JPH11211656A - Method and apparatus for measuring retardation - Google Patents

Abstract

(57) [Summary] To accurately measure the retardation of a sample having a high degree of orientation. SOLUTION: The optical axis of the sample is set to about 45 ° with respect to the polarization direction, and the sample is tilted so that the direction perpendicular to the optical axis is the tilt axis, and the intensity distribution of the analyzer transmitted light with respect to the tilt angle is near zero. The polarizer and the analyzer are placed in a parallel Nicol state at an angle at which the intensity distribution is symmetric, and the optical order and the retardation are determined. Then, based on the optical order in that state, the polarizer and the analyzer are placed in a crossed Nicols state, the sample is tilted, the transmission intensity is measured during the tilt, and the number of times exceeding the maximum or minimum is counted to change the optical order. Ask for. The retardation in the horizontal state or the inclined state is obtained by using the measured value in the parallel Nicol state and the change in the optical order in the orthogonal Nicol state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for measuring the retardation of a birefringent material, and more particularly to a method and an apparatus suitable for measuring the retardation of a sample having a higher order retardation. .

[0002]

2. Description of the Related Art When a synthetic resin material is stretched, it exhibits optical anisotropy. Therefore, the stretching process of the synthetic resin material can be controlled by measuring the optical anisotropy. When the material is the same, the degree of stretching can be determined based on the degree of birefringence for a sheet having a constant thickness, and the thickness can be determined for a sheet having a constant degree of stretching. In a device using polarized light, for example, sheets used in a liquid crystal display device, it is necessary to check polarization characteristics in advance. As one of the polarization characteristics of a sample, a phase shift of two orthogonally polarized lights transmitted through the sample, that is, a retardation is measured.

[0003] The birefringence is represented by the refractive index of an ordinary ray and an extraordinary ray, and 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 indexes and the thickness of the material. By measuring the retardation, the birefringence characteristics of the sheet-like sample can be found.

For example, in a display panel of a liquid crystal display device,
The characteristics when viewed from a direction other than the direction perpendicular to the surface, that is, the viewing angle characteristics are also important characteristics. In order to evaluate the viewing angle characteristics, it is necessary to measure a retardation value when the incident angle of the measurement light with respect to the sample is changed. For example,
A method is adopted in which the retardation value is measured at an inclination angle of 10 ° in the inclination angle range of 0 to 50 °.

[0005] To measure the retardation of a sample,
A 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, a change in light transmitted through the polarizing plate and the sample is recorded, and the retardation is calculated from the result.

[0006] The retardation is observed as a phase difference between an ordinary ray and an extraordinary ray which are made incident on the sample in phase, and is generally expressed by (2nπ + δ). n is a natural number of 0, 1, 2,... and is called an optical order. As the sample becomes thicker, the optical order n also increases.
The change width of the transmitted light intensity obtained by rotating the polarizing plate and the sample relatively depends on δ. What is directly obtained by measurement is δ
Although the optical order n cannot be directly obtained, there are some known methods for obtaining the optical order n.

In analyzing the higher-order structure of a polymer film, it is important in the field of product management and research to evaluate the arrangement of polymer chains, that is, the molecular orientation. The simplest method for evaluating molecular orientation is the birefringence method, which has been conventionally measured by various methods. In the case of a high retardation film such as PET (polyethylene terephthalate), the optical order is also large, and the determination of the optical order is likely to be erroneous in the conventional method, so that accurate retardation may not be measured.

In the on-line measurement, an optical order (a value obtained by adding 1 to an integer part of a quotient obtained by dividing retardation by の of the measurement wavelength: the optical order is used in this sense in the present invention) is given in advance. This is necessary, and there is a problem that the retardation changes during the measurement and cannot be detected even if the retardation shifts to the next optical order. In addition, the same problem occurs not only in the production line of films and the like, but also in research applications, for example, when measuring the retardation while applying tension or heat artificially.

[0009]

A first object of the present invention is to correctly measure the retardation of a sample having a high degree of orientation. A second object of the present invention is to make it possible to accurately measure a change in optical order in online measurement of retardation so that a change in optical order can be measured accurately. It is to be.

[0010]

According to the present invention, in addition to the conventional parallel Nicols method, when the sample is tilted, that is, when the retardation changes, the state is switched to the orthogonal Nicols state and the transmission intensity is measured in real time. First, the change in the optical order is accurately measured, and then the retardation is accurately measured by the parallel Nicol method.

However, this method also assumes that the first retardation is accurately measured. Even in the conventional method, the retardation can be accurately measured in a state where the optical order is low. The three-dimensional refractive index of a sheet-like substance such as a polymer film is generally described using an index ellipsoid. In the two-dimensional refractive index distribution in a plane, when the inclination is inclined with the minimum direction as the inclination axis, the retardation generally decreases as shown by the solid line in FIG. And then increase again. Therefore,
Even for a sample having a high optical order, the optical order can be reduced by tilting the sample with a specific axis as the tilt axis.

