JP5892011B2 - Method and apparatus for measuring birefringence of articles having uniaxial orientation - Google Patents

Description

  The present invention relates to a method and an apparatus for measuring the birefringence of a light-transmitting article having a uniaxial orientation, such as an extruded product such as a tube or a rod, or a uniaxially stretched film sheet.

  As a general method for measuring the phase difference of a light-transmitting object to be measured, the transmission axes of the polarizer and the analyzer are arranged in parallel, and the object to be measured is placed between the polarizer and the analyzer. There is a method (parallel Nicol rotation method) in which the optical element and the analyzer are rotated once while maintaining the parallel Nicol state, and the phase difference and the orientation angle of the object to be measured are obtained from the change in transmitted light intensity at that time.

  In addition, in order to measure the phase difference distribution within a certain area of the transparent resin molded product, an apparatus combining a parallel Nicol rotation method and a CCD camera has been put into practical use. It is used for phase difference distribution measurement for objects to be measured in the low phase difference range.

  Furthermore, in order to measure the phase difference distribution of a transparent resin molded product having a phase change over a wide range of several thousand nm within the measurement area, a polarizer / analyzer and imaging spectrometer with white light and parallel Nicol arrangement are used. There is also an apparatus that measures the phase difference from the spectrum of transmitted light (see Patent Document 1).

  In the manufacture of a medical catheter tube, since the magnitude of molecular orientation is related to elongation resistance and kink resistance, management of birefringence, which is an index of the magnitude of molecular orientation, is important (see Patent Document 2). Birefringence in the tube indicates a difference in refractive index between the longitudinal direction of the tube and the circumferential direction perpendicular thereto. This is because when the birefringence is small, the stretch resistance is small, and in the case of a medical catheter tube, the tube is deformed in the longitudinal direction when the treatment device is inserted, and the position adjustment becomes inaccurate. The same can be said for other medical tubes or general-purpose tubes as well as catheter tubes.

  In Patent Document 2, the phase difference R is measured using a simple retardation measuring instrument manufactured by Oji Scientific Instruments, and the tube thickness t is calculated from the tube outer diameter and the core wire measured using a laser microdiameter, Birefringence is determined as R / t.

JP 2009-281787 A WO2007 / 046348

Journal of the Japan Society of Photography, Vol.27, No.6, pp.478-483 (1990)

  An object of the present invention is to provide a method and an apparatus for simply measuring the birefringence of a light-transmitting article having a uniaxial orientation.

  In the birefringence measuring method of the present invention, a polarizer and an analyzer are arranged in parallel Nicols with a measured object made of a light-transmitting article having a uniaxial orientation, and the transmission axes of the polarizer and the analyzer are measured. In a state that is fixed at a specific azimuth angle θ with respect to the orientation axis of the imaging spectrometer, the measurement light including multi-wavelength components is irradiated to the object to be measured through the polarizer, and the measurement light transmitted through the object to be measured is passed through the analyzer to the imaging spectrometer. The birefringence of the object to be measured is measured by using the phase difference measurement device that enters the transmission light spectrum and captures the transmitted light spectrum and includes the following steps (S1) to (S4).

(S1) calculating and preparing a calculated transmittance spectrum Tcal (λ) (= I (θ) / I ₀ (θ)) in advance for a plurality of phase differences;
(S2) obtaining a transmittance spectrum Tobs (λ) (= I (θ) / I ₀ (θ)) from the transmitted light spectrum of the object to be measured using the phase difference measuring device;
(S3) The phase difference Rm is obtained as the phase difference R corresponding to the calculated transmittance spectrum Tcal (λ) closest to the transmittance spectrum Tobs (λ) among the calculated transmittance spectra Tcal (λ) prepared in step S1. And (S4) a step of obtaining birefringence Δn as Δn = Rm / t by dividing the phase difference Rm obtained in step S3 by the thickness t of the object to be measured.

Here, I ₀ is the detection light intensity when there is no measurement object, I is the detection light intensity when there is a measurement object, and λ is the wavelength of the measurement light.

