Fresnel Diffraction 1.1a
A Java based simulation that generates Fresnel diffraction patterns
When you start up the applet, a circular aperture will be used. This is the pattern generated when a plane source of monochromatic light is shined on a small circular hole (about 5 mm across) in an otherwise opaque object.
The red line is the outline of the geometrical shadow (the shadow which would be cast if there were no diffraction).
You can select a different aperture shape (such as a half plane, double slit, triple slit, rectangle, etc.) from the Aperture popup. Or you can change the size of the circle by dragging the red line with the mouse.