JP2001337035A - Measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CD measuring instrument capable of certainly measuring CD even with respect to a sample large in LD and LB such as a solid or the like. SOLUTION: A spectroscope 2, a polarizer 3, a polarization modulator 4, a sample holder 5 for holding a sample in a rotatable manner, an analyzer 6 and a detector 7 are arranged on the light path of the light emitted from a light source 1, and the output of the detector 7 is given to a signal processor 8. Output signals with a frequency of 50 kHz the same as the modulation frequency of the polarization modulator and a frequency of 100 kHz twice the modulation frequency of the polarization modulator are outputted from the detector, and the signal processor processes the output signals of the detector on the basis of the frequency component corresponding to the modulation frequency of the polarization modulator and the frequency component twice the modulation frequency. A measured value at a position showing the maximum value when the sample is rotated and a measured value at a position showing the minimum value when the sample is rotated are obtained on the basis of LB being the modulation frequency component and CB being the frequency component twice the modulation frequency, and these values are added to be divided by 2 to calculate a real CB value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device, and more particularly, to a measuring device capable of measuring CB (Circular Birefringence) of a sample having a large LB and LD such as a solid.

[0002]

BACKGROUND OF THE INVENTION As is well known, circularly polarized birefringence (CB) refers to a phenomenon in which a right-handed circularly polarized light and a left-handed circularly polarized light have different refractive indices. It is important to measure the CB spectrum of a liquid crystal, a film, or another chiral substance in a non-solution state when examining the optical characteristics and other information of the substance.

Usually, a polarization modulation spectrometer is used to measure the CB spectrum. Therefore, there are systematic errors and spurious signals due to non-ideal optical elements, light modulation elements, polarization characteristics of photodetectors, harmonic response of lock-in amplifiers, and the like.

Further, depending on the measurement sample, LB (Linear
In some cases, the magnitudes of the Birefringence (LD) signal and the LD (Linear Dichroism) signal are about 10 ³ to 10 ⁵ larger than the true CB. Then, the output signal based on the LD or LB becomes an error factor when measuring CB. Therefore,
Conventionally, it has been difficult to accurately measure the true CB spectrum, and it has not been possible to directly measure the true CB.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has as its object to solve the above-mentioned problems and to reliably measure CB even in a sample such as a solid having a large LD and LB. It is an object of the present invention to provide a measuring device capable of performing the measurement.

[0006]

In order to achieve the above-mentioned object, a measuring apparatus according to the present invention comprises a polarizer for linearly polarizing monochromatic light and a polarization state of light transmitted through the polarizer having a predetermined basic condition. A polarization modulator that alternately changes right-handed circularly polarized light and left-handed circularly polarized light to a vertical linear polarization and a horizontal linear polarization simultaneously at twice the fundamental modulation frequency at the modulation frequency, and its polarization. A sample holder arranged in the optical path of the light obtained from the modulator, a detector for detecting the intensity of light passing through an analyzer through which light passing through the sample holder passes, and an output of the detector. It is assumed that the polarization modulation measurement device includes a signal processing unit that performs signal processing based on the signal.

The optical axis of the analyzer is arranged so as to have a difference of 45 degrees from the optical axis of the polarizer. Further, the signal processing unit performs signal processing based on a frequency component corresponding to a modulation frequency in the polarization modulator and a frequency component twice as high as the modulation frequency in the output signal of the detector. LB and the frequency component twice as high as the modulation frequency represent CB, and the measured value at the position showing the maximum value by rotating the sample and the value at the position showing the minimum value by rotating the sample are obtained. , And adding them, and dividing by 2 to calculate a true CB value.

Another solution is to analyze white light linearly polarized by a polarizer, a sample holder disposed in the optical path of the white light, and a polarization state of light passing through the sample. A polarization analyzer including a polarization modulator and an analyzer, a monochromator that converts light obtained from the polarization analyzer into monochromatic light, a detector that detects the intensity of light output from the monochromator, It is assumed that the polarization modulation measurement device includes a signal processing unit that performs signal processing based on the output of the detector.

The polarization modulator converts left and right circularly polarized light into vertical and horizontal linearly polarized light at a frequency corresponding to the basic modulation frequency, and converts vertical and horizontal linearly polarized light into vertical and horizontal linearly polarized light at a frequency twice the basic modulation frequency. -Use polarization modulators that respectively modulate horizontal linearly polarized light.

