RU1770850C - Method of determining spectral directional - hemispheric refraction coefficients of specimens - Google Patents

Abstract

Usage: study of the photometric characteristics of the samples. SUMMARY OF THE INVENTION: a beam section is scanned by a radiation detector or an opaque screen with a hole, current coordinates and voltages of scanned section points are measured, and the reflection coefficient of samples is determined by the formula, 3 ill.

Description

The invention relates to the field of studies of the photometric characteristics of materials, and more particularly, to a technique for measuring spectral directional hemispherical reflection coefficients of samples of materials.

A known method for determining spectral directional hemispherical reflection coefficients, in which the sample and the standard are illuminated sequentially normal to the surface and the intensity of light reflected in the opposite direction is measured, the indicatrix of the back reflection of the sample is measured, the standard and the sample are illuminated at a given angle of incidence and measured the intensity of light reflected in the mirror direction, as well as the angle of rotation of the sample, at which the intensity of reflected light is reduced by 2 times compared to mirror direction, -leniem. and from the results of the measurements, a directional hemispherical reflection coefficient is calculated.

Closest to the invention is a method in which the measured and reference samples are illuminated,

successively placed in the focus of a concave parabolic mirror, using monochromatic light from the side of the parabolic mirror, the measured sample being illuminated at an angle p0 and the reference one at an angle at which it is certified, the radiation reflected by the samples is received and the corresponding voltages U0 and Ue are measured the output of the radiation receiver, placed in the focus of an additional parabolic mirror, coaxial with the first and facing a concave surface, and the directionally hemispherical coefficient is reflected emogo measured sample is found from the ratio:

. p (2rg) / Ee (d, 2l) -.

where re (re. 2) is the passport value of the reflection coefficient of the reference sample.

However, if the radiation response has an uneven angular sensitivity, then the reflection coefficient of the measured sample is determined quite accurately only in the Hume case when

Xi

x | Oh ro

word about

The strange reflection indicatrices of the measured and reference samples are approximately the same. Otherwise, the reflection coefficient of the measured sample is determined with an error, the value of which depends on the nature of the angular sensitivity of the receiver and the type of reflection indicatrix of the measured and reference samples. In addition, additional errors may arise due to the screening of radiation reflected by the samples by structural elements, for example, the samples themselves, mirror frames, etc.

The aim of the invention is to increase the accuracy of determining the spectral directional hemispherical reflection coefficient of the measured sample by reducing the error associated with the uneven angular sensitivity of the radiation receiver. The increase in accuracy achieved by using the invention is confirmed by calculations. An additional advantage of the invention is the possibility of increasing accuracy by taking into account the shielding by structural elements of the reflected radiation of the samples, as well as the ability to measure the relative spatial reflection patterns of the samples.

The goal is achieved by the fact that in the known method, in which the measured and reference samples are illuminated, successively placed in the focus of a concave parabolic mirror, with monochromatic light from the side of the parabolic mirror, the measured sample is illuminated at an angle p0, and the reference one is illuminated at an angle (fa at which it is certified, the radiation reflected by the samples is received and the corresponding voltages at the output of the radiation receiver are measured, the beam section of the beam is scanned sequentially for each of the samples formed by a parabolic mirror, the current coordinates of the scanned cross-section points are measured, the radiation reflected by the samples is received, and the voltages are measured for each scanned cross-section point, and the spectral directional hemispherical reflection coefficient of the measured sample is determined by the formula:

p (p0) 2l) re (re, 2l) x

, Uo (y.z) .. 4 S (V) dS

f HaCv.fl dS

sJ3 S (y) dS

where RE (re, 2 L) is the passport value of the reflection coefficient of the reference sample;

y, z - current coordinates of scanned

beam cross-section points relative to the optical axis of the beam;

Uo (y, z); Ua (y, z) are the dependences of the output voltages of the radiation receiver on the coordinates y, z under illumination, respectively

measured and reference samples;

S (} 3 is the dependence of the sensitivity of the radiation receiver on the angle of incidence of light on the receiver;

Sol 5e - cross-sectional area

beams formed by a parabolic mirror when illuminated, respectively, of the measured and reference samples.

Scanning a section of a beam of rays formed by a parabolic mirror,

can be done in two ways. In the first method, scanning is performed by moving the radiation receiver, and in the second, by moving an opaque absorbing screen with an aperture,

In this case, the radiation reflected by the samples is received by a radiation receiver placed in the focus of an additional parabolic mirror, coaxial with the first and facing a concave surface.

Figure 1 shows a diagram of a device that implements a method for determining reflection coefficients, in which the scanning is carried out by moving

radiation receiver; Fig. 2 is a diagram of a device in which scanning is carried out by moving an opaque absorbing screen with a hole; Fig. 3 shows graphical dependences of the error in determining the reflection coefficient on the illumination angle of the sample for these methods, as well as for the prototype method.

