Engineering Physics

14.9 Fraunhofer diffraction at a circular aperture

The problem of diffraction at a circular aperture was first solved by Airy in 1835. A circular aperture of diameter ‘d ’ is shown as AB in Fig. 14.13. A plane wave front WW’ is incident normally on this aperture. Every point on the plane wave front in the aperture acts as a source of secondary wavelets. The secondary wavelets spread out in all directions as diffracted rays in the aperture. These diffracted secondary wavelets are coverged on the screen SS′ by keeping a covex lends (L) between the aperture and the screen. The screen is at the focal plane of the convex lens. Those diffracted rays traveling normal to the plane of aperture [i.e., along CP_o] are get coverged at P_o.

 

Figure 14.13 ...