JP2009276079A - On-line phase difference measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable on-line measurement even to a measuring object wherein a phase difference R is changed as much as a half of a measuring wavelength λ or more. <P>SOLUTION: A plurality of addition spectrums I<SB>T</SB>calculated with each different phase difference are held, and an addition spectrum measured value I<SB>T</SB>' is calculated from transmission light spectral spectrums I<SB>0</SB>(0), I<SB>0</SB>(45), in the state not having the measuring object and transmission light spectral spectrums I(0), I(45), in the state having the measuring object, and I<SB>T</SB>wherein a difference between the calculated value I<SB>T</SB>and the measured value I<SB>T</SB>' becomes minimum is determined, and a phase difference R(λ) pertinent to the I<SB>T</SB>is adopted as a phase difference Rm(λ) of the measuring object. In this case, following formulas are organized: I<SB>T</SB>'=I(0)/I<SB>0</SB>(0)+I(45)/I<SB>0</SB>(45), I<SB>T</SB>=(C+3)/2, and C=cos (2πR(λ)/λ). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a phase difference measuring apparatus for obtaining at least a phase difference of an object to be measured online.

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

  There is one in which the parallel Nicol rotation method is applied to on-line measurement, and the phase difference and orientation angle of a transparent film / sheet can be measured on-line using a single wavelength measurement light (see Patent Documents 1 and 2). . Such an apparatus is actually used in an optical film manufacturing process. In the case of optical films, there is a target value for the phase difference that is a measurement value, and it is important to produce a uniform film with as little variation as possible. Therefore, the fluctuation range of the phase difference to be measured is very limited. It is a small range. Therefore, even when performing on-line measurement by the parallel Nicol rotation method, the phase difference and the orientation angle can be measured with sufficient accuracy only by measuring at one wavelength.

FIG. 11 shows C (= cos 2πR / λ) represented by the measurement wavelength λ and the phase difference R in the parallel Nicol rotation method with respect to the phase difference R. The figure shown below is a detected intensity figure of transmitted light when the object to be measured having each phase difference is rotated once while the polarizer and the analyzer are kept in a parallel Nicol state.
Japanese Patent No. 2791506 Japanese Patent No. 2927145 Journal of the Japan Society of Photography, Vol.27, No.6, pp.478-483 (1990)

  In the parallel Nicol rotation method, the value of C is obtained from the transmitted light intensity diagram to calculate the phase difference R. When the phase difference R is close to an integral multiple of λ, the detected light intensity diagram becomes a circle, and the phase difference R is calculated. Both the phase difference and the orientation angle have poor measurement accuracy.

  Further, when measured at one wavelength by the parallel Nicol rotation method, as can be seen from FIG. 11, the change range of the phase difference R that can be followed is limited to within half of the measurement wavelength λ. However, in the case of a general film, the change range of the retardation R may be large. For example, when the phase difference and orientation angle of a transparent film / sheet are installed during the film / sheet manufacturing process and an on-line measurement is attempted, the MD direction (longitudinal direction, pulling direction or winding direction) or TD direction (MD direction and There is a case where the variation in the phase difference in the direction (at right angles) is large and the amount of change is several hundred nm or more. Therefore, the parallel Nicol rotation method with one wavelength cannot follow the change of the phase difference R, and the measurement becomes substantially difficult.

  An object of the present invention is to provide an on-line measuring device capable of measuring even an object to be measured whose phase difference R changes by half or more of the measurement wavelength λ.

  The on-line phase difference measuring apparatus of the present invention irradiates a measurement object containing multi-wavelength components such as white light through a polarizer, and the measurement light transmitted through the measurement object passes through the analyzer through a spectrometer ( A phase difference measuring unit that is incident on a dispersion element and a detector to measure a transmitted light spectrum, and calculates a phase difference of the object to be measured from the transmitted light spectrum measured by the phase difference measuring unit. An arithmetic processing unit is provided. In the phase difference measuring unit, the polarizer, the analyzer, and the spectroscope include first and second sets arranged along the moving direction of the object to be measured, and each set of the polarizer and the analyzer includes parallel Nicols. And the first set of polarizers and analyzers are set to a polarization orientation (transmission axis orientation) of 0 ° with respect to the reference orientation, and the second set of polarizers and analyzers are polarization orientations with respect to the reference orientation. Is set to 45 °. The reference azimuth can be arbitrarily set, and can be set to the MD direction, the TD direction, or another azimuth.

