SU1402853A1 - Method of determining dimensions of microparticles - Google Patents

Abstract

The invention relates to measurement instrumentation and can be used to determine the size of microparticles in a gas or liquid medium, as well as on a polished surface. The goal is to simplify the method by using relative measurements and improving the accuracy of sizing by eliminating the dependence on the position of the microparticle relative to the axis of the illuminating laser beam. Microparticles illuminate the combined beams of two lasers, generating radiation at two different wavelengths. Light scattered by microparticles is recorded separately at two wavelengths corresponding to the radiation of the first and second lasers, and the size of the microparticles is determined by the ratio of the two scattered light intensities. 1 il. i (L

Description

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The invention relates to measurement instrumentation and can be used to determine the size of microparticles in a gas or liquid medium, as well as on a polished surface (in particular, the invention can be used to analyze the size distribution of microparticles dust in the spirit, to control the contamination of technological liquids, such as de-ionized water, in semiconductor manufacturing, to control the surface contamination of polished surfaces of optical mirrors and conductor wafers), object of the invention - an increase accuracy | mikrocha- in the determination of the sizes; ticles by eliminating dependence; From microparticles position relative to the axis of the illuminating laser beam, the drawing shows a block diagram of an apparatus for carrying out the method predla- gaemogr.

The device contains the first 1 and second 2 lasers, dichroic focusing mirror 3, 6JIOK 4, scanning unit 5, lens 6, polished; plate 7, on the surface of which there are microparticles, integrating sphere 8, first 9 and second 10 light filters, first 11 and second 12 photomultipliers and signal processing unit 13.

The method is carried out as follows;

Light from lasers 1 and 2 with lengths; waves X and D are incident on a dichroic

eg

jA, g J- p / J-p

and determine the size of the microparticles using preliminary calculations or a calibration curve.

The basis of the method based on the functional dependence of the intensity -. scattered light from microparticle size:

I ras I f

i

one)

g A

20

25

where IP is the intensity of the input light;

-radius particles;

-wavelength

When the laser is operating on the fundamental mode, the radiation intensity in any beam cross section is described by the Gaussian function

 1o "

X / tiJ

(2)

where 1 „

thirty

X

W

center intensity

beam;

distance from beam axis;

spatial parameter

intensity distribution. In the case of a particle not in the center of the beam, where the light intensity is maximum, but on the edge, where it is much smaller, the photodetector registers: 35, the weaker intensity

scattered light, which will lead to the apparent underestimation of the size of the microparticles, and consequently, to the deterioration

accuracy of measurement, i.e. there is a mirror 3, which combines both pu-40 dependence of measurements on the coordinate

ka Then, the combined beam passes through the focusing unit 4, the scanning unit 5, the lens 6 and hits the surface of the optically polished microparticle plate 7. 45

The light scattered by microparticles is collected by means of an integrating sphere 8, directed to light filters 9 and III, which separate the scattered light.

radiation 1p and 1p according to wavelength l, and AI and register it with the appropriate photomultipliers 11 and 12 for

X, Simultaneous illumination of microparticles with a second laser beam with a different wavelength from the first, the formation of both beams with the same intensity distribution over their cross section, the combination of these beams and the separate registration of scattered light for each wavelength allows determining the size of the microparticles according to the intensity ratio of the scattering light recorded at the above wavelengths, and therefore more accurate measurement results. As can be seen from the following formulas, the ratio / i of the intensities of the scattered light at two wavelengths / ,. and D is a function only of the size of the particles and when it is.

50

each wavelength separately. The signals from the photomultiplier outputs are fed to the signal processing unit 13, where the ratio / J intensive is determined; .l 1

noses 1

and I

p scattered light.

eg

jA, g J- p / J-p

and are determined once

microparticle measures using preliminary calculations or a calibration curve.

