SU811121A1 - Absortion meter - Google Patents

Description

The invention relates to the field of technical physics and can be used to measure small (K) indicators of the absorption of solid materials. Devices are known for measuring by a calorimetric method small optical absorption indices 1, 2. A disadvantage of these devices is the large measurement error associated with measuring a large number of parameters. The closest technical solution to the claimed is an absorptiometer for measuring small optical absorption, containing a monochromatic SOURCE with COLLIMATED radiation, a vacuum chamber with transparent windows, in which the sample and reference holders are placed and a compensation circuit for measuring the temperature difference 3. However allows to measure the absorption indices only of optically isotropic and non-rotating plane of polarization of materials. In order to obtain the K value, it is necessary to measure the power of the monochromatic source, the temperature increment of the sample relative to the reference sample (reference) and the thermal time constant of the sample, which significantly increases the measurement time. In this case, the incidence of measurement K is determined by the total error introduced by measuring all these parameters. The aim of the invention is to expand functional possibilities and increase the accuracy of measurements. The goal is achieved by installing a device consisting of two identical dielectric mirrors and a graduated absorbing optical wedge between the sample and standard holders, the device and the sample and standard holders being installed so that the plane passing through the beam going from the sample, and the beam reflected from the first mirror is orthogonal to the plane passing through the beam incident on the second mirror and the beam reflected from it and falling on the standard, while the angle of incidence of the beam on the first The mirror is equal to the angle of incidence to the second and smaller values for the Brewster angle mirror material. The drawing shows a diagram of the absorptiometer. It contains a monochromatic source} with collimated radiation, a vacuum chamber 2 with transparent windows, which serves to reduce heat transfer from the samples, holders with the measured sample 3 and the standard 4, a compensation circuit 5 for measuring the difference of their temperatures, a recording device 6. Moreover, between the sample and A standard installed a device consisting of two dielectric mirrors 7 and 8, made of the same material, and a graduated optical absorbing wedge 9, made of an optically isotropic material yala

The sample to be measured is a cylinder with 1 FLAT polished ends. The standard has the same geometry with the sample being measured and is in identical thermal insulation conditions with it.

The device allows to measure small values of absorbed by equalizing the heating rates of the sample and the reference using a wedge 9. The measurement result does not depend on the degree and preferential direction of the polarization of the monochromatic source, as well as on the optical activity of the sample being measured. Measurements, as in a number of known calorimetric devices, occur in a linear region, i.e., when the sample temperature is incremented in proportion to the time of exposure to the radiation source.

The device works as follows.

The beam with the power / o from a collimated monochromatic source / through a highly transparent window enters the vacuum measuring chamber 2 and then onto the measured sample 3 with a length of about several cm. Radiated power ./), absorbed by the sample, being equal to

/, / o- / o / - - “/ o / Cd where d is the sample length;

.

Accordingly, the radiation power / 9, transmitted by the sample, is equal to

one -/

/about,

/ 2 1 -Ь /

where R is the reflection coefficient of the sample material.

Further, the working beam is successively reflected from mirrors 7 and 5 (the mirrors are transparent to the incident radiation), passes through a wedge 9, structurally designed in such a way that it represents a plane-parallel plate of variable thickness, the entrance and exit surfaces of which are perpendicular to the direction of the beam. The beam then hits the standard 4 with the known absorption coefficient Sa. The independence of the attenuation of the radiation passing through the device from the state of polarization and its preferential direction in the beam is achieved by adopting the relative position of the sample, standard, mirrors and wedge relative to the source of monochromatic radiation. In this case, the attenuation of the intensity after the mirrors is

L "1f) (" 1f), where) and p (| f), respectively, the reflection coefficients for light polarized in the plane of incidence and perpendicular to it incident at an angle φ on the dielectric mirrors 7

and 5 with a refractive index of p. The absorbance index of the standard material is 1 cm and is measured on a spectrophotometer. Since the measured / С does not exceed., The device should be weakened no less than 10 times. Therefore, the reflecting elements and the angle of incidence on them are chosen so that they weaken the radiation by about two degrees, and the building structure is more accurate.

wedge. Due to this, the attenuating device does not overheat. The measurement itself is as follows. In the heating process, using the attenuator 9, to ensure the same rate of heating of the sample and the standard. Then the temperature difference detected by the device 6 will not vary in time. The measured absorption rate is calculated using the following formula:

K - R R K

A.- K.Kr.I., 1

where t is the transmission of the optical wedge;

p and re are, respectively, the density of the sample material and the standard; C and Ce - their specific TB. Capacity.

If more attenuation is required, the device is entered into an even

the number of pairwise identical mirrors.

The described device does not require special equipment for measuring the total light energy passing through the crystal under study.

In addition, the measurement does not require measurement of the heat transfer parameters of the sample. Thus, by reducing the number of parameters to be measured, the time is significantly reduced.

measurement and information processing.

Claims (3)

1.Witte N.N. Determination of Low Bulk absorption coefficient. Applied Optics, V 11, No. 4, 1972, p. 777. 2. PinnoM D. A., Rich T. C. Development of the Calorimetric Method for Making the Optical Absorption Measurement. Applied Optics, v. 12, No. 5, 1973, p. 984-992. 3. Johnson D.C. Measurement of Low Absorption -Coefficients in Crystals. Applied Optics, V 12, No. 9, 1973, p. 2192-2197.