In the case of the parallel Nicol arrangement, the detection light intensity is generally expressed by the following equation.
I (θ)
= I ₀ {α ² cos ⁴ (θ−φ) + sin ⁴ (θ−φ) + (Cα / 2) sin ² 2 (θ−φ)}
(1)
Where C = cos (2πR / λ) (2)

  Here, α is the amplitude transmittance ratio when linearly polarized light is transmitted in two orthogonal optical principal axis directions, φ is the orientation angle of the object to be measured (the direction in which the refractive index of the two optical principal axes of the object to be measured is large) Θ and φ are angles with respect to an appropriately set reference direction.

  In the birefringence measuring apparatus for carrying out the birefringence measuring method of the present invention, a polarizer and an analyzer are arranged in parallel Nicols, and measurement light including multi-wavelength components enters the imaging spectroscope from the polarizer through the analyzer and is transmitted. Spectral spectrum measurement unit for measuring optical spectrum, and holding the measurement object between the polarizer and the analyzer, the orientation axis of the measurement object is a specific azimuth angle θ with respect to the transmission axis of the polarizer / analyzer A sample stage that is positioned so as to be, and an arithmetic processing unit that calculates the birefringence of the object to be measured from the transmitted light spectral spectrum measured by the spectral spectrum measuring unit.

  Then, as shown in FIG. 5 showing a preferred embodiment, the arithmetic processing unit obtains and holds a calculated transmittance spectrum Tcal (λ) for a plurality of phase differences in advance, and a transmittance spectrum holding unit 102, A transmittance spectrum calculating unit 104 that calculates a transmittance spectrum Tobs (λ) from a transmitted light spectrum of the object measured by the spectrum measuring unit, and a calculated transmittance spectrum Tcal held in the transmittance spectrum holding unit 102 A phase difference calculating unit 108 for obtaining a phase difference Rm corresponding to the calculated transmittance spectrum Tcal (λ) closest to the transmittance spectrum Tobs (λ) of the transmittance spectrum calculating unit 104 among (λ); Birefringence calculation for obtaining birefringence Δn as Δn = Rm / t by dividing the phase difference Rm obtained by the phase difference calculation unit 108 by the thickness t of the object to be measured. It is provided with a 112. For example, the phase difference calculation unit 108 calculates the residual sum of squares for each wavelength as the difference between the calculated transmittance spectrum Tcal (λ) and the actually measured transmittance spectrum Tobs (λ), thereby matching the two. Judging.

  The transmittance spectrum holding unit 102 holds a plurality of calculated transmittance spectra Tcal (λ) calculated with different phase differences. For example, the transmittance spectrum holding unit 102 calculates a phase difference range of 100 to 10000 nm for each 10 nm phase difference. The transmittance spectrum Tcal (λ) is obtained and held.

  An imaging spectroscope detects a spectral spectrum in which a linear light incident from a slit is dispersed by a grating in a direction perpendicular to the straight line by a two-dimensional detector such as a CCD camera. A spectrum can be detected at a time. Here, the position on a straight line means a straight line that is perpendicular to the longitudinal direction, that is, the radial direction when the object to be measured is a long object having a tube shape or a rod shape.

  In a preferred form of the birefringence measuring method, the object to be measured is a tube or a rod-like object, and the thickness t of the object to be measured is obtained by processing an image of the object to be measured that has entered the imaging spectrometer. The phase difference measuring device obtains both the phase difference Rm and the thickness t to obtain the birefringence Δn. This eliminates the need to provide a device for determining the thickness t. A method for obtaining the thickness t from the image of the object to be measured that has entered the imaging spectrometer will be described later with reference to FIG.

  Tubes and rods are usually produced by extrusion. Tubes and rods produced by extrusion molding have a uniaxial orientation in the longitudinal direction, so the longitudinal direction becomes the orientation axis direction.

  Corresponding to the birefringence measuring method of this preferred form, in the preferred form of the birefringence measuring apparatus, as shown in FIG. Is further provided with an image processing unit 110 that processes the image of the measurement object incident on the imaging spectroscope and calculates the thickness t of the measurement object, and the birefringence calculation unit 112 includes the measurement object. The thickness t of the measurement object calculated by the image processing unit 110 is used as the thickness t.

