Question

Explain experimental setup for Fraunhofer diffraction with neat diagram. 

Answer 1

1. Set up for Fraunhofer diffraction has a monochromatic source of light S at the focus of a converging lens. Ignoring aberrations, the emerging beam will consist of plane parallel rays resulting in-plane wavefronts.
2. These are incidents on the diffracting element such as a slit, a circular aperture, a double slit, a grating, etc.
3. In the case of a circular aperture, S is a point source and the lenses are bi-convex. For linear elements like slits, grating, etc., the source is linear and the lenses are cylindrical in shape so that the focussed image is also linear.
   
   Set up for Fraunhofer diffraction
4. An emerging beam is an incident on another converging lens that focuses the beam on a screen.