Diffraction Plates for Classroom Demonstrations

The diffraction plate, which consists of an array of many identical apertures or obstacles, produces large Fraunhofer diffraction patterns of sufficiently high intensity such that they may be seen easily with the unaided eye when used with conventional sources. If a small, bright source is observed through a diffraction plate held close to the eye, the Fraunhofer pattern of the apertures appears around the image of the source. If the apertures are randomly distributed over the plate, the pattern produced is characteristic of any one of the apertures in the plate. The pattern produced by a regular array has characteristics of both the individual aperture and of the arrangement. The beautifully colored patterns produced by a white light source are easily seen and photographed. This article describes the computer generation of random and regular arrays of apertures and their applications for classroom demonstrations of the Fraunhofer patterns produced by simple and complex apertures, Babinet's principle, resolution according to the Rayleigh criterion, and many other important aspects of diffraction.