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)
Where θ is the transmission axis orientation of the polarizer / analyzer, I ₀ is the detected light intensity when there is no object to be measured, α is the amplitude transmittance ratio when linearly polarized light is transmitted in the two optical principal axis directions orthogonal to each other , 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), R is the phase difference of the object to be measured, and λ is the measurement wavelength. θ and φ are angles with respect to an appropriately set reference direction.

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, and when considering the entire wavelength in the visible range, the wavelength dependency of α is often negligible.

First, for the sake of simplicity, consider the case where α = 1 in equation (1). The detected light intensities when θ = 0 ° and 45 ° are expressed as I (0) and I (45), and I ₀ (0) and I ₀ are distinguished from I ₀ when θ = 0 ° and 45 °. Assuming that (45), I (0) and I (45) are expressed as follows.
I (0) = {I ₀ (0) / 2} {2+ (C−1) sin ² 2φ} (3)
I (45) = {I ₀ (45) / 2} {2+ (C−1) cos ² 2φ} (4)
The detected light intensities I ₀ (0) and I ₀ (45) when there is no object to be measured are essentially the same, but there may be slight differences in the characteristics of the polarizers and the wavelength characteristics of the spectrometer. Since it is considered, it is treated as something different.

Therefore, after calculating I (0) / I ₀ (0) and I (45) / I ₀ (45), the sum of them is I _{T. T} is expressed as follows.
I _T = (C + 3) / 2 (5)
From equation (5), it is understood that I _T is determined by C, that is, the phase difference R and the measurement wavelength λ, and is not affected by the orientation angle φ of the object to be measured. However, I _{T in} equation (5) is divided by values I ₀ (0) and I ₀ (45) when there is no object to be measured in order to exclude the wavelength characteristics of the polarizer and the spectroscope.

  For example, when a measurement object having a phase difference R of 2000 nm is measured by the parallel Nicol rotation method using a measurement light having a wavelength λ of 590 nm, the detected light intensity diagram when the measurement object is arranged in a state where the orientation angle φ is 0 ° FIG. 1 shows a detected light intensity diagram when the object to be measured is arranged in a state where the orientation angle φ is 20 °. When φ is 0 ° and φ is 20 °, I (0) and I (45) are different, but according to the result of equation (5), I (0) + I (45) depends on φ. It means that it is constant. Also in FIG. 1, it can be seen that I (0) + I (45) is equal when φ is 0 ° and when φ is 20 °.

Since this is true not only for one wavelength but for all wavelengths, the same is true for the spectral spectrum. Further, since the range in which C is possible is -1 to 1, I _T when alpha = 1 becomes a value in the range of 1-2.

Therefore, as shown in FIG. 9, the on-line phase difference measuring apparatus according to the present invention has, as the arithmetic processing unit 10, a plurality of total phase differences I _T (= (C + 3) calculated by varying the phase difference R (λ). ) / 2) a spectral spectrum holding unit 102 that holds the spectral spectrum, and a transmitted light spectral spectrum I ₀ (0), I by two sets of polarizers and analyzers in the state where there is no object to be measured in the phase difference measuring unit. ₀ (45) and the transmitted spectrums I (0) and I (45) of the two sets of polarizers and analyzers in the presence of the object to be measured, the combined spectrum measured value I _T ′ (where I _T ′ = I (0) / I ₀ (0) + I (45) / I ₀ (45)), and the calculated value I _T held in the spectral spectrum holding unit 102 is added up. Difference in measured value I _T ′ calculated by spectrum calculation unit 104 There has been a phase difference calculation unit 106 to the phase difference Rm (lambda) of the phase difference R (lambda) and the measured object seeking I _T corresponding to that I _T which is minimal.

