JP3554374B2 - Polarimeter - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a polarization measuring device, and more particularly to an improvement in a centering mechanism thereof.
[0002]
[Prior art]
One of the optical characteristics of a substance is refraction, and the refractive index is determined by the crystal structure of the substance. The crystal may have two or more refractive indexes, and such a substance is called an anisotropic substance.
[0003]
When linearly polarized light enters an anisotropic substance, two refracted lights are generated for one incident light, one is called ordinary light, the other is called extraordinary light, and the light emitted from the substance is combined with both refracted lights. Elliptically polarized light. The rotation direction of the elliptically polarized light is determined by the direction in which the phases of the ordinary light and the extraordinary light advance, and the vibration direction of the light having the slow phase velocity is called the slow axis, and the vibration direction of the light having the fast phase velocity is called the fast axis.
This phase difference between ordinary light and extraordinary light, that is, birefringence retardation (retardation) is a very important factor in the optical properties of anisotropic materials, and is indispensable for evaluating glass and unstretched films. It is getting.
[0004]
[Problems to be solved by the invention]
On the other hand, accurate measurement of the retardation requires a so-called centering operation for matching the fast axis or slow axis of the refracted light with the linear polarization axis of the incoming light.
However, this centering work has conventionally been performed by experience and trial and error, and has placed a great burden on the operator and has taken a long time for measurement.
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the related art, and an object of the present invention is to provide a polarization measuring apparatus that can automatically perform axis alignment in measuring retardation.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a polarization measuring device according to the present invention includes a lock-in amplifier, an arithmetic unit, and a stage driving unit.
Then, the lock-in amplifier extracts the modulation frequency ω component and / or the 2ω component that is the second harmonic from the output of the detector.
The calculating means calculates an angle difference between a fast axis or a slow axis and the incident polarization axis from the ω component and / or the 2ω component output from the lock-in amplifier.
Further, the stage driving means rotates the sample stage in accordance with the angle difference output from the arithmetic means, and aligns the fast axis or slow axis with the incident polarization axis to perform centering.
[0006]
The arithmetic unit will row directly axes out by detection of zero value 2ω component.
Or, calculating means, both ω component and 2ω component detects the phase angle becomes zero values will rows the axial centering by moving 45 °.
Further, it is preferable that the calculation means shapes the waveform of the ω component or the 2ω component by, for example, a known curve fitting method, and applies the above-described method to the formed waveform to perform centering.
[0007]
[Action]
The polarization measuring device according to the present invention drives the stage based on the phase difference between the fast axis or the slow axis and the incident polarization plane from the ω component and / or 2ω component output from the lock-in amplifier as described above. Therefore, the centering can be automatically performed with high accuracy.
Here, if withered line automatic shaft out by detecting the minimum value of the ω component, when S / N ratio of the original ω component is high, it is possible to perform axial centering a simple technique.
[0008]
According to the method of the first aspect , the centering is performed directly by detecting the zero value of the 2ω component, so that when the amount of axis deviation is small, the centering can be performed accurately and easily. Can be.
According to the method of the second aspect, the zero value (θ ₁ ) of each of the ω component and the 2ω component is detected, and the axis is set by moving by 45 degrees. In addition, even when the S / N ratio is large, centering can be performed accurately and easily.
According to the method of the third aspect , the waveform of the ω component or the 2ω component is shaped by, for example, a known curve fitting method, the method is applied to the formed waveform, and centering is performed. Even when the S / N ratio of the waveform is poor, the method according to claims 2 to 4 can be suitably applied.
[0009]
【Example】
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a polarization measuring device according to one embodiment of the present invention. The polarization measuring device shown in FIG. 1 includes a light emitting system 10, a sample holding system 12, a light receiving system 14, and a control system 16.
The light emitting system 10 includes a monochromator 20 having a light source 18, a polarizer 21, and a photoelastic modulator (PEM) 22. Then, only light having a predetermined wavelength is extracted from the light from the light source 18 by the monochromator 20, converted into predetermined linearly polarized light by the polarizer 21, and further modulated via the PEM 22 at a predetermined modulation frequency ω.
[0010]
The sample holding system 12 includes a transmission type stage 26, and is configured to change the rotational position of the held sample to be measured around the incident optical axis.
The light receiving system 14 includes an analyzer 28 and a photomultiplier (detector) 30. The photomultiplier 30 receives the transmitted light from the sample to be measured from the sample holding system 12 via the analyzer 28 and performs photoelectric conversion.