Therefore, in one aspect of the present invention, as shown in FIG. 2, the polarizer and the analyzer are in a crossed Nicols state, the optical principal axis of the sample is set at about 45 ° with respect to the polarization direction, and the optical principal axis of the sample is provided. By tilting the sample with the direction perpendicular to the tilt axis as the tilt axis and reducing the optical order, light of the selected wavelength is transmitted from the sample through the polarizer through the analyzer, and the intensity of the analyzer transmitted light with respect to the tilt angle is measured. Then, the change of the optical order is obtained, and the polarizer and the analyzer are again brought into a parallel Nicol state in a state where the optical order is reduced, and the sample, the polarizer and the analyzer are relatively rotated once, and the optical order and the retardation are changed. Includes the required steps. Then, the optical order and the retardation of the sample in a horizontal state or an arbitrary tilt state are obtained based on the optical order and the retardation thus accurately obtained.

If the optical order and the retardation at a specific inclination angle are known by another method or the like, as shown in FIG. The retardation in the state can be obtained.

In another aspect of the present invention, a measuring device capable of tilting a sample to a predetermined angle by a specific tilt axis is used, and as shown in FIGS.
To (C), (D1) to (I1),
The retardation value of the sample and the optical order thereof are determined including any one of the steps (D2) to (I2). (A) a step of obtaining an optical principal axis of a sample from the angle dependence of transmitted light intensity when the polarization transmission axis is rotated by one rotation relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols; B) Put the polarizer and the analyzer in a crossed Nicols state,
Positioning the apparatus and the sample so that the optical principal axis of the sample is at about 45 ° to the polarization direction and the direction perpendicular to the optical principal axis of the sample is the tilt axis; (C) polarizing the light of the selected wavelength Transmit the analyzer from the sample through the analyzer, measure the analyzer transmitted light intensity for the tilt angle while tilting the sample to the maximum allowable tilt angle by the tilt axis, the intensity distribution is near zero, and the If there is an angle at which the intensity distribution is symmetrical, select (I1) from the following process group (D1). If there is no such angle, use the following process group (D2) with the maximum inclination angle as the angle. And (G2). The intensity distribution is near zero,
In addition, when there is an angle at which the intensity distribution is symmetric at that angle, as shown in FIG. 4, (D1) the polarization is at an angle at which the intensity distribution is near zero and the intensity distribution is symmetric at that angle. Put the child and analyzer in parallel Nicol state again,
A step of relatively rotating the sample, the polarizer and the analyzer by one rotation to obtain an optical order and a retardation (here, the optical order is N); (E1) bringing the polarizer and the analyzer back into a crossed Nicols state A step of measuring the transmission intensity while measuring the transmission intensity and further tilting the sample to the maximum allowable tilt angle, and counting the number M of times exceeding the maximum or minimum (the optical order at this point is assumed to be N + M), ( F1) A step of bringing the polarizer and the analyzer into a parallel Nicol state again, relatively rotating the sample, the polarizer and the analyzer by one turn, and measuring the retardation with the optical order being N + M. (G1) Polarizer and the analyzer Again in a crossed Nicols state, and measuring the transmission intensity and returning the maximum or minimum number L while returning the tilt angle to the horizontal side by a predetermined angle (optical order is | N + M−
L |), (H1) The polarizer and the analyzer are again brought into a parallel Nicol state, the sample, the polarizer and the analyzer are relatively rotated once, and the retardation is measured by setting the order to | N + ML |. (I1) performing the operations of steps (G1) and (H1) at a plurality of desired angles up to the horizontal position;
Measuring the change in retardation with respect to the angle of inclination.

If the intensity distribution is close to zero even if the angle is inclined to the maximum allowable inclination angle, and there is no angle at which the intensity distribution is symmetrical, as shown in FIG. (G2) is selected from the group (D2). (D2) A step of setting the polarizer and the analyzer again in a parallel Nicol state at the maximum allowable tilt angle, relatively rotating the sample, the polarizer and the analyzer once, and obtaining the optical order and the retardation (here, the optical order) Is assumed to be N ′), (E2) the polarizer and the analyzer are again placed in a crossed Nicols state, the transmission intensity is measured while returning the inclination angle to the horizontal side by a predetermined angle, and the number L of the maximum or minimum is measured. (The optical order is N ′ + L), (F2) the polarizer and the analyzer are again brought into a parallel Nicol state, the sample, the polarizer and the analyzer are relatively rotated once, and the order is N ′ + L. A step of measuring retardation; (G2) a step of performing the operations of steps (E2) and (F2) at a plurality of desired angles up to a horizontal position, and measuring a change in retardation with respect to the inclination angle.

The measuring apparatus of the present invention includes an apparatus for measuring an individual sample and an online measuring apparatus for measuring a continuously flowing sample. One example of an apparatus for measuring an individual sample is a polarizer on the measurement light incident side of the sample, an analyzer arranged in a parallel Nicol state on the emission side, and transmission of a single wavelength measurement light from the polarizer to the analyzer. This is a retardation measuring device that detects the intensity of the measurement light transmitted through the analyzer by rotating the polarization transmission axes of the polarizer and the analyzer relative to the sample while maintaining the polarizer and the analyzer in a parallel Nicols state. . Another example of an apparatus for measuring an individual sample includes a plurality of pairs of polarizers arranged on the incident side of the measurement light and analyzers arranged on the exit side in a parallel Nicol state and having different polarization directions from each other. , The measurement light of a single wavelength is transmitted through the analyzer group, the sample is placed between the polarizer group and the analyzer group, and the retardation of the sample is measured by detecting the measurement light exiting the analyzer group. It is a retardation measuring device. In these retardation measuring devices, the present invention includes a sample holding mechanism for tilting the sample by a specific tilt axis, and a pair of a polarizer and an analyzer in a state of orthogonal Nicols with the sample interposed therebetween. The change in the optical order with the tilt of the sample is determined by the transmitted light intensity by the polarizer and the analyzer in the state, and when the retardation is determined by the transmitted light intensity by the polarizer and the analyzer in the parallel Nicol state, the orthogonal Nicol state The optical order is determined based on the change in the optical order obtained by the polarizer and the analyzer.