The invention is illustrated by the following examples. The device comprises a lightproof chamber 1, a parabolic mirror 2, a measured (reference) sample 3, mounted in the focus of the mirror 2, a flat mirror 4, located under

45 ° to the optical axis of mirror 2, radiation detector 5, illuminator 6, consisting of a light source 7 with a diaphragm 8, a shutter 9 and a radiation receiver 10 of the reference channel. Light Diameter Do Mirrors 2

is selected from the condition Do 4f, where f is the focal length of mirror 2. Flat mirror 4 has the ability to linearly move in a direction perpendicular to the optical axis of mirror 2. which allows

change the angle of incidence of light on the sample 3. The radiation detector 5 can be moved by means of a scanning device in a plane perpendicular to the optical axis of mirror 2. The spectral directional hemispherical reflection coefficient is determined as follows. The measured and reference samples are sequentially placed in the focus of mirror 2, and the flat mirror 4 is set in a position that provides illumination of the samples at the required angles. The light source 7 forms a parallel beam of monochromatic light rays. The source beam modulated by the shutter is sequentially reflected from mirror 4, mirror 2 and falls on the sample, and also after reflection from the shutter it enters the reference channel receiver 10. The radiation reflected by the sample is collected by mirror 2, which forms a parallel beam of rays. By moving the receiver 5, a section of the formed beam is scanned, while the current output voltages of the receiver 5 and receiver 10 are fed to the input of a computing device that calculates the current coordinates y, z of the receiver 5 relative to the optical axis of the mirror 2, and also normalizes the values of the output voltages the receiver 5 relative to the output voltage values of the receiver 10. After performing these operations for the measured and reference samples, the computing device determines the reflection coefficient of the measurement direct sample according to the above relation, where Uo (y, z). U3 (y, z) are the dependences of the normalized values of the output voltages of the receiver 5 on the coordinates y, z when illuminating, respectively, the measured and reference samples. When scanning, the sensitive area of the receiver 5 is at the same angle to the incident radiation; therefore, the value of S (y) is constant and, after putting the integral in the numerator and denominator of the expression, can be reduced.

The device in figure 2 contains the same elements as the device in figure 1, as well as an additional parabolic mirror 11, coaxial with the mirror 2 and facing it with a concave surface, and an opaque absorbing screen 12 with a hole 13. Screen 12 using the device the scan has the ability to move in the plane perpendicular to the optical axis of the mirrors 2 and 11. The receiver 5 is mounted at the focus of the additional mirror 11. The reflection coefficient is determined as follows. The measured and reference samples are also illuminated. as in the previous device. The radiation reflected by the sample is collected by a mirror 2, which forms a parallel beam of rays. A part of the generated beam passes through the hole 13 of the screen 12 and, reflected from the mirror 11, falls on the receiver 5 at an angle y equal to

arctg

4 f used 2 4G 2-u2- 2

where y, z are the coordinates of the hole 13 relative to the axial axis of mirrors 2 and 11;

f is the focal length of the mirror 11.

By moving the screen 12, a section of the formed beam is scanned by the hole 13, while the current output voltages of the receivers 5 and 10 are supplied to the input of a computing device that calculates the current coordinates y, z of the hole 13, the current values of the angle of incidence y, determines the corresponding sensitivity values S ( x) of the receiver 5, and also normalizes the values of the output voltages of the receiver 5 relative to the values of the output voltages of the receiver 10. After performing the above operations for the measured and reference samples in numeral device determines the measured reflectance of the sample according to the above relation.

The values of the output voltages of the receiver 5 in the described devices are normalized in order to exclude the influence on the measurement results of the power drift of the light source 7 With a high stability of the source, the reference channel in the devices may be absent, and computational operations may be performed directly with the output voltages marriages of receiver 5

As an example, FIG. 3 shows the calculated dependences of the relative error in determining the reflection coefficient of the sample from the angle of illumination of the sample p0, confirming the effectiveness of the invention, where curve 1 corresponds to the error in determining the reflection coefficient using the described devices, and curve 2 for devices that implement the prototype method. Calculations for the measured sample with a half-width of the indicatrix of light intensity at the level of 0.5. 20 ° for a diffusely reflecting reference sample and a radiation receiver with a cosine dependence of the angular sensitivity. Light Diameter and Focal Values

The distances of parabolic mirrors in the calculations were taken equal to 240 mm and 60 mm, respectively, and the diameter of the samples was 20 mm.

Claims (3)

1. A method for determining spectral directional hemispherical reflection coefficients of samples, which illuminate the measured and reference samples, successively placed in the focus of a concave parabolic mirror, with monochromatic light from the side of the parabolic mirror, and the small sample is illuminated at an angle p0, and the reference one is illuminated at an angle pe at which it is certified, the radiation reflected by the samples is received and the corresponding voltages are measured at the output of the radiation receiver, and the efficiency is in order to increase the efficiency by reducing the error associated with the uneven angular sensitivity of the radiation receiver, the section of the beam of rays formed by the parabolic mirror is sequentially scanned for each of the samples, the current coordinates of the scanned section points are measured, the reception of radiation reflected by the samples, and voltage measurements are made for each scanned cross-sectional point, and the spectral directional hemispherical reflection coefficient of the measured sample is determined by the formula p (po, 2) -re ((re, 2 p) X 7 and Uo (y.z) sCxr dS 5s3 b (y) where re (re, 2 tg) is the passport value of the reflection coefficient of the reference sample; y, d are the current coordinates of the scanned 10 points of the beam cross section relative to the optical axis of the beam; Uo (y, z), U3 (y.z) are the dependences of the output voltages of the radiation receiver on the coordinates y, z when illuminating, respectively, 15 measured and reference samples; S (y) is the dependence of the sensitivity of the radiation receiver on the angle of incidence of light y on the receiver; So, 5e is the cross-sectional area of 20 beams formed by a parabolic mirror when illuminated, respectively, of the measured and reference samples. 2. The method according to claim 1, about t, l and ch and yu and with the fact that scaling the cross section of the beam of rays 25 is produced by moving the radiation receiver. 3. The method according to claim 1, characterized in that the scanning section of the beam of rays is carried out by moving the opaque 30 of the absorbing screen with an aperture, and the radiation reflected by the samples is received by a radiation receiver placed in the focus of an additional parabolic mirror coaxial with the first 35 and facing a concave surface. Figure 1 S. about/ ) /ABOUT so twenty /ABOUT 7 // FIG. 2 / / 7