The basis of the method based on the functional dependence of the intensity -. scattered light from microparticle size:

I ras I f

i

one)

g A

where IP is the intensity of the input light;

-radius particles;

-wavelength

When the laser is operating on the fundamental mode, the radiation intensity in any beam cross section is described by the Gaussian function

 1o "

X / tiJ

(2)

where 1 „

0

X

W

center intensity

beam;

distance from beam axis;

spatial parameter

intensity distribution. In the case of a particle not in the center of the beam, where the light intensity is maximum, but on the edge, where it is much smaller, the photodetector registers: 5, the weaker intensity

scattered light, which will lead to the apparent underestimation of the size of the microparticles, and consequently, to the deterioration

five

X, Simultaneous illumination of microparticles with a second laser beam with a different wavelength from the first, the formation of both beams with the same intensity distribution over their cross section, the combination of these beams and the separate registration of scattered light for each wavelength allows determining the size of the microparticles by the intensity ratio of the scattered light recorded at the above wavelengths, and therefore more accurate measurement results. As can be seen from the formulas below, the ratio i of the intensities of the scattered light at two wavelengths / ,. and D is a function only of the size of the particles and when it is.

0

the evaluation eliminates the need to find the position (x coordinates) of this particle relative to the beam axis:

g

Where

-li and 1 (

nd LL, lo e f,

l

IP Ig e 1 I and ij

AI)

(3

f -) i l, 1

- intensity in the center of beams at wavelengths and, accordingly, Aj.

Since the spatial intensity distribution over the cross section is the same for both laser beams, i.e. Wj, the dependence (3) has the form

/ i

- I. fi (r / X,)

I about f, (r /,)

(four)

about 2. / L2

Thus, using the proposed method (unlike the well-known ones), reliable results are obtained without

taking into account the position of the microparticles relative to the center of the cross-section of the solar light 25, a separate method is used to determine the size of the micro particles, including the illumination of the micro particles by the first monochromatic laser beam, the relative displacements of the micro particles and the illuminating laser beam, the analysis of the scattered light parameters characterized by the fact that, in order to determine the accuracy of dimensions by eliminating the dependence on the position of the microparticle relative to the axis, the laser beam, the microparticles are additionally simultaneously illuminated by a second monochromatic laser beam with a wavelength different from that of the first monochromatic laser beam, and both beams are formed with the same intensity distribution over their cross section and direct them coaxially, registering

ten

15

20

25 light of the sun is carried out. The formula of the invention is

The method of determining the size of microparticles, including the illumination of the microparticles by the first monochromatic laser beam, the relative displacement of the microparticles and the illuminating laser beam, recording the light scattered by the microparticles, analyzing the parameters of the scattered light, so as to determine the size accuracy by elimination of dependence on the position of the microparticle relative to the axis of the illuminating laser beam; the microparticles additionally simultaneously illuminate the second monochromatic laser beam th of a wavelength different from the wavelength of the first monochromatic laser beam, both beam forming with the same intensity distribution over their cross-section and fed them coaxially races registration

grain beam, which in turn improves the accuracy of determining the size of microparticles.

but at each wavelength, and the size of the microparticles is determined by the ratio of the intensities of the scattered light.

Claims (1)

Claim A method for determining the size of microparticles, including illumination of the microparticles with the first monochromatic laser beam, the relative movement of the microparticles and the illuminating laser beam, registration of the light scattered by the microparticles, analysis of the parameters of the scattered light, characterized in that in order to increase the accuracy of sizing by eliminating the dependence on the position of the microparticles relative to the axis of the illuminating laser beam, the microparticles are additionally · simultaneously illuminated by a second monochromatic laser beam with a wavelength different from the wavelength of the first monochromatic laser beam, both beam forming with the same intensity distribution over their cross-section and naucheta microparticles position relative to the center of the cross section of the laser beam, which in turn improves the accuracy of determining the size of the microparticles. they are controlled coaxially, scattered light is recorded separately at each wavelength, and the sizes of microparticles are determined by the ratio of the intensities of the scattered light.