JP3518313B2 - Method and apparatus for measuring retardation - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 Since a synthetic resin material exhibits optical anisotropy when stretched, it is possible to control the stretching process of the synthetic resin material by measuring the optical anisotropy. 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. 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, it is performed to measure the phase shift of two orthogonally polarized lights that have passed through the sample, that is, the retardation.

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 indices and the material thickness. By measuring the retardation, the birefringence characteristics of the sheet-shaped sample can be known.

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

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 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 optical order. The thicker the sample, the larger the optical 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, the optical order n cannot be directly obtained, but some methods for obtaining the optical order n are known.

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 the 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 also becomes large, and in the conventional method, the optical order is apt to be erroneously determined, and accurate retardation may not be measured.

In the online measurement, the optical order (value obtained by adding 1 to the integer part of the quotient obtained by dividing the retardation by 1/2 of the measurement wavelength: in the present invention, the optical order is used in this sense) is given in advance. However, there is a problem that the retardation changes during the measurement, and it cannot be detected even when the optical order moves to the next optical order. 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 artificially applying tension or heat.

[0009]

The first object of the present invention is to accurately 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 reliably detect a change in the optical order in online measurement of the retardation so that an accurate retardation can be measured even when the change in the optical order occurs. It is to be.

[0010]

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

However, even in this method, it is premised that the first retardation is accurately measured. Even with the conventional method, the retardation can be accurately measured when the optical order is low. The three-dimensional refractive index of a sheet-shaped substance such as a polymer film is generally described by using an index ellipsoid. In the two-dimensional refractive index distribution in a plane, when the minimum direction is tilted, the retardation generally decreases as shown by the solid line in FIG. 1 and further decreases. May reach zero and then increase again. Therefore,
Even in a sample having a high optical order, the optical order can be reduced by inclining a specific axis as an inclination axis.

Therefore, in one aspect of the present invention, as shown in FIG. 2, the polarizer and the analyzer are placed in the orthogonal Nicol state, the optical principal axis of the sample is set to about 45 ° with the polarization direction, and the optical principal axis of the sample is set. While tilting the sample with the direction perpendicular to the tilt axis as the tilt axis to reduce the optical order, the light of the selected wavelength is transmitted from the sample through the polarizer through the analyzer, and the transmitted light intensity of the analyzer with respect to the tilt angle is measured. Then, the change of the optical order is obtained, and the polarizer and the analyzer are brought into the parallel Nicol state again in the state where the optical order is decreased, and the sample, the polarizer and the analyzer are relatively rotated once to obtain the optical order and the retardation. It includes the process of seeking. Then, based on the optical orders and retardations thus accurately obtained, the optical orders and retardations of the sample in the horizontal state or an arbitrary inclined state are obtained.

If the optical order and retardation at a specific tilt angle are known by other methods, as shown in FIG. 3, at least one from the tilted state to the horizontal state is based on that. Retardation in the state can be requested.

