Abstract

A grating, when illuminated by a quasi-monochromatic point source, can form self-images downstream. With a periodic, spatially incoherent source illumination, when the self-images due to all the source points coincide, a high contrast gratinglike structure is formed. In this paper, the Fresnel approximation is used to calculate the diffraction pattern of the object. The resulting intensity pattern is essentially the correlation between the intensity distribution of the spatially incoherent source and the scaled intensity distribution of the Fresnel diffraction of the object. By suitably choosing the plane of observation and the source structure to object structure ratio, a high contrast cross-gratinglike structure can be obtained. Al though the image pattern is the correlation between the source structure and the scaled object structure, the magnification ratio between the self-image and the source structure is the same as that in conventional imaging. We can then consider the self-image to be the image of the source structure, imaged by the object grating. When the illuminating source is imaged to the right of the object grating, the relationship between the self-image and the new source is found to be the same as before.

© 1986 Optical Society of America