JPH02159540A - Double refraction measurement - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement in an entire measuring range regardless of a size of a double refraction phase difference of a sample by using a plurality of measuring lights to determine a series of computed values containing a true value for measured values using a specified formula. CONSTITUTION:A plurality of measuring lights with different wavelengths is incident into a polarizer 3 through a semipermeable mirror 21 from light sources 1a and 1b and further into a photoelastic modulator 4 so that a measuring light modulated in phase irradiates a sample 16. Then, light refracted doubly and transmitted inside the sample 6 is inputted into an analyzer 8 through an analyzer 5 and a photo-multiplier tube 7 to calculate a double refraction phase difference of the sample 6. In this manner, the measuring light is refracted doubly to the same extent with respect to the same sample regardless of a difference in wavelength and when a computed value R is determined from a natural number m, a wavelength lambda and an apparent measured value (r) applying a formula of R=mlambda/2+ or -r for each measurement, a data corresponding to a true phase difference close to each other among each series of computed values. The series of computed values are compared in size between computed values to extract computed values the closest to each other thereby enabling determination of a true phase difference.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for measuring birefringence of a sample to be measured, and in particular a method that can be used over a wide measurement area without being subject to restrictions on the refractive index or thickness of the sample. The present invention relates to a birefringence measurement method that can measure birefringence phase difference with high precision.

[Prior Art] One of the methods for measuring the birefringence of an optically anisotropic object is a measurement method called a phase modulation method [Details can be found in Japanese Patent Application Laid-Open No. 63-82345 proposed by the same inventor as the present invention. issue(
(See Japanese Patent Application No. 61-228814)].

This measurement method will be explained with reference to FIG. 2. In the figure, l
are measurement light 1 (for example, He-Ne laser light), 2 is a filter (monochromator), 3 is a polarizer (for example, a quarter-wave plate) that converts the light passing through the filter 2 into linearly polarized light, and 4 is a photoelastic modulator (Photo-elastic modulator) that continuously and periodically changes the linearly polarized light incident from the polarizer 3 into circularly polarized light, and further changes the circularly polarized light into linearly polarized light to create phase-modulated measurement light. -elastic modulator
), 5 is an analyzer that receives birefringent light inside the sample to be measured 6 (hereinafter abbreviated as sample) and converts it into linearly polarized light;
7 is a photodetector (photomultiplier tube) that converts the light incident from the analyzer 5 into an alternating current signal photocurrent; 8 demodulates and analyzes the photocurrent signal sent from the photodetector 7; An analyzer 9 calculates the birefringence phase difference Δnd (hereinafter abbreviated as phase difference) defined by equations (1) and 2 (2) as a measured value, and 9 is an analysis device that calculates the measured phase difference Δnd, for example, at the azimuth angle θ of the sample 6. This is a display device that displays polar coordinates as a function of (rotation angle around the axis IO of the device).

Δnd= 1n, -n, 1・d (nm)
Formula (1) Δnd−δ・λ/ 2 x (nm)
Equation (2) where n is the refractive index for extraordinary rays, no is the refractive index for normal rays, d is the thickness of the sample, and δ
is the difference between the phase angles of n and no, and λ is the wavelength of the measurement light. According to this measurement method, conventional measurement methods (analyzer rotation method 1 phase compensation method, etc.) Polarization state (
In contrast to measuring the change in ellipticity (change in ellipticity) as a change in light intensity,
Since the absolute value of the phase difference between the phase-modulated normal ray and the extraordinary ray is directly measured, it is not disturbed by noise and can be measured at 0.
It is now possible to measure minute phase differences down to 0.01 nm (the minimum measurable birefringence phase difference Δnd by conventional measurement methods is approximately 2r+m), and the sample 6 can be measured at various angles B with respect to the axis 10. By performing this, there is an advantage that the orientation state of molecules in the thickness direction inside the sample 6 can be measured.

[Problem to be solved by the invention]

However, in this measurement method, the phase difference of the sample 6 is 1/4 of the wavelength of the measurement light (λ-632.8 nm ti
When using e-Ne laser light, approximately 150 nm)
If the measurement value exceeds the conventional measurement method (analyzer rotation method 1
There was a problem that the measured value did not match the measured value obtained by the phase compensation method, etc.).