In the online retardation measuring apparatus, a plurality of pairs of polarizers are arranged on the incident side of the measurement light and the analyzers on the exit side in a parallel Nicol state and different in polarization direction from each other. Transmitting a single wavelength measurement light to the analyzer group, passing the sample between the polarizer group and the analyzer group,
This is to measure the retardation of the sample by detecting the measurement light that has exited the analyzer group. In the present invention, a pair of a polarizer and an analyzer in a crossed Nicols state with the sample interposed is added, and the transmitted light is added. When the change in the optical order is obtained from the intensity, and when the retardation is obtained from the transmitted light intensity of the plurality of pairs of the parallel Nicol state polarizer and the analyzer, the optical order obtained by the orthogonal Nicol state polarizer and the analyzer is obtained. The optical order is determined based on the change.

When the change of the optical order is obtained by the polarizer and the analyzer in the orthogonal Nicol state, the optical order may change from decreasing to increasing or from increasing to decreasing. The change is caused by the transmitted light intensity distribution of the analyzer. It can be determined by becoming symmetric. However, depending on the measurement wavelength, the position where the transmitted light intensity distribution becomes symmetric may overlap with the maximum or minimum of the transmitted light intensity distribution. Therefore, it is preferable that measurement in the orthogonal Nicols state is performed at two different wavelengths, and a wavelength at which the transmitted light intensity distribution becomes symmetrical does not overlap with the maximum or minimum of the transmitted light intensity distribution.

The method itself for determining the retardation value and the optical order n is known, and any known method can be used in the present invention, but a representative one is shown for convenience of explanation. However, the invention is not limited to these exemplary methods.

First, a method of measuring a retardation value will be described. As shown in FIG. 6A, the polarizer p
And the analyzer a are maintained in a parallel Nicol relationship with each other, and are rotated relative to the sample s disposed therebetween to detect the analyzer transmitted light, and the analyzer transmitted light intensity I from the reference position of the sample is measured. When expressed as a function of the rotation angle θ, the following equation is obtained. ^{I = Io {α 2 cos 4} (θ-θ 0) + sin 4 (θ-θ 0) + (1/2) Cαsin 2 2 (θ-θ 0)} ...... (1) The analyzer transmitted light intensity When I is displayed in polar coordinates, FIG.
A 10:00 flower-shaped figure as shown in FIG. here,
Io is the incident light intensity of the sample, α is the ratio of the transmittance of the polarized light oscillating in the two optical principal axes of the sample, and θ ₀ is the angle between the direction of the maximum refractive index of the two optical principal axes and the reference direction. ,
C is represented by the following equation. C = cos (2πR / λ) (2) where λ is the wavelength of the measurement light and R is the retardation value.

On the other hand, from the measured value of I with respect to the rotation angle θ, α
And C are obtained as follows. α = (I _θ0 / I _{θ0 + 90} ) ^1/2 (3) C = (4I _{θ0 + 45} / I _{θ0 + 90} −1−α ² ) / 2α (4) C is determined and the order n Is determined, the retardation value R
Is obtained by the following equation. When n is an even number, R = (− 1) ^{n + 1} (λ / 2π) cos ⁻¹ C + nλ / 2 (5) When n is an odd number, R = (− 1) ^{n + 1} (λ / 2π) ) cos ^-1 C + (n-1) λ / 2 (6)

Although a method for determining the optical order n is known, one method is to determine the phase difference δ corresponding to the retardation value for each of two lights having different wavelengths, and to set the optical order n to 1 , 2, 3,... Are sequentially determined to determine the retardation value. Where the retardation values obtained at different wavelengths coincide, the retardation value to be obtained is the optical order. In addition, a wavelength range that is difficult to obtain accurately depends on the retardation value. In this case, measurement is performed using the other two wavelengths (see JP-A-4-294249).

In another method for determining the optical order n, a phase plate having a variable retardation value, for example, a Babinet Soleil compensator, is superimposed on the sample, and the sample and the phase plate are combined for light of one wavelength. Phase difference based on retardation is 2
In this state, two polarizing plates (light source side is a polarizer and detector side is a detector) are used in this state, using light of another wavelength close to the above-mentioned wavelength, and maintaining a constant polarization direction. 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 optical order of the retardation prepared in advance and this relationship. In this method, the optical order of the retardation of the sample is determined (see Japanese Patent Application No. 5-53024). There are other methods for determining the optical order n, but any method may be employed in the present invention.

In the orthogonal Nicol state as shown in FIG. 7A, the transmission intensity I is expressed by the following equation. I = A · sin 2θ · sin ² (πR / λ) (7) As shown in FIG. 7B, since the optical order changes every λ / 2, the transmission intensity when the retardation changes. If I is measured continuously, the change in the optical order can be known. If the start is just at the maximum or minimum of I, it is not possible to distinguish whether the retardation is decreasing or increasing only by the change of I. Therefore, it is possible to discriminate by using a plurality of wavelengths by slightly shifting the wavelength. And
When the retardation changes from decrease to increase or conversely from increase to decrease by tilting the sample, the transmission intensity I changes as if it were folded back symmetrically with respect to time.