Further, the arithmetic processing unit 10 can express the chromatic dispersion by the following equation using the phase difference as R (λ), and can preliminarily register the coefficients a, b, and c in the equation separately for each material (non-patent). Reference 1).
R (λ) = a + b / (λ ² −c ² ) (6)
The values of the coefficients a, b, and c can be easily obtained by using, for example, a phase difference measuring device KOBRA-WR manufactured by Oji Scientific Instruments.

Here, when the reference wavelength is λ ₀ , the dispersion ratio R (λ) / R (λ ₀ ) at an arbitrary wavelength λ with respect to the reference wavelength λ ₀ can be easily obtained from the equation (6). The reference wavelength can be arbitrarily determined. It is well known that the dispersion ratio R (λ) / R (λ ₀ ) is substantially equal for each material even when the phase difference R (λ) varies depending on the difference in the stretching ratio and thickness of the film. . FIG. 2A shows the wavelength dependence of the retardation R (λ) of five types of PET films, and FIG. 2B shows the wavelength dependence of the dispersion ratio R (λ) / R (λ ₀ ). In practice, the dispersion ratio R (λ) / R (λ ₀ ) substantially overlaps one curve. Therefore, by setting each coefficient of equation (6) 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, while arbitrarily changing the phase difference with respect to the reference wavelength if known wavelength dispersion type retardation of the object, that the spectrum equivalent to I _T of the equation (5) at that time can be freely calculated I mean.

Therefore, in a preferred embodiment of the present invention, as shown in FIG. 9, the arithmetic processing unit 10 calculates the phase difference dispersion ratio R (with respect to the reference wavelength λ ₀ from the wavelength dispersion formula of the phase difference R (λ) for the device under test. The dispersion ratio calculation unit 108 for calculating λ) / R (λ ₀ ) is further provided, and the I _T spectral spectrum held in the spectral spectrum holding unit 102 corresponds to a case where R (λ ₀ ) is changed to a plurality. The phase difference calculation unit 106 calculates the phase difference at the reference wavelength λ ₀ as a phase difference corresponding to I _{T at} which the difference between the calculated value I _T and the measured value I _T ′ is minimized. The phase difference Rm (λ ₀ ) is obtained, and the phase difference Rm (λ) at an arbitrary wavelength λ can be obtained using the dispersion ratio.

Next, a case where the amplitude transmittance ratio α in the two optical principal axis directions is not 1 will be considered. When the value corresponding to the equation (5) when α ≠ 1 is I _T ′, I _T ′ is determined not only by the phase difference R and the measurement wavelength λ, but also by the orientation angle φ of the object to be measured and the amplitude transmittance ratio α. change. For example, assuming a PET film, when the phase difference R at the reference wavelength λ ₀ = 590 nm is 2000 nm, the orientation angle φ = 20 °, and the amplitude transmittance ratio α = 0.95, I (0) / I ₀ (0 ), I (45) / I ₀ (45) and I _T ′ are as shown in FIG. 3, and the maximum value of I _T ′ is not 2. In FIG. 3, I _T is a spectral spectrum when α = 1.

Furthermore, I _T when changing the value of the orientation angle φ and amplitude transmittance ratio α in the condition of the same PET film 'examining the maximum, is shown in Figure 4 when the result in a graph, I _T' of It can be seen that the maximum value is affected by both φ and α. Further, if the phase difference R changes, these relationships also change. Whatever value φ or R when the alpha ≠ 1, in order to determine the accuracy R and φ from the information of the measured I _T ', the maximum value of I _T when alpha = 1 is Considering the fact that it becomes 2, let β1 = 2 / (the maximum value of I _T ′) and consider the spectrum of β1 × I _T ′. When this process is performed for I _T ′ when α = 0.95 in FIG. 3, a curve close to the spectrum of I _T when α = 1 is obtained as shown in FIG. Therefore, after measuring the spectrum of I _T ′ obtained by adding I (0) / I ₀ (0) and I (45) / I ₀ (45) and obtaining the above β1 from the maximum value of I _T ′ , Β1 × I _T ′ is taken as a measured value, and on the other hand, the spectrum of I _T is calculated by the above-described calculation method using the registered chromatic dispersion formula and formula (5), and β1 × I _T ′ and I _The phase difference Rm (λ ₀ ) with respect to the reference wavelength when the difference between the two spectral spectra of _T is minimized is determined.