Further, the optical axis of the analyzer is arranged so as to have a difference of 45 degrees from the optical axis of the polarizer. Further, the signal processing unit performs signal processing based on a frequency component corresponding to a modulation frequency in the polarization modulator and a frequency component twice as high as the modulation frequency in the output signal of the detector. LB and the frequency component twice as high as the modulation frequency represent CB, and the measured value at the position showing the maximum value by rotating the sample and the value at the position showing the minimum value by rotating the sample are obtained. , May be configured to calculate the true CB value by adding them and dividing by 2.

In the present invention, the sample is arranged rotatably.
This rotation is preferably performed automatically or manually performed by providing a rotation mechanism at least in the sample holding unit. However, in the present invention, it is not essential to provide a rotation mechanism in the sample holding unit in this way, and after removing the sample from the sample holding unit and mounting it again at a different rotation angle when mounting it again, the sample is eventually This is because it can be rotated.

CB (apparently: also includes a component based on macroscopic anisotropy depending on rotation) is obtained from a modulation frequency detected when the sample is rotated and a frequency component twice as high. Then, the positive and negative maximum values CBmax of the CB are obtained. Then, when the two values are added and divided by 2, the component based on the macroscopic anisotropy depending on the rotation is removed, so that the true CB is obtained. The principle of obtaining a true CB by such processing is as described in the embodiment. The above arithmetic processing is performed by the signal processing device 8.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a solid-state optical dispersion (ORD) which is a measuring device for measuring true CB according to the present invention.
1 shows a preferred embodiment of a tatory dispersion) measuring device. As shown in the figure, a spectroscope (monochromator) 2, a polarizer 3,
A polarization modulator 4, a sample holding device 5, an analyzer 6, and a detector 7 are arranged, and the output of the detector 7 is provided to a signal processing device 8.

As a result, the light emitted from the light source 1 is converted into monochromatic light by the spectroscope 2, and the monochromatic light is transmitted through the polarizer 3 to become linearly polarized light. , The polarization direction is alternately changed, and circularly polarized light and linearly polarized light are simultaneously formed. When the light emitted from the polarization modulator 4 is applied to the sample attached to the sample holding device 5, birefringence is generated when the light is transmitted through the sample, and the light is output by the analyzer 6. The light is received by the detector 7 instead of the intensity. The detector 7 is, for example, a light-
Since it is an electric conversion element and outputs an electric signal corresponding to the received light intensity, the signal processing device 8 performs predetermined signal processing based on the output signal (electric signal) to calculate CB. I have.

As the spectroscope 2, a prism spectroscope having little adverse effect on polarized light is desirable, but a spectroscope using a diffraction grating may be used. It is generally preferable to use a Glan-Thompson prism as the polarizer 3 and the analyzer 6. In order to ensure completeness as the polarizer 3, a polarizer having a Brewster angle with a quartz plate may be used in combination.
Alternatively, a crystal prism may be used, and the spectroscope and the polarizer may be used.

Since the Glan-Taylor prism uses calcite, the wavelength of 235 nm or less cannot be measured. However, when measuring CD such as a liquid crystal, a film, and other solids as in the present invention, attention should be paid to the visible region. It is applicable enough.

As the polarization modulator 4, for example, PEM can be used. The modulation frequency for the PEM is 50 kHz
And In the case of high-quality PEM, the residual strain α is as small as about 0.1 degrees to about 0.01 degrees.
By using M, the apparent CB caused by LD and LB is made as small as possible. Therefore, a Pockels cell having a large residual distortion of 10 degrees is not preferable. Of course, there is no intention to actively remove such Pockels cells from the scope of the present invention, and it is acceptable to use them according to specifications and requirements. Note that the reference position of the polarization modulator 4 is set to a position where the baseline of the apparatus is straight without a sample placed.

The sample holding device 5 can rotate the sample S around the optical path in a plane orthogonal to the optical path of the irradiated light. As an example, a holder for holding the sample S is rotatably mounted on a mounting table, and the holder is rotated at an arbitrary angle by a rotation output of a motor capable of controlling a rotation angle of a stepping motor or the like, and is stopped. Is to configure. In this case, the rotation angle is preferably controlled based on a control signal from the signal processing circuit 8. In addition, for simplicity, it may be possible to rotate manually.