In another aspect of the present invention, as shown in FIGS. 4 and 5, the following step (A) is used by using a measuring device capable of inclining a sample to a predetermined angle by a specific inclination axis.
From (D1) to (I1),
The retardation value and the optical order of the sample including any of the steps (D2) to (I2) are determined. (A) A step of obtaining the optical principal axis of the sample from the angular dependence of the intensity of transmitted light when the polarization transmission axis is rotated once relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols, ( B) Set the polarizer and the analyzer in the crossed Nicols state,
Positioning the device and the sample so that the optical principal axis of the sample is about 45 ° with respect to the polarization direction, and the direction perpendicular to the optical principal axis of the sample is the tilt axis, (C) Polarizing light of the selected wavelength Transmit the analyzer from the sample through the probe, measuring the analyzer transmitted light intensity against the tilt angle while tilting the sample to the maximum allowable tilt angle by the tilt axis, its intensity distribution becomes near zero, and If there is an angle at which the intensity distribution is symmetric, select (I1) from the following process group (D1). If there is no such angle, use the maximum inclination angle as the angle and select the following process group (D2). ) To (G2). The intensity distribution is near zero,
When there is an angle at which the intensity distribution is symmetric at that angle, as shown in FIG. 4, (D1) the intensity distribution is near zero, and the polarization is made at an angle at which the intensity distribution is symmetric. Put the child and analyzer in parallel Nicol state again,
A step of relatively rotating the sample, the polarizer and the analyzer one revolution to obtain the optical order and the retardation (here, the optical order is N), (E1) the polarizer and the analyzer are brought into the orthogonal Nicol state again. Measuring the transmission intensity during the measurement while further inclining the sample to the maximum allowable inclination angle while measuring the transmission intensity, and counting the number M of times when the maximum or minimum is exceeded (the optical order at this point is N + M), ( F1) A step in which the polarizer and the analyzer are brought into a parallel Nicol state again, the sample and the polarizer and the analyzer are relatively rotated once, and the retardation is measured with an optical order of N + M. (G1) The polarizer and the analyzer In the orthogonal Nicol state again, and while returning the inclination angle to the horizontal side by a predetermined angle, the transmission intensity thereof is measured, and the maximum or minimum number L is measured (optical order is | N + M-
(L |) and (H1) put the polarizer and analyzer in the parallel Nicol state again, relatively rotate the sample, the polarizer and the analyzer one revolution, and measure the retardation with the order as | N + ML | Step (I1) Steps (G1) and (H1) are performed at desired plural angles up to the horizontal position,
The process of measuring the change in retardation with respect to the tilt angle.

When the intensity distribution is close to zero even when the intensity distribution is tilted to the maximum allowable tilt angle, and there is no angle at which the intensity distribution is symmetric, as shown in FIG. Select (G2) from group (D2). (D2) A step of determining the optical order and retardation by making the polarizer and the analyzer parallel to each other in the parallel Nicol state at the maximum allowable tilt angle and relatively rotating the sample, the polarizer and the analyzer once (the optical order here). (N2), (E2) the polarizer and the analyzer are brought into the orthogonal Nicol state again, the transmission intensity is measured while the tilt angle is returned to the horizontal side by a predetermined angle, and the maximum or minimum number L is measured. Step (the optical order is N ′ + L), (F2) the polarizer and the analyzer are brought into the parallel Nicol state again, the sample, the polarizer and the analyzer are relatively rotated once, and the order is N ′ + L. Retardation measurement step, (G2) Steps (E2) and (F2) are performed at a desired plurality of angles up to a horizontal position, and a change in retardation with respect to an inclination angle is measured.

The measuring device of the present invention includes a device for measuring individual samples and an on-line measuring device for measuring continuously flowing samples. An example of an apparatus for measuring an individual sample is a polarizer on the measurement light incident side of the sample, an analyzer is arranged on the exit side in a parallel Nicol state, and a single wavelength measurement light is transmitted from the polarizer to the analyzer. A retardation measurement 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 keeping the polarizer and the analyzer in parallel Nicols state. . Another example of an apparatus for measuring individual samples is a polarizer on the incident side of the measurement light and an analyzer on the exit side in parallel Nicols state, and a plurality of pairs of polarizers are arranged with different polarization directions, and the polarizer group is arranged. To transmit the measurement light of a single wavelength to the analyzer group, arrange the sample between the polarizer group and the analyzer group, and measure the retardation of the sample by detecting the measurement light emitted from the analyzer group. It is a retardation measuring device. Then, in these retardation measuring devices, in the present invention, a sample holding mechanism for inclining the sample by a specific tilt axis, and a pair of a polarizer and an analyzer in a crossed Nicols state sandwiching the sample, the crossed Nicols The change in the optical order due to the tilt of the sample is obtained by the transmitted light intensity by the polarizer and the analyzer in the state, and when the retardation is obtained 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 device, 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 the polarization directions are different from each other. Transmit the measuring light of a single wavelength to the analyzer group, pass the sample between the polarizer group and the analyzer group,
The retardation of the sample is measured by detecting the measurement light emitted from the analyzer group, and in the present invention, a pair of a polarizer and an analyzer that are in a crossed Nicols state with the sample sandwiched is added, and the transmitted light thereof. Obtaining the change in the optical order from the intensity, when obtaining the retardation from the transmitted light intensity of the polarizer and the analyzer in a plurality of pairs of parallel Nicols state, the optical order of the optical order obtained by the polarizer and the analyzer in the orthogonal Nicols state 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 crossed Nicols state, the optical order may change from decrease to increase or increase to decrease. The change is caused by the transmitted light intensity distribution of the analyzer. It can be determined by symmetry. However, depending on the measurement wavelength, the position where the transmitted light intensity distribution is symmetric may overlap with the maximum or the minimum of the transmitted light intensity distribution. Therefore, it is preferable to carry out the measurement in the orthogonal Nicols state at two different wavelengths, and to select a wavelength at which the position where the transmitted light intensity distribution is symmetric does not overlap the maximum or the minimum of the transmitted light intensity distribution.

