Fresnel and Fraunhofer Diffraction Fraunhofer and Fresnel Diffraction Diffraction occurs when a portion of a wave is obstructed in some way and a change in phase or amplitude results. Because of the phase or amplitude difference, the wave will interfere with itself at all points after the obstruction.
Light can be treated as a wave, so light can experience diffraction.
To aid in understanding the nature of light, it is beneficial to make a distinction between diffraction that is observed at a nearby point and diffraction that is observed at a distant point. Because the light travels a long distance before being observed, it is observed as plane waves, which are the same kind of waves that you can see hitting the beach from the ocean. In contrast, if the point of observation is relatively close to the slit, the light will be seen as spherical waves, which are analagous to the waves you can observe by dropping a stone into a pond. If this is the case, we call the resulting interference Fresnel diffraction . A helpful way to first picture spherical waves is to imagine them as circles, as shown on the left side of the picture.