  In a more preferred form of the birefringence measurement method, the azimuth angle θ of the transmission axis of the polarizer / analyzer with respect to the orientation axis of the object to be measured is 45 °, and the calculated transmittance spectrum Tcal (λ) and transmittance spectrum Tobs (λ) Is determined as (1 + C) / 2. Correspondingly, in a preferred embodiment of the birefringence measuring apparatus, the sample stage holds the object to be measured so that the azimuth angle θ of the object to be measured with respect to the transmission axis of the polarizer / analyzer is 45 °. The arithmetic processing unit 10 processes the calculated transmittance spectrum Tcal (λ) and the transmittance spectrum Tobs (λ) as (1 + C) / 2.

  In a further preferred embodiment of the birefringence measuring method, the transmittance spectrum Tobs (λ) obtained in step (S2) and the calculated transmittance prepared in step (S1) are provided between steps (S2) and (S3). The method further includes the step of calculating the corrected transmittance spectrum T′obs (λ) by correcting the transmittance spectrum Tobs (λ) so that the maximum value and the minimum value of each spectrum Tcal (λ) match, and step (S3). Then, the phase difference Rm is obtained using the corrected transmittance spectrum T′obs (λ) instead of the transmittance spectrum Tobs (λ). Correspondingly, in the preferred embodiment of the birefringence measuring apparatus, as shown in FIG. 5 showing a preferred embodiment, the arithmetic processing unit 10 transmits the transmittance spectrum Tobs (λ) calculated by the transmittance spectrum calculating unit 104. ) And the calculated transmittance spectrum Tcal (λ) held in the transmittance spectrum holding unit 102 are corrected so that the maximum value and the minimum value of the calculated transmittance spectrum Tcal (λ) coincide with each other, thereby correcting the corrected transmittance spectrum T′obs. A transmittance spectrum correction unit 106 that calculates (λ) is further included, and the phase difference calculation unit 108 replaces the transmittance spectrum Tobs (λ) with the corrected transmittance spectrum T′obs ( λ) is used to determine the phase difference Rm.

In the equation (1), I ₀ and R depend on the measurement wavelength λ. In addition, α is almost 1 in most cases, but when the phase difference of the object to be measured is large, this corresponds to a large difference in refractive index between the two optical main axes. As a result, a difference also occurs in the transmittance of linearly polarized light with respect to the two optical principal axis directions, and α is smaller than 1. However, even in that case, α is only reduced to about 0.95.

First, for the sake of simplicity, consider the case where α = 1 in equation (1). Assuming that the longitudinal direction of the tube-shaped object to be measured is the reference of the angle, the orientation angle φ of the tube-shaped or rod-shaped object to be measured formed by the extrusion method is the longitudinal direction, so it may be considered that φ = 0 °. In a preferred embodiment, the detected light intensity when θ = 45 ° is expressed as I (45), and I ₀ at this time is expressed as I ₀ (45).
I (45) = I ₀ (45) · (1 + C) / 2 (3)

Therefore, I (45) / I ₀ (45) is determined by C, that is, the phase difference R and the measurement wavelength λ. In general, since the phase difference R also has wavelength dispersion, I (45) / I ₀ (45) is represented as Tcal (λ) and is referred to as a calculated transmittance spectrum. Further, I ₀ (45) and I (45) are actually measured, and the transmittance spectrum obtained as a ratio between them is represented as Tobs (λ).

The chromatic dispersion is expressed by the following equation (4) with the phase difference being R (λ), and the coefficients a, b, and c in the equation can be distinguished and registered for each material in advance.
R (λ) = a + b / (λ ² −c ² ) (4)
The values of the coefficients a, b, and c can be easily obtained by preparing a film-like sample using the same material as the object to be measured, for example, using a phase difference measuring device KOBRA-WR manufactured by Oji Scientific Instruments. Can be sought. Non-patent document 1 describes that the chromatic dispersion can be expressed by the equation (4).

