SU1406453A1 - Method and apparatus for determining the passing of coherent radiation by optical media - Google Patents

Abstract

The invention relates to the field of photometry and can be used in optical instrumentation for monitoring the quality of optical glass. The purpose of the invention is to improve the accuracy of determining the transmission of samples in coherent radiation and to expand the capabilities of the method by determining the presence of inhomogeneities in the sample, as well as monitoring the entire volume of the sample. When forming a flat coherent beam, measuring its energy and determining the transmission of the optical medium (as the ratio of the energy of the beam transmitted through the medium to the initial one), the spatial frequency spectrum of the radiation transmitted through the optical medium sample is formed and the frequencies corresponding to the transmission of the sample geometric dimensions. The dimensions of the Fourier spectrum and its scale are related to the parameters of the sample by certain ratios. After successive sources of coherent radiation, a collimator forming a flat coherent beam, devices for fastening a sample of an optical medium and a Fourier transform lens in the focal plane of the lens, an additional diaphragm is installed, which performs spatial filtering in the Fourier transform plane, which is the focal plane of the lens. The holes in the filter diaphragm at a certain spatial frequency allocate the required region of the spatial frequency spectrum, corresponding either to the transmission of a sample of geometrical data (i.e., a low-frequency component) or to the presence of phase inhomogeneities in the sample (i.e., high-frequency components). ). To determine the transmission of optical media in coherent radiation, monochromatic coherent radiation is used, corresponding to the operating wavelength, which allows the use of spatial filtering and Fourier spectrometry in processing, which improves the accuracy of determining the transmission of optical media samples and relatives in them. In addition, the use of a monochromatic source in measuring the optical parameters of the medium eliminates measurement errors associated with the interaction of the medium and radiation at non-operating wavelengths, due to the fact that the filters used have a finite spectral transmission band. 2 sec. and 2 z. p. f-ly, 4 ill. S (L 05 4 01 00

Description

The invention relates to the field of photometric measurements, namely to methods for determining the transmission of optical media, and can be used in instrument making.

The purpose of the invention is to improve the accuracy of determining the transmission of samples of optical media in coherent radiation, expanding the capabilities of the method by determining the presence of heterogeneity in the sample, controlling the entire volume of the sample.

FIG. 1 shows a diagram of the device that implements the method; in fig. 2 - spatial-frequency spectrum, removed by the proposed method, when measuring the sample transmission without inhomogeneities; in fig. 3 - the same for a sample containing local inhomogeneities of 1-3 mm; in fig. 4 - the same for a sample containing inhomogeneities according to GOST.

The device contains a coherent radiation source 1, a collimator 2 forming a flat coherent radiation front, a sample sample mounting device 3 for an optical medium, a sample of optical medium 4, a Fourier transform lens 5, a spatial frequency filter 6, a photometer sensor 7. The method is carried out using the device as follows. Collimator 2 forms a flat front

coherent radiation of the source 1. The sample 4 of the optical medium is fixed by means of the device 3 for fastening the sample of the optical medium, in which the sample can be rotated around the axis passing through the center of the coherent beam section and which is the optical axis of the entire device. The Fourier transform lens 5 forms the spatial-frequency spectrum of the radiation that passes through the sample of the optical medium 4. In the focal plane of the Fourier lens 5 there is an aperture filter 6 of spatial frequencies in which holes are made to highlight the required areas of the spatial frequency spectrum of radiation transmitted through the sample of the optical medium 4.

The sensor 7 of the photometer measures the energy allocated by the filter aperture 6, the regions of the spatial-frequency spectrum of the radiation transmitted through the sample of the optical medium 4 and the initial energy of the flat coherent beam without the sample. The dimensions of the Fourier spectrum and its scale are related to the parameters of the sample by the relations

ZjTx G

1L - w -

where x, y - the coordinates of the spatial-frequency spectrum;

A is the coherent radiation wavelength;

1406453

f is the focus of the Fourier transform lens;

five

five

0

  - spatial frequencies of radiation transmitted through the sample of the optical medium.

The presence of spatial inhomogeneities in sample 4 is determined by the energy of the selected diaphragm b of the high-frequency components of the spatial-frequency spectrum of the radiation transmitted through

0 sample of the optical medium 4. The absence of energy in this region of the spectrum indicates the absence of phase inhomogeneities in the sample of the optical medium 4. The control of the entire sample volume is carried out by rotating it around the optical axis of the device. The principal difference of the method is the formation of a spatial-frequency radiation spectrum that has passed through the optical medium sample, which allows not only measuring the energy of the radiation transmitted through the sample, but also controlling the presence of phase inhomogeneities in it, which increase the size of the spatial frequency spectrum and lead to to the appearance of higher frequency components in it. When selecting a part of the spatial-frequency spectrum containing high-frequency components corresponding to the presence of phase inhomogeneities in the sample of the optical medium, the presence of inhomogeneities is determined.

