JP3250272B2 - Birefringence measurement method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the amount of birefringence of a transparent material such as glass.

[0002]

2. Description of the Related Art As a method of measuring the amount of birefringence of a transparent sample such as glass, there is a Senarmont method.
This method has been adopted as a "method for measuring the strain of optical glass" of the Japan Optical Glass Industry Association standard.
It is a method adopted as a standard method in ASTM and the like. Hereinafter, the Senarmont method will be described using a method adopted as a standard method in the ASTM (hereinafter referred to as the ASTM method) as an example.

FIG. 16 is a diagram showing a configuration of an apparatus for implementing the ASTM method. In FIG. 16, measurement light emitted from a light source 1 is converted into light of a single wavelength by a monochromatic filter 13, passed through a diffusion plate 14, and then sequentially into a first linear polarizer 2, a sample to be measured 3, 1 The light passes through the 波長 wavelength plate 4 and the second linear polarizer 5 and is observed by the telescope 11. The main axis direction of the quarter-wave plate 4 is set to be 0 ° or 90 ° with respect to the polarization axis direction of the first linear polarizer 2.

The amount of birefringence of the sample 3 to be measured is measured by this apparatus according to the following procedure. First, the first linear polarizer 2
And the second linear polarizer 5 are set to have a crossed Nicols relationship. In this state, the sample 3 to be measured is removed,
While observing the brightness of the light with the telescope 11, the second polarizer 5 is rotated and adjusted around the central axis of the measurement light parallel to the traveling direction of the measurement light, so that the brightness of the observed light is minimized. It may be set as follows.

Next, the sample 3 is reset based on the sample 3, and the sample 3 to be measured is set such that the principal axis direction of the birefringence of the sample 3 is 45 ° with respect to the polarization axis direction of the first linear polarizer 2. I do. This can be achieved by adjusting the rotation of the sample 3 around the central axis of the measurement light while observing the brightness of the light with the telescope 11, so that the brightness of the observed light is maximized.

Next, in this state, the second linear polarizer 5 is rotated and adjusted around the central axis of the measurement light, and an angular position where the brightness of the light observed by the telescope 11 is minimized is obtained.
Assuming that the rotation angle of the second linear polarizer 5 at this time is θ (deg.), The birefringence amount Δ (deg.) Of the sample 3 to be measured is obtained from the following equation (1).
Can be requested.

Δ (deg.) = 2θ ‥‥‥ (1) When the amount of birefringence Δ is obtained in the unit of the wavelength of light (nm), the wavelength of the light used for measurement is set to λ (nm). When the next
It can be obtained by equation (2).

Δ (nm) = (λ (nm) · θ (deg.)) / (180 (deg.)) ‥‥‥ (2)

[0009]

By the way, the measurement accuracy by the above-mentioned conventional method is limited to ± 1 to 3 nm, and it has become impossible to sufficiently meet the recent demand for high precision optical equipment.

This is because, in the conventional method, the sample 3 to be measured is manually rotated while looking through the telescope 11 to find the direction in which the light intensity becomes maximum, and then the second linearly polarized light is looked through the telescope 11. The child 5 is manually rotated to find a direction in which the light intensity is minimized.
The rotation operation and observation are performed by humans. Therefore, it was considered that this was due to the inclusion of errors and reading errors during manual operation. Therefore, a method of removing errors caused by human involvement by automating the rotation operation of the sample 3 and the second linear polarizer 5 and replacing the observation through the telescope 11 with the measurement by a photodetector is considered. Was done.

However, it has been found that the measurement accuracy cannot be improved as expected simply by automating the conventional method. That is, according to the above-mentioned automation, it was found that the dispersion of the measured values due to individual differences or the like can be reduced, but from the viewpoint of the absolute accuracy of the measurement, there is not much difference from the measurement accuracy when a skilled person manually measures. For this reason, it was estimated that the limit of the measurement accuracy of the above-mentioned conventional method was restricted by the principle factor of the measurement. That is, this conventional measuring method is, in principle, "determining the azimuth by finding the position where the brightness of the observation light becomes maximum or minimum". In other words, the position at which the light intensity shows a peak is determined from comparison with the light intensity before and after the position near the peak, and the direction is determined. When the peak position is determined by such a method, when the peak is sufficiently sharp, the peak position can be accurately determined, but the measurement error increases as the peak becomes broader. In the case of the above conventional method, the light intensity (bright and dark) observed to determine each direction
Was estimated to have only a sharpness to ensure the above-mentioned insufficient accuracy. Moreover, in order to determine the peak position from the light intensity before and after the peak, it is necessary to reciprocally rotate the sample 3 and the second polarizer 5 and the like. However, errors due to backlash of the reciprocating rotation mechanism may occur. is there. Furthermore, in the method of comparing light intensities, when converted into an electrical signal by the photodetector, various noises are superimposed on the electrical signal, which may cause an error due to the noise.

The present invention has been made under the above-mentioned background, and an object of the present invention is to provide a method and an apparatus for measuring a birefringence amount capable of sufficiently improving the measurement accuracy.

[0013]

In order to solve the above-mentioned problems, the method for measuring the amount of birefringence according to the present invention comprises the steps of (1) placing a birefringent sample on the optical path axis of the linearly polarized light for measurement; A wavelength plate, a linear polarizer, and a light measuring means are sequentially arranged, and a main axis direction of birefringence of the quarter-wave plate is made coincident with a polarization axis direction of the linearly polarized light for measurement. The axis direction is orthogonal to the polarization direction of the linearly polarized light for measurement, and then the birefringent sample is rotated around the optical path axis, or the sample is fixed and the measurement is performed. While rotating the polarization direction of the linearly polarized light, the quarter-wave plate and the linear polarizer by the same angle, measure the amount of light by the light measuring means and determine the amount of rotation until the measured amount of light shows the maximum, The principal axis direction of birefringence of the birefringent sample is the linearly polarized light for measurement. The polarization axis direction and the polarization axis direction of the linear polarizer is set to form an angle of 45 °, then,
While rotating the linear polarizer around the optical path axis,
The amount of light is measured by the light measuring means to determine an angle at which the measured amount of light becomes a minimum, and at this time, a rotation angle amount of the linear polarizer rotated from the start of rotation until the measured amount of light shows a minimum is obtained. A birefringence amount measuring method for obtaining a birefringence amount of the birefringent sample from an angle amount, wherein a method for obtaining a rotation angle of an optical member when a light amount measured by the light measurement unit indicates a maximum or a minimum is the optical method. The method is characterized in that a method is used in which the member is continuously rotated and an angle indicating the maximum or minimum of the measured light amount is obtained from phase information of a periodic signal obtained from the light measuring means at that time.

Further, as an aspect of the configuration 1, (2)
In the birefringence amount measuring method according to Configuration 1, as a method for obtaining the rotation angle of the optical member when the amount of light measured by the light measuring unit indicates a maximum or a minimum, the optical member is continuously rotated, and then the light measuring unit is used. From a measured value of a periodic signal obtained from the Fourier analysis to determine a curve showing the change in light amount with respect to the rotation angle, from the phase information of this curve to determine the angle indicating the maximum or minimum of the measured light amount, characterized by using Configuration and (3) In the method for measuring the amount of birefringence in Configuration 1, as a method for obtaining the rotation angle of the optical member when the amount of light measured by the light measuring unit indicates a maximum or a minimum, the optical member is continuously rotated. Generating a periodic reference AC signal corresponding to a known rotation angle of the optical member; A periodic signal, that is, an AC signal, is input to a phase meter to determine a phase difference between the signals, and a method is used to determine an angle at which the measured light amount indicates the maximum or minimum from the phase difference.

