SU1226198A1 - Refractometer of disturbed total internal reflection - Google Patents

Abstract

The invention relates to the field of optical instrumentation and is intended to measure the real part of the refractive index of absorbing media of a relatively transparent, highly refractory medium with a known refractive index. In order to improve the measurement accuracy, the high-refractive optical element is designed as a fourth part of a cylinder or sphere with a center of curvature on a flat working surface in contact with the medium, and a polarizing filter and a mirror are fixed on its non-working flat surface, and the illuminator is mounted so that the falling on the optical element, a beam of light of width d is offset relative to the edge formed by its working and non-working surfaces by an amount L - (d / 2), where L is the width of the working surface of the optical element in the plane of incidence, 1 Il. G (L

Description

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The invention relates to optical-mechanical devices and is intended to measure the real part, the complex refractive index Aj n - i g of the absorbing media under study, for example liquids with an absorption index U: 0.02, a relatively transparent highly refractory medium (for example glass) with a known indicator refracted p,

The aim of the invention is to increase the measurement accuracy and simplify the design.

The drawing is a schematic diagram of a disturbed total internal reflection refractometer (ATR).

The device contains an illuminator consisting of a light source 1 and a condenser 2, a collimator with a diaphragm 3, which is installed in the focus of the lens 4, a measuring unit facing a high refractive optical element 5 with a cylindrical entrance surface, the center of curvature of which is on a flat working surface adjoining With the medium under study 6. At a distance of 0.1-0.3 mm from the cylindrical surface of element 5, a fixedly negative flat-concave Inse 7 is installed, the refractive index and radius of curvature of which is refractive index and radius of curvature of the element 5, element 5, the cuvette 8 with the investigated medium 6 are mounted on the limb 9 angle measurement device 10, and so that the center of curvature of the optical element 5 coincides with the center of rotation of the dial 9 angle measurement device 10.

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The high refractive optical element 5 has an additional flat surface perpendicular to the working surface and passing through the center of curvature of the element 5. A polarization filter 11 and an additional mirror 12 are fixed to this additional flat surface with an optical adhesive. The transmittance plane of the polarization filter 1I is angle of 45 or - 45 with respect to the plane of incidence of light. After the collimator lens 4, an interference 13 and a polarization 14 filters magneto-optical modulator 15, a quarter-wave plate 16 and a second magneto-optical modulator 17 are installed along the rays. A flat

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The transmittance bone of the polarization filter 14 is mutually orthogonal to the transmittance plane of the polarization filter 11 and is respectively an angle of -45 or 45 with respect to the plane of incidence of light. The main axes of the quarter-wave plate 16, respectively, coincide with the transmission planes of the polarization filters 11 and 14. The modulators 15 and 17 are made in the same way and are powered by alternating currents of the same frequency, for example, the network frequency w, but in opposite phase. The proposed device also comprises a photodetector 18, a selective amplifier 19 and a reversing motor 20, mechanically connected with the limb 9 of the angle measuring device 10, which constitute the tracking system.

A refractometer of impaired total internal reflection works as follows.

A collimated monochromatic beam of light formed by elements 1–4 and 13 passes a polarization filter I4, modulator 15, quarter-wave plate 16, second modulator 17, negative flat-concave lens 7 and at an angle of OS falls on the interface between two media: glass, from the optical element 5 of the ATR is manufactured, and the medium under study 6. Reflected from the interface between media 5 and 6, the luminous flux passes through the polarization filter 11, reflects from the mirror 12, passes through the polarization filter 11 again and is sensed by the photodetector 18. Under the influence of alternating current frequency 63, magneto-optical modulators 15 and 17 convert linear polarized light so that a change in both the azimuth of polarization (f and the phase difference S between the P and S components by for example, 0.01 of the maximum value. This achieves a periodic imposition of forced oscillations on the polarization parameters C) with frequency, and which change as the angle of incidence oi changes.

