SU851208A1 - Device for measuring reflection factors - Google Patents

Description

(54) DEVICE FOR MEASURING COEFFICIENTS

I

The invention relates to a measurement technique and can be applied in research and analysis of materials by measuring reflection coefficients.

A device for measuring the reflection coefficients of a polished surface, made in the form of a radiation source, a measured part and a radiation emission monitor, in which a measured part is introduced and output from a light beam, is known. In the measurement, the total incident light flux 1 is taken as the reference.

A disadvantage of the known device is that the light beam turns over after reflection from the mirror under study. Due to the fact that radiation receivers have non-uniform sensitivity over the receiving area, turning the beam causes a systematic measurement error.

The closest in technical essence to the present invention is a device containing optically coupled between itself a source and a radiation receiver, periodically entered into a beam standard. As a reference in this device using

A dielectric plate, the reflection coefficient of which is calculated using Fresnel formulas, or an aluminum coated glass plate, the reflection coefficient of which is about 0.90.

 However, the reflection coefficient of the aluminum coating is determined with low accuracy (± 1%), the coating is aging and, therefore, the reflection coefficient is changing. All this limits the accuracy of measurements of large, close to unity, reflection coefficients.

The purpose of the invention is to improve the accuracy in measuring reflection coefficients close to one.

This goal is achieved by the fact that

15 device containing an optically interconnected source and receiver of radiation, periodically introduced into the beam standard, the latter made in the form of an optical system of one-time full internal reflection with a face of total internal reflection parallel to the optical axis of the device, and on both sides of the sample under study two identical symmetrical trihedral prisms that together with the sample under study are a symmetric optical system such as the Watersworth scheme.

In this case, the optical system of single full internal reflection is made in the form of a Dove prism made up of 5 trihedral prism of total internal reflection and a tetrahedral prism with faces parallel to the output face of the trihedral prism, while the prisms are separated by an air gap.

FIG. 1 shows the scheme of the device, when working with the standard; in fig. 2 - the same when working with the test sample.

The device includes a radiation source 1, a radiation receiver 2, a test sample 3, symmetrical trihedral prisms 5 and 4, a trihedral prism 6 of total internal reflection, a tetrahedral prism 7.

The standard is a prism of total internal reflection of the Dowe prism type, the reflecting face of which is parallel to the optical axis of the device. To eliminate the difference in radiation losses on the refracting faces of the prisms in the reference and working channels, the reference is made as a combination of two prisms 6 and 7, separated by an air gap. The prism 6 is a triangular total internal reflection, with three working faces, the reflecting face of which is parallel to the optical axis of the device. Prism 7 is four-sided, with two working faces that are parallel to each other and parallel to the output face of prism 6. Prisms 6 and 7 complement each other up to Dowe prism.

To create the same working conditions, prisms 4-7 are made of the same material. 35

The device works as follows.

A reference — a system of prisms 6 and 7 — is introduced into the working beam. Light from the radiation source 1 passes through a parallel beam through prisms 6 and 7, having undergone a total internal reflection in the prism 6, and hits the radiation receiver 2. The signal taken from the radiation receiver is taken as J o. and corresponds to the reference reflection.

Then the prisms 6 and 7 are removed from the beam, 45 and in their place are the prisms 4 and 5 with test sample 3 between them. The light from the radiation source 1 passes through a prism 4, hits the sample under study 3, is reflected from it and, after passing

through a prism 5, enters the radiation receiver 2. The signal J, taken from the radiation receiver, characterizes the reflection from the sample under study. The reflection coefficient is determined by the formula

R Comparative tests of the proposed device show that the accuracy of measurements of reflection coefficients close to one increases by an order of magnitude. In addition, systematic measurement errors are eliminated due to uneven sensitivity across the receiving area of the photodetector, due to the fact that both the reference and studied channels have the same number of reflections.

Claims (2)

1. A device for measuring reflection coefficients containing optically interconnected source and receiver of radiation, periodically introduced into the beam standard, characterized in that, in order to improve the accuracy of measurements of reflection coefficients close to one, the standard is made in the form of a single optical system total internal reflection with the edge of total internal reflection parallel to the optical axis of the device, and on both sides of the sample under study two identical symmetrical trihedral prisms are installed Together with the sample under study, s constitute a symmetrical optical system such as the Watersworth scheme. 2. A device according to claim 1, characterized in that the optical system of a single full internal reflection is made in the form of a Dowe prism composed of a trihedral total internal reflection prism and a tetrahedral prism with faces parallel to the output face of the trihedral prism, the prisms being separated by an air gap . Sources of information taken into account in the examination 1. Motovilov, O. A. On measuring the absolute values of the reflection coefficients. - OMP, 1968, No. 2, p. nineteen. 2. Kudr Vtseva, G. G., Fedotova G. S. A prefix to the spectrophotometer for measuring the reflection of light from the surface of samples with a diameter up to 300 mm. - OMP, 1976, No. 2, p. 73.