Further, the birefringence amount measuring device according to the present invention comprises: (4) an optical device for generating linearly polarized light for measurement;
Rotating the birefringent sample around the optical path axis with a birefringent sample, a quarter-wave plate, a linear polarizer, and light measuring means sequentially arranged on the optical path axis of the linearly polarized light for measurement. Or the sample is fixed and the polarization direction of the linearly polarized light for measurement, a mechanism for rotating the quarter-wave plate and the linear polarizer by the same angle, and a mechanism for independently rotating and driving the linear polarizer. A rotation driving device provided with the light amount change information sent from the light measuring means, and a rotation angle by the rotation driving device is obtained from phase information of a periodic change curve indicating a light amount change with respect to a rotation angle. And a processing device for obtaining the amount of birefringence.

[0016] As an aspect of the configuration 4, (5)
In the birefringence amount measuring device according to Configuration 4, the processing device obtains a periodic change curve indicating a light amount change with respect to the rotation angle by performing Fourier analysis on the light amount change information transmitted from the light measuring means, and obtains a phase change curve from the phase information. (6) a configuration characterized in that a rotation angle by the rotation drive device is obtained to obtain a birefringence amount of the sample;
The birefringence amount measuring device according to Configuration 4, further comprising a reference AC signal generator that generates a periodic reference AC signal corresponding to a known rotation angle of the optical member that is rotationally driven by the rotational driving device; A phase meter for inputting an AC signal indicating a change in the amount of light transmitted from the light measuring means and a reference AC signal transmitted from the reference AC signal generator and transmitting a phase difference therebetween, and A configuration is used in which a device having a processing function of obtaining the amount of birefringence of the sample by obtaining the rotation angle by the rotary driving device based on the transmitted information is used.

[0017]

According to the method of the first aspect, as a method for obtaining the rotation angle of the optical member when the amount of light measured by the light measuring means indicates the maximum or the minimum, the optical member is continuously rotated. A method of obtaining an angle indicating the maximum or minimum of the measured light amount from the phase information of the obtained periodic signal is used. That is, unlike the conventional method, the position at which the light intensity shows a peak is determined from the phase information instead of determining the azimuth by determining from the comparison with the light intensity before and after the vicinity thereof. . For this reason, it has become possible to remarkably improve the measurement accuracy as compared with the conventional method of determining the peak position by intensity comparison.
In addition, since the rotational scanning for obtaining the phase information does not need to be reciprocating rotation, it is possible to prevent the possibility of the backlash problem caused by the reciprocating rotation mechanism, and to determine the peak position or the phase difference from the phase information. In addition, even if there is a change in the partial intensity, the probability that the change directly leads to an error can be significantly reduced, and therefore, the influence of noise in the measurement system can be substantially eliminated.

As a specific mode of the method of the configuration 1, as in the configuration 2, a method using a Fourier analysis technique,
Some use a phase meter. With the Fourier analysis method, the measurement mechanism can be relatively simple,
In the case of using a phase meter, the measurement time can be reduced.

Further, according to the constitutions 4 to 6, it is possible to obtain an apparatus capable of executing the method of the constitutions 1 to 3, respectively.

[0020]

EXAMPLES First Embodiment FIG. 1 is a diagram showing a configuration of a birefringence measurement apparatus according to a first embodiment of the present invention. Hereinafter, referring to FIG.
A method and apparatus for measuring the amount of birefringence according to an example will be described.

In FIG. 1, reference numeral 1 denotes a light source, and a first light source is sequentially arranged on the optical path axis of the measuring light emitted from the light source 1.
A linear polarizer 2, a sample to be measured 3, a quarter-wave plate 4, a second linear polarizer 5, and a photodetector 10 are arranged.

The sample to be measured 3 and the second linear polarizer 5
Are rotatably attached to the rotating stage 6 and the rotating stage 7, respectively. The rotation stage 6 and the rotation stage 7 each include a rotation mechanism for rotatably holding the sample 3 to be measured and the second linear polarizer 5 and a pulse motor for driving the rotation mechanism. The rotation is controlled. The motor driver 9 is controlled by a command of the arithmetic processing unit 12 and gives a predetermined rotation to the sample 3 to be measured and the second linear polarizer 5.

The arithmetic processing unit 12 stores and executes a predetermined program. In addition to the control of the motor driver 9, the arithmetic processing unit 12 receives a light intensity signal detected by the photodetector 10, and
It has a function of performing a predetermined conversion and executing a Fourier analysis process and other arithmetic processes described later.

The light source 1 is preferably a light source that generates monochromatic light (for example, a laser, an LED, or the like, which transmits light emitted from a white light source through a monochromatic filter), but light having a width in the wavelength direction may be used. it can. In this case, the reference wavelength of the quarter-wave plate 4 may be set as the center wavelength (or the center-of-gravity wavelength) of the used light. In this embodiment, the light source 1
An output-stabilized He-Ne laser (wavelength 633 nm) was used.

A Glan-Thompson prism was used as the first linear polarizer and the second linear polarizer 5, and a silicon photodiode was used as the photodetector 10. Further, as the sample 3 to be measured, usually, glass or the like is a target. In this embodiment, a quartz wave plate having a product guarantee value of 47.5 ° ± 2 ° in phase difference is used as a reference sample.

The amount of birefringence is measured by the above-described apparatus in the following manner. First, the first linear polarizer 2
And the second linear polarizer 5 are set in a relationship of orthogonal Nicols, and the two main axis directions of the quarter-wave plate 4 (the fast axis direction and the slow axis direction are orthogonal to each other). Is set to match the polarization directions of the first linear polarizer 2 and the second linear polarizer 5 (initial setting state).

Next, the sample 3 to be measured is set on the rotary stage 6, and the sample 3 to be measured is rotated around the optical path axis. At this time, the light intensity signal detected by the photodetector 10 is processed by the arithmetic processing unit 12 (The rotary stage 7 is stationary). Then, the light intensity signal obtained by the photodetector 10 draws a cosine wave-like change curve. This is because when the polarization direction of the incident linearly polarized light with respect to the measured sample 3 coincides with one of the principal axes of the birefringence of the measured sample 3 due to the rotation of the measured sample 3, the light has passed through the quarter-wave plate 4. The polarization state of the light is linearly polarized light that matches the polarization direction of the first linear polarizer 2, and as a result, the light intensity passing through the second linear polarizer 5 is minimized. On the other hand, the polarization direction of the incident linearly polarized light with respect to the sample 3 and the direction of the principal axis of birefringence of the sample 3 are 4
When the angle is 5 °, the polarization state of the light passing through the quarter-wave plate 4 is equal to the polarization direction of the first linear polarizer 2 by the amount corresponding to the birefringence of the sample 3 to be measured. Becomes inclined linearly polarized light. As a result, the intensity of light passing through the second linear polarizer 5 becomes maximum. Here, the polarization directions of 0 degree and 1
Since 80 degrees represents the same azimuth, the light intensity passing through the second linear polarizer 5 repeats a four-cycle cosine change when the measured sample 3 makes one rotation. The sample 3 to be measured is rotated from the azimuth of 0 degree, and the azimuth of the sample 3 when the light intensity reaches the maximum for the first time is the principal axis direction of birefringence.

Assuming that the light intensity obtained from the photodetector is S0, the rotation angle of the sample 3 is β, the principal axis direction of the birefringence of the sample 3 is γ, and the birefringence of the sample 3 is Δ. The above change curve can be expressed by the following equation (3).

S 0 = １ ／ (1−cosΔ) {1−cos (4β + 4γ)} (3) FIG. 2 shows the light intensity obtained by the photodetector 10 when the sample 3 is actually rotated. This shows the state of change. It can be seen that the light intensity changes four cycles on the cosine wave. Here, light intensity is taken in at a pitch of 5 ° from 0 ° to 360 ° (72 points were measured). Rotation angle 0
The angle up to the position where the light intensity first reaches a maximum with respect to ° is the initial phase.

