Engineering Physics

14.6 Fresnel and Fraunhofer diffraction

According to Fresnel, diffraction is due to the interference of the various secondary wave lets originated from the wave front which are not obstructed by the obstacle. The diffraction phenomena are divided into two classes, they are (i) Fresnel diffraction and (ii) Fraunhofer diffraction.

(i) Fresnel diffraction: In this class of diffraction, the source of light and the screen are at finite distance from the diffracting aperture or obstacle having sharp edge. The wave front incident on the aperture or obstacle is either spherical or cylindrical.

(ii) Fraunhofer diffraction: In this class of diffraction the source of light and the screen are at infinite distance from the diffraction aperture or obstacle ...