SU1476353A1 - Method for measuring optic constants of absorbing media - Google Patents

Abstract

The invention relates to the measurement of optical constant refractive indices N and absorbance * 98 of absorbing media. The purpose of the invention is to improve the accuracy of measurements. The measurement is made by calibrating the initial level of the reflection coefficient behind a critical angle of incidence of light and then measuring two or more reflection coefficients to a critical angle of incidence. In this case, the calibration is performed at a wavelength located in the transparency region of the medium under study. 2 Il.

Description

The invention relates to technical physics and can be used in refractometric devices designed to study optical constants (refractive index n and absorption index e) of intensely absorbing media.

The purpose of the invention is to improve the measurement accuracy of optical constant absorbing media.

FIG. Figure 1 shows the dependences of the refractive index p and the absorption coefficient ee on the wavelength K of the radiation used; in fig. 2 shows the dependence of the reflection coefficient R on the angle of incidence in the radiation on the boundary of the test medium with the reference one for different regions of the spectral absorption of the test medium.

The method is carried out as follows.

The angle of incidence in the light is set at the boundary of the element of the disturbed total internal reflection with the reference and test media above a critical angle.

6 and calibrate the initial level of the reflection coefficient by equalizing the intensities of the reference and working photometric fields by attenuating the intensity of the incident light.

In the absorbing medium (Fig. 1), along with the region of intense absorption, there are always regions of transparency. Correspondingly, in the regions of se0, the move n (K) has a normal character, and in the absorption region, it is anomalous.

The dependence ((6) for an arbitrary wavelength A, o in the absorption region of this medium (Fig. 2) shows that, when the reflection coefficient K does not reach the maximum value, it is always less than this value by the value A / depending on the value of 3f. The calculation shows that in the range of Ј 10 + 2-10 3, the D # o value lies within 545%.

Calibration of the initial reflection coefficient level by leveling the intensities of the reference and working photos Ј

ABOUT

coke

with

metric fields at a wavelength K o in the absorption region of the medium would lead to calibration errors by the magnitude of the xy. The same amount of error is introduced with further measurement of R at, since the value of R is measured from the previously recorded initial level. Such an error leads to an error of measurement of p and eV (5-10) 4, which is unacceptable. In particular, for metrological certification of refractometry of impaired total internal reflection (ATR), the required measurement error is at the level of (5-10) X

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Therefore, the calibration of the initial level of the reflection coefficient is not performed at the working wavelength K o in the absorption region of the medium under investigation, but at the wavelength, and K1 is chosen in the transparency region of the medium.

For these areas, the reflection coefficient is R -100%, i.e., is practically zero. The absence of an error excludes, respectively, the error in the further measurement of R at.

The method is implemented without structural changes on the reflective installation of impaired total internal reflection (ATR), equipped with a monochromator, extracting the required wavelengths for initial calibration of the reflection coefficient (K1) and for operational measurements (Ko).

The method was tested in an exemplary metrological installation of ATR. The unit is intended for metrological certification of commercially available ATR refractometers. At the facility, measurements of optical constants p and # p of a number of model means in the form of a solution of rhodamine 6G various concentrations are carried out. The solutions have an intense light absorption band in the spectral region of 0.48-0.55 µm and are practically transparent outside this band, i.e., at A., 45 µm and 60 µm.

The measurement of the optical constants is carried out both when calibrating and measuring R at the wavelength Ko in the absorption region of the solution, and for the length in the transparency region of the solution. Measurements of R in the absorption region are made at two wavelengths: (A, o), 589 µm and (Co), 546 µm. The error in determining n and 3Ј is no more than (1-2) and does not depend on the magnitude of the absorption coefficient.

Thus, the proposed method allows, in comparison with the known method, an increase in the accuracy of measurement of n and x practically by the order, which makes it possible to significantly improve the accuracy of the metrological certification of the ATR refractometers, and when using the proposed method for monitoring optical continuous flow technological media, it improves

5 product quality due to more precise control of its optical characteristics.

Claims (1)

Invention Formula A method for measuring optical permanent absorbing media, including illumination of the interfaces of an element of impaired total reflection with the test and reference media with light beams at an angle of incidence greater than the critical angle of total internal reflection, recording the intensities of the reflected beams and equalizing these intensities to some value which is taken as the initial level of the reflection coefficient, by a change in the intensities of the incident beams, and a subsequent measurement relative to this initial level of at least two reflection coefficients from the indicated interfaces at the wavelength of the radiation source corresponding to the absorption region 5 of the studied medium at angles of incidence smaller than the critical angle of total internal reflection, which are judged on optical constant absorbing media, characterized in that, in order to improve the measurement accuracy, the recording of the intensities of the reflected beams when equalizing the values of these intensities are performed at a wavelength radiation source corresponding to the region of transparency of the studied medium. 0 L sh a 1