JPH02242137A - Double refraction analysis apparatus - Google Patents

Abstract

PURPOSE:To achieve an expansion of a measurable range by arranging a polarizer, a phase difference modulation means, an analyzer and an output adjustable photodetector to compute a phase delay from amplitudes of two kinds of frequencies contained in outputs thereof and an azimuth of a sample orientation. CONSTITUTION:Monochromatic light of a light source 10 is turned to a linearly polarized light with an analyzer 12 and passed through a vibrator with a voltage of fHz applied with a PEW controller 16 of an optically elastic modulation element 14 having an optical axis at 45 deg. to an X axis to cause a phase difference between X-axis and Y-axis components. The modulation light is passed through a transparent sample 20 held on a rotary stage 18 to be turned to a linearly polarized light with an analyzer 24 with a direction of transmission axis thereof at 45 deg. to the X axis to detect an intensity of light with a photomultiplier 26, an output of which is supplied to a preamplifier 28, an FHz amplifier 36 and a 2fHz amplifier 38 to determine a phase delay at an irradiation point P with a microcomputer 46 from amplitudes and an orientation azimuth theta of the sample via synchronous rectifiers 40 and 42 and a multiplexer 44.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a birefringence analyzer, and in particular, a birefringence analyzer suitable for analyzing samples with relatively large birefringence such as polymer films and liquid crystal films. Regarding.

[Prior art] Conventional birefringence analyzers calculate the phase lag in birefringence from an arc sine function, so the phase lag is between 1π/2 and 1π/2.
It could only be determined within the range of π/2. Therefore, it has not been possible to measure samples with relatively large phase delays exceeding the above range, such as polymer films, which are easily oriented by stretching.

[Problems to be Solved by the Invention] In view of the above-mentioned problems, an object of the present invention is to provide a birefringence analysis device that can measure a wide range of phase delays.

means for adjusting the output of the photodetector so that the value of the DC component included in the output of the photodetector is constant; sample rotation means for rotating the sample around its light irradiation point; means for detecting the amplitude A of a signal component of a frequency fHz included in the output;
The apparatus includes means for detecting the amplitude All of the fHz signal component, and means for calculating the phase delay by determining the amplitude A and A v t when the sample is rotated.

[Means for Solving the Problems] In order to achieve this object, the birefringence analyzer according to the present invention includes a polarizer that converts incident monochromatic light into linearly polarized light, and a polarizer that converts the linearly polarized light into ±45° with respect to its polarization plane. phase difference modulation means for alternately generating left and right elliptical (circle included in the ellipse) polarized light by changing the phase difference between the two components at a frequency r when the light is decomposed into linearly polarized light components with a plane of polarization; an analyzer that enters the light after passing through the sample and converts it into linearly polarized light; a photodetector that detects the intensity of the linearly polarized light that has passed through the analyzer;
Effect] Amplitudes A+ and Af+ are maximized by adjusting the gain of the amplifier, where Δ is the phase delay and θ is the azimuth angle of the sample orientation with respect to the reference plane (a plane that passes through the transmission axis of the polarizer and is parallel to the direction of light propagation). When the values are normalized to 1, they can be expressed by the following equations.

A t= sinΔ+cos2θ −・−(1)
A tr-8in” (Δ/2)・51n40...(2
) Therefore, for example, the ratio R of the maximum value of self-amplitude is R=s
inΔ/sin” (Δ/2) = tan(Δ/2)/
2 − ·−(, (), and the phase delay can be obtained in the range of −π to π.

The same conclusion as above can be obtained regarding the ratio of the maximum values of the differential values of the amplitudes A r and A wr with respect to θ.

[Example code] Hereinafter, the present invention will be described in detail based on the drawings.

(1)-Example FIG. 1 shows the configuration of a birefringence analyzer.

The monochromatic light emitted from the light source 10 is linearly polarized through a polarizer I2 and then passed through a photoelastic modulator (PEM)+
Pass through 4.

Here, in the xYz orthogonal coordinate system shown in FIG. 2, if the Z direction is the light traveling direction and the transmission axis direction of the polarizer 12 is the X direction, then the optical axis direction of the photoelastic modulator 14 is the 45'.

In FIG. 1, an alternating current voltage V of fHz is supplied from the PE controller 16. When 5 inches (2πrt) is applied between the electrode plates of the vibrator of the photoelastic modulation element 14, the polarizer 1
Phase difference δ between the X-axis component and Y-axis component of linearly polarized light passing through 2
−6°5in (2πrt>) occurs. This frequency f is, for example, 50 kllz. Also, the voltage amplitude V.

Preferably, the phase difference amplitude 6° is J, C6,)=0
, i.e. δ. = 2.405.

Here, jo indicates a zero-order Bessel function.