[0025]

8 and 9 show an embodiment of a birefringence measuring apparatus used in the present invention for measuring a retardation by tilting a sample in the present invention. Measurement light from a white light source 2, for example, a halogen lamp, is guided by an optical fiber 4 and emitted as a parallel light beam by a condenser lens 6. A filter 8, a polarizing plate 14 as a polarizer, a sample 22, and a polarizing plate 18 as an analyzer are arranged in the optical path from the condenser lens 6 to the light receiving element 24 in order from the condenser lens 6 side. .

The filter 8 has a filter holding plate 10 so that the order n can be obtained by measurement at a plurality of wavelengths.
A plurality of filters having different transmitted light characteristics are arranged along the circumferential direction. One of the filters is selected by a stepping motor (not shown) that rotates the filter holding plate 10 and inserted into the optical path of the measurement light. 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 arrangement position of the filter 8 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, that is, in a parallel Nicols state, and are held by holding disks 16 and 20, respectively. The holding disks 16 and 20 are respectively connected to pulleys 28 and 30 fixed on a shaft 32 via belts 25 and 26, respectively, and the shaft 32 is rotated by a stepping motor 34 so that the two polarizing plates 14 and 18 are rotated. Are integrally rotated. Holding disc 1 with polarizing plate 14 attached
A mark of a reflector is provided on one side of the side surface of 6, and the initial position of the rotation of the polarizing plates 14 and 18 is detected by detecting the reflector by a photoelectric detector.

A mirror 36 is disposed on the optical axis between the polarizing plate 14 and the sample 22 so as to be detachable from the optical path, and a polarizing plate 38 is provided on the optical axis between the mirror 36 and the sample 22, which also has an optical path. It is arranged so that it can be attached and detached. The polarizing plate 38 and the polarizing plate 18 are used with their polarization directions determined so that the polarization methods are orthogonal to each other, that is, in a crossed Nicols state. The laser beam enters the pair of the polarizing plate 38 and the polarizing plate 18 via the mirror 36.

As a means for measuring the retardation in a state where the sample 22 is tilted, 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. The sample 22 is held by a sample holding device so as to perform the measurement. In FIG. 8, the illustration of the sample holding device is omitted.

FIG. 9 shows details of the sample holding device. A hole 72 is provided in the center of the sample holding table 70, a concave portion is formed by hollowing out the back surface, and a holding plate 74 for holding and holding the sample is provided at two places on the upper surface. A rotating table 78 having a ring-shaped convex portion 76 that fits into the concave portion on the back surface of the sample holder 70 is attached to the substrate 80, and holds the sample holder 70 so as to be rotatable around an axis perpendicular to the sample surface. I have. A belt 86 is mounted between a side surface of the sample holder 70 fitted on the rotating table 78 and a pulley 84 attached to a rotation shaft of the stepping motor 82, and the motor 82 rotates the sample holder 70. The motor 82 is also on the substrate 8
0, the pulley 84 and the sample holder 70
And the turntable 7 so that the
8 mounting surfaces are configured. Shafts 88 and 90 are attached to a pair of side surfaces of the substrate 80, and are arranged such that the central axes of the shafts 88 and 90 come to the surface of the sample holder 70. These axes 88 and 90 are supported by the birefringence measurement device main body. A pulley 62 is attached to one shaft 88, and a belt 64 is hung between a pulley 66 of a stepping motor 68 provided on the birefringence measuring device main body side and the pulley 62, and the substrate 80 is tilted by the motor 68. Can be

Referring back to FIG. 8, when measuring in a parallel Nicols state, the mirror 36 and the polarizing plate 38 are removed from the optical path. Sample 2 placed between polarizing plates 14 and 18
In 2, the measurement light having the wavelength selected by any of the filters is transmitted through the polarizing plate 14 and is incident thereon, and the measurement light transmitted through the sample 22 is incident on the light receiving element 24 through the polarizing plate 18 and is measured. . The transmitted light intensity is measured by rotating the polarizing plates 14 and 18 while keeping them in a parallel Nicols state.

By measuring in the state of parallel Nicols, the direction of the optical principal axis, the retardation, and the optical order can be obtained. On the other hand, when the measurement is performed in the orthogonal Nicol state, the mirror 36 and the polarizing plate 38 are arranged in the optical path, and the polarizing plate 18 and the polarizing plate 18 are arranged in the orthogonal Nicol state.
Is adjusted and fixed, and a laser beam is incident via the mirror 36. With the polarizing plate 38 and the polarizing plate 18 being fixed, the optical principal axis of the sample is set to about 45 ° with respect to the polarization direction, and the sample is inclined around the inclined axis with the direction perpendicular to the optical principal axis as the inclined axis. Measure the light intensity. The change in the optical order can be obtained by the measurement in the crossed Nicols state.

Although not shown, an amplification circuit is provided for amplifying the detection output of the light receiving element 24, and an A / D converter is provided for converting the amplified output into a digital signal. The output converted into a digital signal is taken into a computer that performs both data processing and operation control of the measuring device, and the result of the data processing is displayed on a display device such as a CRT and output to a printer. The computer processes the measurement data and sends a pulse to each motor to control the rotation of each motor.

