SU1402864A1 - Method of measuring reflection factor of optical material - Google Patents

Abstract

The invention relates to the field of optical instrumentation and can be used in assessing the quality of optical glass by absorption and reflection losses. The purpose of the invention is to increase the accuracy of the reflection coefficient measurement. Two samples are used. Comparisons, characterized by transmittances, and the reflection coefficient of the test material is determined by (ah-a, c) Zpl + Ca / (a,), where r is the reflection coefficient of the test material; aj (and PA and 3) (d - reflexometer readings for radiation fluxes, reflected by the test material, plane-parallel and wedge-shaped reference samples, respectively; D ,, transmittance coefficients of the plane-parallel and wedge-shaped comparison samples. 5 СО

Description

The invention relates to photomethods, rii and can be used in optical instrument making in assessing the quality of optical glass by absorption and reflection loss.

The purpose of the invention is to improve the measurement accuracy by eliminating the need to determine the reference reflectance of the comparison sample.

: The method is carried out as follows.

; As a comparison sample, you choose: a plane-parallel plate i with a measured transmittance and a wedge-shaped plate with a measured% transmittance, both of which comparison samples must be made of a non-absorbing and non-scattering material. To determine the coefficient: Г the reflections of the sample under study, measurements are made of the fluxes reflected by the sample (a), the sample’s (a), shgoskopa- parallel plate (a) and the wedge-shaped 1 plate (.).

; The coefficient g of the reflection of the test material is determined by the formula

1 iSxlSj AiJi-nA-iiS p.G. ,

gx: x

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where a. and a c are the quantities characterizing the radiation fluxes, reflected respectively by the test material, plane-parallel and wedge-visible comparison patterns; PLO 1 is the transmittance of plane-parallel and wedge-shaped comparison samples, respectively.

The essence of the method is as follows.

Coefficient measurement; The reflection of the test sample without a reference can be considered as finding the sample location on the shsal of reflection coefficients by interpolating between the reference points (zero and one) corresponding to the imaginary standards (absolutely black body and perfect mirror). In any real reflexometer, the scale of the reflection coefficients is not strictly linear. When using any receivers and amplifying circuits, the output device reading for various reasons is not strictly proportional to the radiation flux reaching the receiver:

0

0

five

0

i

The true scale of reflection coefficients of an refractometer between zero and one is an unknown function, only close, but not coincident with a straight line. The reflection coefficient of the sample, measured as the ratio of the reflected flux to the incident one, will contain an error due to the nonlinearity of the photometric characteristics of the reflexometer ranging from zero to one. This error is a little less when the scale section from the reflection coefficient of the standard to one (or from zero to the reflection coefficient of the standard) is used for interpolation. The proposed method uses two silica glass ethanol with reflection coefficients approximately equal to 0.0350 and 0, 0687. Deviations from linearity on such a narrow interval of the scale are incomparably smaller than on the whole scale, and consequently, there will be less measurement error of the test sample, the reflection coefficient of which falls within this interval. But these considerations are valid only under the condition that the reference reflection coefficients of the standards are as reliable as zero and one in ab-. salt method. Therefore, such standards have been selected for which the transmittance, rather than the reflection coefficients, is to be measured. Measurement of the transmittance can be done with an error not exceeding 10,0005, the same accuracy will be valid for the reflection coefficient of the plane-parallel pattern, and for the wedge-shaped the error will be even smaller, no more than +0,0003.

In addition, the essence of the proposed method is that when implementing the method, two samples are used at the same time with the reflection coefficients of one obviously larger, and the second, obviously lower than the expected reflection coefficient of the test glass, and these samples are measured so that not necessary, it is enough to know the transmittance. These two properties, generally speaking, are completely independent, but one can imagine such comparison patterns for which the reflection coefficients are uniquely associated with these coefficients. In fact, you can

select reference samples made in the form of plane-parallel and wedge-shaped plates 2-5 mm thick made of quartz glass. Absorption and scattering in a quartz glass of such thickness is immeasurably small. Multiple reflection beams in a plane-parallel plate are added to the transmitted and reflected streams, and all that is not passed is reflected from two surfaces, i.e. The coefficient g g ,,, of the reflection of a plate is unambiguously expressed through its transmittance f:

1,707. For higher refractive and highly reflective glasses, it is more profitable to use comparison samples.

from sapphire, which makes it possible to measure the reflection coefficients of all optical glasses and most optical crystals with n 2,247. An analysis of the calculation formula indicates that the contribution of transmittance errors to the reflectance error of the test material is about 0.0003.

Claims (1)

Invention Formula ch  the wedge beams of multiple reflections go to the sides, not added either to the transmitted stream or to the reflected from one first surface. Since the coefficient / C of the wedge transmission is  kA  (l-r.,) i, TO Hz reflection coefficient is cl one - Such comparison samples do not need to measure their reflection coefficients, it is sufficient to measure their transmittances J ,,. and cd Believed that the signals a at n / i and a cl the receiver of the reflexometer is pro- grammed to the streams falling on it, reflected respectively by the test glass with the reflection coefficient g, plane-parallel and wedge-shaped comparison samples, it is possible to make a proportion: UKL cells ah - akl a pl a cl from which it is easy to obtain a formula for calculating the reflection coefficient of the test glass from the transmittance of the two comparison samples and the readings of the reflectometer for them and for the test glass. Quartz glass comparison samples allow measurement of the reflection coefficients of optical glasses with a refractive index from 1.458 to 0 five 0 A method for measuring the reflection coefficient of optical materials, including measurement of radiation fluxes reflected by the test material and the first comparison sample in the form of a wedge-shaped plate, characterized in that, in order to improve accuracy, the radiation flux reflected by the second reference sample, made in a parallel plate, and the transmittance of both comparison samples, while the comparison samples are made of nonabsorbent and non-scattering material, and the reflection coefficient jf g test material is determined by the formula 35 , () Jni + (anu.-ax) t i - - - -) PL KA 0 five 0 where a, a „, and a n and / 1 кл the values characterizing the radiation fluxes are reflected, respectively, by the test material, plane-parallel and wedge-shaped comparison samples; the transmittance of the plane-parallel and wedge-shaped comparison samples, respectively.