SU1696852A1 - Method for surface relief determination - Google Patents

Abstract

The invention relates to a measuring and control technique and can be used for contactless control of surface topography by holographic methods. The aim of the invention is to expand the class of objects to be studied by providing independent adjustment of the contrast and depth distance. The object is placed in a chamber containing an absorbing liquid, illuminated with a collimated beam of coherent radiation of one wavelength, and a hologram is recorded. After that, the composition of the absorbing liquid is changed and the hologram is again recorded. The interference pattern is restored, according to which the surface relief is judged.

Description

The invention relates to an instrumentation technique and can be used for contactless control of surface topography by holographic methods.

The aim of the invention is to expand the class of objects to be studied by providing independent adjustment of the contrast and depth distance.

The invention is carried out as follows.

The object will be placed in the immersion chamber. ru filled with the first immersion absorbing medium (ft ni + ixj). A topographic image is recorded using collimated coherent radiation with a wavelength of A. As a reference and object beam. The medium in the chamber is replaced with the second absorbing immersion medium (A2 P2 + 1x2). As with the first exposure, a hologram is recorded. After reconstructing, two topographic images interfere, forming a contour map of the object over the distance between the maxima, the relative relief is determined in the interference pattern, and information on the absolute surface relief is obtained from changes in intensity at the maxima and minima (change in contrast).

After restoration, two wave fronts interfere with amplitudes proportional to

4 l

Am amRe i -t- Z (nm + iXm),

where am is the amplitude of the incident light;

R is the reflection coefficient of the object surface;

A- used wavelength;

Z is the distance from the camera window to a point on the object;

(/

WITH

aa aa

N

Fri, xm are real and imaginary parts of the complex refractive index (nm).

After a series of transformations, it can be shown that the depth distance AZ between the contours is determined

AZ

2 (P2-P1)

In the general case of absorbing media, the refractive index is determined by the Kramers-Kronig ratio

2 × Ap x (Ac) d AO

A2-Ai

where Ao is the integration parameter;

AN, Ak are the wavelengths defining the integration interval;

Po is the refractive index determined by the spectral regions in the wavelength range O, AN and A, oo.

The contrast P of the interference pattern varies with the thickness of the absorbing layer and is determined by the ratio

P ch (Z (xi-X2) +. N)

-one

Thus, AZ and P are the main parameters that allow to determine both the relative and absolute surface relief.

In the prototype, the depth distance is determined both by the wavelengths AI and Аa, and by the refractive indices, П2, given by the positions of these frequencies on the spectral line. The contrast is controlled by the values of the absorption coefficients xi and xa of the spectral line and the corresponding wavelengths AI and Aa. Thus, the depth and contrast

ten

15

20

25

thirty

35

40

they are determined by the characteristics of the laser radiation AI and A2 and are strictly related to the properties of the absorption line.

In the proposed method, the difference P2 ni, which determines the depth distance, can be made independent of the change that sets the contrast drop with depth. If during the first exposure in the chamber there was the first liquid in which the first dye was diluted, then during the second exposure another liquid with a different refractive index should be used to independently adjust the parameters of the interference pattern. Another dye or dye must be dissolved in it may not be used at all (then the change in contrast is completely determined by the absorption of the first liquid). Similar manipulations with independent changes between the refractive index and absorption coefficients can be made with gases.

Claims (1)

Claims The method of determining the surface relief, consisting in placing an object in a chamber containing an absorbing medium, illuminating an object with a collimated coherent radiation beam, recording a hologram, reconstructing the resulting hologram, analyzing the interference pattern and determining the interference fringes and values their intensities in maxima and minima determine the absolute relief, characterized in that, in order to expand the class of objects under study, the illumination of the object are emitted with radiation of one wavelength, and when recording a hologram, the first exposure is performed, the composition of the absorbing medium in the chamber is changed, and the second exposure is performed.