FIG. 10 schematically shows an embodiment in which the present invention is applied to an online measuring apparatus. The structure of the light source portion is the same as that of the embodiment of FIG. 8, and the measurement light from the light source 2 of white light is guided to the condenser lens 6 by the optical fiber 4. However, in the embodiment shown in FIG. 10, the condensing lens 6 irradiates the parallel light spread to the area to be irradiated with light at the same time in order to irradiate a plurality of parts which are close to each other but different at the same time. Optical system. The measuring light is transmitted from the condenser lens 6 to the light receiving element groups 24-1 to 24-6,
In the optical path reaching 25, a narrow band filter 8a, polarizer groups 14-1 to 14-6, 15 and analyzer groups 18-1 to 18-6, 19 are arranged in this order from the condenser lens 6 side. Light transmitted through the polarizer groups 14-1 to 14-6, 15 is transmitted through the analyzer groups 18-1 to 18-6, 19, respectively, and is incident on the light receiving element groups 24-1 to 24-6, 25, respectively. Are positioned so that The corresponding polarizer pairs of the polarizer groups 14-1 to 14-6 and the analyzer groups 18-1 to 18-6 are in a parallel Nicol state, and their polarization directions are shifted by 60 °. Is stipulated.
The polarization directions of the polarizer 15 and the analyzer 19 are determined so as to be in a crossed Nicols state.

The sample 22a moves across the optical path between the polarizer groups 14-1 to 14-6 and 15 and the analyzer groups 18-1 to 18-6 and 19, and online measurement is performed. An amplifier 40 is provided for each of the light-receiving element groups 24-1 to 24-6 and 25 to amplify the detection output, and an analog signal is used to sequentially select the amplified output at a constant time interval, for example, 1 millisecond interval. A multiplexer 42 is provided. An A / D converter 44 is provided to convert the output selected by the analog multiplexer 42 into a digital signal, and the output converted to a digital signal is taken into a computer that performs both data processing and operation control of the measuring device.

It is necessary to adjust the polarization directions of the polarizer 15 and the analyzer 19 in the crossed Nicols state so as to be 45 ° with respect to the main optical axis of the sample. Therefore, the polarizer group 14
-1 to 14-6, 15 and analyzer group 18-1 to 18-6
The holding disks 19 are respectively held by holding disks similar to the holding disks 16 and 20 shown in the embodiment of FIG. 8, and these holding disks are also respectively connected to the shafts via belts similarly to the embodiment of FIG. By being connected to the pulley fixed on the top, respectively, the shaft is rotated by the stepping motor,
Polarizer groups 14-1 to 14-6, 15 and analyzer group 18-1
It is preferable that 〜18-6 and １９19 can be integrally rotated while maintaining the polarization state of each other.
Since the optical principal axis of the sample 22a is always detected by the measured values of the transmitted light intensity from the polarizer groups 14-1 to 14-6 and the analyzer groups 18-1 to 18-6 in the parallel Nicols state, the main axis is detected. The polarizer groups 14-1 to 14-6 are controlled by a computer that has taken in the data so that the polarization directions of the polarizer 15 and the analyzer 19 in the orthogonal Nicols state form 45 ° with respect to the optical principal axis direction. 15 and analyzer group 18-1
Rotate the holding disks # 18-6, # 19. as a result,
Even if the optical principal axis direction of the sample which is moved and measured online is changed, the polarizer 15 and the analyzer 1 are in the orthogonal Nicol state.
The polarization direction of the sample 9 can always follow the optical axis direction of the sample at 45 °.

Two pairs of polarizers and analyzers in the orthogonal Nicol state are provided, and light of different wavelengths is incident on each of the two pairs of the polarizers and the analyzer in the orthogonal Nicol state. A pair of a polarizer and an analyzer whose transmitted light intensity at the start of measurement does not become a maximum or a minimum can be selected, or a pair of a polarizer and an analyzer in a crossed Nicols state has two different measurement lights. It is preferable that any one of the above can be selected so as to be incident, and a wavelength at which the transmitted light intensity at the start of measurement does not become maximum or minimum can be selected.

FIG. 11 shows two pairs of a polarizer and an analyzer in the orthogonal Nicols state, and light of different wavelengths is incident on each of the two pairs of the polarizer and the analyzer in the orthogonal Nicols state. 1 shows an on-line measuring device adapted to be used. The optical fiber 4 for guiding the measuring light from the light source 2 branches and guides the measuring light to both the condenser lenses 6 and 6b. A condenser lens 6, which converts the measurement light guided by the optical fiber 4 into parallel light, a narrow band filter 8, a group of polarizers 14-1 to 14-6 in parallel Nicol state, and a group of analyzers 18-1 to 18-6. ,
A pair of polarizer 15 and analyzer 19 in a crossed Nicols state,
The configuration of the light receiving element groups 24-1 to 24-6 and 25 is shown in FIG.
It is the same as that shown in FIG. In FIG. 11, a pair of polarizers 15b and an analyzer 19b in a crossed Nicols state are further provided with the sample 22a interposed therebetween. Measuring light passing through the condensing lens 6b is guided to the polarizer 15b through a narrow band filter 8b designed different transmission wavelength lambda ₂ and the narrow-band filter 8 (transmission wavelength lambda _1). Sample 22 from polarizer 15b
a, the measurement light transmitted through the analyzer 19b is
Is detected by

The detection output of the light receiving element 25b is output to the amplifier 4 together with the detection outputs of the light receiving element groups 24-1 to 24-6 and 25.
After being amplified by 0 and selected by the analog multiplexer 42 and sequentially converted into digital signals by the A / D converter 44, the digital signals are taken into a computer which performs both data processing and operation control of the measuring device.