Modulated light from the photoelastic modulator 14 passes through a transparent sample 20, such as a polymer film, held on a stage 18. This stage I8 is operated by the steno controller 22 in steps of 1°, for example, with the light irradiation point P of the sample 20 as the center in order to obtain the phase delay of the birefringence at the light irradiation point.
0", and in order to obtain this phase delay distribution, the stage 18 is rotated by 36 degrees, for example, in 5 degree increments around the central axis C of the stage 18.
degree, and the distance r from the central axis C to the light irradiation point P is changed, for example, in steps of IIIm.

As shown in FIG. 2, the light passing through the sample 20 passes through an analyzer 24 whose transmission axis is oriented at 45° with respect to the X-axis, and is converted into linearly polarized light, whose light intensity is detected by a photomultiplier tube 26. .

The output of the photomultiplier tube 26 is subjected to current/voltage conversion by a preamplifier 28 , and then only a DC component is extracted and voltage amplified by a DC amplifier 30 and is supplied to a control terminal of a power supply 32 . The power supply 32 adjusts the dynode voltage applied to the photomultiplier tube 26 so that the output of the DC amplifier 30 is constant.

On the other hand, the output of the preamplifier 28 is supplied to an r II Z AC amplifier 36 and a 2r11□ AC amplifier 38, in which only AC components of frequencies fHz and 2f[1, respectively, are taken out and voltage amplified, and then sent to an fHz synchronous rectifier 40. 2 "H
2 synchronous rectifier 42. fil, synchronous rectifier 4
0.2 fHz synchronous rectifier 42 control terminal 1. - let
, a r tl z synchronization pulse and a 2 rnz synchronization pulse from the PEM controller I6, respectively. fH
The z synchronous rectifier 40 and the 2fllZ synchronous rectifier 42 each synchronously rectify the AC voltage supplied from the fez AC amplifier 36.2 r II z AC amplifier 38 to obtain the amplitude of each AC component, and supply this to the multiplexer 44 .

The multiplexer 44 connects the fHz synchronous rectifier 40 based on a control signal supplied from the microcomputer 46.
and the output of the 2 r If z synchronous rectifier 42 are alternately supplied to the A/D converter 48 . The A/D converter 48 converts this into digital data and supplies it to the microcomputer 46.

The microcomputer 46 reads the data supplied from the A/D converter 48 and calculates the amplitude Af. based on the above equations (1) and (2). Find A21 (amplitude is AC amplifier 36.
(normalized by adjusting the gain of 38), the maximum value of these is determined by changing 0, the phase delay Δ at the irradiation point P is determined based on the above equation (3), and this is sent from the stage controller 22. The supplied sample 20 is supplied to the printer 50 and recorded in correspondence with the positional coordinates of the irradiation point P.

By repeating such processing for each measurement point (r+, φ1), a phase lag distribution on the sample 20 is obtained.

(2) Test Example FIG. 3 is a graph of the amplitudes A, Af, of a certain irradiation point, measured by the apparatus of the above embodiment.

Sample 20 is a polypropylene film, and θ is 80 to θ in 1° increments. The range is +100°.

[Effects of the Invention] As explained above, the birefringence analyzer according to the present invention has an excellent effect of being able to measure phase retardation in a range twice that of the conventional method, and can be used for polymer films and liquid crystal films. It greatly contributes to the analysis of samples with relatively large birefringence, such as.

[Brief explanation of drawings]

1 and 2 relate to one embodiment of the present invention, in which FIG. 1 is a block diagram of a birefringence analyzer, and FIG. 2 is an optical system layout diagram. FIG. 3 relates to a test example, and shows the amplitude Ar, Af, relative to 0 at a certain light irradiation point. This is a graph of In the figure, IO is the light source 12, the polarizer +4 is the photoelastic modulator 16, the PEM controller 18 is the stage 20, the sample 22 is the stage controller 24, the analyzer 26 is the photomultiplier tube 28, the preamplifier 30 is the DC amplifier 32 is the power supply 36 is fHz AC amplifier 38 let 2 flz AC amplifier 40 is f II
The Z synchronous rectifier 42 is a 2 fHz synchronous rectifier 44 is a multiplexer 46, and the microcomputer 48 is an A/D converter.

Claims (1)

[Claims] A polarizer (12) that converts incident monochromatic light into linearly polarized light; and a polarizer (12) that converts incident monochromatic light into linearly polarized light; Phase difference modulation means (
14, 16), an analyzer (24) into which the modulated light enters after passing through the sample (20) and converts it into linearly polarized light; and an analyzer (24) that detects the intensity of the linearly polarized light that has passed through the analyzer (24). a photodetector (26); and means (28 to 32) for adjusting the output of the photodetector so that the value of the DC component included in the output of the photodetector is constant.
and a sample rotation means (18, 22) for rotating the sample around its light irradiation point, in a birefringence analyzer comprising: a signal component with a frequency fHz included in the output of the photodetector (26). means for detecting the amplitude A_f (28, 36, 40
, 44, 48) and means (28, 38) for detecting the amplitude A_2_f of a signal component with a frequency of 2 fHz included in the output of the photodetector (26).
, 42, 44, 48); and means (46) for calculating the phase delay by calculating the values of the amplitudes A_f and A_2_f when the sample is rotated.