RU1818545C - Method of measuring double refraction - Google Patents

Abstract

Usage: instrumentation. SUMMARY OF THE INVENTION: A measured sample is irradiated with a monochromatic polarized light beam at two wavelengths. The light beam is polarized so that the plane of polarization is at an angle of 45 [deg.] with the main axes of the measured sample. Such a wavelength is chosen that the compensated phase difference corresponds to an integer number of periods. By changing the wavelength of light, the phase difference is compensated. At the time of compensation, the fractional part of the phase difference of the light is determined. The full period of the phase difference of light f of the transmitted sample is determined by the formula / (360 (h. -At)), where m is the integer part of the period of the difference of light without taking into account the dispersion of birefringence, the K-fractional part of the period of the difference of light phases without taking into account the dispersion birefringence, AI and Ar are the wavelengths of light, pi is the phase difference of the light transmitted through the specimen at the wavelength г. From the established full period of the phase difference, the total phase difference of the light transmitted through the sample is determined. Then, with a known transverse dimension of the sample, birefringence is determined. 1 ill. SG C

Description

A method for measuring birefringence (BFR) of substances belongs to the field of measurement technology and can be used both for creating means for controlling birefringence of substances and for measurements of industrial and research nature.

The purpose of the invention is to increase accuracy and expand the measurement range.

The method is based on the fact that the birefringence dispersion at these wavelengths cannot be such that

the phase difference at these wavelengths was in different periods up to several tens of periods, therefore, choosing the value of the phase difference for AI corresponding to an integer number of periods, we obtain the fractional part of the phase difference for A2 in the same period.

Improving the accuracy of the measurement of birefringence is ensured by eliminating the error in the correction of the auxiliary wavelength and fractional order of interference depending on the dispersion of the birefringence of the sample.

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The extension of the measuring range is achieved by eliminating the need for calibration.

A method for measuring the birefringence of substances containing features similar to those distinguishing the claimed solution from the prototype was not found.

The drawing shows an example implementation of the described method.

The light from the source 1 through the monochromator 2 and the polarizer 3 is directed to the measured sample 4, after the sample 4 the light is transmitted through the quarter-wave plate 5, the analyzer b is sent to the photodetector 7, and the signal from the photodetector 7 is sent to the meter 8 .

A monochromatic light beam with wavelength A is polarized so that the plane of polarization makes an angle of 45 ° with the main axes of the measured sample 4. The quarter-wave plate 5 is oriented so that one of its main axes coincides with the plane of polarization 3

Changing the wavelength Ai compensate for the phase difference so that it corresponds to an integer number of β-periods. The moment of compensation is determined by the minimum signal of the meter 8, received from the photodetector 7. Then, the wavelength of light is changed so that it is possible to detect the uncompensation of light transmitted through sample 4. Then, by rotating the analyzer b, the light is compensated to a minimum and by a doubled angle of rotation of the analyzer 6 determine the phase difference of the light with a wavelength of Yes. Using the dependence, the phase difference period is determined, and from the phase difference period and the measured value of the phase difference, the total phase difference for the wavelength of the wavelet A-t or Aa is determined from the dependence

The total phase difference at the wavelengths of light AI and A2 are equal, respectively,

mind

wg

2: Dp1 d th

2l: Dp2sG Ј

(1)

(2)

where t is the phase difference period

P. pi the fractional parts of the phase difference for AI, Aa, correspondingly degree,

d.- the path length of light in the substance MJ;

Ant, Ana - birefringence coefficients

Ai, Aa- the wavelength of light M.

Dividing equation (1) by (2) we obtain

Lies 11 -shch- A2-

Ani

An 2

A2-Ai

(3)

Since m is an integer, without taking into account the birefringence dispersion ratio Am / Ana, m is obtained as a mixed fraction, where for Ani Ana, the integer fraction of the fraction is equal to m. If, when measured at the wavelength Ai, the compensated phase difference corresponds to an integer number of periods, that is, the fractional part of the phase difference (p 0, you can write:

(m + k)

p2.ki

360 (A2 -AO

Discarding the fractional part in the expression, we obtain the number m, the total phase difference of the light transmitted by the measured sample at wavelength A2 is determined by the formula

2

m

2 L: Ap2 d

therefore, the birefringence coefficient at the wavelength Aa is

(4)

A check of equation (1) shows that it is valid for all substances within several tens of periods of phase difference,

The use of the claimed method for measuring the birefringence of substances as compared with the prototype allows to obtain higher measurement accuracy by eliminating the error of correction of the auxiliary wavelength and fractional order of interference depending on the dispersion of the birefringence of the sample. When using the claimed method

the need for standardization is eliminated; this makes it possible to expand the measurement range. The method is especially effective in measuring small-sized objects of thin chemical threads, films, geological sections, etc.

The invention eliminates the effect of birefringence dispersion. Given that the phase difference of the last period is measured by the Senarmon method, the proposed method allows to increase

birefringence accuracy of substances. The measurement error in this case is (0.1-1)%.

Claims (1)

SUMMARY OF THE INVENTION A method for measuring the birefringence of substances, comprising irradiating a measured sample of a substance with monochromatic polarized light beams of two wavelengths, measuring the fractional parts of the phase differences at these wavelengths, and determining birefringence at a known sample size, characterized in that in order to increase accuracy and expand the measurement range, select: wavelengths are selected from the condition that the compensated phase difference corresponds to an integer number of periods, then the wavelength of light is changed, ompensiruyut and phase difference. the moment of compensation determines the fractional part of the phase difference period, and the complete One phase difference of light passing through the sample is determined by the formula 360 (Xg -AT) where m is the integer part of the period of the phase difference of the light without taking into account the dispersion of birefringence; K is the fractional part of the phase difference period of the light without taking into account the birefringence dispersion;  L.1, Az - wavelengths of light; (pi is the phase difference of the light transmitted through the sample at wavelength AI from the established full period of the phase difference, the total phase difference between the light transmitted through the sample is determined, and its birefringence is determined.