main axis of the phase plate coincides with the direction of the optical main axis of the sample, the phase plate is A rotation mechanism that rotates around the measurement optical path, a light detection unit that detects the measurement light that has passed through the polarization / analysis unit, the phase plate and the sample, wavelength selection in the filter unit, and the polarization / light detection unit. Rotation, retardation change of the phase plate The moving mechanism and controls the operation of the rotating mechanism, the birefringence measurement apparatus having a data processing and control unit, the calculating the retardation of the sample takes in the output signal of the photo detecting portion. 2. The data processing / control section selects the measurement light of the first wavelength by the filter section, operates the moving mechanism to dispose the phase plate on the measurement optical path, and sets the rotation mechanism. When operated, the direction of the optical principal axis of the phase plate coincides with the direction of the optical principal axis of the sample, and the phase difference based on the retardation obtained by combining the sample and the phase plate with respect to the measurement light of the first wavelength is an integer of 2π. After changing the retardation of the phase plate so as to double, the measurement light of the second wavelength close to the first wavelength is selected by the filter unit, and the polarization / analysis unit is set to the sample. By making one rotation relatively, the relationship between the maximum value Io and the minimum value Im of the transmitted light intensity at that time is applied to the relationship between the order of the retardation created in advance and the above relationship, and The order n is determined and its Birefringence measuring device according to claim 1, further comprising a means for calculating a retardation. 3. The data processing / control section of the photodetection section when the polarization / light detection section is rotated once relative to a sample with the phase plate removed from the measurement optical path. A detection unit for detecting whether a ratio or a difference between the maximum value Io and the minimum value Im of the output signal is within a predetermined reference range is provided, and the maximum value Io and the minimum value Im of the output signal of the photodetector are provided. When the ratio or difference is within the reference range, the retardation is calculated based on the maximum value Io and the minimum value Im, and the ratio or difference between the maximum value Io and the minimum value Im of the output signal of the photodetector is calculated. When it is not within the reference range, the moving mechanism is operated to arrange the phase plate on the measurement optical path, and the rotating mechanism is operated to make the direction of the optical main axis of the phase plate coincide with the direction of the optical main axis of the sample. , 1/4 of the measuring light of the first wavelength
After changing the retardation of the phase plate so as to form a wavelength plate, the polarization / analysis unit is rotated once relative to the sample, and the maximum value Io of the output signal of the photodetection unit at that time is obtained. The birefringence measuring device according to claim 1, further comprising means for calculating a retardation based on the minimum value Im. 4. The data processing / control unit selects the measurement light of the first wavelength by the filter unit, operates the moving mechanism to dispose the phase plate on the measurement optical path, and controls the rotation mechanism. When operated, the direction of the optical principal axis of the phase plate coincides with the direction of the optical principal axis of the sample, and the phase difference based on the retardation obtained by combining the sample and the phase plate with respect to the measurement light of the first wavelength is an integer of 2π. After changing the retardation of the phase plate so as to double, the measurement light of the second wavelength close to the first wavelength is selected by the filter unit, and the polarization / analysis unit is set to the sample. By making one rotation relatively, the relationship between the maximum value Io and the minimum value Im of the transmitted light intensity at that time is applied to the relationship between the order of the retardation created in advance and the above relationship, and The order n is determined and its And the maximum output signal of the photodetector when the polarization / detector is rotated once relative to the sample with the retardation calculating means removed from the measurement optical path. A detection unit for detecting whether or not the ratio or difference between the value Io and the minimum value Im is within a predetermined reference range, and the ratio or difference between the maximum value Io and the minimum value Im of the output signal of the photodetector. Is within the reference range, the retardation is calculated based on the maximum value Io and the minimum value Im, and the maximum value Io and the minimum value Im of the output signal of the photodetector are calculated.
When the ratio or the difference with is not within the reference range, the moving mechanism is operated to arrange the phase plate on the measurement optical path, and the rotating mechanism is operated to set the direction of the optical principal axis of the phase plate to the optical axis of the sample. After matching the direction of the principal axis and changing the retardation of the phase plate so that it becomes a quarter-wave plate for the measurement light of the first wavelength, the polarization / analysis unit is moved relative to the sample. 2. The birefringence measuring device according to claim 1, further comprising: a unit that makes a full rotation, and calculates a retardation based on a maximum value Io and a minimum value Im of the output signal of the photodetector at that time. . 5. The apparatus further comprises a mechanism for rotating the sample in its plane and a mechanism for tilting the sample around a straight line along the surface of the sample, wherein the data processing / control unit rotates and tilts the sample at a constant angle. However, the birefringence measuring apparatus according to claim 1, further comprising means for calculating retardation. 6. A half-wave plate for the measurement light of the first wavelength is further provided so as to be able to enter and leave the measurement optical path, and the data processing / control unit is configured to provide the sample and the phase with respect to the measurement light of the first wavelength. When the retardation of the phase plate is changed so that the retardation based on the retardation of the plate and the plate becomes an integral multiple of 2π, the retardation when the sample, the phase plate, and the ½ wavelength plate are combined. The birefringence measuring device according to claim 2, 4 or 5, further comprising means for removing the half-wave plate from the measurement optical path after adjusting the phase plate so that is an integer multiple of π.