Therefore, in another preferred embodiment of the present invention, as shown in FIG. 9, the arithmetic processing unit 10 further includes a correction coefficient calculation unit 110 that calculates 2 / (maximum value of I _T ′) as the correction coefficient β1, The phase difference calculation unit 106 can use the corrected measured value spectrum β1 × I _{T ′} corrected by β1 as the measured value I _{T ′} to be compared with the calculated value I _T.

Also in this case, when the phase difference calculating unit 106 obtains the phase difference Rm (λ ₀ ) at the reference wavelength λ ₀ as the phase difference, the phase difference Rm (at any wavelength λ using the dispersion ratio). λ) can be determined.

As yet another preferred mode, the phase difference calculation unit 106 can calculate the residual sum of squares for each wavelength as the difference between the calculated value I _T and the actually measured value I _T ′.

  Next, a method for determining the orientation angle φ of the object to be measured will be described. In order to determine the orientation angle φ, in still another preferred embodiment of the present invention, as shown in FIG. 9, the arithmetic processing unit 10 includes a polarizer and an analyzer whose polarization direction is either 0 ° or 45 °. The optical principal axis of the object to be measured with respect to the same polarization azimuth as in the actual measurement using the transmitted light spectral spectrum measured value I (0) or I (45) in the set of and the phase difference Rm (λ) obtained by the phase difference calculation unit 106 A plurality of transmitted light spectral spectrum calculation values I (0) or I (45) calculated by changing φ are compared, and the optical principal axis φ when the difference is minimized is set as the orientation angle φm of the object to be measured. An orientation angle calculation unit 112 is further provided.

The orientation angle calculation unit 112 uses I (0) / I ₀ (0) or I (45) / I ₀ (45) as I _S ′ instead of the actually measured transmitted light spectrum spectrum value I (0) or I (45). {2+ (C-1) sin ² 2φ} / 2 or {2+ (C-1) cos ² 2φ} / as Is instead of the transmitted light spectral spectrum calculation value I (0) or I (45) 2 may be used.

The maximum value of the spectrum of I (0) / I ₀ (0) and I (45) / I ₀ (45) is 1 when α = 1, but the maximum value when α ≠ 1 is It will not be 1. Therefore, the orientation angle calculation unit 112 may correct the maximum value of I _s ′ to 1 and compare it with the transmitted light spectral spectrum calculation value Is.

Also, since the polarizer / analyzer orientation focuses only on two angles of 0 ° and 45 °, when the orientation angles φ = 22.5 ° and −67.5 °, I (0) = I (45). In order to determine the orientation angle φ, one of the spectral spectra of I (0) / I ₀ (0) and I (45) / I ₀ (45) may be used. It is easier to judge the coincidence with the calculated value by adopting the larger spectrum. Therefore, I when the _{α ≠ 1 (0) / I} 0 (0), I (45) / I 0 (45) , respectively of the maximum value I _0max, and _I 45max, -90 ° the value of phi to 90 The following results were obtained when the magnitude of both was examined in the range of °.
When −90 ° ≦ φ <−67.5 °, I _0max > I _45max
When −67.5 ° ≦ φ <22.5 °, I _0max ≦ I _45max
I _0max ≧ I _45max when 22.5 ° ≦ φ ≦ 90 °

It was also found that the spectrum corresponding to the larger value of I _0max and I _45max has a large change with respect to the wavelength. Therefore, after investigating which of I _0max and I _45max is larger, attention should be paid to the larger spectral spectrum.

