Answer to Question #102670 in Optics for sakshi

Question

Fraunhofer diffraction is a special case of Fresnel diffraction. Explain. Also discuss the concept of Fresnel half-period elements.

Answer 1

When an opaque screen is illuminated with plane wave, then the light spread over the screen as the result of diffraction, if the observation is seen from the far of the screen then it does not change in structure, but as distance is further increased, then the situation is called the Fraunhofer differaction.

As closer to the aperture, the diffraction pattern further does change with distance, that is called the Fresnel diffraction.

concept of Fresnel half-period elements: It confirms the wave nature of light.Fresnel divided the whole wavefront into the large number of small elements, which is called the zones. The resultant amplitude at any point is called the secondary wave at that points form the various zones.

The area of each half period zone is same.