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Photodetector .18 perceives light changing by law

1 - ---- l-Cos 29. Cos + А «К Sin 2у - SinS. Cos 2v) - Sincot,

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A 3 12 where Ig is the intensity of the light incident on the polarization filter 1.4;

light transmission coefficient through the optical circuit; modulation amplitude. If the angle of incidence51 of light OI is smaller, the pseudocritical avg arc + ti where n and Ee are relative to the refractive indices and absorption, then the effect of the predominance of a double relative change in the azimuth of linear polarization 2 if over the relative change in the phase difference S Mediums 5 and 6 are variable components of the CO frequency of the photodetector 18 signal in phase will be the same as the excitation phase of the modulator 17. And if oi. :, as a result of the predominance of the relative change in the phase difference S over the azimuth 2 (f is variable, the signal of the photodetector 18 in phase will be the same as the excitation phase of the modulator 15, i.e. differs by and radians compared to the cases considered. The variable signal component of the photodetector 18 is amplified by the selective amplifier 19 and is applied to the control winding of the engine 20, which through the reducer moves the limb 9 together with element 5 and the medium under study.

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At ° C Kf, when 2 (f S, in: the signal spectrum of the photodetector 18 disappears the first harmonic of frequency co and the engine 20 stops. The value of the measured real

the part n of the complex refractive index n p - j of the medium under investigation is determined by the formula n n, Sinoc p, where n is the previously known refractive index of the glass of element 5.

The refractometer can be made in other versions. For example, the illuminator and the photodetector can be swapped, and instead of magneto-optical, electro-optical or electromechanical modulators can be used.

The proposed refractometer of the disturbed total internal reflection has a number of advantages in comparison with 55 known ones.

The device has only one mobile node consisting of an optical

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element 5 with a polarization filter 11, a mirror 12 and a cuvette 8, and the test medium 6, which is fixed on limb 9. This eliminates a number of faults associated with the movement of the photodetector and increases the accuracy of the measurement of the angle of light incidence, therefore , increase the accuracy of measurements of the refractive index of the medium under study 7. At the same time, the design is simplified.

In the device, the polarization / filter 11 is fixed together with the mirror 12 on the optical element 5, which eliminates the influence of the reflection of polarization light from the mirror 12 on the state of polarization of the light and significantly reduces the path length of the polarized light beam in glass between the polarization filters. It also improves the accuracy of measurements.

The proposed design of the refractometer simplifies its adjustment and measurement process, which boils down to automatic control of the pseudocritical angle with the help of a simple tracking system and solution using the built-in or installed separately micro calculator simple equalized n п,.

Claims (1)

Invention Formula Refractometer of impaired total internal reflection, containing an illuminator and a collimator, interference and polarization filters sequentially arranged along the light beam, two modulators of the state of polarization of light with a quarter-wave plate located between them, a measuring unit containing a high-refractive optical element with a cylindrical or a spherical entrance surface whose center of curvature is on a flat working surface in contact with the test medium, a negative flat-concave lens, the refractive index and radius of curvature of which is equal to the refractive index and radius of curvature of a highly refractive optical element, while the measuring unit is mechanically connected with an angle measuring device, the center of rotation of which coincides with the center of curvature of the optical element and the second polarization filter, plane the polarizations of which are mutually orthogonal to the plane of polarization of the first polarization filter and make up an angle of +45 with the plane of incidence of light as well as a photodetector, electrically connected to a tracking system, characterized in that, in order to improve measurement accuracy and simplify the design, a mirror is additionally introduced into the refractometer, and a high-refractive optical element The coping is made in the form of a fourth part of a cylinder or sphere, on the non-working flat surface of which a second polarization filter and a mirror are successively fixed, and the illuminator is installed so that the light beam incident on the Optical element is wide. d is displaced relative to the edge formed by its working and non-working surfaces by where L is the width of the working - r L - 2 - 2 whose surface of the optical element in the plane of incidence. 20 Editor L.Gratillo Compiled by C, Golubev Tehred N. Bonkalo Order 2 18/36 Circulation 778 Subscription VNIISH State Committee of the USSR for inventions and discoveries 113035, Moscow, Zh-35, Rauschska nab. 4/5 Production and printing company, Uzhgorod, Projecto st., 4 Proofreader T. Kolb