The arithmetic processing unit 12 reads these 72
An arithmetic process of performing Fourier analysis of the measured values is performed, and the principal axis direction of the birefringence of the sample 3 to be measured is automatically calculated by calculating １ ／ of the initial phase of the four-period component.

The principal axis direction of the birefringence of the sample 3 was found to be 69.7 degrees as a result of the arithmetic processing. It should be noted that, without using Fourier analysis, it is also possible to obtain the values by reading them directly from the graph.However, since the measurement points are intermittent, the reading accuracy deteriorates and each measurement value contains an irregular error. However, the accuracy of obtaining the main axis direction is reduced.

Next, the rotating stage 6 is driven so that the principal axis direction of the birefringence of the sample 3 thus determined is 45 ° with respect to the polarization direction of the first linear polarizer 2. 155.3 ° (= 180 ° − (69.7 ° −4)
5.0 °)) rotate.

Next, when the polarization azimuth of the second linear polarizer 5 is rotated, the light intensity after passing through the second linear polarizer 5 changes as follows (the rotary stage 6 is stationary). As described above, when the polarization direction of the incident linearly polarized light with respect to the sample to be measured 3 and the direction of the principal axis of the birefringence of the sample to be measured 3 are set to 45 °, the polarization of the light passing through the quarter-wave plate 4 The state is linearly polarized light whose polarization direction is inclined by an amount corresponding to the amount of birefringence of the sample 3 to be measured with respect to the polarization direction of the first linear polarizer 2. As a result, when the polarization direction of the second linear polarizer 5 and the polarization direction of the linearly polarized light emitted from the quarter-wave plate 4 match, the light intensity obtained by the photodetector 10 becomes maximum, and the second When the polarization direction of the linear polarizer 5 is orthogonal to the polarization direction of the linearly polarized light emitted from the quarter-wave plate 4, the light intensity becomes minimum. 0 ° and 180 ° of polarization direction
Represent the same azimuthal angle, the intensity of the light after passing through the second linear polarizer 5 is two-cycle cosine change while the second linear polarizer 2 (only) makes one rotation. Will be repeated. By rotating the second linear polarizer 2 from the 0 ° azimuth, twice the azimuth angle of the second linear polarizer 2 when the light intensity first becomes maximum is the birefringence (Δ) of the sample 3 to be measured. It is.

Now, the light intensity obtained by the photodetector is S1, the rotation angle of the second polarizer 5 is θ, and the birefringence of the sample 3 is Δ
Then, the change curve can be represented by the following equation (4).

S 1 = 1 + cos (2θ−Δ) (4) Then, the second linear polarizer 5 is rotated by the rotary stage 7 (the rotary stage 6 is stationary), and the rotation of the second linear polarizer 5 is made one rotation. The light intensity signal detected by the light detector 10 is continuously taken into the arithmetic processing unit 12. FIG. 3 shows how the light intensity obtained by the photodetector 10 changes when the second linear polarizer 5 is actually rotated. It can be seen that the light intensity changes two cycles on the cosine wave. here,
The light intensity is taken in at a pitch of 5 ° from 0 ° to 360 ° (72 points were measured). With reference to the rotation angle of 0 °, the angle up to the position where the light intensity first reaches the maximum is the initial phase. Fourier analysis of these 72 measured values gives
By calculating the initial phase of the two periodic components, the birefringence (Δ) of the sample 3 to be measured is automatically obtained. The birefringence of this sample was determined to be 46.3 ° as a result of the calculation. It should be noted that, without using Fourier analysis, it is also possible to directly read from the graph to obtain, but because the measurement points are intermittent, the reading accuracy deteriorates, and since each measurement value contains an irregular error, In addition, the accuracy of obtaining the main axis direction decreases.

The result of measuring the same sample with a commercially available birefringence measuring apparatus was 46.9 °, indicating a good agreement. However, the dispersion of the measured values in each of the 20 measurements is ±
0.2 °, and ± 1.1 when using a commercially available device.
°. The variation in the measured values when determining the principal axis of birefringence was also ± 0.2 °. Thus, it can be said that the measurement accuracy according to the present embodiment is about 0.5 digits better than that of a commercially available device.

Second Embodiment FIG. 4 is a view showing a configuration of a birefringence measuring apparatus according to a second embodiment of the present invention. Hereinafter, referring to FIG.
A method and apparatus for measuring the amount of birefringence according to an example will be described.
This embodiment is different from the first embodiment in that, instead of rotating the sample 3 to be measured, the polarization direction of the linearly polarized light to be incident on the sample 3 to be measured, the quarter-wave plate 4, and the second
Except that the linear polarizer 5 is rotated in synchronization with the linear polarizer 5, it has the same configuration as that of the first embodiment. Therefore, in the following description, common parts are denoted by the same reference numerals, and detailed description is omitted. The following description focuses on the differences from the first embodiment.

In FIG. 4, in this embodiment, instead of rotating the sample 3 to be measured in the above-described first embodiment,
Conversely, the sample 3 to be measured is fixed, and instead of the first linear polarizer 2, the quarter-wave plate 4, and the second linear polarizer 5,
Attach one to each of the rotary stages 6, 8, and 7,
These are configured to rotate synchronously at a rotation ratio of 1: 1: 1. The rotary stages 6, 8, 7 are the first
The same structure as the rotary stages 6, 8, 7 in the embodiment
It has a function and is similarly driven by the motor driver 9.

The measuring principle of this embodiment is the same as that of the first embodiment. That is, the first embodiment is different from the first embodiment in that when the principal axis of the birefringence of the sample 3 is determined, the polarization direction (principal axis direction) of each polarizing element of the measurement optical system is rotated instead of rotating the sample 3. That is, the first linearly polarized light 2 and 1 /
The difference is that the four-wavelength plate 4 and the second linear polarizer 5 are rotated in synchronization. However, since the relative positional relationship between the principal axis direction of the birefringence of the sample 3 to be measured and the polarization direction of the light incident on the sample 3 is the same as in the first embodiment, the obtained results are exactly the same. Become.

The feature of this embodiment is that, for example, even if the sample 3 to be measured is too large to be mounted on a rotary stage and cannot be rotated, measurement can be performed.

The light source 1 must have the conditions described in the first embodiment, and further must have the condition that it emits unpolarized light or circularly polarized light. This is to prevent the intensity of light passing therethrough from changing when the first linear polarizer 2 rotates. In this embodiment, the light source 1 has a wavelength of 633n.
An output-stabilized He-Ne laser that emits circularly polarized light at m (a type that incorporates a quarter-wave plate immediately after the emission window of a laser tube that emits linearly polarized light to emit circularly polarized light) For the sample 3 to be measured, a quartz wave plate having a product guarantee value of 47.5 ± 2 ° was used.

FIG. 5 shows that the first linear polarizers 2 and 1/4
FIG. 4 shows how the light intensity obtained by the photodetector 10 changes when the wave plate 4 and the second linear polarizer 5 are synchronously rotated at a rotation ratio of 1: 1: 1. It can be seen that the light intensity changes in four cycles in a cosine wave shape. Here, from 0 ° to 3
The light intensity was measured at a pitch of 5 ° up to 60 ° (72 points were measured). With reference to the rotation angle of 0 °, the angle up to the position where the light intensity first reaches the maximum is the initial phase. These 7
By performing Fourier analysis on the two measured values and calculating を of the initial phase of the four-period component, the principal axis direction of the birefringence of the sample 3 to be measured is automatically obtained. The principal axis direction of the birefringence of this sample was determined to be 30.8 ° as a result of calculation.