The method itself for obtaining 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 will be shown for convenience of description. However, the invention is not limited to these exemplary methods.

First, the method of measuring the retardation value will be described. As shown in FIG. 6A, the polarizer p
And the analyzer a are kept in a parallel Nicol relationship with each other, and are rotated relative to the sample s arranged therebetween, and the analyzer transmitted light is detected, and the analyzer transmitted light intensity I is measured from the reference position of the sample. 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) This analyzer transmitted light intensity When I is displayed in polar coordinates,
It becomes a ten o'clock flower-shaped figure as shown in (B). here,
Io is the incident light intensity of the sample, α is the ratio of the transmittances of polarized light oscillating in the two optical principal axes of the sample, and θ ₀ is the angle between the maximum refractive index direction of the two optical principal axes and the reference direction. ,
C is represented by the following formula. C = cos (2πR / λ) (2) 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 calculated 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 obtained, and the order n If it is decided, the retardation value R
Is calculated by the following formula. 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 obtain the phase difference δ corresponding to the retardation value for each of two lights having different wavelengths, and set the optical order n to 1 The retardation value is obtained while changing in order of 2, 3, 3. Then, the point where the retardation values obtained at different wavelengths are the same is the required retardation value, which is the optical order. In addition, depending on the retardation value, a wavelength range that is difficult to obtain accurately appears, and in that case, measurement is performed using the other two wavelengths (see Japanese Patent Laid-Open No. 4-294249).

As another method for determining the optical order n, a phase plate having a variable retardation value, for example, a Babinet Soleil compensating plate is superposed on the sample, and the sample and the phase plate are aligned with 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. The 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 created in advance and this relationship. Then, the optical order of retardation of the sample is determined (see Japanese Patent Application No. 5-53024). Although there are other methods for determining the optical order n, any method may be adopted in the present invention.

In the crossed Nicols state as shown in FIG. 7A, the transmission intensity I is expressed by the following equation. I = A · sin ² θ · sin ² (πR / λ) (7) As shown in FIG. 7 (B), the optical order changes every λ / 2, so the transmission intensity when the retardation changes If I is continuously measured, the change in optical order can be seen. When the start is 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 with a slight wavelength shift. And
When the sample is tilted and the retardation starts to decrease and then increases, or vice versa, the transmission intensity I changes so as to be folded back symmetrically with respect to time.

[0025]

EXAMPLE FIG. 8 and FIG. 9 show an example of the birefringence measuring apparatus used in the aspect of measuring the retardation by inclining the sample according to the present invention. Measuring 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 flux 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 this order from the condenser lens 6 side in the optical path from the condenser lens 6 to the light receiving element 24. .

