SU1122941A1 - Method of measuring reflection factor and test-object for application thereof - Google Patents

Abstract

1. A method of measuring the reflection coefficient, which includes irradiating a test object with a known reflection coefficient by a light flux, measuring the reflection coefficient of a test object, calculating a photometric calibration correction for the difference between the known and measured reflection coefficients and measuring the reflection coefficient of the object under study, and calculating the actual reflection coefficient of the object under investigation the measured reflection coefficient and the photometric calibration correction, which differs 1 With the fact that The aim is to measure the reflection coefficients smaller than 1.8%, the test object is irradiated with linearly polarized light, the dependence of the reflection coefficient of the test object is measured on the angle p between the polarization direction of the irradiating light and the direction of the polarization of the test object in the range of angles and 0-90 °, and the photometric calibration correction & R (p) is determined from the ratio (P1, p1p) - - R | "stn, where R p is the reflection coefficient of the test object for S and P components of the irradiating light; S is the component of polarization of light, perpendicular to the plane of incidence; Р - amounted to a polarization of light, parallel to the plane of incidence. 2. A test object for measuring the reflection coefficient containing a flat optical element made of a material with a refractive index of 1.3-4.0, characterized in that, in order to improve the accuracy of measurement of reflection coefficients less than 1.8%, In addition, a second flat optical element installed at an angle of 120 ° is introduced.

Description

ISO is related to the field of instrumentation technology and can be used to measure small reflection coefficients, such as reflection coefficients of anti-reflective coatings. A known method for measuring the transmittance includes irradiating an object with a stream of light, measuring the intensity of light transmitted through the object, determining photometric calibration corrections using filters, polarizers and other optical elements with a known transmittance and determining the transmittance of the object taking into account the calibration corrections. However, the use of this method in measuring the reflection coefficient is not always possible. There is also known a method for measuring the reflection coefficient, which includes irradiating a test object with a known reflection coefficient, measuring the reflection coefficient of a test object, calculating the photometric calibration correction for the difference between the known and measured reflection coefficients, and measuring the actual reflection coefficient of the object under investigation. the object according to the measured reflection coefficient and photometric calibration correction. The method is carried out using a test object containing a flat optical element made of a material with a refractive index of 1.3-4.0 2j. The disadvantage of this method is the impossibility of accurately measuring reflection coefficients less than 1.8%, since optical media with a refractive index less than 1.3 do not exist. The aim of the invention is to improve the accuracy of measurement of reflection coefficients less than 1.8%. This goal is achieved by the fact that according to the method of measuring the reflection coefficient, including the irradiation of a test object with a known reflection coefficient by a light flux, the measurement of the reflection coefficient of an object, the calculation of the photometric calibration correction for the difference between the known and measured reflection coefficients of the test object, from 412 measurements the reflection coefficient of the object under study and the calculation of the real reflection coefficient of the object under study from the measured reflection coefficient and photometry With a standard calibration correction, the test object is irradiated with linearly polarized light, the dependence of the reflection coefficient of the test object (Ru, ..) on the angle p between the direction of polarization of the incident light and the direction of its own polarization of the test object, the angle interval (p) 0 is measured -90, and the photometric calibration correction 1 (UR) is determined from the relation - R2, cosjO-R | , UR - R. De R ,, ,, reflectance of the material of the test object for the S and P components of the irradiating light; a polarization of light perpendicular to the plane of incidence; the polarization of light parallel to the plane of incidence. In this case, the method is carried out with the help of a test object containing a flat optical element made of a material with a refractive index of 1.3-4.0, in which a second flat optical element is additionally installed at an angle of 60 2 (120 ° to the first. Fig. 1 shows a section of the test object at an angle of 2L between the optical surfaces of 60 ° (2 bo); in Fig. 2 - 60 ° "from 2tL to 3 - 2Y in Fig. 4 - 90 °; in Fig. 5 2 ° C 120 °; in Fig. 6 the relative position of the irradiating linearly polarized light and the test object. Test object 1 contains two flat optical elements a and b, which are set at an angle of 2c6 to each other. Irradiated light 2 falls on the surface H reflected from it light 3 - on the surface b and reflected from the surface b the light 4 is directed to the photodetector of the measuring device (4 mg. 2- 4) The reflection coefficient of such a test object depends on the refractive index of the material of the test object, an angle of 2-6 between two flat optical elements a and b, and for linearly polarized light, on the direction of polarization of the irradiating light. The test object is designed for double reflection of the incident light (from surfaces a and b). Thus, the test object corresponds to the working conditions of the angle of 2ct- defined by the inequality 60 (Fig. 1 and 5). The reflection coefficient is transparent to the test object, depending on the orientation of the linearly irradiating illuminated light. formalism of the vector and Jones matrix. The plane of incidence of the irradiation light on the test object is chosen perpendicular to the line of intersection of the planes a and b (Fig. 6). In this case, the direction 5 of the self-polarization of the test object, i.e. the direction for which the P-polarization of the irradiating linear polarized light does not change, is also perpendicular to the intersection line of the flat optical elements a and b. The reflection coefficient of the test object depends on the angle p between the direction 6 of the polarization of the irradiating light and the direction 5 of the own polarization of the test object. The reflection coefficient R of test volume 1 is equal to the sum of the squares that make up the Jones vector at the output of the test object E RpocverH + | Е R2 cos + + R | ). The Jones vector of the output of the test object is OUT Object (p) -Epoliz. toUi - I - Jones matrix, describing the reflection from the test object; cosj) a sinp matrix of rotational orientation describing a change in the orientation of the irradiating linearly polarized light relative to the test object; Jones vector of irradiating linearly polarized light Rn is the reflection coefficient of the material of the test object for S (perpendicular) and P (parallel) components of the irradiating light; angle between the direction of polarization of the irradiating light and the direction of self-polarization of the test object. The exclusion patient R is tested from the value of R R between the direction of the polarizing light and the directional polarization of the test O, to the value R Rg 0 ° L. 1 shows the angles of which R is 1.8%) With the angle difference 2 between the planar elements and the differences of the refractive index of the test object.

