JP2001141602A - System and method for evaluating double refraction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure double refraction of an object larger than full wavelength of an optical signal being used with a desired accuracy. SOLUTION: The system for evaluating double refraction comprises an optical system for acquiring an optical signal bearing information concerning to double refraction of an object Sa (a white light source 1, a polarizer 2, an analyzer 3, and a spectrometer 4), and means PC5 for analyzing the period of a component varying in cosine with respect to the wave number thereof based on the optical signal acquired through the optical system and determining double refraction in a specified wavelength region of the object Sa from that analysis data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a birefringence measuring apparatus and a method for evaluating birefringence, and more particularly to a method for evaluating birefringence of a sample exhibiting large birefringence, such as evaluation of the degree of orientation, crystallinity, and crystal quality of a polymer. The present invention relates to a device and method for measuring an absolute value.

[0002]

2. Description of the Related Art Conventionally, as an automatic measuring method of birefringence,
“Phase modulation method”, “rotational analyzer method”, “optical heterodyne method” and the like are known. In any of these automatic birefringence measurement methods, a parallel beam is transmitted through a sample, and the transmitted light is received by a photodetector to detect a change in the polarization state due to the birefringence of the sample.

[0003] Among them, the "phase modulation method" modulates the polarization state of incident light to be incident on a sample using a photoelastic modulator, and obtains birefringence from the difference between the polarization states of the incident light before and after transmission through the sample. Is the way. In the “rotational analyzer method”, a light intensity signal accompanying the rotation of the analyzer is detected by the light detector while rotating the analyzer placed between the sample to be measured and the light detector, and the intensity is detected. This is a method of analyzing the polarization state after transmission through the sample from the change to obtain birefringence. Furthermore, the "optical heterodyne method" is a method of transmitting two linearly polarized light components orthogonal to a sample and interfering the two polarized light components with an analyzer to obtain a birefringence phase difference from a beat signal obtained. It is.

[0004]

The automatic birefringence measurement method described above is characterized by its extremely high detection accuracy.
On the other hand, it was difficult to measure birefringence larger than birefringence corresponding to one wavelength at the wavelength used for measurement.
The reason is that in these automatic birefringence measurement methods, since light is treated as a single wave, a value larger than 360 degrees (= 1 wavelength) is periodically folded to 360 degrees or less.

[0005] The measurement of such a large birefringence is particularly necessary in the field of material inspection / evaluation processes, for example, when inspecting the degree of orientation and crystallinity of a polymer, or when evaluating the quality of crystals. In addition, it is expected that the need for inspection and evaluation in such a field will further increase with the recent reduction in size, miniaturization, and high precision of optical materials and their materials. Therefore, it is necessary to provide a technique for measuring a sample exhibiting a large birefringence as described above with a desired accuracy according to the needs in the same manner as in the automatic birefringence measurement method described above.

The present invention has been made in view of such a conventional problem. In the measurement of birefringence of an object to be measured, birefringence larger than one wavelength of an optical signal used therein is measured with a desired accuracy. That is its purpose.

[0007]

In order to achieve the above object, a birefringence evaluation apparatus according to the present invention comprises an optical system for obtaining an optical signal carrying information on the birefringence of a measurement object ("birefringence measurement optical system"). ), Analyzing the period of a component that changes in a cosine wave shape with respect to the wave number based on the optical signal obtained by the optical system, and determining the birefringence in a predetermined wavelength region of the measurement target from the analysis data. And birefringence analysis means to be obtained.

The birefringence analyzing means analyzes the dependence of the birefringence on the wavelength by adjusting a wave number region for analyzing a period of a component which changes in a cosine wave with respect to the wave number, and analyzes the dependence of the birefringence on the wavelength. It is possible to provide a means for determining birefringence in an arbitrary wavelength region to be measured.

The optical system includes a light source that emits an optical signal having a continuous spectral distribution toward the object to be measured, and a pair of polarized light disposed at a position sandwiching the object to be measured on an optical path of the optical signal from the light source. It is possible to have a detector and an analyzer, and a spectroscope arranged on an optical path of an optical signal from the light source and dispersing the optical signal.