The filter 8 has a filter holding plate 10 so that the order n can be obtained by measurement with a plurality of wavelengths.
A plurality of filters having different transmitted light characteristics are arranged along the circumferential direction of. A stepping motor (not shown) that rotates the filter holding plate 10 selects one of the filters and inserts it 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 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 the polarization directions thereof are parallel to each other, that is, in the parallel Nicol state, and are held by the 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 both polarization plates 14 and 18 are rotated. Are rotated integrally. Holding disk 1 with polarizing plate 14 attached
A mark of a reflector is provided on one side surface of 6, and the initial position of rotation of the polarizing plates 14 and 18 is detected by detecting this reflector with a photoelectric detector.

A mirror 36 is removably arranged on the optical axis between the polarizing plate 14 and the sample 22, and a polarizing plate 38 is also arranged on the optical axis between the mirror 36 and the sample 22, which is also the optical path. It is arranged to be removable. The polarizing directions of the polarizing plate 38 and the polarizing plate 18 are determined so that their polarization methods are orthogonal to each other, that is, they are in the orthogonal Nicol state. Laser light is incident on the set of the polarizing plate 38 and the polarizing plate 18 via the mirror 36.

As a means for measuring the retardation of the sample 22 in a tilted state, the sample 22 can be rotated in its plane and the sample is tilted about a straight line along the surface of the sample 22. The sample 22 is held by the sample holding device so that In FIG. 8, the sample holding device is not shown.

The 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 the central axes of the shafts 88 and 90 are arranged so as to come to the surface of the sample holder 70. These shafts 88 and 90 are supported by the main body of the birefringence measuring device. A pulley 62 is attached to one of the shafts 88, and a belt 64 is hung between the pulley 66 of a stepping motor 68 provided on the body side of the birefringence measuring device and the pulley 62, and the substrate 80 is tilted by the motor 68. To be

Returning to FIG. 8, the mirror 36 and the polarizing plate 38 are removed from the optical path when the measurement is performed in the parallel Nicol state. Sample 2 installed between polarizing plates 14 and 18
The measurement light having a wavelength selected by one of the filters passes through the polarizing plate 14 to enter 2, and the measurement light passing through the sample 22 passes through the polarizing plate 18 and enters the light receiving element 24 for photometry. . The transmitted light intensity is measured by rotating the polarizing plate 14 and the polarizing plate 18 while keeping them in the parallel Nicols state.

The measurement in the state of parallel Nicols makes it possible to determine the optical principal axis direction, retardation, and optical order. On the other hand, when the measurement is performed in the crossed Nicols state, the mirror 36 and the polarization plate 38 are arranged in the optical path, and the polarization plate 18 and the polarization plate 18 are placed in the crossed Nicols state.
The rotation angle is adjusted and fixed, and the laser light is made incident through the mirror 36. While the polarizing plates 38 and 18 are fixed, the optical principal axis of the sample is set to about 45 ° with respect to the polarization direction, and while the sample is tilted around the tilt axis with the direction perpendicular to the optical principal axis as the tilt axis, Measure the light intensity. The change in the optical order can be obtained by the measurement in the orthogonal Nicol state.

Although not shown, 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. The output converted into a digital signal is taken in by a computer which has 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 device. The structure of the light source portion is similar to that of the embodiment shown in FIG. 8, and the measuring 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 of FIG. 10, the condensing lens 6 irradiates the parallel light spread to the area to be irradiated with light at the same time so that a plurality of parts that are close to each other but are different can be irradiated with the measurement light at the same time. It is an optical system that does. The measurement light is transmitted from the condenser lens 6 to the light receiving element groups 24-1 to 24-6.
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 in the optical path reaching 25. The light transmitted through the polarizer groups 14-1 to 14-6 and 15 passes through the analyzer groups 18-1 to 18-6 and 19 and is incident on the light receiving element groups 24-1 to 24-6 and 25, respectively. It is 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 the parallel Nicols state, and the polarization directions are shifted by 60 °. Has been defined.
The polarization directions of the polarizer 15 and the analyzer 19 are determined so as to be in the crossed Nicols state.

