SU1608507A1 - Method of measuring gradient of refraction index of transparent objects - Google Patents

Abstract

The invention relates to physical optics and can be used to study the refractive index gradient of transparent objects with a rough surface in flaw detection, optics of scattering media, optical instrumentation and other areas of science and technology. The aim of the invention is to improve the accuracy of measurements and the expansion of the class of objects under investigation to samples with a rough surface. For this purpose, the intensity of the radiation transmitted by the speckle photograph of the set of zones of correlation of the surface of the object under study is measured. The method uses the recording of speckle photographs in a crossed polarizer and an analyzer, the irradiation of the resulting transposer with differently polarized radiation field components on the object's surface, measuring the intensity, which determines the refractive index gradient of transparent objects. 1 il.

Description

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The invention relates to physical optics and can be used to study the index of refraction in the thickness of open-faceted face glasses, cubic zirconias, plast-, etc., which is important in opium: optic, scattering media optics, first instrument making and other science and technology, inventions - increasing the point of measurement and expanding the class of shaken objects on samples with a wooded surface. la drawing shows a diagram of a device; TWA, which implements the method, the device contains a source of 1 gcheni, a quarter-wave plate 2, a polarizer 3, a telescopic system 4, an object 5, lenses

 6 and 7, analyzer 8, speckle photo 9 of the object surface, photoelectric receiver 10,

The method is carried out as follows.

A radiation source 1, such as an LG-38 laser, produces single-mode radiation. Plate 2 forms the circular polarization of the laser beam. Polarizer 3 transmits a laser wave whose polarization plane is perpendicular to the plane of incidence. The telescopic system 4, consisting of two lenses and a diaphragm between them, expands the beam and forms:

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The wave front is flat. This wave passes through object 5, on the surface of which, correlation zones are formed. Lens 6 projects a coherent image of the object's surface in the plane of speckle photograph 9. Analyzer 8 transmits light oscillations whose plane coincides with the plane of incidence. The resulting speckle photograph of the surface is projected by a set of radiation correlation zones that passes through: analyzer 8, which is rotated within the angles of orientation of the axis of the O-90 transmission relative to the plane of incidence. Lens 7 concentrates the flux transmitted through the speckle photograph 9 to the surface of the photoelectric receiver 10. Measurement of the intensity of the transmitted light by the speckle photograph system and the analyzer on changes in the orientation angle of the transmission axis of the light oscillation plane is obtained. with a rough interface between two environments. In the process of propagation of a plane wave front of linearly polarized radiation in the layer of matter with a gradient of the refractive index P (n), an elliptically polarized component arises in the transmitted laser radiation flux. The magnitudes of the ellipticity and azimuth of the polarization of the light wave D in the local part of the object are related to the local value of the refractive index gradient n1

by ratio

, And wj 1 v rg hj

The intensity of light fluctuations within the correlation zone, measured in a situation of a crossed polarizer and analyzer, is described by the expression

I; f-sin2. (),

5 0 5 n

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0

where is the orientation of the axis of the analyzer relative to the plane of incidence. The refractive index gradient of a transparent sample with a rough surface is calculated from the equation

 P (p) n dn Ql (o6),

I,.

where P (p) is the distribution of local values of the gradient of the refractive index over the entire sample area;

I (pt) is the intensity of the radiation that has passed through the speckle photograph of the correlation zones of the rough surface;

Q - proportionality coefficient, determined analytically by the following algorithm: „00 LPG

  4f

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 -pi P dp;) j,

where f (h) and R (p;) are the probability distributions of the heights of the asperities and azimuths of the polarization of the correlation zones, having the form.

one

f (h)

lk h.

where CO, and A; - respectively, the ellipticity and azimuth of the polarization of the light wave; - wavelength illuminating

Sveta; h j - the height of microroughness

rough surface of a transparent object.

As a result of the statistical modulation of the laser wave over the entire sample area, an ensemble of correlation zones with statistically distributed parameters and, and n is formed on the rough interface of two media; .

R (

R,-)

3-,. d

P1 2 l (

 f

xtgpi Ctg fi;) e} where hg is the mean value of the height mi

irregularities;

n is the refractive index of the substance of the object.

Therefore, based on the measured intensity I (ot) of light transmitted by the spectrum with the photograph of the correlation zones of the rough surface with different orientations of the axis of the analyzer, it is possible to uniquely determine the gradient 1

Dent is the index of refraction of pro- (large objects with a rough surface above the interface between two media.

The proposed method expands the power of measuring the gradient of the refractive index in the transparent sample; With a rough surface, which is unattainable in the known method, and also allows for the use of inaccurate measurements of this parameter, since the accuracy of the intensity measurement is 0.05%. Consequently, the method permits measurements of the refractive index gradient 2-3 times higher than the accuracy achieved in a known method, i.e. it is possible to measure the local value of the refractive index gradient of a transparent sample to a value of - 10.

F o

rmula of invention

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A method for measuring the gradient of the refraction of transparent objects, including the irradiation of the sample under study with laser radiation, the projection of the field of a diffuse sample of radiation into the plane of the photo layer, the recording of a speckle photograph of this

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l, sounding speckle photographs by laser radiation and recording; laser radiation transmitted through it, characterized in that, in order to increase the measurement accuracy and expand the class of objects to be examined on samples with a rough surface, irradiate the sample being examined with collimated laser radiation, the plane of oscillation of the vector of electric intensity perpendicular to the plane of incidence is projected the field of radiation scattered by the sample into the photollo plane through the analyzer, whose transmission axis coincides with the plane of incidence, the sounding of the registered The speckle photographs are taken by projecting onto it a coherent image of the surface of an object formed by its correlation zones through an analyzer that is rotated through an angle O - 90 relative to the plane of incidence, and during recording the dependence of the radiation intensity passed through the speckle photograph, measured from the angle of rotation of the analyzer, by which the gradient of the refractive index of transparent objects is calculated.

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Claims (1)

RMA of the invention, sounding speckle photography by laser radiation and registration of laser radiation transmitted through it, characterized in that 5 that, in order to increase the accuracy of measurements and expand the class of objects to be studied on samples with a rough surface, irradiate the sample with collimated laser radiation, the plane of oscillation of the electric vector of which is perpendicular to the plane of incidence, project the field of radiation scattered by the sample into the plane of the photo layer through the analyzer, the transmission axis which coincides with the plane of incidence, sounding of the recorded speckle photograph is carried out by projecting coherent dimensional image of the object surface, formed by its correlation zones through the analyzer, which is rotated by an angle of 0 - 90 ° relative The method of measuring the gradient of the refractive index of transparent objects, including irradiating the studied sample with laser radiation, projecting the field of the scattered cure by the sample into the plane of the photo layer, recording the speckle photo of this along the plane of incidence, and when registering, measure the dependence of the radiation intensity transmitted through the speckle photo on the angle of rotation of the analyzer, which calculates the gradient of the refractive index of transparent objects.