The birefringence analyzing means, when the pair of polarizers and the analyzer are arranged in parallel Nicols, the birefringence retardation of the object to be measured, its birefringence, its thickness, and The angles formed by the birefringent main axis and the transmission axis of the polarizer are Δ, δn, d, and φ, respectively, and the wavelength of the optical signal, its light intensity, and the DC component of the light intensity with respect to the wavelength region to be measured. , Its wave number is λ, I
(Λ), IDC, and k, and a predetermined system-dependent coefficient is S (λ).

(Equation 3) It is possible to provide a means for analyzing so as to satisfy the following expression.

The birefringence analyzing means, when the pair of polarizers and the analyzer are arranged in a crossed Nicols state, the birefringence retardation of the object to be measured, its birefringence, its thickness, and The angles formed by the birefringent main axis and the transmission axis of the polarizer are represented by Δ, δn, d, and φ, respectively.
The wavelength of the optical signal, its light intensity, the DC component of the light intensity with respect to the wavelength region to be measured, its wave number is λ, I
(Λ), IDC, and k, and a predetermined system-dependent coefficient is S (λ).

(Equation 4) It is possible to provide a means for analyzing so as to satisfy the following expression.

[0012] The spectroscope may be arranged on an output side of the analyzer or on an incident side of the polarizer on an optical path of the optical signal.

The optical system further includes a photodetector for detecting the optical signal on the optical path of the optical signal on the exit side of the analyzer, and the birefringence analyzing means detects the optical signal by the optical detector. A birefringence analysis of the measurement object may be performed based on the signal.

The optical system may further include a two-dimensional image sensor for imaging the optical signal on the optical path of the optical signal on the exit side of the analyzer. It is possible to perform a birefringence analysis of the measurement object based on the signal obtained.

Further, according to the birefringence evaluation method of the present invention, the light intensity of an optical signal carrying information on the birefringence of an object to be measured is input, and the wave number is cosine-wave-shaped based on the input light intensity. The method is characterized in that the period of the changing component is analyzed, and birefringence in a predetermined wavelength region of the measurement object is obtained from the analysis data.

Further, the recording medium on which the program according to the present invention is recorded inputs the light intensity of an optical signal carrying information on the birefringence of the object to be measured, and, based on the inputted light intensity, gives a cosine to the wave number. The method is characterized in that a cycle of a component that changes in a wave shape is analyzed, and a program for calculating birefringence in a predetermined wavelength region of the measurement object is recorded in a readable manner from the analysis data.

The recording medium in this case is ROM, RAM,
A flash memory, a card-shaped recording medium (such as a PC card), a hard disk, a magnetic disk, a magneto-optical disk, an optical disk, etc. Is also applicable.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a birefringence evaluation apparatus according to the present invention will be described below in detail with reference to the drawings.

The birefringence evaluation apparatus shown in FIG. 1 uses a pair of polarizers 2 sandwiching a sample Sa to measure white light emitted from a light source having a continuous spectral distribution (hereinafter, referred to as a “white light source”) 1. And enters the spectrometer 4 through the analyzer 3,
The transmitted light intensity for each wavelength of the white light separated by the spectroscope 4 is converted into a computer (a personal computer (P
C)) Transfer to 5 and execute a program based on the birefringence measurement algorithm set in advance as a program or the like based on the measurement principle of the present invention in the PC 5 to thereby perform the birefringence measurement of the sample Sa to be measured. It has become.
In this configuration, a white light source 1, a polarizer 2, an analyzer 3,
The spectroscope 4 forms the optical system of the present invention.

Here, the measurement principle of the present invention will be described.

First, in order to clarify the significance of the measurement principle of the present invention and its significance, a related art (Japanese Unexamined Patent Application Publication No.
The details of JP-A-142322, JP-A-4-307312, JP-A-10-82697, JP-A-11-10728, and JP-A-10-10041 were examined in detail. The results of the study will be described.

1) Japanese Patent Application Laid-Open No. H11-142322 discloses that a two-dimensional distribution of birefringent interference fringes is imaged and the phases of the fringes are connected (unwrapped) based on the fringe distribution. A method for measuring a large birefringence exceeding the wavelength of a light source based on wavelength birefringence data is described. The polarization analysis optical system according to this method has a configuration including a light source, a polarizer, a λ / 4 plate 1, a sample, a λ / 4 plate 2 (change in direction), an analyzer (rotation), and an image sensor.

