Diffraction
When the light falls on the obstacle whose size is comparable with the wavelength of light then the light bends around the obstacle and enters the geometrical shadow. This bending of light is diffraction.
We can define Diffraction as bending of light when it passes around the edge of an object. But the proportion of bending depends on the relative size of the wavelength of light to the size of the opening. So If the opening is greater than the wavelength of light, the bending will be almost negligible. Whereas if the two are closer in size or equal, the amount of bending is noticeable and can be easily seen with the naked eye.
Types of Diffraction
There are two types of diffraction
1. Fresnel Diffraction: Fresnel diffraction occurs when light from a point source meets an obstacle. The waves are spherical and the pattern observed is a fringed image of the object.
2. Fraunhofer Diffraction: Fraunhofer diffraction occurs with plane wave-fronts with the object situated at infinity. The pattern observed is a fringed image of the source and in a particular direction.
Comparison
| Fresnel Diffraction | Fraunhofer Diffraction |
| 1 If the screen and the source of light is at a finite distance from the obstacle, then the diffraction is called Fresnel diffraction. | 1 If the source of light and screen is at an infinite distance from the obstacle then the diffraction is called Fraunhofer diffraction. |
| 2 To obtain Fresnel diffraction, zone plates are used. | 2 To obtain Fraunhofer diffraction, the single-double plane diffraction grating is used. |
| 3 The waterfronts falling on the obstacle in case of Fresnel diffraction are not plane. | 3 The wavefronts falling on the obstacle in case of Fraunhofer diffraction are planes. |
| 4 No convex lens is needed to converge spherical wavefronts. | 4 Plane diffracting wavefronts are converged via a convex lens. |
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