The analyzer 6 is also rotatable so that the angle of the optical axis (in particular, the angle with the optical axis of the polarizer 3 and the like) can be changed and adjusted. Further, in order to accurately set the reference position (angle) of the analyzer 6, the angle of the analyzer 6 is determined so that the baseline when no sample is placed in the sample holding device 5 becomes zero. Can be achieved.

Since the detector 7 has a very small CD signal,
For example, it is preferable to use a highly sensitive detector such as a photomultiplier tube (PMT). Then, the detector 7 outputs a 50 kHz component that is the same as the modulation frequency and 10
A 0 kHz component is output. And
The CB is obtained based on the 100 kHz component of the second harmonic.

Further, the output signal from the detector 7 is CB
Is a very small signal, so the synchronous detection method is actually used. That is, the output of the detector 7 is actually connected to a lock-in amplifier for extracting a frequency component, and a signal component of a predetermined frequency output from the lock-in amplifier is supplied to the signal processing device 8. Note that a lock-in amplifier may be included in the category of the signal processing device 8.

The signal processing device 8 has a function of performing arithmetic processing based on an output signal from the detector 7 according to a procedure described later, and a control signal (a sample holding device 5) for various devices.
, Etc.).

Next, the function of the signal processing device 8 will be described while explaining the procedure and principle of measurement. The signal obtained by the present measurement apparatus is theoretically analyzed using a Mueller matrix as follows. That is, the monochromatic incident light Iin,
Polarizer P, polarization modulator M, sample S, detector A, detector D
Is given as follows.

[0024]

(Equation 1)

[0025]

(Equation 2)

Here, θ is the rotation angle of the sample from the x-axis. When there is no chromophore in the measurement wavelength region, that is, when there is no CD, LD, LD ', the following is performed.

[0027]

(Equation 3)

[0028]

(Equation 4)

[0029]

(Equation 5)

The intensity Id of the light received by the detector 7 is given by the following equation by performing the above matrix calculations.

[0031]

(Equation 6)

If the sample has no chromophore, CD =
Since LD = LD ′ = 0, the above equation (8) becomes as follows.

[0033]

(Equation 7)

Δ = δ ₀ sin ωt δ ₀ : modulation amplitude ω: modulation frequency, and sin (δ +
α), cos (δ + α) can be approximately developed as in the following equation by Fourier transform.

[0035]

(Equation 8)

Here, J ₀ (δ ⁰ m) and J ₁ (δ ⁰ m
) And J ₂ (δ ⁰ m) are the zero-order, first-order, and second-order Bessel functions, respectively. Thus, the ωm and 2ωm components are as follows.

[0037]

(Equation 9)

[0038]

(Equation 10)

Accordingly, when a PEM having a small α is used for the optical modulator, sin α can be approximated to 0, and the above equations (10) and (11) are as follows.

[0040]

[Equation 11]

[0041]

(Equation 12)

Further, assuming that CD = LD = LD '= 0, the following equation can be obtained by substituting into the above equations (10)' and (11) '.

[0043]

(Equation 13)

[0044]

[Equation 14]

As is apparent from the above equation (12),
The detected ω _m signal is LB. The 2ω signal is an apparent CB. And, generally, CB is L
Since it is smaller on the order of 10 ^-2 to 10 ^-3 than B and LB ', it is difficult to detect CB by the presence of large LB and LB'. Therefore, the following equation is further obtained from equation (13).

[0046]

(Equation 15)

This ApCB changes with the rotation of the sample and rotates at 4θ. And the positive maximum value (+) ApCBmax of ApCB is:

[0048]

(Equation 16)

The positive maximum value (+) ApCBma
When the sample is rotated by 45 degrees from the angle x, the negative maximum value (-) ApCBmax expressed by the following equation is obtained.

[0050]

[Equation 17]

The midpoint between the above-mentioned positive maximum value and negative maximum value, that is, when both values are added and divided by 2, the following equation is obtained. The value is the true CB.

[0052]

(Equation 18)

Therefore, in the present embodiment, 2 of the detected signals
The true CB can be measured by monitoring the double frequency component (2ω signal), finding the maximum and minimum values, and taking the average (dividing by 2). More specifically, the 2ω signal is monitored while rotating the sample, and a position where the maximum value of AppCBmax is obtained is searched for.