The problem is that when two waves with different phase velocities travel in the same direction, the wave crest of the wave with the faster phase velocity overtakes the crest of the slower wave one after another, so the absolute value of the phase difference is constant. This is due to the general phenomenon that it increases and decreases in cycles.
For example, when the measurement light passes through the sample 6 having a phase difference of λ/2+rnm as shown in FIG. When reaching 4nm, the maximum value λ/4nr
s, and as the measurement light advances further, it gradually decreases, and when the measurement light reaches λ/2 nm, the phase difference of the measurement light becomes zero, and in section 14 it increases again, and the phase difference of the measurement light decreases. , becomes rnm, the sample 6 is emitted, and this phase difference rnm is detected as a measurement value. Therefore, the measured value appears to be an upper value and does not represent the phase difference that the sample 6 has, that is, the true phase difference. In addition, as shown in FIG. 4, sample 6 has a true phase difference of λ/2-rnm.
Similarly, the measured value is measured assuming that the apparent value is above rm.

If we generalize the above situation so that it can be applied to samples with even larger true phase differences, we can find the relationship between the true phase difference and the measured value as shown in equation (3) or Figure 5. I understand that.

R=mλ/2±r Equation (3) where R is the calculated value, 2m is zero and a natural number, λ is the wavelength, and r is the measured value.

Therefore, in order to find the true phase difference from the measured value r, it is necessary to extract the calculated value corresponding to the true phase difference from the series of calculated values R shown in 2(3).

In view of the above problems, the present invention extracts the true phase difference from the calculated values shown in 2(3) to enable all measurements exceeding one-fourth of the wavelength of the measurement light, and as a result, It is a technical problem to provide a birefringence measurement method that can measure birefringence retardation with high precision over the entire measurement region including measurement of minute retardation.

[Means for Solving the Problems] The configuration of the present invention for achieving the above-mentioned problems includes irradiating a measurement sample with phase-modulated measurement light and detecting the polarization state of the light transmitted through the sample. In the birefringence measurement method of measuring the birefringence phase difference of the sample, a plurality of lights with different wavelengths are individually irradiated onto the sample to be measured to measure the birefringence phase difference, and each calculation formula mλ is used for each measurement. /2±r (where λ is the wavelength of the light for measurement, r is the measured value 2m is zero and a natural number) to obtain a series of calculated values corresponding to different values of m, and the results are obtained for all measurements. The series of calculated values are compared in magnitude, and the closest calculated value is adopted as the true value of the birefringence phase difference.

[Effect]

Measurement light irradiated from a plurality of light sources exhibits birefringence to the same degree for the same sample even if the wavelengths are different. Therefore, when formula (3) is applied to each measurement to obtain a series of calculated values, each series of calculated values includes data corresponding to true phase differences that are close to each other. Therefore, the true phase difference can be determined by comparing the magnitudes of a series of computed values and extracting the closest computed values.

[Examples] First, the present invention will be explained in detail, and then embodiments of the present invention will be explained with reference to the drawings.

The measurement method of the present invention consists of the following three processes.

(i) Prepare multiple measurement lights (or light sources) in advance, measure each measurement light separately in the same manner as before, and obtain the measured value r (ntrr) for each measurement. If the measured value is less than or equal to 174 of the wavelength λ of the measurement light, this measured value indicates a true phase difference.If the measured value exceeds 1/4λ, proceed to the next process.

(ii) A series of calculated values R is obtained for each measured value using the above-mentioned equation (3) (the true phase difference is included in this series of calculated values R).

(iii) When the magnitude of the calculated values is compared between a series of calculated values obtained for each measurement and the closest calculated value is extracted, this calculated value is the true phase difference.

A single measurement light cannot extract the true phase difference from a series of calculated values, but if multiple measurement lights within the visible range are used, the phase difference can be almost the same even if the wavelengths are different. Therefore, the true phase difference can be easily determined.

Next, an example will be described. Regarding the reference numerals and symbols in the drawings, the same reference numerals and symbols are attached to the parts that perform the same functions as the respective parts of the measuring device used when explaining the conventional technology, and the explanation thereof will be omitted.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention, and this apparatus includes two types of measuring light: He
-2 for irradiating with Ne laser light (λ = 632.8 nm) and semiconductor laser light (λ = 780 nm)
Two lights i1a, lb are arranged, and each light source 1a, lb is arranged.
The measuring light irradiated from b is made to enter the polarizer 3 via the semi-transparent mirror 21, and other than the above, there is no difference from the conventional device.