As an example, consider the case where attention is paid to I (0) / I ₀ (0). β2 = 1 / I _0max is obtained, and I _S ′ = β2 × I (0) / I ₀ (0) is taken as the spectrum of the measured value. On the other hand, while changing φ in the range of −90 ° ≦ φ <−67.5 ° and 22.5 ° ≦ φ ≦ 90 ° by calculation, Rm (λ) and (3) previously determined The spectral spectrum of I _S = I (0) / I ₀ (0) when α = 1 is calculated using the equation, and the remaining two spectral spectra of the measured value I _S ′ and the calculated value I _S are calculated. The orientation angle φm when the difference sum of squares is minimized is determined.

When paying attention to I (45) / I ₀ (45), β2 = 1 / I _45max, and instead of the equation (3), the equation (4) is used and −67.5 ° ≦ φ <22.5 The orientation angle φm is determined by changing φ in the range of °.

  FIG. 6 is a flowchart summarizing the most preferable method in the procedure for determining the phase difference Rm (λ) described above, and FIG. 7 collectively shows the most preferable method in the procedure for determining the orientation angle φm described above. It is a flowchart.

According to the present invention, transmitted light spectrums I ₀ (0), I ₀ (45) by two sets of polarizers and an analyzer in the absence of an object to be measured, and two sets in the state of an object to be measured. From the transmitted light spectrums I (0) and I (45) by the polarizer and the analyzer, the total spectrum measured value I _T ′ (= I (0) / I ₀ (0) + I (45) / I ₀ (45) ), And a plurality of summed spectra I _T (= (C + 3) / 2) calculated with different phase differences are compared, and I _T that minimizes the difference is obtained and corresponds to the I _T Since the phase difference R (λ) is the phase difference Rm (λ) of the object to be measured, the phase difference Rm (λ) is accurately determined even for an object to be measured whose phase difference R changes by more than half of the measurement wavelength λ. And since it can measure in a short time, an on-line measuring device is realizable.

  Further, a plurality of values calculated by changing the optical principal axis φ of the object to be measured for the same polarization direction as the actual measurement using the actually measured transmitted light spectrum spectrum value I (0) or I (45) and the obtained phase difference Rm (λ). If the optical principal axis φ when the difference is minimized is taken as the orientation angle φm of the object to be measured, the calculated value I (0) or I (45) of the transmitted light spectrum is compared. Can be measured with high accuracy and in a short time, an on-line measuring device that measures both the phase difference Rm (λ) and the orientation angle φm can be realized.

  FIG. 8 is a schematic configuration diagram of the first embodiment of the on-line phase difference measuring apparatus according to the present invention. The phase difference of the object to be measured from the phase difference measuring unit and the transmitted light spectrum measured by the phase difference measuring unit. And an arithmetic processing unit 10 for calculating the orientation angle. A portion excluding the arithmetic processing unit 10 and the DUT 6 constitutes a phase difference measuring unit.

  In the phase difference measuring unit, the light source 1 is, for example, a light source that guides light from a halogen lamp with a light guide, and supplies white light as measurement light including multi-wavelength components. The light source 1 may be a light source using a white LED (light emitting diode).

  In order to irradiate the measuring object 6 that is moving with linearly polarized measuring light, two polarizers 4 a and 4 b are arranged along the moving direction of the measuring object 6 so as to face one surface of the measuring object 6. . Two analyzers 5a and 5b are arranged on the other surface side of the device under test 6 so as to face the polarizers 4a and 4b with the device under test 6 interposed therebetween. The polarizer 4a and the analyzer 5a are arranged in a parallel Nicols state, and the polarizer 4b and the analyzer 5b are also arranged in a parallel Nicols state. When the reference azimuth is the MD direction (the moving direction of the DUT 6), the first set of polarizers 4a and the analyzer 5a have the polarization azimuth set to 0 ° with respect to the reference azimuth, and the second set of polarizers 4b. The analyzer 5b has a polarization azimuth of 45 ° with respect to the reference azimuth.