The procedure for obtaining birefringence with this configuration is λ
The image data is fetched into a personal computer while the analyzer is rotated at predetermined rotation steps by setting the quarter plate 2 at the 0-degree direction, and the analyzer is rotated at the predetermined rotation by setting the λ / 4 plate 2 at the 45-degree direction. While rotating the image data for each step, the image data is imported to a personal computer, and the above operation is performed at two wavelengths.
The birefringence order is determined.

In this method, a mechanical operation for rotating the wave plate or the polarizer is required, and it is difficult to reduce the measurement time. Further, two wavelengths are used to determine the birefringence order. However, if errors are mixed in the respective measured values, it can greatly affect the order determination.

2) JP-A-4-307312 discloses that
A sample is sandwiched between a pair of polarizers to transmit white light,
This is a method for spectroscopic measurement. A method is described in which an extreme value of the obtained spectral transmittance data is measured to determine birefringence.

This method mentions only a single extreme value in the wavelength scanning range of the spectral transmittance data, and limits the measurement range of birefringence.

3) JP-A-10-82697 discloses that
A method is described in which birefringence is measured independently at a plurality of wavelengths, and the order is determined from these measured values. In order to further increase the measurement accuracy, a method of superposing a reference phase plate having a known birefringence on a sample and measuring the portion where the accuracy is deteriorated due to a problem on the measurement principle is adopted.

Although this method has a possibility that high accuracy can be expected in principle, in order to maximize its performance, the orientation of the reference phase plate and the birefringent principal axis of the sample to be measured must be accurate. It is necessary to superimpose this position, and accuracy is required for this positioning.

Further, since it is necessary to insert and remove the reference phase plate, a mechanical operation is included, and it becomes difficult to reduce the measurement time.

Further, it is considered that by setting the wavelength dispersion coefficient, more accurate birefringence measurement can be performed, and the measurement result of the birefringence distribution of the stretched nylon film is illustrated (see FIG. 7 in the same publication). ). Although a slight improvement is seen in the variation of the distribution value curve when the coefficient of variance is set, a small fluctuation component of some remaining distribution value curves is a measurement error in principle. No discussion has been made as to whether the measured value is an actual birefringence value, and the reliability of the measured value remains questionable.

4) JP-A-11-10728 discloses that
A method is described in which a sample is sandwiched between a pair of polarizers, a white light source is incident from one side, and the spectrum of transmitted light is spectrally measured. In the case of a sample with a large birefringence, many peaks are shown in the transmitted light spectrum.The wavelengths of any two of the peaks are determined, and the wavelength interval and the number of peaks in the interval are determined. Calculating refraction.

This method is excellent in that a birefringent sample having a large value can be obtained in a short time without including a mechanical operation in a birefringence measuring system. Since there are two data, it is necessary to set a large difference between the two wavelengths in order to increase the measurement accuracy. Conversely, in the case of a sample whose birefringence has wavelength dependence,
It is necessary to perform measurement by reducing the difference between the two wavelengths, but in this case, there is a disadvantage that the measurement error increases.

Further, when noise is mixed in the signal, peak position detection is more affected. In addition, in the case of a sample having a light absorption property in a part of the wavelength region to be measured, a peak may not clearly appear, and the sample to be measured is limited. Further, there is a drawback that the average birefringence in a specific wavelength region cannot be obtained because the wavelength at which the peak occurs is obtained. That is, when comparing two samples having the same material but different birefringences, it is not possible to obtain the birefringence for the same wavelength range, so that the comparison cannot be made accurately.

As an example, consider the change in birefringence in the process of stretching a film. Observing the spectral spectrum while stretching the film, the peak position appears to move from the long wavelength side to the short wavelength side as the film is stretched. If birefringence is observed in this process, the wavelength corresponding to the peak position of the spectrum observed at each time will move. When evaluating birefringence, it is often necessary to specify the corresponding wavelength. Therefore, this method has a drawback that the stretching process cannot be displayed in real time under the same evaluation conditions. Since a multi-channel spectrometer is used for the detection system, it is necessary to scan the sample in order to obtain a two-dimensional distribution of birefringence.