As can be seen from the table. 1, the interval of the angles p, for which the calibration correction is determined, at intermediate values of n must lie in the range of O -90.

The measurement of the ratio of a 15-layer bilayer antireflection coating in the spectral range 640-760 nm is made using an MSFP-2 microscope spectrophotometer and using the proposed method and test object. Relative measurement accuracy of the reflection coefficient of the device

MSFP-2 is ± 1.5% with R 1% and + 0.08% with R 1% 2.

The accuracy of measuring the reflection coefficient using the proposed method and test object is determined by the accuracy of setting the angle p, i.e. accuracy of installation of the polarizer. When using a polarizer with an angle setting accuracy, the reflection coefficient measurement accuracy is 0.005%.

The measurement results are shown in Table. 2

table 2

From tab. 2 shows that the relative, Q on the measurement error on the MSFP-2 device reaches 80%, and using / ./,

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Claims (2)

1. A method of measuring the reflection coefficient, including irradiating a test object with a known reflection coefficient by the light flux, measuring the reflection coefficient of the test object, calculating a photometric calibration correction for the difference between the known and measured reflection coefficients, measuring the reflection coefficient of the studied object and calculating the real reflection coefficient of the studied object from The measured reflection coefficient and photometric calibration correction are distinguished by the fact that, in order to to improve the accuracy of measuring reflection coefficients less than 1.8%, the test object is irradiated with linearly polarized light, the dependence of the reflection coefficient of the test object on the angle p between the direction of polarization of the irradiating light and the direction of proper polarization of the test object in the angle range y 0-90 °, and the photometric calibration correction & K (p) is determined from the relation 4 8 ^) = R ^ cos ^ - R * »si.ny>, where and Rp is the reflection coefficient <Г of the test object. for the S and P components of the irradiating light; S - component of the polarization of light perpendicular to ^{: - the} plane of incidence; P is the component of the polarization of light parallel to the plane of incidence. 2. A test object for measuring reflection coefficient, comprising a flat optical element made of a material with a refractive index of 1.3-4.0, characterized in that, in order to improve the accuracy of measuring reflection coefficients less than 1.8%, an additional second flat optical element is introduced at an angle of 60 ° <2ο (<120 °.