Next, the rotating stage 6 is driven so that the principal axis direction of the birefringence of the sample 3 thus determined becomes 45 ° with respect to the polarization direction of the first linear polarizer 2. Is rotated 14.2 ° (= 45.0 ° -30.8 °).

Next, the second linear polarizer 5 is connected to the rotating stage 7
(The rotation stage 6 is stationary), and the light intensity signal detected by the photodetector 10 for one rotation of the second linear polarizer 5 is continuously taken into the arithmetic processing unit 12. Here, light intensity was taken in at 5 ° pitches from 0 ° to 360 ° (72 points were measured). With reference to the rotation angle of 0 °, the angle up to the position where the light intensity first reaches the maximum is the initial phase. Fourier analysis of these 72 measured values gives
By calculating the initial phase of the two periodic components, the birefringence (Δ) of the sample 3 to be measured is automatically obtained. The birefringence of this sample was determined to be 46.1 ° as a result of the calculation, and the measurement accuracy was almost the same as in the first example.

Third Embodiment FIG. 6 is a view showing a configuration of a birefringence measuring apparatus according to a third embodiment of the present invention. Hereinafter, referring to FIG.
A method and apparatus for measuring the amount of birefringence according to an example will be described.
This embodiment is different from the second embodiment in that the first embodiment
Instead of rotating and driving the linear polarizer 2, a half-wave plate 15 rotatable around the optical path axis is newly disposed between the first linear polarizer 2 and the sample 3 on the optical path axis, 1
Second Embodiment Except that the half-wave plate 15, the quarter-wave plate 4, and the second linear polarizer 5 are synchronously rotated and driven so that the rotation ratios thereof become 1: 2: 2, respectively. Therefore, in the following description, common parts are denoted by the same reference numerals, detailed description thereof will be omitted, and parts different from the first embodiment will be mainly described.

In FIG. 4, in this embodiment, the first linear polarizer 2 is fixed instead of rotating the first linear polarizer 2 in the above-described second embodiment, and a new arrangement is provided instead. The half-wave plate 15 is set on the rotary stage 6, and the half-wave plate 15, the quarter-wave plate 4, and the second
Rotational drive was performed synchronously so that the rotation ratio with the linear polarizer 5 was 1: 2: 2. That is,
This embodiment is different from the above-described second embodiment in that when the principal axis of birefringence of the sample 3 to be measured is obtained, instead of rotating the first linear polarizer 2, the half-wave plate 15 and the quarter-wave plate are used. The difference is that the plate 4 and the second linear polarizer 5 are rotated synchronously. The rotary stages 6, 7, 8 have the same structure and function as in the second embodiment, and are driven by the motor driver 9 in the same manner.

The feature of this embodiment is the same as that of the second embodiment in that even when the sample 3 to be measured is large and cannot be rotated by being mounted on a rotary stage, the second embodiment is the same as the second embodiment. In the present embodiment, the polarization state of the light emitted from the light source 1 is arbitrary. In this embodiment, an output stabilized He-Ne laser (wavelength 633 n
m), and a quartz wave plate having a guaranteed product value of 47.5 ° ± 2 ° was used as the sample 3 to be measured.

First, the direction of the linearly polarized light emitted from the half-wave plate 15 is set so that the direction of the polarization axis of the second linear polarizer 5 is orthogonal, and the two main axis directions of the quarter-wave plate 4 are set. Are set so as to overlap the two orthogonal polarization directions, and initialization is performed. Here, the half-wave plate 15 is
It has a function of rotating the incident linear polarization direction by twice the relative azimuth with respect to the fast axis. For example, 1
When linearly polarized light that is inclined by 15 ° with respect to the fast axis direction of the half-wave plate 15 is incident, the emitted linearly polarized light direction becomes １ ／.
It is inclined by 30 ° with respect to the fast axis of the wave plate 15. Accordingly, when the half-wave plate 15 rotates 360 °, the polarization direction of the linearly polarized light emitted from the half-wave plate 15 in FIG.
It will rotate by 0 °. Therefore, in this embodiment, in order to obtain the same operation as that of rotating the first linear polarizer 2 in the second embodiment, the half-wave plate 15, the quarter-wave plate 4, the second It is necessary to synchronously rotate the linear polarizer 5 with a rotation ratio of 1: 2: 2, respectively.

Next, the half-wave plate 15 and the quarter-wave plate 4
And the second linear polarizer 5 are rotated (rotation ratio 1: 2: 2) around the optical axis, and the light detected by the photodetector 10 for one rotation of the half-wave plate 15 is rotated. The intensity signal is continuously taken into the arithmetic processing unit 12. Here, the light intensity obtained by the photodetector is S0 ', the rotation angle of the half-wave plate 15 is β', the principal axis direction of the birefringence of the sample 3 is γ, and the amount of birefringence of the sample 3 is Δ. Then, the change curve in this case can be represented by the following equation (5).

S 0 ′ = 2１ ／ (1−cosΔ) {1−cos (8β′−4γ)} (5) FIG. 7 shows the actual half-wave plate 15 and quarter-wave plate 4. FIG. 5 shows how the light intensity obtained by the photodetector 10 changes when the and the second linear polarizer 5 are synchronously rotated at a rotation ratio of 1: 2: 2. It can be seen that the light intensity changes eight cycles on the cosine wave. Here, 2 from 0 ° to 360 °
The light intensity was measured at a pitch of 180 ° (180 points were measured). With reference to the rotation angle of 0 °, the angle up to the position where the light intensity first reaches the maximum is the initial phase. By performing Fourier analysis of these 180 measured values and calculating １ ／ times the initial phase of the eight-period component, the principal axis direction of the birefringence of the sample 3 to be measured is automatically obtained. The principal axis direction of the birefringence of this sample was determined to be 16.3 ° as a result of the calculation.

Note that the curve in FIG. 7 does not show an accurate cosine wave change. This is because the half-wave plate 15 is not correctly formed, and this error appears as a two-period component and a four-period component. However, this error is not an error with respect to obtaining the azimuth of the main axis of birefringence since only eight period components are extracted by Fourier analysis.

Next, the polarization direction of the linearly polarized light passing through the half-wave plate 15 is set to 45 ° with respect to the main axis direction of the sample 3 to be measured, and the main axis direction of the quarter-wave plate 4 is measured. The polarization axis direction of the second linear polarizer 5 is 45 ° with respect to the principal axis direction of the sample 3 and the polarization axis direction of the linearly polarized light emitted from the half-wave plate 15 is 45 ° with respect to the principal axis direction of the sample 3 to be measured. The second linear polarizer 5 is arranged so as to be orthogonal to the direction of the polarization axis, and thereafter, the second linear polarizer 5 is rotated around the optical axis in the same manner as in the second embodiment. The birefringence of the sample 3 is determined from the initial phase by Fourier analysis of the cosine wave-like change curve of the signal. The birefringence of this sample was determined to be 46.4 ° as a result of the calculation, and the measurement accuracy was almost the same as in the second embodiment.

Fourth Embodiment FIG. 8 is a diagram showing a configuration of a birefringence measuring apparatus according to a fourth embodiment of the present invention. Hereinafter, with reference to FIG.
A method and apparatus for measuring the amount of birefringence according to an example will be described.

The basic configuration of this embodiment is the same as that of the first embodiment. That is, in FIG. 8, the light emitted from the light source 1 passes through the first linear polarizer 2, the sample to be measured 3, the quarter-wave plate 4, and the second linear polarizer 5, and is detected by the photodetector 10. It has become so. The difference between this embodiment and the first embodiment is that the first embodiment uses the Fourier analysis technique to obtain the principal axis direction of the sample 3 to be measured and the rotation angle of the second linear polarizer 5. On the other hand, in this embodiment, a periodic reference AC signal corresponding to a known rotation angle of the optical member to be rotated is generated, and this reference AC signal and a periodic signal obtained from the photodetector, that is, an AC signal, are generated. The difference is that the phase difference is input to the phase meter and the phase difference is obtained, and the phase difference is obtained from the phase difference.