  The measurement light from the light source 1 is guided by the light guide 2 and irradiated to the polarizers 4a and 4b through the condenser lenses 3a and 3b. Measurement light transmitted from the polarizers 4a and 4b through the DUT 6 and the analyzers 5a and 5b is collected by the respective condensing lenses 7a and 7b, and passes through the light guides 8a and 8b to the spectroscopes 9a and 9b. Led. Each of the spectroscopes 9a and 9b includes a dispersion element such as a grating and a detector such as a CCD camera.

  The transmitted light intensities separated and detected by the spectroscopes 9a and 9b are taken into the arithmetic processing unit 10 to calculate the phase difference Rm (λ) and the orientation angle φm of the object to be measured 6 as described above. Is done. The arithmetic processing unit 10 is realized by a dedicated computer or a general-purpose personal computer.

  FIG. 10 is a schematic configuration diagram of a second embodiment of the on-line phase difference measuring apparatus of the present invention. Two polarizers 24 a and 24 b are arranged along the moving direction of the DUT 6 so as to face one surface of the DUT 6. The polarizers 24a and 24b are arranged so as to extend in the entire width direction of the object 6 to be measured, and the respective light sources 21a and 21b are also measured in order to irradiate the respective polarizers 24a and 24b with white measurement light. The object 6 is arranged extending in the entire width direction. Two analyzers 5a and 5b are arranged on the other surface side of the device under test 6 so as to face the polarizers 4a and 4b with the device under test 6 interposed therebetween. The configuration of the optical system on the light receiving side that collects the measurement light transmitted through the analyzers 5a and 5b by the respective condensing lenses 7a and 7b and guides them to the spectroscopes 9a and 9b through the light guides 8a and 8b is shown in FIG. However, in the embodiment of FIG. 10, the optical system on the light receiving side is supported so as to be movable in the width direction of the DUT 6.

  The polarizer 24a and the analyzer 5a are arranged in a parallel Nicol state, the polarizer 24b and the analyzer 5b are also arranged in a parallel Nicol state, and the polarizer 24a and the analyzer 5a are polarized with respect to the reference direction with the reference direction as the MD direction. The azimuth is set to 0 °, and the polarization azimuth of the polarizer 24b and the analyzer 5b is set to 45 ° with respect to the reference azimuth.

  The respective transmitted lights dispersed by the spectroscopes 9a and 9b are taken into the arithmetic processing unit 10, and the phase difference Rm (λ) and the orientation angle φm of the DUT 6 are calculated as described above.

  According to the embodiment of FIG. 10, the change in the width direction of the DUT 6 can be measured by scanning the optical system on the light receiving side.

It is a figure which shows the detected light intensity when the to-be-measured object which has a certain phase difference in a parallel Nicol rotation method is measured with a certain measurement wavelength. (A) is a figure which shows the wavelength dependence of retardation when a PET film is measured, (B) is a figure which similarly shows the wavelength dependence of a dispersion ratio. It is a figure which shows the example of the spectrum of the detection light handled by this invention. It is a figure which shows the relationship between the amplitude transmittance | permeability ratio (alpha) of a to-be-measured object, and the maximum value of the spectral spectrum _IT 'of detection light. Shows a comparison of the spectrum I _T when the as obtained by correcting the spectrum I _T of the detection light 'alpha = 1. It is a flowchart which shows the most preferable method in the determination procedure of phase difference Rm ((lambda)) in this invention. It is a flowchart which shows the most preferable method in the determination procedure of orientation angle | corner (phi) m in this invention. It is a schematic block diagram which shows a 1st Example. It is a block diagram which shows the arithmetic processing part in the Example. It is a schematic block diagram which shows 2nd Example. It is a figure which shows the relationship between C and phase difference R in a parallel Nicol rotation method, and the relationship of a detected light intensity figure.