5) JP-A-10-10041 discloses that
A method is described in which a sample is sandwiched between a pair of polarizers, a white light source is incident from one side, and the spectrum of transmitted light is spectrally measured. In the case of a sample having a large birefringence, many peaks are shown in the transmitted light spectrum, and the birefringence at each peak wavelength is determined. Further, the same operation is performed for the second samples having the same material but different thicknesses, and the birefringence and the wavelength dispersion of the birefringence of the samples are accurately obtained. This method has the advantage that the absolute value of the wavelength dispersion value of birefringence can be obtained, but has the inconvenience that samples having different thicknesses exhibiting the same birefringence must be prepared.

6) As another method, which is a more qualitative method, the optical system sandwiching the sample between a pair of polarizers is irradiated with white light, and the interference color of the sample that is visually observed from the other side. A method of comparing the color sample with a predetermined color sample to determine birefringence is also known (Tsuboi: "Polarizing microscope", Iwanami Shoten, 1979). However, according to this method, it is difficult to quantify the amount of birefringence, and when the magnitude of birefringence generally exceeds about 2000 nm, the color of the interference color drops, and the color becomes white. Refraction cannot be identified.

According to the above study, it has been confirmed that the above-described problem has occurred in the birefringence measurement / determination method using the interference spectrum because the parameter for the interference signal is a wavelength.

Therefore, based on these studies, the present invention has focused on enabling measurement of birefringence in consideration of wavelength dependency from a periodic signal obtained from an interference spectrum.

Specifically, in the birefringence evaluation apparatus shown in FIG. 1 described above, when the polarizer 2 is arranged in a state of parallel Nicols with respect to the analyzer 3, the pair 2 and 3 are used. The light intensity I (λ) passing through the optical system can be expressed by the following equation by a Mueller matrix calculation or a Jones vector calculation.

[0040]

(Equation 5) In this equation (1), λ is the wavelength, IDC is the DC component of the amount of light with respect to the wavelength λ, S (λ) is a system-dependent coefficient, and φ is the angle between the transmission axis of the polarizer 2 and the main birefringence axis of the sample Sa. , Δ are the birefringence retardation of the sample Sa.

Among them, the birefringence retardation Δ of the sample Sa can be rewritten as the following equation.

[0042]

(Equation 6) In the equation (2), δn is the birefringence index (n
s-nf), d is the thickness of the sample Sa, k is the wave number (frequency)
It is.

From the analysis of these equations, it is noted that the frequency component with respect to the wave number k (= 2π / λ) is equal to the birefringence (δn · d) from the relationship shown on the right side of the equation (2). The following findings were obtained.

A) When the sample Sa is irradiated with white light, its spectral transmittance component changes in a cosine wave with respect to the wave number k.

B) The change in the angle φ between the transmission axis of the polarizer 2 and the birefringent main axis of the sample Sa does not depend on the frequency of the cosine wave curve generated by the birefringence, but affects only the amplitude component.

According to the fact of the above a), the birefringence of the sample Sa can be determined by obtaining the period that changes in a cosine wave with respect to the wave number k from the optical signal of the sample Sa obtained by the optical system shown in FIG. . Moreover, the dependence of the birefringence on the wavelength can be obtained by appropriately adjusting the wave number region for analyzing the period of the component that changes in the form of a cosine wave with respect to the wave number k. Birefringence can be determined.

Also, due to the fact b), in the birefringence measurement, the angle φ between the transmission axis direction of the polarizer of the measurement optical system and the birefringence main axis direction of the sample does not affect the birefringence measurement accuracy. The birefringence principal axis direction can be obtained from the change in the amplitude of the cosine wave component of the light intensity change obtained when φ is relatively changed, so that the birefringence amount and the principal axis direction are independent without being influenced by each other. Can be sought.

The above is the gist of the measurement principle of the present invention.

The PC 5 shown in FIG. 1 sets a program based on an algorithm in accordance with the above measurement principle in a recording medium such as a memory in advance, and simultaneously collects the data of the amount of transmitted light from the optical system in real time or after the collection. The CPU (MPU) executes the program of the recording medium at the time of analysis to calculate the birefringence in the desired wavelength region of the sample Sa, and display the result on a display or output to a paper medium as necessary. It is possible to do.