In this embodiment, as shown in FIG. 9, the means for generating the reference AC signal is formed by alternately disposing the light blocking portions 27a and the light transmitting portions 27b on the annular portion of the annular plate at equal intervals. Optical chopper 27 formed of
And a first reference light source 18, a first reference light detector 19, and a second reference light source 30, which are disposed opposite to each other with the annular portions of the choppers interposed therebetween. The second reference light detector 31 is used.

The sample 3 to be measured and the second linear polarizer 5 can be fixed to the center holes of the choppers 27 and 28, respectively.
8 is incorporated in the rotary stages 6 and 8. That is, when the rotary stage 6 is driven to rotate, the chopper 27 incorporated in the rotary stage 6 and the sample 3 to be measured attached to the chopper 27 rotate integrally, and when the rotary stage 8 is driven to rotate, The chopper 28 incorporated in the rotary stage 8 and the second linear polarizer 5 attached to the chopper 28 rotate integrally. Therefore, when the choppers 27 (the sample 3 to be measured) and 28 (the second linear polarizer 5) are rotated by the rotation stages 6 and 8, the first
Light emitted from the reference light source 18 and the second reference light source 30 alternately repeats blocking and passing. Therefore, the first reference light detector 1
9 and the second reference light detector 31, the chopper 27
A reference AC signal corresponding to the rotation of (sample 3 to be measured), 28 (second linear polarizer 5) is transmitted.

The signal sent from the first reference light detector 19 is sent to the first phase meter 17, and the signal sent from the second reference light detector 31 is sent to the second phase meter 26. It has become.

The first phase meter 17 includes a first reference light detector 19
Signal and one of the two signals transmitted from the photodetector 10 and branched into two, the phase difference between these two AC signals is measured, and the result is calculated by the arithmetic processing unit 1.
Send to 2. Similarly, the second phase meter 26 receives the AC signal transmitted from the second reference photodetector 31 and the other of the two signals transmitted from the photodetector 10 and receives the two AC signals. It measures the phase difference of the signal and sends the result to the arithmetic processing unit 12.

The measuring procedure according to this embodiment is as follows. First, the sample 3 to be measured is mounted on the optical chopper 27 incorporated in the rotary stage 6. Then, the rotation stage 6 is driven to rotate, and the sample 3 to be measured and the optical chopper 2 are rotated.
7 are rotated integrally (here, the rotating stage 7 is in a stationary state). The light intensity obtained by the photodetector 10 is as described above.
According to the equation (3), when the sample 3 to be measured makes one rotation,
The change in the cycle is the same as in the previous example. When four optical choppers 27 (see FIG. 9) are used, the light intensity obtained by the first reference photodetector 19 also changes in four cycles.

Here, when the rotating stage 6 is continuously driven to continuously rotate the sample 3 to be measured and the optical chopper 27 (the rotating stage 7 is stationary), the optical detector 10 and the first reference optical detector 19 obtain the same. This signal can be handled as an AC signal. An AC signal obtained by the photodetector 10 (hereinafter, referred to as an AC A signal) is a cosine-wave AC signal, and a signal obtained by the first reference photodetector 19 (hereinafter, referred to as an AC signal).
AC signal) is a rectangular wave AC signal.

When the AC A signal and the AC B signal are input to the first phase meter 17 and phase detection is performed using the AC B signal as a reference signal, a quarter of the obtained phase amount becomes a birefringent main axis. The orientation is obtained (see FIG. 10). As a result of using the same sample as the first embodiment as the sample 3 to be measured, the output of the phase meter is
The angle of the main axis of birefringence is 35.2 deg.
It was determined to be 8.8 deg.

Then, the main axis direction of the sample 3 to be measured is 45 ° with respect to the polarization axis direction of the first linear polarizer 2.
Arrange so that

Next, the amount of birefringence of the sample 3 to be measured is determined by rotating the second linear polarizer 5. In this case, the photodetector 1
According to the equation (4), the light intensity signal obtained at 0 changes in two cycles while the rotation stage 7 makes one rotation (this is also exactly the same as the previous example). Therefore, the optical chopper 28 incorporated in the rotary stage 7 uses two blades.

Here, when the rotary stage 7 is continuously rotated, signals obtained by the photodetector 10 and the second reference photodetector 31 can be handled as AC signals. An AC signal obtained by the photodetector 10 (hereinafter referred to as an AC C signal) becomes a cosine-wave AC signal, and a signal obtained by the second reference photodetector 31 (hereinafter referred to as an AC D signal).
Is a rectangular wave AC signal.

The AC C signal and the AC D signal are
When the signal is input to the phase form 26 and phase detection is performed using the AC D signal as a reference signal, the amount of birefringence of the sample 3 is determined because the obtained phase amount is equal to the sample 3. As a result of the actual measurement, the output of the phase meter = the amount of birefringence was determined to be 46.0 deg. This result is in good agreement with the value obtained in the first embodiment. The measurement time was about 10 seconds.

The feature of this embodiment is that the measurement time can be shortened as compared with the method using Fourier analysis described above. This is because the rotation speed of the rotary stage can be made higher and the calculation time for Fourier analysis is not required.

Fifth Embodiment FIG. 11 is a view showing a configuration of a birefringence measuring apparatus according to a fifth embodiment of the present invention. Hereinafter, the method and apparatus for measuring the amount of birefringence according to the fifth embodiment will be described with reference to FIG.

The basic configuration of this embodiment is the same as that of the second embodiment. However, in the second embodiment, Fourier analysis is used to obtain the principal axis direction of the sample 3 to be measured, the rotation angle of the second linear polarizer 5, and the like. On the other hand, in this embodiment, a periodic reference AC signal corresponding to a known rotation angle of the optical member to be rotated is generated, and the reference AC signal and the cycle obtained from the photodetector are used. The difference is that a target signal, that is, an AC signal, is input to a phase meter, and the phase difference is obtained, and the phase difference is obtained from the phase difference.

In this embodiment, the same means as that of the fourth embodiment is used as a means for generating a reference AC signal. Therefore, the configuration of this embodiment is very similar to that of the fourth embodiment. Have. Therefore, in the following, the same components as those of the fourth embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The following description focuses on differences from the fourth embodiment.

This embodiment differs from the fourth embodiment in that the sample 3 is rotated by attaching the sample 3 to the chopper 27 incorporated in the rotary stage 6 in the fourth embodiment. The difference is that the polarizer 2 is mounted on a chopper 27 incorporated in the rotary stage 6 and is rotated. The other configuration is the same as that of the fourth embodiment.

The measuring procedure according to this configuration is as follows. First, the rotary stage 6 is driven to drive the first linear polarizer 2.
And the optical chopper 27, and the rotary stage 8 and the second
The rotary stage 7 on which the linear polarizer 5 is mounted is driven to rotate so that their rotation ratio becomes 1: 1: 1.
At this time, the light intensity obtained by the photodetector 10 changes in four cycles while the rotation stage 6 makes one rotation according to the equation (3), as in the previous example. Light chopper 27
If four blades are used (see FIG. 9), the light intensity obtained by the first reference light detector 19 also changes in four cycles.

Here, when the rotary stages 6, 7, 8 are continuously rotated, the light detector 10 and the first reference light detector 19 are rotated.
Can be handled as an AC signal. An AC signal (hereinafter, referred to as an AC E signal) obtained by the photodetector 10 is a cosine-wave AC signal,
The signal obtained by the reference light detector 19 (hereinafter, referred to as an AC F signal) is a rectangular wave AC signal.