The control system 16 includes a lock-in amplifier 31 that extracts a modulation frequency ω and a 2ω component that is a second harmonic from the output of the photomultiplier 30, and controls the phase advance axis and incident change based on the output of the lock-in amplifier 31. It includes a calculating means (CPU) 32 for calculating a phase difference with the surface, and a stage driving means 34 for rotating the transmission type sample stage 26 based on an instruction of the CUP 32.
[0011]
The CPU 32 controls the PEM controller 38 and the monochrome driver 40, respectively, and the measurement data obtained through the CUP 32 is subjected to desired data processing by the computer 42. A CRT 44, a printer 46, and a keyboard 48 are connected to the computer 32, and desired device settings are made via the keyboard 48. Various control states, obtained data, and the like are displayed and output to the CRT 44 and the printer 46. .
[0012]
When the sample to be measured is mounted and fixed on the sample stage 26, for example, the fast axis of the sample to be measured and the incident light applied to the sample to be measured Centering is performed to make the polarization axis coincide with the polarization axis.
That is, first, the CPU 32 enters predetermined polarized light into the sample to be measured whose fast axis direction is unknown, and obtains the transmitted light output from the photomultiplier 30.
[0013]
The output of the photomultiplier 30 is sequentially monitored by a CPU 32. The CPU 32 gives an instruction to the stage driving means 34 to rotate the stage 26, that is, the sample to be measured around the incident optical axis. Then, the output of the photomultiplier 30 is separated by the lock-in amplifier 31 into an ω component and a 2ω component. The ω component and the 2ω component are a (ω) = − cos (2θ) sin (Δ)
a (2ω) = sin (4θ) sin ² (Δ / 2)
Indicated by
here,
θ: azimuth angle of the fast axis Δ: phase difference angle Accordingly, the relationship between the sample rotation angle (θ) and the ω component and the 2ω component is shown in FIG.
[0014]
In FIG. 2, Y ₁ is a polarization axis of the incident light, it is sufficient to match the fast axis of the sample to be measured and the polarization axis Y _1. Then, the polarization axis Y ₁ and the fast axis and the minimum value ω component is matched state, 2 [omega component indicates zero.
Among the centering methods, the following method can be considered as a particularly simple one.
▲ 1 ▼ a direct axis out by detecting the minimum value omega ₁ of omega component.
(2) Direct alignment is performed by detecting the zero value (2ω) ₁ of the 2ω component.
{Circle around (3)} The phase angle (ω ₂ , (2ω) ₂ ) at which both the ω component and the 2ω component have zero values is detected, and the axis is set by returning the phase angle by 45 degrees.
(4) The waveform of the ω component or the 2ω component is shaped by, for example, a known curve fitting method, and the methods (1) to (3) are applied to the shaped waveform.
In the present invention, any of the methods is applicable.
The method (1) is the simplest method, but since the degree of output change is small with respect to the rotation angle θ near the minimum value, it is applied especially when the S / N ratio of the original ω component waveform is high. Hateful.
In the method (2), the degree of output change is large with respect to the rotation angle θ because the zero point is detected, and the accuracy is higher than in the method (1). Therefore, it is an extremely simple method when the amount of axis deviation of the sample is small, but it is difficult to apply when the amount of axis deviation is large.
The method of (3) detects the zero value of each of the ω component and the 2ω component, so that the accuracy is high. Further, since the zero value of both components is in units of 90 degrees, the case where the axial deviation amount is relatively large There is an advantage that it can also be applied.
The device (4) is particularly suitable when the S / N ratio of the original waveform is low. Since the corrected waveform after the curve fitting has substantially no distortion, sufficient centering can be performed even by applying the above methods (1) to (3). Further, for example, data can be collected at various intervals as necessary, such as every 1 degree, every 5 degrees, every 10 degrees, and the like, and the curve can be estimated, so that the processing time can be reduced.
[0015]
After the centering is performed as described above, the calculation of retardation Γ and the like is performed.
Note that the retardation Γ has the following relationship with the phase difference angle Δ.
Δ = (Γ / λ) * 360
= Δ ₀ + n * 360
Here, n: order (natural number), Δ ₀ : reduced phase difference angle (0 ≦ Δ ₀ <360).
To determine the zone of Δ, the amplitude a0 (2ω) of a (2ω) is obtained by rotating the sample by about 100 degrees.
