FORMING OF A FACE IMAGE OF AN EXTENDED ABSOLUTELY ABSORBING SLIT HOLE WITH AN ARBITRARY OPENING IN COHERENT LIGHT
Yu. V. Chugui
Technological Design Institute of Scientific Instrument Engineering, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Fresnel and Fraunhofer diffraction, Fourier optics, diffractional Fraunhofer spectra of extended objects, volumetric slit hole, optical dimensional inspection
Abstract
The features of formation of face images of extended absolutely slit objects with an arbitrary opening of holes are studied in a coherent-optical system. On the base of the constructive approximation of the spectra of spatial frequencies (Fraunhofer diffractional patterns) of objects with different dimensions of front and back apertures, formulas for the field in the image of the front face are obtained and analyzed. Cases of objects with significantly expanding and significantly narrowing apertures of an extended hole (the differences in aperture sizes are much larger than the size of the Fresnel zone) are investigated in detail. It is found that the image structure of faces depends on the type of the opening. With a positive opening, where the back face is in the shadow region, the field at the output of the system corresponds to the image of the front face; with a negative opening, the image of the back face is observed. It is shown that error of determination of boundaries in the image of the active face of the object is inversely proportional to the square of the aperture difference. The invariant properties of the projection system for forming images of external faces of extended holes with an arbitrary opening are analyzed.
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