SU1481651A1 - Method of determining absorption degree in optical medium - Google Patents

Abstract

The invention relates to optical measuring instruments and can be used in the construction of measuring instruments for parameters of the optical medium. The aim of the invention is to reduce errors in measuring the degree of absorption of radiation in an optical medium. This is achieved by extracting the first harmonics of the modulation frequency at two spatially separated points and comparing their phases. The method makes it possible to measure the degree of absorption of radiation in areas of small size and spatial filtering of signals from reflectors in the case of the presence of foreign objects reflecting light, which is especially important under production conditions. 1 il.

Description

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The invention relates to optical measuring instruments and can be used in the construction of measuring instruments for parameters of the optical medium.

The aim of the invention is to reduce measurement errors.

The method is as follows.

Monochromatic radiation with harmonic amplitude modulation is emitted in the direction of two identical reflectors installed at the boundaries of the investigated portion of the optical medium on which the degree of absorption of radiation is to be determined. Reflected signals interact (interfere) in the plane of two quadratic photodetectors, the apertures of which are much smaller than the width of the interference band and are spaced from each other by

a distance equal to a quarter of its period, with one of the photodetectors located at the maximum of the interference band. The degree of radiation absorption on the path between the otkrepatel is characterized by the value ./P1, where P, PJ are the signal powers in the plane of the apertures of the photodetectors from the near and far reflectors

Measurement of the degree of absorption of radiation in the investigated area of the optical medium is based on the selection of the first harmonics of the modulation frequency in two spatially separated photodetectors and a comparison of their phases. The measurement results are most reliable in the case of a large amplitude of the emitted harmonics and a noticeable difference in their phases due to the absorption of radiation.

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in the study area However, with this one value of the phase difference corresponds to two values of the degree of absorption of radiation in the optical medium q and q. To eliminate ambiguity, change the modulation frequency and repeat the measurements. In view of the fact that measurements on this frequency band are at the maximum readings of millivoltmeter 16, to which the output signal of amplifier 10 is supplied, then the photo detector 6 is set at the maximum of the interference band, and the photo detector 7 is shifted relative to the max.

Tote have less confidence, the maximum of the interference band on

since the signal levels will be significantly less, the measurements obtained are used to disambiguate the main measurements. With an additional two values obtained - 15 from the division of the propagation velocity

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Lowering the absorption of radiation q and q4, compare the values of q and qa and consider as reliable one of the parameters that is closer to one of the values of q3 and q4.20 i

The drawing shows a diagram of the device that implements the method.

The radiation of the monochromatic source 1 passes through the modulator 2, in which the amplitude modulation of the radiation is carried out according to the harmonic law with the frequency of the harmonic signal coming from the generator 3. From the output of the modulator 2, the radiation enters the direction of the investigated portion of the optical medium, at the boundaries of which are reflectors A and 5. The signals reflected by the reflectors 4 and 5 are received by quadratic photodetectors 6 and 7 installed in the far-field zone. From the outputs of quadratic photodetectors 6 and 7, signals are fed to filters 8 and 9, which separate the first harmonic of the modulation frequency of the radiation. The output signals 40 of filters 8 and 9 are amplified in amplifiers 10 and 11 and are fed to phase detector 12. The output signal of phase detector 12 is fed to calculator 13 of the degree of radiation absorption, in which the degree of absorption of signals on the path between the reflector is determined by the magnitude of the phase difference of the signals mi The output signal of the calculator 13 is recorded by the recorder 14. 50

Before starting the measurements, the photodetector 6 with the help of the block 15 mechanical movements moves in the plane of the location of the reflectors and perpendicular

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radiation per length of the test area, provides optimal conditions for measuring the degree of absorption of radiation.

The proposed method makes it possible to measure the degree of absorption of radiation in areas of small size and spatial filtering of signals from reflectors in the presence of extraneous, reflective light objects, which is especially important under production conditions.

Claims (1)

Invention Formula The method for determining the degree of absorption of radiation in an optical medium by sending monochromatic radiation modulated according to a harmonic law to the investigated area of the medium at the point of maximum of the interference band and at the midpoint between its maximum and minimum of signals reflected from the two reflectors installed at the boundaries the selection in the received signals of the first harmonic of the modulation frequency, so that. distinguished — in order to reduce measurement errors, monochromatic radiation is modulated with a frequency equal to 1/8 from dividing the rate of propagation of radiation by the length of the test section, phase difference is measured at two points of reception of the first harmonic frequency, modulated by radiation with a frequency different from the first one, similarly measured phase difference at two receiving points at this frequency cularly to the direction of arrival of the reflection and, according to the obtained values of different signals, the phase indices are fixed at the modulation of the different positions of the two maxima by the interference frequency, the parameter being sought is judged. a distance equal to one quarter of the distance between the maxima of the interference fringes. With a frequency of 1/8 25 thirty 20  , s 40 about 50 x 35 45 radiation per length of the test area, provides optimal conditions for measuring the degree of absorption of radiation. The proposed method makes it possible to measure the degree of absorption of radiation in areas of small size and spatial filtering of signals from reflectors in the presence of extraneous, reflective light objects, which is especially important under production conditions. Invention Formula The method for determining the degree of absorption of radiation in an optical medium by sending monochromatic radiation modulated according to a harmonic law to the investigated area of the medium at the point of maximum of the interference band and at the midpoint between its maximum and minimum of signals reflected from the two reflectors installed at the boundaries the selection in the received signals of the first harmonic of the modulation frequency, so that. distinguished — in order to reduce measurement errors, monochromatic radiation is modulated with a frequency equal to 1/8 from dividing the rate of propagation of radiation by the length of the test section, phase difference is measured at two points of reception of the first harmonic frequency, modulated by radiation with a frequency different from the first one, similarly measured phase difference at two receiving points at this frequency