Therefore, according to this embodiment, in the birefringence measurement of the object to be measured, even if the birefringence has a desired wavelength region of the optical signal used therein, for example, a birefringence of a wavelength larger than one wavelength, the measurement can be performed with a predetermined accuracy. It becomes possible to measure.

Also, in this embodiment, the birefringence measurement using the interference spectrum of the related arts 1) to 6) described above is performed.
Compared with the determination method, the measurement method does not use the parameter for the interference signal as the wavelength but considers the wavelength dependence from the periodic signal obtained from the interference spectrum with respect to the wave number, and thus has the following advantages.

In the birefringence measurement, a mechanical operation for rotating an optical system such as a wave plate or a polarizer is not necessarily required, so that the measurement time can be reduced. In addition, since the continuous wavelength is used instead of the two wavelengths to determine the birefringence order, the birefringence is less susceptible to errors. -The wavelength range in the measurement of birefringence can be set arbitrarily. -The measurement error does not increase even in the case of a sample having a wavelength dependence of birefringence. -When comparing two samples of the same material with different birefringence, the birefringence for the same wavelength region can be obtained, so that both can be accurately compared and evaluated. For example, the stretching process of a film can be displayed in real time. -It is not necessary to prepare samples having different thicknesses showing the same birefringence. -Birefringence can be easily quantified with a relatively simple configuration.・ Measurement is possible even for samples having partial light absorption in the wavelength range to be measured.

The effectiveness of the above-described principle of measuring birefringence and its effect was also confirmed by actual experiments by the present inventor himself. Hereinafter, an experimental example will be described.

(Experimental Example) Analysis method of periodic component When calculating the period for wave number k in the above measurement principle, use waveform analysis such as Fourier analysis, maximum entropy method, and wavelet transform in order to prevent the effects of noise included in the signal beforehand. Is preferred. In general, noise appears as a high-frequency signal, so that it can be easily distinguished from a birefringent signal at a frequency level. Among them, the maximum entropy method has been confirmed to be particularly effective in increasing the accuracy of the measurement of the present invention because the frequency resolution is higher than other methods.

2. 1. Spectroscope Examples of the spectroscope 4 shown in FIG. 1 include: 1) a wavelength scanning type or wavelength selection type spectrometer having a structure in which a diffraction grating or a prism is rotated to guide wavelengths having different diffraction angles to an exit slit one after another. 2) a multi-channel type spectroscope in which a diffraction grating or a prism is fixed and a light receiving element array (for example, a linear CCD) in which light emitted therefrom is arranged one-dimensionally;
Or 3) AOTF (acousto-optic tunable filter)
Can be used. In short, the spectroscope 4 can be arbitrarily selected as long as it is a device that can be a means for extracting an arbitrary monochromatic light from white light.

When a multi-channel type is used as an example of the spectroscope 4, the light intensity obtained here can be obtained only for the wavelength determined by the configuration of the spectroscope. Must be arranged at equal intervals in the wave number domain, so that it becomes necessary to perform data preprocessing using a technique such as interpolation. FIG. 2 shows the result of actually verifying this.

FIG. 2 shows a signal obtained by a system using a multi-channel type spectroscope, and a result obtained by performing interpolation processing using this signal and calculating data at equal wavenumber intervals. . The interpolation processing here is performed by fitting using a quadratic curve using measured data at four points near the required wave number.

In FIG. 2, points indicated by gray triangles are measured values, and points indicated by black circles are calculated values after interpolation. As a result, the measured value and the calculated value are in good agreement, as is apparent from FIG. 2, and it is experimentally confirmed that the interpolation does not affect the subsequent waveform analysis at all. Proven.

The method of the interpolation processing is not limited to the quadratic fitting, and may use a higher-order linear function, spline interpolation, or the like. In FIG. 2, the interval of the calculated data is given priority to the clarity of the present principle.
Although eight points were used, more data may be used in actual calculation processing. In particular, when Fourier analysis is used as waveform analysis, it is preferable to use more points because the resolution of the calculated frequency depends on the number of data points.