The AC E signal and the AC F signal are converted to the first signal.
When the phase is input to the phase form 17 and phase detection is performed using the AC F signal as a reference signal, １ ／ times the obtained phase amount is obtained as the main axis direction of birefringence. As a result of actual measurement, the output of the phase meter = 8
The direction of the main axis of 6.1 deg and birefringence was 21.5 deg.

Then, the azimuths of the rotary stages 6, 7, 8 are adjusted and arranged so that the main axis azimuth of the sample 3 to be measured is 45 ° with respect to the polarization axis azimuth of the first linear polarizer 2. Then, the procedure of rotating the second linear polarizer 5 to obtain the birefringence of the sample 3 to be measured is exactly the same as that of the above-described fourth embodiment, and therefore the description is omitted. As a result of the actual measurement, the output of the phase meter = the amount of birefringence was determined to be 46.0 deg. This result is in good agreement with the value obtained in the first embodiment. The measurement time was about 10 seconds.

In this embodiment, the optical chopper 2
Although 7 is arranged on the rotating stage 6, it may be arranged on the rotating stage 8. Further, it can be arranged together with the optical chopper 28 on the rotary stage 7.

The feature of this method is that the measurement time can be shortened,
In addition, it is possible to measure even a sample whose measurement target 3 is large and cannot be integrally rotated by being mounted on a rotary stage.

Sixth Embodiment FIG. 12 is a view showing a configuration of a birefringence measuring apparatus according to a sixth embodiment of the present invention. Hereinafter, the method and apparatus for measuring the amount of birefringence according to the sixth embodiment will be described with reference to FIG.

The basic configuration of this embodiment is the same as that of the third embodiment. In the third embodiment, the main axis direction of the sample 3 to be measured and the rotation angle of the second linear polarizer 5 are determined. In contrast to using the Fourier analysis technique, in this embodiment, a periodic reference AC signal corresponding to a known rotation angle of the optical member to be rotated is generated, and the reference AC signal and a photodetector are used. The difference is that a periodic signal, that is, an AC signal, is input to a phase meter, and the phase difference is obtained, and the phase difference is obtained from the phase difference.

In this embodiment, the same means as that of the fifth embodiment is used as a means for generating a reference AC signal. Therefore, the configuration of this embodiment is very similar to that of the fifth embodiment. Have. Therefore, in the following, the same components as those of the fifth embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The following description focuses on differences from the fifth embodiment.

This embodiment is different from the fifth embodiment in that the first linear polarizer 2 is mounted on a chopper 27 incorporated in the rotary stage 6 for rotation in the fifth embodiment. In this example, the sample 3 to be measured and the first linear polarizer 2 are fixed, and instead, the half-wave plate 15 newly disposed between them is set on the chopper 27 incorporated in the rotary stage 6. 1/2 wavelength plate 15,
The quarter-wave plate 4 and the second linear polarizer 5 were driven to rotate in synchronization with each other so that the rotation ratio was 1: 2: 2. That is, this embodiment is different from the fifth embodiment in that the half-wave plate 1 is used instead of rotating the first linear polarizer 2 when obtaining the principal axis of birefringence of the sample 3 to be measured.
The difference is that the fifth and quarter-wave plates 4 and the second linear polarizer 5 are rotated synchronously.

The measurement procedure according to this configuration is as follows. First, the rotary stage 6 is driven to drive the half-wave plate 15
And the optical chopper 27 are rotated integrally, and in synchronization with this, the rotation ratio of the rotation stage 8 to which the quarter-wave plate 4 is attached and the rotation stage 7 to which the second linear polarizer 5 is attached is 1: 1. Rotate to make 2: 2. At this time, the fact that the light intensity obtained by the photodetector 10 changes in eight cycles while the rotation stage 6 makes one rotation according to the equation (5) is the same as in the previous example. When eight light choppers are used, the light intensity obtained by the first reference light detector 19 also changes in eight cycles.

Here, when the rotary stages 6, 7, 8 are continuously rotated, the light detector 10 and the first reference light detector 1 are rotated.
The signal obtained in 9 can be handled as an AC signal. AC signal obtained by the photodetector 10 (hereinafter, referred to as
The AC signal is a cosine-wave AC signal, and the signal obtained by the first reference light detector 19 (hereinafter, an AC H signal) is a rectangular AC signal.

When the AC G signal and the AC H signal are input to the first phase form 17 and phase detection is performed using the AC H signal as a reference signal, １ ／ times the obtained phase amount is duplicated. It is obtained as the principal axis direction of refraction. Output of phase meter = 5 as a result of actual measurement
As a result, the orientation of the principal axis of birefringence of the measured sample 3 was determined to be 14.0 deg.

Next, the azimuths of the rotating stages 6, 7, 8 are set so that the principal axis azimuth of the sample 3 to be measured is 45 ° with respect to the polarization azimuth of the linearly polarized light emitted from the half-wave plate 15. The procedure for adjusting and arranging the angle and then rotating the second linear polarizer 5 to determine the amount of birefringence of the sample 3 to be measured is exactly the same as in the above-described fifth embodiment, and a description thereof will be omitted.
As a result of the actual measurement, the output of the phase meter = the amount of birefringence is 46.0 deg.
I was asked. This result is in good agreement with the value obtained in the first embodiment. The measurement time was about 10 seconds.

In this embodiment, the optical chopper 2
Although 7 is arranged on the rotating stage 6, it may be arranged on the rotating stage 8. Further, it can be arranged together with the optical chopper 28 on the rotary stage 7.
However, when the optical chopper is disposed on the rotary stages 7 and 8, the rotation ratio is different from that of the rotary stage 6, so that an optical chopper having four blades must be used.

The feature of this method is that the measurement time can be shortened,
In addition, the measurement can be performed even when the sample 3 to be measured is large and cannot be integrally rotated by being placed on the rotating stage, and the polarization state of the light emitted from the light source 1 can be arbitrarily determined.

Seventh Embodiment FIG. 13 is a view showing a configuration of a birefringence measuring apparatus according to a seventh embodiment of the present invention. Hereinafter, a method and an apparatus for measuring the amount of birefringence according to the seventh embodiment will be described with reference to FIG. Although the basic configuration of this embodiment is the same as that of the first embodiment, the specific configuration is different.

In FIG. 13, light emitted from the light source 1 passes through the optical chopper 16, is diffused by the lens 20, and is irradiated on the diffusion plate 14. In order to obtain a signal synchronized with the rotation of the optical chopper 16, the third reference light source 32 and the third
The reference light detector 33 is disposed to face the optical chopper 16. As a result, the light applied to the diffusion plate 14 blinks at a frequency synchronized with the optical chopper 16, that is, becomes intensity-modulated light (hereinafter, referred to as intensity-modulated light). When a light source having strong coherence, such as a laser, is used as the light source 1, the diffusion plate 14 is rotated around the optical axis in order to prevent speckle. In this embodiment, the light emitted from the diffusion plate 14 serves as a secondary light source.

The light emitted from the diffusion plate 14 passes through the first linear polarizer 2 and the sample 3 placed on the rotating stage 6 and enters the observation telescope 21. The observation telescope 21 includes a 波長 wavelength plate 4, an objective lens 22, and a beam splitter 23.
, An eyepiece 24, a second linear polarizer 5 mounted on the rotary stage 7, and a relay lens 25.

The light that has passed through the quarter-wave plate 4 becomes focused light by the objective lens 22, and is further split into two by the beam splitter 23. Beam splitter 23
One of the condensed lights divided by the above passes through the second linear polarizer 5, and once becomes focused, becomes divergent light again, is converged again by the relay lens 25, and is detected by the photodetector 10.