Q In addition, the method allows measurement of the transmittance of optical samples of various geometrical dimensions. In this case, the sample sizes are determined by the possibility of forming a parallel beam of coherent radiation with the cross section required to brighten the entire sample, and the dimensions of the Fourier transform lens.

Since the Fourier spectrum has a central symmetry and the components forming it correspond to the phase incursions of radiation in a controlled medium (the sign of the phase incursion is not determined), the sensor controls the phase incursion at a certain section of the sample at a fixed sample position. Consequently, to control the entire volume of the sample over all its sections, a centrally symmetric sensor (ring) or sample rotation in a plane parallel to the spectrum formation plane is required around an axis perpendicular to the spectrum plane and the symmetry passing through its center.

0

Example. Measurements of the transmission of samples of optical media with a diameter of up to 120 mm (PI-120 plates) are carried out on the basis of the OSK-2 optical bench equipment. The transmittance of the PI-120 plate is measured.

5 by the known method. Next, the transmission of the same plate is measured on an SF-18 spectrophotometer, and then by the proposed method. Next to the plate (1/16

surface area) a fine local coating is applied with a transmittance close to unity and a refractive index close to the refractive index of the source material, which meets the requirements of OST3.4924-81 p.2. The transmittance measurements are again made using the three previous techniques. The measurement results are shown in the table.

The spatial-frequency spectra taken using the proposed method are used to measure the sample transmission without inhomogeneities (Fig. 2); a sample containing local inhomogeneities of 1-3 mm (Fig. 3); sample containing inhomogeneities corresponding to p. 2 OST 3.4924-81. In these graphs, Е is the voltage on the photometer sensor with a working diameter of 10 µm; 2.- deviation of the position of the photometer sensor from the optical axis of the device. The dotted line denotes the spatial-frequency spectra of the radiation that has passed through the device without a sample of the optical medium.

The proposed method and device for its implementation allows to automate the sampling process for measuring the transmission of optical media, measure the parameters of samples of various geometrical dimensions, and improve the accuracy and reliability of measurements in coherent radiation. A device that implements the proposed method reduces the time required to prepare samples of the optical medium for measurement by 3 times; the measurement accuracy increases by an order of magnitude (to 0.005%). At the same time, labor productivity is increased by measuring the transmission of optical media in coherent radiation by a factor of 2-3, and reliable monitoring of the optical homogeneity of the medium is carried out.

Claims (4)

Invention Formula . A method for determining the transmission of coherent radiation by optical media, which consists in forming a flat coherent monochromatic electromagnetic radiation beam, measures the energy of this beam, directs the radiation beam to the sample, and calculates the transmittance value of the optical medium, characterized in that 0 The accuracy of determining the transmission of large-sized samples is carried out by Fourier transform of the radiation transmitted through the sample, the spatial frequencies corresponding to the geometric dimensions of the part of the sample through which the radiation beam passes are obtained from the obtained Fourier spectrum, and the transmission are as the ratio of the energy of the selected region of the spectrum to the initial energy. 2. The method according to claim 1, characterized in that, in order to expand the capabilities of the method by determining the presence of inhomogeneities in the sample, after the Fourier transform 5 radiation transmitted through the sample, additionally allocate a portion of the Fourier spectrum that does not contain spectral compositions of the factors corresponding to the transmission of the part of the sample through which the radiation beam passes, and it is judged that there are inhomogeneities by a positive energy value corresponding additionally part of the Fourier spectrum. 3. Method of CPU. 1 and 2, characterized in that, in order to control the entire sample volume of the optical medium, it is rotated around an axis passing through the center of the cross section of the coherent beam. 4. A device for determining optical coherent radiation transmission. , media containing sequentially located and optically interconnected source of coherent radiation, a collimator forming a flat coherent beam of electromagnetic radiation, a device for fastening an optical sample from the environment, a Fourier transforming lens, a photometer sensor located in the focal plane of the lens, characterized in that, in order to improve the accuracy of determining the transmission of large-sized samples, to expand the possibilities by determining the sample inhomogeneities and to control the entire sample, it is additionally equipped with diaphragms- filters of spatial frequencies, transmissive and shadow, located in the focal plane of the Fourier lens in front of the sensor and equipped with a mechanism of their alternate input to the optical b, the optical axis of the collimator, the top-Fourier lens, its focal point and the center of the photometer detector lie on the same straight, with fastening device samples were ob0 arranged rotatably around its given straight. According to OST 3.4924-81 based on OSK-2 According to OST 3.4924-81 on the spectrophotometer SF-18 According to the proposed method based on OSK-2 0,930,930,930,93 0.927-0.9240.927 0.9264 0.9262 0.9262 0.8346  that 10th -10 th of 1Q 20 cho ft ,. "/ G -W -20 -10 o 10 th JO" g ffHxfl  p "f (P". J 1