3. Effectiveness of the Birefringence Measurement Principle of the Present Invention In order to examine the effectiveness of the above-described measurement principle, a sample Sa was placed on an experimental apparatus shown in FIG.
The sample Sa shown in FIG. 4, that is, 25 phase films having a birefringence of about 530 nm, and 25 layered films were superposed in layers with the same principal axis direction, using an XY stage 6 and a driver 7 added thereto. The sample Sa was placed on the sample stage 6, and the birefringence of each layer was measured sequentially.

As a result, as shown in FIG. 5, it was confirmed that the number of layers of the phase film as the sample Sa was proportional to the signal period (birefringence) obtained from the output of the spectroscope 4. As a result, the validity of this measurement principle was experimentally proved.

4. Method of Determining Main Spindle Orientation of Sample According to equation (1) above, it can be seen that the main shaft orientation φ is proportional to the amplitude value of the cosine wave curve generated by birefringence. Then, when the amplitude of the cosine wave curve is measured while rotating the pair of the polarizer 2 and the analyzer 3 and the principal axis direction of the sample Sa relatively around the optical axis, the position showing the maximum amplitude is the angle between the two. Is relatively 45 degrees.

FIG. 6 shows an experimentally verified result. This experiment was performed using a Babinet Soleil compensator (BSC) as the sample Sa. The measurement results when the principal axis direction is rotated 180 degrees at a 5-degree pitch without changing the set birefringence amount of the BSC are shown. The black circle in FIG. 6 indicates the period of the measured cosine wave curve (ie, the amount of birefringence).
And the triangular marks indicate the amplitude values of the cosine wave curve.
These are the results of FFT analysis.

As is clear from FIG. 6, only at the point where the main axis of the sample Sa and the axis of the polarizer 2 overlap, the amplitude of the cosine wave curve becomes zero, so that the amount of birefringence cannot be measured. Other than that, it shows a constant value without depending on the set angle of the BSC. Also, the amplitude changes depending on the set value of the bearing,
In addition, the maximum value is shown at points where the amplitude is 0 degree and 90 degrees, and 4
It can be seen that the minimum value is shown at the point of 5 degrees. Therefore, it is possible to determine the amplitude value of the cosine wave curve with respect to the relative setting angle of the orientation between the sample Sa and the polarizer 2, and determine the orientation of the main axis from those values.

Specifically, if the sample Sa is mounted on a rotary holder that rotates around the optical axis, or the polarizer 2 and the analyzer 3 are mounted on the same rotary holder, the sample Sa and the sample Sa are polarized. The relative azimuth angle with the child 2 can be changed. The direction of the sample Sa can be determined by sequentially obtaining the amplitude of the cosine wave curve while rotating the rotary holder and obtaining the initial phase of the obtained curve (which changes in the form of a cosine wave). Alternatively, the point indicating the maximum value of the curve may be determined using interpolation means such as fitting.

5. Method for Determining Relative Birefringence at Each Wavelength A method of relatively determining the birefringence at each wavelength from the cosine wave curve shown in FIG. 2 will be described. The method described above is a method for directly calculating the absolute value of birefringence, but the value obtained therefrom is the average birefringence in an arbitrary wavelength range. Here, a method of obtaining birefringence in each monochromatic light will be described.

In FIG. 2, when the measuring optical system is a parallel Nicols, the wavelength at which the light quantity becomes maximum is the birefringence retardation value Δ.

(Equation 7) Is the case. As described above, the change in the light amount changes in a cosine wave with respect to the retardation Δ. That is, by calculating the phase of the cosine wave curve by Fourier analysis or the like, the amount of birefringence at each wavelength can be determined in more detail.

6. In the case where the polarizer / analyzer pair is in a crossed Nicol arrangement, the above example has been described on the assumption that the polarizer / analyzer pair is in a parallel Nicol state.However, the present invention is not limited to this. Can be analyzed in exactly the same way. That is, in the case of crossed Nicols, the same measurement may be performed by rewriting the above equation (1) as the following equation.

[0069]

(Equation 8) Also in this case, it is not affected at all by frequency measurement.