When ₀ reference wavelength lambda which can be arbitrarily set, (4) distribution ratio R (lambda) / R (lambda ₀₎ at any wavelength lambda for the reference wavelength lambda ₀ from equation easily obtained. It is well known that the dispersion ratio R (λ) / R (λ ₀ ) is almost equal for each material even when the phase difference R (λ) of the object to be measured differs due to the difference in the draw ratio or the thickness. Yes. For example, FIG. 2A shows the wavelength dependence of retardation of five types of PET films, and FIG. 2B is a graph showing the wavelength dependence of the dispersion ratio when λ ₀ is 590 nm. In fact, the dispersion ratio actually overlaps one curve.

Therefore, by setting each coefficient of the equation (4) and registering the chromatic dispersion equation, the dispersion ratio with respect to the reference wavelength can also be obtained, and R (λ ₀ ) is changed by a predetermined range within a predetermined range in calculation. Then, R (λ) can be easily calculated for an arbitrary wavelength each time. That is, if the wavelength dispersion formula of the phase difference of the object to be measured is known, it means that the calculated transmittance spectrum Tcal (λ) at that time can be freely calculated while arbitrarily changing the phase difference with respect to the reference wavelength. .

Therefore, in the birefringence measuring method according to a further preferred embodiment of the present invention, the calculated transmittance spectrum Tcal (λ) in step (S1) is based on the wavelength dispersion formula of the phase difference R (λ) for the object to be measured. This is calculated from the corresponding phase difference R (λ) when the phase difference R (λ ₀ ) at the wavelength λ ₀ is changed to a plurality.

Correspondingly, in the preferred form of the birefringence measuring apparatus, as shown in FIG. 5 showing a preferred embodiment, the arithmetic processing unit 10 calculates the phase difference R (λ) of the measured object from the wavelength dispersion formula. It further includes a dispersion ratio calculating unit 100 for calculating a dispersion ratio R (λ) / R (λ ₀ ) of the phase difference with respect to the reference wavelength λ ₀ , and the transmittance spectrum Tcal (held by the transmittance spectrum holding unit 102). λ) is calculated from the corresponding R (λ) when R (λ ₀ ) is changed to a plurality in the dispersion ratio calculation unit 100.

More specifically, an operation of measuring each transmitted light spectrum I ₀ (45) and I (45) at each position on a straight line is performed. Here, the term “on a straight line” means, for example, a straight line in the radial direction (Y direction) of the DUT 6 as shown in FIG. The direction is the X direction. I (45) differs depending on each position (Y) on the straight line. The transmittance spectrum calculation unit 104 calculates the ratio of the transmitted light spectrum I ₀ (45) and I (45) to obtain the transmittance spectrum Tobs (λ). However, for example, the graph of Tobs (λ) and Tcal (λ) when measuring a tube with R (λo) of 1510 nm is as shown by a thin solid line and a broken line in FIG. Therefore, in a preferred embodiment, the maximum value and the minimum value of Tobs (λ) and Tcal (λ) are examined, correction coefficients are calculated so that they match, and the measured transmittance spectrum is corrected by the following equation. Calculate T′obs (λ).
T'obs (λ) = (Tobs (λ) −Tobs (λ) .mv-min) / K (5)
However,
K = (Tobs.mv-max (λ) −Tobs (λ) .mv-min) / (Tcal (λ) .max−Tcal (λ) .min)
Tobs (λ) .mv-min: Minimum value of moving average of measured transmittance spectrum Tobs (λ) Tobs (λ) .mv-max: Maximum value of moving average of measured transmittance spectrum Tobs (λ) Tcal (λ) .max: Maximum value of the calculated transmittance spectrum Tcal (λ) .max: Minimum value of the calculated transmittance spectrum.