On the other hand, the other condensed light split by the beam splitter 23 passes through the eyepiece, and the sample 3 to be measured can be observed by the naked eye from behind.

The light detected by the photodetector 10 is transmitted by the objective lens 22 and the relay lens 25 to any one point (measurement point; this point must coincide with the center of rotation of the rotary stage 6). ). The eyepiece 24 is used for observing and adjusting this measurement point with the naked eye. Note that the eyepiece 24 can be replaced with an image sensor.
In this case, a signal output from the image sensor is received by a monitor and observed on the monitor.

The light detected by the light detector 10 is input to the lock-in amplifier 29. The lock-in amplifier 29
Using the signal obtained by the third reference light detector 33 as a reference signal, the synchronous detection of the intensity modulated light is performed, and a signal proportional to the intensity is output and sent to the arithmetic processing unit 12. As a result, the signal input to the arithmetic processing unit 12 is exactly the same as the signal input to the arithmetic processing unit 12 in the first embodiment. Therefore, rotating the sample 3 to determine the principal axis of birefringence and rotating the second linear polarizer 5 to determine the amount of birefringence can be performed using exactly the same method as in the first embodiment. The description is omitted.

This embodiment is characterized in that, for example, the surface of the sample 3 to be measured is not a smooth surface as in the case of optical polishing, but a ground glass surface, an irregular surface shape, or disturbance. The measurement can be performed even when the light intensity is high and the amount of light reaching the photodetector 10 is small (in a state where the S / N ratio of the signal is poor). This is a lock-in amplifier 2
This is because 9 (synchronization detection) has a function of selectively amplifying and outputting only a signal having the same frequency as the reference signal obtained by the reference light detector 33, that is, an intensity modulation signal. Note that the configuration of this embodiment can be applied to a method and an apparatus having the second embodiment and the third embodiment as a basic configuration.

Eighth Embodiment FIG. 14 is a view showing a configuration of a birefringence measuring apparatus according to an eighth embodiment of the present invention. Hereinafter, the method and the apparatus for measuring the amount of birefringence according to the eighth embodiment will be described with reference to FIG. Although the basic configuration of this embodiment is the same as that of the above-described fourth embodiment, the specific configuration has a configuration obtained by applying the configuration of the above-described seventh embodiment. Therefore, the same parts as those of the seventh embodiment will be described with the same reference numerals.

In FIG. 14, light emitted from the light source 1 passes through the optical chopper 16, is diffused by the lens 20, and is irradiated on the diffusion plate 14. In order to obtain a signal synchronized with the rotation of the optical chopper 16, the third reference light source 32 and the third
The reference light detector 33 is disposed to face the optical chopper 16. As a result, the light applied to the diffusion plate 14 blinks at a frequency synchronized with the optical chopper 16, that is, becomes intensity-modulated light (hereinafter, referred to as intensity-modulated light). When a light source having strong coherence, such as a laser, is used as the light source 1, the diffusion plate 14 is rotated around the optical axis in order to prevent speckle. In this configuration, light emitted from the diffusion plate 14 serves as a secondary light source.

The light emitted from the diffuser 14 passes through the first linear polarizer 2 and the sample 3 to be measured placed on the rotary stage 6 and enters the observation telescope 21. An optical chopper 27 is arranged on the rotation stage 6. The first reference light source 18 is used to obtain a signal synchronized with the rotation of the optical chopper 27.
And the first reference light detector 19 are arranged to face each other with the optical chopper therebetween.

Further, an optical chopper 28 that rotates integrally with the second linear polarizer 5 and the rotary stage 7 is disposed on the rotary stage 7, and a second optical chopper 28 is provided to obtain a signal synchronized with the rotation of the optical chopper 28. The reference light source 30 and the second reference light detector 31 are arranged to face each other with the optical chopper 28 interposed therebetween.

The observation telescope 21 comprises a quarter-wave plate 4, an objective lens 22, a beam splitter 23, and an eyepiece 2.
4 and a second linear polarizer 5 mounted on a rotary stage 7
, A relay lens 25, and an optical chopper 28 that rotates integrally with the second linear polarizer 5 on the rotary stage 7.
A second reference light source 30 for obtaining a signal synchronized with the rotation of the optical chopper 28, a second reference light detector 31 disposed opposite to the optical chopper 28,
It is composed of

The light that has passed through the 板 wavelength plate 4 becomes converged light by the objective lens 22 and is further split into two by the beam splitter 23. Beam splitter 23
One of the condensed lights divided by the above passes through the second linear polarizer 5, and once becomes focused, becomes divergent light again, is converged again by the relay lens 25, and is detected by the photodetector 10.

On the other hand, the other condensed light split by the beam splitter 23 passes through the eyepiece, and the sample 3 to be measured can be observed from behind by the naked eye.

The light detected by the photodetector 10 is transmitted by the objective lens 22 and the relay lens 25 to an arbitrary point (measurement point; this point must coincide with the center of rotation of the rotary stage 6). ). The eyepiece 24 is used for observing and adjusting this measurement point with the naked eye. Note that the eyepiece 24 can be replaced with an image sensor.
In this case, a signal output from the image sensor is received by a monitor and observed on the monitor.

The light detected by the photodetector 10 is input to a lock-in amplifier 29.
Using the signal obtained by the third reference light detector 33 as a reference signal, synchronous detection of intensity-modulated light is performed, a signal proportional to the intensity is output, and the signal is split into two, one of which is the first.
The other is input to the phase meter 17 and the other is input to the second phase meter 26.

The first phase meter 17 includes a first reference light detector 19
Is used as a reference signal to perform phase detection and output the result to the arithmetic processing unit 12. Second phase meter 26
Performs phase detection using the signal obtained by the second reference light detector 31 as a reference signal, and outputs the result to the arithmetic processing unit 12.

Optical chopper 16 and optical chopper 27
Is appropriately set so that the frequency of the optical chopper 16 is increased, and when the sample 3 is rotated, the light intensity obtained by the photodetector 10 is subjected to intensity modulation by the optical chopper 16, It changes in the form of a cosine wave that changes four periods while the sample under test 3 makes one rotation. FIG. 15 schematically illustrates this state.

The signal thus modulated is supplied to the lock-in amplifier 29 together with the reference signal from the third reference light detector 33.
, The output signal from the lock-in amplifier 29 represents only the envelope of the signal shown in FIG. 15, that is, a signal that changes in a cosine wave shape.

As a result, the signal input to the arithmetic processing unit 12 is exactly the same as the signal input to the arithmetic processing unit 12 in the configuration of the fourth embodiment. Therefore,
The sample 3 to be measured is rotated to find the principal axis of birefringence,
Since the method of rotating the linear polarizer 5 to obtain the amount of birefringence may be exactly the same as that of the fourth embodiment, the description is omitted.

The feature of this configuration is that, for example, the sample to be measured 3
The surface is not a smooth surface like optical polishing, it is a ground glass surface, or the surface shape is irregular,
Alternatively, measurement can be performed even when the intensity of disturbance light is high and the amount of light reaching the photodetector 10 is small (in a state where the S / N ratio of the signal is poor), and the measurement time can be further reduced. This is because the lock-in amplifier 29 (synchronization detection) has a function of selectively amplifying and outputting only a signal having the same frequency as the reference signal obtained by the reference light detector 33, that is, an intensity modulation signal. It is.

The configuration of this embodiment can also be applied to a method and an apparatus having the above-described fifth and sixth embodiments as the basic configuration. In each of the above embodiments, for example, the principal axis direction of birefringence is obtained using the method and apparatus of the first embodiment,
A combination such as obtaining the amount of birefringence using the method and apparatus of the fourth embodiment is also possible.Furthermore, the main axis direction of birefringence is obtained using the method and apparatus of the fifth embodiment,
A combination of obtaining the amount of birefringence using the method and apparatus of the first embodiment is also possible. That is, the above-described embodiments can be applied in various combinations.