7. Other Configuration Examples Also, the device configuration is not limited to the configuration shown in FIG.
Any method that can implement the measurement principle of the present invention can be applied. One example of this is shown in FIGS. 7 and 8, respectively. Here, the same components as those described above are denoted by the same reference numerals, and description thereof will be omitted or simplified.

The device for evaluating birefringence shown in FIG. 7 has a device (spectroscope) 4 for splitting white light out of the same configuration as described above.
Is placed closer to the light source 1 than the pair of the polarizer 2 and the analyzer 3 which are disposed opposite to each other with the same sample Sa as above, and the spectroscope 4 is connected to the PC 5 via the spectroscope driver 4a, and A photodetector 8 forming a part of the optical system of the present invention is installed on the light exit side of the analyzer 3 on the road.

According to this configuration, an arbitrary monochromatic light is continuously extracted from the spectroscope 4 and the monochromatic light is extracted from the polarizer 2,
The light passes through the sample Sa and the analyzer 3, and the transmitted light is detected by the photodetector 8. At this time, while controlling the spectroscope 4 via the spectroscope driver 4 a by the PC 5, monochromatic light is taken out at equal wavenumber intervals, and the light intensity is sequentially measured by the photodetector 8. A curve can be obtained. Subsequent frequency measurement may be performed in exactly the same manner as described above.

The birefringence evaluation device shown in FIG.
It is expanded to the dimension measurement, and is included in the device configuration (white light source 1, polarizer 2, analyzer 3, spectroscope 4, spectroscope driver 4a, PC5, and photodetector 8) shown in FIG. In this configuration, a photodetector 8 forming a part of an optical system is replaced with a two-dimensional image pickup device (CCD camera in the example in FIG. 8) 9. With this configuration, it becomes possible to take out monochromatic light at equal wave number intervals by the spectroscope 4 and sequentially take in images by the CCD camera 9.

In this case, the cosine wave curve similar to the above is represented by C
It can be obtained by connecting the same coordinates of the images obtained from the CD camera 9. Therefore, by repeating the frequency analysis operation for the number of pixels, the two-dimensional distribution of birefringence can be measured. Further, as a pre-process of the frequency analysis, the number of pixels of the image can be appropriately averaged to reduce the number.

FIGS. 9A and 9B show the results of measurements based on the method extended to the two-dimensional measurement described above.
In this measurement, the wavelength between 460 and 610 nm was divided into 64 at equal wavenumber intervals, and images at each wavelength were captured as pixels (number of pixels: 256 * 256). The obtained image was averaged, the data was dropped to 20 * 20 points, and birefringence calculation was performed. The sample to be measured Sa is an injection portion when the plastic case of the floppy disk is molded. FIG. 9A shows an original image (256 * 256),
FIG. 9B shows the analysis results (20 * 20).

According to FIGS. 9A and 9B, a birefringence distribution similar to that of polarized light observation was observed as seen in the original image. The only difference between the two patterns is that
This is because the measurement principle in the present invention is not affected by the birefringent principal axis of the sample.

[0077]

As described above, according to the present invention, in the measurement of birefringence of a measurement object, birefringence larger than one wavelength of an optical signal used therein can be measured with desired accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic overall configuration diagram showing a birefringence evaluation apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a component of a light intensity that changes in a cosine wave shape with respect to a wave number (an example in which data is interpolated using a multi-channel type spectroscope).

FIG. 3 is an overall configuration diagram showing an outline of an experimental apparatus.

FIG. 4 is a schematic perspective view showing an outline of a phase film used as an experimental sample.

FIG. 5 is a graph showing the relationship between the number of layers of the phase film and the signal period (birefringence) obtained from the output of the spectroscope.

FIG. 6 is a graph illustrating a method of determining a principal axis direction of a sample.

FIG. 7 is a schematic configuration diagram showing a birefringence evaluation device when a photodetector is used.

FIG. 8 is a schematic configuration diagram showing a birefringence evaluation device when extended to two-dimensional measurement.

