出典:Wikipedia
出典:『Wikipedia』 (2011/07/21 02:00 UTC 版)
In optics, a Poisson spot is a bright point which appears due to Fresnel diffraction at the center of the wave shadow of a circular object. It is also sometimes called an Arago spot or a Fresnel bright spot. The experiment played an important role in the discovery of the wave nature of light (see history section below) and is a common way to demonstrate that light behaves as a wave for example in undergraduate physics laboratory exercises. The basic experimental setup is shown in the figure on the right. The wave source must be at least smaller in diameter than the circular object casting the shadow and the dimensions of the setup must comply with the requirements for Fresnel diffraction. Namely, the Fresnel number must satisfy