ABSTRACT
The diffraction phenomenon is the deviation of a ray of light propagating in the vicinity of an obstacle or essentially the spread of light into areas of geometrical shadow. This phenomenon cannot be explained by geometric optics or ray optics. To illustrate this, the chapter discusses two aspects of diffraction, namely Fraunhofer diffraction (also called far field diffraction) and Fresnel diffraction (also called near field diffraction). Fraunhofer diffraction corresponds to the case where the dimensions of the diffracting elements such as slits, diaphragms, etc., are very small and the distances from the light source and observation screen to the plane containing the diffracting element are large. For this part, and unlike the cases of Fresnel diffraction, the distance between any arbitrary point of the diaphragm and any arbitrary point of the observation screen is equal to the distance between both planes.
