Light Diffraction Overview

Summary:

Light diffraction is a phenomenon in which light waves bend around obstacles and enter the geometric shadow of the obstacle. Two types of diffraction are Fresnel and Fraunhofer. Fresnel diffraction occurs when the light source and the point of observation are a finite distance from the obstacle, resulting in circular or cylindrical incidents and diffracted wavefronts. In contrast, Fraunhofer diffraction requires the light source and observation point to be at an infinite distance from the obstacle, producing plane incident and diffracted wavefronts.

In Fresnel diffraction, no lenses are needed to study it in the lab, but the mathematical treatment is complicated. The centre of the diffraction pattern can be bright or dark, and the maxima and minima are not well-defined. On the other hand, Fraunhofer diffraction requires two biconvex lenses for the lab study, its mathematical treatment is easier, the centre of the diffraction pattern is always bright, and the maxima and minima are well defined.

Fresnel also proposed the concept of half-period zones to explain the interference of wavelets and the resultant intensity of light. These zones are concentric areas on a wavefront, each with a radius that is proportional to the square root of a natural number. The areas of these zones are approximately the same, and the secondary wavelets from any two consecutive zones reach a point with a half-period time difference.

Excerpt:

Light Diffraction Overview

The peculiarity of the binding of light waves around the obstacle and going into the region of the Geometrical shadow of the obstacle is called diffraction of light.

Conditions needed for diffraction:

Light Diffraction Overview

There is an opening of diameter d. (a) When λ << d, the rays continue in a straight-line Path and the ray approximation remains valid. (b) When λ ≈ d, the rays spread out. After passing through the opening. (c) When λ >> d, the opening behaves as a point source emitting spherical waves.