The sample 22a is moved 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 amplifying the detection output of each of the light receiving element groups 24-1 to 24-6 and 25, and an analog circuit is provided to sequentially select the amplified output at constant time intervals, for example, 1 millisecond intervals. 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 into the digital signal is taken into a computer that has 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 orthogonal Nicols state to be 45 ° with respect to the optical principal axis of the sample. Therefore, the polarizer group 14
-1 to 14-6 and 15 and analyzer groups 18-1 to 18-6 and
19 are respectively held on holding discs similar to the holding discs 16 and 20 shown in the embodiment of FIG. 8, which in turn are each connected via a belt in the same manner as in the embodiment of FIG. By connecting each with the pulley fixed on the top and rotating its shaft by the stepping motor,
Polarizer groups 14-1 to 14-6 and 15 and analyzer group 18-1
It is preferable that -18 to 6 and 19 can be integrally rotated while maintaining their polarization states.
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 Nicol state, it is detected. Further, the polarizer groups 14-1 to 14-6 are controlled by a computer that takes in data so that the polarization directions of the polarizer 15 and the analyzer 19 in the orthogonal Nicol state are 45 ° with respect to the optical principal axis direction. 15 and analyzer group 18-1
Rotate the holding discs ~ 18-6,19. as a result,
Even if the optical principal axis direction of the sample that is moved and measured online is changed, the polarizer 15 and the analyzer 1 in the orthogonal Nicols state
The polarization direction of 9 can always follow the optical axis of the sample at 45 °.

Two pairs of the polarizer and the analyzer in the crossed Nicols state are provided, and light of different wavelengths is made incident on each of the two pairs of the polarizer and the analyzer in the crossed Nicols state. A pair of polarizer and analyzer is selected so that the transmitted light intensity at the start of measurement does not become maximum or minimum, or the measurement light of two different wavelengths is used for the pair of polarizer and analyzer in the crossed Nicols state. It is preferable that any one of the above can be selected to be incident, and the wavelength at which the transmitted light intensity at the start of measurement does not become maximum or minimum can be selected.

In FIG. 11, two pairs of polarizers and analyzers in the orthogonal Nicols state are provided, and light of different wavelengths is incident on each of the two pairs of polarizers and analyzers in the orthogonal Nicols state. 2 is a diagram showing an online measuring device configured to perform the above. The optical fiber 4 that guides the measurement light from the light source 2 is branched to guide the measurement light to both the condenser lenses 6 and 6b. A condenser lens 6 for converting the measurement light guided by the optical fiber 4 into parallel light, a narrow band filter 8, polarizer groups 14-1 to 14-6 and analyzer groups 18-1 to 18-6 in a parallel Nicol state. ,
A pair of polarizer 15 and analyzer 19 in the orthogonal 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 0. In FIG. 11, a pair of the polarizer 15b and the analyzer 19b in the orthogonal Nicols state are further provided with the sample 22a interposed therebetween. The measurement light passing through the condenser lens 6b is guided to the polarizer 15b through a narrow band filter 8b designed to have a transmission wavelength λ ₂ different from the narrow band filter 8 (transmission wavelength λ ₁ ). Sample 15 from polarizer 15b
a, the measurement light transmitted through the analyzer 19b receives the light receiving element 25b.
Detected by.

The detection output of the light receiving element 25b is detected by 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, selected by the analog multiplexer 42 and sequentially converted into a digital signal by the A / D converter 44, the signal is taken into a computer which has 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 Nicol state. Now, it is assumed that the retardation of the sample has changed as shown in FIG. 12A at the measurement wavelength λ ₁ .
That is, at time t ₁ , the optical order monotonously increased and changed from 2 to 3, and at time t ₂ , the optical order changed from increase to decrease and the optical order changed from 3 to 2. 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 cannot be determined at time t ₂ whether the retardation is increasing or decreasing. However, due to a wavelength λ ₂ different from λ ₁ (for example, λ ₁ <λ ₂ ), a polarizer and analyzer pair in the orthogonal Nicols state at the measurement wavelength λ ₂ , for example, as shown in FIG.
When the transmitted light intensity of the pair of the polarizer 15b and the analyzer 19b in No. 1 is measured, as shown by a broken line in FIG.
_{At 2} , it can be determined that the retardation has changed from increasing to decreasing.