In this process, for example, AppCBmax obtained by the signal processing device 8 is output to a monitor connected to the signal processing device 8, and the user monitors the monitor while manually rotating the sample. When a positive peak is reached, rotation can be stopped. Also, instead of performing such manual operation, the signal processing device 8 sends a rotation command to the drive motor of the sample holding device while measuring AppCB, and sends the rotation command to the drive motor when ApCB reaches the maximum value. By sending a stop command, the position of the maximum positive value can be automatically obtained. Then, the CB spectrum is measured at the stopped angular position.

Next, a point at which the maximum value of AppCB becomes a negative value,
That is, the sample is rotated 45 degrees from the stop position,
The CB spectrum is measured in that state. Then, a new spectrum is generated by adding the obtained two spectra and dividing by two. This spectrum becomes the true CB spectrum of the sample. On the other hand, the following equation is obtained from the above equation (12).

[0056]

[Equation 19]

From this, by measuring the ω signal (50 kHz), the linear birefringence of the sample can be obtained. That is, the ω signal is rotated by 2θ, the sample is rotated to the position where the ω signal is maximized, and the spectrum is measured at this position, whereby the wavelength dependence of LBmax and the LB dispersion curve are obtained.

Therefore, according to the present apparatus, LB and ApCBmax can be measured by measuring the ω signal and 2ω signal, and the true CB can be obtained from ApCBmax based on the rotation of the sample and the predetermined arithmetic processing described above. it can.

In the above description, no chromophore (C
D = LD = LD ′ = 0), but the case of having a chromophore will now be described. CD, LD,
When having LD ', the ω signal (Signal ω)
Is as follows.

[0060]

(Equation 20)

The sample having the LD also has the LB. And
Generally, CD is 10 ⁻² to 10 compared to LD and LB.
^-3 small. Furthermore, LD is one order of magnitude smaller than LB. Therefore, in a normal fixed sample, CD + 1/2 (LD′LB
-LDLB ') is negligible compared to LB, LB'. Therefore, the above equation can be approximated as the following equation.

[0062]

(Equation 21)

Therefore, LB is obtained from the ω signal.
However, when LB is reduced, LD is inevitably also reduced. Therefore, 1/2 (LD′LB−LDLB ′) can be ignored, and
CD contributes to the ω signal. Which of LB and CD contributes more can be specified as follows. That is,
First, equation (11-1) is as follows.

[0064]

(Equation 22)

At a certain wavelength, the sample is rotated, and the APPCB accompanying the rotation is measured. At this time, when the value of ApCB changes at 2θ, the contribution of LD to ApCB is larger than that of LB, and when it changes at 4θ, the contribution of LB increases. Also, since LD is usually one digit smaller than LB,
The above equation (11-2) can be approximated as follows.

[0066]

(Equation 23)

If the measured value of AppCB accompanying the rotation of the sample shows a change that can be approximated by cos4θ, A
Since the contribution of LD to ppCB is small, the above equation (11)
-3) is the ApC in the wavelength region where no chromophore exists.
B is equal to the equation (13-1). Therefore, a true CB spectrum is obtained by a method of adding the positive maximum value and the negative maximum value described above and dividing by two.

On the other hand, when the value of App CB changes with the rotation of the sample and can be approximated by cos 2θ, LB
It means that LD is larger than
2) is as follows.

[0069]

(Equation 24)

Also in this case, as shown in the following equation,
While rotating the sample, measure the ApCB and measure the ApCB spectrum at the position where the maximum positive value (+) ApCBmax is obtained, and then rotate the sample to obtain the negative maximum value (−) ApCB.
An AppCB spectrum at a position where Bmax is obtained is measured.
Then, by adding the two spectra and dividing by 2, a true CB spectrum is obtained.

[0071]

(Equation 25)

As described above, in each case, App
The spectrum of the positive maximum value and the negative maximum value of CB is obtained, and they are added together and then divided by 2 to obtain the true CB spectrum.

FIGS. 3 and 4 show a second embodiment of the present invention. In the present embodiment, the arrangement order of the optical elements is different from that of the first embodiment. That is, the light emitted from the light source 1 is given to the polarizer 3 and linearly polarized light is directly irradiated on the sample S of the sample holding device 5. And
A polarization modulator (PEM) is provided after the sample holding device 5.
4, an analyzer 6, a spectrometer 2, a detector 7, and a signal processing device 8 are arranged in this order. The intensity Id of the light received by the detector 7 in such a configuration is given by the Mueller matrix operation as follows.

[0074]

(Equation 26)

Here, P _x ² , P _y ² , 2a are the azimuths of the spectroscope from the x-axis, y-axis and x-axis. And CD
When L = LD ′ = 0, the following equation is obtained.