Explanation of symbols

1, 21a, 21b Light source 4a, 4b, 24a, 24b Polarizer 5a, 5b Analyzer 9a, 9b Spectrometer 10 Arithmetic processing unit 102 Spectral spectrum holding unit 104 Total spectrum calculating unit 106 Phase difference calculating unit 108 Dispersion ratio calculating unit 110 Correction coefficient calculation unit 112 Orientation angle calculation unit

Claims (7)

A phase difference measurement unit that measures the transmitted light spectrum by measuring light containing multi-wavelength components irradiating the moving object to be measured through the polarizer, and passing the object to be measured through the analyzer and entering the spectrometer. The polarizer, analyzer, and spectrometer include first and second sets arranged along the moving direction of the object to be measured, and each set of polarizer and analyzer is in a parallel Nicols state. And the first set of polarizers and analyzers is set to 0 ° polarization orientation relative to the reference orientation, and the second set of polarizers and analyzers is set to 45 ° polarization orientation relative to the reference orientation. A phase difference measuring unit,
An arithmetic processing unit that calculates at least the phase difference of the object to be measured from the transmitted light spectrum measured by the phase difference measuring unit,
The arithmetic processing unit is a spectroscope that holds a plurality of combined spectra I _T (= (C + 3) / 2) (where C = cos (2πR (λ) / λ)) calculated with different phase differences. A spectrum holding unit;
Two sets of polarizers and analyzers in a state where there is no object to be measured in the phase difference measuring unit, and two sets of light spectrums I ₀ (0) and I ₀ (45) in a state where there is an object to be measured. The combined spectrum measured value I _T ′ (where I _T ′ = I (0) / I ₀ (0) + I (45) / I ₀ (45).)
Phase difference R (lambda corresponding to the I _T seeking I _T the difference of the spectrum holding Found calculated by the calculated value I _T held the summed spectrum calculation section to section I _T 'is minimized ) Is an on-line phase difference measuring device provided with a phase difference calculating unit that sets the phase difference Rm (λ) of the measured object. 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 I _T spectral spectrum held in the spectral spectrum holding unit is calculated from the corresponding R (λ) when R (λ ₀ ) is changed to a plurality of values,
The phase difference calculation unit obtains a phase difference Rm (λ ₀ ) at the reference wavelength λ ₀ as a phase difference corresponding to I _{T at} which the difference between the calculated value I _T and the measured value I _T ′ is minimized, and uses the dispersion ratio. The on-line phase difference measuring apparatus according to claim 1, wherein the phase difference Rm (λ) at an arbitrary wavelength is obtained. The arithmetic processing unit further includes a correction coefficient calculation unit that calculates 2 / (maximum value of I _T ′) as the correction coefficient β1;
The phase difference calculator online phase difference measuring apparatus according to claim 1 or 2 using the calculated value I _T measured value is compared with I _T 'as .beta.1 in corrected corrected measured value spectrum .beta.1 × I _T'. The on-line phase difference measurement according to any one of claims 1 to 3, wherein the phase difference calculation unit calculates a residual sum of squares for each wavelength as a difference between a calculated value _IT and an actual measurement value _IT '. apparatus.   The arithmetic processing unit transmits the transmitted light spectrum spectrum measured value I (0) or I (45) in a pair of a polarizer and an analyzer whose polarization direction is 0 ° or 45 °, and the obtained phase difference Rm ( λ) is used to compare a plurality of transmitted light spectral spectrum calculation values I (0) or I (45) calculated by changing the optical principal axis φ of the object to be measured with respect to the same polarization azimuth as in the actual measurement, and the difference is minimized. The on-line phase difference measurement apparatus according to claim 1, further comprising an orientation angle calculation unit that sets an optical principal axis φ at the time of becoming an orientation angle φm of an object to be measured. The orientation angle calculation unit substitutes I (0) / I ₀ (0) or I (45) / I ₀ (45) as I _S ′ instead of the measured values I (0) or I (45) of the transmitted light spectrum. use,
{2+ (C-1) sin ² 2φ} / 2 or {2+ (C-1) cos ² 2φ} / 2 is used as Is instead of the transmitted light spectral spectrum calculation value I (0) or I (45). The on-line phase difference measuring apparatus according to claim 5, wherein The on-line phase difference measuring apparatus according to claim 6, wherein the orientation angle calculation unit corrects the maximum value of I _S ′ to be 1, and compares the corrected value with a transmitted light spectral spectrum calculation value I _S.

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