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

The measuring apparatus shown in FIGS. 10 and 11 can be applied to the measurement of individual samples as shown in FIG. 8 instead of online. In that case, the sample holding device shown in FIG. 9 can be utilized to hold and tilt the sample. To measure the retardation using this measuring device, the polarizer group 14-1 to 14-6 and the analyzer group 18-1 to 18 in a parallel Nicol state with the sample in a horizontal state are used.
The optical principal axis direction is obtained from the transmitted light intensity of −6, and the sample is rotated so that the optical principal axis of the sample forms about 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 tilt of the sample is the same as that shown in the embodiment of FIG. To measure the retardation at each tilt 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 used in the embodiments of FIGS. 10 and 11. It is determined by detecting the intensity of transmitted light while the groups 18-1 to 18-6 are fixed.

[0043]

According to the present invention, the optical axis of the sample is set to about 45 ° with respect to the polarization direction with the polarizer and the analyzer in the orthogonal Nicols state, and the sample is tilted with the direction perpendicular to the optical axis of the sample as the tilt axis. As the optical order is reduced, it includes the step of obtaining the optical order and retardation under the condition of parallel Nicols between the polarizer and the analyzer in the state where the optical order is decreased. The optical order and retardation of can be accurately obtained. Then, based on the optical order and the retardation in that state, the optical order and the retardation of the sample in the horizontal state or an arbitrary inclined state can be accurately obtained. Also, in the online measurement of retardation, by providing a pair of a polarizer and an analyzer in the crossed Nicols state, it becomes possible to detect a change in the optical order during the measurement.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a first aspect of the measuring method of the present invention.

FIG. 3 is a flowchart showing a method of applying the measuring method of the present invention when the optical order and retardation at a specific inclination angle are known.

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

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

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

FIG. 7 is a diagram illustrating a case where a polarizer and an analyzer have a relationship of orthogonal Nicols, and (A) 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 an embodiment of the measuring apparatus of the present invention.

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

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

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

12A and 12B are diagrams showing an operation of the example, FIG. 12A is a diagram showing a time variation of retardation, and FIG. 12B is a transmitted light intensity of a polarizer and an analyzer in a crossed 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

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-82697 (JP, A) JP-A-9-89761 (JP, A) JP-A-6-241987 (JP, A) JP-A-5- 240777 (JP, A) JP 4-294249 (JP, A) JP 3-25347 (JP, A) JP 6-249774 (JP, A) JP 8-201277 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 JISST file (JOIS)

Claims (9)

