chapter  9
Diffraction II
Fresnel Diffraction
WithAjawad I. Haija, M. Z. Numan, W. Larry Freeman
Pages 39

The locations of the source and screen in the setup of Fraunhofer diffraction were arranged to be effectively at infinity from the diffraction device, a slit-like aperture, or a diffraction grating. Such condition simplified the treatment significantly; it made it possible to treat the emitted wavelets at the aperture as plane waves, all having the same phase and amplitude. They differ in phase as they reach an observation point P on the screen, but all reach the point with the same amplitude. However, Fresnel diffraction, also known as near-field diffraction, is free from any particular limitation. The setup requires a source, a diffracting device, and a screen. Thus, Fresnel diffraction involves a variety of variables that influence its formation. Among the early observations of Fresnel diffraction were the effect of a sharp-edge obstacle on light illuminating the area behind the obstacle, where light spread over an area beyond geometric limits and a series of bright and dark bands were observed. This chapter details mathematical analyses for diffraction from straight edges, rectangular openings, and circular apertures.