Next, a specific example of measuring the birefringence phase difference Δnd using this device will be described. First, it is assumed that a 1le-Ne laser beam is irradiated using the light 'rA1a, and a measured value r is determined in the same manner as in the conventional method, and that r = 50 nm is obtained.

Here, in equation (3), λ = 632.8 nm,
Set r = 50 nm, m = o, 1, 2, 3, 4, 5
．． 6''. When the calculation is performed, the following series of calculated values are obtained as the value of R. For convenience, each calculated value is shown with a subscript.

m÷6; R6・so” +50=1948.4nm Next, use the light source 1b to irradiate semiconductor laser light, obtain the measured value in the same manner as before, and now the measured value is r.
Suppose that =80r++++ is obtained.

Here, in equation (3), λ = 780 nm, r =
Set it to 80 nm, m=o, 1 as in the first measurement.
, 2° 3.4.5.6..., the following series of calculated values is obtained as the value of R.

m = 0; RO4a o ”” 80nmm=
Q; Ro-go=80nmm=1; R
+ + 116 = 470nWIm = l; R
+-go=310nmm=2; Rz-eo=
860nmm=2; Rz-ao=700r+n+m
= 3; R:++ao=1250nmm=3;
Rz3-5o=1090n◎m=4; R4
-go=1640nmm=4; R4-ao=1
480nmm = 5; Rs+go=2030n
mm=5; Rs-no=1870nmm
= 6 i R6+io=2420nmm =
6; After performing the above calculations for R66-l1o-2260n, a series of calculated values for r = 50 nm and a series of calculated values for r = 80 nm are compared with each other, Rs, so = 1632 nm, R4 * sa = 164
0 nm (marked with ◎ in the left column of each row) is the closest, so the true phase difference of the sample is 1640 to 1632 nm.
It turns out that m.

If the birefringence phase difference of the sample to be measured has a wavelength dispersion characteristic, it may be corrected by multiplying it by a coefficient corresponding to this wavelength dispersion characteristic.

It should be noted that the present invention is not limited to the above-described embodiments, and that, for example, three or more types of light sources may be used instead of two types of light sources, and that He-N may be used as the light source.
It goes without saying that other types of light sources within the visible range may be used instead of e-laser light and semiconductor laser light, and other various changes may be made within the scope of the invention. It is.

〔Effect of the invention〕

As described above, the present invention exhibits the following excellent effects.

(i) Obtain a measured value for each measurement using multiple measurement lights, use a predetermined calculation formula for each measured value to obtain a series of calculated values including the true value, and Since the magnitudes of the calculated values are compared and the closest calculated value is adopted, it is possible to perform highly accurate measurements over the entire measurement region regardless of the magnitude of the birefringence phase difference of the sample.

[11] As a result of item (i), for example, B, films (for optical memory of optical computers), vapor deposited films, etc. with small birefringence retardation to large birefringence retardation, such as alignment for liquid crystal televisions. Membrane [Δnd is approximately 800 angstroms],
Glass, quartz, Langmur-Blozet (Δ
Measurements can be made on a wide range of materials, including materials with a nd of approximately 50 angstroms.

(iii) By installing one device to carry out this method, there is no need to install multiple measuring devices in parallel according to the measurement area as in the past, and equipment costs can be significantly reduced. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a birefringence measurement device for carrying out the method of the present invention, FIG. 2 is a block diagram showing the configuration of a birefringence measurement device using a conventional phase modulation method, and FIG.
FIG. 4 and FIG. 5 are both explanatory diagrams showing the relationship between the true phase difference and the measured value. la, lb...Light source 3...Polarizer 4...Photoelastic modulator 5...Analyzer 6...Measurement sample
7... Photodetector 8... Analysis device 9
... Display device 21 ... Semi-transparent mirror

Claims (1)

[Claims] In a birefringence measurement method that measures the birefringence phase difference of the sample by irradiating the sample with phase-modulated measurement light and detecting the polarization state of the light that has passed through the sample, multiple The birefringence phase difference is measured by irradiating each sample with the light of
Apply λ/2±r (where λ is the wavelength of the measurement light, r is the measured value, and m is zero and a natural number) to obtain a series of calculated values corresponding to different values of m, and for all measurements. A method for measuring birefringence, characterized in that the series of calculated values obtained are compared in magnitude, and the closest calculated value is adopted as the true value of the birefringence phase difference.