An example of online measurement according to the embodiment of FIG. 10 or the embodiment of FIG. 11 will be described with reference to FIG. While moving the sample 22a, the retardation and the optical order are measured by the polarizer groups 14-1 to 14-6 and the analyzer groups 18-1 to 18-6 in the parallel Nicols state. Now, the retardation of the sample when the measurement wavelength lambda ₁ is assumed to have changed as shown in FIG. 12 (A).
That is, at time t ₁ , the optical order monotonically increased, and the optical order changed from 2 to 3, and at time t ₂ , the optical order changed from 3 to 2, changing from increasing to decreasing. At this time, the transmitted light intensity of the pair of the polarizer 15 and the analyzer 19 in the orthogonal Nicols state is shown in FIG.
2 (B) is shown by a solid line. In the case of the measurement wavelength λ _1, it can not determine whether the decreased whether the retardation at time t ₂ is increasing. However, due to a wavelength λ ₂ different from λ ₁ (eg, λ ₁ <λ ₂ ), a pair of a polarizer and an analyzer in the orthogonal Nicol state at the measurement wavelength λ ₂ , for example, FIG.
When the transmitted light intensity of the pair of the polarizer 15b and the analyzer 19b in FIG. 1 is measured, as shown by a broken line in FIG.
_{In step 2} , it can be determined that the retardation has changed from increasing to decreasing.

In the apparatus shown in FIG. 11, pairs of the polarizer 15 and the analyzer 19 in the orthogonal Nicols state are in the parallel Nicols state, and the polarizer groups 14-1 to 14-6 and the analyzer groups 18-1 to 18-6 are in the same state.
Although it is located at the position to receive the measurement light of the same wavelength as
The pair of polarizers 15 and the analyzer 19 are connected to a polarizer group 14-1.
14-6, and away from the analyzer groups 18-1 to 18-6, the polarizer 15b and the analyzer 19b in the orthogonal Nicol state may be arranged near the pair. Even in that case, measurement light beams having different wavelengths are incident on the pair of polarizers 15 and the analyzer 19 and the other pair of polarizers 15b and the analyzer 19b in the orthogonal Nicols state.

The measuring apparatus shown in FIGS. 10 and 11 can be applied to measurement of an individual sample as shown in FIG. 8 instead of online. In that case, the sample holding device shown in FIG. 9 can be used to hold and tilt the sample. In order to measure the retardation using this measuring device, the polarizer groups 14-1 to 14-6 and the analyzer groups 18-1 to 18-18 in the parallel Nicols state with the sample in a horizontal state are used.
The direction of the optical principal axis is determined based on the transmitted light intensity of −6, and the sample is rotated so that the optical principal axis of the sample is approximately 45 ° with the polarization directions of the polarizer 15 and the analyzer 19 in the orthogonal Nicols state. Then, the sample is tilted with the direction perpendicular to the optical main axis of the sample as the tilt axis. The measurement of the change of the optical order with the inclination of the sample is the same as that shown in the embodiment of FIG. In the measurement of the retardation at each inclination angle, the polarizer 8 and the analyzer 18 are rotated in the embodiment of FIG. 8, but the polarizer groups 14-1 to 14-6 and the analyzer are rotated in the embodiments of FIGS. It is determined by detecting the transmitted light intensity of the groups 18-1 to 18-6 while keeping them fixed.

[0043]

According to the present invention, when the polarizer and the analyzer are in a crossed Nicols state, the optical axis of the sample is set to about 45 ° with respect to the polarization direction, and the sample is tilted with the direction perpendicular to the optical axis of the sample as the tilt axis. The optical order is reduced, the polarizer and the analyzer include a step of obtaining the optical order and retardation under a state of parallel Nicols in a state where the optical order is reduced, so that the optical order is reduced. The optical order and retardation can be determined accurately. Then, based on the optical order and the retardation in that state, the optical order and the retardation of the sample in a horizontal state or an arbitrary inclined state can be accurately obtained. Also, in the on-line measurement of retardation, by providing a pair of a polarizer and an analyzer in a crossed Nicols state, a change in the optical order during the measurement can be detected.

[Brief description of the drawings]

FIG. 1 is a diagram showing changes in the tilt angle and retardation of a sample.

FIG. 2 is a flowchart illustrating a first aspect of the measurement method of the present invention.

FIG. 3 is a flowchart showing a method in which the measuring method of the present invention is applied to a case where the optical order and retardation at a specific tilt angle are known.

FIG. 4 is a flowchart showing a second aspect of the measurement method of the present invention.

FIG. 5 is a flowchart showing a third aspect of the measurement method of the present invention.

6A and 6B are diagrams illustrating a case where a polarizer and an analyzer have a parallel Nicol relationship, wherein FIG. 6A is a schematic diagram of an optical system,
(B) is a diagram showing the transmitted light intensity.

7A and 7B are diagrams illustrating a case where a polarizer and an analyzer have a crossed Nicols relationship, wherein FIG. 7A is a schematic diagram of an optical system,
(B) is a diagram showing the transmitted light intensity.

FIG. 8 is a schematic perspective view showing one embodiment of the measuring device of the present invention.

FIG. 9 is a perspective view showing a sample holding device used in the embodiment.