(57) [Claims] 1. A polarizer is disposed on the measurement light incident side of the sample, and an analyzer is disposed on the emission side, and the polarizer and the analyzer are kept in a predetermined polarization azimuth relationship, and the polarization transmission axis of the polarizer and the analyzer are used as the sample. 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 by a specific tilt axis, the following steps (A) to ( A method for measuring retardation, characterized in that the retardation value of a sample including C) and its order are obtained. (A) obtaining the optical principal axis of the sample from the angle dependence of the intensity of transmitted light when the polarization transmission axis is rotated once 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 the orthogonal Nicol state, the optical principal axis of the sample is set to about 45 ° with the polarization direction, and the sample is tilted with the direction perpendicular to the optical principal axis of the sample as the tilt axis to reduce the optical order. Meanwhile, a step of transmitting the light of the selected wavelength from the sample through the polarizer to the analyzer and measuring the analyzer transmitted light intensity with respect to the tilt angle to obtain the change in the optical order, (C) The sample is tilted horizontally. In at least one of the states in which the optical order is decreased, the polarizer and the analyzer are brought into the parallel Nicol state again, and the sample, the polarizer, and the analyzer are relatively rotated once to obtain the optical order and the retardation. 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 polarizer and the analyzer are kept in a predetermined polarization azimuth relationship, and the polarization transmission axes of the polarizer and the analyzer are arranged on the sample. 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 by a specific tilt axis, the following steps (A) to ( A retardation measuring method comprising: obtaining a retardation value and its order in a horizontal state of a sample including C), the optical order and retardation of which are known at a specific inclination angle. (A) obtaining the optical principal axis of the sample from the angle dependence of the intensity of transmitted light when the polarization transmission axis is rotated once relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols; B) The optical axis of the sample is set to about 45 ° with respect to the polarization direction, and the sample is tilted to the predetermined tilt angle with the direction perpendicular to the optical axis of the sample as the tilt axis, and then the polarizer and the analyzer are orthogonal to each other. In a state where the sample is tilted, light of a selected wavelength is transmitted from the sample through the polarizer through the analyzer, and the analyzer transmitted light intensity with respect to the tilt angle is measured to obtain the 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 placed in the horizontal state and the polarizer and the analyzer are brought into the parallel Nicol state again, and the sample, the polarizer and the analyzer are rotated once relative to each other. Let me give you a letter The process of seeking 3. A polarizer is disposed on the measurement light incident side of the sample, and an analyzer is disposed on the emission side, and the polarizer and the analyzer are kept in a predetermined polarization azimuth relationship, and the polarization transmission axes of the polarizer and the analyzer are used as the sample. Using the 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 to a predetermined angle by a specific tilt axis, the following steps ( A) to (C) are included, and the retardation value of the sample and its optical order are calculated by including any of the process groups (D1) to (I1) and the process groups (D2) to (I2). Characteristic retardation measurement method. (A) obtaining the optical principal axis of the sample from the angle dependence of the intensity of transmitted light when the polarization transmission axis is rotated once relative to the sample in a state where the polarizer and the analyzer are in parallel Nicols; B) Position the device and the sample so that the polarizer and the analyzer are in the orthogonal Nicols state, the optical axis of the sample is about 45 ° with the polarization direction, and the direction perpendicular to the optical axis of the sample is the tilt axis. Step (C) Transmit light of a selected wavelength from a sample through a polarizer through an analyzer, and measure the analyzer transmitted light intensity 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 near zero and there is an angle at which the intensity distribution is symmetric, select (I1) from the following process group (D1). If there is no such angle, The maximum tilt angle As a step of selecting (G2) from the following step group (D2), (D1) the polarizer and the analyzer are brought into parallel Nicol state again at that angle, and the sample, the polarizer and the analyzer are relatively set to 1