  Correspondingly, as shown in FIG. 5 showing a preferred embodiment, the arithmetic processing unit 10 stores the transmittance spectrum Tobs (λ) calculated by the transmittance spectrum calculating unit 104 and the transmittance spectrum holding unit 102. The transmittance spectrum for correcting the transmittance spectrum Tobs (λ) so that the maximum value and the minimum value of each of the stored calculated transmittance spectra Tcal (λ) coincide with each other to calculate the corrected transmittance spectrum T′obs (λ). A correction unit 106 is further provided. In this case, the phase difference calculating unit 108 obtains the phase difference Rm using the corrected transmittance spectrum T′obs (λ) calculated by the transmittance spectrum correcting unit 108 instead of the transmittance spectrum Tobs (λ). For example, the phase difference calculation unit 108 calculates a residual sum of squares for each wavelength as a difference between the calculated transmittance spectrum Tcal (λ) and the actually measured corrected transmittance spectrum T′obs (λ). Judgment is made between the two.

  Next, a case where the amplitude transmittance ratio α in the two optical principal axis directions is not 1 will be considered. When α ≠ 1, place θ = 45 ° in equation (1) and compare Tcal (λ) when α is 1 and 0.95 when PET is R (λo) = 1500 nm. Then, as shown in FIG. 4, the maximum transmittance varies depending on the value of α. However, the actually measured transmittance is as shown in Tobs (λ) in FIG. 3, and it can be seen that the maximum and minimum values deviate from the calculated values more than the influence of α. Therefore, Tcal (λ) is always obtained with α = 1, and the measured value is corrected by the above-described transmittance spectrum correction unit 106.

  In a preferred embodiment, the object to be measured is a tube or a rod-like object, and the thickness t of the object to be measured is obtained by processing an image of the object to be measured that has entered the imaging spectrometer. A method for obtaining the birefringence Δn by obtaining both the phase difference Rm and the thickness t will be specifically described. FIG. 8 is an example of a captured image of an imaging spectrometer when measuring a tube-shaped object, and there is a portion that does not transmit measurement light but is shaded, and light is actually transmitted through the tube diameter. The central part of the direction. Further, since only the central portion in the tube radial direction corresponds to twice the wall thickness t of the tube, it is not necessary to measure the phase difference in the shaded portion of FIG.

  A method of determining the central portion in the radial direction of the object to be measured by image processing from the captured image of the imaging spectroscope and further obtaining the tube thickness t or the rod-shaped diameter D will be described.

  As shown in FIG. 8, the tube-like object to be measured provides four black belt-like images. The four belt-like dark-to-light or light-to-dark transition points are obtained and are designated as Y1 to Y8 from the smaller Y coordinate.

  The outer diameter is the distance from Y1 to Y8. Since this distance is the diameter D when the object to be measured is a rod, the image processing unit 110 can calculate the diameter D of the rod from the captured image of the imaging spectrometer.

  The inner diameter Din of the tube-shaped object to be measured is (1 / K) outside the band width from the positions Y4 and Y5 detected as the two inner black band-like edges because of the curved surface.

Therefore, the outer diameter Dout, the inner diameter Din, and the wall thickness t of the tube are expressed by the following equations.
Dout = Y8−Y1 (6)
Din = Y5-Y4 + (Y4-Y3) / K + (Y6-Y5) / K (7)
t = (Dout−Din) / 2 (8)

  Although K in the formula (7) varies depending on the refractive index of the tube material, it has been found by the inventors that K is approximately “3”. Although depending on the required measurement accuracy, if the approximate value of birefringence is acceptable, the wall thickness t of the tube can be calculated by the above equations (6) to (8) with K = 3.

  If a highly accurate birefringence value is required, K may be determined for each tube material. K can also be obtained by calculation from the refractive index, but as a practical method, for the tube of the material to be measured, the captured image of the imaging spectrometer is measured as shown in FIG. K can be determined by measurement. When K is obtained in advance for each material of the tube to be measured, it is stored in the image processing unit 110 so that the image processing unit 110 can obtain the tube from the captured image of the imaging spectroscope by the above formulas (6) to (8). The wall thickness t can be calculated.

  Further, when the thickness t or the diameter D of the object to be measured is measured by another method, the value may be input at the start of the measurement of this apparatus.

If the tube thickness t or the rod-shaped diameter D is obtained, the birefringence calculating unit 112 can calculate the birefringence Δn by the following equation.
Δn = Rm (λo) / 2t or Δn = Rm (λo) / D (9)

  FIG. 6 is a flowchart summarizing the most preferable method in the procedure for determining the birefringence Δn described above.