FIG. 10 is a schematic perspective view showing an on-line measuring device according to another embodiment of the present invention.

FIG. 11 is a schematic perspective view showing another embodiment of the online measuring device.

12A and 12B are diagrams showing the operation of the embodiment, wherein FIG. 12A is a diagram showing the time change of the retardation, and FIG. 12B is a diagram showing the transmitted light intensity of the polarizer and the analyzer having the orthogonal Nicols relationship at that time FIG.

[Explanation of symbols]

2 Light source 8, 8a Filter 14, 14-1 to 14-6, 15, 15b Polarizer 18, 18-1 to 18-6, 19, 19b Analyzer 22, 22a Sample 24, 24-1 to 24-6 25, 25b light receiving element

Claims (9)

[Claims] 1. A polarizer is arranged on a measurement light incident side of a sample and an analyzer is arranged on an emission side of the sample, and the polarization transmission axis of the polarizer and the analyzer is maintained on the sample while maintaining the polarizer and the analyzer in a predetermined polarization orientation relationship. Using a measuring device capable of detecting the intensity of the measurement light transmitted through the analyzer by rotating relative to the analyzer and tilting the sample along a specific tilt axis, the following steps (A) to ( A method for measuring a retardation, comprising determining the retardation value of a sample and its order, including C). (A) a step of obtaining the optical principal axis of the sample from the angle dependence of the transmitted light intensity when the polarization transmission axis is rotated by one rotation relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols; B) The polarizer and the analyzer are placed in a crossed Nicols state, the optical principal axis of the sample is set at about 45 ° to the polarization direction, and the sample is inclined with the direction perpendicular to the optical principal axis of the sample as the tilt axis to reduce the optical order. A step of transmitting the light of the selected wavelength through the polarizer from the sample through the analyzer and measuring the intensity of the transmitted light with respect to the tilt angle to obtain a change in the optical order; (C) the sample is horizontally moved from the tilted state. In at least one state where the optical order is reduced between the states, the polarizer and the analyzer are again brought into a parallel Nicol state, and the sample, the polarizer and the analyzer are relatively rotated once, and the optical order and the retardation are reduced. Ask Process. 2. A polarizer is arranged on the measurement light incident side of the sample and an analyzer is arranged on the emission side, and the polarization transmission axis of the polarizer and the analyzer is maintained on the sample while maintaining the polarizer and the analyzer in a predetermined polarization orientation relationship. Using a measuring device capable of detecting the intensity of the measurement light transmitted through the analyzer by rotating relative to the analyzer and tilting the sample along a specific tilt axis, the following steps (A) to ( A method for measuring retardation, comprising determining a retardation value and its order in a horizontal state of a sample whose optical order and retardation at a specific tilt angle are known, including C). (A) a step of obtaining the optical principal axis of the sample from the angle dependence of the transmitted light intensity when the polarization transmission axis is rotated by one rotation relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols; B) After making the optical axis of the sample approximately 45 ° with respect to the polarization direction, and tilting the sample to the predetermined tilt angle with the direction perpendicular to the optical axis of the sample as the tilt axis, the polarizer and the analyzer are crossed at right angles to each other. (C) transmitting a light of a selected wavelength through the polarizer from the sample to the analyzer while tilting the sample in the state, and measuring the intensity of the analyzer transmitted light with respect to the tilt angle to obtain a change in the optical order; In at least one state where the sample is between the tilted state and the horizontal state, the sample is set in the horizontal state, and the polarizer and the analyzer are again brought into the parallel Nicol state, and the sample, the polarizer, and the analyzer are relatively rotated once. Let's do a letter show The process of finding the 3. A polarizer is arranged on the measurement light incident side of the sample and an analyzer is arranged on the emission side, and the polarization transmission axis of the polarizer and the analyzer is maintained on the sample while maintaining the polarizer and the analyzer in a predetermined polarization orientation relationship. Using a measuring device capable of detecting the intensity of the measurement light transmitted through the analyzer by relatively rotating the sample and tilting the sample to a predetermined angle by a specific tilt axis, the following step ( A) including the steps from (D) to (I1) and the steps from (D2) to (I2) including (A) to (C), and obtaining the retardation value of the sample and its optical order. Characteristic retardation measurement method. (A) a step of obtaining the optical principal axis of the sample from the angle dependence of the transmitted light intensity when the polarization transmission axis is rotated by one rotation relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols; B) The polarizer and the analyzer are placed in a crossed Nicols state, the main optical axis of the sample is set to about 45 ° with respect to the polarization direction, and the apparatus and the sample are positioned so that the direction perpendicular to the main optical axis of the sample is the tilt axis. (C) transmitting the light of the selected wavelength through the polarizer from the sample to the analyzer, and measuring the transmitted light intensity of the analyzer with respect to the tilt angle while tilting the sample to the maximum allowable tilt angle by the tilt axis. If the intensity distribution is close to zero and there is an angle at which the intensity distribution is symmetric, (I1) is selected from the following process group (D1), and if there is no such angle, The maximum tilt angle is the angle (G2) from the following step group (D2): (D1) At that angle, the polarizer and the analyzer are again brought into a parallel Nicol state, and the sample, the polarizer and the analyzer are relatively set at 1