When a ₀ (2ω) ≦ 0.5, Δ is the first or fourth quadrant,
When a ₀ (2ω)> 0.5, Δ is the second or third quadrant.
[0016]
The polarization modulation spectral transmission measuring device obtained as described above can detect minute retardation of 1 nm or less, and thus can be a powerful means for measuring spectral birefringence of glass, unstretched film, and the like.
In addition, tracking small changes in photoelastic coefficient when a small strain is applied to glass, etc., or samples with small anisotropy or wavelength dispersion such as phase difference, transparent film with small anisotropy, alignment state of alignment film, etc. It is also expected to be applied in small liquid fields that require measurement.
[0017]
【The invention's effect】
The polarization measuring device according to the present invention drives the stage based on the phase difference between the fast axis or the slow axis and the incident polarization plane from the ω component and / or 2ω component output from the lock-in amplifier as described above. Therefore, the centering can be automatically performed with high accuracy.
Here, if the line of example an automatic shaft out by detecting the minimum value of the ω component, when S / N ratio of the original ω component is high, it is possible to perform axial centering a simple device.
Then, according to the apparatus of claim 1, wherein, by performing the direct axis out by performing the zero value detection of 2ω component, when the amount of axial deviation is small, accurately, and easily by performing the axial centering Can be.
According to the second aspect of the present invention, the zero value (θ1) of each of the ω component and the 2ω component is detected, and the axis is set by returning the axis by 45 degrees. Even when the / N ratio is large, centering can be performed accurately and easily.
According to the apparatus of the third aspect , the waveform of the ω component or the 2ω component is shaped by, for example, a known curve fitting method, the method is applied by the formed waveform, and centering is performed. Even when the S / N ratio of the waveform is poor, the method according to claim 1 or 2 can be suitably applied.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a schematic configuration of a polarization measuring device according to one embodiment of the present invention.
FIG. 2 is an explanatory diagram of an operation of a calculation means of the present invention.
[Explanation of symbols]
Reference Signs List 21 polarizer 22 photoelastic modulator 26 sample stage 30 detector 31 lock-in amplifier 32 arithmetic means (CPU)
34 Stage driving means

Claims (3)

A polarizer that gives predetermined linearly polarized light to light emitted from the light source,
A photoelastic modulator for modulating light at a predetermined modulation frequency ω,
A sample stage on which the sample to be measured is placed, and the rotation position of which can be changed around the optical axis with respect to the incident light given the polarization modulation ,
A detector for measuring light intensity through the sample to be measured on the sample stage,
In a polarimeter equipped with
A lock-in amplifier that extracts a modulation frequency ω component and / or a 2ω component that is a second harmonic from an output of the detector;
Calculating means for calculating an angle difference between a fast axis or a slow axis and a polarization axis of the polarizer from the ω component and / or the 2ω component output from the lock-in amplifier;
Stage drive means for rotating the sample stage according to the angle difference output by the arithmetic means, aligning the fast axis or slow axis, and the polarization axis of the polarizer, and performing centering ,
A polarimeter according to claim 1, wherein said calculating means directly performs centering by detecting a zero value of a 2ω component . A polarizer that gives predetermined linearly polarized light to light emitted from the light source,
A photoelastic modulator for modulating light at a predetermined modulation frequency ω,
A sample stage on which the sample to be measured is placed, and the rotation position of which can be changed around the optical axis with respect to the incident light given the polarization modulation ,
A detector for measuring light intensity through the sample to be measured on the sample stage,
In a polarimeter equipped with
A lock-in amplifier that extracts a modulation frequency ω component and / or a 2ω component that is a second harmonic from an output of the detector;
Calculating means for calculating an angle difference between a fast axis or a slow axis and a polarization axis of the polarizer from the ω component and / or the 2ω component output from the lock-in amplifier;
Stage drive means for rotating the sample stage according to the angle difference output by the arithmetic means, aligning the fast axis or slow axis, and the polarization axis of the polarizer, and performing centering ,
A polarization measuring apparatus , wherein the calculating means detects a phase angle at which both the ω component and the 2ω component have a zero value, and performs a centering by moving the phase angle by 45 degrees therefrom . Apparatus according to claim 1 or 2, wherein calculating means, a waveform of from ω component 2ω component, waveform shaping by the curve fitting method, by applying the method of claim 1 or 2, wherein in the forming the waveform, the axis out A polarization measuring device.

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