Step of rotating to determine the optical order and retardation (here, the optical order is N), (E1) The polarizer and the analyzer are brought into the orthogonal Nicol state again and the transmission intensity is measured, and the maximum allowable tilt angle of the sample Measuring the transmission intensity while tilting up to, and counting the number M of times when the maximum or minimum is exceeded (the optical order at this point is N + M), (F1) the polarizer and the analyzer are put in the parallel Nicol state again. , The step of rotating the sample, the polarizer and the analyzer relatively once, and measuring the retardation with the optical order being N + M. (G1) The polarizer and the analyzer are brought into the orthogonal Nicol state again, and the tilt angle is set to a predetermined angle. While returning to the horizontal side only, the transmission intensity is measured and the maximum or minimum number L is measured (optical order is | N + ML |), (H1) The polarizer and the analyzer are parallel again. State, the sample, the polarizer and the analyzer are rotated once relative to each other, and the retardation is measured by setting the order to | N + ML |, (I1) Steps (G1) and (H1) are horizontally moved. Measuring the change in retardation with respect to the tilt angle by performing a plurality of desired angles up to (D2) making the polarizer and the analyzer parallel to the Nicol state again at the maximum allowable tilt angle, and the sample, the polarizer and the analyzer. Relative rotation of 1 to obtain the optical order and retardation (here, the optical order is N ′), (E2) the polarizer and the analyzer are brought into the orthogonal Nicol state again, and the tilt angle is set to a predetermined angle. Only while returning to the horizontal side, the transmission intensity is measured and the maximum or minimum number L is measured (the optical order is N '+ L), (F2) The polarizer and the analyzer are put in the parallel Nicol state again. The step of rotating the sample relative to the polarizer and the analyzer one revolution, and measuring the retardation with the order of N ′ + L, (G2) Steps (E2) and (F2) are performed in a desired plurality of positions up to the horizontal position. The step of measuring the change in retardation with respect to the inclination angle at the angle of. 4. A polarizer is arranged on the measurement light incident side of the sample, and an analyzer is arranged on the emission side in a parallel Nicol state, and the polarizer and the analyzer transmit the measurement light of a single wavelength to the analyzer. 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 analyzer relative to the sample while maintaining the parallel Nicols state A sample holding mechanism that tilts with
A pair of a polarizer and an analyzer in a crossed Nicols state sandwiching the sample is provided, and the change in the optical order due to the tilt of the sample is obtained by the transmitted light intensity by the polarizer and the analyzer in the crossed Nicols state, and the parallel Nicols When determining the retardation by the transmitted light intensity by the polarizer and the analyzer in the state, characterized by determining the optical order based on the change in the optical order obtained by the polarizer and the analyzer in the crossed Nicols state Retardation measuring device. 5. A plurality of pairs of polarizers are arranged on the incident side of measurement light and on the exit side in a parallel Nicol state, and the polarization directions are different from each other, and a single wavelength is provided from the polarizer group to the analyzer group. In the retardation measurement device that transmits the measurement light of, arranges the sample between the polarizer group and the analyzer group, and measures the retardation of the sample by detecting the measurement light emitted from the analyzer group. A sample holding mechanism that tilts with a specific tilt axis,
A pair of a polarizer and an analyzer in a crossed Nicols state sandwiching the sample is provided, and the change in the optical order due to the tilt of the sample is obtained by the transmitted light intensity by the polarizer and the analyzer in the crossed Nicols state, and the parallel Nicols When determining the retardation by the transmitted light intensity by the polarizer group and the analyzer group of the state, characterized by determining the optical order based on the change in the optical order obtained by the polarizer and the analyzer in the crossed Nicols state And a retardation measuring device. 6. A plurality of pairs of polarizers are arranged on the incident side and the exit side of the measurement light in a parallel Nicol state and the polarization directions are different from each other, and a single wavelength is provided from the polarizer group to the analyzer group. In the online type retardation measuring device for measuring the retardation of the sample by transmitting the measurement light of, passing the sample between the polarizer group and the analyzer group, and detecting the measurement light emitted from the analyzer group. , A pair of a polarizer and an analyzer placed in a crossed Nicol state with a sample sandwiched between them is added, and the change in optical order is obtained from the transmitted light intensity. The retardation measuring apparatus is characterized in that the optical order is determined on the basis of the change in the optical order obtained by the polarizer and the analyzer in the crossed Nicols state when the retardation is obtained from the above. 7. The polarization direction of the polarizer and the analyzer in the orthogonal Nicols state is the direction of the optical axis of the sample obtained by detecting the measurement light transmitted through the polarizer group and the analyzer group in the parallel Nicols state. 7. The retardation measuring device according to claim 6, further comprising a mechanism for rotating and automatically following the polarization directions of at least the polarizer and the analyzer in the orthogonal Nicols state so as to always make about 45 °. 8. A pair of polarizers and analyzers in the orthogonal Nicols state is further added, and light of different wavelengths is made incident on the two pairs of polarizers and analyzers in the orthogonal Nicols state. The retardation measuring device according to any one of claims 4 to 7, which obtains a change in optical order at two wavelengths. 9. A pair of a polarizer and an analyzer in a crossed Nicols state are made to enter measurement light of two different wavelengths, and after passing through the analyzer, they are separated for each wavelength to determine the transmitted light intensity at each wavelength. The retardation measuring device according to any one of 4 to 7 to be measured.