According to the present invention, the polarizer and the analyzer are arranged in parallel Nicols, and the transmission axis of the polarizer / analyzer is fixed at a specific azimuth angle θ with respect to the orientation axis of the object to be measured having a uniaxial orientation. A transmittance spectrum (= I (θ) /) consisting of the detected light intensity I ₀ (θ) of transmitted light in the absence of the object to be measured and the detected light intensity I (θ) of transmitted light when the object to be measured is present. I ₀ (θ)) is used to compare the calculated transmittance spectrum Tcal (λ) obtained in advance and prepared for a plurality of phase differences with the actually measured transmittance spectrum Tobs (λ). Since the phase difference Rm corresponding to the calculated transmittance spectrum Tcal (λ) closest to λ) is set as the phase difference of the object to be measured, the object having a high phase difference whose phase difference range is several thousand nm. Even if it exists, the phase difference can be easily measured.

It is a schematic block diagram which shows one Example. (A) is a figure which shows the wavelength dependence of phase difference of PET film, (B) is a figure which similarly shows the wavelength dependence of a dispersion ratio. It is a figure which shows the example of the transmittance | permeability spectrum handled by this invention. It is a figure which shows the influence of the amplitude transmittance | permeability ratio (alpha) of a to-be-measured object with respect to a calculated transmittance spectrum. It is a block diagram which shows the arithmetic processing part in one Example. It is a flowchart which shows the determination procedure of birefringence (DELTA) n in one Example. It is the schematic which shows an imaging spectroscope. It is an example of the captured image of an imaging spectroscope.

  FIG. 1 is a schematic configuration diagram of an embodiment in which the birefringence measuring apparatus of the present invention is applied for measuring a tube or a rod-like object. The birefringence measurement apparatus includes a sample stage 5, a spectral spectrum measurement unit, and an arithmetic processing unit 10 as main components.

  The sample stage 5 holds the object to be measured 6 in the center of the measurement field between the polarizer 4 and the analyzer 7 of the spectroscopic measurement unit, and the orientation axis of the object to be measured 6 is transmitted through the polarizer 4 and the analyzer 7. Positioning is performed with respect to the axis so as to have a specific azimuth angle θ. In a preferred example, the specific azimuth angle θ is 45 °.

  The spectroscopic spectrum measurement unit transmits a set of a polarizer 4 and an analyzer 7 arranged in parallel Nicols, optical systems 1, 2 and 3 for allowing measurement light including multi-wavelength components to enter the polarizer 4, and the analyzer 7. And an imaging spectroscope 9 for measuring the transmitted light spectrum by receiving the measured light through the lens 8.

  The optical system that allows measurement light including multi-wavelength components to enter the polarizer 4 includes a light source 1, a light guide 2, and a condenser lens 3. The light source 1 is, for example, a halogen lamp, and supplies white light as measurement light including multiple wavelength components. The light source 1 may be a light source using a white LED (light emitting diode). Light from the light source 1 is guided to the condenser lens 3 by the light guide 2.

  The polarizer 4 is for irradiating the object to be measured 6 with linearly polarized measurement light, and is disposed between one surface of the object to be measured 6 and the condenser lens 3. An analyzer 7 is disposed opposite to the polarizer 4 on the other surface side of the measurement object 6 with the measurement object 6 interposed therebetween. The polarizer 4 and the analyzer 7 are fixedly arranged in a parallel Nicols state. The measurement object 6 is positioned by the sample stage 5 so that the longitudinal direction of the measurement object 6 is the reference azimuth and the polarization azimuth (θ) is 45 ° as a preferred form.

  The measurement light transmitted through the analyzer 7 is taken into the imaging spectroscope 9 through the lens 8. The lens 8 is a set of lenses constituting a microscope or a lens for a camera (for example, a CCD camera). The size of the visual field and the spatial resolution that can be captured are determined by the magnification of the lens 8, the size of the light receiving element (for example, CCD element) included in the imaging spectroscope 9, and the number of pixels in the Y direction. Here, the longitudinal direction of the DUT 6 is defined as the X direction, and the direction orthogonal thereto, that is, the radial direction of the DUT 6 is defined as the Y direction.