[0076]

[Equation 27]

Therefore, the signal detected by the detector is
ω and Signal2ω are the same as the expressions (10) and (11) described in the first embodiment, respectively. Therefore,
As in the first embodiment, based on the 2ω signal,
Positive maximum value (+) ApCBmax and negative maximum value (-) Ap
A true CB spectrum can be obtained by calculating the CB spectrum of pCBmax, adding them, and dividing by two. According to the present embodiment, the spectroscope 2 has a large polarization characteristic, but a bright grating monochromator can be used.

FIGS. 5 to 7 show the experimental results actually measured using the apparatus of the first embodiment. As shown in FIG. 5, ApCB is measured while rotating the sample for each wavelength, and its positive maximum value and negative maximum value are obtained.
As a result, as shown in FIG. 6, spectra of a positive maximum value CBmax and a negative maximum value CBmin are obtained. Then, by adding these two spectra and dividing by 2, a true CB spectrum is obtained as shown in FIG.

[0079]

As described above, according to the present invention, the true CB can be measured by simple arithmetic processing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a CB measuring device according to the present invention.

FIG. 2 is a diagram showing the optical arrangement.

FIG. 3 is a diagram showing a second embodiment of the CB measuring device according to the present invention.

FIG. 4 is a diagram showing the optical arrangement.

FIG. 5 is a view showing an experimental result.

FIG. 6 is a diagram showing experimental results.

FIG. 7 is a view showing an experimental result.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source 2 spectrometer 3 polarizer 4 polarization modulator 5 sample holding device 6 analyzer 7 detector 8 signal processing device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G020 AA04 AA05 CA13 CA15 CB04 CB43 CC02 CC13 CC29 CD03 CD15 CD22 CD33 CD36 2G059 AA02 BB10 BB15 DD13 EE01 EE05 EE12 GG06 HH02 HH03 JJ05 JJ06 JJ18 JJ19 KK01 MM01

Claims (2)

[Claims] 1. A polarizer for linearly polarizing monochromatic light, and a polarization state of light transmitted through the polarizer is converted into clockwise circular polarization and counterclockwise circular polarization at a predetermined basic modulation frequency at the same time. A polarization modulator that alternately changes to vertical linear polarization and horizontal linear polarization at twice the frequency, a sample holder disposed in the optical path of light obtained from the polarization modulator, and the sample holder A detector for detecting the intensity of light passing through an analyzer through which light has passed, and a signal processing unit for performing signal processing based on the output of the detector; The arrangement is such that the optical axis of the photon has a difference of 45 degrees with respect to the optical axis of the polarizer, and the signal processing unit includes a frequency component corresponding to a modulation frequency in the polarization modulator among output signals of the detector. Double frequency component of the modulation frequency The signal processing is performed based on LB, which is the modulation frequency component, and the frequency component twice as high as the modulation frequency represents CB. The measured value at the position where the sample shows the maximum value by rotating the sample, and the sample is rotated A measurement device that calculates the true CB value by obtaining values at the position showing the minimum value, adding them, and dividing by two. 2. A white light linearly polarized by a polarizer, a sample holder disposed in an optical path of the white light, a polarization modulator and an analyzer for analyzing a polarization state of light passing through the sample. And a monochromator that converts the light obtained from the ellipsometer into monochromatic light, a detector that detects the intensity of light output from the monochromator, and the output of the detector. A polarization modulation measurement device provided with a signal processing unit that performs signal processing, wherein the polarization modulator converts left and right circularly polarized lights into vertical and horizontal linearly polarized lights at a frequency corresponding to a basic modulation frequency, and vertical and horizontal linearly polarized lights. At a frequency twice the fundamental modulation frequency.
A polarization modulator that modulates the light into horizontal linearly polarized light, wherein the optical axis of the analyzer is arranged with a difference of 45 degrees with respect to the optical axis of the polarizer, and the signal processing unit is configured to output signals of the detector. The signal processing is performed based on the frequency component corresponding to the modulation frequency in the polarization modulator and the frequency component twice as high as the modulation frequency. The LB as the modulation frequency component and the frequency component twice as high as the modulation frequency are Represents CB, the measured value at the position showing the maximum value by rotating the sample and the value at the position showing the minimum value by rotating the sample, adding them and dividing by 2 gives the true CB value A measuring device that calculates