9 is a schematic view of a photographic image showing an example of a two-dimensional measurement result by the birefringence evaluation device shown in FIG. 8, (a) is an original image, and (b) is an analysis result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 White light source 2 Polarizer 3 Analyzer 4 Spectrometer 4a Spectrometer driver 5 PC (Personal computer) 6 XY stage 7 XY stage driver 8 Photodetector 9 CCD camera (2D imaging element)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukitoshi Otani 2-24-16 Nakamachi, Koganei-shi, Tokyo F-term within the Faculty of Engineering, Tokyo University of Agriculture and Technology 2G059 AA02 BB10 EE05 HH02 JJ05 JJ06 JJ19 JJ20 KK04 MM01 MM04 MM09 PP01 2G086 EE07 EE12

Claims (10)

[Claims] 1. An optical system for acquiring an optical signal carrying information on birefringence of a measurement object, and analyzing a period of a component which changes in a cosine wave with respect to the wave number based on the optical signal acquired by the optical system. A birefringence analyzing means for obtaining birefringence in a predetermined wavelength region of the object to be measured from the analysis data. 2. The invention according to claim 1, wherein the birefringence analyzing means adjusts a wave number region for analyzing a period of a component which changes in a cosine wave shape with respect to the wave number, so that the birefringence depends on a wavelength. A birefringence evaluation device comprising means for analyzing a degree and obtaining birefringence in an arbitrary wavelength region of the measurement object from the analysis data. 3. The optical system according to claim 2, wherein the optical system emits an optical signal having a continuous spectral distribution toward the object to be measured, and the object to be measured on an optical path of the optical signal from the light source. A pair of polarizers and analyzers arranged at positions sandwiching the light source, and a spectroscope arranged on an optical path of an optical signal from the light source and dispersing the optical signal. . 4. The birefringence analyzing means according to claim 3, wherein the birefringence analysis means comprises a birefringent retardation of the object to be measured when the pair of polarizers and the analyzer are arranged in a state of parallel Nicols. The birefringence, its thickness, and the angles formed by the principal axis of the birefringence and the transmission axis of the polarizer are Δ, δn, d, and φ, respectively, and the wavelength of the optical signal, its light intensity, and the object to be measured. Assuming that the direct current component of the light intensity for the wavelength region to be expressed is λ, I (λ), IDC, and k, and the predetermined system-dependent coefficient is S (λ), the birefringence of the measurement object is Equation 1 A birefringence evaluation device comprising means for performing analysis so as to satisfy the following equation: 5. The birefringence analysis means according to claim 3, wherein the birefringence analysis means includes a birefringent retardation of the object to be measured when the pair of polarizers and the analyzer are arranged in a crossed Nicols state. Its birefringence, its thickness,
And the angles formed by the birefringent principal axis and the transmission axis of the polarizer are Δ, δn, d, and φ, respectively, and the wavelength of the optical signal, its light intensity, and the direct current of the light intensity with respect to the wavelength region to be measured. Assuming that the components and their wave numbers are λ, I (λ), IDC, and k, and a predetermined system-dependent coefficient is S (λ), the birefringence of the object to be measured is given by: A birefringence evaluation device comprising means for performing analysis so as to satisfy the following equation: 6. The invention according to claim 3, wherein the spectroscope is arranged on an emission side of the analyzer or an incidence side of the polarizer on an optical path of the optical signal. Birefringence evaluation device. 7. The birefringence analysis means according to claim 3, wherein the optical system further comprises a photodetector for detecting the optical signal on an optical path of the optical signal on the emission side of the analyzer. Is a device for performing a birefringence analysis of the object to be measured based on a signal detected by the photodetector. 8. The invention according to claim 3, wherein the optical system further includes a two-dimensional image pickup device that picks up an optical signal on an optical path of the optical signal on an emission side of the analyzer,
The birefringence evaluation device, wherein the birefringence analysis means performs birefringence analysis of the measurement target based on a signal imaged by the two-dimensional imaging device. 9. An optical signal carrying information on birefringence of an object to be measured is input, and a period of a component which changes in a cosine wave with respect to the wave number is analyzed based on the input optical signal. A birefringence evaluation method, wherein birefringence in a predetermined wavelength region of the measurement object is obtained. 10. An optical signal carrying information on birefringence of an object to be measured is inputted, and a period of a component which changes in a cosine wave with respect to the wave number is analyzed based on the inputted optical signal,
A recording medium in which a program for calculating birefringence in a predetermined wavelength region of the measurement object is readable recorded from the analysis data.