  The imaging spectroscope 9 has a configuration as shown in FIG. 7, for example, and receives linear light in the Y direction through the slit 9a, splits it with the grating 9b, and receives it with the monochrome CCD camera 9d. The grating 9b splits the light at each position on the line in the Y direction in the X direction. Specifically, ImSpector V8 (a product of JFE Techno-Research Corporation) can be used as the imaging spectrometer 9.

  The arithmetic processing unit 10 calculates the birefringence of the measured object from the transmitted light spectrum measured by the spectrum measuring unit, and has the configuration shown in FIG. 5 already described.

  A portion excluding the arithmetic processing unit 10, the sample stage 5 and the DUT 6 constitutes a spectral spectrum measurement unit.

  The transmitted light intensity separated and detected by the imaging spectroscope 9 is taken into the arithmetic processing unit 10 and the phase difference Rm (λ) of the device under test 6 is calculated as described above. The arithmetic processing unit 10 is realized by a dedicated computer or a general-purpose personal computer.

DESCRIPTION OF SYMBOLS 1 Light source 2 Light guide 3 Condensing lens 4 Polarizer 5 Sample stand 6 Measured object 7 Analyzer 8 Lens 9 Imaging spectrometer 9a Slit 9b Grating 9c CCD element 9d CCD camera 10 Arithmetic processing part 100 Dispersion ratio calculation part 102 Transmittance Spectrum holding unit 104 Transmission spectrum calculation unit 106 Transmission spectrum correction unit 108 Phase difference calculation unit 110 Image processing unit

Claims (10)