Rotating to determine the optical order and retardation (the optical order here is N); (E1) the polarizer and the analyzer are again placed in a crossed Nicols state, and the sample is further subjected to the maximum allowable tilt angle while measuring the transmission intensity. The transmission intensity is measured while tilting up to this point, and the number of times M exceeding the maximum or minimum is counted (the optical order at this time is assumed to be N + M). (F1) The polarizer and the analyzer are brought into a parallel Nicol state again. (G1) a step of rotating the sample, the polarizer and the analyzer relatively once, measuring the retardation by setting the optical order to N + M, (G1) bringing the polarizer and the analyzer back into a crossed Nicols state, and setting the tilt angle to a predetermined angle. Measuring the transmission intensity and returning the maximum or minimum number L (the optical order is | N + M−L |), while returning to the horizontal side only (H1). State, and the sample, the polarizer and the analyzer are relatively rotated once, and the order is set to | N + ML− to measure the retardation. (I1) Steps (G1) and (H1) are performed horizontally. (D2) The polarizer and the analyzer are again brought into a parallel Nicol state at the maximum allowable tilt angle, and the sample, the polarizer and the analyzer are measured at a plurality of desired angles up to the position and measuring the change in retardation with respect to the tilt angle. A step of relatively rotating the photon by one rotation to obtain an optical order and a retardation (the optical order here is N ′); (E2) the polarizer and the analyzer are again placed in the orthogonal Nicol state, and the inclination angle is set to a predetermined angle. Measuring the transmission intensity while returning the beam to the horizontal side by an angle, and measuring the maximum or minimum number L (the optical order is N ′ + L); (F2) the polarizer and the analyzer are again brought into a parallel Nicol state (G2) a step of rotating the sample, the polarizer and the analyzer by one rotation, and measuring the retardation with the order being N ′ + L; And measuring the change in retardation with respect to the tilt angle. 4. A polarizer is arranged on a measurement light incident side of a sample and an analyzer is arranged in a parallel Nicol state on an emission side, and a single wavelength measurement light is transmitted from the polarizer to the analyzer, and the polarizer and the analyzer are connected to each other. A retardation measuring device that rotates the polarization transmission axes of the polarizer and analyzer relative to the sample while maintaining the parallel Nicols state and detects the intensity of the measurement light transmitted through the analyzer. A sample holding mechanism for tilting by
A polarizer and a pair of analyzers in a crossed Nicols state with a sample interposed are provided, and the change in the optical order with the inclination of the sample is determined by the transmitted light intensity by the polarizers and the analyzer in the crossed Nicols state, and the parallel Nicols state is obtained. When obtaining the retardation by the transmitted light intensity by the polarizer in the state and the analyzer, the optical order is determined based on the change in the optical order obtained by the polarizer in the orthogonal Nicol state and the analyzer. Retardation measuring device. 5. A polarizer on the incident side of the measurement light and a plurality of analyzers on the emission side are arranged in a parallel Nicol state with different polarization directions, and a single wavelength is provided from the polarizer group to the analyzer group. A sample is placed between the polarizer group and the analyzer group, and the retardation measuring device for measuring the retardation of the sample by detecting the measurement light exiting the analyzer group. A sample holding mechanism for tilting by a specific tilt axis,
A polarizer and a pair of analyzers in a crossed Nicols state with a sample interposed are provided, and the change in the optical order with the inclination of the sample is determined by the transmitted light intensity by the polarizers and the analyzer in the crossed Nicols state, and the parallel Nicols state is obtained. When obtaining retardation by the transmitted light intensity by the polarizer group and the analyzer group in the state, the optical order is determined based on the change in the optical order obtained by the polarizer in the orthogonal Nicol state and the analyzer. Retardation measuring device. 6. A polarizer is arranged on the incident side of the measurement light, and a plurality of analyzers are arranged on the emission side in a parallel Nicol state and in different polarization directions from each other. An on-line retardation measuring device that transmits the measurement light of the sample, passes the sample between the polarizer group and the analyzer group, and measures the retardation of the sample by detecting the measurement light that has exited the analyzer group. A pair of a polarizer and an analyzer in a crossed Nicols state with a sample interposed is added, and a change in the optical order is obtained from the transmitted light intensity, and the transmitted light intensities of the plurality of pairs of the parallel Nicol state polarizer and the analyzer are obtained. A retardation measurement device for determining an optical order based on a change in the optical order obtained by the polarizer and the analyzer in the orthogonal Nicol state when obtaining the retardation from the retardation. 7. The polarization directions of the polarizer and the analyzer in the orthogonal Nicols state with respect to the optical principal axis direction of the sample obtained by detecting the measurement light transmitted through the polarizers and the analyzers in the parallel Nicols state. 7. The retardation measuring apparatus according to claim 6, further comprising a mechanism for rotating at least the polarizers in the orthogonal Nicol state and the polarization directions of the analyzer so as to automatically follow the angle of about 45 [deg.]. 8. A pair of a polarizer and an analyzer in the orthogonal Nicol state is further added, and light beams having different wavelengths are made incident on the two pairs of the polarizer and the analyzer in the orthogonal Nicol state. The retardation measuring device according to claim 4, wherein a change in an optical order is obtained at two wavelengths. 9. A pair of a polarizer and an analyzer in a crossed Nicols state is irradiated with measurement light of two different wavelengths, and after passing through the analyzer, is separated for each wavelength to reduce the transmitted light intensity at each wavelength. The retardation measuring device according to any one of 4 to 7, which measures the retardation.