[0110]

As described in detail above, the present invention relates to a method and an apparatus for measuring the amount of birefringence, which apply the principle of the so-called Senarmont method, as a method for obtaining an angle at which the amount of light measured by the light measuring means indicates the maximum or minimum. An optical member to be rotated around the optical path axis of the measuring light is continuously rotated, and an angle indicating the maximum or minimum of the measuring light amount is obtained from phase information of a periodic signal obtained from the light measuring means at that time. Thus, a birefringence amount measuring method and apparatus capable of sufficiently improving the measurement accuracy are obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a birefringence measuring apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating a curve of a change in light intensity with respect to a rotation angle of a sample according to the first embodiment.

FIG. 3 is a diagram illustrating a curve of a change in light intensity with respect to a rotation angle of a second linear polarizer.

FIG. 4 is a diagram showing a configuration of a birefringence amount measuring device according to a second embodiment.

FIG. 5 is a diagram illustrating a curve of a change in light intensity with respect to a rotation angle of an optical member according to a second embodiment.

FIG. 6 is a diagram showing a configuration of a birefringence measuring apparatus according to a third embodiment.

FIG. 7 is a diagram illustrating a curve of a change in light intensity with respect to a rotation angle of a half-wave plate according to a third embodiment.

FIG. 8 is a diagram showing a configuration of a birefringence amount measuring apparatus according to a fourth embodiment.

FIG. 9 is a diagram showing an optical chopper.

FIG. 10 is an explanatory diagram of an AC signal input to a phase meter.

FIG. 11 is a diagram showing a configuration of a birefringence measuring apparatus according to a fifth embodiment.

FIG. 12 is a diagram showing a configuration of a birefringence measuring apparatus according to a sixth embodiment.

FIG. 13 is a diagram showing a configuration of a birefringence amount measuring device according to a seventh embodiment.

FIG. 14 is a diagram showing a configuration of a birefringence amount measuring device according to an eighth embodiment.

FIG. 15 is a diagram schematically showing an output signal of a photodetector in an eighth embodiment.

FIG. 16 is an explanatory diagram of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... 1st linear polarizer, 3 ... Sample to be measured, 4 ...
1/4 wavelength plate, 5 ... second linear polarizer, 6, 7, 8 ... rotary stage 9 ... motor driver, 10 ... photodetector, 11 ...
Telescope, 12: arithmetic processing unit (CPU), 13: monochromatic filter, 14: diffuser plate, 15: 1/2 wavelength plate, 16: optical chopper, 17: first phase meter, 18: first reference light source, 19 ... 1st reference light detector, 20 ... lens, 21 ... observation telescope, 22 ... objective lens, 23 ... beam splitter, 24 ... eyepiece, 25 ... relay lens, 26 ... second phase meter, 27 ... optical chopper, 28 ... Optical chopper, 29: lock-in amplifier, 30... Second reference light source, 3
DESCRIPTION OF SYMBOLS 1 ... 2nd reference light detector, 32 ... 3rd reference light source, 33 ... 3rd reference light detector

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 21/21-21/23 G01J 4/00-4/04

Claims (6)

(57) [Claims] 1. A birefringent sample, a quarter-wave plate, a linear polarizer, and a light measuring means are sequentially arranged on the optical path axis of the linearly polarized light for measurement, with respect to the polarization direction of the linearly polarized light for measurement. The principal axis directions of the birefringence of the １ ／ wavelength plate are made to coincide with each other, and the polarization axis direction of the linear polarizer is orthogonal to the polarization direction of the linearly polarized light for measurement. Next, around the optical path axis, While rotating the birefringent sample, or while the sample is fixed, while rotating the polarization direction of the linearly polarized light for measurement, the quarter-wave plate and the linear polarizer by the same angle, the optical measurement means The amount of light is measured, and the amount of angle rotated until the measured amount of light shows the maximum is determined, and the principal axis direction of the birefringence of the birefringent sample is the polarization axis direction of the linearly polarized light for measurement and the linear polarizer. Set at 45 ° to the polarization axis direction. While rotating the linear polarizer around the optical path axis, the light measuring means measures the amount of light to determine an angle at which the measured amount of light is minimized. A birefringence amount measuring method for obtaining a rotation angle amount of the rotated linear polarizer and obtaining a birefringence amount of the birefringent sample from the rotation angle amount, wherein a light amount measured by the light measurement unit is a maximum or a minimum. As a method of determining the rotation angle of the optical member when indicating, the optical member is continuously rotated, and at that time, the angle indicating the maximum or minimum of the measured light amount is determined from the phase information of the periodic signal obtained from the light measuring means. A method for measuring the amount of birefringence, characterized by using a method. 2. The method for measuring the amount of birefringence according to claim 1, wherein the optical member is continuously rotated as a method for determining a rotation angle of the optical member when the amount of light measured by the light measuring unit indicates a maximum or a minimum. At that time, a curve indicating a change in light amount with respect to a rotation angle is obtained by Fourier analysis from an actual measurement value of a periodic signal obtained from the light measuring means, and an angle indicating the maximum or minimum of the measured light amount is obtained from phase information of the curve. A method for measuring the amount of birefringence, characterized by using a method. 3. The method for measuring the amount of birefringence according to claim 1, wherein the optical member is continuously rotated as a method for determining a rotation angle of the optical member when the amount of light measured by the light measuring unit indicates a maximum or a minimum. Along with this, a periodic reference AC signal corresponding to a known rotation angle of the optical member is generated, and this reference AC signal and a periodic signal obtained from the light measuring means, that is, an AC signal, are input to a phase meter. A method of measuring the amount of birefringence, characterized by using a method of obtaining the phase difference and obtaining an angle at which the measured light amount indicates the maximum or minimum from the phase difference. 4. An optical device for generating linearly polarized light for measurement, a birefringent sample, a quarter-wave plate, a linear polarizer, and light measuring means sequentially arranged on the optical path axis of the linearly polarized light for measurement. Rotating the birefringent sample around the optical path axis or rotating the birefringent sample fixed and rotating the polarization direction of the linearly polarized light for measurement, the quarter-wave plate and the linear polarizer by the same angle. A rotation driving device having a mechanism, and a mechanism for independently rotating and driving the linear polarizer; and a periodic change curve indicating a light amount change with respect to a rotation angle by inputting light amount change information sent from the light measuring means. A birefringence amount measuring device, comprising: a processing device that obtains a birefringence amount of the sample by obtaining a rotation angle by the rotation driving device from phase information. 5. The birefringence amount measuring device according to claim 4, wherein the processing device performs a Fourier analysis on the light amount change information transmitted from the light measuring means, thereby performing a periodic change indicating the light amount change with respect to the rotation angle. A birefringence measuring apparatus characterized by having a processing function of obtaining a curve and obtaining a rotation angle of the rotation drive device from the phase information to obtain a birefringence of the sample. 6. The birefringence amount measuring apparatus according to claim 4, wherein a reference AC signal is generated to generate a periodic reference AC signal corresponding to a known rotation angle of the optical member rotationally driven by the rotation driving device. An apparatus is added. As the processing device, a phase in which an AC signal indicating a change in the amount of light transmitted from the light measuring unit and a reference AC signal transmitted from the reference AC signal generating device are input and a phase difference between them is transmitted. A birefringence measuring device characterized by using a device having a processing function for obtaining a birefringence amount of the sample by obtaining a rotation angle by the rotation driving device based on information transmitted from the phase meter. .