The polarizer and analyzer are arranged in parallel Nicols across the object to be measured that consists of a light-transmitting article having uniaxial orientation, and the transmission axis of the polarizer / analyzer is in a specific orientation with respect to the alignment axis of the object to be measured. In a state where the angle θ is fixed, the measurement light containing multi-wavelength components is irradiated to the object to be measured through the polarizer, and the measurement light that has passed through the object to be measured is incident on the imaging spectroscope through the analyzer. A birefringence measuring method for measuring birefringence of an object to be measured by using a phase difference measuring apparatus to be taken in and including the following steps.
(S1) calculating and preparing a calculated transmittance spectrum Tcal (λ) (= I (θ) / I ₀ (θ)) in advance for a plurality of phase differences;
(S2) obtaining a transmittance spectrum Tobs (λ) (= I (θ) / I ₀ (θ)) from the transmitted light spectrum of the object to be measured using the phase difference measuring device;
(S3) A step of obtaining the phase difference Rm as a phase difference corresponding to the calculated transmittance spectrum Tcal (λ) closest to the transmittance spectrum Tobs (λ) among the calculated transmittance spectra Tcal (λ) prepared in step S1. (S4) The birefringence Δn is obtained by dividing the phase difference Rm obtained in step S3 by the thickness t of the object to be measured. Δn = Rm / t
Asking for steps.
Here, I ₀ is the detection light intensity when there is no measurement object, I is the detection light intensity when there is a measurement object, and λ is the wavelength of the measurement light. The object to be measured is a tube or a rod-like object,
The thickness t of the object to be measured is obtained by processing the image of the object to be measured that has entered the imaging spectroscope, so that both the phase difference Rm and the thickness t are obtained with a single phase difference measuring device, and the birefringence Δn is obtained. The birefringence measuring method according to claim 1 to be obtained. The azimuth angle θ of the transmission axis of the polarizer / analyzer with respect to the orientation axis of the object to be measured is 45 °, and the calculated transmittance spectrum Tcal (λ) and transmittance spectrum Tobs (λ) are (1 + C) / 2
The birefringence measuring method according to claim 1 or 2, which is obtained as follows.
Here, C = cos (2πR / λ) (R: phase difference). Between the steps (S2) and (S3), the transmittance spectrum Tobs (λ) obtained in the step (S2) and the calculated transmittance spectrum Tcal (λ) prepared in the step (S1). A step of calculating a corrected transmittance spectrum T′obs (λ) by correcting the transmittance spectrum Tobs (λ) so that the maximum value and the minimum value coincide;
The birefringence according to any one of claims 1 to 3, wherein in the step (S3), the phase difference Rm is obtained by using the corrected transmittance spectrum T'obs (λ) instead of the transmittance spectrum Tobs (λ). Measuring method. The calculated transmittance spectrum Tcal (λ) in the step (S1) has a plurality of phase differences R (λ ₀ ) at the reference wavelength λ ₀ based on the wavelength dispersion formula of the phase difference R (λ) for the object to be measured. The birefringence measurement method according to claim 1, wherein the birefringence measurement method is calculated from a corresponding phase difference R (λ) when changed to. A spectroscopic spectrum measurement unit in which a polarizer and an analyzer are arranged in parallel Nicols, and measurement light including multi-wavelength components enters the imaging spectroscope through the analyzer through the analyzer and measures a transmitted light spectroscopic spectrum,
A sample stage that holds the object to be measured between the polarizer and the analyzer, and is positioned so that the orientation axis of the object to be measured is a specific azimuth angle θ with respect to the transmission axis of the polarizer / analyzer;
An arithmetic processing unit that calculates the birefringence of the object to be measured from the transmitted light spectrum measured by the spectrum measuring unit,
The arithmetic processing unit obtains and holds a calculated transmittance spectrum Tcal (λ) in advance for a plurality of phase differences, and a transmittance spectrum holding unit;
A transmittance spectrum calculating unit for calculating a transmittance spectrum Tobs (λ) from a transmitted light spectrum of the object measured by the spectrum measuring unit;
Of the calculated transmittance spectra Tcal (λ) held in the transmittance spectrum holding unit, the calculated transmittance spectrum Tcal (λ) closest to the transmittance spectrum Tobs (λ) calculated by the transmittance spectrum calculating unit A phase difference calculation unit for obtaining a corresponding phase difference Rm;
By dividing the phase difference Rm obtained by the phase difference calculation unit by the thickness t of the object to be measured, birefringence Δn is obtained as follows: Δn = Rm / t
A birefringence measuring device comprising: a birefringence calculating unit obtained as described above. When a tube or a rod-like object is measured as the object to be measured, the image processing unit further includes an image processing unit that processes an image of the object to be measured incident on the imaging spectrometer and calculates a thickness t of the object to be measured.
The birefringence measuring apparatus according to claim 6, wherein the birefringence calculating unit uses the thickness t of the measurement object calculated by the image processing unit as the thickness t of the measurement object. The sample stage holds the measurement object such that the azimuth angle θ of the alignment axis of the measurement object with respect to the transmission axis of the polarizer / analyzer is 45 °,
The arithmetic processing unit calculates the calculated transmittance spectrum Tcal (λ) and the transmittance spectrum Tobs (λ) by (1 + C) / 2.
The birefringence measuring apparatus according to claim 6 or 7, which is processed as follows. The transmittance so that the maximum value and the minimum value of the transmittance spectrum Tobs (λ) calculated by the transmittance spectrum calculation unit and the calculated transmittance spectrum Tcal (λ) held by the transmittance spectrum holding unit coincide with each other. A transmittance spectrum correction unit that corrects the spectrum Tobs (λ) and calculates a corrected transmittance spectrum T′obs (λ);
The phase difference calculation unit obtains the phase difference Rm using the corrected transmittance spectrum T′obs (λ) calculated by the transmittance spectrum correction unit instead of the transmittance spectrum Tobs (λ). The birefringence measuring apparatus according to any one of the above. The arithmetic processing unit further includes a dispersion ratio calculating unit that calculates a dispersion ratio R (λ) / R (λ ₀ ) of the phase difference with respect to the reference wavelength λ ₀ from the wavelength dispersion formula of the phase difference R (λ) of the object to be measured. Prepared,
The transmittance spectrum Tcal (λ) held in the transmittance spectrum holding unit is calculated from the corresponding R (λ) when R (λ ₀ ) is changed to a plurality of values. The birefringence measuring apparatus according to any one of claims 9 to 9.